Core capture and recovery from unconsolidated or friable formations and methods of use

Patent metadata

Field	Value
Publication number	US-9518463-B2
Application number	US-201213526639-A
Country	US
Kind code	B2
Filing date	Jun 19, 2012
Priority date	Jun 22, 2011
Publication date	Dec 13, 2016
Grant date	Dec 13, 2016

Abstract

Methods and systems for enhanced capture and recovery of core samples from unconsolidated or friable formations are provided using drilling fluids that permit increased overpressures to preserve the ability to cut core samples and to strengthen the core samples obtained. Drilling fluids used during capture and recovery of core samples may comprise a solid particulate loss prevention material having a size range from about 150 microns to about 1,000 microns. The solid particulate loss prevention material prevents fracture initiation and propagation in the subterranean formation to allow the use of higher overpressures than would otherwise be possible. Thus, by circulating drilling fluid in the borehole while drilling a core sample, higher overpressures may be achieved, which have been found to be beneficial during core capture and recovery by maintaining core integrity and avoiding core loss. In this way, core sample integrity is improved, yielding more accurate representations of the subsurface.

First claim

The invention claimed is:

1. A method for obtaining a core sample from a friable or unconsolidated formation comprising the steps of:
drilling a core sample from a borehole that intersects the friable or unconsolidated formation;
circulating a drilling fluid in the borehole while drilling the core sample, wherein the drilling fluid comprises a solid particulate loss prevention material having an average size range from 100 mesh (about 150 microns) to 18 mesh (about 1,000 microns); maintaining an overpressure of at least about 200 psi to about 1200 psi; capturing and recovering the core sample from the unconsolidated formation; wherein the step of maintaining the overpressure is performed during the steps of drilling the core sample, circulating the drilling fluid, and recovering the core sample; wherein the step of drilling is limited to a rate of penetration of a rate less than that which would fluidize the core sample at the overpressure; and wherein the step of circulating further comprises the step of circulating a drilling fluid in the borehole at a flow rate of less than about 150 gpm.

2. The method of claim 1 wherein the solid particulate loss prevention material:
has an average size of from about 250 microns to about 600 microns including about 300 microns, about 350 microns, about 400 microns, about 450 microns, about 500 microns, about 550 microns and about 600 microns;
is at least 75 percent by weight in a size range of from 60 mesh (about 250 microns) to 30 mesh (about 600 microns) including 50 mesh (about 300 microns), 45 mesh (about 350 microns), 40 mesh (about 400 microns), about 450 microns, 35 mesh (about 500 microns), about 550 microns and 30 mesh (about 600 microns);
is petroleum coke, gilsonite, calcium carbonate, glass, ceramic, plastic, nut shells, or any combination thereof; and
is formed substantially in the shape of spheroids, hollow beads, pellets, tablets, an isometric shape, an angular shape, or any combination thereof.

3. The method of claim 1 wherein the borehole is a deviated borehole including boreholes at an angle greater than about 20 degrees, about 30 degrees, about 40 degrees, about 50 degrees, about 60 degrees, about 70 degrees, about 80 degrees from vertical or nearly horizontal.

4. The method of claim 1 wherein the drilling fluid has a concentration of solid particulates from about 2 pounds per barrel (ppb) to 150 ppb, including approximately 2 ppb, 2.5 ppb, 3.4 ppb, 5 ppb, 7.5 ppb, 10 ppb, 15 ppb, 20 ppb, 25 ppb, 30 ppb, 34 ppb, 42 ppb, 50 ppb, 75 ppb, 80 ppb, 100 ppb, 125 ppb, or 150 ppb dependent upon the specific gravity of the loss prevention material and the mud weight of the drilling fluid.

5. The method of claim 1 :
wherein the core sample extends in one continuous segment of greater than 10 feet including approximately 10 feet, 15 feet, 20 feet, 25 feet, 30 feet, 35 feet, from about 10 feet to about 35 feet, from about 15 feet to about 30 feet; and
wherein the diameter of the core sample is about 2 inches to about 6 inches including about 2 to 2⅞ inches, about 3 to 3⅞ inches, about 4 to 4⅞ inches, about 5 to 5⅞ inches, about 2¼ inches, about 2½ inches, about 2¾ inches, about 3¼ inches, about 3½ inches, about 3¾ inches, about 4¼ inches, about 4½ inches, about 4¾ inches, about 5 inches, about 5¼ inches, about 5½ inches, about 5¾ inches, to about 6 inches.

