DRILLING FLUID AND METHOD FOR DRILLING IN COAL-CONTAINING FORMATIONS

• US 20170058178A1
• Filed: 11/10/2016
• Published: 03/02/2017
• Est. Priority Date: 08/26/2010
• Status: Active Grant

• Current Assignee: Canadian Energy Services L.P. (Ces Energy Solutions Corp.)
• Original Assignee: Canadian Energy Services L.P. (Ces Energy Solutions Corp.)
• Inventors: SMITH, CARL KEITH
• Granted Patent: US 9,969,920 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: C09K 8/05 containing inorganic compounds only, e.g. mixtures of clay and salt
• 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

Abstract

A drilling fluid and method for drilling in a coal containing formation with a mixed metal-viscosified drilling fluid including at least 0.05% calcium sulfate.

Claims

1. A drilling fluid comprising:

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

at least 0.05% calcium sulfate (w/v).

2. The drilling fluid of claim 1 wherein the drilling fluid comprises 15 to 50 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 the at least 0.05% calcium sulfate.

3. The drilling fluid of claim 1 wherein the drilling fluid comprises 25 to 45 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 0.05 to 1.0% calcium sulfate.

4. The drilling fluid of claim 1 wherein the drilling fluid comprises about 30 to 40 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 0.1 to 0.5% calcium sulfate.

5. The drilling fluid of claim 1 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 about pH 10;

adding the calcium sulfate.

6. The drilling fluid of claim 1 further comprising at least one of a fluid loss control additive and/or a lost circulation material.

7. The drilling fluid of claim 1 wherein the drilling fluid includes a yield point of greater than 10 Pa.

8. The drilling fluid of claim 1 wherein the calcium sulfate is in the form of gypsum.

9. The drilling fluid of claim 1 wherein the calcium sulfate concentration is 0.5 to 50 kg/m3.

10. The drilling fluid of claim 1 further comprising an amount of potassium salt selected from the group consisting of potassium sulfate, potassium chloride, potassium acetate and potassium formate.

11. The drilling fluid of claim 1 wherein the pH is adjusted using caustic soda or caustic potash.

12. The drilling fluid of claim 1 wherein the bentonite is in the form of untreated bentonite.