STANFORD GEOTHERiMAL PROGRAiM STANFORD UNIVERSITY

STANFORD, CALIFORNIA 94305

SGP-TR-45

STIMULATION AND RESERVOIR ENGINEERING

OF GEOTHERMAL RESOURCES

THIRD ANNUAL REPORT

DOE-LBL CONTRACT NO. 167-3500

SEPTEMBER 1980

f o r t h e p e r i o d

October 1, 1979 , t h r o u g h September 30, 1980

Henry J. Ramey, J r . , and P a u l Kruger C o- P r i n c i p a l I n v e s t i g a t o r s

.

PREFACE

T h i s p u b l i c a t i o n i s t h e t h i r d annua l p r o g r e s s r e p o r t under t h e De-

par tment of Energy c o n t r a c t DOE-LBL-167-3500 w i t h t h e Lawrence Berkeley

Labora to ry .

1980.

It c o v e r s t h e p e r i o d from October 1, 1979 through September 30,

The S t a n f o r d Geothermal Program w a s i n i t i a t e d by t h e N a t i o n a l

S c i e n c e Foundat ion i n 1972 and con t inued under t h e Energy Research and

Development A d m i n i s t r a t i o n (now DOE) a f t e r 1975. The c e n t r a l o b j e c t i v e

c o n t i n u e s t o be r e s e a r c h i n geothermal r e s e r v o i r e n g i n e e r i n g t echn iques

aimed a t s t i m u l a t i n g t h e development of a commercial geothermal i n d u s t r y

i n t h e Uni ted S t a t e s . A p a r a l l e l o b j e c t i v e i s t h e t r a i n i n g of e n g i n e e r s

f o r employment i n t h e geothermal i n d u s t r y .

S t a n f o r d Geothermal Program i s t o m a i n t a i n a b a l a n c e between l a b o r a t o r y

s t u d i e s of t h e geothermal r e s o u r c e and f i e l d exper iments . T h i s g u a r a n t e e s

a b a l a n c e between advancing t h e unders tand ing of geothermal r e s o u r c e ex-

t r a c t i o n , and t h e r a p i d t r a n s f e r of t h e r e s u l t s of t h e s t u d i e s t o f i e l d

o p e r a t i o n s of t h e i n d u s t r y .

A t h i r d o b j e c t i v e of t h e

The S t a n f o r d Geothermal Program c o n t a i n s f o u r major s t u d y a r e a s f o r

deve lop ing p r a c t i c a l methods and d a t a f o r geothermal r e s e r v o i r e n g i n e e r i n g

and r e s e r v o i r a s sessment : (1) energy e x t r a c t i o n , ( 2 ) bench- scale f low

exper iments , (3 ) r e s e r v o i r t racer t e c h n i q u e s , and ( 4 ) w e l l t e s t a n a l y s i s .

I n a d d i t i o n , t h e Program m a i n t a i n s a n e f f o r t t o b r i n g t h e r e s u l t s of t h e

r e s e a r c h t o t h e geothermal community i n t h e form of t e c h n i c a l r e p o r t s , a

weekly geothermal seminar throughout t h e academic y e a r , and an i n t e r n a t i o n a l

ii

a n n u a l workshop i n geo the rmal r e s e r v o i r e n g i n e e r i n g . Th i s annua l r e p o r t

d e s c r i b e s t h e r e s u l t s o b t a i n e d i n t h e f o u r a r e a s of geothermal r e s e r v o i r

e n g i n e e r i n g , and a c t i v i t i e s f o r t r a n s f e r r i n g t h e r e s u l t s t o t h e geothermal

community.

Of s i g n i f i c a n t h e l p i n t h e s u c c e s s f u l complet ion of t h e o b j e c t i v e s

of t h i s program i s t h e ready s u p p o r t by members of i n d u s t r y , v a r i o u s f e d e r a l

a g e n c i e s , n a t i o n a l l a b o r a t o r i e s , and u n i v e r s i t y programs. These p e r s o n n e l

p r e s e n t l e c t u r e s i n t h e weekly seminar and annua l geothermal workshop,

and serve i n program s e l e c t i o n and i n o t h e r ways impor tan t t o t h e program.

The names a r e t o o numerous t o c i t e h e r e . However, l i s t i n g s may be found

i n t h e p r e f a c e of t h e Workshop Proceed ings and i n t h e Appendices of t h i s

r e p o r t . Of c o u r s e , a major c o n t r i b u t o r i s t h e Department of Energy th rough

t h e Lawrence Berkeley Labora to ry .

Henry J. Ramey, Jr. and P a u l Kruger

iii

c

TABLE OF CONTENTS

PREFACE . . . . . . . . . . . . . . . . . . . . . . . . . . . . INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.0 ENERGY EXTRACTION . . . . . . . . . . . . . . . . . . . . . 4

(a) Energy Extraction Modeling . . . . . . . . . . . . . . . 4

(b) Thermal Stress Cracking Experiments . . . . . . . . . . 18 2.0 BENCH-SCALE EXPERIMENTS . . . . . . . . . . . . . . . . . . 26

(a) Absolute Permeameter . . . . . . . . . . . . . . . . . . 26

(b) Large Core Apparatus . . . . . . . . . . . . . . . . . . 29

(c) Vapor Pressure Lowering . . . . . . . . . . . . . . . . 32

3.0 RADON TRACER TECHNIQUES . . . . . . . . . . . . . . . . . . 35

(a) Radon Transient Analysis . . . . . . . . . . . . . . . . 36

(b) Radon Transect Analysis . . . . . . . . . . . . . . . . 45

(c) Radon Emanation Studies . . . . . . . . . . . . . . . . 56

4.0 hTLL TEST ANALYSIS . . . . . . . . . . . . . . . . . . . . . 60

(a) Constant Pressure Testing . . . . . . . . . . . . . . . 60

(b) Parallelepiped Models . . . . . . . . . . . . . . . . . 61

(c) "Slug Test" DST Analysis . . . . . . . . . . . . . . . . 62

(d) Analysis of Wells with Phase Boundaries . . . . . . . . 65

(e) Internal Well Flows . . . . . . . . . . . . . . . . . . 69

(f) Naturally Fractured Reservoirs . . . . . . . . . . . . . 71 (g) Temperature-Induced Wellbore Storage Effects . . . . . . 7 7

5.9 CONCLUSIONS AND RECOMMENDATIONS . . . . . . . . . . . . . . 81

iv

. REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

APPENDIX A: PARTICIPANTS IN THE STANFORD GEOTHERMAL PROGRAM . . . . 89 APPENDIX B: TECHNICAL REPORTS . . . . . . . . . . . . . . . . . . . 90 APPENDIX C: PUBLICATIONS AND TECHNICAL PRESENTATIONS . . . . . . . . 93 APPENDIX D: TRAVEL AND TECHNICAL MEETING ATTENDANCE . . . . . . . . 96 APPENDIX E: SGP SPONSORED MEETINGS . . . . . . . . . . . . . . . . . 98

V

INTRODUCTION

The research effort of the Stanford Geothermal Program is focused on

geothermal reservoir engineering. The major objective of the program is

to develop techniques for assessing geothermal reservoirs through better

interpretation of physical models, mathematical analysis, and field experi-

ments to obtain real wellbore and reservoir data. Efficient utilization

of geothermal resources requires an understanding of reservoir productivity

and longevity, and methods to extend the life of the resources through

production stimulation and increased fluid and energy extraction.

To accomplish t h i s objective, a balance is maintained between labora-

tory studies and field applications. One goal is to develop the mathematical

description of observed reservoir behavior. Physical models are used to

calibrate mathematical models by an understanding of the physical and

chemical mechanisms occurring in the reservoir. Another goal is to develop

new methods for observing reservoir behavior and to test them in the field.

In this report, individual projects are grouped under four main areas

of study :

(1) Energy Extraction

( 2 ) Bench-Scale Flow Experiments

(3) Radon and Noncondensible Tracer Techniques

( 4 ) Well Test Analysis

The section on energy extraction experiments concerns the efficiency

with wnich the in-place heat and fluids can be produced. Energy extraction

considerations are of importance to the geothermal industry in decisions

1

~~ ~

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concerning liquid recharge and potential commercialization of liquid-

dominated hydrothermal resources.

Reservoir Model which evaluates energy extraction by a method of fluid

production is important in these considerations. Initial experiments

on thermal fracturing by hydrothermal stressing have been completed. The

development of a model useful for assessing the heat extraction potential

of hydrothermal resources has progressed to a satisfactory point where a

lumped-parameter model of energy extraction based on rock size distribution

with two-phase flow can be examined.

The research on the large Geothermal

The section on bench-scale flow experiments covers the results of

three models used to examine the properties of flow through porous media

at elevated temperatures and pressures. A small core model was used to

study the effect of temperature level on absolute permeability, a second

larger core model equipped with a capacitance probe for determining water

and steam saturation in a porous medium was used to measure steam-water

relative permeability, and a third model was operated to determine the

mechanism of vapor pressure lowering in porous media. Important findings

were made in all studies during the year.

The section on radon tracer techniques describes the efforts to test

several geothermal reservoirs by both transient and transect test procedures.

The results of radon flow transients in the vapor-dominated reservoirs at

The Geysers, California; Serrazzano, Italy; and in several liquid-dominated

reservoirs were reported at several symposia. Further measurements at the

fields at Wairakei, New Zealand; and at Los Azufres and Cerro Prieto,

Mexico, were completed. Analysis of the first radon evaluation of reservoir

performance was completed in the Phase I test of the LASL Hot Dry Rock

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Program. The r e s u l t s of t h e f i r s t t r a n s e c t a n a l y s e s of exper iments a t Cer ro

P r i e t o , Wai rake i , and The Geysers were r e p o r t e d .

m u l t i - t r a c e r e v a l u a t i o n of geothermal r e s e r v o i r s , comparison of t h e ammonia-

To s a t i s f y t h e need f o r

to- radon r a t i o s were inc luded i n the t r a n s e c t s t u d i e s .

of t h e bench- sca le exper iments t o d e f i n e t h e s o u r c e term as a f u n c t i o n of

r e s e r v o i r pa rame te r s w a s completed.

The f i r s t phase

The s e c t i o n on w e l l t e s t a n a l y s i s d e s c r i b e s s e v e r a l new developments:

a n a l y s i s of w e l l t e s t d a t a f o r w e l l s produced a t c o n s t a n t p r e s s u r e , p a r a l l e

ep iped models, s l u g t e s t DST a n a l y s i s , p r e s s u r e t r a n s i e n t behav io r i n

n a t u r a l l y f r a c t u r e d r e s e r v o i r s , temperature- induced w e l l b o r e s t o r a g e e f f e c t s ,

phase boundary e f f e c t s on r e i n j e c t i o n and b o i l i n g i n p r o d u c t i o n , and w e l l b o r e

c y c l i n g .

The r e s e a r c h conducted ove r t h e p a s t y e a r has produced s e v e r a l impor-

t a n t r e s u l t s , some of which are be ing examined i n c o n t i n u i n g s t u d i e s . I n

t h e f i n a l s e c t i o n of t h i s r e p o r t , c o n c l u s i o n s are o f f e r e d a long w i t h recom-

mendat ions f o r areas of f u t u r e research which may l e a d t o improvements i n

t h e development of new geothermal r e s o u r c e s .

The Appendices t o t h i s r e p o r t d e s c r i b e some of t h e S t an fo rd Geothermal

Program a c t i v i t i e s t h a t r e s u l t i n i n t e r a c t i o n s w i t h t h e geothermal community.

These occur i n t h e form of SGP T e c h n i c a l Repor t s , p r e s e n t a t i o n s a t t e c h n i c a l

mee t ings , p u b l i c a t i o n s i n t h e open l i t e r a t u r e , and t h e series of Q u a r t e r l y

Seminars and t h e Annual Workshop on Geothermal Rese rvo i r Engineer ing .

1. ENERGY EXTRACTION

Energy e x t r a c t i o n r e s e a r c h concerned two main areas: numer ica l modeling

of e x t r a c t i o n expe r imen t s and the rma l stress c r a c k i n g exper iments . P r o g r e s s

i n b o t h s t u d i e s i s r e p o r t e d .

( a ) Energy E x t r a c t i o n Modeling, by John S u l l i v a n , Research A s s i s t a n t ,

and A n s t e i n Hunsbedt, Consu l t ing A s s i s t a n t P r o f e s s o r .

An a n a l y t i c model f o r t h e l i n e a r f low of w a t e r i n a f r a c t u r e d geo-

the rma l r e s e r v o i r s y s t e n q r e f e r r e d t o as t h e l i n e a r sweep model, was d e s c r i b e d

by I r e g u i e t a l . (1978) and d e s c r i b e d by Hunsbedt e t a l . ( 1 9 7 9 ) . T h i s one-

d imens iona l model may be used t o compute t h e water t empera tu re as a f u n c t i o n

of t i m e and space i n t h e i d e a l i z e d geothermal sys tem p i c t u r e d i n F i g u r e 1-1.

I n t h e model c o l d water e n t e r s t h e fo rma t ion through a ser ies of i n j e c t i o n

w e l l s a t p o i n t A , and f lows h o r i z o n t a l l y t o a series of p r o d u c t i o n w e l l s

a t p o i n t B. The i n j e c t i o n and p r o d u c t i o n f l o w r a t e s are s t e a d y , and t h e

p e r m e a b i l i t y of t h e fo rma t ion i s such t h a t t h e f low i s uni form. The

r e s e r v o i r p r e s s u r e p r e v e n t s b o i l i n g i n t h e fo rma t ion . The r o c k s i z e

d i s t r i b u t i o n i s assumed t o b e independent of t h e d i s t a n c e X between t h e

i n j e c t i o n and p r o d u c t i o n w e l l s . Hea t ing from t h e su r round ing rock media

i s inc luded by a c o n s t a n t ex terna l . h e a t t r a n s f e r .

The s o l u t i o n t o t h e p a r t i a l d i f f e r e n t i a l e q u a t i o n developed i n t h e

model w a s o b t a i n e d u s i n g a Lap lace t r a n s f o r m a t i o n t echn ique combined w i t h

a numer ica l i n v e r s i o n a l g o r i t h m ( S t e h f e s t , 1970) . A comparison of a n a l y t i c

and e x p e r i m e n t a l d a t a o b t a i n e d from t h e SGP Large R e s e r v o i r :lode1

p i c t u r e d i n F i g u r e 1- 2 w a s a l s o p r e s e n t e d by I r e g u i e t a l . and Hunsbedt e t a l .

F u r t h e r comparisons were g i v e n i n t h e P r o c e e d i n g o f t h e F i f t h Workshop on

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FIG. 1-1: LINEAR SWEEP MODEL

-6-

I N LE T/O UT L ET PIPING

* Thermocouple reference numbers @ R o c k number 1

FIG. 1- 2 : THERMOCOUPLE MAP OF LARGE RESERVOIR MODEL

-7 -

Geothermal Reservoir Engineering for the most recent experiment conducted

for the experimental conditions listed in Table 1-1.

observed water temperatures to linear sweep model results obtained by the

Laplace transformation/numerical inversion solution showed considerable

disagreement at some points in the reservoir. Figure 1-3 shows the

experimental and computed water temperatures as functions of time at various

pointsin the physical model. The slopes of the computed temperature curves are

generally greater than the experimental data suggest. This difference has been

studied extensively during this year.

