Methods for reducing lost circulation in wellbores

• US 20020040812A1
• Filed: 06/14/2001
• Published: 04/11/2002
• Est. Priority Date: 05/14/1999
• Status: Active Grant

• Current Assignee: Broadleaf Industries, Inc.
• Original Assignee: Broadleaf Industries, Inc.
• Inventors: Heying, Theodore L.
• Granted Patent: US 6,581,701 B2
• Time in Patent Office: Days
• US Class Current: 175/72
• CPC Class Codes: C09K 8/035 Organic additives
• CPC Class Codes: C09K 8/512 containing cross-linking agents
• CPC Class Codes: E21B 21/003 Means for stopping loss of drilling fluid plastering the borehole wall E21B33/138

Abstract

This invention discloses methods for reducing lost circulation in wellbores. The invention utilizes certain selected water swellable polymers that swell at a rate slow enough to reach the lost circulation zone of a well before those polymers have swollen to an extent that disrupts the drilling process. These selected polymers may be used alone or in conjunction with other lost circulation materials which do not swell or also swell slowly enough to reach the lost circulation zone without interfering with the drilling operation. Mixtures of such materials are also disclosed.

Claims

1. A method for reducing the loss of circulation fluids into flow passages of a subterranean formation during well drilling, completion, or workover operations, said circulation fluids being selected from the group consisting of drilling fluids, completion fluids and workover fluids said method comprising:

(a) introducing into a circulation fluid selected from a group consisting of drilling fluids, completion fluids and workover fluids an effective amount of a solid, water insoluble but gel-forming polyacrylamide polymer which has a particle size distribution in the range of about 0.50 millimeters to about 5.0 millimeters and which swells from about 25 to 300 times its weight of tap water when placed therein, and

(b) allowing the gel-forming polymer to enter the lost circulation zone and allowing the gel-forming polymer to remain in said zone to absorb the aforesaid weight of water and swell to the appropriate volume thereby reducing the loss of said circulation fluid upon resuming well drilling, completion or workover operation.

3. The method of claim 1, wherein said water swellable polymer is a partially hydrolyzed, crosslinked polyacrylamide.

4. The method of claim 1, wherein the selected water soluble polymer is an alkali metal salt of said partially hydrolyzed, crosslinked polyacrylamide.

5. The method of claim 3 wherein the said salt is the sodium salt of said partially hydrolyzed polyacrylamide.

6. The method of claim 4 wherein the particle size distribution of said salt of said water soluble polymer is in the range of about 0.50 millimeters to about 5.0 millimeters.

15. The method of claim 1 wherein the particle size of said water swellable polymer is chosen so that the polymer reaches the depth of the borehole where it is required to prevent further loss of said drilling, completion or workover fluid from the lost circulation zone before it is completely swollen.

17. A method for removing said water swollen polymer from the lost circulation zone of claim 1 or 2 by adding an aqueous solution of acid or metallic salt thus causing said swollen polymer to dissolve or disintegrate.

2. A method for reducing the loss of circulation fluids into flow passages of a subterranean formation during well drilling, completion or workover operations, said circulation fluids being selected from the group consisting of drilling fluids, completion fluids and workover fluids, said method comprising:

(a) introducing into a circulation fluid selected from a group consisting of drilling fluids, completion fluids and workover fluids an effective amount of a solid, water insoluble but gel-forming polyacrylamide polymer which has a particle size distribution in the range of about 0.50 millimeters to about 5.0 millimeters and which swells from about 25 to 300 times its weight of tap water at room temperature when placed therein, and

(b) introducing a second, solid, hydrophilic lost circulation material in an amount equal to the weight of the said water swellable polymer or up to 150 times the weight of the said water swellable polymer, and

(c) allowing both the said gel-forming polymer and the other lost circulation material to enter the lost circulation zone and allowing the said aforementioned materials to remain in said zone to absorb water and swell to the expected volume thereby reducing the loss of said circulation fluid upon resuming well drilling, completion or workover operation.

7. The method of claim 2 wherein the second lost circulation material is compressed and compounded cottonseed hulls.

8. The method of claim 2 wherein the second lost circulation material is fiber derived from molten rock.

9. The method of claim 2 wherein the second material is ground walnut hulls.

10. The method of claim 2 wherein the second material is kenaf fibers.

11. The method of claim 2 wherein the second material is ground oyster shells.

12. The method of claim 2 wherein said water swellable polymer is previously admixed with the aforesaid other solid lost circulation material before it is added to the said drilling mud, completion fluid or workover fluid.

13. The method of claim 2 wherein said water swellable polymer and other aforesaid solid lost circulation materials are added simultaneously to said drilling fluid, completion fluid or workover fluid.

14. The method of claim 2 wherein the said water swellable polymer and other aforesaid solid, water swellable polymer are added sequentially in either order to said drilling fluid, completion fluid or workover fluid.

16. The method of claim 2 wherein the particle size of said water swellable polymer is chosen so that the polymer reaches the depth of the borehole where it is required to prevent further loss of said drilling, completion or workover fluid from the lost circulation zone before it is completely swollen.

18. The method of claim 17 where the removing agent is an aqueous solution of hydrochloric acid.

19. The method of claim 17 where the removing agent is an aqueous solution of acetic acid.

20. The method of claim 17 where the removing agent is an aqueous solution of sodium chloride.

21. A method for removing the swollen mixture formed in the lost circulation zone of claim 2 by adding an aqueous solution of an acid or metallic salt thus causing the swollen mixture to dissolve or disintegrate.

22. The method of claim 21 where the removing agent is an aqueous solution of hydrochloric acid.

23. The method of claim 21 where the removing agent is an aqueous solution of acetic acid.

24. The method of claim 21 where the removing agent is an aqueous solution of sodium chloride.