Determining dew precipitation and onset pressure in oilfield retrograde condensate
First Claim
1. A method for detecting dew precipitation in a sample of formation fluid located downhole in an oilfield reservoir, comprising:
- (a) isolating a sample of formation fluid downhole;
(b) illuminating the sample downhole with fluorescence excitation light;
(c) measuring at least one characteristic of fluorescence emission from the sample;
(d) reducing pressure on the sample;
(e) repeating steps (b) to (d); and
(f) detecting dew precipitation when a change is detected in a parameter that is a function of the at least one characteristic of fluorescence emission.
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Abstract
A method and apparatus detects dew precipitation and determines dew precipitation onset pressure in a sample of formation fluid located downhole in an oilfield reservoir. In a preferred embodiment, the method includes (a) isolating a sample of formation fluid downhole; (b) illuminating the sample downhole with fluorescence excitation light; (c) measuring at least one characteristic of fluorescence short from the sample; (d) reducing pressure on the sample; (e) repeating steps (b) to (d); (f) detecting dew precipitation when a change is detected in a parameter that is a function of the at least one characteristic of fluorescence emission; and (g) setting dew precipitation onset pressure equal to pressure on the sample when the change in the parameter is detected. The parameter preferably is a function of fluorescence intensity and fluorescence red shift, and the change is an increase in fluorescence intensity and detection of fluorescence red shift. Also, the function includes a ratio of a measured intensity at a first wavelength to a reference intensity, and the reference intensity is a function of a measured intensity at a second wavelength.
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Citations
15 Claims
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1. A method for detecting dew precipitation in a sample of formation fluid located downhole in an oilfield reservoir, comprising:
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(a) isolating a sample of formation fluid downhole; (b) illuminating the sample downhole with fluorescence excitation light; (c) measuring at least one characteristic of fluorescence emission from the sample; (d) reducing pressure on the sample; (e) repeating steps (b) to (d); and (f) detecting dew precipitation when a change is detected in a parameter that is a function of the at least one characteristic of fluorescence emission. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12)
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13. A method for detecting dew precipitation in a sample of formation fluid located downhole in an oilfield reservoir, comprising:
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(a) illuminating the fluid sample downhole with fluorescence excitation light at a first excitation wavelength; (b) measuring fluorescence intensity emitted from the fluid sample under reduced pressure in a fluid sample cell to produce a measured intensity value; and (c) detecting dew precipitation when the measured intensity value is greater than a reference intensity value.
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14. A tool for detecting dew precipitation in a fluid sample located downhole in an oilfield reservoir, comprising:
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a tool body including a fluid sample cell adapted to take a sample of formation fluid downhole in the oilfield reservoir; means for isolating a sample of formation fluid downhole; means for illuminating the sample downhole with fluorescence excitation light; means for repeatedly reducing pressure on the sample and measuring at least one characteristic of fluorescence emission from the sample; and means for detecting dew precipitation when a change is detected in a parameter that is a function of the at least one characteristic of fluorescence emission.
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15. A tool for detecting dew precipitation in a fluid sample located downhole in an oilfield reservoir, comprising:
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a tool body including a fluid sample cell adapted to take a sample of formation fluid downhole in the oilfield reservoir; means for illuminating the fluid sample downhole with fluorescence excitation light at a first excitation wavelength; means for measuring fluorescence intensity emitted from the fluid sample under reduced pressure in a fluid sample cell to produce a measured intensity value; and means for detecting dew precipitation when the measured intensity value is greater than a reference intensity value.
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Specification