The comparison of

Another solution for the linear sweep model was obtained using a finite

difference numerical technique to check the adequacy of the Laplace

transform inversion method. Comparison of results from the numerical

solution, also given in Figure 1-3, shows poor agreement with the Laplace in-

version solution. Although neither solution is sufficiently reliable at

this time, it is believed that the finite difference solution may be better,

based on extensive

size.

parametric studies involving varying time step and mesh

The observation that the computed temperature versus time curves are

generally steeper than the experimental curves led to further examination of

the behavior of the physical system and the model assumptions. The

tempesature-time characteristic of the water entering the model follows

an exponential, rather than a step change assumed in the mathematical

nodel. This was deduced from the steel temperatures measured at the

lower parts of the vessel by thermocouples 301 and 302 in Figure 1-2. These

temperatures and the measured inlet water temperature are given in

Figure 1-4. The actual water temperature entering the flow distribution

baffle was not measured, but is believed to be only slightly lower than the

steel temperature measured by thermocouple 301.

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t i m e c o n s t a n t of 0.57 h r , on t h e water t empera tu re cu rves i s i l l u s t r a t e d i n

F igu re 1-5.

t h e Laplace t r ans fo rm i n v e r s i o n s o l u t i o n modi f ied t o i n c l u d e an e x p o n e n t i a l

i n l e t c o n d i t i o n i s similar t h e t h e expe r imen ta l r e s u l t s .

couraging . However, t h e r e i s a t i m e l a g t h a t cannot be exp la ined a t t h i s

t i m e . P a r t of t h i s problem may be r e l a t e d t o a x i a l h e a t conduct ion i n

t h e rock lwa te r matrix, and h e a t t r a n s f e r from t h e s t ee l v e s s e l .

l a t t e r e f f e c t i s modeled by a c o n s t a n t h e a t t r a n s f e r term i n t h e p r e s e n t

l i n e a r sweep model.

Th i s f i g u r e shows t h a t t h e s l o p e of t h e cu rves computed by

T h i s i s en-

The

The e f f e c t of a x i a l conduct ion i n t h e rock lwa te r m a t r i x w a s i n v e s t i -

ga t ed u s i n g a second f i n i t e d i f f e r e n c e numer ica l model. R e s u l t s of t h i s

comparison i s g iven i n F i g u r e 1-6 and shows t h a t a x i a l convec t ion r educes

t h e s l o p e o f t h e cu rves . The t i m e l a g a l s o appea r s t o be reduced. The

e f f e c t s o f a x i a l conduct ion and t h e exponen t i a l water i n l e t c o n d i t i o n ,

t o g e t h e r , a r e t h e r e f o r e expec ted t o g i v e computed r e s u l t s which a g r e e

w e l l w i t h t h e expe r imen ta l d a t a . However, a s i g n i f i c a n t e f f o r t w i l l be

r e q u i r e d t o improve t h e model by i n c l u d i n g f e a t u r e s of t h e p h y s i c a l

system t h a t a r e c u r r e n t l y n o t modeled.

behavior of t h e s t e e l v e s s e l .

One such f e a t u r e i s t h e t r a n s i e n t

The i n c l u s i o n of a x i a l conduct ion i n t h e model p rovided a n independent

check on t h e accuracy of t h e two f i n i t e e lement s o l u t i o n s . The l a t e s t

s o l u t i o n matches t h e e a r l i e r f i n i t e d i f f e r e n c e s o l u t i o n f o r t h e s p e c i a l

case of v e r y low a x i a l conductance. Thus, i t appea r s t h a t t h e f i n i t e

d i f f e r e n c e s o l u t i o n s may be more a c c u r a t e t han t h e Laplace t r ans fo rm

s o l u t i o n . It i s a n t i c i p a t e d t h a t t h i s problem w i l l b e f u r t h e r s t u d i e d

because t h e Laplace t r a n s f o r m s o l u t i o n i s s i m p l e r t o a p p l y .

-13-

i W 7 0

-14-

1 1 I 1 0 0 0 0

0 0 0 0 .;t m c\I -

-15-

The r e s u l t s of t h e s e comparisons show t h a t t h e mathemat ica l modeling

of t h e l a b o r a t o r y system needs f u r t h e r improvement.

of t h e h e a t t r a n s f e r e f f o r t s a re t o model t h e behav io r of l a r g e- s c a l e

systems such a s shown i n F i g u r e 1-1.

i n t h e p r e s e n t l i n e a r sweep model are be ing s t u d i e d .

h e a t t r a n s f e r from t h e s t e e l v e s s e l which releases a n amount of energy

comparable t o that from t h e rock . The o t h e r i s modeling h e a t t r a n s f e r from

t h e d i f f e r e n t f ragments composing t h e s imula ted geothermal system.

o b j e c t i v e of p r e v i o u s exper iments w a s t o de te rmine whether t h e one-

lump rock h e a t t r a n s f e r model u s i n g i n t h e l i n e a r sweep model w a s adequate .

To do t h i s , i t i s necessa ry t o model t h e h e a t t r a n s f e r from t h e v e s s e l

a c c u r a t e l y s o t h a t t h e " w a l l e f f e c t " can b e e l i m i n a t e d as an u n c e r t a i n t y .

Cur ren t work on t h i s p r o j e c t i s proceeding a long two p a t h s : one i n v o l v e s

a d d i t i o n a l exper iments , and t h e o t h e r i n v o l v e s more d e t a i l e d a n a l y t i c

models.

The long-term o b j e c t i v e s

There fo re , t h e two t y p e s of u n c e r t a i n t y

One concerns modeling

The

P r e p a r a t i o n i s underway t o conduct exper iments i n t h e l a r g e r e s e r v o i r

model u s i n g r e g u l a r l y shaped g r a n i t e b locks as shown i n F i g u r e 1- 7 . The

u s e of r e g u l a r s i z e d rocks should a l l o w a d e t a i l e d modeling of t h e rock

h e a t t r a n s f e r which can be compared to theone- lump parameter approach

p r e v i o u s l y used f o r rocks of d i s t r i b u t e d s i z e and shape. It a l s o p e r m i t s

e v a l u a t i o n of a l a r g e range o f t h e number of h e a t t r a n s f e r u n i t s parameter.

Thus, i t i s a n t i c i p a t e d t h a t v a l u e s of h e a t t r a n s f e r u n i t s as low as

3.0 can be ach ieved i n t h e p r e s e n t exper imenta l system, which i s w e l l i n t o

t h e " hea t t r a n s f e r l i m i t e d" r e g i o n . The expected exper imenta l c o n d i t i o n s

f o r t h e p lanned exper iments a r e g iven i n Table 1-1. A l a r g e r number of

thermocouples w i l l be in t roduced i n t o t h e rock and water m a t r i x t o p rov ide

a l a r g e r number of t empera tu re measurements, i n c l u d i n g t h e water i n l e t

t empera tu re d i s t r i b u t i o n , a n d t o p r o v i d e c r o s s- s e c t i o n a l temperature g r a d i e n t s

-16-

At

1 ! 10"

ROCK GEOMETRY 1 ROCK GEOMETRY 2

T I

FIG. 1-7: ROCK LOADING CONFIGURATION

-17-

to be used in the planned two-dimensional analysis of the heat transfer.

This analysis will be with improved mathematical models of the laboratory

system, using the finite element method. Emphasis is on accurate modeling

of the various elements of the steel vessel such as the heavy flanges.

The modeling techniques will also be adapted to large scale geothermal

systems. The initial goal of these models will be to consider the

wall effect and to gain confidence in the use of the one-lump rock heat

transfer model over the appropriate range of number of heat transfer units.

Results of these studies will be compared to results from the current linear

sweep model based on the Laplace transfonnsolution. Improvement in the

solution technique may provide a simple and convenient tool for assessing

heat transfer performance of fractured geothermal systems. A s these goals

are achieved, the modeling method will be used to compute the heat transfer

performance of large-scale fractured hydrothermal systems, such as the

Baca field in New Mexico and the Los Alamos fracturing experiment at the

Site 2 location.

-18-

(b) Thermal Stress Cracking Experiments, by R. Rana, Engineer's

Degree Candidate in Mechanical Engineering and Professor Drew Nelson.

In fractured rock hydrothermal reservoirs, water circulation induces

tensile thermal stresses in a layer below the cooled rock surface.

Murphy (1978) showed analytically that these stresses have the potential

to create self-driven cracks of sufficient depth and aperture to enhance

energy extraction and prolong production life.

generated by reinjection of fluids into naturally fractured hydrothermal

reservoirs. Aside from the potential of producing self-driven cracks,

thermal stressing may also influence both the mechanical and thermal prop-

erties of the rock. Changes in these properties can, in turn, affect the

thermal cracking process itself and the heat transfer characteristics of

rocks (even without self-driven cracks). During the past year, an ex-

ploratory study was conducted to investigate the effects of thermal

stressing on rock strength and porosity experimentally.

Such stresses may also be

To produce thermal stress, granite slabs (2-1/2" x 10" x l/4") were

first slowly heated (at rates of less than 2'F/min) to a temperature of

450'F in the modified air bath shown schematically in Figure 1-8.

slabs were maintained at elevated temperature for several hours to assure

uniformity of temperature, which was confirmed by thermocouple readings

taken at various locations inside one of the slabs. To induce thermal

stress, the ''exposed" face shown in Figure 1-8 was then sprayed with 70°F

water from numerous small jets. This face was insulated until just before

quenching to minimize initial, undesired temperature gradients.

The

To estimate thermal stress due to quenching, one-dimensional heat

flow in the length direction of the slab was assumed. The transient

-19-

WATER SPRAY

INSULATION /

%RAN I TE SLAB \

INSULATING COVER, REMOVED JUST PRIOR TO QUENCHING

FIG. 1-8: THERMAL STRESS EQUIPMENT

.. temperature distribution T(z,t) was estimated (Ozisik, 1968) from the

following closed-form solution for a slab of finite thickness with in-

sulated sides:

where:

8 = normalized temperature

= initial slab temperature Ti

Too = water temperature

z = distance inward from quenched face

t = time

k = thermal conductivity

d = thermal diffusivity

h = surface heat transfer coefficient between water and rock

To estimate h for the given quenching condition, T(z,t) was measured

along the centerline of several slabs with thermocouples cemented in place

at the ends of holes drilled in from the side. Comparison of measured

T(z,t) with that based on Equation

This estimate was confirmed by the measured cooling of a copper block

heated to 450°F and quenched with the same spray system.

2 1-1 indicated h - % 300 Btu/hr-ft - O F ) .

Assuming linear elastic, isotropic and homogeneous behavior (Johns, 1965),

the thermal stresses due to quenching were estimated from:

where :

c* =

E =

a =

v =

b =

0 =

The T ( z , t )

J 0

normal ized stress (same i n x and y d i r e c t i o n s of F ig . 1-8)

modulus of e l a s t i c i t y

c o e f f i c i e n t of thermal expansion

P o i s s o n ' s r a t i o

l e n g t h of b l o c k

normal ized t empera tu re d e f i n e d i n Equat ion (1-1)

behavior determined from Equat ion 1-1 was s u b s t i t u t e d i n t o

Equat ion 1- 2 , and numerical i n t e g r a t i o n performed t o o b t a i n O*. The

e s t i m a t e d normal ized the rmal stress as a f u n c r i o n of t i m e and p o s i t i o n

a long t h e s l a b c e n t e r l i n e i s shown i n F ig . 1-9.

S i e r r a- w h i t e g r a n i t e (ob ta ined from t h e Raymond, C a l i f o r n i a , q u a r r y )

w a s used i n a l l tests. For t h e g iven quenching c o n d i t i o n s , no l a r g e- s c a l e

c r a c k i n g was observed, b u t none w a s r e a l l y expected because of t h e small

specimen s i z e , and t h e freedom of t h e s l a b t o c o n t r a c t upon coo l ing .

T o i n v e s t i g a t e p o s s i b l e changes i n s t r e n g t h due t o thermal s t r e s s i n g ,

t h e b locks were c u t i n t o smaller r e c t a n g u l a r specimens (1-1/2" x 3" x 0.3")

and loaded t o f r a c t u r e i n t h r e e- p o i n t bending. Based on e i g h t specimens

from a n unquenched b lock , t h e mean e l a s t i c a l l y - c a l c u l z t e d bending stress

a t t h e f r a c t u r e w a s 1830 p s i , w i t h a c o e f f i c i e n t of v a r i a t i o n of 15%. The

bending s t r e n g t h of specimens t a k e n from v a r i o u s p o s i t i o n s a long t h e l e n g t h

of quenched s l a b s i s shown i n F ig . 1-10, a long w i t h t h e s t r e n g t h s of

specimens taken from s l a b s which had been s u b j e c t e d t o f i v e c y c l e s of

1.0

0 . 8

0 . 6

0 . 4

0 . 2

0

- 0 . 2

-22-

c (l- v ) E a ( T j - T a )

FIG. 1-9: ESTIMATED THERMAL STRESS DISTRIBUTION IN GRANITE BLOCK

n 250C .- m a. W

12000 I- ill * 1500 W

z 1000 0 2

z W

23 500

0 (

m

- A

0

A €3

0 8

8 ------ ---- %- - - -

0 - 0 0

a

VIRGIN ROCK

0 0 ONE QUENCH 0 A FIVE QUSNCHES

I i I 1 I I I I I 1 2 4 6 8 70

Z ( in)

F I G . 1-10: B E N D I N G S T R E N G T H OF S P E C I N E N S TAKEN F R O Y BLOCK

-24-

quenching.

mens taken from r e g i o n s of compressive thermal stress. A l s o , t h e l o s s of

s t r e n g t h i s a p p a r e n t l y n o t caused by h e a t i n g a l o n e ( t o 450'F). It may be

due t o mic rocrack ing caused by t e n s i l e the rmal stress. Dye p e n e t r a n t w a s

There i s a s i g n i f i c a n t r e d u c t i o n i n s t r e n g t h i n t h o s e s p e c i-

a p p l i e d t o one f a c e of some of t h e specimens a f t e r bend t e s t i n g .

though i t w a s found t h a t t h i s does n o t p r o v i d e a s a t i s f a c t o r y way of

obse rv ing mic rocrack ing , i t w a s noted t h a t i n unquenched specimens, t h e

dye e i t h e r d i d n o t seep through t o t h e o t h e r s i d e o r d i d s o ve ry s lowly.

In specimens which had exper ienced t e n s i l e the rmal stress, t h e dye pene-

t r a t e d q u i c k l y , i n d i c a t i n g a l i k e l y i n c r e a s e i n p o r o s i t y and p e r m e a b i l i t y .

A l -

P o r o s i t y measurements were made on t h e same specimens used i n t h e

bend tests .

unquenched specimens w a s 1 .6%, w h i l e t h e average f o r specimens e x p e r i e n c i n g

one and f i v e a p p l i c a t i o n s of t e n s i l e the rmal stress w a s 3 .8 and 4.8%, respec-

t i v e l y . The i n c r e a s e i n p o r o s i t y is c o n s i s t e n t w i t h t h e b e l i e f t h a t micro-

c r a c k i n g occur red i n r e g i o n s of t e n s i l e the rmal stress.

The s a t u r a t i o n method w a s used. The average p o r o s i t y of

The above r e s u l t s were o b t a i n e d from tests conducted a t a tmospher ic

p r e s s u r e . I d e a l l y , tests should b e conducted under s imula ted t e c t o n i c

stresses. N e v e r t h e l e s s , t h e observed r e d u c t i o n i n rock s t r e n g t h and

i n c r e a s e i n p o r o s i t y caused by t e n s i l e the rmal s t r e s s i n g i s encouraging in

terms of f a v o r i n g t h e fo rmat ion and growth of l a r g e the rmal c r a c k s i n

r e s e r v o i r s . It a l s o seems p l a u s i b l e t h a t t e n s i l e the rmal stress may a l t e r

rock h e a t t r a n s f e r behav io r by changing thermal p r o p e r t i e s ( e .g . , con-

d u c t i v i t y ) i n t h o s e r e g i o n s n e a r t h e s u r f a c e where such stresses are

s i g n i f i c a n t . F u r t h e r tests t o i n v e s t i g a t e t h i s phenomena would be d e s i r a b l e .

