Claims
- 1. A method for validating a downhole connate water sample drawn from formation surrounding a well, comprising:drilling the well with a water-based mud containing a water-soluble dye; obtaining a sample of formation fluid downhole; measuring optical density of the sample downhole; and validating the sample if sample optical density is acceptably low.
- 2. A method according to claim 1, further repeating said act of obtaining a sample of formation fluid downhole and said act of measuring optical density of the sample downhole to obtain optical density from each of a series of samples.
- 3. A method according to claim 1, wherein said water-soluble dye is a blue dye.
- 4. A method according to claim 1, wherein said water-soluble dye is a dye selected from a group of dyes, the group consisting of Acid Blue #1 (EMI-600) and Acid Blue 9, alphazurine FG.
- 5. A method according to claim 1, wherein said water-soluble dye is a dye that is active in the ultraviolet region of the spectrum.
- 6. A method according to claim 1, wherein said water-soluble dye is a fluorescent dye.
- 7. A method according to claim 1, wherein said water-soluble dye is added to said water-based mud to produce a concentration within the range 0.2-2.0 kg/m3 (200-2000 mg/L).
- 8. A method according to claim 1, wherein measuring optical density includes measuring optical density at a first wavelength to obtain a first optical density, measuring optical density at a second wavelength to obtain a second optical density, and subtracting said second optical density from said first optical density.
- 9. A method according to claim 8, wherein said first wavelength and said second wavelength are close in wavelength.
- 10. A method according to claim 1, further comprising:determining scattering from a series of optical density values; and validating a sample if the scattering is acceptably low.
- 11. A method according to claim 1, further comprising:calculating from a series of optical density values an asymptotic value indicative of water-based mud filtrate fraction; and validating a sample if the asymptotic value is stable.
- 12. A method for validating a downhole connate water sample drawn from formation surrounding a well, comprising:drilling the well with a water-based mud; obtaining a sample of formulation fluid downhole; measuring at least one characteristic of downhole fluid indicative of water-based mud filtrate contamination levels in the sample; and; validating the sample if the at least one measured characteristic is acceptably low.
- 13. A method according to claim 11, wherein said at least one measured characteristic is optical density.
- 14. A method according to claim 11, wherein said at least one measured characteristic is fluorescence emission, ion concentration, or relative ion concentration.
- 15. A method according to claim 11, wherein said water-based mud contains a predetermined salt concentration, and wherein said at least one measured characteristic is conductivity or resistivity.
- 16. A method for determining when to collect a sample of downhole fluid drawn from a formation surrounding a well, comprising:measuring at least one characteristic of downhole fluid indicative of water-based mud filtrate contamination levels in downhole fluid drawn from a formation surrounding the well over a period of time; and using said measurements to determine when to collect a sample of said downhole fluid.
- 17. A method according to claim 16, wherein said characteristic is optical density, fluorescence emission, conductivity, resistivity, ion concentration, or relative ion concentration.
- 18. A method according to claim 16, wherein said water-based mud filtrate contains a water-soluble dye.
Parent Case Info
This application claims priority from co-pending U.S. Provisional Application No. 60/333,890 filed Nov. 28, 2001. This application is also related to co-owned U.S. Pat. Nos. 3,780,575 and 3,859,851 to Urbanosky, co-owned U.S. Pat. Nos. 4,860,581 and 4,936,139 to Zimmerman et al., co-owned U.S. Pat. No. 4,994,671 to Safinya et al., co-owned U.S. Pat. Nos. 5,266,800 and 5,859,430 to Mullins, co-owned U.S. Pat. No. 6,274,865 to Shroer et al., and co-owned, co-pending U.S. application Ser. No. 09/300,190, filed May 25, 2000.
US Referenced Citations (19)
Foreign Referenced Citations (2)
Number |
Date |
Country |
2 288 618 |
Oct 1995 |
GB |
2 355 033 |
Nov 2001 |
GB |
Provisional Applications (1)
|
Number |
Date |
Country |
|
60/333890 |
Nov 2001 |
US |