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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 t-blasingame@tamu.edu

Petroleum Engineering 613Natural Gas Engineering

Texas A&M University

Lecture 08:Well Testing

Historical Perspectives

PETE 613(2005A)

Slide 2Well Testing Historical Perspectives

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)

Slide 3Well Testing Historical Perspectives

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

Origin of the "Deliverability" Relation

PETE 613(2005A)

Slide 4Well Testing Historical Perspectives

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)

Slide 5Well Testing Historical Perspectives

Well Testing Historical PerspectivesMulti-Rate Testing

Multi-Rate Testing

PETE 613(2005A)

Slide 6Well Testing Historical Perspectives

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)

Slide 7Well Testing Historical Perspectives

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)

Slide 8Well Testing Historical Perspectives

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 bqsc2 must be known (...need alternative approach).

PETE 613(2005A)

Slide 9Well Testing Historical Perspectives

Well Testing Historical PerspectivesExpected Results:

Pressure Transient Analysis (PTA)Production Analysis (PA)

Origin of the "Deliverability" Relation

PETE 613(2005A)

Slide 10Well Testing Historical Perspectives

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)

Slide 11Well Testing Historical Perspectives

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)

Slide 12Well Testing Historical Perspectives

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)

Slide 13Well Testing Historical Perspectives

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)

Slide 14Well Testing Historical Perspectives

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

Producing Time, days

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

Gas FlowrateWellbore Pressure

Production Data: Example 2

PETE 613(2005A)

Slide 15Well Testing Historical Perspectives

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 DropPressure Drop Derivative

Pressure Transient Data: Example 1

PETE 613(2005A)

Slide 16Well Testing Historical Perspectives

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)

Slide 17Well Testing Historical Perspectives

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

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0

Producing Time, days

Oil

Pro

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nR

ate,

ST

BD

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