SC Hein Tight Gas

8/8/2019 SC Hein Tight Gas

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Evaluation of Tight Gas ReservoirsEvaluation of Tight Gas Reservoirs

Victor Hein, P.E.Victor Hein, P.E.

Ryder Scott CompanyRyder Scott Company

June 2009June 2009


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Resource PyramidResource Pyramid

Small Volumes

Large Volumes

Increas e

dDemand

BetterT

echnologyHigh

Quality

Medium

Quality

Low

Quality

Coalbed

Methane

Gas

Shales

Tight

Gas

1000 md

100 md

1 md

0.1 md

0.001 md

0.0001 md Contin

uedDri

llingan

dDevelopme n

t


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Gas Consumption North AmericaGas Consumption North America


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Gas Consumption WorldGas Consumption World


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OECD CountriesOECD Countries

AustraliaAustriaBelgiumCanada

Czech RepublicDenmarkFinlandFrance

GermanyGreeceHungaryIcelandIreland

ItalyJapanKoreaLuxembourgMexico

NetherlandsNew ZealandNorwayPolandPortugalSlovak RepublicSpainSweden

SwitzerlandTurkeyUnited Kingdom

United States
http://www.oecd.org/country/0,3377,en_33873108_33873229_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873245_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873261_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873277_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873293_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873309_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873360_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873376_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873402_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873421_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873438_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873476_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873500_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873516_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873539_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873555_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873574_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873610_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873626_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873658_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873681_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873739_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873764_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873781_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873806_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873822_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873838_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873854_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873870_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873870_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873854_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873838_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873822_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873806_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873781_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873764_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873739_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873681_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873658_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873626_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873610_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873574_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873555_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873539_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873516_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873500_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873476_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873438_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873421_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873402_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873376_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873360_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873309_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873293_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873277_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873261_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873245_1_1_1_1_1,00.htmlhttp://www.oecd.org/country/0,3377,en_33873108_33873229_1_1_1_1_1,00.html


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World Gas ReservesWorld Gas Reserves


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Excludes Russia


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Overview of World Gas ReservesOverview of World Gas Reserves


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Significant Gas FactsSignificant Gas Facts

Tight Gas 20% of US Production

Unconventional Gas 44% of 2005 US Production

Unconventional Gas 49% of 2030 US Production

2005 OECD 38 % Worlds Gas Production 2005 OECD 50 % Worlds Gas Consumption

2030 OECD 27 % Worlds Gas Production

2030 OECD 42 % Worlds Gas Consumption


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Tight Gas Resource TriangleTight Gas Resource Triangle

58 TCF produced through 2000 34 TCF Proven Reserves in 2001

Technically Recoverable volume 185 TCF

Undiscovered 350 TCF Additional GIP 5000 TCF

Source GTI 2001


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Tight Gas CharacteristicsTight Gas Characteristics

Low Permeability (


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Evaluation MethodsEvaluation Methods

Volumetrics Material Balance

Decline Curves

Production History Matching

Advanced Production Analysis

Simulation


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VolumetricsVolumetrics


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Archie EquationsArchie EquationsClean SandClean Sand

For low porosity sandstones:

a is typically 1.0m initially thought to be 2.0, later used values of 1.8-2.0

for tight gas


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Shaley SandShaley Sand

Fertl and Hammack reduction of Simandoux

Original Simandoux (widely used) based on very limited

samples

Vsh is effective shale volume, fraction

F is from shale corrected porosity

Rsh is the resistivity of the shale in sand recommends0.4R of shale beds

Hilchie 1982

Advanced Well Log Interpretation

D it P itD it P it


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Density PorosityDensity PorosityCorrections for InvasionCorrections for Invasion

Clean SandClean Sand

Density gets most of response from 3-4 from wellbore

Solve equations by trial and error

Initial guess for b is from mf= 1 + 0.73P where P is

Salinity in ppm divided by 1,000,000

Calculate gas density or estimate from following figure

When numbers converge you have answerHilchie 1982



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Density Neutron PorosityDensity Neutron Porosity


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Density Neutron PorosityDensity Neutron PorosityType I Invasion ProfileType I Invasion Profile

Hilchie 1982


Very deep or very shallow invasion - logs read same fluid

Quick approach below, best simultaneous eq using Rxo

Density Neutron PorosityDensity Neutron Porosity


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Density Neutron PorosityDensity Neutron PorosityType II Invasion ProfileType II Invasion Profile