The r e s u l t s would be u s e f u l i n augmenting t h e h e a t e x t r a c t i o n model be ing

developed f o r l a r g e s i z e hydrothermal r e s e r v o i r s t o i n c l u d e changes i n

-25-

i n h e a t t r a n s f e r p r o p e r t i e s due t o the rmal stresses under r e i n j e c t i o n over

t h e p roduc t ion l i f e t i m e of t h e r e s e r v o i r .

2.0 BENCH-SCALE EXPERIMENTS

Several experimental studies were conducted with small cores of porous

media. In general, the objective of all experiments was to determine

fundamental characteristics of flow important to field reservoir engineer-

ing. These experiments have been collected as "bench-scale experiments."

There are three main pieces of equipment involved: the small core appara-

tus¶ the large core apparatus, and the vapor-pressure lowering apparatus.

(a) Absolute Permeameter, by A. Sageev, Ramona Rolle, and Renee Rolle,

M.S. candidates in Petroleum Engineering, and Prof. H. J. Ramey, Jr.

Most of the efforts during the year were devoted to the rebuilding and

recalibration of the apparatus. This equipment has been in continuous use

for years. Both the coreholder and piping had to be replaced, and

placed in a new air bath.

in that it allowed substitution of a redesigned coreholder and some new

instrumentation. Recently, eight test runs were conducted, during which

several problems were identified and corrected. The results of these test

runs are presented, and the subsequent technical improvements are summar-

ized.

The rebuilding of the apparatus was also useful

At present, the apparatus is being used to measure absolute permea-

bility of silica sand to distilled water. It is anticipated that further

mechanical improvements will be made in order to attain a greater repro-

ducibility of results.

A s a check on the newly assembled equipment, some permeability measure-

ments were made at various temperatures. In a typical run, summarized in

-26-

-27-

Fig. 2-1, the confining pressure was 2000 psig, the average pore pressure

was 200 psig, and the temperature was varied over a range of 70°F to 300 F. 0

In general, there was no strong effect of temperature on the absolute

permeability to water.

lows :

The observations made during the run were as fol-

a. The initial room temperature permeability was around 4880 md.

b. After one cycle, the room temperature permeability dropped by

This lower value was also evident after the second heating 150 md.

cycle.

c. During the first heating, the permeability remained constant up

to 250°F.

d.

e.

In both cycles, the 250°F and 300°F permeabilities were the same.

The second heating cycle did not show significant hysteresis.

f. The measured values ranged from about 2% to 3%.

g. The calculated errors ranged from about 6% to 10%.

Some earlier test runs indicated a few of the same trends, although

there were technical problems (e.g., flowrate dependence) which were identi-

fied and corrected.

The sand used was Ottawa silica sand single mesh 150-120. The fluid

was distilled water, flowing at a rate ranging from 200 cclhr to 900 cc/hr

at room conditions.

After the first test runs, the equipment was improved in order t o get

a better monitoring of the temperature distribution and the pressure dif-

ferential, and also to achieve a laminar linear flow with minimal end ef-

fects. Changes were made one at a time, with a test run made after each

change. This allowed the evaluation of each problem. For example, the

-28-

I I I I I I I I r-

rl -rl 4

Q la rn

I 1 1 1 t

a w

I I I I 1 I I I I I

0 0 M

0 0 -

0

w pi

ri .. I

ru

-29-

apparent permeability increased by 30% after working the core plugs to a

better design. This indicated that there had been serious end effects

which had caused most of the dependence of the permeability on the flowrate.

Other improvements made were:

a. pressure tap location,

b. temperature control. and monitoring, and

C. flowrate control.

The behavior of the apparatus is now satisfactory. A report on this

work will be completed soon by Sageev. Some additional improvements may

be carried out in the near future to make a more reliable system. How-

ever, the main undertaking of current work will be the actual use of the

new system in both absolute and relative permeability determinations as

functions of temperature level and confining pressure. This apparatus can

be operated at much higher pressure levels than the large core apparatus.

(b) Large Core Apparatus, by Morse Jeffers and Mark Miller, Engineer's

Degree candidates, F. Rodriguez, Ph.D. candidate in Petroleum Engineering,

and Prof. H. J. Ramey, Jr.

This project is a continuation of several years of experimental work

investigating the relative permeabilities of laboratory cores to steam and

water (see Counsil, 1979, and Counsil and Ramey, 1979). Despite overcoming

many difficult experimental problems, the steam/water relative permea-

bility results have proved unsatisfying. Counsil found little effect of

temperature upon gas-water relative permeabilities for a synthetic cement-

sand consolidated porous medium.

to behave more like a limestone. Temperature sensitivity has never been

evident for limestones. In order to investigate the effect of the rock

We now suspect the artificial "sandstone"

-30-

matrix type, it was decided to perform runs with natural sandstones. Our

intention is to perform experiments for the case of two immiscible liquids.

To this end, the equipment has been redesigned and rebuilt. The require-

ments for the new apparatus were two-fold. First, it was necessary that

the apparatus be able to measure relative permeabilities of water-oil-

consolidated rock systems at elevated temperatures under unsteady-state

conditions. Second, it was considered desirable t o investigate dependence

of relative permeability on fluid distribution and/or flow direction. In

order to do this, flow in either direction of the core is required.

Figure 2-2 shows schematically the design of the new apparatus. The

equipment will be used for a constant flowrate displacement at a given

temperature. Measurements can be made of cumulative displaced liquid as

a function of cumulative injection, time, and pressure drop at room tempera-

ture, and this information corrected for temperature effects to derive an

appropriate method of relative permeability calculation at elevated tem-

peratures.

The apparatus is currently undergoing test and calibration, consisting

of the following:

a. air bath calibration (because of the poor insulation of the air

bath, temperature has been found to be a function of room temperature),

b. calibration of the dead volumes in the system, and

c. metering system calibration.

A consolidated sandcore with $I = 39%, length = 69 cm, and diameter =

5.08 cm has been prepared and mounted in the apparatus for testing purposes.

1 - -

-31-

I- Z W z W CK 3 cn U W z W & 3 cn cn W E a

I I I I I I I I I I I I

I I I I I I

Iy

Z W > 0

II I

Q

4 !.-?---’’ f l e t

W

0 0 0

J

m 3

3 c PI PI c 1 d31v3H3tld I w a: w o I

I W 3 s

W 3 s

W 3 9

W

!? n W W z

3 a 5 3

cy

.. .. c\l

I t-4 1 -J -

0 e I 1

crl W

-32-

(c) Vapor Pressure Lowering, by Dr. C.H. Hsieh and Prof. H.J.

Ramey , Jr . This bench-scale study involves an investigation of vapor pressure

lowering effects for liquid gas interfaces in the pore space of a porous

medium. Because of classic work in this field, it was believed that

these effects could be attributed to capillarity; however, the results

of this program indicated that the major cause of vapor pressure lowering

effects in a porous medium were probably caused by adsorption-desorption

phenomena. Consequently, a Brunauer-Emmett-Teller (1938) adsorption ap-

paratus was constructed which could be operated at various temperature

levels in an air bath. The mass of various gases adsorbed in several

sandstones was measured over a range of temperatures. The gases used in

this study included nitrogen, methane, and water vapor over temperature

ranges from room temperature to 300 F. Complete details of the result9

of this study are available in a dissertation by Hsieh (1980). Figure

2-3 shows typical results for adsorption of water vapor in a sandstone.

In general, the following important observations were made. Micropore

adsorption of water vapor is capable of storing a mass of water ten times

as great as the mass of steam in the pore space of a porous medium. This

is true at elevated temperatures, and appears to be one possible explana-

tion for the location of the liquid water in vapor-dominated geothermal

systems such as The Geysers steamfield in California and the Larderello

(Italy) vapor-dominated steamfields. This observation appears to agree

with conclusions reached during the year on the radon study cited in Sec-

tion 3 of this report.

The state of the adsorbed water appears to be somewhere between that

0

of a liquid and a solid. A new dialectric constant probe designed for

-33-

I I -

z 0

z 0

U H

.. m I hl

-34-

this equipment appears capable of measuring liquid contents for this type

of adsorption.

tories' experimental work.

This new probe design may have application in other labora-

The major effort during the past year on this project involves the

completion of analysis of Dr. Hsieh's data and his dissertation.

new measurements on a variety of additional cores were planned, and some

extremely low permeability samples were obtained. It is intended to ob-

tain samples of greywacke similar to The Geysers reservoir rock material

and other samples pertinent for geothermal vapor-dominated systems.

paper on this work has been offered for inclusion at the California Re-

gional Meeting of the Society of Petroleum Engineers in March 1381.

However,

A

3. RADON TRACER TECHNIQUES

During the current year, three major research studies were completed.

These were all aimed in different ways at establishing the value of radon

as an internal tracer in geothermal reservoirs. The work carried out has

been, or will shortly be, presented as dissertations. These studies related

to (1) radon transients in vapor-dominated reservoirs, (2 ) radon transect

analysis, and (3) radon emanation studies. Two advances arising from the

studies were the improvement of wellhead sampling techniques to reduce the

sampling and concentration standard error to less than 2 3%, and the use of

ammonia analysis of the well fluid to complement the radon analyses. An

important encouragement to this program has been the growing adoption of

radon measurements for geothermal reservoir evaluation by other laboratories.

To date radon studies are carried out at the Lawrence Berkeley Laboratories

(H. Wollenberg), Los Alamos Scientific Laboratory (J. Grigsby), New Mexico

Institute of Mining and Technology (M. Wilkening) in the U.S., and in

Italy (F. D'Amore), New Zealand (N. Whitehead), Mexico (D. Nievas), and

Japan (5 . Satomi).

Radon studies in the Stanford Geothermal Program fall into three

categories, each complementing the other two in our efforts to learn more

about the movement of fluid in geothermal reservoirs. Transient analysis

(the change in radon content with time) in the fluid discharging from a

single well is useful in deducing general properties of a reservoir, during

pressure transient analysis, a standard technique for measuring such

properties as the porosity and the permeability-thickness. With the

assumption that radon is conserved with the steam in the transport to the -35-

-36-

wellhead, concentration changes with changes in flowrate (or pressure)

are also useful in examining reservoir properties.

nique was given by Warren and Kruger (1979).

A review of this tech-

Radon transect analysis, described by Semprini and Kruger (1980),

gives us the radon concentration gradient along a line of geothermal wells

that span the structural features of a reservoir. The relationship of the

concentration of radon, with a half life of 3 . 8 days, to the concentration

of ammonia, a stable gas, has been determined f o r several transects.

The third group of studies was to evaluate the dependence of radon

concentration at the wellhead on the emanation characteristics of the

reservoir. Initial studies of emanation as a function of reservoir temper-

ature, pressure, and pore fluid were reported by Macias, Semprini, and

Kruger (1980).

(a) Radon Transient Analysis, by Gary Warren, Research Assistant,and

Paul Kruger.

Gary Warren completed his Engineer Degree dissertation with a review

of the status of radon transient measurements in vapor-dominated geothermal

reservoirs. Radon transient experiments had been run at The Geysers in

California and at Larderello in Italy.

and Kruger (1975) and D'Amoreet al. (1978), Warren developed a conical flow

model based on radon flow from a horizontal boiling front at constant flux.

This gives, at the wellbore,

Combining the work of Stoker

H tan 0 -At r N 2 ~ r x R e dx

0

(3-1)

-37-

where N = number of radon atoms reaching wellbore per unit time

R = radon flux across the boiling front (atoms/m 2 sec)

8 = angle of conic slice in the reservoir (from the well axis)

H = depth of the steam reservoir (m)

= travel time from boiling front to wellhead, given for Darcy tr

flow as 2 2 H sec 8 t =

r i; 3K AP

The radon concentration at the wellhead is given by

(3-2)

where L = average distance for the pressure gradient consistent with

the pressure drop Ap actual flow rate

Ap = pressure difference between boiling front and wellbore (atm)

K = reservoir permeability (darcy)

p = steam viscosity (cps)

A = cross sectional area of reservoir at boiling point (m ) 2

However, radon is also emanated in the steam zone of the reservoir, and

this additional flow t o the wellhead is given by

( 3 - 4 ) - Ah 3 secte)] d8dh

3voro

where r is the wellbore radius defining the upper limit of the reservoir. W

-38-

For Darcy f low, t h e wel lhead c o n c e n t r a t i o n of radon from t h e steam zone i s

W ‘r

The t o t a l radon c o n c e n t r a t i o n a t t h e wel lhead i s t h u s

(3-5)

S e v e r a l tests have been run o v e r t h e p a s t few y e a r s t o e v a l u a t e t h e

A summary of i n fo rma t ion a t t a i n a b l e from radon-mass t r a n s i e n t a n a l y s i s .

t h e s e tests is g iven i n Table 3-1.

dominated r e s e r v o i r s w a s r e p o r t e d by Warren and Kruger (1979).

s u l t s of t h e f i r s t of t h e s e tests has been r e p o r t e d ear l ier . A t r a n s i e n t

of 1223 days was observed fo l lowing t h e scheduled change i n f l o w r a t e .

However, a p e r i o d of seismic a c t i v i t y occurred j u s t b e f o r e t h e f l o w r a t e

change. Th i s made t h e a n a l y s i s of t h e t rans iept somewhat u n c e r t a i n , i n

t h a t a l eas t squa res f i t t o t h e c o n c e n t r a t i o n d a t a could be made by s tar t-

i n g t h e t r a n s i e n t from t h e mean v a l u e b e f o r e f l o w r a t e change o r ex t rapo-

l a t i n g t h e cu rve backwards t o t h e t i m e of f l o w r a t e change. These two

e x p o n e n t i a l cu rves r e s u l t e d i n h a l f p e r i o d s which b racke ted t h e decay

c o n s t a n t f o r . However t h e u n c e r t a i n t y in t roduced cannot r u l e o u t

o t h e r p r o c e s s e s , such as mixing, as c o n t r i b u t i n g t o t h e observed t r a n s i e n t .

Unfo r tuna te ly , because of a l t e r e d c o n d i t i o n s a t t h i s p a r t of The Geysers

f i e l d , t h e experiment cannot be r epea t ed .

An a n a l y s i s of f o u r tests i n vapor-

The re-

222R,

The f i r s t of two exper iments a t t h e G r o t t i t a n a w e l l a t L a r d e r e l l o ,

I t a l y confirmed t h e l i n e a r dependence of [Rn] on f l o w r a t e , b u t w i th a

-39-

TABLE 3-1: SUMMARY OF RADON TRANSIENT EXPERIMENTS

No. of Loca t ion Wells Condi t ions

VaporDominated

Rapid change i n f l o w r a t e ( i . e . r a p i d AQ)

The Geysers

L a r d e r e l l o 1 I s o l a t e d w e l l , r a p i d AQ

The Geysers 2 10- flowing w e l l f i e l d , AQ i n one w e l l

b n i t o r i n g i n second w e l l

The Geysers 1 Two AQ's i n w e l l i n nonproducing f i e l d

L a r d e r e l l o 1 I s o l a t e d w e l l , two AQ

Puma

Liquid-Dominated

1 Short-term tests i n one w e l l a t two f l o w r a t e s

P e t r o thermal

Fenton H i l l R e c i r c u l a t i o n of i n j e c t e d f l u i d i n f r a c t u r e system

Observa t ions

P r o p o r t i o n a l t r a n s i e n t w i t h pe r iod - 12+3 days

P r o p o r t i o n a l t r a n s i e n t w i t h pe r iod - 0.5k0.5 days

No change i n [Rn] i n e i t h e r w e l l

T r a n s i e n t build- up du r ing c o n s t a n t Q wi th changes w i t h AQ

P r o p o r t i o n a l t r a n s i e n t i n f i r s t AQ, nonpropo r t i ona l t ransient i n second AQ

No change i n [Rn] over t h e two s h o r t test p e r i o d s

Buildup of [Rn] over pe r iod of a p p l i e d p r e s s u r e

AQ = Change i n f low rate.

