An Evaluation of the use of Drillers' Logs in Lithologic Studies of the Ogallala Formation of the Southern High Plains of Texas

JBty C.A. Wilson, J. T. Smith, G.L. Thompson &nd W.M.Sandeen____________

U.S. GEOLOGICAL SURVEYWATER RESOURCES DIVISION

Prepared by the U. S. Geological Survey in cooperation with the Texas Water Development Board

June 1972

7Z-

CONTENTS

Page

Abstract------------------ ------ ------ ._ __-__--.-_-------- i

Introduction ---- -- --- -- ------------------ _--_ ----- 2

Purpose and scope of the project----- ------------------- -- 2

Location and extent of the area---- -------- - 2

Methods of investigation---- ------ .--- ------------- 4

Availability of data --- -- ------ -- ------------------- 4

Computer analysis of drillers' logs and other hydrologic

data - -- ----- -- _-----_----__-_-- ------------- 7

Test-hole drilling ---- ----------- --------- ------ 12

Geophysical logging -- - - ------ -- ---------------- 15

Methods of measuring hydraulic conductivity- -- ------------ 22

Results of the investigation------- ---- - ---- ---------- 25

Utility of drillers' logs 25

Utility of computer analysis of drillers' logs---------- --- 29

Reference cited----------- ----------- -- ----__--_._-_---- 35

11

TABLES

Page

Table 1. Availability of water-well drillers' logs in

counties where data were prepared for computer

analyses _-_-______,_-___ _-_-_--___. ____»____ 5

2. Lithologic lexicon of the Ogallala Formation-- ------ n

3. Summary of geophysical logging of wells in the

Ogallala Formation- - - - - - --- -- 21

ill

AN EVALUATION OF THE USE OF DRILLERS' LOGS

IN LITHOLOGIC STUDIES OF THE

OGALLALA FORMATION OF THE

SOUTHERN HIGH PLAINS OF TEXAS

PROGRESS REPORT 1970-71

By

C. A. Wilson, J. T. Smith, G. L. Thompson,and W. M. Sandeen

U.S. Geological Survey

ABSTRACT

Logs made by water-well drillers were analyzed in conjunction with

test-hole drilling and geophysical logging to evaluate usefulness of

the driller's log in delineating areas that would be suitable for artifi­

cial recharge of the Ogallala Formation. This preliminary study indicates

that lack of detailed and accurate information in many drillers' logs

prevents their use as a reliable source of lithologic information. For

many applications, such as evaluation of potential areas for artificial

recharge, the value of more complete and more accurate information will

be readily apparent as these applications become more widespread. More

effort will be required in collecting lithologic information as part of

the drilling operations.

-1-

100°

Counties in which geophysical

50 100 Miles

Counties in which geophysical logs and drillers' logs were obtained

FIGURE I.-Location of the study area and counties in which data were collected

-3-

Values given on drillers' logs such as water levels, are accurate; but

information on quantitative values such as well yields and drawdowns, which

were estimated or which are given as representative, may contain gross

errors. Many well locations, especially those given on application forms

for well permits or on well-data reports, are of questionable accuracy.

A greater degree of accuracy in determining well-site elevations is now

possible through the use of 7 1/2- and 15-minute Geological Survey topo­

graphic maps.

Table 1 shows the availability of drillers' logs in counties where

the data were prepared for computer analysis. These logs were screened

to eliminate those that: (1) Did not show the base of the Ogallala;

(2) could not be located to an estimated accuracy of 1 mile on 7 1/2- or

15-minute topographic maps; or (3) did not have a continuous sequence of

lithology. Locations for most of the logs selected for computer analysis

are accurate to within 1/4 mile.

More logs were available in Lubbock County and in the northern one-

fifth of Lynn County because these areas are within the boundaries of the

High Plains Underground Water Conservation District No. 1. The District

requires that a driller's log and well-construction data be filed upon

completion of each well.

-5-

METHODS OF INVESTIGATION

Availability of Data

Drillers' logs of water wells are sources of extensive data on the litho-

logy and structure of the Ogallala Formation of the Southern High Plains; in

1969, there were about 59,000 irrigation wells in the area. Most of the logs

are in the files of the Texas Water Development Board, the High Plains Under­

ground Water Conservation District No. 1, and the U.S. Geological Survey.

