Prediction of Pore Pressure–Induced Stress Changes during Hydraulic Fracturing of Heterogeneous Reservoirs through Coupled Fluid Flow/Geomechanics

AbstractDuring hydraulic fracturing, the filtration of fracturing fluid increases the pore pressure in the vicinity, resulting in pore pressure–induced stress in the reservoir. In order to study the evolution of pore pressure–induced stress during fracturing, based on Biot’s theory, a dynamic simulation model of single-fracture or multifracture propagation was established through coupled fluid flow and geomechanics. In the model, the heterogeneity of the reservoir and the influence of pore elasticity of reservoir rock were considered. Further, the finite volume and iterative methods were used to solve the model. The results show that the heterogeneity of reservoir permeability and porosity has a great influence on the distribution of pore pressure–induced stress, and it will make the induced stress distribution more complicated, resulting in local stress prominence. The distribution of pore pressure–induced stress during fracturing is quite different from that of hydraulic fracture opening–induced stress. With the increase of fracturing time, the distribution of pore pressure–induced stress shows a certain regularity, and the minimum horizontal principal stress shows a higher level near the fracture and a lower level on the left and right sides. However, the maximum horizontal principal stress is higher near the fracture and lower at the fracture tip (upper and lower parts of the fracture). Under certain conditions, pore pressure–induced stress will reverse the horizontal principal stress in the local area. Considering the influence of pore elasticity, the pore pressure will increase because of the fracturing fluid filtration, resulting in further increase in reservoir permeability and porosity, which in turn will increase fracturing fluid filtration. Through this study, the distribution of induced stress in the hydraulic fracturing process can be described more accurately, which can provide some guidance for hydraulic fracturing design and theories.