Hilchie 1982


Invasion on order of 3-4 but not beyond neutron

Simultaneous equations for density with Rxo device best

Use density porosity only will be somewhat high


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Combined Archie EquationCombined Archie EquationClean SandClean Sand


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Pi k tt Pl t E l


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Pickett Plot Example

Th i N P d


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Their New ProcedureTheir New Procedure

R1(T1+6.77) = R2(T2+6.77)


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ConclusionsConclusions


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ConclusionsConclusions


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Net pay 18ft

Net pay added using highresolution is 50 feet!

High Resolution in Layered SandsHigh Resolution in Layered Sands


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Net PayNet Pay

Low Permeability Zones Often Have ExtensiveTransition Zones

Calibrate Cutoffs with Cores

Archie Equation Breaks Down at Very Low Porosities

for m = 2

Watch Out for Laminated Sands Below Vertical

Resolution of Logs


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Data IntegrationData Integration


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General Observations Log AnalysisGeneral Observations Log Analysis

Tight gas systems often contain layered and/or

dispersed clay (analysis methods different) Core data and FMI often critical to understanding

type system and existence of fractures

Must depth shift logs particularly in layered system

Calibrate logs and k estimates to cores Consider special core analysis in new plays

Full logging suite required for shaley sands


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What Is Effective Drainage Area?What Is Effective Drainage Area?

1 Year

0.1 md

0.0001 md0.001 md

0.01 md

10 Years

0.1 md

0.0001 md0.001 md

0.01 md


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Effective Drainage AreaEffective Drainage Area

Drainage Area f(k, Xf, Porosity, Geometry)

Have Dependent Relationship Between

Effective Drainage Area and Recovery Factor

Should Define Effective Drainage Area Relative

to Time and Recovery Factor


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Core AnalysisCore Analysis

CER, Holditch & Assoc 1991

Analysis critical to understanding of layered or

complex reservoir

Must measure rock properties under NOB(Jones andOwens, Soeder and Randolf)

Can have ten fold or more reduction in permeability

due to NOB at 0.01 md and below

Lower permeability rocks - smaller pore throats

Reduction of k with net overburdenReduction of k with net overburden


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CER, Holditch & Assoc 1991



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Mesaverde FormationMesaverde Formation


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Estimation of Permeability From LogsEstimation of Permeability From LogsExample Timurs Equation

c

wi

ma

S

Kk

=

c = 2 since k inversely proportional to surface area

squared and Swi proportional to surface area

Plot vs2)( wiSk straight line with slope m on log log

and y axis intercept at Ka

m related to tortuosity of the rockKukal, Simons SPE 13880

Estimation of k in very tight rocksEstimation of k in very tight rocks


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Estimation of k in very tight rocksEstimation of k in very tight rocks Timurs: little data < 1 md, also unstressed k

Predicted k two orders of magnitude high for 0.1d < k < 0.1md

Clay increases tortuosity, surface area

Better method: plot k(Swi**2) vs. ((1-Vcl) on log log plot

where: Swi and Vcl in fractions

K includes effect of overburden at 1.0 psi/ft

Swi must be at irreducible

must correct k to Kg

Derived from Mesaverde core date in Western Colorado

Kukal, Simons SPE 13880


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Estimating k where SEstimating k where Swiwi unknownunknown

86.3))1((4.171 clVk =

Porosity and Vcl in fractions

Only slightly less accurate that equation with Swi

Derived from Mesaverde also works in Travis Peak in

East Texas

Other examples of slot pore geometry are Albertas

deep Spirit River, East Texas Cotton Valley,Piceance Cozzette, Wyoming

Should be useful in many low k sandstones

Kukal, Simons SPE 13880

Plot k vs. ((1-Vcl)) on log log plot


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Material Balance P/ZMaterial Balance P/Z


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P/Z Based on Tank ModelP/Z Based on Tank Model

Constant Volume

No Efflux or Influx

Pressure Gradients Small

Measured Pressures Representative of Average

Pressure

Tight Gas P/Z PlotTight Gas P/Z Plot


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Tight Gas P/Z PlotTight Gas P/Z Plot

R di f D i R di l FlR di f D i R di l Fl


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Radius of Drainage Radial FlowRadius of Drainage Radial Flow


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Transient vs. Boundary FlowTransient vs. Boundary Flow

Constant Rate Example

Cross Section

Plan View

3500

2500

4000

3000

2000

Boundary Dominated

Well Performance

f(Volume, PI) Transient Well P

f(k, skin, ti

Fekete RTA

Documentation

T i t B d FlT i t B d Fl


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Transient vs. Boundary FlowTransient vs. Boundary Flow

Transient Flow

Early time or lowpermeability.

