ABSTRACT:

Field mine-back experiments and core-through experiments have shown that hydraulic fractures in the reservoir are often not planar. Complex growth of hydraulic fractures is evident in these field experiments. Microseismic data is often used to represent the complexity of created fractures in the formation. Numerical models that have been used to capture the complexity of these created fractures require discretized fracture networks (DFN) as an input. Such models rely on the input DFN as a characterization of the reservoir heterogeneity. In this work we show that it is possible to obtain fracture complexity in the absence of any reservoir heterogeneity. We show that competing fracture propagation can induce a heterogeneous stress state in the rock. This new heterogeneous stress state is induced by the spatial variation of the stress shadow of the propagating fractures. Multiple fracture growth modelling in three dimensions is essential to capture this phenomenon. Using fully 3D numerical simulations, we implicitly calculate the stress shadow in the vicinity of multiple propagating fractures. These fractures are allowed to grow out-of-plane in the simulations. Simultaneously propagating fractures compete with each other for fluid and width while propagating in length and height. Variations in the width of the fractures in the length and height direction induces variation in the induced stress shadow. We show that this variation in the stress shadow can cause a propagating fracture to bifurcate and fork into multiple fractures. We discuss the factors that induce this branching behavior and explain the implications of fracture branching on the distribution of proppant in such multi-stranded fractures.

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