AIFE American Institute of Formation Evaluation

Drill Stem Test Pressure Data

AIFE Quality Coding System ©

AIFE's expert personnel have re-evaluated each drill stem test from the source documents according to criteria identified over forty years of experience, providing a newly comprehensive and reliable base for decision making. The following is a brief look at the methods by which this re-evaluation was accomplished. A fully detailed study of how these standards were arrived at is available upon request.

These Quality Codes grade drill stem tests according to the following signatures:


A
Best Quality
1. Test mechanically sound - No  Plugging/No Skidding
2. Recorder used-chart good,  pressures compare
3. Flow pressure verify recoveries  and/or flow rates
4. Bottom packer held on straddle tests
5. Recorder depths given
6. Recorder within interval tested
7. ISI stabilized, or nearing  stabilization with increments
8. Preflow time long enough to release hydrostatic head
9. KB elevation given
10. Two good shut-ins required
11. PMAX Range of approximately 1 to 10 Ibs. (7 to 69 kPa) from read shut-in pressure
88. Fluid to surface on flows (irregularities)
99. Flow incremented


B

Nearing Stabilization
12. Slight mechanical difficulties, but does not affect the test
13. Shut-ins not fully stabilized
15. Recorder pressures disagree from 1 to 19 PSI (7 to 131 kPa)
after recorder drag and depth difference
17. PMAX range of approximately 20 to 35 Ibs. (138 to 241 kPa)
from read shut-in pressure
48. Flow pressures do not verify recoveries
88. Plugging, fluid to surface, resets on flows (irregularities)
99. Flows incremented


C

Caution(Plugging)
18. Some mechanical difficulties evident on chart, however, does not appear to affect pressure data
19. Recorders run above the interval
21. Preflow not opened long enough, possibly slightly supercharged
22. Packer may have leaked slightly
24. Recorder pressures disagree from 20 - 29 PSI (138 to 200 kPa) after recorder drag and depth difference
25. Only one recorder, must be within interval
26. PMAX range of approximately 30 to 85 lbs.(207 to 586 kPa) from read shut-in pressure
27. Only one good shut-in
88. Plugging, fluid to surface, resets on flows (irregularities)
99. Flows incremented


D

Questionable
28. Not totally mechanically sound
29. Only one recorder, run inside above the interval
30. No recorder depth or questionable
31. No KB elevation
33. Questionable interval depths.
34. Supercharged ISI, FSI follows long valve open period
35. No chart from below bottom packer
36. Recorder pressures disagree from 30 PSI (206.8 kPa) and over after recorder drag and depth difference
37. PMAX range of approximately 80 to 150 Ibs.(552 to 1034.2 kPa) from read shut-in pressure
79. Cannot define a valid P-Max (test indicates definite drawdown) P-Max filled with the initial shut-in pressure
88. Plugging, fluid to surface, reset on flows (irregularities)
99. Flows incremented


E

Low Permeability,
Low Pressure
38. Covers all requirements of Code A, however, low permeability
and low pressure, unable to extrapolate
39. Low permeability, low pressure, but problems encountered
throughout test
46. Low permeability, relatively high pressure for "E" Code
88. Plugging, fluid to surface resets on flows (irregularities)
99. Flows incremented


F

Low Permeability,
High Pressure
40. Covers all requirements of Code A, however, low permeability
and high pressure (CAUTION: Watch for Cushion)
41. Low permeability, high pressure. but problems encountered
throughout test
47. Low permeability. relatively low pressure for "F" code
88. Plugging, fluid to surface, resets on flows (irregularities)
99. Flows incremented


G

Misrun (Flow only)
42. No shut-ins taken
43. No useable pressures
44. No useable data
45. Flow only
63. Unable to obtain initial packer seat
64. Lost seat after tool opened
65. No elements ruptured
66. Top elements ruptured
67. Bottom elements ruptured
68. Both elements ruptured
69. Plugged tool
70. Unable to reach test depth
71. Tool failure
72. Personnel failure
73. Belly spring turning
74. No reason available
75. Other
76. Mud dropped in annulus when tool opened (seat held)
77. Skidding tools when opening or during flow
90. Front page only, misrun


Note: Quality code information is programmed into the data base, as listed, by both letter and number, e.g. B13, G64. This is done to enhance the reliability of the data base. Should a user wish to investigate any specific coding instance, classification details are immediately retrievable.

From a drill stem test, the average effective permeability can be calculated to reservoir conditions using a set mathematical formula. In a practical sense, one of the required formula parameters, such as viscosity of the fluid, may not always be readily available. Reliable ratings, however, can be qualitatively assigned from the Pressure/Recovery Charts based on the nature of the build-up curves related to flow and pressure data.


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