-40-

much shorter transient period of

are shown in Fig. 3-1.

0.5k0.5 days, The data for this test

Since the effective transient constant is greater

than 0.7 day-', much larger than the radioactive decay constant of

h = 0.18 day-', a process other than radioactive decay must be responsible

for the observed transient. Such processes might be changes in emanatiag

power with pressure changes in the formation and changes in fluid density

with changes in thermodynamic state.

both a linear and non-linear change in radon concentration with the two

changes in flowrate. The data are shown in Fig. 3-2. The first change

reproduced adequately the data in the first test, but a second change in

flowrate resulted in a lower, but nonlinear change in radon concentration.

The data are illustrated in Fig. 3-2 (Kruger, Cederberg, and Semprini~ 1 9 7 8 ) .

A summary of all the Grottitana data is given in Table 3-2.

The second test at Grottitana showed

TABLE 3-2: RADON TRANSIENT TESTS AT GROTTITANA, ITALY

Test No.

1

2

2

Flowrate Range Q ( t/hr 1

7.5- 11.8

8.1- 1 1 . 3

4.6- 5.0

Mean Radon-Flowrate Ratio

[Rnl /Q

7.33 k 0.76

7.8 f 0.3

11.5 2 0.6

The processes that could account for the observed nonlinear relation in-

clude (1) increased reservoir pressure at lower flowrates, resulting in

increased emanation in fractured rock, ( 2 ) nonlinear emanation from the

boiling front, ( 3 ) condensation of steam under subcooled transit .to the

wells, and ( 4 ) incorrect flowrate measurements at the very low flowrates.

Plans are underway to run a third transient test at Grottitana with mon-

itoring in a nearby well.

t

-41-

-

TIME (days)

FIG. 3-1: RADON TRANSIENT DATA; GROTTITANA, SERRGZZANO, ITALY

I I 1 I I I I I

C 2 4 6 a IO 12 14 16 18

'12

IO

0 8

h .c \

6 c

0 U

4

2

3 1

EUPSED TIME (days)

FIG. 3-2: RADON DATA; GROTTITANA WELL, ITALY

-4 2-

The two additional tests at different areas of The Geysers provided

interesting observations. The first was carried out in a newer area when

one of two twin generators was under repair and the operators were able

to reduce flow in one of the ten wells feeding the second generator.

concentrations were monitored in two wells and two flowrate changes were

carried out in one of the wells. The results, as shown in Fig. 3-3, Warren

and Kruger (1979), showed a constant radon concentration in both wells

over the total period of flowrate changes. These observations suggest

two alternatives: (1) that the steam source was common to all ten wells

that supply steam to the operating unit (thus a 50% change in flowrate in

one well might be expected to produce only a 5% change in the overall

radon concentration, a change too small to observe); or (2) that the

difference in mean concentration between the two wells might be due to

local variations in radium content or emanating power, or to a partitioning

of flow through the multiple-fractured formation resulting in a distribu-

tion of transit times to the individual wells. These data suggested the

Radon

use of transect analysis to see if a distribution of steam age exists

across the reservoir.

The last test was an extended test of a well in a new production zone

where the power plants had not yet been installed.

long test during which the flowrate stabilized over a two-week period.

Sampling at this established flowrate was carried out for three weeks,

through a reduction in flowrate and then for two further weeks at full

flow. These samples showed an increase in radon concentration with

cyclic fluctuations (Fig. 3 - 4 ) . A least squares fit through the cycle

averaged data for this period of the test showed an exponential increase

of the form:

Flow commenced for a

-43-

4- z 8 2 - [L

Geysers AQ AQ

TIME (days)

FIG. 3-3: RADON TRANSIENT DATA, WELLS VI-1 AND VI-3, THE GEYSERS, CALIFORNIA. WELL VI-3 FLOWRATE CONSTANT AT 235 klb/hr.

-44-

Rn- Flow Tronsient Test The Geysers Well IV-62

e ? (Rn] nCi/kg

f l l \ l l A P IO* Dsia

0 6 1 2 1 TIME (days)

FIG. 3 - 4 : RADON TRANSIENT DATA, WELL IV-62, THE GEYSERS, CALIFORNIA

-45-

J (3-7) -0.062t

C = 2.4 + 3.8 [l - e

wi th C i n nCi/kg and t i n days (Fig. 3-5). Following the f lowrate change

of 50% on day 38 a t t h e end of t h a t period, t h e mean radon concentra t ion

decreased by 14%, a s i g n i f i c a n t decrease considering t h e genera l t rend

of increase wi th sus ta ined f l u i d production. On r e t u r n of f lowra te t o

f u l l va lue , t h e radon concentra t ion aga in began t o increase . Warren

and Kruger (1979) noted s e v e r a l models which might account f o r t h e ob-

served data . This tes t underscored t h e need t o ob ta in radon measurements

e a r l y i n t h e production h i s t o r y of new w e l l s .

expected t o inc rease a t constant production i f t h e steam production a t

e a r l y times dep le tes t h e nearby pore volume of l i q u i d water and t h e

bo i l ingf ron tmoves s u f f i c i e n t l y f a r i n t o t h e r e s e r v o i r t o have f u l l

mixing.

normal on- line production of f l u i d f o r e l e c t r i c i t y genera t ion , s u f f i c i e n t

oppor tun i t i e s occur i n U.S. f i e l d s and abroad t o continue t h e development

of a radon t r a n s i e n t a n a l y s i s method.

j o i n t p ressure t r a n s i e n t and mass t rans ient a n a l y s i s should be c a r r i e d

out t o compare t h e information obtained by p ressure response and mass

flow response t o changes i n wellhead flow rates.

The emanation of radon i s

Although it i s d i f f i c u l t t o ob ta in f lowrate reduct ion during

A t some f u t u r e opportune t i m e , a

(b) Radon Transect Analysis , by L e w i s Semprini, Research Ass i s t an t ,

and Paul Kruger.

During t h e cur ren t year, L e w i s Semprini completed t h e labora tory work

on radon t r a n s e c t experiments a t th ree geothermal f i e l d s : t h e vapor-

dominated f i e l d a t The Geysers, Ca l i fo rn ia , and a t the l i q u i d dominated

f i e l d s a t Wairakei, New Zealand and Cerro P r i e t o , Mexico. The o b j e c t i v e

-46-

I I I I I I

Radon- Flow Transient Test The Geysers Well IV-62

0 Flowrote (IO5 Ib/hr) 0 (Rn] (nCi/kqI (grouped doto)

-

-

-

-

-

1 I I I I I I I 1 I

0 IO 20 30 40 50 60 70 80 90 TIME (days)

FIG. 3-5: RADON TRANSIENT DATA, WELL IV-62, GROUPED ANALYSIS

-47-

of the . radon t r ansec t a n a l y s i s is t o examine t h e concentrat ion gradien ts

of radon and o ther noncondensable gas components i n t he geof lu id along a

l i n e of w e l l s i n t e r s e c t i n g s i g n i f i c a n t s t r u c t u r a l f e a t u r e s i n the r e se rvo i r .

The purpose is t o provide temporal information on t h e flow regime ac ros s

t h e r e se rvo i r .

d i c a t e changes i n the source of both steam and radon emanation. To de ter-

mine i f observed v a r i a t i o n s i n radon concentrat ion are r e l a t e d t o t r anspor t

r a t h e r than t o r ad ioac t ive decay, measurements are a l s o made of ammonia

i n the same samples.

a b l e gases.

by Semprini and Kruger (1980).

I f t h e concentrat ions are not t i m e dependent, they in-

Ammonia is a l l s tab le" gas component i n t he noncondens-

Details of t h e method and sampling procedures are descr ibed

Radon t r a n s e c t s have been run i n t h e o lde r producing zone a t The

Geysers i n 1978 and 1979. The r e s u l t s of these two tests are given i n

Fig. 3-6; t h e g rad ien t s i n radon concentrat ion show a s imi lar t rend of

decreasing concentrat ion along t h e t r ansec t . I n t h e la t ter tes t , t he

r a t i o of radon t o ammonia, shown i n Fig. 3- 7 , i nd i ca t e s a l i n e a r c o r r e l a t i o n

between the two gases and suggests t h a t these two have a s imi lar source i n

t he r e s e r v o i r and undergo similar t r anspor t processes. Fig. 3- 8 , which

ampl i f i e s t h e i n i t i a l sharp g rad ien t on t h e l e f t , shows the d a t a i n re-

l a t i o n t o t he r e s e r v o i r cross- sect ion published by Lipman, e t aL(1977) .

A discuss ion of t h e poss ib l e processes cons i s t en t wi th the observed da t a

are given by Semprini and Kruger (1980).

#

A t r a n s e c t experiment was conducted a t Wairakei, New Zealand, where

a l a r g e d i f f e r ence i n radon concentrat ion had been measured i n w e l l s a c ros s

t h e major Wairakei and o the r f a u l t s .

b o t t l e s were shipped t o Wairakei t o obta in samples along t r a n s e c t s p a r a l l e l

and normal t o t h e major f a u l t .

A s a r e s u l t , a number of our s tee l

The r e s u l t s of t h i s test are given i n

-48-

80r \<Rn, Jan 1978

\ 9, Y \

0 .- c Y

T E U

I I I I I I 4 h i 4 b k I. 8 I 9 I IO I It ’ I I ’ 12 I3 13’ 14 15 L

WELLS ALONG TRANSECT

FIG. 3-6: RADON TRANSECTS ACROSS THE OLDER PRODUCING ZONE OF THE GEYSERS FIELD

/ RADON -AMMONIA CORRELATION /”/

50 GEYSERS TRANSECTS // / ‘I /

= 4.5 n C i /Kg yo / /

SLOPE = .0742

CORRELATION COEFFICIENT = .973

Y O / 8

y o

r - 0 100 200 300 400 500 600 700

N H 3 ( m g l l )

FIG. 3-7: THE RADON-AMONNIA CORRELATION FOR THE 1979 TRANSECT ACROSS THE GNSERS FIELD

6C L

50

40

30

20 J W > W -I

W cn 0 I- W >

J W e I- W W LL

a

- G

I I I I E Y m m 2000- I1 11 - II

COOL ROCK

FRACTURE CONTINUITY

- 1000- WITH POOR

-2000-

-3000-

-4000-

b

-49-

REGIONAL DRAINAGE SYSTEM

0 500 1OOOFt. ~~

Horizontal Scale

FIG. 3-8: THE MATCH BETWEEN THE RADON CONCENTRATION AND THE LOCAL GEOLOGY IN A SECTION OF THE GEYSERS

-50-

Table 3 3 . Horne and Kruger (1979) suggested t h a t t he radon concentrat ion

may be co r re l a t ed with f l u i d enthalpy based on t h e mixed f l u i d na tu re a t

Wairakei; a lower l iqu id- aqui fer and an upper s t e a m zone.

concent ra t ion noted f o r a vapor-dominated system can be modified f o r a

geothermal f l u i d of steam s a t u r a t i o n , x, as

The equi l ibr ium

EmPf

pL c = x - + (1-X) -

T PV

where x, (1-x), P L r e f e r t o t h e l i q u i d phase.

are given i n Fig. 3-9. A discuss ion of these da t a are given by Semprini

and Kruger (1980).

P v r e f e r t o t h e s a t u r a t i o n and dens i ty of t h e vapor phase and

The c o r r e l a t i o n of t h e t r a n s e c t d a t a

The t r a n s e c t study a t Cerro P r i e t o w a s conducted as a j o i n t p r o j e c t

wi th the Coordinadora Ejecut iva de Cerro P r i e t o of t h e Comisi6n Federal de

E lec t r i c idad of Mexico. Resul t s from the two t r a n s e c t experiments con-

ducted i n October 1979 and March 1980 are given i n Tables 3-4 and 3-5.

The wellhead radon concent ra t ion ranged from 0.16 t o 3.60 nCi/kg i n the

21 w e l l s t e s t e d ; t he ammonia concentrat ion ranged from 17.6 t o 59.3 mg/l,

based on mass balance a t t h e cyclone separa tors .

t h e water phase were est imated wi th empir ica l p a r t i t i o n c o e f f i c i e n t s fram

mass balance measurements a t s eve ra l cyclone sepa ra to r s i n t he f i e l d .

Radon and ammonia i n

The loca t ion of w e l l s along each of t h e t r a n s e c t s is shown i n Fig. 3-10.

The corresponding ammonia, radon and enthalpy content along the four t ran-

sect l i n e s are shown i n Fig. 3-11. The r e s u l t s show high content of a l l

t h ree components i n w e l l s M45, M48, M84 which are producing two-phase

f l u i d s of high vapor content i n t h e c e n t r a l southern area of the f i e l d .

-- I

-51-

rl

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3 In

In m d

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m

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m

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m r- d

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v)

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m

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rl

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Ti 0

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B

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9

m I- m

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-52-

1500

1400 h

0 Y ‘ I300 2 Y

z 1200 -I

I I- Id

a

z 1100

1000

900

Radon - Enthalpy Correlation WAIRAKEI TRANSECT

Best Fit Line Y = 966 k J/ kg

coefficient =.94 1’

Slope = 184 Corre io t ion

260°C Reservoir,,,/

m3(pore volume),/

/ 156nCi / = -

I I I I I I .5 1.0 1.5 20 2.5 3.0

Rn ( n C i / k q ) wellhead

FIG. 3-9: THE RADON-ENTHALPY CORRELATION FOR WAIRAKEI, NEW ZEALAND

FIG. 3-10: LOCATION OF WELLS AND CROSS-SECTIONS OF THE CERRO PRIETO TRANSECT TESTS

- I

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m

OD 0 d

ut 0 d

0 m &

!2

d

m m

0 co

N W

0

W

N 9

W

CQ co H

m

co d

co U m d

0 d d

m N rl

0 In

&

In

\o

h

N m

'j. 0 4

co W

U h

0

N m d

N

U U d

m h

h

W U

9 N 4

02 co

N W

0

\D m d

QI

rr) m

1 ? g -_. co N

m I n N U m a r l r l

m d m d c o

h 4 0 4 . m

In

0 U

9 co d

u)

2

W W

d

co v)

N

h

h

h

U m

9 d d

In co

QI N

d

N m d

/ , - I

-55-

A ENTHALPY (kJ/kq) x IO3

* - O r cross-section p\ P

-e-- 1, ~ #--+ -- -0L

0 Radon (nCi/kg) 2.01 o Ammonia ( m g / I ) xi02

0 1 M 9 0 M 5 0 M 5 1 M 4 8 M 6 4 MI02 M I 0 9 M II M 5 M 2 7 M B M 4 8 Mgl 01

Cross- Section A-B Cross-section C-E 3

2

MI05 M50 M5I M91 MU 03 MI1 M I 7 M 2 5 M31 M35 M 4 5 M 5 0 M90 0

M 30

I

FIG. 3-11: CERRO PRIETO CROSS-SECTION; AMMONIA - W O N - ENTHALPY WELLHEAD FLUID

-56-

Production from the nor thern s e c t i o n of t h e f i e l d w a s p r imar i ly l i q u i d

with lower (and more uniform) enthalpy, radon and ammonia content .

The radon-enthalpy c o r r e l a t i o n a t Cerro P r i e t o is shown i n Fig. 3-12.

The l i n e a r c o r r e l a t i o n i s not as good as the one observed i n the Wairakei

experiment (Semprini and Kruger, 1980). The c o r r e l a t i o n , however , does

i n d i c a t e t h e radon concentrat ion i s dependent on two-phase condit ions i n

t h e r e se rvo i r . Several processes t h a t could lead t o these observed va r i-

a t i o n s from a l i n e a r c o r r e l a t i o n of radon and enthalpy are being evaluated.