Flow that occurs when the

pressure pulse is

moving into an infinite orsemi infinite acting

reservoir.

The fingerprint of the

reservoir. Contains

information about

reservoir properties ie k

Boundary Flow

Late time flow behavior. Typically dominates long

term production data.

Reservoir is in a state of

pseudo-equilibrium massbalance.

Contains information

about reservoir pore

volume (OGIP).

Fekete RTA

Documentation


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Time to Pseudo Radial FlowTime to Pseudo Radial Flow

3

006328.02 =

ft

fXDxc

kt

t

Lee, Wattenbarger SPE Textbook 5

D ti f Fl P i d HF W llD ti f Fl P i d HF W ll


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Duration of Flow Periods HF WellDuration of Flow Periods HF Well

Lf (ft) k(md) telf tsprf

100 1 0.3 hrs 51.2 hrs100 0.01 27.3 hrs 213 days

1,000 0.01 114 days 58 years

100 0.001 11.4 days 5.8 years

1,000 0.001 3.1 years No way!!

= 0.15, CrD = 100, = 0.03 cp, ct = 0.0001 1/psi

Ti h G P B ild T


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Tight Gas Pressure Buildup TestsTight Gas Pressure Buildup Tests

very important to run prefrac BU for k and Pwsi

prefrac results can insure on proper straight line after

production period of significant length for pseudo radial

common problem in PT tests is that shut in period is too

short

too short of flow period can also be a problem i.e

wellbore unloading is incomplete (mass rate at surface

exceeds mass rate out perforations)

consider bottom hole shut-in (tubing plug) if afterflow

exceeds maximum practical test time

P B ild T t D i


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Pressure Buildup Test DesignPressure Buildup Test Design

make estimates of kgfrom guess then test data

estimate end of WBS

estimate beginning of pseudo radial flow

estimate onset of BDF

post frac estimates for time use type curves

SPE 17088, Dr. W. J. Lee


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Static Material Balance ProblemsStatic Material Balance Problems

Difficult to Analyze Due to Required SI Time,

Heterogeneity, Large Pressure Gradients

Common Curved Behavior

Can Result in Large Errors for GIP which are Generally

Low for Early Cum Values Increased SI Times Help but GIP Generally Low

Scatter = f(Pressure Gradients, Heterogeneity)


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Static Material Balance SummaryStatic Material Balance Summary

Get Pre Frac Initial Pressure Use Longer SI Times if Possible

Existence of Straight Line Does Not Insure Tank

Behavior

If Curved or Two Slopes Look at Later Straight Line

If Possible, QC Shut-in Times


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Flowing Material BalanceFlowing Material Balance

FTP converted to FBHP

Pseudo Pressure and Pseudo Time to Correct for

Viscosity and Compressibility Changes

Uses BDF flow equation for Gas simplified to

pssp

pa

i

pssp bp

GG

bp

q 11+

=

Iterative Process Dependent on guess for OGIP Plot Normalized Rate and Cum Prod

Fl i M t i l B lFlo ing Material Balance


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ppq

p

pa

p

G



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Curve is concave up until PSS - generally yielding

minimum OGIP Model is well in Center of Circle

Liquid Loading, Condensate Ring, Scale, etc. can

Affect Results

Dont use where Water Drive or Abnormal Pressure Use with Caution for High Perm Variations

Can be Useful but be Careful


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Decline CurvesDecline Curves


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D li C E ti ADecline Curve Equations Arps


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Decline Curve Equations - ArpsDecline Curve Equations - Arps

Exponential

Hyperbolic

A T diti l A l iA T diti l A l i


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Arps Traditional AnalysisArps Traditional Analysis

Based on Empirical Observations Exponential (D is constant)

Hyperbolic (D changes with time, 0


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Types of Decline Curves - ArpsTypes of Decline Curves - Arps


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Criteria for Arps AnalysisCriteria for Arps Analysis

Well Produced at or near Capacity Constant Flowing Bottom Hole Pressure

Drainage Area Remains Constant (BDF has been

Achieved)

Same Completion


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What About b > 1 ?What About b > 1 ?

