Method to improve the quality of a formation fluid sample

• US 6,178,815 B1
• Filed: 07/30/1998
• Issued: 01/30/2001
• Est. Priority Date: 07/30/1998
• Status: Expired due to Term

• Current Assignee: Schlumberger Technology Corporation (SLB)
• Original Assignee: Schlumberger Technology Corporation (SLB)
• Inventors: Felling, Michelle Mary, Morris, Charles W., Butsch, Robert J.
• Primary Examiner(s): Williams, Hezron
• Assistant Examiner(s): WIGGINS, JOHN DAVID
• Application Number:
  US09/126,513
• Time in Patent Office: 915 Days
• Field of Search: 731/521.8, 731/521.9, 731/522.3, 731/525.5, 731/522.7, 731/523.1, 731/522.1, 731/525.9, 250/255, 166/250.07, 166/254.2, 175/48, 175/50
• US Class Current: 73/152.19
• CPC Class Codes: E21B 49/10 using side-wall fluid samplers or testers
• CPC Class Codes: G01N 33/2823 Raw oil, drilling fluid or polyphasic mixtures

Abstract

The present invention provides a method for improving the quality of a formation fluid sample by taking the sample at a time when the formation fluid composition contains the most favorable portion of hydrocarbons. This task is accomplished by determining in real-time, the composition of the fluid flowing into a downhole tool from the formation. This method determines the optical density of the fluid as the fluid flows through the tool. An optical spectrum is generated from the density measurement. The optical spectrum is compared to a composite spectrum generated from a database of known fluid samples. As a result of the comparisons, there is a determination of the derivations between corresponding features of the two spectra. Adjustments are made to the components of the composite spectrum until the deviations between the two spectra are at an acceptable minimum. Determinations of the fluid composition are made from the composition of the composite spectrum at the minimum deviation. The sampling process begins when the fluid composition has a desirable fractional component of hydrocarbons in the fluid.

Claims

1. A method of determining the composition of a fluid in an earth formation comprising the steps of:

generating a measured spectrum of the fluid flowing from said earth formation;

establishing a composite spectrum from predetermined individual fluid responses including predicting the fluid response when the fluid is unknown, and

selecting two oils that bracket the predicted fluid response; and

determining the composition of the fluid from a comparison of said measured spectrum and said composite spectrum.

2. The method of claim 1 wherein a spectral fitting process is used in said spectra comparison.

3. The method of claim 2 wherein said spectral fitting process comprises:

comparing said measured spectrum to said composite spectrum to determine the best fit between said measured spectrum and said composite spectrum;

evaluating the quality of the said best fit; and

adjusting the components of said composite spectrum until said best fit is within an acceptable tolerance.

4. The method of claim 3 wherein said fluid composition is determined from said adjusted composite spectrum.

5. The method of claim 1 further comprising before the step of establishing a composite spectrum the step of providing an initial set of formation fluid parameters, said parameters being based on an estimate of possible formation fluid materials, said fluid parameters being used to establish an initial composite spectrum.

6. The method of claim 5 wherein said formation fluid material parameters include water, hydrocarbons, and formation and borehole filtrates.

7. The method of claim 5 further comprising the step of determining physical properties of the fluid, said properties could include API gravity, density, gas/oil ratio, water salinity and viscosity.

8. The method of claim 1 wherein in the step of determining the composition portions of each material in said composite spectrum are established using modeling techniques.

9. The method of claim 8 wherein said statistical modeling techniques include a weighted linear regression technique.

10. The method of claim 9 wherein said weighted linear regression technique comprises computing the portion of each material in said composite spectrum by assigning a weight to each material in said composite spectrum.

11. The method of claim 3 wherein said adjusting step comprises:

varying the portions of each material in said composite spectrum and comparing said measured and composite spectra.

12. The method of claim 1 wherein said formation fluid flows through a downhole tool.

13. The method of claim 1 further comprising the step of monitoring the flow regime of the fluid from said fluid composition.