Among them are (1) l a c k of r ad ioac t ive equi l ibr ium i n t h e two-phase f l u i d s

a f t e r phase separa t ion , and (2) changes i n f l u i d dens i ty due t o v a r i a t i o n s

i n r e s e r v o i r temperature along the var ious flow paths.

The r e s u l t s from the radon t r ansec t experiments a t Wairakei and Cerro

P r i e t o i n d i c a t e t h a t two-phase flow i n hot water systems can be s tudied

using radon. Future radon t r ansec t and t r a n s i e n t experiments i n these

and o the r developed hot water systems w i l l a i d i n s tudying two-phase flow

i n g r e a t e r d e t a i l .

(c) Radon Emanation Studies , by Luis Macias-Chapa, Research Ass is tan t

and Paul Kruger.

During t h e cu r r en t year , Luis Macias completed a series of measure-

ments of radon emanation i n a 3-unit phys ica l model of a f r ac tu red geo-

thermal r e se rvo i r . I n t h i s model t h e closed na tu re of t h e system al lows

radon buildup without f l u i d t r anspor t u n t i l t he system is swept out f o r

radiochemical ana lys i s .

high temperature a i r ba th is shown i n Fig. 3-13.

A cross- sect ion of t he model i n t he l a r g e volume,

The emanating power of radon from rock is dependent on seve ra l rock-

f l u i d p rope r t i e s , notably the rock type ( s t r u c t u r e and radium content ) ,

-57-

I /

2400- 0 . 320°C Reservoir

:45,< 0

,' 280°C Reservoir 168nCi

'= m3(pore volume)

2200 - h

Y

Predicted from Equilibrium >r

0 9 1800 -

Calculations

/*, I I I I I I I I

,200; I 2 3 4 Rn (nCi/kg) wellhead

FIG. 3-12: CORRELATION OF RADON AND ENTHALPY FOR CERRO PRIETO TRANSECTS

WATER TRAP

NITROGEN

FIG. 3-13: RADON EMANATION SYSTEPI

-5 8-

the rock size (radon recoil and diffusion), the pore fluid type

[density and saturation), and the thermodynamic variables of pressure and

temperature.

For his experiments Macias fixed the first two named variables

by selecting a greywacke rock, representative of the rock in The Geysers

area, and a rock size compatible with the model scale.

were thus reduced to temperature, pressure and pore fluid, and for the

latter he used a noncondensable gas (nitrogen), water, and steam.

The variables

Results for all the experiments, illustrated in Fig. 3-14, suggest a

mechanism for radon emanation which depends on the presence of liquid

water in the pore spaces. Thus for dry nitrogen and liquid water, the

results show little variation of emanation with pressure and an increase

with the changes in temperature. The steam result, in contrast, shows an

increase in emanation with pressure. The early nitrogen result (Fig. 3-14a)

also shows a similar increase along with a marked drop in emanation in the

279OC test. Radon emanation is dependent on the density of the pore fluid

and may be expected to be low for superheated steam and dry nitrogen pore

fluids. If water is present, however, then the emanation would be greater.

These results are particularly interesting in light of the work

recently carried out by Hsieh (1980) on water absorption. Hsieh's work

indicated that liquid water may be absorbed in micropores in a porous

medium under superheated steam conditions. The radon results fit in with

this conclusion. A preliminary report covering early results was pre-

sented by Macias, Semprini and Kruger (1980). A full discussion of the

study and the results will be available shortly (L. Macias, Engineering

Thesis).

u N 0

1::

U

n N 0

-39-

n

N

I I 1 2 In

( % I NOIlVNVW3 NOQV8

n a W

- v)

4.0 WELL TEST ANALYSIS

Well test analysis offers a rapid way to perform an initial assessment

of geothermal systems. Well testing includes both pressure drawdown and

buildup testing, and interference testing. Development of new well test

analyses continues to receive major emphasis in the Stanford Geothermal

Program.

and papers presented on a variety of well test analysis methods. The follow-

ing summarizes some of the more important results.

During the year, quite a few studies were completed, and reports

(a) Constant Pressure Testing, by Dr. C. Ehlig-Economides and Prof.

H.J. Ramey, Jr.

Although the conditions which result in constant pressure flow often

exist for geothermal production and injection wells, the methods for

analyzing the resulting rate transients and pressure buildup for such

wells have been incomplete or nonexistent. The objective of this work was

to review the existing methods of analysis and to contribute new solutions

where needed in order to produce a comprehensive well test analysis package

for wells produced at constant pressure. The work was completed during

the year, and a technical report, SGP-TR-36, has been published. Other

publications of results from this project are given by Ehlig-Economides

and Ramey (April, June, November 1979).

The methods described in this work are:

- Determination of permeability and skin effect by type-curve match- ing with a graph of log rate vs log flow time for an infinite system.

-60-

-61-

- Determination of permeability and skin effect from a semilog

straight line on a graph of reciprocal rate vs log of flow time.

- Determination of reservoir volume and approximate shape from a

graph of log rate vs flow time after the onset of exponential decline.

- Analysis of transient rates when the wellhead pressure is constant. - Determination of permeability and skin effect from an interference

test by type-curve matching with a graph of log pressure drop vs log flow

time for an infinite system.

- Determination of wellbore storage, skin effect, and fracture half- length for fractures penetrated by a wellbore, and other inner boundary

effects, by type-curve matching of early pressure buildup data with con-

ventional pressure transient solutions.

- Horner buildup analysis for wells produced at constant pressure.

- Analogous methods for the Matthews, Brons, and Hazebroek determi- nation of static reservoir pressure.

(b) Parallelepiped Models, by D. Ogbe and M. Economides, Ph.D.

Candidates in Petroleum Engineering, and Prof. R.N. Horne, Prof. F.G.

Miller, and Prof. H.J. Ramey, Jr.

These models have been successful in demonstrating three-dimensional

Last year's work in this area boundary effects in geothermal reservoirs.

focused on a three-dimensional reservoir contained on all sides and at the

top by impermeable boundaries, with a constant pressure boiling surface at

the base. These models (either with a partially penetrating well or frac-

ture) were used successfully to analyze well test data from The Geysers

and the Travale-Radicondoli fields (see Economides et al., 1980). This

year's activities extended the model to include the configuration of a

-62-

three-dimensional reservoir with a boiling surface at the base and a con-

densation surface at the top. This situation is characteristic of the

Kawah Kamojang field in Indonesia, and also of some parts of The Geysers.

Typical drawdowns for such a system are illustrated in Fig. 4-1.

objective of this study is to produce generally useful type-curves with

an emphasis on detection of the outer limits of the reservoir. It is

also intended that these models be used to represent the entire drainage

volume for a power plant (encompassing ten or more wells).

The

(c) "Slug Test" DST Analysis, by K. Shinohara, Ph.D. Candidate in

Petroleum Engineering, and Prof. H.J. Ramey, Jr.

The solutions for the slug test (decreasing flowrate) drill stem test

(DST), including wellbore storage and skin effect, were presented by

Ramey et al. in 1975. In field data from slug test DSTs, an initial

period of constant flowrate can often be observed. A new model which in-

cludes the initial constant flowrate for a slug test was developed. Type-

curves were graphed which were then matched with field data. Two examples

of the quality of the match between actual data and a slug test type-curve

are shown in Fig. 4-2.

the flow period and the pressure buildup after a short initial shut-in in

a DST. A special feature of the new type-curves is that they may be used

to estimate the initial formation pressure from the initial cleanup flow

pressure buildup data even when the flow is so short that a Horner buildup

graph is not possible (see Shinohara and Ramey, 1979).

The slug test type-curves can be applied to both

In deep, high-rate wells, the inertia and momentum of the liquid

moving in the wellbore become important. Most available pressure transient

solutions neglect these phenomena. Sometimes the inertia effect can cause

-63- I I *

0 0 - - II

n \

r

.

II

c C

cu II

'n s

I1

c ' n

0 " t o y 0 0 0 0 0

3 1 W S 901 * ' ad

-64-

- - _ MINUTES

FIG. 4- 2: FIELD DATA MATCHED WITH SLUG TEST AND CONSTANT RATE TYPE -CURV E S

-65-

oscillation of the liquid level in the wellbore. An approximate method

using an exponentially damped fluctuation was presented by van der Kamp

in 1976.

sure behavior, which is often of interest. A complete analytical solution

for this problem was found, and the resulting type-curves were graphed and

matched with field examples. Figure 4-3 shows some of the new solutions.

The parameter % represents the fractional liquid level rise following

the sudden removal of the liquid from a static wellbore. This acts like

opening a bottomhole valve in a DST when there is air in the drill pipe!.

The parameter a is:

However, this method cannot be applied to the early time pres-

2

where L is the well depth and g is the acceleration of gravity.

symbols have their usual meaning. The term a is a new parameter which

considers momentum or inertia of fluid in the wellbore. A value a = 0

is the usual slug test. When a reaches values of 10 or more, the re-

sults differ greatly from the slug test.

or more. Both the skin effect and wellbore storage affect the results

significantly.

This theory can also be applied to closed-chamber DSTs and water in-

Other 2

2

2 5

Oscillations occur when a2 = 10

jection falloff tests. These results were published by Shinohara and

Ramey (1979, 1980), and also as SGP-TR-39, Shinohara (April 1980).

(d) Analysis of Wells with Phase Boundaries, by Profs. R.N. Horn@,

A. Satman, and H.J. Ramey, Jr.

-66-

I

M 0 -

N 0 -

.. m

I U

-67-

The analysis of pressure tests in geothermal reservoirs is often

complicated by two-phase effects. This work investigated the effect of a

phase boundary at a constant radial distance from the well, produced, for

example, by the flashing of a water reservoir during production or by the

injection of water into a steam or two-phase reservoir.

tion may be recognized from a time shift in the buildup (or falloff) semi-

log straight line. In some cases, the distance to the phase boundary can

be estimated by graphing the transition pressure response against time on

Cartesian coordinates.

from the Broadlands geothermal field in New Zealand confirmed the appli-

cability of the technique and demonstrated that the injected volume (which

is known) may be used with the buildup data to calculate porosity and

This configura-

Field data (provided by Malcolm Grant of the DSIR)

swept" volume. 11

The analysis also indicates the possibility of determining compres-

This en- sibility and permeability contrasts across the phase boundary.

ables estimation of the reservoir porosity and relative permeabilities in

the two-phase region.

guise the pressure response and make parameter determination difficult.

In a few cases, wellbore storage effects can dis-

It was concluded that:

a. In a reservoir with a radial discontinuity, the mobility ratio

may be determined from the relative slopes of the early and long-time

semilog straight lines, as in Fig. 4- 4 .

b. In cases where the hydraulic diffusivity is also discontinuous,

the early and long-time semilog straight lines are removed from one

another by a distance dependent on the diffusivity ratio (as in Fig. 4-5) .

This distance may be indeterminable if a mobility ratio also exists.

c. In the case of an infinite reservoir, the position of the dis-

continuity does not affect the determination of the mobility or diffusivity

- --

-68-

, O t \ \

L--; 0.1 10 100 1000

t D A

FIG. 4-4: PRESSURE DRAWDOWN RESPONSE AS A FUNCTION OF MOBILITY RATIO. DIFFUSIVITY RATIO 1.

3.0 "I 6= 1

FIG. 4-5: PRESSURE DRAWDOWN RESPONSE AS A FUNCTION OF DIFFUSIVITY RATIO. MOBILITY RATIO 1.

-69-

ratios since the pressure response is geometrically similar for physi-

cally realistic times.

d. In the case of a finite system, the interception of a boundary

may occur before the appearance of the semilog outer region response,

in which case the analysis will not be possible.

e. At the end of the first semilog straight line there may exist a

period of pseudosteady-state flow that permits the direct calculation of

the volume of reservoir "inside" the phase boundary.

Figure 4-6 shows an injection falloff in Broadlands well number BR26

which proved accessible to the new method of analysis.

This work was presented by Horne and Satman (1980), and Horne, Sat-

man, and Grant (1980a). A s an informal cooperative program with the New

Zealand Department of Scientific and Industrial Research, it will also be

presented at the 1980 New Zealand Geothermal Workshop in November 1980,

as Horne, Satman, and Grant (1980b).

(e) Internal Well Flows, by M. Castaneda-Oliveras, M.S. Candidate in

Petroleum Engineering, and Prof. R.N. Horne.

Experience in analysis of temperature and pressure profiles in geo-

thermal wells has indicated that flow frequently occurs from one produc-

tion (interval) level to another--even though the well may be shut in at

the wellhead. This flow occurs because pressure gradients in the reser-

voir are frequently greater than hydrostatic, while those in the well are

restricted to be hydrostatic unless the fluid is moving. The resulting

pressure imbalance causes the well to flow from one level (interval) to

another. The recognition of these flows has been the subject of study by

Grant (1979) based on a number of observations, including temperature

-70-

I

4

AP 1b.l

3

1

1

0

//” -2.3 bar/cycle

9 J I I I I

1 10 100 0.1 0.01

At lminl

FIG. 4-6: PROJECTION FALLOFF TEST ON WELL BU6. SEMILOG COORDINATES.

-71-

profiles during heatup, injection, etc. The present study investigated

the difference between the observed pressure gradient in a shut-in well,

and the inferred hydrostatic pressure gradient calculated using the simul-

taneously measured temperature.

Analyzing a shut-in temperature/pressure log from well M-9 at Cerro

Prieto, it was determined that internal flow occurred below a depth of

2500 feet since the observed well pressure gradient changed sharply from

hydrostatic at this depth (see Fig. 4- 7) . This well proved to be an ex-

cellent demonstration of the method because it is actually perforated at

this depth; thus confirming the conclusion of the pressure gradient com-

parison.

Further tests using different Cerro Prieto wells are in progress.

It is .anticipated that the method may be useful for the one-step recog-

nition of producing levels and internal flows, and may even be able to

detect other perturbations such as casing leaks. The rapid evaluation of

internal flows is of importance in the correct interpretation of all other

pressure tests, and should be considered a first step in any pressure test.

(f) Naturally Fractured Reservoirs, by G. Da Prat, Ph.D. Candidate,

Petroleum Engineering, Prof. H. Cinco-Ley, and Prof. H.J. Ramey, Jr.

This study presents solutions for declining production rates under

Solu- constant pressure production in a naturally fractured reservoir.

tions for dimensionless flowrate are based on the model presented by

Warren and Root (1963).

Cinco-Ley (1979) to include wellbore storage and skin effect. In the

present study, the model was extended to include constant producing

pressure in both infinite and finite systems. Figure 4-8 shows the

The model was extended previously by Mavor and

-72-

C

40C

00c

1200

1600

2400

c w-

3600

4000.

f 2000 a W 0

I I I I I I I

2800

3200

I I I I I I I

A FROM PRESSURE LOG

0 FROM HYDROSTATIC GRADIENT PERFORATED INTERVAL = 2348 = 2816 f t

c

A

PRESSURE GRADIENT, psialf t X I 0 0

FIG. 4-7: PRESSURE VS DEPTH FOR WELL Y-9, CERRO PRIETO, MEXICO

-73-

F I G . 4-8: qD VS tD FOR CONSTANT PRESSURE PRODUCTION; CLOSED BOUNDARY

= 50, SKIN FACTOR = 0) (‘eD

results obtained for a finite, no-flow outer boundary.

a rapid decline initially, becomes nearly constant for a period, and then

a final decline in rate takes place. The new type-curves of the analyti-

cal solutions are graphed in terms of the following dimensionless param-

eters:

The flowrate shows

2.637~10-~ k, t L t, =

km 2

kf X = a - r

where k and k are fracture and matrix permeabilities, respectively, f m

OfCf and 4 C are fracture and matrix porosity-compressibility products, m m respectively, and a is the interporosity shape factor. The two parameters

and w are then new governing dimensionless groups, and the remaining

symbols have their standard SPE interpretation.