Other, but less extensive data include well schedules, water-level measure­

ments, drawdown-yield measurements, pumpage inventories, well-location maps,

results of aquifer tests, and water-quality analyses. Very little of the

data in the Geological Survey files have been, gathered since 1958. Data in

the files of the Texas Water Development Board date mostly from 1964 to 1971;

the most recent material is the most abundant. Some geophysical logs may

be available from oil-company files.

A limited amount of geologic data and water-quality analyses are available

from the Geology Departments of Texas Tech and Texas A§M Universities. Some

field data and ground-water depletion surveys are available from the files of

consulting geologists and engineers who have worked in the area. Well-

construction data are available from the records of water-well drilling

contractors.

-4-

Tabl

e 1.

--Av

aila

bili

ty of w

ater-well

dril

lers

' lo

gs in

counties wh

ere

data

were prepared for

computer an

alys

es

Appr

oxim

ate

number of

Coun

ty

irrigation we

lls

I/

Arms

tron

g

Briscoe

Cros

by

Garz

a

Hale

Lubbock

Lynn

Swisher

212

650

2,082 60

4,400

6,200

2,466

4,60

0

Approximate

number of

Number of lo

gs

Number of lo

gs selected

dril

lers

' lo

gs available

avai

labl

e to

in

sa

mple

se

ts an

d to

th

e st

udy

samp

le population

coded

on formats

149

213

267 39

1,33

4

2,66

4 2J

2,470

3/

2,19

2

811

97 117

139 39

672

2,39

4 2J

+2,1

00 3/

1,992

452

66 93 128 27 326

786

2/

831

3/

489

275

I/

Texa

s Water

Deve

lopm

ent

Boar

d, 1969.

2j

Nort

hern

one-half o

f Lubbock

Coun

ty (north of

la

titu

de 33

°37'

30")

.

3/

Sout

hern

one-half o

f Lu

bboc

k County.

Computer Analysis of Drillers' Logs and Other Hydrologic Data

The formats developed for coding drillers' logs and other geologic and

hydrologic data are shown on figures 2a and 2b. The lithologic lexicon for

the Ogallala Formation is given in table 2.

The procedures used in manual processing of drillers' logs for coding

are illustrated by the systems flowchart shown on figure 3. The coded

formats were mailed to the New Mexico District for conversion into punched

cards for computer input.

A sample of the available logs were used for an initial evaluation of

the usefulness of drillers' logs. Sample set No. 1 consists of one log

per 2 1/2-^minute quadrangle, and set No. 2 consists of two logs per 2 1/2-

minute quadrangle, or 25 percent of all logs in the quadrangle, whichever

is greater. Not all quadrangles, however, will have enough logs (minimum

of three) for a complete sample selection.

The purpose of the second set was to compare the results based on the

greater sampling with that obtained from the first set. If the results

were not comparable, successive samplings would be tried to see if a suit­

able match was obtained.

-7-

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\Detarmina lat.,\long., * elev. itfroa topo.napi/\for lag* in /laanple seta/

Figure 3. Flowchart for manu&l procenini; of drillers' logs

-10-

Tabl

e 2.

--Li

thol

ogic

le

xico

n of the

Ogal

lala

Formation

Rock

type

Bentonite

Blue

Boul

der

Boulders

Break

Cali

che

Capr

ock

Cavi

tyCh

alk

Clay

Cong

lome

rate

Dirt

Fullers

eart

hGr

avel

Gumb

oHardpan

Hone

ycom

bLakebed

Laye

rsLe

dge

Ledges

Lime

Lira

eroc

kLimestone

Mixture

Muck

Mud

Packsand

Pebble

Red

Redbed

Redbeds

Riverbed

Rock

Rocks

Quar

tzSand

Sandrock

Sand

rock

sSandstone

Shal

eSh

ell

Shel

lsSilt

Slag

Soapstone

Stone

Soil

Streak(s)

Subs

oil

Surf

ace

Tops

oil

Water

Whit

e rock

Wate

rsan

d

Code

BENT

BLU

BLDR

BLDRS

BRK

CLCH

CPRK

CAVT

CHK

CLY

CGL

DIRT

FLET

HGV

LGMB0

HDP

HNYCB

LKEBD

LYRS

LDG

LOGS

LME

LMRK

LS MXTRE

MUCK

MD PCKS

DPBL

REDD

RDBD

RDBDS

RVRB

DRK RK

SQT

ZSD SD

RKSDRKS

SS SH SHEL

SHELS

SLT

SLAG

SPST

NST S0IL

STR(S)