Wrong Interpretation

Transient Flow instead of Boundary Dominated

Effects of b FactorEffects of b Factor


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Effects of b FactorEffects of b Factor

Cox, et alSPE 78695

Deep Tight Gas ExampleDeep Tight Gas Example


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Deep Tight Gas ExampleDeep Tight Gas Example

0.0009 < k < 0.07 md

Spacing 80 acresPwsi = 16,200 psia

BHT 400 deg F

Porosity = 6.6%Sw = 36%

Kv/Kh = 0.001

Thickness = 200

Rushing, et al SPE 109625

Xf= 300 (unless specified)

Fracture k = 100md

Effects of Layers on b ExponentsEffects of Layers on b Exponents


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Effects of Layers on b ExponentsEffects of Layers on b Exponents

Years b

1 Lay

b

4 Lay

b

8 Lay

b

16Lay

Error

(%)

1Layer

Error

(%)

4Layer

Error

(%)

8Layer

Error

(%)

16Layer

1 3.62 2.78 2.89 2.97 132 110 117 128

5 2.95 1.35 1.30 1.39 58 22 11 20

10 1.48 1.04 1.18 1.26 19 8 9 11

20 0.58 1.01 1.04 0.96 0.1 7 7 3

Effects of Xf on b ExponentsEffects of Xf on b Exponents


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Effects of Xf on b ExponentsEffects of Xf on b Exponents

Years b

Xf=50

b

Xf=100

b

Xf=300

b

Xf=500

Error

(%)

Xf=50

Error

(%)

Xf=100

Error

(%)

Xf=300

Error

(%)

Xf=500

1 4.01 3.60 2.78 1.91 145 139 110 78

5 1.53 1.44 1.35 1.20 34 25 22 12

10 1.10 1.08 1.04 1.03 14 10 8 7

20 1.07 1.06 1.01 0.96 0.11 9 7 6

Synthetic Single ReservoirSynthetic Single Reservoir


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80 acres80 acres

Cheng, Lee, McVay

SPE 108176



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80 acres80 acres

Cheng, Lee, McVay

SPE 108176



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80 acres80 acres

Cheng, Lee, McVay

SPE 108176



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80 acres80 acresall data includedall data included

Cheng, Lee, McVay

SPE 108176

All predictions from regression are too high

All values of b >1.0

b is proportional to Di

Percent error increases as b increases

Correct values for b cannot be directly obtained

from transient data



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80 acres80 acres

Cheng, Lee, McVay

SPE 108176

Stabilization time was 4.4 years

Discarded all data prior to 5.0 years

b generally decreases with time and all b values < 1.0

Results indicate that using only stabilized data sufficiently accurate

Decline Curve EstimateDecline Curve Estimate

Si l L b i d 1 0Si l L b t i d t 1 0


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Single Layer, b constrained to 1.0Single Layer, b constrained to 1.0

Cheng, Lee, McVay

SPE 108176


Si l L b t i d t 1 0Si l L b t i d t 1 0


79/131


Cheng, Lee, McVay

SPE 108176


Si l L b t i d t 1 0Si l L b t i d t 1 0


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Cheng, Lee, McVay

SPE 108176

b= 1.0 results in either underestimates oroverestimates

At early times production generally

underestimated

Forecasts tend to be more stable as more

late time data are included in the analysis

Additional ObservationsAdditional Observations


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Additional Observationsdd o a Obse a o s

Cheng, Lee, McVay

SPE 108176

b for stabilized flow related to reservoir drivemechanism, fluid properties and reservoir conditionsFetkovich et al 1996, Chen and Teufel 2002

b decreases as reservoir depletes

Average b during entire depletion phase will be < 1Chen and Teufel 2002

Improved Analysis TechniqueImproved Analysis Technique


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Improved Analysis Techniquep y q