Figures 4-9 and 4-10 show the solution for a homogeneous system

compared to a fractured reservoir. An important conclusion of

this work is that a type-curve matching based only on the initial decline

can lead to erroneous values for the dimensionless wellbore outer radius,

r if the system is considered homogeneous. X and w should be obtained

from pressure buildup analysis, and these values used to define the par-

ticular type-curve to be used in production forecasting or matching for

eD ’

1 , - -

-75-

h

0

I1

- -

-76-

0 0 0 Lo

-77-

estimation of reservoir size.

curve illustrating the long period of constant flowrate for large r

Knowing X and w, some information about reservoir geometry such as the

apparent matrix block dimensions and fracture storativity can be obtained

from a type-curve matching.

Figures 4-11 and 4-12 show another type-

' s . eD

Portions of this work were presented at the SPE of AIME Annual Fall

Meeting in Dallas, Texas, 1980 (Da Prat, Cinco-Ley, and Ramey, 1980). Work

will continue in this area.

( 8 ) Temperature-Induced Wellbore Storage Effects, by U. Araktingi,

M.S. in Petroleum Engineering, and Prof. H.J. Ramey, Jr.

Wellbore storage is usually attributed to pressure changes occurring

in the well. This study found that wellbore storage is also affected by

heat transmission and the resulting temperature changes that result from

flow in the well. The inner boundary condition for solution of the dif-

fusivity equation for a single-phase well in an infinite radial reservoir

was stated so as to include a wellbore storage term depending on tempera-

ture changes. Using Laplace transform methods, an exact solution des-

cribing the pressure behavior of the fluid in the system was sought.

ever, due to the form of the term describing temperature changes in the

wellbore, it was not to find a simple solution form. Nonetheless, the

problem was prepared for solution using numerical inversion.

systems were also considered, and the inner boundary condition describing

such a situation was also derived. Several examples of two-phase systems

were described wherein the importance of temperature changes was apparent.

An M.S. report was completed by Araktingi (1980). Further work is planned

on this important class of problems.

How-

Two-phase

1 1

-78-

a c

\D I 0 cl X VI

II

3 v

R

.. rl rl I U

L!) H Fr

- _I

-79-

c

I 0 rl x m It

r.:

rl 0

m

d II

3 W

.. N rl I .3

k

-80-

In addition to the preceding, many other field applications of well

test analysis were conducted and reported during the year.

performed and analyzed in the Ching-Shui Field, Taiwan (see Ramey and

Kruger,eds.,1979), a new type-curve for interference testing was re-

ported by h e y (3rd LBL Well Testing Workshop, 1980), and planning and

analysis of preliminary well tests in the Miravalles Field, Costa Rica,

were completed (Ramey, November 1980) during July 1980.

Tests were

5.0 CONCLUSIONS AND RECOMMENDATIONS

This year was probably the most productive and surprising in the

history of the Stanford Geothermal Program. Dr. Hsieh's measurements

of the water adsorbed in the micropores of consolidated porous media

indicated that a major source of the fluid produced from vapor-dominated

geothermal systems could be adsorbed water. His observations lend cre-

dence to a theory proposed by Don White and Pat Muffler, and provided

additional evidence to the gravitational field changes observed

by Denlinger, Isherwood, and Kovach (1979). Furthermore, observations by

Macias and Kruger concerning the radon emanating characteristics of the

formation and their dependecce on pore liquid also support the view that

it is necessary that an adsorbed liquid phase be present in vapor-dominated

geothermal systems.

Program suddenly focused on the major problem of production of geothermal

steam from vapor-dominated systems: where is the liquid phase?

recommendation is that both works be continued for the coming year to

further verify the conclusion suddenly evident during the past year.

Thus two separate parts of the Stanford Geothermal

An obvious

A key feature of the Stanford Geothermal Program has been a focus of

attention on the behavior of fractured systems. Almost every presently

commercially developed geothermal system and proposed geothermal system

depends on the existence of fractures. In some cases, the fractures are

natural and in others they are induced by such techniques as hydraulic

fracturing.

aimed in this direction.

year's effort on fractured systems lie in the area of well test analysis.

Efforts on energy extraction in well test analysis have been

Perhaps the most important results from this

-81-

r

-82-

Studies on the behavior of reservoir models containing either natural or

hydraulically-induced fractures have been significant during this year.

Perhaps the most surprising result, however, came from studies of naturally

fractured reservoirs. Frequently these systems are produced at essentially

constant pressure, and declining rate-time results are observed. Analytic

calculations have indicated that for many of these systems, the rate will

eventually stabilize and hold at nearly constant rate for decades of time.

A second important result in the study of fractured systems has been

the steady development of the one-lump model of heat extraction based on

the heat transfer from an equivalent sphere concept developed successively

by Hunsbedt, Kuo, and Iregui. The natural continuation is to continue

the analytical means for rapid evaluation of commercial resources while

improving the experimental data base for the model.

attempted in one or more large-scale systems.

Analysis will be

Many other surprising results from well test analysis were found

during the year. A major new area of study was discovered in an investi-

gation of well inertia and momentum effects for testing of high rate pro-

ducing wells.

with phase boundaries in the near well regions. Problems of this type

include the boiling of a hot geothermal liquid while flowing toward a

well.

densate into a geothermal system. It appears that the pressure-time data

of such well tests include information heretofore unsuspected. The most

important of this information concerns the volume of the near well region.

Other surprising results were found for analysis of wells

Other problems are concerned with reinjection of cold water con-

The research efforts involving radon as an in-situ tracer blossomed

during the current year. Three engineering theses were developed, involving

r

-83-

the use .of radon transient analysis for reservoir characterization, trans-

ect analysis for reservoir structural and flow properties, and emanation

studies for evaluating release mechanisms of chemical components with the

produced geo fluids. Another important realization was the large number

of laboratories adapting radon measurement techniques for their specific

purposes. Future efforts should consider not only the in-situ radon as

a tracer, but its relation to other released components and its relation

as a mass transient tracer to pressure transient behavior under well flow-

rate changes and long-term production.

Another important area for study concerning well test analysis concerns

internal well flows from one interval to another, and temperature-induced

wellbore storage effects. It was discovered that geothermal well tempera-

ture depth profile is frequently affected to an extraordinary degree by

flow from one interval to another.

storage effects caused by temperature changes due to heat transmission.

Both studies constitute the new areas for investigation. Work conducted

during the year perhaps reveals more problems than were solved.

Another major effect concerns wellbore

From the preceding, it is clear that many problems have been solved

during the last year, and many other problems identified. The main empha-

sis of the Stanford Geothermal Program will continue to be research focused

directly towards supporting the development of field operations. It is

recommended that all existing programs continue throughout the coming year

with modifications discussed.

One of the most important aspects of the Stanford University Geo-

thermal Program may only be inferred from the preceding. A large number

of researchers are involved in the various aspects of the program discussed

, in this report.

gest research effort in the petroleum engineering department, the impact

of this program on the students graduating from Stanford is not easily

assessed. Many students who enter our program intending to follow gas

and oil production become intrigued by geothermal production, and enter

the geothermal industry upon graduation.

from geothermal operations throughout the world have been invited to Stan-

ford to attend graduate courses in geothermal reservoir engineering.

recent years, visiting scholars from France, the Soviet Union, Taiwan,

Italy, and Mexico have attended this program. During the coming year,

inquiries have been received from candidates from The People's Republic

of China and Costa Rica. One of the most important products of the Stan-

ford Geothermal Program is that it continues to train engineers entering

the geothermal industry worldwide.

district engineers for all of the Union Oil Geothermal operations inter-

nationally.

trained engineers who carry the technology to the industry.

that the staff of engineer Research Associates on the Stanford Geothermal

Program for the 1980-81 academic are the most talented that we have used

throughout the history of this program.

Since the Stanford Geothermal Program is the second lar-

In addition, visiting scholars

In

Stanford University graduates are

We feel that the very best mode of technology transfer is via

We are pleased

There are many other important aspects to this program not evident

in the preceding. One of the most important parts of the Stanford Geo-

thermal Program is the annual December Workshop on Geothermal Reservoir

Engineering. The fifth annual meeting was held in December 1979, and

the Proceedings issued shortly thereafter. The Sixth Annual Workshop

on Geothermal Reservoir Engineering will be held at Stanford in December

1980. This meeting is regularly attended by approximately 100 members

-85-

' o f the international geothermal community. The Proceedings of this

meeting have become one of the primary technical documents of geothermal

reservoir engineering. In addition, a geothermal seminar is held weekly

throughout the academic year. The program for the 1979-80 academic year

is listed in the appendix.

the Stanford Geothermal Program present seminars during this program, and

the seminars are widely attended by members of the geothermal community

in the California area.

Speakers from both within and beyond the

It is pleasant to see the international geothermal energy industry

growing, and we look forward to making our contribution to this effort

during the coming years.

REFERENCES

Araktingi, U.: "Thermally-Induced Wellbore Storage Effects," M.S. Report, Stanford University, Stanford, California, Oct. 1980.

Brunauer, S., Emmett, P.H., and Teller, E.: "Adsorption of Gases in Multimolecular Layers," J. Am. Chem. SOC. (1938), 60, 309-319. -

Counsil, J.R.: "Steam-Water Relative Permeability," Ph.D. Dissertation, Stanford University, Stanford, California, May 1979; SGP-TR-37,

Counsil, J.R., and Ramey, H.J., Jr.: "Drainage Relative Permeabilities Obtained from Steam-Water Boiling Flow and External Gas Drive Experiments," Trans., Geothermal Resources Council (19791, 3, 141. -

D'Amore, F., Sabroux, J.C., and Zettwoog, P.: "Determination of Charac- teristics of Steam Reservoirs by Radon 222 Measurements in Geo- thermal Fluids," Paleoph (1978/79) , 114, 253-261.

Da Prat, G., Cinco-Ley, H., and Ramey, H.J., Jr.: "Decline Curve Analysis Using Type-Curves for Two-Porosity Systems," Paper SPE 9292, pre- sented at the 55th Annual conference, SPE of AIME, Dallas, Texas, Sept. 21-24, 1980.

Denlinger, R.P., Isherwood, W.F., and Kovach, R.L.: "An Analysis of Gravity and Geodetic Changes Due to Reservoir Depletion at The Geysers," Trans., Geothermal Resources Council (19791, 2, 153.

Ehlig-Economides, C., and Ramey, H . J . , Jr.: "Pressure Buildup for Wells Produced at a Constant Pressure," Paper SPE 7985, presented at the 49th Annual California Regional Meeting, SPE of AIME, Ventura, Cali- fornia, Apr. 18-20, 1979(a).

Ehlig-Economides, C., and Ramey, H.J., Jr.: "Transient Rate Decline Analy- sis for Wells Produced at Constant Pressure," Paper SPE 8387, pre- sented at the 54th Annual Technical conference and Exhibition, SPE of AIME, Las Vegas, Nevada, Sept. 23-26, 1979(b).

Ehlig-Economides, C., and Ramey, H.J., Jr.: "Constant Pressure Testing for Geothermal Wells," Proc., New Zealand Geothermal Workshop, Auckland, New Zealand (Nov. 1979~)~ 255.

Economides, M.J., Ogbe, D., and Miller, F.G.: ''Pressure Buildup Analysis of Geothermal Steam Wells Using a Parallelepiped Model," Paper SPE 8886, presented at the 50th Annual California Regional Meeting, SPE of AIME, Pasadena, California, Apr. 1980.

-86-

-87-

Grant, M.A.: "Interpretation of Downhole Measurements in Geothermal Wells," Department of Scientific and Industrial Research, Applied Mathematics Division, Report No. 88 (Dec. 1979).

Horne, R.N., and Kruger, P.: "Cross-Section of Radon Concentration at Wairakei," Proc., New Zealand Geothermal Conference (19791, 97.

Horne, R.N., and Satman, A.: "A Study of Drawdown and Buildup Tests in Wells with Phase Boundaries," Trans., Geothermal Resources Council (Sept. 1980), - 4, 345.

Horne, R.N., Satman, A., and Grant, M.A.: "Pressure Transient Analysis of Geothermal Wells with Phase Boundaries," Paper SPE 9274, pre- sented at the Fall Meeting, SPE of AIME, Dallas, Texas, Sept. 21-24, 1980 (a).

Horne, R.N., Satman, A., and Grant, M.A.: "Pressure Transient Analysis of Geothermal Wells with Phase Boundaries," s., New Zealand Geothermal Workshop 1980, Auckland, New Zealand (Nov. 1980b).

Hsieh, C.H.: "Vapor Pressure Lowering in Porous Media," Ph.D. Dissertation, Stanford University, Stanford, California, May 1980; SGP-TR-38,

Hunsbedt, A., Iregui, R., Kruger, P., and London, A.L.: "Energy Recovery from Fracture-Stimulated Geothermal Reservoirs," ASME Paper 79-HT-92, San Diego, California, Aug. 6-8, 1979.

Iregui, R., Hunsbedt, A., Kruger, P., and London, A.L.: "Analysis of Heat Transfer and Energy Recovery in Fractured Geothermal Reservoirs," SGP-TR-31 (June 1978).

Johns, D.P.: Thermal Stress Analysis, Pergamon Press, Oxford (1965).

Kruger, P., Cederburg, G., and Semprini, L.: "Radon Data - Phase I Test LASL Hot Dry Rock Project, January 23 - April 27, 1975," SGP-TR-27 (1978).

Lipman, S.C., Strobel, C.S., and Gulati, M.S.: "Reservoir Performance of The Geyser Field," Proc., Larderello Workshop (1977).

Macias-Chapa, L., Semprini, L., and Kruger, P.: "Radon Emanation and Transect Studies," Paper SPE 8990, presented at the International Symposium on Oilfield and Geothermal Chemistry, Stanford, Cali- fornia, May 1980.

Mavor, M.J., and Cinco-Ley, H.: "Transient Pressure Behavior of Naturally Fractured Reservoirs," Paper SPE 7977, presented at the 49th Annual California Regional Meeting, SPE of AIME, Ventura, California, Apr. 18-20, 1979.

Murphy, H.D.: "Thermal Stress Cracking and the Enhancement of Heat Extrac- tion from Fractured Geothermal Reservoirs," LASL Report LA-7235-MSY (Apr. 1978).

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Ozisik, M.: Boundary Value Problems of Heat Conduction, International Text- book, Scranton (1968).

Ramey, H.J., Jr.: "Drawdown and Buildup Type-Curve for Interference Test- ing, 3rd Invitational Symposium on Well Testing, Lawrence Berkeley Laboratory, Berkeley, California, Mar. 1980.

I I

Ramey, H.J., Jr.: "The Miravalles Geothermal Reservoir, Costa Rica," Stan- ford Geothermal Program Seminar, November 6, 1980.

Ramey, H.J., Jr., Agarwal, R.G., and Martin, I.: "Analysis of 'Slug Test' or DST Flow Period Data," J. Can. Pet. Tech. (July-Sept. 19751, 1-11.

Semprini, L., and Kruger, P.: "Radon Transect Analysis in Geothermal Reservoirs," Paper SPE 8890, presented at the California Regional Meeting, SPE of AIME, Los Angeles, California, Apr. 1980.

Shinohara, K.: "A Study of Inertial Effect in the Wellbore in Pressure Transient Well Testing," Ph.D. Dissertation, Stanford University, Stanford, California, Apr. 1980; SGP-TR-39.

Shinohara, K., and Ramey, H.J., Jr.: "Analysis of 'Slug Test' DST Flow Period Data with Critical Flow," Paper SPE 7981, presented at the 49th Annual California Regional Meeting, SPE of AIME, Ventura, Cali- fornia, Apr. 18-20, 1979(a).

