Study of Stress Changes in Unconventional Reservoirs with Coupled Flow and Geomechanics Simulations

The development of unconventional reservoirs in us follows this practice: parent wells are first drilled, then infill wells are drilled to produce the region between parent wells. One of the key factors for the success of this strategy is to find out the stress change induced by parent well production and how to generate efficient fracture geometry for infill wells. The first work in this paper is the analysis of the stress distribution after parent well production. This analysis is based on a real field model. The lower-than-expected infill well production rate is first analyzed, then possible causes for this poor production performance are checked. Based on the real field model, stress is calculated after the parent well’s production. To precisely simulate hydraulic fractures, the swarm effect is considered. Results show that due to non-uniform fracture geometry in the parent well, an irregular depletion area and large stress change region are induced in the reservoir; frac hits still can be induced from the irregular depletion area between the staggered parent and infill wells; Parent well depletion not only changes reservoir stress in the layer of the parent well but also alters stress in the lower layer of the infill wells. Secondly, the efficiency of subsequent parent well water injection is analyzed. Different injection designs are simulated to investigate the influence of factors like reservoir fluid type, injection pressure, and injection volume. Results show that subsequent parent well water injection mainly restores the stress and pressure near the wellbore; it is more efficient in the oil-water two-phase case than in cases with gas. The third work is the simulation of hydraulic fracture closure during production. A 3D geomechanics simulator is developed. Then it is coupled to GURU, a fully compositional simulator, using a modified fixed stress coupling method. A relationship derived by Bandis and the Cubic Law are used to calculate the fracture closure and the fracture permeability change. Simulations show that fracture closure mainly affects the early production stage; at different locations along a fracture, fracture width and permeability change show different trends