1. Well Testing — Historical Perspectives
Petroleum Engineering 613
Natural Gas Engineering
Texas A&M University
Lecture 08:
Well Testing —
Historical Perspectives
T.A. Blasingame, Texas A&M U.
Department of Petroleum Engineering
Texas A&M University
College Station, TX —
PETE 613
(2005A)

2. Well Testing — Historical Perspectives
Origin of the "Deliverability" (or Backpressure) Relation
Empirical.
Used to assess "open flow" potential of gas wells.
Does not provide a "time-dependent" behavior.
Multi-Rate Testing
Historically, 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 Analysis
Expected Results: Pressure Transient Analysis (PTA).
Example Data Sets: PTA and Production data.
Basic Plots: Lee Text Example 2.2 (Pressure Buildup).
PETE 613
(2005A)

3. Origin of the "Deliverability" Relation
Well Testing — Historical Perspectives
Origin of the "Deliverability"
(or Backpressure) Relation
PETE 613
(2005A)

4. History of the "Deliverability" Equation
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 to Production Practices — Rawlins and Schellhardt (USBM Monograph, 1935).
PETE 613
(2005A)

5. Well Testing — Historical Perspectives
Multi-Rate Testing
Well Testing — Historical Perspectives
Multi-Rate Testing
PETE 613
(2005A)

6. Deliverability Testing: Basics
a. "Standard" 4-point test deliverability test — note that the rates increase (to protect the reservoir).
c. Modified "Isochronal" test sequence — note that each "buildup" is not required to achieve pi.
b. "Isochronal" test sequence — note that each "buildup" is required to achieve pi.
d. Governing equations for "deliverability" test analysis/interpretation.
PETE 613
(2005A)

7. Deliverability Testing: Orientation
a. Basic "pressure-squared" relation that is presumed to describe gas flow — analogous form can be derived from steady-state flow theory (Darcy's law).
b.Traditional "deliverability" plot — probably derived from empirical plotting of data.
PETE 613
(2005A)

8. Deliverability Testing: Orientation
a."Rate-squared" (or velocity-squared) formulation — analogous form can be derived from steady-state flow theory (Forchheimer Eq.).
b. Modified "deliverability" plot — note that bqsc2 must be known (... need alternative approach).
PETE 613
(2005A)

9. Origin of the "Deliverability" Relation
Well Testing — Historical Perspectives
Expected Results:
Pressure Transient Analysis (PTA)
Production Analysis (PA)
PETE 613
(2005A)

10. Expected Results from PTA
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 flow regime is a characteristic behavior derived from an analytical solution — e.g., the constant pressure derivative function for infinite-acting radial flow (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 to perform simultaneous analysis/modelling procedures. Provides estimates of dynamic formation properties: (i.e., model parameters)
Radial Flow: k, S, CD
Fractured Wells: k, xf, FCD, CfD
Horizontal Wells: kr, kr/kv, hwell, (effective length) zw (position), ChD
Dual porosity reservoir properties: w, l
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.
PETE 613
(2005A)

11. Expected Results from PA
Expected Results of Production Analysis (PA):
"Conventional" decline curve analysis: (Arps, etc.) — empirical relations used to provide estimates of recovery and forecasts of future performance.
"Model-based" analyses: Using analytical/numerical reservoir models to perform simultaneous analysis/modelling procedures. Provides estimates of dynamic formation properties (k, S, xf, dual porosity properties, 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?)
PETE 613
(2005A)

12. PTA and PA Data Quality and Data Artifacts
Well Testing — Historical Perspectives
Reservoir Performance Analysis:
PTA and PA Data Quality and Data Artifacts
PETE 613
(2005A)

13. Production Data: Example 1
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).
PETE 613
(2005A)

14. Production Data: Example 2
Production Example 2: UPR22 Gas Well (Mid-Continent (US))
Rate and pressure data affected by fluid loading.
Seasonal cycles in demand/production.
PETE 613
(2005A)

