Downhole PV tests for bubble point pressure
First Claim
1. A method for estimating a property of a fluid comprising:
- fitting a curve to pressure and volume data points for a fluid obtained using a downhole tool;
computing a second derivative of pressure with respect to volume from the curve;
estimating the property of the fluid at a point where slope of the second derivative is zero; and
storing a value of the estimated property of the fluid in a suitable medium.
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Accused Products
Abstract
The present invention provides an objective bubble point pressure determination method enables new applications of downhole PV (Pressure Volume) test results such as in situ measurement of the bubble point pressure for use as a quality control parameter for sampling. The present invention provides a method and apparatus to fit data points to a curve and to smooth these points over an interval of N points. The derivative of the curve is determined to obtain peak acceleration. The peak acceleration represents the bubble point pressure. This bubble point pressure is verified by comparison to changes in fluid compressibility and visual observation of a pressure volume plot history.
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Citations
29 Claims
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1. A method for estimating a property of a fluid comprising:
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fitting a curve to pressure and volume data points for a fluid obtained using a downhole tool; computing a second derivative of pressure with respect to volume from the curve; estimating the property of the fluid at a point where slope of the second derivative is zero; and storing a value of the estimated property of the fluid in a suitable medium. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for estimating a property of a fluid comprising:
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fitting a set of curves to data selected for one of pressure and volume, pressure and temperature, and volume and temperature for the fluid obtained using a downhole tool; computing a second derivative relating to the selected one of pressure and volume, pressure and temperature, and volume and temperature from each curve in the set of curves; comparing the computed second derivatives to estimate the property of the fluid; and storing an estimated value of the property of the fluid in a suitable medium. - View Dependent Claims (15, 16, 17)
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18. A compute-readable medium containing instructions that when executed by a computer perform a method for estimating a property of a fluid comprising:
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fitting a curve to data points for a selected one of pressure and volume, pressure and temperature and, volume and temperature for the fluid obtained using a downhole tool; computing a second derivative relating to the selected one of pressure and volume, pressure and temperature, and volume and temperature from the fitted curve; estimating the property of the fluid at a point where the slope of the second derivative is zero; and storing a value of the estimated property of the fluid in a suitable medium. - View Dependent Claims (19, 20, 21)
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22. A computer-readable medium containing instructions that when executed by a computer perform a method for estimating a property of a fluid comprising:
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fitting a set of curves to data points for a selected one of pressure and volume, pressure and temperature, and volume and temperature for the fluid obtained using a downhole tool; computing a second derivative relating to the selected one of pressure and volume, pressure and temperature, and volume and temperature from each curve in the set of curves; comparing the computed second derivatives to estimate the property of the fluid; and storing a value of the property of the fluid in a suitable medium. - View Dependent Claims (23, 24, 25)
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26. An apparatus for estimating a property of a fluid comprising:
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a sensor unit for measuring at least two of a set consisting of pressure, volume and temperature of the fluid downhole; a processor programmed to fit a curve to data points for a selected one of pressure and volume, pressure and temperature, and volume and temperature for the fluid; compute a second derivative relating the selected one of pressure and volume, pressure and temperature and volume and temperature from the curve; estimate the property of the fluid at a point where the slope of the second derivative is zero; and store a value of the estimated parameter of the fluid in a suitable medium. - View Dependent Claims (27, 28, 29)
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Specification