Chen 2002

Calculate bE Pi = initial reservoir pressure

Pp,n = is normalized pseudo pressure

Cgi is isothermal compressibility @ Pi Zi evaluated at Pp, Zwfevaluated at Pwf



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p o ed a ys s ec quep y q

Cheng, Lee, McVay

SPE 108176



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p y qp y q

Cheng, Lee, McVay

SPE 108176

Back extrapolate to get qi at zero delta time



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p y qp y q

Cheng, Lee, McVay

SPE 108176

Back extrapolate to get Di at zero delta time


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Multi LayerMulti Layer


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Multi LayerMulti Layer

Cheng, Lee, McVay

SPE 108176

Estimate b at 0.6

No theoretical basis, based on observed results from a

few field and synthetic cases

Other procedures are the same

Decline Curve Analysis CBMDecline Curve Analysis CBM


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Rushing, Perego, Blasingame studied CBM behavior

using simulation (SPE 114514)

Long term b exponents ranged from 0.20 to 0.80 Early decline behavior for many wells was

exponential becoming more hyperbolic with time

None of the simulated cases exhibited long term

exponential behavior due to non linearrelationships between key coal properties and

either pressure or saturation

Wells with higher Pwf(all other factors being equal)

exhibited higher b values for long term production

Improved Decline Curve AnalysisImproved Decline Curve Analysis


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Additional method proposed by Ilk, Rushing, Perego,

and Blasingame (SPE116731)

Presents power law lost ratio method Presents diagnostic curves to aid in decline type

- hyperbolic, exponential

Method has merit, however, industry probably

slow to replace traditional decline curve methods

Summary Conventional AnalysisSummary Conventional Analysis


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Fit Hyperbolic when in BDF

Research Terminal Declines! Research Time in Transient Flow!

See if can Fit with b 1.0

Use Improved or advanced methods

Analogies Should Have Similar Completions

Similar Reservoir Parameters

Similar Spacing

Sufficient Production History for Reliable Analysis

Type Curve Changes With SpacingType Curve Changes With Spacing


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yp g p gyp g p g

1,000

10,000

100,000

0 20 40 60 80 100 120

Gas[M

cf]

Months

1,000

10,000

100,000

0 20 40 60 80 100 120

Gas[M

cf]

Months

1,000

10,000

100,000

0 20 40 60 80 100 120

Gas[M

cf]

Months

160

acre80 acre

40 acre


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Production History MatchingProduction History Matching

Production History MatchingProduction History Matching


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y gy g

Example PROMAT Single-Phase, Single-Layer Analytical Model

combined with Regression Analysis

Fast + Can Provide Accurate k, S (Xf) and sometimes

Drainage Area Accuracy Good where k Variation not big (Sergio Vera, MS

Thesis, Texas A&M 12/2006)

Production History Match ExampleProduction History Match Example


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Production History Matching - ProblemsProduction History Matching - Problems


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Non-Unique Solutions without Good Reservoir

Description

Pre-frac k can Over Estimate Reserves

Inaccurate in Layered Systems with Large

Permeability Variations

Accuracy Increases with Production Data

Multi-Layer Models often Require Detailed Data such

as Production Logs, etc.


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Advanced Production AnalysisAdvanced Production Analysis

Flow Periods for Fractured WellFlow Periods for Fractured Well


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Most of flow due to expansion in fracture

Generally too early to be of practical use

Often masked by WBS

Cinco et al 1981



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Two types of linear flow simultaneously occur

Most of flow comes from formation

Cannot determine frac length just from bilinear flow Plot of Pwfvs t**1/4 is straight line, plot of P or m(p)

vs time is slope on log log plot Cinco et al 1981



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Cinco et al 1981

Occurs only where high conductivity fracture, CrD 100

Continues approxtLfD = 0.016

Plot of Pwfvs. t**1/2 is straight line, plot of P or m(p)vs time is slope on log log plot



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Transition period between linear flow and radial flow

Badazhkov et al (SPE 117023) contains method and

references

Cinco et al 1981



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Fracture functions as extended wellbore consistent witheffective wellbore radius concept

Large Lf compared to drainage area can mask due to

BDF

Begins at tLfD ofapprox 3 for CrD 100, less for lower CrD

Pwfvs log t is straight lineCinco et al 1981


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Tight Gas FlowTight Gas Flow


