Multi-Stage, Multi-Wellbore Hydraulic Fracturing Simulation in Naturally Fractured Reservoirs Using Cohesive Zone Model

Microseismic surveys have demonstrated the abundance of natural fractures where shear slippage occurs due to hydraulic fracturing. These natural fractures and their intersection with hydraulic fractures significantly complicate the optimization of hydraulic fracturing strategies especially in shale resources with multiple simultaneous or sequential stimulation stages. The clusters’ hydraulic connection within a stage may substantially influence the hydraulic fracture propagation pattern considering the highly variable perforation efficiencies of clusters. These complexities promote the proposed developments in our poro-elastic cohesive zone models for hydraulic fracturing in Abaqus. Our model adopts a validated cohesive traction-separation response for fracture propagation and a well-established, mechanism-based intersection model. The model is integrated with a novel universal wellbore-perforation model for simultaneous and sequential fracturing along three stimulation stages and wellbores. Each stage contains three fracture clusters hydraulically connected through the wellbore during or after the corresponding stage stimulation. The natural fracture (NF) network is retrieved stochastically based on Monte Carlo sampling, and perforation tunnel lengths are modeled using fully damaged cohesive elements at perforation locations. The model quantified limited cluster stimulation, the activation of a complex NF network, and fluid infiltration depending on the stimulation scenario, wellbore pressure drop, randomly distributed perforation lengths, and fracturing fluid viscosity. The complex stimulation patterns is featured by further control on cluster stimulation in the sequential fracturing case compared to the simultaneous case especially in the presence of non-uniform shaped-charge perforations. This improved model enhances the reliability on numerical simulations for hydraulic fracturing design.