Download - Texas A&M University Lecture 08: Well Testing Historical ... · PDF filePETE 613 (2005A) Slide —1 Well Testing — Historical Perspectives T.A. Blasingame, Texas A&M U. Department

PETE 613(2005A)

Slide — 1Well Testing —Historical Perspectives

T.A. Blasingame, Texas A&M U.Department of Petroleum Engineering

Texas A&M UniversityCollege Station, TX 77843-3116

+1.979.845.2292 — [email protected]

Petroleum Engineering 613Natural Gas Engineering

Texas A&M University

Lecture 08:Well Testing —

Historical Perspectives

PETE 613(2005A)


Well Testing — Historical PerspectivesOrigin of the "Deliverability" (or Backpressure) RelationEmpirical.Used to assess "open flow" potential of gas wells.Does not provide a "time-dependent" behavior.

Multi-Rate TestingHistorically, VERY popular — still used quite often,

especially on new wells to estimate deliverability and"non-Darcy" flow effects.

Keep it simple — a "4-point" test is appropriate.Isochronal testing is very difficult to implement.

Pressure Transient AnalysisExpected Results: Pressure Transient Analysis (PTA).Example Data Sets: PTA and Production data.Basic Plots: Lee Text Example 2.2 (Pressure Buildup).

PETE 613(2005A)


Well Testing — Historical PerspectivesOrigin of the "Deliverability"(or Backpressure) Relation

Origin of the "Deliverability" Relation

PETE 613(2005A)


Gas Well Deliverability:The original well deliverability

relation was completely empiri-cal (derived from observations),and is given as:

This relationship is rigorous (i.e.,it can be derived) for low pres-sure gas reservoirs, (n=1 for lami-nar flow).

From: Back-Pressure Data on Natural-Gas Wells and Their Application toProduction Practices — Rawlins andSchellhardt (USBM Monograph, 1935).

History of the "Deliverability" Equation

nwfppCgq )( 22

PETE 613(2005A)


Well Testing — Historical PerspectivesMulti-Rate Testing

Multi-Rate Testing

PETE 613(2005A)


Deliverability Testing: Basics

a. "Standard" 4-point test deliverability test — notethat the rates increase (to protect the reservoir).

b. "Isochronal" test sequence — note that each"buildup" is required to achieve pi.

c. Modified "Isochronal" test sequence — note thateach "buildup" is not required to achieve pi.

d. Governing equations for "deliverability" testanalysis/interpretation.

PETE 613(2005A)


Deliverability Testing: Orientation

a. Basic "pressure-squared" relationthat is presumed to describe gasflow — analogous form can bederived from steady-state flow theory(Darcy's law).

b.Traditional "deliverability" plot —probably derived from empiricalplotting of data.

PETE 613(2005A)


Deliverability Testing: Orientation

a."Rate-squared" (or velocity-squared) formulation — analogousform can be derived from steady-state flow theory (ForchheimerEq.).

b. Modified "deliverability" plot —note that bqsc

2 must be known (...need alternative approach).

PETE 613(2005A)


Well Testing — Historical PerspectivesExpected Results:

Pressure Transient Analysis (PTA)Production Analysis (PA)

Origin of the "Deliverability" Relation

PETE 613(2005A)


Expected Results of Pressure Transient Analysis (PTA):— "Conventional" PTA: Use of semilog and other specialized plots to

estimate reservoir properties from a particular "flow regime" (i.e., a flowregime is a characteristic behavior derived from an analytical solution —e.g., the constant pressure derivative function for infinite-acting radialflow (IARF)). Examples of other specialized plots: square-root and fourth-root of time plots for fractured wells.

— "Model-based" analyses: Using analytical/numerical reservoir models toperform simultaneous analysis/modelling procedures. Provides estimatesof dynamic formation properties: (i.e., model parameters)Radial Flow: k, S, CDFractured Wells: k, xf, FCD, CfDHorizontal Wells: kr, kr/kv, hwell, (effective length) zw (position), ChDDual porosity reservoir properties: ,

Data Requirements/Assessment/Review:— Typically involves very accurate measurements of bottomhole pressures

(this is a priority).— Rate history is most often the weakest link — must perform "due

diligence" and obtain the best possible rate history.— Should use downhole shut-in device to minimize wellbore storage.

Expected Results from PTA

PETE 613(2005A)


Expected Results of Production Analysis (PA):— "Conventional" decline curve analysis: (Arps, etc.) — empirical relations

used to provide estimates of recovery and forecasts of futureperformance.

— "Model-based" analyses: Using analytical/numerical reservoir models toperform simultaneous analysis/modelling procedures. Providesestimates of dynamic formation properties (k, S, xf, dual porosityproperties, etc.)

— "Model-based" forecasting: A direct extension of model-based analysis— generation of a time-dependent pressure and/or rate forecast.

