US 9,518,463 B2 · Core capture and recovery from unconsolidated or friable formations and methods of use

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.

Claims14

Dependent claims

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.

4 more elements

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.

2 more elements

Dependencies are inferred from the claim text.

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

Life of this patent

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

Life of this patent

Abstract

Claims14