Hydraulic fracturing is a well-established and widely used technique in unconventional resources. However, the mechanics of propagation of hydraulic fracture (HF) in naturally fractured reservoirs and the interaction between the induced HF and multiple fractures during a HF treatment is complicated and not well understood. Such understanding is critical to engineering design of production parameters in engineered geothermal systems as well as in shale gas and light oil production. The objective of fluid injection in these applications varies from creating HF to increasing the permeability of the surrounding rock mass, or “stimulation” of the reservoir. Fluid flow propagation and its effect on naturally fractured reservoirs can be studied using Discrete Fracture Network (DFN) approach. In this approach DFN models are created using a statistical description of fractures, and are explicitly represented in the numerical model. During injection, several mechanisms can lead to permeability enhancement, including: • Opening of pre-existing fractures due to the increase in pressure or the decrease in effective normal stress (This mechanism is reversible; in other words, the fracture will close once pressure dissipates and therefore, fluid injection often needs to be accompanied with injecting proppant into the affected fractures.); • Initiation and propagation of HF, which also results in increase in fracture network connectivity. • Opening of pre-existing fractures due to slip-induced dilation, which is referred to as hydro-shearing or shear stimulation, and is permanent; and • Extension of the pre-existing fractures and increase in connectivity of the fracture network; This paper presents the results of numerical modeling of interaction between propagating hydraulic fracture in low permeability formations with the pre-existing DFN. In this approach the DFN is modelled explicitly using the adopted numerical approach based on a discrete element method. In this method formation is presented as an assembly of blocks separated by joints or fracture planes. This work presents three-dimensional studies performed using 3DEC (Itasca, 2011) software. A series of sensitivity studies are described in terms of different DFN characteristics and for different open-hole completion lengths along the borehole.

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