Numerical study on hydraulic fracturing in different types of georeservoirs with consideration of H²M-coupled leak-off effects

With the increase in the world’s energy consumption and the change in climate, unconventional energy resources become more and more popular. Since geological formations of low or ultra-low permeability are usually involved, hydraulic fracturing is one of the most important tools for their exploitation. The objective of this paper is to investigate hydraulic fracturing and its hydro-mechanical influences on different types of georeservoirs, including tight gas, oil, and geothermal reservoirs. Based on the previous work of hydraulic fracturing simulation with FLAC3D^plus, the multi-phase multi-component flow simulator TOUGH2MP is coupled for the numerical study. A new coupling approach is designed with special consideration of the H²M-coupled process in different types of georeservoirs. For the simulation, a generic 3D ¼ model (200 × 300 × 200 m, consisting of 50 m caprock, 100 m reservoir formation, and 50 m base rock) is adopted. The simulations are run under comparable reservoir and operative conditions. The results show that fracture propagation and proppant concentration are comparable with a short period of slurry injection (80 min × 6 m³/min). The fracturing fluid does not penetrate deep into the formation. Due to the high compressibility of gas, the induced pore pressure is much lower than that in oil and geothermal reservoirs, although the final leak-off ratio is comparable. The hydraulic fracturing causes stress reorientation in georeservoirs. According to the criterion of 5° stress reorientation, the minimum fracture spacing for a multiple fracture system in the assumed geothermal reservoir is 73 m, while that in an oil and gas reservoir is 66 and 60 m, respectively. This work expands on the numerical simulator as well as the understanding of hydraulic fracturing in unconventional georeservoirs. The results of this study can be used further to optimize the fracture spacing in a multiple hydraulic fracture system in different reservoir types.