Method for measuring formation properties with a time-limited formation test
First Claim
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1. A method for determining at least one formation fluid property using a formation tester, comprising:
- collecting a first set of data points representing pressures in a pretest chamber of the formation tester as a function of time during a first pretest;
determining a set of parameters for a second pretest, the set of parameters being determined based on estimated formation properties derived from the first set of data points and a time remaining for performing the second pretest;
performing the second pretest using the set of parameters;
collecting a second set of data points representing pressures in the pretest chamber as a function of time during the second pretest; and
determining the at least one formation fluid property from the second set of data points.
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Abstract
An apparatus and method for determining at least one downhole formation property is disclosed. The apparatus includes a probe and 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.
91 Citations
21 Claims
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1. A method for determining at least one formation fluid property using a formation tester, comprising:
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collecting a first set of data points representing pressures in a pretest chamber of the formation tester as a function of time during a first pretest;
determining a set of parameters for a second pretest, the set of parameters being determined based on estimated formation properties derived from the first set of data points and a time remaining for performing the second pretest;
performing the second pretest using the set of parameters;
collecting a second set of data points representing pressures in the pretest chamber as a function of time during the second pretest; and
determining the at least one formation fluid property from the second set of data points. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
isolating a volume of a drilling fluid in a flow line that is in fluid communication with the pretest chamber of the formation tester;
collecting a set of data points representing pressures in the pretest chamber as a function of time while moving a piston in the pretest chamber; and
determining the mud compressibility from the set of data points.
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7. The method of claim 5, wherein the mud compressibility is used to determine a condition for terminating a drawdown phase in the first pretest.
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8. The method of claim 7, wherein the condition for terminating the drawdown phase is based on finding a straight line having a fixed slope, the straight line representing a flow line expansion in the drawdown phase.
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9. The method of claim 8, wherein the fixed slope is determined by the mud compressibility, a flow line volume, and the piston drawdown rate.
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10. The method of claim 8, wherein the finding the straight line is performed by finding a series of consecutive data points in the drawdown phase having substantially identical intercepts on a pressure versus time plot when each of the data points is fitted to a line with the fixed slope.
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11. The method of claim 8, wherein the finding the straight line is performed by finding a series of consecutive data points in the drawdown phase having substantially identical variances when each of the data points is fitted to the straight line with the fixed slope.
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12. The method of claim 5, further comprising determining a mud filtration rate after the determining the mud compressibility.
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13. The method of claim 12, wherein the finding the mud filtration rate comprises:
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isolating a volume of the drilling fluid in a flow line that is in fluid communication with the pretest chamber and a formation;
compressing the volume of the drilling fluid with the piston;
collecting data points representing pressures in the pretest chamber as a function of time after the compressing is terminated; and
determining the mud filtration rate from the data points.
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14. The method of claim 12, wherein the mud filtration rate is used to determine a condition for terminating a drawdown phase in the first pretest.
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15. A method for determining at least one formation fluid property using a formation tester in a formation penetrated by a borehole, comprising:
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collecting a first set of data points representing pressures in a pretest chamber of the formation tester as a function of time during a first pretest;
determining an estimated formation pressure and an estimated formation fluid mobility from the first set of data points;
determining a set of parameters for a second pretest, the set of parameters being determined based on the estimated formation pressure, the estimated formation fluid mobility, and a time remaining for performing the second pretest;
performing the second pretest using the set of parameters;
collecting a second set of data points representing pressures in the pretest chamber as a function of time during the second pretest; and
determining the at least one formation fluid property from the second set of data points. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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Specification