Data Requirements/Assessment/Review:— Are production data available? (BOTH rates and PRESSURES!)— Is the well completion history available? (review for issues)— PVT and static reservoir properties? (must be assessed/included)— Is the production "analyzable?" (can major issues be resolved?)

Expected Results from PA

PETE 613(2005A)


Well Testing — Historical PerspectivesReservoir Performance Analysis:

PTA and PA Data Quality and Data Artifacts

PTA and PA Data Quality and Data Artifacts

PETE 613(2005A)


Production Example 1: Sewell Ranch No. 1 (North Texas (US))Rate and pressure data affected by water loading.Late-time data affected by line pressure (other wells in flow system).

Sewell Ranch Well No. 1 — Barnett Field (NorthTexas)

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

0 500 1000 1500 2000 2500 3000 3500 4000

Producing Time, days

Gas

Pro

du

ctio

nR

ate,

MS

CF

D

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Su

rfac

eP

ress

ure

,psi

g

Gas FlowrateWellbore Pressure

Production Data: Example 1

PETE 613(2005A)


Production Example 2: UPR22 Gas Well (Mid-Continent (US))Rate and pressure data affected by fluid loading.Seasonal cycles in demand/production.

UPR22 Gas Well — Mid-Continent (US)

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

0 250 500 750 1000 1250 1500


Gas

Pro

du

ctio

nR

ate,

MS

CF

D

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Cal

cula

ted

BH

P,p

sia


Production Data: Example 2

PETE 613(2005A)


Pressure Transient Example 1: Bourdet (SPE 12777)Production history effects are obvious.Interpretation should consider "no rate" and "rate" history cases.

a.No Rate History: (t format) Pressure drop andpressure drop derivative versus shut-in time(Bourdet (SPE 12777)).

b.Rate History: (te format) Pressure drop andpressure drop derivative versus Agarwalsuperposition time (Bourdet (SPE 12777)).

Bourdet Example (SPE 12777) (Dt e Format)

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02

Dt e , hr

Dp

and

Dp

',p

si

Pressure DropPressure Drop Derivative

Bourdet Example (SPE 12777) (Dt Format)

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02Dt , hr

Dp

and

Dp

',p

si


Pressure Transient Data: Example 1

PETE 613(2005A)


Pressure Transient Data: Example 2

Pressure Transient Example 2: DaPrat (SPE 13054)Dual porosity/naturally fractured reservoir (PSS interporosity flow).Illustrates the sensitivity of the pressure derivative function.

DaPrat Example (Well Mach 3X, SPE 13054) ( Dt Format)

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03Dt , hr

Dp

and

Dp

',p

si

Pressure DropPressure Drop Derivative (L=0.2)Pressure Drop Derivative (L=0.3)Pressure Drop Derivative (L=0.4)Simulated Pressure DropSimulated Pressure Drop Derivative

PETE 613(2005A)


Data Artifacts Example 1: Womack Hill Field (Alabama (US))Note the various events (value of annotated production records).No pressure data (typical).

Womack Hill Well No. 1633 — Womack Hill Field (Alabama)

1.E+01

1.E+02

1.E+03

1.E+04

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

1000

0

1100

0


Oil

Pro

du

ctio

nR

ate,

ST

BD

0

200

400

600

800

1000

1200

1400

1600

1800

2000

Est

imat

edB

HF

PP

ress

ure

,psi

a

Oil FlowrateWellbore Pressure

Pro

rate

dP

rod

uct

ion

Init

ial

Dep

leti

on

(no

pre

ssu

resu

pp

ort

)

Rec

om

ple

tio

n

Aci

dS

tim

ula

tio

n

Co

nve

rsio

nto

Jet

Pu

mp

p wf assumed constant

Data Artifacts: Example 1

PETE 613(2005A)


Data Artifacts Example 2: Told Well 3 (Colombia)pwf NOT synchronous with qo (pwf from fluid levels).Note that effect of pump change is captured by pwf and qo.

Well Told 3 — Colombia (South America)

1.E+02

1.E+03

1.E+04

0

200

400

600

800

1000

1200

1400

1600

1800

2000


Oil

Pro

du

ctio

nR

ate,

ST

BD

0

250

500

750

1000

1250

1500

1750

2000

2250

2500

Est

.BH

FP

ress

ure

,psi

a

Oil FlowrateWellbore Pressure

Pu

mp

Ch

ang

e

p wf not synchronouswith rate profile


PETE 613(2005A)


Data Artifacts Example 3: Canada Gas Wellpwf NOT synchronous with qg at early/intermediate times.Dispersion in pwf at middle times not reflected in the qg function.

Gas Well (Poor Early Time Data) — (Canada)

1.E+02

1.E+03

1.E+04

1.E+05

0 50 100

150

200

250

300

350

400

450

500

550

600


Gas

Pro

du

ctio

nR

ate,

MS

CF

D

0

500

1000

1500

2000

2500

3000

3500

Cal

c.B

HF

Pre

ssu

re,p

sia


qo

and

pw

f

incr

easi

ng

p wf variations notsynchronized with q g


PETE 613(2005A)


Data Artifacts Example 4: Southeast TX Gas Well (US)Multiple completion changes.Issues related to pressure profile — measure bottomhole pressure?

