Formation tester pretest using pulsed flow rate control
First Claim
1. A method for performing a pretest on a permeable rock formation containing a fluid having a bubble point comprising:
- (a) disposing a formation pressure tester containing a chamber in a wellbore in the formation such that fluid communication is allowed between the tester and the formation but not between the tester and the wellbore;
(b) increasing the volume of the chamber so as to create a pressure differential between the tester and the formation;
(c) stopping step (b) when a measured value reaches a predetermined value;
(d) allowing fluid to flow into the chamber, thereby increasing the pressure within the chamber; and
(e) repeating steps (b)-(d) until the volume of the chamber reaches a predetermined volume.
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Abstract
The present invention is directed to methods and apparatus for using a formation tester to perform a pretest, in a formation having low permeability, by intermittently collecting a portion of fluid at a constant drawdown rate. The drawdown pressure is monitored until a maximum differential pressure is reached between the formation and the tester. Then the piston is stopped until the differential pressure increases to a set value, at which time the piston is restarted. The controlled intermittent operation of the piston continues until a set pretest volume is reached. The modulated drawdown allows for an accurate collection of pressure versus time data that is then used to calculate the formation pressure and permeability. The present invention also finds applicability in logging-while-drilling and measurement-while drilling applications where power conservation is critical.
53 Citations
22 Claims
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1. A method for performing a pretest on a permeable rock formation containing a fluid having a bubble point comprising:
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(a) disposing a formation pressure tester containing a chamber in a wellbore in the formation such that fluid communication is allowed between the tester and the formation but not between the tester and the wellbore;
(b) increasing the volume of the chamber so as to create a pressure differential between the tester and the formation;
(c) stopping step (b) when a measured value reaches a predetermined value;
(d) allowing fluid to flow into the chamber, thereby increasing the pressure within the chamber; and
(e) repeating steps (b)-(d) until the volume of the chamber reaches a predetermined volume. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A method for performing a pretest on a permeable rock formation containing a fluid having a bubble point comprising:
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(a) disposing a formation pressure tester containing a chamber in a wellbore in the formation such that fluid communication is allowed between the tester and the formation but not between the tester and the wellbore;
(b) increasing the volume of the chamber so as to create a pressure differential between the tester and the formation;
(c) stopping step (b) when a measured value reaches a predetermined value;
(d) allowing fluid to flow into the chamber, thereby increasing the pressure within the chamber; and
(e) repeating steps (b)-(d) until the volume of the chamber reaches a predetermined volume;
wherein the rate of volume increase in step (b) is sufficiently greater than the rate of flow of fluid out of the formation that the pressure in the chamber would drop below the bubble point of the fluid if the volume of the chamber were increased to the predetermined volume in a single step; and
wherein the pressure in the chamber is maintained above the bubble point of the fluid. - View Dependent Claims (11, 12, 13, 14)
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15. An apparatus for performing a pretest on a permeable rock formation containing a fluid having a bubble point comprising:
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a body;
a flowline disposed within said body, said flowline being in fluid communication with the formation;
a piston sealingly disposed in said body such that movement of said piston relative to said body changes the volume of said flowline, wherein the piston is actuated between an on mode in which it moves with respect to said body and an off mode in which it is stationary with respect to said body; and
a control system that controls the movement said piston in response to a measured parameter and prevents the volume of the flowline from exceeding a predetermined maximum volume;
wherein the rate of change in the volume of said flowline when said piston is in the on mode is sufficiently greater than the rate of flow of fluid out of the formation that the pressure in the chamber would drop below the bubble point of the fluid if the volume of the chamber were increased to the predetermined maximum volume in a single step. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22)
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Specification