DRILLING FLUID AND METHOD FOR DRILLING IN COAL-CONTAINING FORMATIONS

• US 20100089650A1
• Filed: 03/03/2008
• Published: 04/15/2010
• Est. Priority Date: 03/02/2007
• Status: Active Grant

• Current Assignee: Canadian Energy Services L.P. (Ces Energy Solutions Corp.)
• Original Assignee: Techstar Energy Services Inc.
• Inventors: Smith, Carl Keith, Stoian, Stefan Alexandru
• Granted Patent: US 8,387,723 B2
• Time in Patent Office: Days
• US Class Current: 175/65
• CPC Class Codes: C09K 2208/12 Swell inhibition, i.e. using additives to drilling or well treatment fluids for inhibiting clay or shale swelling or disintegrating
• CPC Class Codes: C09K 8/16 characterised by the inorganic compounds other than clay
• CPC Class Codes: C09K 8/206 Derivatives of other natural products, e.g. cellulose, starch, sugars
• CPC Class Codes: E21B 21/003 Means for stopping loss of drilling fluid plastering the borehole wall E21B33/138
• CPC Class Codes: E21B 21/062 by mixing components
• CPC Class Codes: E21B 21/068 using chemical treatment

Abstract

A drilling fluid and method for drilling in a coal containing formation. The method includes: providing a mixed metal-viscosified drilling fluid including at least 1% potassium salt; circulating the drilling fluid through the well; and drilling into a coal seam.

Claims

1. A method for drilling in a coal containing formation, the method comprising:

providing a mixed metal-viscosified drilling fluid including at least 1% potassium salt;

circulating the drilling fluid through the well; and

drilling into the coal seam.

2. The method of claim 1 wherein providing the mixed metal-viscosified drilling fluid includes providing an aqueous-based drilling fluid including 15 to 45 kg/m3 bentonite, mixed metal viscosifier at a weight ratio of 1:

8 to 1;

12, viscosifier to bentonite, a base to maintain the pH above about 10.0 and at least 1% potassium salt.

3. The method of claim 1 wherein providing the mixed metal-viscosified drilling fluid includes providing an aqueous-based drilling fluid including about 30 kg/m3 bentonite, a mixed metal viscosifier in a quantity of about 1:

10 MMO, MMH or MMOH to bentonite with a pH controlled to greater than pH 11 and 1 to 5% potassium salt.

4. The method of claim 1 wherein providing the mixed metal-viscosified drilling fluid includes:

mixing bentonite in water to form a bentonite mixture;

adding a mixed metal viscosifier to the bentonite mixture;

adjusting pH to greater than above about pH 10;

adding the potassium salt.

5. The method of claim 4 further comprising adding any of fluid loss control additives and/or lost circulation materials.

6. The method of claim 1 wherein providing the mixed metal-viscosified drilling fluid includes obtaining a drilling fluid with a yield point greater than 10 Pa.

7. The method of claim 1 continuing circulation with entrained coal fines in the drilling fluid.

8. The method of claim 7 wherein rheology of the drilling fluid is substantially maintained.

9. The method of claim 1 wherein circulating the drilling fluid is initiated prior to drilling into the coal seam.

10. The method of claim 1 wherein circulating the drilling fluid is maintained while a coal seam is open to the drilling fluid.

11. The method of claim 1 wherein circulating the drilling fluid is initiated substantially at surface.

12. The method of claim 1 wherein the potassium salt is selected from the group consisting of potassium sulfate, potassium chloride, potassium acetate and potassium formate.

13. The method of claim 1 wherein the potassium salt is potassium sulfate.

14. The method of claim 4 wherein the pH is adjusted using caustic soda, caustic potash, potassium carbonate or soda ash.

15. A drilling fluid comprising:

an aqueous mixture of bentonite and a mixed metal viscosifier with a pH above about pH 10; and

at least 1% potassium salt.

16. The drilling fluid of claim 15 wherein the drilling fluid comprises 15 to 45 kg/m3 bentonite, mixed metal viscosifier at a weight ratio of 1:

8 to 1;

12, viscosifier to bentonite, a base to maintain the pH above about 10.0 and at least 1% potassium salt.

17. The drilling fluid of claim 15 wherein the drilling fluid comprises 20 to 40 kg/m3 bentonite, mixed metal viscosifier at a weight ratio of 1:

9.5 to 1;

10.5, viscosifier to bentonite, a base to maintain the pH between about 10.5 to 13 and about 1-10% potassium salt.

18. The drilling fluid of claim 15 wherein the drilling fluid comprises about 30 kg/m3 bentonite, a mixed metal viscosifier in a quantity of about 1:

10 MMO, MMH or MMOH to bentonite with a pH controlled to greater than pH 11 and 1 to 5% potassium salt.

19. The drilling fluid of claim 15 wherein the drilling fluid is prepared by:

mixing bentonite in water to form a bentonite mixture;

adding a mixed metal viscosifier to the bentonite mixture;

adjusting pH to greater than above about pH 10;

adding the potassium salt.

20. The drilling fluid of claim 15 further comprising at least one of a fluid loss control additive and/or a lost circulation material.

21. The drilling fluid of claim 15 wherein the drilling fluid includes a yield point of greater than 10 Pa.

22. The drilling fluid of claim 15 wherein the potassium salt is selected from the group consisting of potassium sulfate, potassium chloride, potassium acetate and potassium formate.

23. The drilling fluid of claim 15 wherein the potassium salt is potassium sulfate.

24. The drilling fluid of claim 15 wherein the potassium sulfate concentration is 20 to 50 kg/m3.

25. The drilling fluid of claim 15 wherein the pH is adjusted using caustic soda, caustic potash, potassium carbonate or soda ash.