Simulation of multi-fracture interference and optimization of stimulated reservoir volume in layered shale using finite element and response surface method

Staged multi-cluster fracturing in horizontal wells is essential for developing shale oil reservoirs. The stress shadow caused by competitive fracture propagation and bedding interactions is highly complex. A three-dimensional flow-stress-damage coupled numerical model based on the finite element method was developed. It is used to simulate the non-planar propagation behavior and stimulated reservoir volume (SRV) of hydraulic fractures (HFs) when they encounter bedding planes. The HFs may experience arrest, deflection, penetration, and combined bifurcation under different conditions such as cluster spacing, number of clusters, in situ stress, bedding tensile strength, and construction factors in layered shale. The response surface methodology (RSM) was employed to analyze the sensitivity and coupling effects on SRV and identify optimal parameter combinations. The results indicate that the bedding structure and stress interference lead to transverse asymmetric propagation. Intermediate fractures tend to deflect or arrest due to stress superposition, while adjacent fractures commonly exhibit vertical reverse propagation patterns. Reduced cluster spacing and an excessive number of clusters increase fracture interference, thus limiting vertical propagation. A moderate vertical stress difference and bedding tensile strength promote the formation of complex fractures. RSM analysis reveals that injection rate and cluster spacing are the most sensitive factors affecting SRV, while the number of clusters has the least sensitivity, with each factor's influence being nonlinear. Optimizing the interrelationships between cluster spacing, injection rate, and viscosity is crucial for enhancing SRV and fracture network efficiency. These findings provide insights into fracture geometry control mechanisms and SRV optimization strategies in Jiyang Depression's layered shale reservoirs.