Numerical simulation of multi-hole fracture competition initiation and propagation

Abstract

Perforation is the key to the successful implementation of hydraulic fracturing, and the study of perforation parameters is of great significance for reservoir reconstruction and oil and gas exploitation. A finite element model is established to simulate multi-hole fractures' initiation and propagation based on the global embedded cohesive zone model. In the model, the reservoir is considered a dense, low-permeability porous elastic medium, wherein the coupling effect of fluid and geomechanics during fracturing is considered. The KGD analytical solution is consistent with the simulation results, verifying the cohesive zone model's accuracy. The results show that there are four competitive modes for multi-hole crack initiation. Firstly, the cracks open initially and remain open; secondly, the hole is open but not cracked; thirdly, the initial initiation extends and then closes; finally, the initial crack did not start in the late crack. With the increase of perforation density, the perforation initiation rate and average fracture pressure gradually decrease, and the fracture complexity in the near-wellbore area increases. With the increase of displacement and viscosity, the initial crack rate, the number of main cracks and microcracks formed in the hole tend to increase, while horizontal stress difference has an inversely proportional trend. In the presence of multiple perforating holes, the crack propagation presents a change from complex to simple, and the number of cracks presents a change from more to less. The expansion mode is formed with 2–4 main cracks and micro-cracks as auxiliary.

Keywords

• Fracture propagation
• Perforation density
• Hydraulic fracturing
• Competitive initiation
• Cohesive zone model