Methods and apparatus for the downhole characterization of formation fluids

• US 20040104341A1
• Filed: 12/03/2002
• Published: 06/03/2004
• Est. Priority Date: 12/03/2002
• Status: Active Grant

• Current Assignee: Schlumberger Technology Corporation (SLB)
• Original Assignee: Schlumberger Technology Corporation (SLB)
• Inventors: Ramakrishnan, Terizhandur S., Mullins, Oliver C., Fujisawa, Go, Jiang, Li, Goodwin, Anthony, Betancourt, Soraya S., Pop, Julian, Elshahawi, Hani
• Granted Patent: US 7,081,615 B2
• Time in Patent Office: Days
• US Class Current: 250/255
• CPC Class Codes: E21B 49/0875 determining specific fluid parameters
• CPC Class Codes: G01N 1/12 Dippers; Dredgers
• CPC Class Codes: G01N 25/04 of melting point; of freezing point; of softening point
• CPC Class Codes: G01N 33/2823 Raw oil, drilling fluid or polyphasic mixtures
• CPC Class Codes: G01N 7/00 Analysing materials by measuring the pressure or volume of a gas or vapour
• CPC Class Codes: G01N 9/36 Analysing materials by measuring the density or specific gravity, e.g. determining quantity of moisture methods of measurement in general G01N9/02 - G01N9/32

Abstract

Methods and apparatus for investigating a hydrocarbon bearing geological formation traversed by a borehole are disclosed. A borehole tool is used to acquire a sample of fluid in the formation. Compositional analysis of the fluid sample is conducted to provide a determination of the composition of the sample. The sample composition is then related to a model of the thermodynamic behavior of the fluid; i.e., the mass fractions of the fluid components are used as inputs to an equation of state (EOS) to predict the phase behavior of the fluid.

Claims

1. A method of investigating a hydrocarbon bearing geological formation traversed by a borehole, comprising:

a) acquiring a sample of fluid in the formation with a formation fluid sampling tool located in the borehole;

b) conducting a compositional analysis of the fluid sample located in the sampling tool while said sampling tool is in the borehole;

c) relating the compositional analysis to a model of the thermodynamic behavior of the fluid.

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

d) based on said relating, predicting a phase behavior of fluid remaining in the formation.

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

d) based on said relating, generating a pressure-temperature plot of at least one of said sample and fluid remaining in the formation.

4. A method according to claim 3, wherein:

said pressure-temperature plot includes an indication of a critical point.

5. A method according to claim 3, wherein:

said pressure-temperature plot includes an indication of at least one of a bubble line and a dew line.

6. A method according to claim 3, wherein:

said pressure-temperature plot includes an indication of a critical point, an indication of a bubble line, and indication of a dew line, and an indication of an ambient condition of the formation.

7. A method according to claim 2, wherein:

said sample of fluid is a contaminated sample which is contaminated with drilling mud,

said conducting a compositional analysis includes correcting for said drilling mud contamination in order to obtain an indication of an uncontaminated composition of fluids in the geological formation, and

said relating the compositional analysis relates an uncontaminated composition to said model of said fluid.

8. A method according to claim 7, further comprising:

e) determining whether said contamination significantly affects said predicting a phase behavior.

9. A method according to claim 8, further comprising:

f) determining whether to terminate sampling based on a determination obtained at step e).

10. A method according to claim 7, further comprising:

f) repeating steps a) and b) for a plurality of samples at a first location in the borehole;

g) predicting a contamination clean-up rate based on step f); and

h) determining whether to terminate sampling based on step g).

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

e) determining whether said fluid in the formation is either condensate or volatile oil.

12. A method according to claim 11, further comprising:

if said fluid in the formation is determined to be condensate, finding an indication of a dew pressure for said fluid at an ambient temperature in said formation;

comparing said dew pressure to an ambient reservoir pressure; and

using results of said comparing, indicating a desired maximum drawdown pressure for said acquiring a sample.

13. A method according to claim 12, further comprising:

adjusting a drawdown pressure for said acquiring step based on said desired maximum drawdown pressure.

14. A method according to claim 11, further comprising:

if said fluid in the formation is determined to be a volatile oil, finding an indication of a saturation pressure for said fluid at an ambient temperature in said formation;

comparing said saturation pressure to an ambient reservoir pressure; and

using results of said comparing, indicating a desired maximum drawdown pressure for said acquiring a sample.

15. A method according to claim 11, further comprising:

if said fluid is determined to be a volatile oil, acquiring multiple samples at different drawdown pressures in order to find a bubble point for the fluid in the formation.

16. A method according to claim 1, wherein:

said conducting a compositional analysis comprises measuring an optical absorption spectrum of said fluid and conducting a pseudo-compositional analysis by translating said absorption spectrum into concentrations or mass fractions of compositional groups.

17. A method according to claim 16, wherein:

said compositional groups include a first group containing ethane, propane, butane, and pentane fractions, and a second group containing hexane and heavier components (C₆H₁₄+).

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

repeating steps a) and b) for multiple fluid samples, wherein step d) comprises predicting phase behavior with a level of certainty.

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

repeating steps a) through d) at multiple locations in the borehole.

27. An apparatus according to claim 12, wherein:

said means for acquiring a sample of fluid includes means for adjusting a drawdown pressure of said apparatus and means for monitoring acquired samples in order to find a bubble point for the fluid in the formation.

20. An apparatus for investigating a hydrocarbon bearing geological formation traversed by a borehole, comprising:

a) a borehole tool including means for acquiring a sample of fluid in the formation and means for conducting a compositional analysis of the sample of fluid; and

b) means for relating the compositional analysis to a model of the thermodynamic behavior of the fluid.

21. An apparatus according to claim 20, wherein:

said means for conducting a compositional analysis includes optical means for analyzing the sample.

22. An apparatus according to claim 20, wherein:

said means for relating includes means for predicting a phase behavior of fluid remaining in the formation.

23. An apparatus according to claim 22, further comprising:

c) means for generating a pressure-temperature plot of at least one of the sample and fluid remaining in the formation.

24. An apparatus according to claim 23, wherein:

said pressure-temperature plot includes an indication of a critical point.

25. An apparatus according to claim 23, wherein:

said pressure-temperature plot includes an indication of at least one of a bubble line and a dew line.

26. An apparatus according to claim 23, wherein:

said pressure-temperature plot includes an indication of a critical point, an indication of a bubble line, and indication of a dew line, and an indication of an ambient condition of the formation.

28. An apparatus according to claim 20, wherein:

said means for conducting a compositional analysis comprises means for measuring an optical absorption spectrum of said fluid and for conducting a pseudo-compositional analysis by translating said absorption spectrum into concentrations or mass fractions of compositional groups.

29. An apparatus according to claim 28, wherein:

said compositional groups include a first group containing ethane, propane, butane, and pentane fractions, and a second group containing hexane and heavier components (C₆H₁₄+).