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General Behavior

Small Xf compared to ROI Linear to Pseudo Radial less common

Large Xf compared to ROI

Long Term Linear Flow followed by BDF

Infinite Acting Linear Systems

Parallel Reservoir or No Flow Boundaries

Analysis of Linear FlowAnalysis of Linear Flow


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Plot of (m(pi)-m(pwf))/qg vs t**1/2 yields straight lines of

different slopes

Slope departs from analytical value as flow rates or

degree of drawdown become higher

Dont see the same degree of departure from analytical

solutions for pseudo radial flow



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Ibrahim and Wattenbarger SPE 100836



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Analysis of Linear FlowAnalysis of Linear FlowCorrections to Constant PCorrections to Constant Pwfwfcase for Drawdowncase for Drawdown


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Define Dimensionless Drawdown as:

Define correction factor as:

Solutions become

Analysis of Linear FlowAnalysis of Linear FlowCorrections to Constant PCorrections to Constant Pwfwfcase for Drawdowncase for Drawdown


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Analysis of Linear FlowAnalysis of Linear FlowS iSynopsis


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SynopsisSynopsis

Ibrahim and WattenbargerSPE 100836

cAk from slope of (m(pi)m(pwf))/qg vs sqrt(t) plot

Determine pore volume from slope and time to end of

linear flow, OGIP by including rock and fluid properties

Cannot determine k independently without Ac

Slope ofsqrt(t) plot affected by drawdown for constant

pwfcase

Without correction factor can be in error by up to 22%

at maximum drawdown No correction factors yet available for constant rate

case



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Combines Concepts from Pressure Transient Analysiswith Production Data

Allows for Determination of k and S or Xf in Transient

Region, OGIP from BDF

Newer Methods (Post Fetkovich) Allow Changes inOperating Conditions

Can also use for Diagnostic Analysis (Transient, BDF,

Interference)


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FetkovitchFetkovitch


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Combination of Analytical Transient Model and

Traditional Arps

Vertical Well, Center of Closed Circle, Single Phase

Fluid

Requires Constant Flowing Bottom Hole Pressure - less

useful for gas wells

Type Curve Match of Qd and Td against actual rate

versus time


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Blasingame, et alBlasingame, et al

S l t M d l


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Select Model

Radial

Infinite Conductivity Fracture

Finite Conductivity Fractures

Elliptical FlowHorizontal Well

Obtain match, multiple functions should fit same TC

Possible to obtain k and S or Xf

Can obtain OGIP if in BDF

Blasingame, et al


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Blasingame and othersBlasingame and others


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Tight gas reservoirs can suffer from non unique

solutions

Must have good idea of OGIP to reduce the non-

uniqueness problem

Even prefrac buildup for k and a post-frac buildupfor Xfdoes not guarantee a unique solution

Can use decline curves or FMB to estimate OGIP

Important Type Curve TechniquesImportant Type Curve Techniques


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Palacio and Blasingame (SPE 18799, Fekete RTA documentation) Agarwal, Gardner, et al (SPE 57916, Fekete RTA documentation)

Important Other MethodsImportant Other Methods


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Crafton, Reciprocal Productivity Index (SPE 37409, 49223)

Ozkan,et al

Transient RPI for Horizontal Wells (SPE 77690, 110848)

Reservoir SimulationReservoir Simulation


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Reservoir SimulationReservoir Simulation


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Gold Standard for Evaluation

Expensive, Time and Data Intensive Danger is Experience Level of Hands On Workers

or Weakest Link

Simulation Requires Knowledge of General

Reservoir Engineering and Production Engineering

Must have People in you Organization to

Understand Work Process, Results and Integrate

with Common Sense


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Cox et al SPE 98035

re Generally Proportional to Lf, k


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Cox et al SPE 98035

re Generally Proportional to Lf, k


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Cox et al SPE 98035

Practical Limit Exists for Geometry and low k


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Cox et al SPE 98035

Synopsis for Accurate EvaluationSynopsis for Accurate Evaluation


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Industry Acceptance and Time Constraints RequireMostly Traditional Decline Analysis

Volumetrics Must be Augmented with Core Data,Analogy, Information from More AdvancedMethods or Insights from Performance particularlyat Lower Permeability

Advanced Methods are useful for ObtainingK, S, or Xf for Transient Flow

OGIP for Boundary Dominated Flow andsometimes Linear Flow

For OGIP, Confirm from Several Methods or withReservoir Simulation or Analytical Model

Your Most Powerful ToolsYour Most Powerful Tools


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Peer Reviews!

Integrated Methodology


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SC Hein Tight Gas

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