Integrating rock ductility with fracture propagation mechanics for hydraulic fracture design

Abstract

The invention relates to the calculation of parameters to inform hydraulic stimulation of non-conventional hydrocarbon-bearing rock formations, such as shales. Unlike conventional formations, non-conventional formations tend to display elastic-plastic behavior and have stress-strain characteristics which with substantial non-linear regions. A parameter which has been termed Elastic Index (EI) is proposed, together with a demonstration of how this parameter, when coupled with principles of fracture mechanics, may be used to extract meaningful calculated or estimated values for e.g.; total required volume of fracturing fluid; treating pressure; fracturing fluid viscosity; proppant size; and proppant concentration.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a non-provisional application which claims benefit under 35 USC §119(e) of and priority to U.S. Provisional Application Ser. No. 61 / 828,368 filed 29 May 2013, entitled “INTEGRATING ROCK DUCTILITY WITH FRACTURE PROPAGATION MECHANICS FOR HYDRAULIC FRACTURE DESIGN,” which is incorporated by reference herein in its entirety.STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0002]None.FIELD OF THE INVENTION[0003]This invention relates to hydraulic stimulation (“fracking”) in shale and other unconventional subterranean hydrocarbon reservoirs.BACKGROUND OF THE INVENTION[0004]Shale and other non-conventional formations such as tight gas, mudstone, siltstone and marl systems are becoming an increasingly important source of hydrocarbon resources. Such unconventional resources, however, present challenges not only in their extraction but also in the analysis of their properties in order to design strategies for drill...

AI Technical Summary

Benefits of technology

[0014]The inventors have investigated the stress-strain curve for a number of different types of non-conventional hydrocarbon-bearing rock. They have found that the stress-strain is likely to comprise an initial non-linear portion as the rock is initially loaded. This region, known as a poro-elastic region, is not always present, though. The poro-elastic region, if present, is followed by a linear (elastic) region up to the yield point, and then normally a

Problems solved by technology

Such unconventional resources, however, present challenges not only in their extraction but also in the analysis of their properties in order to design strategies for drilling and treatment such as hydraulic stimulation (“fracking”).

Calculation of the above parameters has proven problematic in shale and other non-conventional rock, which appears to have geomechanical properties which differ substantially from conventional rock.

Shale and other non-conventional rock, however, do not always behave in this way and often show a considerable degree of plastic behavior.

This will generally produce incorrect results and often a large amount of trial and error is also involved.

However, the brittleness approach has been shown to provide inaccurate predictions for shale properties and the “frackability” of non-conventional reservoirs.

This may lead to a dependence of apparent fracture toughness on confining pressure for mode-I cracks

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