Methods and apparatus to characterize stock-tank oil during fluid composition analysis

• US 7,586,087 B2
• Filed: 04/20/2007
• Issued: 09/08/2009
• Est. Priority Date: 01/24/2007
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (SLB)
• Original Assignee: Schlumberger Technology Corporation (SLB)
• Inventors: Hegeman, Peter S., Dong, Chengli
• Primary Examiner(s): Porta; David P
• Assistant Examiner(s): Gaworecki; Mark R
• Application Number:
  US11/738,156
• Publication Number:
  US 20080173445A1
• Time in Patent Office: 872 Days
• Field of Search: 250/255, 250/301
• US Class Current: 250/255
• CPC Class Codes: E21B 47/113 using electrical indications; using light radiations
• CPC Class Codes: E21B 49/087 Well testing, e.g. testing for reservoir productivity or formation parameters

Abstract

Methods and apparatus to characterize stock-tank oil during fluid composition analysis are disclosed. A disclosed example method to characterize a fluid associated with an underground geological formation comprises obtaining a sample of the fluid associated with the underground geological formation, determining, in a borehole associated with the underground geological formation, a stock-tank oil type for the sample of the fluid associated with the underground geological formation, and determining a property of the fluid associated with the underground geological formation based on the stock-tank oil type.

Claims

1. A method to characterize a fluid associated with an underground geological formation, the method comprising:

obtaining a sample comprising the fluid associated with the underground geological formation;

measuring, in a borehole associated with the underground geological formation, an optical property of the fluid, wherein the optical property is measured by a grating spectrometer and filter-array spectrometer;

determining, in the borehole, a stock-tank oil type for the sample associated with the underground geological formation, wherein the stock-tank oil type is determined based on the optical property; and

determining a property of the sample associated with the underground geological formation based on the stock-tank oil type.

2. A method as defined in claim 1, wherein determining the stock-tank oil type for the fluid associated with the underground geological formation comprises:

transmitting light to the fluid;

measuring an effect on the transmitted light caused by the fluid; and

comparing the measured effect to two or more reference effects for hydrocarbon types to determine the stock-tank oil type.

3. A method as defined in claim 2, wherein the measured effect is a light absorption.

4. A method as defined in claim 1, wherein the stock-tank oil type represents a fraction of the fluid that is a waxy stock-tank oil.

5. A method as defined in claim 1, wherein the stock-tank oil type represents a fraction of the fluid that is a branched alkane stock-tank oil.

6. A method as defined in claim 1, wherein the optical property comprises a light absorption spectrum, and further comprising normalizing the spectrum based upon the absorption measured at about 1740 nanometers.

7. A method as defined in claim 6 further comprising correcting the spectrum for the methane content.

8. A method as defined in claim 1, further comprising:

measuring one or more optical densities of the fluid at one or more wavelengths; and

computing a normalized live oil spectrum based on the one or more measured optical densities, wherein the stock-tank oil type is determined based on the normalized live oil spectrum.

9. A method as defined in claim 8, wherein the one or more wavelengths are between about 1725 nanometers and 1814 nanometers.

10. A method as defined in claim 1, wherein the property of the fluid is one of a gas-oil-ratio (GOR) value, a mass ratio and a partial density.

11. A method as defined in claim 1, wherein the property of the fluid is representative of the composition of the fluid.

12. A method as defined in claim 1, further comprising logging at least one of the determined stock-tank oil type or the determined fluid property.

13. An apparatus to characterize a fluid associated with an underground geological formation, the apparatus comprising:

a device to obtain a sample of the fluid associated with the underground geological formation;

an optical sensor to measure an optical property of the sample of the fluid;

an analyzer to determine a stock-tank oil type for the sample of the fluid based on the optical property;

a grating spectrometer; and

a filter-array spectrometer.

14. An apparatus as defined in claim 13, wherein the optical sensor is to be operated in a borehole associated with the underground geological formation.

15. An apparatus as defined in claim 13, wherein the analyzer is to determine at least one of a gas-oil-ratio or a mass ratio based on the stock-tank oil type.

16. An apparatus as defined in claim 13, wherein the stock-tank oil type represents a fraction of the sample of the fluid that is a waxy stock-tank oil.

17. An apparatus as defined in claim 13, wherein the stock-tank oil type represents a fraction of the sample of the fluid that is a branched-alkane stock-tank oil.

18. An apparatus as defined in claim 13, wherein the optical sensor measures the optical property at a wavelength between about 1725 nanometers and 1814 nanometers.

19. A method comprising:

transmitting light to a sample of an underground geological formation;

measuring an indication of absorption of the transmitted light by the sample; and

comparing the measured indication of absorption to two or more absorptions for respective ones of two or more hydrocarbon types to determine a parameter of the sample, wherein the two or more hydrocarbon types include at least a waxy hydrocarbon and a non-waxy hydrocarbon.

20. A method as defined in claim 19, wherein the parameter of the sample is a stock-tank oil type.

21. A method as defined in claim 20, wherein the stock-tank oil type represents one of a fraction of the sample comprising a waxy stock-tank oil and a fraction of the sample comprising a branched alkane stock-tank oil.

22. A method as defined in claim 20, further comprising determining a second parameter of the sample based on the stock-tank oil type.

23. A method as defined in claim 22, wherein the second parameter is as gas-oil-ratio (GOR) value.

24. A method as defined in claim 19, wherein the sample is a fluid sample, and wherein measuring the indication of absorption of the light by the sample comprises measuring a portion of the light that passes through the sample.

25. A method as defined in claim 19, wherein the sample includes a surface of the underground geological formation, and wherein measuring the indication of absorption of the light by the sample comprises measuring a reflection of the light by the sample.