SS0I

LSU

RFTS

0IL

WTR

WHRK

WTSD

Rock

-type

modifier

Argillaceous

Bed

Bentonite

Calcareous

Cali

che

Cap

Capr

ock

Chal

kCh

alky

Clea

nCr

ysta

llin

eDense

Flin

tFo

ssil

ifer

ous

Glassy

Gran

ite

Gum

Gumbo

Gumm

yGy

psum

Hone

ycom

bLake

Lime

Lime

yLoam

Mica

Mired

Mixture

Muddy

Multicolor

Pea

Pebble

Quar

tzQu

ick

Rive

rRocky

Sand

Sand

ySh

aly

Soli

dSu

gar

Water

Code

ARC

BD BENT

LIMY

CLCH

CP CPRK

CHK

CHKY

CLN

XLN

DNS

FLNT

F0SL

GL GRNT

GUM

GMB0

GUMM

YGYP

HNYC

BLAKE

LME

LMY

LOAM

MICA

MIRD

MXTRE

MDY

MLC0L

PEA

PEBB

LEQT

ZQC

KRVR

RKY

SD SDY

SHY

S0LID

SGR

WTR

Color

Blac

kBlue

Bluish gray

Brow

nBuff

Crea

mDark

Gray

Grayish

whit

eGreen

Gree

nish

Light

Multicolor

Orange

Pale blue

Pink

Red

Redd

ish

Redd

ish

brow

nTan

Whit

eYe

llow

Yellowish

Code BLK

BL BLGY

BRN

BUFF

CRM

DK GY GYWH

GN GNIS

HLT MLC0

L0RNG

PLBL

PK RED

RDSH

RBR

TAN

WH YEL

YWSH

Cementation

Ceme

nted

Cement

Crystallized

\

Grain

size

Coar

se

Code

CMTD

CMT

CRYLD

Code

CCoarse-grained CG

RDFine

Fine-grained

' Me

dium

Medium-fine

Medi

um-c

oars

eSmall

Angularity

Sharper

Angular

Hardness

Hard

Soft

F FGRD

M MF MC SML

Code

SHRPR

ANG

Code

HD SFT

Miscellaneous

Bear

ing

Bloc

kyBreaks

Brok

enCa

ves

Caving

Chip

sCrumbly

Doug

hDry

Firm

Fres

hHeavy

Heav

ier

Joint

Jointed

Ledge

Ledg

esLe

nse

Lenses

Loose

Mostly

Medium- loose

Pack

Packed

Poro

usPo

wder

ySeams

Shee

tsShell

Shel

lySp

ots

Sticky

Streak

Streaks

Stringer

sStrip

Stri

psSu

rfac

eTi

ght

Tough

Code

BRNG

BLKY

BRKS

BRKN

CVS

CVG

CHIP

SCR

MBY

DGH

DRY

FIRM

FRES

HHVY

HVR

J0NT

JTD

LDG

LOGS

LENS

ELNS

LSE

MSTLY

MLSE

PCK

PCKD

P0RS

PWDY

SEAMS

SHTS

SHEL

SHEL

YSPS

STCK

YSTR

STRS

STRGS

STRP

STRP

SSURF

TT TGH

Neutral

Amount

And

At Ball

sBase

Big

Bits

Clea

tyDe

epEq

ual

Fair

Few

Free

Good

In Layer

Laye

rsLi

ttle

Mixed

Not

Not

repo

rted

Of Or Real

Scat

tere

dSlightly

Small

So Some

Thin

To Very

Weak

W|th

Code

AMT

+ , AND

AT BALL

SBA

SEBIG

BTS

CLTY

DEEP

=, EQ

UAL

FR FEW

FREE

G IN LYR

LYRS

LTL

MXD

N0T

NREP

T0F 0R RE

ALSCAT

SL SML

S0 S0ME

THN

T0 V WEAK

WITH

The general processing systems used by the New Mexico District are shown

on figures 4, 5, and 6. After a series of error checks, updating, sorting,

and merging, all coded data for each county are stored on magnetic tape. The

computer output is obtained by using a program that lists the desired terms

from the Ogallala lithologic lexicon (table 2) or terms used in the New

Mexico District data file (OMNIANA). The requested information is retrieved

from storage by the computer and can be converted into a variety of data out­

put such as coordinate points, value plots, tables, graphs, or visual displays

This study is primarily concerned with an output series of contour maps

based on lithologic or structural data. Coordinate points, based on lati­

tude and longtitude, are plotted by an off-line plotting device. The desired

values are printed adjacent to the coordinate point, and these values may

then be contoured by hand. The values could be contoured by machine if the

computer were programmed for this operation»

Test-Hole Drilling

During fiscal year 1971, 58 test holes (total footage of 5,617 feet)

were completed in 80 days of auger drilling in Briscoe, Hale, and Swisher

