Title of Paper:Effect of discontinuity stress shadows on hydraulic fracture re-orientation

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Date of Publication:2017-01-01

Journal:INTERNATIONAL JOURNAL OF ROCK MECHANICS AND MINING SCIENCES

Included Journals:SCIE、EI

Volume:91

Page Number:179-194

ISSN No.:1365-1609

Key Words:Hydraulic fracture re-orientation; Stress shadow effect; Differential stress; Rock mass homogeneity, Numerical modelling

Abstract:Hydraulic fracturing has been applied to the cave mining industry as a pre-conditioning method to improve rock mass caveability and fragmentation sizes. In theory, the hydraulic fracture orientation is dictated by and is perpendicular to the minimum in-situ stress orientation. Such orientations will not always result in the creation of a blocky rock mass to aid caveability. The understanding of hydraulic fracture re-orientation induced by the stress shadow effect is important for either avoiding the undesirable interaction between multiple transverse hydraulic fractures or taking advantage of this phenomenon to Create prescribed hydraulic fractures that result in the creation of blocky rock masses. In this paper, the existing knowledge of the stress shadow effect around a pre-existing discontinuity is reviewed. A 3D numerical modelling code, Rock Failure Process Analysis (RFPA) is used to investigate factors influencing hydraulic fracture re-orientation. It is established that hydraulic fractures can be forced to propagate in desired directions if advantage is taken of the stress shadow effect in combination with knowledge of rock mass homogeneity and site far field stress conditions. Both the differential stresses between sigma(2) and sigma(3) and between sigma(1) and sigma(3) affect the hydraulic fracture re-orientation geometry. The minimum far field stress magnitude has no direct impact on hydraulic fracture re-orientation. Rock mass homogeneity significantly influences how far a hydraulic fracture propagates along its predefined orientation from its initiation point before re-orientation.