Fracture Containment in Layered Formations Revisited Using the Dual Criterion

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ABSTRACT: The fracture containment caused by the bedding planes (BPs) inside one deep pay zone is studied numerically by a hydraulic fracture simulator, with a focus on the effects of the frictional and conductive behaviors of the bedding plane on fracture nucleation on it and subsequent growth. The dual criterion proposed by Leguillon (2002, Eur. J. Mech. - A Solids 21, 61-72) is used for finding the fracture nucleation size (FNS), beyond which a mature fracture can develop. Like the size of the fracture process zone measured experimentally, the FNS is also on the order of millimeters. The numerical results for a field situation revealed that, under the conditions of in-situ stress of approximately 100 MPa, the FNS is around 2 mm, although it slightly increases with an enhancing injection rate. Using such an FNS, a smaller BP conductivity with an aperture less than 10-7 m generates vertical transverse fracture propagation, but for one with an aperture of 10-5 m, fracture deflection into the BP constrains fracture height. A small coefficient of friction can play a role in limiting fracture height when the BP is permeable. The existence of many permeable BPs with a relatively large conductivity in a pay zone would be likely to constrain the fracture height as found in the field.

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