1. Well Performance Analysis in a Multiwell Gas Condensate Reservoir—
Arun Field, Indonesia
Presented at
SPE Advanced Technology Workshop
Well Testing in Gas Condensate Reservoirs
1-2 April 2000, Calgary, Alberta, Canada
T. Marhaendrajana, Texas A&M University
N.J. Kaczorowski, Mobil E&P (U.S.)
T.A. Blasingame, Texas A&M University

2. Summary—Well Test Analysis
A representative summary of the analysis and interpretation of well test data taken from the Arun Gas Field (Sumatra, Indo-nesia) (Single-phase gas analysis is used).
2-zone radial composite reservoir model is effective for diagnosing the effects of con-densate banking at Arun Field.
Application of a new solution for the analysis and interpretation of well test data that exhibit "well interference" effects.

3. Summary—Production Data Analysis
Analysis and interpretation of production data using (single-phase) decline type curve analysis:
Permeability-thickness product
Skin factor
Original and movable gas-in-place
Comparison of results from well test and production data analyses vary—but these variations appear to be consistent.

4. N General Information—Arun Field (Indonesia) Field Description
Located in Northern part of Sumatra, Indonesia
Retrograde gas reservoir
One of the largest gas fields in the world
Arun Field has 111 wells:
79 producers
11 injectors
4 observation wells
17 wells have been abandoned
Field Description
Arun Field N

5. Major Phenomena Observed at Arun Field
Liquid accumulation near wellbore (conden-sate banking)
Need to know the radial extent of the condensate bank for the purpose of well stimulation.
Well interference effects (well test analysis)
Well interference effects tend to obscure the "standard" flow regimes—in particular, the radial flow response.
This behavior influences our analysis and inter-pretation efforts, and we must develop an alter-native analysis approach for well test data affected by multiwell interference effects.

6. Well Test Analysis Strategy
Condensate banking phenomenon:
Used a 2-zone radial composite reservoir model—the inner zone represents the "con-densate bank," and the outer zone represents the "dry gas reservoir." (reported kh-values are for the "outer zone")
Well interference effects:
Developed a new method for the analysis of well test data from a well in multiwell reservoir where we treat the "well interference" effect as a "Regional Pressure Decline." (This pheno-mena is observed in approximately 35 cases)

7. Well Test Analysis: Examples
Well C-I-18 (A-096)—Test Date: 28 Sep. 1992
Radial composite effects.
Multiwell interference effects.
Well C-IV-01 (A-060) [Test Date: 25 Feb. 1993]

8. WT Example 1: Log-log Summary Plot
Raw data
Corrected
Improvement of
pressure derivative.
Infinite-acting Reservoir Model
(Does not include non-Darcy flow)
Pseudopressure Functions, psi
Condensate banking
region.
Higher mobility
region.
Closed boundary at 160 ft?
(includes non-Darcy flow).
Effective shut-in pseudotime, hrs

9. WT Example 1: Horner (Semilog) Plot
Well C-I-18 (A-096) [Test Date: 28 September 1992]
Condensate banking
region.
Higher mobility
region.
Shut-in Pseudopressure, psia
Raw data
Corrected
Horner pseudotime, hrs (tp = 1.56 hr)

10. WT Example 1: Muskat Plot (single well pavg plot)
Well C-I-18 (A-096) [Test Date: 28 September 1992]
pp,avg = psia
Data deviate from the "Muskat line"
—indicating interference effects
from surrounding wells.
Onset of boundary
dominated flow
(single well analogy).
Shut-in pseudopressure, psia
"Transient flow"
dppws/dDta, psi/hr

11. WT Ex. 1: "Well Interference" Plot (radial flow only)
Well C-I-18 (A-096) [Test Date: 28 September 1992]
Intercept is used to
calculate permeability.
Slope is used in the
pressure correction.
(Dpp')Dtae, psi
(Dpp')Dtae <0, indicating multiwell
interference effects.
Dta2/ Dtae

12. WT Example 2: Log-log Summary Plot
Well C-IV-01 (A-060) [Test Date: 25 February 1993]
Raw data
Corrected
Improvement of
pressure derivative.
Pseudopressure Functions, psi
Condensate banking
region.
Closed boundary at 330 ft?
(includes non-Darcy flow).
Infinite-acting Reservoir Model
(Does not include non-Darcy flow)
Higher mobility
region.
Effective shut-in pseudotime, hrs

