Method for measuring formation properties with a time-limited formation test

• US 20040045706A1
• Filed: 05/09/2003
• Published: 03/11/2004
• Est. Priority Date: 09/09/2002
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Inventors: Follini, Jean-Marc, Pop, Julian, Hache, Jean-Michel
• Granted Patent: US 7,263,880 B2
• Time in Patent Office: Days
• US Class Current: 166/250.07
• CPC Class Codes: E21B 49/00 Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells
• CPC Class Codes: E21B 49/008 by injection test; by analysing pressure variations in an injection or production test, e.g. for estimating the skin factor measuring pressure E21B47/06
• CPC Class Codes: E21B 49/10 using side-wall fluid samplers or testers

Abstract

An apparatus and method for determining at least one downhole formation property is disclosed. The apparatus includes a pretest piston positionable in fluid communication with the formation, and a series of flowlines pressure gauges, and valves configured to selectively draw into the apparatus for measurement of one of formation fluid and mud. The method includes performing a first pretest to determine an estimated formation parameter; using the first pretest to design a second pretest and generate refined formation parameters whereby formation properties may be estimated.

Claims

1. A method for determining downhole parameters using a downhole tool positioned in a wellbore adjacent a subterranean formation, comprising:

(a) establishing fluid communication between a pretest chamber in the downhole tool and the formation via a flowline, the flowline having an initial pressure therein;

(b) moving a pretest piston positioned in the pretest chamber in a controlled manner to reduce the initial pressure to a drawdown pressure;

(c) terminating movement of the piston to permit the drawdown pressure to adjust to a stabilized pressure;

(d) repeating steps a-c until a difference between the stabilized pressure and the initial pressure is substantially smaller than a predetermined pressure drop; and

(e) determining one or more downhole parameters from an analysis of one or more of the pressures.

2. The method of claim 1 wherein the pretest piston is moved at a fixed rate.

3. The method of claim 1 wherein the pretest piston is moved such that a predetermined change in volume in the flowline occurs.

4. The method of claim 1 wherein the movement of the pretest piston is controlled by controlling one of reduction of pressure in the flowline, rate of pressure change in the flowline, incremental volume change the pretest chamber and combinations thereof.

5. The method of claim 1 wherein the duration of step (c) is longer than step (b).

6. The method of claim 1 further comprising determining when to terminate step (c).

7. The method of claim 1 further comprising setting the downhole tool.

8. The method of claim 1 wherein the step of determining comprises determining one of mud compressibility, formation pressure, wellbore pressure, mobility and combinations thereof.

9. The method of claim 1 further comprising measuring one of a wellbore pressure, a formation pressure and combinations thereof.

10. The method of claim 9 further comprising determining the difference in pressure between the formation pressure and the wellbore pressure.

11. The method of claim 1 wherein an estimation of the formation pressure is determined from the initial and stabilized pressures.

12. The method of claim 11 wherein the larger of the initial and stabilized pressures is an estimation of the formation pressure.

13. The method of claim 1 further comprising determining whether to perform a measurement phase.

14. The method of claim 13 wherein the parameters are used to design a measurement phase pretest.

15. The method of claim 14 further comprising performing a measurement phase pretest.

16. A method for determining formation parameters using a downhole tool positioned in a wellbore adjacent a subterranean formation comprising:

a. measuring a first pressure in a flowline that is in fluid communication with the subterranean formation;

b. moving a pretest piston in a controlled manner in a pretest chamber to create a predetermined pressure drop in the flowline;

c. stopping the pretest piston after a selected movement of the pretest piston;

d. allowing the pressure in the flowline to stabilize; and

e. repeating steps (a)-(d) until a difference between the stabilized pressure in the flowline and the first pressure in the flowline is substantially smaller than the predetermined pressure drop;

f. determining an initial estimate of the formation parameters from an analysis of one or more of the pressures.

g. designing pretest criteria for performing a second pretest based on the initial estimate of the formation parameters;

h. performing a pretest of the formation according to the designed pretest criteria whereby a refined estimate of the formation parameters is determined.

