Numerical investigation of complex hydraulic fracture network in naturally fractured reservoirs based on the XFEM

The propagation of hydraulic fracture network in naturally fractured shale reservoirs remains a complicated and challenging issue. To reveal the propagation principle of the complex fracture network, a numerical fracturing model is presented on the basis of the extended finite element method (XFEM) in this work. The intersection criterion containing five intersection patterns is studied. True triaxial fracturing experiment is conducted to verify the fracture geometry obtained from our model. After that, hydraulic fracturing in naturally fractured formations is studied to investigate the influences of natural fracture azimuth on fracture network geometry. The numerical results show that, hydraulic fracture is inclined to open the obtuse angle side of natural fracture in uniform azimuth model. In random azimuth condition, occurring of various intersection patterns enables complex fracture network to generate easier. And hydraulic fracture is harder to propagate if it is closer to the middle domain due to the squeezing effect. Meanwhile, the fracture network can penetrate deeper shale layer under large in-situ stress difference. In addition, the stimulation effect (e.g., Stimulated Reservoir Volume) in random azimuth condition is much stronger than that in uniform azimuth condition. The findings in this work are of benefit to provide us a better understanding of complex hydraulic fracture network and develop high-efficiency fracturing technology.

Automated summary

This study presents a numerical fracturing model based on the extended finite element method (XFEM) to reveal the propagation principle of complex fracture network in naturally fractured shale reservoirs. The results indicate that hydraulic fracture tends to open the obtuse angle side of natural fracture in uniform azimuth model and complex fracture networks are easier to generate under random azimuth conditions.