New Insights on the Geometry of Simultaneous Multiple Fracture Propagation in Laminated Shale Reservoirs Considering the Effects of Bedding Planes and Stress Interference

Multi-stage horizontal well fracturing has been widely applied to exploit unconventional shale oil & gas resources. The shale reservoir generally contains a large number of bedding planes with lower strength, which have a great effect on the growth of hydraulic fractures. In this paper, the 3D discrete lattice method is applied to establish a 3D model of simultaneous multiple fracture propagation for laminated shale reservoirs. This model considers the influence of stress interference, perforation friction, fluid-mechanical coupling, and bedding planes. The effects of geological and engineering parameters on multiple fracture propagation are studied. The bedding plane activation efficiency and variation coefficient of fracture length are both proposed to quantitatively evaluate the stimulating effect. The simulation results show that the geometry of each fracture within a stage is obviously different. The existence of bedding planes will increase the fluid filtration, resulting in reduction of fracture geometry. Under the combined effect of bedding planes and stress interference, the bedding planes are more easily activated by hydraulic fracture under the condition of low bedding cohesion, low vertical-horizontal stress difference, small cluster space, high injection rate, and low fracturing fluid viscosity. However, those factors have a smaller impact on the fracture uniformity. The research results of this paper provide an effective method for accurately predicting the geometry of simultaneously propagated fractures in laminated shale reservoirs for horizontal wells. This method is applied in Well L1 in the Eastern Sichuan Basin, China, and the monitoring results indicate that a complex fracture system has been formed through hydraulic fracturing operation, and ideal productivity has been achieved.