Shinohara, K., and Ramey, H.J., Jr.: "Slug Test Data Analysis, Including the Inertia Effect of the Fluid in the Wellbore," Paper SPE 8208, presented at the 54th Annual Fall Meeting, SPE of AIME, Las Vegas, Nevada, Sept. 23-26 , 1979 (b) .

Stehfest, H.: "Numerical Inversion of Laplace Transforms, Algorithm No. 368," Communications of the ACM (Jan. 1970), - 13.

Stoker, A., and Kruger, P.: "Radon Measurements in Geothermal Systems," presented at the Second United Nations Symposium on the Use and Development of Geothermal Energy, San Francisco, California, 1975.

van der Kamp, G.: "Determining Aquifer Transmissivity by Means of Well Response Tests: the Underdamped Case," Water Resources Research (Feb. 1976), - 12, No. 1, 71-77.

Warren, G.J.: "Radon Transients in Vapor-Dominated Geothermal Reservoirs," Engineer's Thesis, Dept. of Civil Engineering, Stanford University, Stanford, California, 1979.

Warren, G., and Kruger, P.: "Radon Transients in Vapor-Dominated Geothermal Reservoirs," Paper SPE 8000, presented at the 49th Annual California Regional Meeting, Ventura, California, Apr. 18-20, 1979.

Warren, J.E., and Root, P.J.: "The Behavior of Naturally Fractured Reser- voirs," SPE J. (Sept. 1963) , 245-255.

APPENDIX A: PARTICIPANTS IN THE STANFORD GEOTHERMAL PROGRAM

PRINCIPAL INVESTIGATORS :

Paul Kruger Henry J. Ramey, Jr.

PROGRAM MANAGERS :

Christine Ehlig-Economides Ian Donaldson (Sept. 1980)

ASSOCIATED FACULTY:

William E. Brigham Heber Cinco-Ley George M. Homsy Roland N. Horne Anstein Hunsbedt A. Louis London Frank G. Miller Drew Nelson Subir Sanyal Abdurrahman Satman

RESEARCH ASSISTANTS:

Petroleum Engineering Morse Jeffers Mark Miller Ramona Rolle Renne Rolle Abraham Sageev Kiyoshi Shinohara Mario Castaneda Chih-Hang Hs ieh Giovanni Da Prat Fernando Rodriguez Udo Araktingi

Civil Engineering Petroleum Engineering

Petroleum Engineering Petroleum Engineering

Petroleum Engineering University of Mexico Chemical Engineering Petroleum Engineering Civil Engineering Mechanical Engineering Petroleum Engineering Mechanical Engineering Petroleum Engineering Petroleum Engineering

Civil Engineering Luis Macias-Chapa Kazuichi Satomi Lewis Semprini

Mechanical Engineering John Sullivan Raj iv Rana

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APPENDIX B: TECHNICAL REPORTS

SGP-TR-1 * Paul Kruger and Henry J. Ramey, Jr., "S

SGP-TR-2 *

SGP-TR-3 *

SGP-TR-4 *

SGP-TR-5 *

SGP-TR- 6

SGP-TR-7 *

SGP-TR-8 *

SGP-TR-9

SGP-TR-10 *

SGP-TR-11

SGP-TR-12 *

SGP-TR-13

SGP-TR-14

SGP-TR-15

SGP-TR-16

* Out of p r i n t -90-

tmula t ion and Reservoir Engineering of Geothermal Resources," P rogress Report No. 3, June, 1974.

Norio Arihara, "A Study of Non-isothermal and Two-phase Flow Through Consolidated Sandstones," November, 1974.

F ranc i s J. Cas&, "The Ef fec t of Temperature and Confining Pressure on F lu id Flow P r o p e r t i e s of Consolidated Rocks," November, 1974.

Alan K. S toker and Paul Kruger, "Radon Measurements i n Geothermal Systems," January, 1975.

Paul Kruger and Henry J. Ramey, Jr., "Stimulat ion of Geothermal Aquifers ," Progress Report No. 1, March, 1973.

Henry J. Ramey, Jr., W i l l i a m E. Brigham, Hsiu-Kuo Chen, Paul G. Atkinson, and Norio Arihara, "Thermodynamic and Hydrodynamic P r o p e r t i e s of Hydrothermal Systems," A p r i l , 1974.

Anste in Hunsbedt, Paul Kruger, and Alexander L. London, "A Laboratory Model of Stimulated Geothermal Reservoirs ," February, 1975.

'Henry J. Ramey, Jr., and A. Louis London, "St imula t ion and Rese rvo i r Engineering of Geothermal Resources," P rogress Report No. 4, August, 1975.

Paul Kruger , "Geothermal Energy Development , November, 1975 . Ming-Ching Tom Kuo, Paul Kruger, and W i l l i a m E. Brigham, "Heat and Mass Trans fe r i n Porous Rock Fragments," December, 1975.

Ans te in Hunsbedt, Paul Kruger, and A. L. London, Laboratory S t u d i e s of St imulated Geothermal Reservoirs ,I1 December, 1975.

Paul Kruger and Henry J. Ramey, Jr., e d i t o r s , "Geothermal Rese rvo i r Engineering," Proceedings, Workshop on Geothermal Reservoir Engineering, Stanford Univers i ty , December, 1975.

Muhacmadu A r u n a , "The E f f e c t s of Temperature and Pressure on Abso lu te Permeabi l i ty of Sandstones," May, 1976.

Paul G. Atkinson, "Mathematical Modelling of Single- phase Nonisothermal F l u i d Flow through Porous Media," May, 1976.

Hsiu-Xuo Chen, "Measurement of Water Content of Porous Media Under Geothl-mal System Condit ions ," August , 1976.

M i n g d i n g Tom Kuo, Paul Kruger, and W i l l i a m E. Brigham, "Shape F a c t o r C o r r e l a t i o n s f o r Trans ient Heat Conduction from I r r e g u l a r Shape3 Rock Fragments t o Surrounding Fluid," August, 1976.

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L SGP-TR-17

. ( SGP-TR-18

SGP-TR- 19

SGP-TR-20 *

SGP-TR- 21

SGP-TR-22

SGP-TR-23

SGP-TR-24

SGP-TR-25 *

SGP -TR- 26

SGP-TR-27

SGP-TR-28

SGP-TR-29

S GP- TR-3 0

S GP-TR- 31

SGP-TR-32

SGP-TR-33

SGP-TR-34

Stephen D. Chicoine, "A Phys ica l Model of a Geothermal System--Its Design and Construct ion and Its Appl ica t ion to Reservoi r Engineering," June, 1975.

Paul G. Atkinson, "Numerical Simulation of Two-phase Boi l ing Flow i n a Linear Hor izonta l Porous Medium," December, 1975.

Roger P. Denlinger , "An Evaluat ion of t h e Capaci tance Probe As a Technique f o r Determining Liquid S a t u r a t i o n s I n Laboratory Flow Experiments," June 4, 1975.

Summaries: ing, December 1-3, 1976.

Paul Kruger and Henry J. Ramey, Jr., F i n a l Report to Nat ional Science Foundation. 'I

Second Workshop on Geothermal Reservoir Engineer-

Gary Warren, "Radon i n Vapor-Dominated Geothermal Reservoirs ," December, 1978.

Chih-Hang Hsieh, "Progress Report on Experiments on Water Vapor P res su re Lowering Re la t ing t o C a p i l l a r i t y and Adsorption- Desorption," November, 1977.

Syed M. Tar iq , "A Study of t h e Behavior of Layered Rese rvo i r s wi th Wellbore Storage and Skin Effec t , " December, 1977.

Proceedings: Third Workshop on Geothermal Reservoi r Engineering, December 14-16, 1977.

Lesl ie S. Mannon and Pau l G. Atkinson, "The R e a l G a s Pseudo- P res su re f o r Geothermal Steam," September, 1977.

Paul Kruger and Lewis Semprini, "Radon Data--Phase I T e s t , Los Alamos S c i e n t i f i c Laboratory, LASL Hot Dry Rock P r o j e c t , January 27-April 12 , 1978. I'

Paul Kruger and Henry J. Ramey, Jr., "Stimulat ion and Reservoir Engineering of Geothermal Resources ,'I F i r s t Annual Report t o U.S. Department of Energy, Apr i l 1978. Kiyoshi Shinohara, "Calculat ion and Use of Steam/Water Relatfve Pe rmeab i l i t i e s i n Geothermal Reservoirs," June 1978.

Proceedings:Fourth Workshop on Geothermal Rese rvo i r Engineering, December 13-15, 1978.

Roberto I r e g u i , Anstein Hunsbedt, Paul Kruger, and Alexander L. London, "Analysis of t h e Heat Transfer L imi t a t ions on the Energy Recovery from Geothermal Reservoirs ," June 1978.

Paul Kruger and Henry J. Ramey, Jr., Stanford Geothermal Program Progress Report No. 7 t o t h e U.S. Department of Energy f o r t h e Period October 1, 1978 t o December 31, 1978.

Paul Kruger, L e w i s Semprini, G a i l Cederberg, and Luis Macias, "Recent Radon Trans i en t Experiments,"December 1978.

P a t r i c i a Arditty,"The Ea r th T i d e E f f e c t s on Petroleum Reservoirs; Preliminary Study," May 1978.

* Out of p r i n t .

1 -92-

I SGP-TR-35 Paul Kruger and Henry J. Ramey, Jr., "Stimulation and Reservoir Engineering of Geothermal Resources," Second Annual Report t o 4 U. S. Department of Energy/LBL. DOE-LBL P1673500, September 1979.

SGP-TR-36 Chr i s t i ne A. Ehlig-Economides, "Well T e s t Analysis f o r Wells Produced at a Constant Pressure," June 1979.

John R. Counsil , "Steam-Uater Rela t ive Permeabi l i ty ," May 1979. SGP-TR-37

SGP-TR-38 Chih-Hang Hsieh, "Vapor Pressure Lowering i n Porous Media," 1979.

SGP-TR-39

SGP-TR-40

SGP-TR-41

Kiyoshi Shinohara, "A Study of I n e r t i a l Effect in t h e Wellbore i n P res su re Trans ien t Well Test ing," 1980.

Proceedings: F i f t h Workshop on Geothermal Reservoi r Engineering, December 12-14, 1979.

Kern H. Guppy, "Non-Darcy Flow i n Wells w i t h a F i n i t e Conduct ivi ty Vertical Fracture ," Spring 1980.

APPENDIX C: PUBLICATIONS AND TECHNICAL PRESENTATIONS

Araktingi, U.: "Thermally-Induced Wellbore Storage Effects," M.S. Report, Stanford University, Stanford, California, Oct. 1, 1980.

Counsil, J.R.: "Steam-Water Relative Permeability," Ph.D. Dissertation, Stanford University, Stanford, California, May 1979; SGP-TR-37, to be published.

Counsil, J.R., and Ramey, H.J., Jr.: "Drainage Relative Permeabilities Obtained from Steam-Water Boiling Flow and External Gas Drive Ex- periments," Trans. Geothermal Resources Council (1979), 2, 141.

Da Prat, G., Cinco-Ley, H., and Ramey, H.J.,.Jr.:"Decline Curve Analysis Using Type-Curves for Two-Porosity Systems," Paper SPE 9292, pre- sented at the 55th Annual conference of the SPE of AIME, Dallas, Texas, September 21-24, 1980.

Ehlig-Economides, C., and Ramey, H.J., Jr.: "Pressure Buildup for Wells Produced at a Constant Pressure," Paper SPE 7985, presented at the 49th Annual California Regional Meeting, SPE of AIME, Ventura, California, Apr. 18-20, 1979(a).

Ehlig-Economides, C., and Ramey, H.J., Jr.: "Transient Rate Decline Analy- sis for Wells Produced at Constant Pressure," Paper SPE 8387, pre- sented at the 54th Annual Technical conference and Exhibition, SPE of AIME, Las Vegas, Nevada, Sept. 23-26, 1979(b).

Ehlig-Economides, C., and Ramey, H.J., Jr.: "Constant Pressure Testing for Geothermal Wells," Proc., New Zealand Geothermal Workshop, Auck- land, New Zealand (Nov. 1979~)~ 255.

Economides, M.J., Ogbe, D., and Miller, F.G.: "Pressure Buildup Analysis of Geothermal Steam Wells Using a Parallelepiped Model," Paper SPE 8886, presented at the 50th Annual California Regional Meeting, SPE of AIME, Pasadena, California, Apr. 1980.

Horne, R.N., and Kruger, P.: "Cross-Section of Radon Concentration at Wairakei," Proc. , New Zealand Geothermal Conference (1979) , 97

Horne, R.N., and Satman, A.: "A Study of Drawdown and Buildup Tests in Wells with Phase Boundaries," Trans., Geothermal Resources Council (Sept. 1980), - 4, 345.

Horne, R.N., Satman, A., and Grant, M.A.: "Pressure Transient Analysis of Geothermal Wells with Phase Boundaries," Paper SPE 9274, pre- sented at the 55th Fall Meeting, SPE of AIME, Dallas, Texas, Sept. 21-24, 1980(a).

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___

-94-

Horne, 'R.N. , Satman, A. , and Grant, M.A. : "Pressure Transient Analysis of Geothermal Wells with Phase Boundaries," Proc., New Zealand Geo- thermal Workshop 1980, Auckland, New Zealand (Nov. 1980b).

Hsieh, C.H.: "Vapor Pressure Lowering in Porous Xedia," Ph.D. Disserta- tion, Stanford University, Stanford, California, May 1980; SGP-TR- 38, to be published.

Hunsbedt, A., Iregui, R., Kruger, P., and London, A.L.: "Energy Recovery from Fracture-Stimulated Geothermal Reservoirs," ASME Paper 79-HT-92, San Diego, California, Aug. 6-8, 1979.

Iregui, R., Hunsbedt, A., Kruger, P., and London, A.L.: "Analysis of Heat Transfer and Energy Recovery in Fractured Geothermal Reser- voirs," SGP-TR-31 (June 1978).

Kruger, P., Cederburg, G., and Semprini, L.: "Radon Data - Phase I Test LASL Hot Dry Rock Project, January 23-27, 1975,"SGP-TR-27 (1978).

Macias-Chapa, L., Semprini, L., and Kruger, P.: "Radon Emanation and Transect Studies, Paper SPE 8990, presented at the International Symposium on Oilfield and Geothermal Chemistry, Stanford, Cali- fornia, May 1980.

I

Mavor, M.J., and Cinco-Ley, H.: "Transient Pressure Behavior of Naturally Fractured Reservoirs," Paper SPE 7977, presented at the 49th Annual California Regional Meeting, SPE of AIME, Ventura, California, Apr. 18-20, 1979.

Ramey, H.J., Jr.: "Drawdown and Buildup Type-Curves for Interference Testing," presented at the 3rd Invitational Symposium on Well Test- ing, Lawrence Berkeley Laboratory, Berkeley, California, Mar. 1980.

Ramey, H.J., Jr.: "The Miravalles Geothermal Reservoir, Costa Rica," pre- sented at the Stanford Geothermal Program Seminar, Nov. 6 , 1980.

Ramey, H.J., Jr., and Kruger, P. (eds.): "Proceedings of the 5th Stanford Workshop on Geothermal Reservoir Engineering," Stanford, California, (Dec. 1979), SGP-TR-40, 1979.

Semprini, L., and Kruger, P.: Radon Transect Analysis in Geothermal Reser- voirs," Paper SPE 8890, presented at the California Regional Meeting, SPE of AIME, Los Angeles, California, April 1980.

Shinohara, K.: "A Study of Inertial Effect in the Wellbore in Pressure Transient Well Testing," Ph.D. Dissertation, Stanford University, Stanford, California, Apr. 1980, SGP-TR-39, to be published.

Shinohara, K., and Ramey, H.J., Jr.: "Analysis of 'Slug Test' DST Flow Period Data with Critical Flow," Paper SPE 7981, presented at the 49th Annual California Regional Meeting, SPE of AIME, Ventura, Cali- fornia, Apr. 18-20, 1979(a).