Counties. The drilling unit, which was provided by the U.S. Geological

Survey from Denver, Colorado, is equipped with 5-foot sections of a 5 3/4-

inch diameter hollow-stem auger. The unit is also equipped with a split-

spoon sampling device for taking undisturbed formation samples for laboratory

analysis.

-12-

Keypunch data on cards

& verify

Old 0g lexicon listings Haw data deck

Good datareturned to

Ogallala project

Error check program

Oldmaster

storage ifavailable

Correct & return

Bad cards returned to

Ogallala project

Error-printout to Ogallala project

Explanation of symbols

r Manual operation

Input/ output

Punched cards

Document

ieti< tape

Figure k. Systems flowchart for processing coded formats

-13-

\Punch desired\ lithologic\ terms forSubroutines

Subroutines:Call- up tables (class­ ification, manip­ ulation & accu­ mulation of data)

Resultsproofed byOgallalaproj ectpersonnel

Program ordata

errors corrected

Explanation of symbols

letic tape

Punched cards

Figure 5. Systems flowchart for table-generating programs

-14-

De»ired \data )

points I

Figure 6. Systems flowchart for plotting data positions and values

-IS-

Two test holes, one deep (100 to 150 feet) and one shallow (40 to 50

feet) were drilled at most sites. First the deeper hole was drilled, logged,

and sampled at 5-foot intervals or at changes in lithology. After the hole

was completed, a gamma-ray log was made through the hollow-stem auger, and

then the auger was removed. Another gamma-ray log was made in the uncased

hole. In addition, electrical and caliper logs were made at some sites,

and some undisturbed samples were taken at the bottom of the holes. All of

the data acquired by these operations were used to construct a lithologic

log of the test hole.

The second, shallower hole was usually drilled about 10 feet or less

from the first hole and was bottomed in a relatively impermeable layer of

clay or silt. The desired depth was determined from analysis of the logs

of the deeper hole, and an undisturbed sample was taken with the split-spoon

sampler to determine the hydraulic conductivity.

Geophysical Logging

Geophysical well logs, including gamma-ray, electrical, caliper, and

temperature, were used mainly to identify and to determine the boundaries

of various lithologic units penetrated by the well. Some additional data

on water quality, water temperature, and sediment consolidation can be

obtained from the logs.

-16-

A total of 309 logs was made in 222 wells and test holes during fiscal

years 1970 and 1971. Gamma-ray logs were made in all test holes and wells.

Electrical logs were made in some uncased wells and other types of logs were

made in a few selected wells and test holes. Table 3 gives the number and

types of logs made in the various counties of the study area.

A comparison of the lithologic log and the gamma-ray log for test hole

AK-11-12-8A is shown on figure 7. On completion of drilling a test hole,

it is best to make a gamma-ray log through the hollow-stem auger or drill

stem because caving of the hole may occur when the drilling tools are removed,

A second gamma-ray log is made after the auger or drill stem is removed.

Casing, auger, and drill stem all tend to subdue the response received by

the logging instruments. The difference in the character of the gamma-ray

log made through the hollow-stem auger and in the same hole after the auger

was removed is shown on figure 8.