6. The method of claim 1 :
wherein the loss prevention material is at least 75 percent by weight in a size range of from 60 mesh (about 250 microns) to 30 mesh (about 600 microns);
wherein the loss prevention material is calcined petroleum coke, calcium carbonate, nut hulls, or any combination thereof;
wherein the drilling fluid has a concentration of about 2 to about 150 pounds of solid particulates per barrel of drilling fluid;
wherein the core sample extends in one continuous segment of from about 15 feet to about 30 feet;
wherein the core sample has a diameter and wherein the diameter of the core sample is about 2 inches to about 6 inches; and
wherein the overpressure is from about 300 psi to about 1200 psi.

7. The method of claim 1 :
wherein the solid particulate loss prevention material has an average size of from 60 mesh (about 250 microns) to 30 mesh (about 600 microns);
wherein the core sample extends in one continuous segment of from about 10 feet to about 35 feet; and
wherein the core sample has a diameter and wherein the diameter of the core sample is about 2 inches to about 6 inches.

8. A method for obtaining a core sample from a friable or unconsolidated formation comprising the steps of:
drilling a core sample from a borehole that intersects the friable or unconsolidated formation, wherein the core sample extends in one continuous segment of from about 10 feet to about 35 feet, wherein the core sample has a diameter and wherein the diameter of the core sample is about 2 inches to about 6 inches; circulating a drilling fluid in the borehole while drilling the core sample, wherein the drilling fluid comprises a solid particulate loss prevention material having an average size of from 60 mesh (about 250 microns) to 30 mesh (about 600 microns), such that the solid particulate loss prevention material is adapted to mitigate fracture initiation and propagation in the friable or unconsolidated formation or in a subterranean zone adjacent to or above the friable or unconsolidated formation; maintaining an overpressure of at least about 200 psi to about 1200 psi; and capturing and recovering the core sample from the unconsolidated formation; wherein the step of maintaining the overpressure is performed during the steps of drilling the core sample, circulating the drilling fluid, and recovering the core sample.

9. The method of claim 8 wherein the solid particulate loss prevention material:
has an average size of from about 250 microns to about 600 microns including about 300 microns, about 350 microns, about 400 microns, about 450 microns, about 500 microns, about 550 microns and about 600 microns;
is at least 75 percent by weight in a size range of from 60 mesh (about 250 microns) to 30 mesh (about 600 microns) including 50 mesh (about 300 microns), 45 mesh (about 350 microns), 40 mesh (about 400 microns), about 450 microns, 35 mesh (about 500 microns), about 550 microns and 30 mesh (about 600 microns);
is petroleum coke, gilsonite, calcium carbonate, glass, ceramic, plastic, nut shells, or any combination thereof; and
is formed substantially in the shape of spheroids, hollow beads, pellets, tablets, an isometric shape, an angular shape, or any combination thereof.

10. The method of claim 8 wherein the borehole is a deviated borehole including boreholes at an angle greater than about 20 degrees, about 30 degrees, about 40 degrees, about 50 degrees, about 60 degrees, about 70 degrees, about 80 degrees from vertical or nearly horizontal.

11. The method of claim 8 wherein the drilling fluid has a concentration of solid particulates from about 2 pounds per barrel (ppb) to 150 ppb, including approximately 2 ppb, 2.5 ppb, 3.4 ppb, 5 ppb, 7.5 ppb, 10 ppb, 15 ppb, 20 ppb, 25 ppb, 30 ppb, 34 ppb, 42 ppb, 50 ppb, 75 ppb, 80 ppb, 100 ppb, 125 ppb, or 150 ppb dependent upon the specific gravity of the loss prevention material and the mud weight of the drilling fluid.

12. The method of claim 8 :
wherein the core sample extends in one continuous segment of greater than 10 feet including approximately 10 feet, 15 feet, 20 feet, 25 feet, 30 feet, 35 feet, from about 10 feet to about 35 feet, from about 15 feet to about 30 feet; and
wherein the diameter of the core sample is about 2 inches to about 6 inches including about 2 to 2⅞ inches, about 3 to 3⅞ inches, abo

Assignees

• Hedges James H
• Beardmore David H
• Conocophillips Co

Inventors

• Hedges James H
• Beardmore David H

Classifications

• E21B21/003

  Means for stopping loss of drilling fluid (plastering the borehole wall E21B33/138) · CPC title

• E21B49/02 Primary

  by mechanically taking samples of the soil · CPC title