Method for measuring formation properties with a time-limited formation test
First Claim
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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,(b) establishing an initial pressure in the flowline;
(c) moving a pretest piston positioned in the pretest chamber in a controlled manner to reduce the initial pressure to a drawdown pressure;
(d) terminating movement of the piston to permit the drawdown pressure to adjust to a stabilized pressure;
(e) repeating steps b–
d until a difference between sequential stabilized pressures is substantially smaller than a predetermined pressure drop; and
(f) determining one or more downhole parameters from an analysis of one or more of the pressures.
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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.
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Citations
39 Claims
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1. A method for determining downhole parameters using a downhole tool positioned in a wellbore adjacent a subterranean formation, comprising:
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(a) establishing fluid communication between a pretest chamber in the downhole tool and the formation via a flowline, (b) establishing an initial pressure in the flowline; (c) moving a pretest piston positioned in the pretest chamber in a controlled manner to reduce the initial pressure to a drawdown pressure; (d) terminating movement of the piston to permit the drawdown pressure to adjust to a stabilized pressure; (e) repeating steps b–
d until a difference between sequential stabilized pressures is substantially smaller than a predetermined pressure drop; and(f) determining one or more downhole parameters from an analysis of one or more of the pressures. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15)
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16. A method for determining formation parameters using a downhole tool positioned in a wellbore adjacent a subterranean formation comprising:
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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 sequential stabilized pressures 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. - View Dependent Claims (17, 18, 19, 20, 21)
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22. A method for estimating a formation pressure using a formation tester disposed in a wellbore penetrating a formation, comprises:
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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 sequential stabilized pressures in the is substantially smaller than the predetermined pressure drop; andf. determining the formation pressure based on a final stabilized pressure in the flowline. - View Dependent Claims (23, 24, 25, 26, 27)
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28. A method of determining mud compressibility using a downhole tool positioned in a wellbore adjacent a subterranean formation, comprising:
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capturing wellbore fluid in the formation tester, the wellbore fluid in fluid conununication 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; and creating a pretest, wherein at lease one parameter of the pretest is determined based on a deviation from expected mud compressibility characteristics. - View Dependent Claims (29, 30, 31, 32, 33, 34, 35, 36, 37, 38)
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39. A method for determining downhole parameters using a downhole tool positioned in a wellbore adjacent a subterranean formation, comprising:
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(a) establishing fluid communication between a pretest chamber in the downhole tool and the formation via a flowline; (b) establishing an initial pressure in the flowline; (c) moving a pretest piston positioned in the pretest chamber in a controlled manner to reduce the initial pressure to a drawdown pressure; (d) terminating movement of the piston to permit the drawdown pressure to adjust to a stabilized pressure; (e) repeating steps b–
d until a difference between one of sequential stabilized pressures and drawdown pressures is substantially smaller than a predetermined pressure drop; and(f) determining one or more downhole parameters from an analysis of one or more of the pressures.
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Specification