Coupled h-m fracture interaction using fem with zero-thickness interface elements
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Intensive hydraulic fracturing is a procedure employed for low permeability reservoir stimulation. This technique consists of generating a sequence of regularly spaced parallel fractures (multi-stage fracturing). The generation of a fracture involves the modiﬁcation of the local stress state, and therefore, in the case of multi-stage fracturing, the propagation of a certain fracture can be aﬀected by the injection sequence, as it has been observed with microseismicity monitoring . This paper describes a study of this technique by means of the Finite Element Method with zero-thickness interface elements for the geo-mechanical modelling of discontinuities . The technique consists in inserting interface elements in between standard elements to allow jumps in the displacement solution ﬁelds. For the mechanical problem, their kinematic constitutive variables are relative displacements, and the corresponding static variables are stress tractions. The relationship between variables is controlled via a fracture-based constitutive law with elasto-plastic structure . Concerning the hydraulic problem, the interface formulation includes both the longitudinal ﬂow (with a longitudinal conductivity parameter strongly dependent on the fracture aperture), as well as and the transversal ﬂow across the element . Previous work by the authors focused on the validation of the method, the analysis a single fracture plane problem [5, 6]. In this case the method is extended to allow free propagation of fractures in any direction, by means of inserting interface elements between all continuum elements. The results presented in this paper analyse the eﬀect of material properties, in particular fracture characterization, in the propagation and the eﬀect of diﬀerent major to minor principal horizontal stress ratio, on the trajectory and interaction of the fractures.