Simulating production from complex fracture networks is complicated due to different rates of closure of propped and unpropped fractures in a heterogenous time-varying stress field. Most of the existing models for simulating production from such hydraulic fractures do not consider geomechanics or use pressure as a proxy for changing the fracture conductivity. The closure of the unpropped fracture portion loses conductivity promptly, resulting in a fast decline rate in unconventional wells. However, most of the existing models are not capable of distinguishing the difference of propped and unpropped region in the fracture network. In this work, we developed a fully coupled, compositional, geomechanical fracturing and reservoir simulation model for simulating fracture propagation, proppant transport, proppant settling, flowback and fracture closure in complex fracture networks and applied this to field cases in the tight oil shale reservoirs.

Our numerical model implicitly handles reservoir deformation and compositional multiphase fluid flow in rock matrix and propped/unpropped fractures. The simulation process consists of fracture creation during hydraulic fracturing and then modeling the shut-in and fracture closure followed by flowback over a period of several years. Total and effective stresses during production are calculated considering both pore pressure changes and mechanical opening of fractures. Closure of propped/unpropped fractures is modeled using an improved Barton-Bandis contact model. Previously published lab-measurements (Wu et al., 2017) for conductivity of propped and unpropped fractures as a function of effective stress are used as inputs for the closure model.  The effects of proppant distribution, proppant size and different rates of fracture closure in propped and unpropped portions of the fracture are studied in using both planar fracture and complex fracture network.

We show that the productivity of a fractured well is directly related to the proppant placement in the fractures. Achieving uniform proppant placement and reducing the proppant settling is beneficial in improving the fractured well productivity. This work will enable a better understanding of fracture closure during production, improving the accuracy of production forecasts and understanding inter-well interference.