Determining dew precipitation and onset pressure in oilfield retrograde condensate

• US 20040000636A1
• Filed: 12/03/2002
• Published: 01/01/2004
• Est. Priority Date: 06/26/2002
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (Schlumberger NV)
• Original Assignee: Schlumberger Technology Corporation Incorporated In The State of Texas
• Inventors: Terabayashi, Toru, Kinjo, Hideki, Nighswander, John, Yoshida, Satoko, Mullins, Oliver C., Fujisawa, Go, Dong, Chengli, Kurkjian, Andrew, Groenzin, Henning
• Granted Patent: US 7,002,142 B2
• Time in Patent Office: Days
• US Class Current: 250/269.1
• CPC Class Codes: E21B 47/11 using tracers; using radioactivity
• CPC Class Codes: E21B 49/005 Testing the nature of borehole walls or the formation by using drilling mud or cutting data
• CPC Class Codes: E21B 49/084 with means for conveying samples through pipe to surface
• CPC Class Codes: E21B 49/10 using side-wall fluid samplers or testers
• CPC Class Codes: G01N 21/64 Fluorescence; Phosphorescence
• CPC Class Codes: G01N 33/241 for hydrocarbon content drilling mud G01N33/2823; drilling per se E21B; prospecting G01V
• CPC Class Codes: G01N 33/2823 raw oil, drilling fluid or polyphasic mixtures hydrocarbon content of earth materials G01N33/241; prospecting G01V; drilling per se E21B

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.

Claims

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.

2. A method according to claim 1, further comprising:

(g) setting dew precipitation onset pressure equal to pressure on the sample when the change in the parameter is detected.

3. A method according to claim 1, wherein the parameter includes a function of fluorescence intensity, and the change includes an increase in fluorescence intensity.

4. A method according to claim 3, wherein the parameter also includes a function of at least one other fluorescence characteristic.

5. A method according to claim 4, wherein the at least one other fluorescence characteristic is fluorescence red shift.

6. A method according to claim 5, wherein the parameter 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.

7. A method according to claim 6, wherein the function includes a ratio of a measured intensity at a first wavelength to a reference intensity.

8. A method according to claim 7, wherein the reference intensity is a function of a measured intensity at a second wavelength.

9. A method according to claim 1, wherein the parameter is a function of fluorescence lifetime, and the change is decrease in fluorescence lifetime.

10. A method according to claim 1,

wherein isolating a fluid sample downhole includes enclosing the sample in a fluid sample cell having a window;

wherein illuminating the fluid sample includes selectively illuminating the fluid sample in an interrogation volume adjacent to the window, and

wherein measuring at least one characteristic of fluorescence emission includes measuring fluorescence intensity emitted from the interrogation volume.

11. A method according to claim 10, wherein the fluorescence excitation light is polarized and directed onto the window at the Brewster angle.

12. A method according to claim 10, wherein the fluorescence excitation light is polarized in a first direction, and fluorescence light received by a detector is polarized in a second direction, the second direction being orthogonal to the first direction.

13. A method for detecting dew precipitation in a sample of formation fluid located downhole in an oilfield reservoir, comprising:

(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.

14. A tool for detecting dew precipitation in a fluid sample located downhole in an oilfield reservoir, comprising:

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.

15. A tool for detecting dew precipitation in a fluid sample located downhole in an oilfield reservoir, comprising:

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.