The effect of logging through the casing of a large-diameter well is

shown by the gamma-ray log of well XT-11-20-5A (fig. 8), located about 800

feet east of well XT-11-20-5B. Logging below the water table increases the

loss of response in addition to the loss caused by the casing. Gamma-ray

logs made in gravel-packed or cemented wells are not accurate because the

measured radioactivity is caused by both the sediments and the gravel pack

or cement. Figure 9 shows a comparison of gamma-ray logs in well SP-24-32-8A

made first in the open test hole and then after the well was reamed out,

cased, gravel-packed, and cemented.

-17-

AK IH2-8A

Armstrong County 34°46'26"N I0r32'5l" Elev. 3412 feet

Gamma- ray Uncased 5 3/4-inch

dia. test hole

Radiation increases

-i 0Lithologic log

Soil

501

I001

ISO1

200'

oL

10 20i

30i

40i

50

COUNTS PER SECOND

Clay

Silty clay

Sandycaliche(caproc

Finesandandinter-

bedded caliche layers

Sand

Sandand

gravel

0

(red bed)

FIGURE 7-Gamma-ray log and lithologic log of test-hole AK IH2-8A in Armstrong County

-18-

XT

ll-

aO

-5B

XT

II-2

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Sw

ishe

r C

ount

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. 34

03 f

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Gam

ma-

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tog

Cas

ing

5 3/

4-in

ch

$tee

l au

ger

Rad

iatio

n in

crea

ses

Uth

o lo

gic

log

CO i

50'

100'

150'

1020

_i

CO

UN

TS

PE

R

SEC

ON

D

Son

Silt

y ca

liche

Cal

iche

No

retu

rns

Sand

(p

oor

retu

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Gam

ma-

ray

log

Unc

ased

5 3

/4 i

nche

s

Rad

iatio

n in

crea

ses

-i

0 50'

100'

-J

150'

102

0

i30

40

_i

CO

UN

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PE

R

SEC

ON

D

Sw

ishe

r C

ount

y34

° 41

* 12

" N

101°

32'

46"

Ele

v. 3

4OI

feet

Gam

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ray

log

Cos

ing

15 i

nche

s

Rad

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n in

crea

ses

50'

100'

150'

200'

1020 i

30

_IC

OU

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P

ER

SE

CO

ND

FIG

UR

E 8.

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paris

on o

f ga

mm

a-ra

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ade

thro

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uger

, in

the

ope

n ho

le,

nnrf

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a

nan

rhw

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<u*r

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nti

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SP

24-3

2-8

AS

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4-3

2-8

A

Lubb

ock

Cou

nty

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30'2

8"

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2° 0

2'5

4'

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30

0 f

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ock

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nty

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lev.

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eet

Gam

ma-

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Unc

ased

9

5/8

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dia

test

ho

le

Rad

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n in

crea

ses

-i

0

Drilli

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501

I00

1

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Dril

lers

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g

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ma-

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ch d

ia.

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sing

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avel

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le.

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to 1

78 f

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lo

g U

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ed 9

5/8

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dia.

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e

J

200'

1020

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_I

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Sand

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oy

and

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Gra

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and

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erat

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San

d

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grav

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eous

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oten

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ity

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ater

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0 501

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1

150'

1014

1822

2630

2001

DIA

ME

TER

OF

WE

LL B

OR

E,

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NC

HE

S

FIG

UR

E 9

.-Com

paris

on o

f drille

rs'

log

and

vario

us g

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ysic

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ogs

mad

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wel

l S

P 2

4-3

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A i

n Lu

bboc

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ount

y

Tabl

e 3.--Summary

of geophysical

logg

ing

of wel

ls in th

e Og

alla

la Fo

rmat

ion

Coun

ty

Armstrong

Bail

ey

Bris

coe

Castro

Cros

by

Floy

d

Garz

a

Hale

Lamb

Lubbock

Lynn

Martin

Farmer

Randall

Swisher

Tota

l number of

well

s lo

gged

21

1 21 1 10 8 2 74 3 24 13 1 2 2 39

Gamm

a -ray

24

1

20

1 13 9 3 79 3 28 12

1 2 2 45

Type

of

Resi

stiv

ity

and

spontaneous

pote

ntia

l

2 1 8 - - 1 - 13 - 7 1 - - - 5

geophysical

log

Cali

per

Temperature

- 1 2 - - - - 3 - 3 9

1 - - - 2

Conductivity

- - 1 - - - - - - 4 - - - - -

Tota

l22

2 243

3812

Methods of Measuring Hydraulic Conductivity

The methods used in determining the hydraulic conductivity of the

sediments were by laboratory analyses of core samples.