15. Pressure Transient Data: Example 1
a. No Rate History: (Dt format) Pressure drop and pressure drop derivative versus shut-in time (Bourdet (SPE 12777)).
b. Rate History: (Dte format) Pressure drop and pressure drop derivative versus Agarwal superposition time (Bourdet (SPE 12777)).
Pressure Transient Example 1: Bourdet (SPE 12777)
Production history effects are obvious.
Interpretation should consider "no rate" and "rate" history cases.
PETE 613
(2005A)

16. 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.
PETE 613
(2005A)

17. Data Artifacts: Example 1
Data Artifacts Example 1: Womack Hill Field (Alabama (US))
Note the various events (value of annotated production records).
No pressure data (typical).
PETE 613
(2005A)

18. Data Artifacts: Example 2
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.
PETE 613
(2005A)

19. Data Artifacts: Example 3
Data Artifacts Example 3: Canada Gas Well
pwf NOT synchronous with qg at early/intermediate times.
Dispersion in pwf at middle times not reflected in the qg function.
PETE 613
(2005A)

20. Data Artifacts: Example 4
Data Artifacts Example 4: Southeast TX Gas Well (US)
Multiple completion changes.
Issues related to pressure profile — measure bottomhole pressure?
PETE 613
(2005A)

21. Data Artifacts: Example 5
a. Semilog Plot: (Dt format) Pressure versus shut-in time (South Texas Gas Well (US)) — Packer leak (most likely cause).
b. Log-log Plot: (Dt format) Pressure drop and pressure drop derivative versus shut-in time time (South Texas Gas Well (US)) — Packer leak (most likely cause).
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.
PETE 613
(2005A)

22. Data Artifacts: Example 6
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.
PETE 613
(2005A)

23. Well Test Analysis — Basic Plots
Well Testing — Historical Perspectives
Well Test Analysis — Basic Plots
PETE 613
(2005A)

24. Well Test Analysis: Basic Plots (Lee Text Example)
a. Log-log "preliminary analysis" plot — wellbore storage and radial flow (Cs, k).
b. Cartesian "early-time" plot — used to analyze wellbore storage (p0, Cs).
c. Cartesian "Arps" plot — used to estimate average reservoir pressure.
d. Semilog "middle-time" plot — used to analyze radial flow behavior (k, s).
e. Horner "middle-time" plot — used to analyze radial flow behavior (k, s, p*).
f. Log-log "summary" plot — summary of all analysis (Cs, k, s, A, etc).
PETE 613
(2005A)

25. Basic Plots: "Preliminary" Log-log Plot
Pressure drop function does not give much resolution.
Pressure drop derivative function shows wellbore storage/radial flow.
PETE 613
(2005A)

26. Basic Plots: Early Cartesian Plot
Used to estimate wellbore storage coefficient (slope of trend).
Pressure at start of the test estimated from extrapolation.
PETE 613
(2005A)

27. Basic Plots: Late Cartesian Plot (PBU)
Basic Plots: Late Cartesian Plot (Pressure Buildup)
NOT a universally valid plot (ONLY valid for very late times).
Average reservoir pressure estimated from extrapolation.
PETE 613
(2005A)

28. Basic Plots: Semilog Plot (MDH)
Basic Plots: Semilog Plot (Miller-Dyes-Hutchinson)
NOT corrected for rate history.
Can be difficult to interpret (semilog straight line needs orientation).
PETE 613
(2005A)

29. Basic Plots: Horner Semilog Plot
CORRECTED for rate history.
Used to estimate permeability, skin factor, average reservoir pressure.
PETE 613
(2005A)

30. Basic Plots: "Summary" Log-log Plot
Used to show simulated reservoir response (based on analysis).
Multiple data functions used to orient analysis/interpretation.
PETE 613
(2005A)

31. Module 4: Well Test Analysis — Work Relations
Given data — Lee text (1st edition), Example 2.2.
Working relations — Lee text (1st edition), Example 2.2).
PETE 613
(2005A)

32. Well Testing — Historical Perspectives
Petroleum Engineering 613
Natural Gas Engineering
Texas A&M University
Lecture 08:
Well Testing —
Historical Perspectives
(End of Lecture)
T.A. Blasingame, Texas A&M U.
Department of Petroleum Engineering
Texas A&M University
College Station, TX —
PETE 613
(2005A)