13. WT Example 2: Horner (Semilog) Plot
Well C-IV-01 (A-060) [Test Date: 25 February 1993]
Condensate banking
region.
Shut-in Pseudopressure, psia
Higher mobility
region.
Raw data
Corrected
Horner pseudotime, hrs (tp = 2.61 hr)

14. WT Example 2: Muskat Plot (single well pavg plot)
Well C-IV-01 (A-060) [Test Date: 25 February 1993]
pp,bar = psia
Onset of boundary
dominated flow.
Shut-in pseudopressure, psia
"Transient flow"
dppws/dDta, psi/hr

15. WT Ex. 2: "Well Interference" Plot (radial flow only)
Well C-IV-01 (A-060) [Test Date: 25 February 1993]
Intercept is used to
calculate permeability.
(Dpp')Dtae <0, indicating multiwell
interference effects.
(Dpp')Dtae, psi
Slope is used in the
pressure correction.
Dta2/ Dtae

16. Correlation of Well Test Results—Arun Field
Maps:
kh (outer-zone (gas) permeability).
skin factor.
non-Darcy flow coefficient.
Radius of condensate bank.
Correlation of non-Darcy flow coefficient and the permeability-thickness product (kh).

17. kh Map kh distribution ap-pears reasonable.
3 major "bubbles" of kh noted, pro-bably erroneous.
kh shown is for the "outer" zone (when the radial compo-site model is used).
kh Map

18. Skin Factor Map Skin factor distri-bution appears very consistent.
Areas of "high skin" indicate need for individual well stimulations.
Skin factors are calculated based on the "inner" zone of the radial compo-site model (when rc-model is used).

19. D (Non-Darcy) Map This map indicates a uniform distribution.
"high" and "low" regions appear to be focused near a single well.
Relatively small data set (30 points).
D (Non-Darcy) Map

20. Condensate Radius Map
Good distribution of values—"high" spots probably indicate need for individual well stimulations.
Relatively small data set (32 points).

21. D (Non-Darcy)—kh Crossplot
D-kh crossplot indi-cates an "order of magnitude" correla-tion.
Verifies that non-Darcy flow effects are systematic.
Slope = 2

22. Production Data Analysis: Arun Field
Well C-I-18 (A-096)
Limited history (no EURMB analysis possible).
Erratic performance.
Reasonable match on decline type curve.
Well C-IV-01 (A-060)
Good history (well was down for almost two years in ).
Sparse p/z data for EURMB analysis.
Early data match on decline type curve is questionable.
Late performance data deviate from material balance trend on decline type curve, indicat-ing "well interference" effects.

23. WPA Example 1: Well History Plot

24. WPA Example 1: Decline Type Curve Plot
Fetkovich-McCray Decline Type Curve
(No Well Interference Effects)

25. WPA Example 2: Well History Plot

26. WPA Example 2: EURMB Plot

27. WPA Example 2: Decline Type Curve Plot
Fetkovich-McCray Decline Type Curve
(No Well Interference Effects)

28. WPA Example 2: Decline Type Curve Plot
Fetkovich-McCray Decline Type Curve
(Includes Well Interference Effects)

29. Correlation of Production Analysis Results—Arun Field
Production data analyzed using decline type curve
analysis—single-phase (gas) pp and ta used.
Flow Properties:
Volumetric Properties:
Maps: kh
skin factor
Crossplots:
khWT—khWPA
sWT—sWPA
Plots:
G vs. time
EURMB vs. time
kh vs. time
Crossplots:
G—EURMB
EURPI—EURMB

30. kh shown is com-puted using decline type curve analysis on early production (pp and ta used).
kh distribution ap-pears reasonable (albeit lower than WT estimates).
A few "bubbles" of kh noted, these are probably erroneous.
kh Map

31. Skin Factor Map
Skin factors com-puted using decline type curve analysis on early production.
Skin factors from WPA are lower than WT estimates.

