Method for making and using a drilling fluid
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.
1. A method for drilling a well into a formation, the method comprising:
providing a mixed metal-viscosified drilling fluid including 15 to 45 kg/m 3 bentonite, and a mixed metal viscosifier of inorganic magnesium/aluminum hydroxide and greater than 3% and up to 10% potassium sulfate (w/v);
circulating the drilling fluid through the well; and
maintaining the viscosity of the drilling fluid at a yield point of greater than 10 Pa.
2. The method of claim 1 wherein providing the mixed metal-viscosified drilling fluid includes providing an aqueous-based drilling fluid including the 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 the potassium sulfate.
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/m 3 bentonite clay, the 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 the potassium sulfate to an upper limit of 5%.
4. The method of claim 1 wherein providing the mixed metal-viscosified drilling fluid includes:
mixing bentonite clay in water to form a bentonite mixture;
adding the mixed metal viscosifier to the bentonite mixture;
adjusting pH to greater than above about pH 10;
adding the potassium sulfate.
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 further comprising continuing circulation with entrained coal fines in the drilling fluid.
7. The method of claim 6 wherein rheology of the drilling fluid is substantially maintained.
8. The method of claim 1 wherein circulating the drilling fluid is maintained while a coal seam is open to the drilling fluid.
9. The method of claim 1 wherein circulating the drilling fluid is initiated substantially at surface.
10. The method of claim 4 wherein the pH is adjusted using caustic soda.