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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

    2000

    3000

    4000

    5000

    6000

    7000

    8000

    9000

    1000

    0

    1100

    0

    Producing Time, days

    Oil

    Pro

    du

    ctio

    nR

    ate,

    ST

    BD

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