Gas Well with Evolving Condensate — (Southeast TX (US))

1.E+02

1.E+03

1.E+04

1.E+05

0 50 100

150

200

250

300

350

400

450

500

550

600


Gas

Pro

du

ctio

nR

ate,

MS

CF

D

05001000150020002500300035004000450050005500600065007000

Su

rfac

eP

ress

ure

,psi

g


Flo

wu

pA

nn

ulu

s

Flow up Casing

Flow up Tubing


PETE 613(2005A)


Data Artifacts Example 5: South Texas Gas Well (US)Gas well with anomalous pressure "jump" — packer leak?No "reservoir" mechanism (other than injection) could produce feature.

a.Semilog Plot: (t format) Pressure versus shut-in time (South Texas Gas Well (US)) — Packerleak (most likely cause).

b.Log-log Plot: (t format) Pressure drop andpressure drop derivative versus shut-in timetime (South Texas Gas Well (US)) — Packerleak (most likely cause).

Sanger Gas Well Case (South Texas (US))

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03

Dt , hr

pw

f,p

sia

PressureSanger Gas Well Case (South Texas (US))

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02 1.E+03

Dt , hr

Dp

and

Dp

',p

si



PETE 613(2005A)



Data Artifacts Example 6: Mid-Continent Gas Well (US)Changing wellbore storage and condensate banking (very high skin).Interpretation depends on understanding of reservoir and fluids.

Dunn Prefracture Pressure Buildup (Condensate Banking)(Mid-Continent (US))

1.E+00

1.E+01

1.E+02

1.E+03

1.E+04

1.E-03 1.E-02 1.E-01 1.E+00 1.E+01 1.E+02

Shut-In Pseudotime, Dt a , hr

Pse

ud

op

ress

ure

Dro

p, D

pp

and

Dp

p',

psi


PETE 613(2005A)


Well Testing — Historical PerspectivesWell Test Analysis — Basic Plots

Well Test Analysis — Basic Plots

PETE 613(2005A)


Well Test Analysis: Basic Plots (Lee Text Example)

a. Log-log "preliminary analysis"plot — wellbore storage andradial flow (Cs, k).

b. Cartesian "early-time" plot —used to analyze wellborestorage (p0, Cs).

d. Semilog "middle-time" plot —used to analyze radial flowbehavior (k, s).

e. Horner "middle-time" plot —used to analyze radial flowbehavior (k, s, p*).

f. Log-log "summary" plot —summary of all analysis (Cs, k,s, A, etc).

c. Cartesian "Arps" plot — usedto estimate average reservoirpressure.

PETE 613(2005A)


Basic Plots: "Preliminary" Log-Log PlotPressure drop function does not give much resolution.Pressure drop derivative function shows wellbore storage/radial flow.

Basic Plots: "Preliminary" Log-log Plot

PETE 613(2005A)


Basic Plots: Early Cartesian PlotUsed to estimate wellbore storage coefficient (slope of trend).Pressure at start of the test estimated from extrapolation.

Basic Plots: Early Cartesian Plot

PETE 613(2005A)


Basic Plots: Late Cartesian Plot (Pressure Buildup)NOT a universally valid plot (ONLY valid for very late times).Average reservoir pressure estimated from extrapolation.

Basic Plots: Late Cartesian Plot (PBU)

PETE 613(2005A)


Basic Plots: Semilog Plot (Miller-Dyes-Hutchinson)NOT corrected for rate history.Can be difficult to interpret (semilog straight line needs orientation).

Basic Plots: Semilog Plot (MDH)

PETE 613(2005A)


Basic Plots: Horner Semilog PlotCORRECTED for rate history.Used to estimate permeability, skin factor, average reservoir pressure.

Basic Plots: Horner Semilog Plot

PETE 613(2005A)


Basic Plots: "Summary" Log-Log PlotUsed to show simulated reservoir response (based on analysis).Multiple data functions used to orient analysis/interpretation.

Basic Plots: "Summary" Log-log Plot

PETE 613(2005A)


Given data — Lee text (1st edition),Example 2.2.

Module 4: Well Test Analysis — Work Relations

Working relations — Lee text (1stedition), Example 2.2).

PETE 613(2005A)


T.A. Blasingame, Texas A&M U.Department of Petroleum Engineering

Texas A&M UniversityCollege Station, TX 77843-3116

+1.979.845.2292 — [email protected]

Petroleum Engineering 613Natural Gas Engineering

Texas A&M University

Lecture 08:Well Testing —

Historical Perspectives(End of Lecture)

Download - Texas A&M University Lecture 08: Well Testing Historical ... · PDF filePETE 613 (2005A) Slide —1 Well Testing — Historical Perspectives T.A. Blasingame, Texas A&M U. Department

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