-95-

Shinohara, K., and Ramey, H.J., Jr.: "Slug Test Data Analysis, Including the Inertia Effect of the Fluid in the Wellbore," Paper SPE 8208, presented at the 54th Annual Fall Meeting, SPE of AIME, Las Vegas, Nevada, Sept. 23-26, 1979(b).

Warren, G.J.: "Radon Transients in Vapor-Dominated Geothermal Reservoirs," Engineer's Thesis, Department of Civil Engineering, Stanford Uni- versity, Stanford, California, 1979.

Warren, G., and Kruger, P.: "Radon Transients in Vapor-Dominated Geo- thermal'Reservoirs," Paper SPE 8000, presented at the 49th Annual California Regional Meeting, SPE of AIME, Ventura, California, Apr. 18-20, 1979.

APPENDIX D: TRAVEL AND TECHNICAL MEETING ATTENDANCE

Geothermal Resources Council Annual Meeting, Reno, Nevada, Sept. 1979.

Baza , J. Castanier, L. Ehlig-Economides, C. Macias, L.

Roux, B. Sanyal, S.K. Satman, A.

Annual Fall Meeting, Society of Petroleum Engineers, Las Vegas, Nevada, Sept. 1979.

Brigham, W.E. Castanier, L. Ehlig-Economides , C. Marsden, S.S.

Miller, F.G. Ramey, H.J., Jr. Sanyal, S.K. Satman, A.

1979 New Zealand Geothermal Workshop, Auckland, New Zealand, Oct. 1979.

Ehlig-Economides, C.

Well Testing Symposium, Lawrence Berkeley Laboratory, Mar. 1980.

Brigham, W.E. Castanier, L. Horne, R.N.

Miller, F.G. Ramey, H.J., Jr. Sanyal, S.K.

50th Annual California Regional Meeting, Society of Petroleum Engineers, Pasadena, California, Apr. 1980.

Brigham, W . E. Ehlig-Economides, C. Gobran, B. Horne, R.N.

Ramey, H.J., Jr. Roux, B. Sanyal, S. Semprini, L.

Field Visits to Cerro Prieto Field, Mexico (various dates)

Castaneda, M. Horne, R.N. Miller, F.G.

Ramey, H.J., Jr. Semprini, L.

Electric Power Research Institute Geothermal Conference, Monterey, Cali- fornia, June 1980.

Horne, R.N. Kruger, P.

Semprini, L.

ASME-AIChE Heat Transfer Meeting, Orlando, Florida, July 1980.

Horne, R.N.

-96-

-97-

.

Geothermal Resources Council Annual Meeting, Salt Lake City, Utah, September 1980.

Castanier , L. Kruger, P. Horne, R.N. Miller, F.G.

APPENDIX E: SGP SPONSORED MEETINGS

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STANFORD GEOTHERMAL PROGRAiM

FIFTH A N N U A L WORKSHOP ON GEOTHERMAL RESERVOIR E N G I N E E R I N G

STANFORD UNIVERSITY

DECEMBER 12- 14 , 1 9 7 9

P R O G R A M

WEDNESDAY, DECEMBER 12 1979 - 0800 REGISTRATION, TRESIDDER UNION, Upsta i rs Lobby

0900 SESSION I - OVERVIEW Chairman: Paul Kruger (Stanford Geothermal Program)

R. A. Gray - Department of Energy

J. H. Howard and W. J. Schwarz - Lawrence Berkeley Laboratory

H. J. Ramey, Jr. - Stanford Geothermal Program

V. Roberts - Electric Power Research I n s t i t u t e

1030 Coffee

1040 SESSION 11 - PRESSURE TRANSIENT ANALYSIS Chairmen: Frank G. Miller (SGP) and Manuel Nathenson (USGS)

D. Goldman and D. M. Callan (EG&G Idaho, Inc.), "Testing and Reservoir Param-

U. Ahmed, K. M. Wolgemuth, A. S. Abou-Sayed, A. H. Jones (Terra Tek), "Injec-

eters i n Geothermal Wells a t Raft River, Idaho"

t i o n Capabi l i ty of t h e Raft River Geothermal S i t e"

a t Broadland s"

Observation Wells i n a Geothermal Field"

W e l l Spacing and Recharge i n a Geothermal F ie ld (Cerro P r i e t o )"

* P. F. Bixley (MWD, N.Z.) and M. A. Grant (DSIR, N.Z.), "Reinjection Test ing

M. Sa l tuklaroglu (ELC, I t a l y ) , " In ter ference Effect of Producing W e l l s on

M. Sa l tuklaroglu (ELC), "Use of Observation Well Data i n Determining Optimum

1200 LUNCH, TRESIDDER UNION, Main Lounge (Room 281)

1320 SESSION 11, continued,

C.R.Y. Chang (CPC, Taiwan) and H. J. Ramey, Jr. (SGP), " W e l l I n te r fa rence Test i n Chingshui Geothermal Field"

f erence Testing" * G. Bodvarsson (Oregon S t a t e Univ.), "Capacitive Per tu rba t ions I n W e l l I n te r -

* W i l l not be presented.

-100-

M. J. Economides and E. L. Fehlberg (Shell), "Two Short-Time Buildup Test

A. F. Moench (USGS) and G. Neri (ENEL), "Analysis of Gabbro 1--Steam Pres-

K. Y. Shen and C.R.Y. Chang (CPC, Taiwan), "Pressure Buildup Tests of Well

H. N. Fisher and J. W. Tester (LASL), "An Analysis of the Pressure Transient

Analyses for Shell's Geysers Well D-6, a Year Apart"

. sure Buildup Test"

CPC-CS-4T, Chinshui Geothermal Field"

Testing of a Man-Made Fractured Geothermal Reservoir" 1500 Coffee 1520 R. F. Harrison and C. K. Blair (Terra Tek) and D. S. Chapman (Univ, of Utah),

"Development and Testing of a Small Moderate Temperature Geothermal

J. Hanson (LLL), "Tidal Pressure Response Well Testing at the Salton Sea

M. J. Economides (Shell), "Shut-In and Flowing Bottom Hole Pressure Calcula-

M.C.T. Kuo (Occidental), "A Portable Geothermal Well Testing System"

Hosted Cocktails, FACULTY CLUB, The Red Lounge

sys tern"

Geothermal Field, California, and Raft River, Idaho"

tion for Geothermal Steam Wells"

1730- 1830

THURSDAY, DECE'MBER 13, 1979 '

0830

j i

0950

1015

. 1200

1320

SESSION I11 - MODELING Chairmen: John H. Howard (LBL) and

G. h t a e l l i 226 P. E. Liguori (ELC), "A Power Plant Oriented Geothermal Subir K. ;Sanyal (SGP)

Simulation Model"

J. W. Pritchett (SSS), "A Semi-Analytic Description of Two-Phase Flow near

K. Pruess and R. C. Schroeder (LBL), "Geothermal Reservoir Simulations with

G. F. Pinder and L. Abriola (Princeton Univ.), "Block Response to Beinjection

Coffee S. K. Sanyal and S. Brown (SGP) , L. Fandriana (Amoco) , and S. Juprasert

Production Wells in Hydrothermal and Geopressured Reservoirs"

SHAFT 7 9"

in a Fractured Geothermal Reservoir"

(LBL), "Sensitivity Study of Variables Affecting Fluid Flow in Geother- mal Wells"

E. J. Zais (Zais and Assoc.), "A Technical Analysis of Geothermal Production

T. D. Riney (SSS), "A Preliminary Model of the East Mesa Hydrothermal System"

M. L. Sorey (USGS) and L. F. Fradkin (DSIR, New Zealand), "Validation and Comparison of Different Models of the Wairakei Geothermal Reservoir''

Data by Decline Curve Methods"

LUNCH, TRESIDDER UNION, Main Lounge (Room 281)

SESSION 111, continued

T. N. Narasimhan and K. P. Goyal (LBL), "A Preliminary Simulation of Land Subsidence at the Wairakei Geothermal Field in New Zealand"

-101- W. E. Brigham (SGP) and G. Neri (ENEL), "Preliminary Results on a Depletion

Model for the Gabbro Zone (Northern Part of Larderello Field)"

1420. Coffee 1500 PANEL DISCUSSION: Geothermal Reservoir Models--Simulation vs. Reality

Discussants: W. E. Brigham (SGP), C. W. Morris (Republic Geothermal), G. F. Pinder (Princeton Univ.), Karsten Pruess (LBL), M. L. Sorey (USGS)

* I. Donaldson (DSIR) and M. L. Sorey (USGS), "The Best Uses of Numerical Simulators"

1800 RECEPTION (Hosted Cocktails) and BANQUET - FACULTY CLUB FRIDAY, DECEMBER 14, 1979

0820 SESSION IV - FIELD DEVELOPMENT Chairman: George A. Frye (Aminoil) H. Alonso E., B. Dominguez A., R. Molinar C. (CFE), M. J. Lippmana, E*

Schroeder, and P. A. Witherspoon (LBL), "Update of Reservoir Engineer- ing Activities at Cerro Prieto"

Development in the Valles Caldera, New Mexico" P. Atkinson and M. S . Gulati (Union Geothermal), "Status Report on Geothermal

* M. A. Grant (DSIR), "Interpretation of Downhole Measurements at Baca" S . C. Chiang, J. J. Lin, C.R.Y. Chang, and T. M. Wu (CPC, Taiwan), "A Pre-

liminary Study of the Chingshui Geothermal Area, I-Lan, Taiwan"

P. H. Messer (Philippines Geothermal, Inc.), "Injection Performance in the Bulalo Geothermal Field, Makiling-Banahao Area, Philippines"

A. Truesdell (USGS), "Aquifer Boiling May Be Normal in Exploited High- Temperature Geothermal Systems"

1000 Coffee

1020 SESSION V - RESERVOIR PHYSICS H. Ucok, I. Ershaghi (USC), G. R. Olhoeft (USGS), and L. L, Handy (USC),

D. V. Nelson and A. Hunsbedt (SGP), "Progress in Studies of Energy Extraction

P. Kruger, L. Macias C., and L. Semprini (SGP), "Radon Transect and Emanation

"Resistivity of Brine Saturated Rock Samples at Elevated Temperatures"

from Geothermal Reservoirs"

Studies"

Ngawha" * N. E. Whitehead (DSIR), "Radon 22 Measurements at Wairakei, Broadlands and

MOVIE: "GEOTHERMAL ENERGY" - Union Oil Company of California 1200 LUNCH, TRESIDDER UNION, Main Lounge (Room 281)

1320 SESSION VI - PRODUCTION ENGINEERING Chairman: William E. Brigham (SGP)

S . K. Sanyal (SGP), L. Wells, and R. E. Bickham (SSS), "Fracture Detection from Geothermal Well Logs"

P. Cheng and M. Karmarkar (Univ. of Hawaii), "The Application of Two-Phase Critical Flow Models for the Determination of Geothermal Wellbore Discharge Characteristics"

* Will not be presented.

-102-

G. Bodvarsson (Oregon State Univ.), "Elastomechanical Phenomena and the

C. Y. Chiang and C . R . Y . Chang (CPC, Taiwan), "Application of the Horner Fluid Conductivity of Deep Geothermal Reservoirs and Source Regions"

Method to the Estimation of Static Reservoir Temperature during Drill-'

B. Roux and S. K. Sanyal (SGP), "Improved Approach to Estimating True Reser- . ing Operations"

voir Temperature from Transient Temperature Data" * R. James (DSIR) , "Reinjection Strategy"

* Will not be presented.

-103-

STANFORD GEOTHERMAL PROGRAM STANFORD UNIVERSITY

STANFORD, CALIFORNIA 94305

SEMINAR SCHEDULE

AUTUNN QUARTER 1979 ROOM 113 MITCHELL BUILDING

Date

Oct. 11

Oct. 18

Oct. 25

Nov. 1

Nov. 8

Ncv. 15

Nov. 29

Dec. 7

Topic

Organizational Meeting

A Depletion Model for the Gabbro Zone, Larderel l 0, I t a l y

Fracture Detection from Geothermal We1 1 Logs

Laboratcry a d Field Studies of Radon Trans po r t

Calculation o f h-fqrmance of Steam Wells

An Improvsd !%:hod fo r Estimating True Reser- voir Tenprature from Transient Temperature Data

Application o f Unsteady State Overall Heat Transfer Coefficient Concept to Geothermal Injection Wells

A Review of the N ~ w Zealand Geothermal Con- ference

THURSDAYS 1 :15-2:30 p.m.

Speaker

H. J. Ramey

W. E. Brigham

S . K. Sanyal

L. Macias, L. Semprini

3 . R. Baza

B. P. Roux

A. Satman

C. A. Ehlig-Economides

-104-

STANFORD GEOTHERMAL PROGRAM STAN FORD UNIVERSITY

STANFORD. CALlFORNIA 94305

SEMINAR SCHEDULE

Winter Quarter 1979/80 Room B67, Mi tche l l Building Thursdays, 1:15 to 2:30 pm

DATE

JAN. 24

JAN. 31

FEB. 7

FEB. 14

FEB. 21

FEB. 28

MAR. 7

TOPIC

GEOTHERMAL EXPLORATION AND WELL TESTING IN TAIWAN

RADIOISOTOPE AND STABLE ISOTOPE TRACER STUDIES AT THE WAIRAKEI GEOTHERIIAL FIELD, NEW ZEA- LAND

A PRELIMINARY SIMULATION OF LAND SUBSIDENCE AT THE WAIRAKEI GEOTHERMAL FIELD, NEW ZEA- LAND

STATUS OF THE ENEL GEOTHERMAL PROGRAM AND A REPORT ON THE RECENT TRIP TO ITALY

A SENI-ANALYTIC DESCRIPTION OF TWO-PHASE now NEAR PRODUCTION WELLS I N HYDROTHERMAL AND GEOPRESSURED RESERVOIRS

RISK ASSESSMENT MODELING FOR GEOTHERMAL DEVELOPMENT

MODELING HYDROTHERMAL SYSTEMS I N THE BASIN AND RANGE PROVINCE

SPEAKER

CARL C W G , CHINESE PETROLEUM COW.

ROLAKD HORNE, STAKFORD UNIVERSITY

T.N. NAR9SIMHAN, LBL

MICHAEL ECONOMIDES,

STANFORD UNIVERSITY F. G. MILLER,.

J . W . PRITCHBTT, SYSTMS, SCIENCE, AND SOFTWARE

K. GOLABI, WOODWARD & CLYDE CONSULTANTS

MIKE SOREY, U.S.G.S.

-105-

STANFORD UNIVERSITY STANFORD. CALIFORNIA 94303

STANFORD GEOTHERMAL PROGRAM

R e p l y t o :

Dr. C. Ehlig-Economides Petroleum Engineering Department

Spring Quarter, 1980

Date

Apr 17

Apr 2 4 . May 1

May 8

May 15

May 22

May 29

SEMINAR SCHEDULE

Room B67 Mitchell Building Thursday 1:15-2:30

Topic

Injection Capability at the Raft River Geothermal Site

The Tiwi Geothermal Reservoir, Philippines

Nonlinear Analysis of Two-Phase Geothermal Well Tests

Chemical Changes in Cerro Prieto Reservoir Fluids due to Exploitation

Geothermal Reserve Evaluation

Review of Magma Power Company's East Mesa Geothermal Binary Electric Generating Plant

Assessment of Low Temperature Geothermal Resources of the U.S.

Speaker

A. Abou-Sayed Terra Tek, Inc.

P. Messer Union Geothermal

Mike O'Sullivan U. of Auclcland, N.Z.

A1 Truesdell U.S.G.S.

Jack Howard U.S.G.S.

Tom Hinrichs Magma Power

Marshall Reed U.S.G.S.