Core samples taken during the test-hole drilling program were analyzed

by the U.S. Geological Survey in Denver, Colorado, or by the Texas Water

Development Board. The core samples were analyzed for vertical hydraulic

conductivity, porosity, specific yield, and grain-size distribution. Some

samples from the deeper intervals were analyzed for horizontal hydraulic

conductivity. In addition, 10 bag samples were repacked and analyzed for

hydraulic conductivity, porosity, specific yield, and grain-size distribution,

The results of laboratory analyses of most of the samples are shown by

the graphs on figures 10 and 11. The minimum vertical hydraulic conductiv-r Q

ity of the samples was 5.8x10 ft/day (feet per day) or 2.05x10 cm/sec

(centimeters per second) in test-hole 11-45-2B (Briscoe County) at a depth

of 15 to 16 feet. Grain-size analysis for the sample in hole 11-45-2B shows

that 45 percent of the sediment is of clay size or finer (less than 4 micro­

meters) and 75 percent is silt size or less (less than 0.0625 millimeter).

-22-

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of c

ore

sam

ples

_2 The maximum vertical hydraulic conductivity was 34.5 ft/day (1.22x10

cm/sec) in test-hole 11-60-2A (Hale County) at a depth of 47 to 47.5 feet.

In the sample from test-hole 11-60-2A, about 20 percent of the material is

of silt size or less, and 75 percent is smaller than fine, sand (less than

0.25 millimeter). Grain-size percentages varied over a wide range, but the

average was about 64 percent clay and silt. The porosities of the samples

ranged from 25.1 to 45.5 percent.

RESULTS OF THE INVESTIGATION

Utility of Drillers 1 Logs

Many of the lithologic terms used on drillers' logs are vague or may

have several different meanings. For example, some of the descriptions of

rock types include such terms as "blue," "red," "break," "dirt," "lakebed,"

"ledge," "mixture," and "mud and rock" (table 2). Very often, an interval

of the formation may be described as "clay, sand, and caliche" or "sand and

rock layers."

The term "sand" means little on a driller's log because "sand" by

definition, is a particle size, and much of the Ogallala Formation is composed

of fine-grained sediments of low hydraulic conductivity. Few drillers use

standard particle-size ranges (American Geological Institute, 1960 p. 253),

so sediments described as "sand" may be very fine and practically imperme­

able or may be very coarse and highly permeable. The term "silt" is seldom

used by the drillers, but a high percentage of the Ogallala Formation is

composed of silt-size particles.

-25-

A series of commercial drillers' logs, the corresponding geophysical

logs, and the interpretations of the geophysical logs are shown on

figure 12.

Good correlation for both lithology and boundaries of the units is

shown for logs AK-11-12-9A and KY-11-49-6A. Log XT-11-17-2A correlates

well witn the Geological Survey log of the samples collected at the well,

but mucn less so with the commercial driller's log. Drillers' logs for

wells XT-11-36-5A and JW-23-04-9A also cannot be correlated well with the

geophys i cal logs.

The preparation of good lithologic logs of the Ogallala Formation is

difficult because of the complex and rather variable lithology of the

deposits. In general, the thicknesses and depths of the different rock

types shown on drillers' logs are not closely comparable with those shown

by geophysical logs. Differences, many of them amounting to several tens

of feet, are attributed to difficulty in interpretation of depth of samples

during drilling. Much of the difficulty stems from the fact that the drill

commonly has reached a greater depth by the time material from a given

depth reacnes the surface. In consequence, the driller's logs commonly

indicate a greater thickness of water-bearing sand or gravel than is shown

on the geophysical log. Great care is needed in order to estimate more

closely, from drilling characteristics (for example, difficulty of drilling),

the depths at which significant changes in material occur.

-26-

The completeness and accuracy of the additional information given on

drillers' logs (such as location, well-construction data, static water level,

yield, and drawdown) differs considerably from one log to another. The

casing size, screened or slotted intervals and size, gravel-pack or straight-

wall designations, pump description, and engine or motor size are incompletely

described in many logs. Measurements or estimates of static water levels

and pumping levels are commonly included, but in many logs, the time or date

of measurement is not given. Yields estimated or based on the pump discharge-

pipe diameter (a convenient method commonly used) are at best approximate,

and may be greatly in error. The specific-capacity values calculated from

the given discharge values are therefore approximations also.

