Extended finite element-based cohesive zone method for modeling simultaneous hydraulic fracture height growth in layered reservoirs

Abstract

In this study, a fully coupled hydromechanical model within the extended finite element method (XFEM)-based cohesive zone method (CZM) is employed to investigate the simultaneous height growth behavior of multi-cluster hydraulic fractures in layered porous reservoirs with modulus contrast. The coupled hydromechanical model is first verified against an analytical solution and a laboratory experiment. Then, the fracture geometry (e.g. height, aperture, and area) and fluid pressure evolutions of multiple hydraulic fractures placed in a porous reservoir interbedded with alternating stiff and soft layers are investigated using the model. The stress and pore pressure distributions within the layered reservoir during fluid injection are also presented. The simulation results reveal that stress umbrellas are easily to form among multiple hydraulic fractures’ tips when propagating in soft layers, which impedes the simultaneous height growth. It is also observed that the impediment effect of soft layer is much more significant in the fractures suppressed by the preferential growth of adjoining fractures. After that, the combined effect of in situ stress ratio and fracturing spacing on the multi-fracture height growth is presented, and the results elucidate the influence of in situ stress ratio on the height growth behavior depending on the fracture spacing. Finally, it is found that the inclusion of soft layers changes the aperture distribution of outmost and interior hydraulic fractures. The results obtained from this study may provide some insights on the understanding of hydraulic fracture height containment observed in filed.