Discrete element method simulation of competitive fracture propagation in staged multi-cluster fracturing in shale oil reservoirs

Abstract

Hydraulic fracture dynamics are complex due to interactions with geological features such as bedding, joints, and microcracks, which complicate multi-cluster fracking processes. This study employs a discrete element method-based numerical simulation to investigate competitive fracture propagation in multi-cluster fracking of laminated shale, focusing on how perforation cluster settings influence fracture geometry in layered formations. Additionally, considering the prevalent high-angle natural fractures (NFs) in continental shales, the research examines the competitive propagation of multiple hydraulic fractures within these NF zones. Fracture propagation near certain perforation clusters exhibits unevenness, resulting in diverse final fracture geometries due to competitive propagation effects. A greater number of clusters lead to more diverse fracture patterns, while larger cluster spacing reduces stress interference during multi-fracture propagation. Varied fracture shapes may result from stress disruptions that unevenly affect adjacent fractures, causing early termination in some and reducing cluster efficiency. For more than five clustered stages, refracturing with temporary diversion is recommended to enhance cluster efficiency. Furthermore, the reservoir zone after multi-cluster fracturing features complex fractures near the well (Area I) and simpler ones farther out (Area II). Proximity to NFs enhances complexity near the well but inhibits hydraulic fracture propagation farther from the wellbore. Therefore, designing reasonable cluster spacing based on the reservoir’s permeability and drainage radius is essential for maximizing the pay zone of Areas I and II. This research elucidates competitive fracturing dynamics in multi-clustered laminated shale reservoirs, informing the theoretical basis for reservoir unit division and providing foundation for further optimized development strategies.