In general, the commercial driller's log is more accurate for the inter­

vals below the water table than for those above it. Greater accuracy below

the water table probably reflects closer attention given to the drilling

and logging procedures. The base of the Ogallala Formation is usually picked

where the lithology changes from sand or sand and gravel to red clay or shale,

blue clay or shale, or limestone.

As the usefulness of this information becomes more widely recognized,

greater emphasis will be placed on the observation and recording of these data.

It should be noted that the wells have usually been drilled to extract water

for the least possible cost, and in practice there has been little demand for

the accuracy and detail that can be obtained from careful construction of a

lithologic log during drilling and from a complete summary of the test data.

-28-

Utility of Computer Analysis of Drillers' Logs

To determine the utility of computer analysis, data from drillers' logs

of wells in Briscoe, Hale, and Swisher Counties were used as input. A sample

of the initial computer printout showing a tabulation of the data is shown

on figure 13.

After tabulation, the data can be manipulated by using different table-

generating programs (figure 5). For example, the "total selected sands"

routine is a program designed to examine all lithologic data on each log

and to accumulate the thickness of permeable lithologic units such as sand

and gravel.

Lithologic rock terms and modifiers used by drillers to indicate good

permeability are: Medium-grained sand; medium sand; coarse-grained sand;

coarse sand; medium-coarse sand; sand and gravel; gravel; medium-coarse

gravel; medium gravel; fine gravel; coarse-grained gravel; river gravel;

layers of gravel; small gravel; some gravel; big sand; big gravel; scattered

boulders; loose boulders; and some boulders.

In general, the program is written so that the "total selected sands"

include all intervals containing gravel, boulders, and sands coarser than

medium. A page of computer output, showing the lithology of a log and the

accumulated "total selected sands" for the entire log and for the total above

the base of the Ogallala, is shown on figure 14.

-29-

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t> TSOIL.

CLCH .ANO

SO

32SO

BRN

65 CLCH .AND

RK

j.25 SO

QGLTH

OGLTH

OGLTH

QGLTH

OGLTH

125

so.AND

CLCH

OGLTH

OGLTH

IbO SO

UH

.AND

CLY

J»2G

4!>GuuOUGuGu6Dtiu53U04

GOC

16U

1/G SO

BkN

OGLTH

170

2u3 WTR

*ANO

GVL

OGLTH

2G3

2Gd CLY

OGLTH

32 SO

»QRNG .AMU

CLCH

O&LTH

FOR UNIQUc NUHBER GQQOOOQQQ^

TOTAL S£LcC(£D SANO THICKNESS FOR THIS LOG

33.0

TOTAL SELEGTEO SAND THICKNESS TO

QGALLALA BASE =

33.0

The data selected and accumulated by the table-generating programs are

best analyzed by plotting the values on a map. Figure 15 is a Calcom plot

of the locations of drillers' logs in southeastern Hale County for sample

sets 1 and 2. The locations, which are represented by squares, are plotted

by latitude and longitude. The series of numbers to the left of the point

designate the county and the well number. The well number used for this

plot, whicn is a "unique number" ("figs. 2a and 2b) assigned by the programmer

is not related to the State well number. The numbers to the right show the

land-surface elevation. The values given as "0.0" indicate the placement of

other data that may be desired for that point. Latitude and longitude are

shown next to tne intersection symbols (+); however, not all values are shown

on tnis sample of the Calcom plot.

This project was terminated before preparation of a computer program to

combine the plotting program with the manipulating and accumulating programs,

such as "total selected sands." If this had been done, values of "total

selected sands" would be printed in place of one of the "0.0" shown on

figure 15.

Other data that could be generated with the plotting routine include

tne altitude of tne base of the Ogallala Formation and the total thickness

of clay, silt, and other similar rock types that occur in the upper 40 and

100 feet of the Ogallala Formation (fig. 16).

-32-

REFERENCE CITED

American Geological Institute, 1960, Glossary of geology and related

sciences, with supplement: American Geol. Institute, Washington,

D.C., 397 p.

-35-