17. The method of claim 16, wherein the selected movement of the pretest piston is based on a prescribed change in a property in the flowline, wherein the property is one of reduction of pressure in the flowline, rate of pressure change in the flowline, an incremental volume extracted in the pretest chamber, a rate of change of the volume of the pretest chamber and combinations thereof.

18. The method of claim 16, wherein the predetermined pressure drop is less than a difference between a pressure and a formation pressure.

19. The method of claim 16, further comprising:

(f) repeating steps (a)-(d) an additional time to obtain a new stabilized pressure in the flowline, the new stabilized pressure is used as an initial estimate of a formation pressure in the designing pretest criteria.

20. The method of claim 16, wherein the moving the pretest piston in a controlled manner is based on a selected rate of volume increase in the flowline, the selected rate of volume increase being based on a calculation that takes into account a mud compressibility.

21. The method of claim 16, wherein the moving the pretest piston in a controlled manner is based on a selected rate of pressure drop in the flowline, the selected rate of pressure drop being based on a calculation that takes into account a mud compressibility.

22. A method for estimating a formation pressure using a formation tester disposed in a wellbore penetrating a formation, comprises:

a. measuring a first pressure in a flowline that is in fluid communication with the subterranean formation;

b. moving a pretest piston in a controlled manner in a pretest chamber to create a predetermined pressure drop in the flowline;

c. stopping the pretest piston after a selected movement of the pretest piston;

d. allowing the pressure in the flowline to stabilize;

e. repeating steps (a)-(d) until a difference between the stabilized pressure in the flowline and the first pressure in the flowline is substantially smaller than the predetermined pressure drop; and

f. determining the formation pressure based on a final stabilized pressure in the flowline.

23. The method of claim 22, wherein the selected movement of the pretest piston is based on a prescribed change in a property in the flowline, wherein the property is a volume or a pressure.

24. The method of claim 22, wherein the predetermined pressure drop is less than a difference between a mud hydraulic pressure and a formation pressure.

25. The method of claim 22, further comprising:

(f) repeating steps (a)-(d) an additional time before the determining the formation pressure.

26. The method of claim 22, wherein the moving the pretest piston in a controlled manner is based on a selected rate of volume increase in the flowline, the selected rate of volume increase being based on a calculation that takes into account a mud compressibility.

27. The method of claim 22, wherein the moving the pretest piston in a controlled manner is based on a selected rate of pressure drop in the flowline, the selected rate of pressure drop being based on a calculation that takes into account a mud compressibility.

28. A method of determining mud compressibility using a downhole tool positioned in a wellbore adjacent a subterranean formation, comprising:

capturing wellbore fluid in the formation tester, the wellbore fluid in fluid communication with a pretest chamber having a movable piston therein;

selectively moving the piston in the pretest chamber to alter the volume of captured fluid in the downhole tool;

measuring the pressure of the captured fluid; and

estimating mud compressibility from the measured pressure.

29. The method of claim 28 further comprising determining one of the wellbore pressure, the wellbore temperature and combinations thereof.

30. The method of claim 29 wherein the step of determining is performed at a desired depth.

31. The method of claim 30 further comprising using the mud compressibility to determine downhole parameters at the desired depth.

32. The method of claim 28 further comprising using the mud compressibility to determine downhole parameters.

33. The method of claim 28 further comprising comparing the mud compressibility with an estimated mud compressibility determined from wellbore parameters.

34. The method of claim 33 wherein the wellbore parameters are one of the mud density, mud pressure, mud temperature and combinations thereof.

35. The method of claim 28 wherein the step of capturing is performed by sealingly engaging the downhole tool with an impermeable surface in the wellbore such that wellbore fluid is trapped therein.

36. The method of claim 28 wherein the impermeable surface is casing lining the wellbore.

37. The method of claim 28 wherein the movement of the piston creates one of a compression of the fluid, a decompression of the fluid and combinations thereof.

38. The method of claim 28 further comprising adjusting the estimated mud compressibility using a correction factor.

39. The method of claim 28, wherein the mud compressibility is determined by extrapolating a compressibility value determined at a different temperature or a different pressure.