32. khWT—khWPA Crossplot
khWT estimates are clearly higher than khWPA estimates.
khWT estimates are "current," khWPA estimates are "ini-tial."
Variation is system-atic—decline type curve analysis uses earliest production data for kh (and s) estimates.

33. sWT—sWPA Crossplot
sWT estimates are "current," sWPA estimates are "ini-tial."
Could argue that this plot shows the "evolu-tion" of the skin fac-tor.
sWPA estimates should be higher, tied to kh estimation in decline type curve analysis.

34. Gas Reserves from Decline Type Curve Analysis

35. Estimated Ultimate Recovery from Material Balance

36. Flow Capacity (kh) from Decline Type Curve Analysis

37. G (Decline Type Curve)—EURMB Crossplot
G-EURMB crossplot indicates excellent agreement of com-puted results.

38. EURPI—EURMB Crossplot
EURPI—EURMB cross-plot shows excellent correlation of results.
Verifies that these analyses are consis-tent.

39. Well Performance Analysis in a Multiwell Gas Condensate Reservoir—
Arun Field, Indonesia
Presented at
SPE Advanced Technology Workshop
Well Testing in Gas Condensate Reservoirs
30 September- 1 October 1999, Houston, TX.
T. Marhaendrajana, Texas A&M University
N.J. Kaczorowski, Mobil E&P (U.S.)
T.A. Blasingame, Texas A&M University

40. Well Test Analysis: Examples (extra)
Well C-IV-11 (A-084)—Test Date: 5 Jan. 1992
Multiwell interference effects.
Well C-IV-11 (A-084)—Test Date: 4 May 1992
Radial composite effects.

41. Example 3: Log-log Summary Plot
Well C-IV-11 (A-084) [Test Date: 5 January 1992]
Raw data
Corrected
Improvement on
pressure derivative.
Pseudopressure Functions, psi
Closed boundary at 150 ft?
(includes non-Darcy flow).
Infinite-acting Reservoir Model
(Does not include non-Darcy flow)
Effective shut-in pseudotime, hrs

42. Example 3: Horner (Semilog) Plot
Well C-IV-11 (A-084) [Test Date: 5 January 1992]
Shut-in Pseudopressure, psia
Raw data
Corrected
Horner pseudotime, hrs (tp = 1.62 hr)

43. Example 3: Muskat Plot (single well pavg plot)
Well C-IV-11 (A-084) [Test Date: 5 January 1992]
pp,bar = 1920 psia
Onset of boundary
dominated flow.
Shut-in pseudopressure, psia
"Transient flow"
dppws/dDta, psi/hr

44. Example 3: "Well Interference" Plot (radial flow only)
Well C-IV-11 (A-084) [Test Date: 5 January 1992]
Intercept is used to
calculate permeability.
Slope is used in the
pressure correction.
(Dpp')Dtae, psi
Presence of multiwell
interference effects is unclear
Dta2/ Dtae

45. Example 4: Log-log Summary Plot
Well C-IV-11 (A-084) [Test Date: 4 May 1992]
Raw data
Corrected
Improvement on
pressure derivative.
Pseudopressure Functions, psi
Condensate banking
region.
Infinite-acting Reservoir Model
(Does not include non-Darcy flow)
Closed boundary at 197 ft?
(includes non-Darcy flow).
Higher mobility
region.
Effective shut-in pseudotime, hrs

46. Example 4: Horner (Semilog) Plot
Well C-IV-11 (A-084) [Test Date: 4 May 1992]
Condensate banking
region.
Shut-in Pseudopressure, psia
Higher mobility
region.
Raw data
Corrected
Horner pseudotime, hrs (tp = 1.63 hr)

47. Example 4: Muskat Plot (single well pavg plot)
Well C-IV-11 (A-084) [Test Date: 4 May 1992]
pp,bar = psia
Onset of boundary
dominated flow.
Shut-in pseudopressure, psia
"Transient flow"
dppws/dDta, psi/hr

48. Example 4: "Well Interference" Plot (radial flow only)
Well C-IV-11 (A-084) [Test Date: 4 May 1992]
Intercept is used to
calculate permeability.
Slope is used in the
pressure correction.
(Dpp')Dtae, psi
(Dpp')Dtae >0, no clear indication of
multiwell interference effects.
Dta2/ Dtae