Drilling fluid and method for drilling in coal-containing formations

• US 8,387,723 B2
• Filed: 03/03/2008
• Issued: 03/05/2013
• Est. Priority Date: 03/02/2007
• Status: Active Grant

• Current Assignee: Canadian Energy Services L.P. (Ces Energy Solutions Corp.)
• Original Assignee: Tech-Star Fluid Systems Inc.
• Inventors: Stoian, Stefan Alexandru, Smith, Carl Keith
• Primary Examiner(s): SUCHFIELD, GEORGE A
• Application Number:
  US12/529,583
• Publication Number:
  US 20100089650A1
• Time in Patent Office: 1,828 Days
• Field of Search: None
• US Class Current: 175/72
• 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 a 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 mixed metal viscosifier 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 4 wherein the pH is adjusted using caustic soda, caustic potash, potassium carbonate or soda ash.

7. 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.

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

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

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

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

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

13. 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.

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