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Hydraulic Fracturing Using Pulsed Pressurization

IP.com Disclosure Number: IPCOM000199519D
Publication Date: 2010-Sep-07
Document File: 2 page(s) / 89K

Publishing Venue

The IP.com Prior Art Database

Abstract

A concept is disclosed for improved hydraulic fracturing of ductile subsurface formations,such as gas shales containing high clay contents. The concept involves oscillating the pressure of a fracturing fluid to take advantage of time-dependent geomechanical behavior. Pressure oscillations may be controlled to occur over several seconds or even fractions of a second. Preferably, the oscillations are created downhole so to avoid diffusion and weakening of a pressure pulse when traveling down a long wellbore.

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Hydraulic Fracturing Using Pulsed Pressurization

Robert D. Kaminsky and Michael E. McCracken

ExxonMobil Upstream Research Company

Abstract

A concept is disclosed for improved hydraulic fracturing of ductile subsurface formations, such as gas shales containing high clay contents. The concept involves oscillating the pressure of a fracturing fluid to take advantage of time-dependent geomechanical behavior. Pressure oscillations may be controlled to occur over several seconds or even fractions of a second. Preferably, the oscillations are created downhole so to avoid diffusion and weakening of a pressure pulse when traveling down a long wellbore.

Problem Being Solved

For shale gas to be produced at economic rates from reservoirs, the formation of large hydraulic fractures is required in the reservoirs. Certain gas shales are composed of relatively ductile rocks. Large hydraulic fractures may not be able to be formed in ductile rocks since the crack tip blunts and does not propagate well. Thus, methods to generate large hydraulic fractures in ductile shales are needed.

Description of Solution Concept

The concept (see Figure 1) involves a pressurization scheme to form hydraulic fractures in ductile subsurface formations, such as high clay content shales. Rather than applying a fairly constant fluid pressure during fracturing, the pressure of the fracturing fluid is relatively rapidly oscillated many times to take advantage of time-dependent geomechanical behavior (c.f., thixotropic behavior). Many ductile materials behave more brittle-like when rapidly loaded. Shale ductility generally increases as its Young's Modulus decreases and Poisson's Ratio increases (for example, see SPE Paper 115258). Published studies on ductility of rock as a function of loading rate include Chong et al., "Effects of Strain Rate on Oil Shale Fracturing", Int. J. Rock. Mech. Min. Sci. & Geomech., 17, 35-43, 1980; Chong et al., "Strain rate dependent mechanical properties of Western oil shale", 28th US Symposium on Rock Mechanics, 157-164, 1987; and, Kipp et al., "Strain-rate dependence fracture initiation", International J. of Fracture, 16(5), 471-478, 1980.

Pressure oscillations may be controlled to occur over several seconds or even fractions of a second (e.g., 0.1 or 0.5 seconds) - however, explosive fracturing is to be avoided so that traditional fracturing equipment may be used. The pressure pulsations may be generated at the surface or downhole. Preferably, the oscillations are created downhole so to avoid pulse diffusion and weakening when traveling down a long (somewhat elastic) we...