Numerical Investigation on Hydraulic Fracturing of Extreme Limited Entry Perforating in Plug-and-Perforation Completion of Shale Oil Reservoir in Changqing Oilfield, China

In recent years, multi-stage hydraulic fracturing for shale oil reservoirs is developing toward a shorter cluster spacing and a larger number of clusters per stage. The objective is to improve the stimulation performance by reducing the fracturing stages and creating more hydraulic fractures in terms of cost-efficiency in geological engineering. Field tests demonstrate the uneven distribution of fluid volume among clusters and only a few perforation clusters contribute to productivity. The extreme limited entry (XLE) completion is an effective method to improve the efficiency of perforation clusters. However, the influence of several controlling parameters on the cluster effectiveness during XLE completion remains elusive. Therefore, a 3D field-scale hydraulic fracturing model for XLE completion based on the lattice method is developed for the case of shale oil reservoirs of Changqing oilfield in China. In this model, perforation friction, geological factor such as stress difference between adjacent clusters, and filtration of fracturing fluid are considered. The numerical results are compared with field data (i.e., injection pressure and cluster efficiency) obtained from the fracturing construction and the step-down test. The influences of injection rate, cluster spacing, cluster number, and stress difference between adjacent clusters on the fracture morphology, cluster efficiency and injection pressure of XLE completion are discussed in detail. The results show that perforation friction is the most critical factor that affects the efficiency of perforation cluster during XLE completion. A guide chart of cluster efficiency under various differential geological stresses between adjoining clusters is proposed. According to this guide chart, the required perforation friction under different cases can be obtained, and then the related perforation parameters (i.e., perforation diameter and number) can be determined. The research results provide theoretical guidance for optimization of XLE completion in geological reservoirs.