A Study of Hydraulic Fracture Geometry Concerning Complex Geologic Condition in Shales

Abstract

AbstractThe Lujiaping shale gas formation in Sichuan Basin, SW China, is 1400m deep and has high dip angles. Moreover, it is also subjected to the strike-slip fault geostress and contains highly developed bedding planes and natural fractures. The complex geologic condition makes the fracturing treatment effect hard to predict. This paper aims to establish a simulation model to predict the created hydraulic fracture geometry so as to provide appropriate stimulation strategy. Based on the discrete element method, a novel three-dimensional fracture propagation model is established. The transverse isotropy constitutive relations are primarily introduced to characterize the layered shale in the high dip angle formation. Then, the model is used to investigate how the hydraulic fracture geometry changes with different parameters, such as in-situ stress distribution, natural fracture density, fluid viscosity, and pump rate. The model is validated through experimental data, which shows the simulation result is in accordance with the experimental observation. Taking the complex geologic conditions as the initial condition and assuming the formation dip angle as 50°, the high differential stress which is the difference between overburden stress and minimum horizontal stress enhances the fracture propagation in the vertical direction. At 5 MPa of differential stress, the increase of fracturing fluid viscosity can reduce the influence of bedding plane on fracture geometry. The increase of pump rate is helpful to decrease the restriction of bedding plane on fracture propagation so as to improve the stimulation effect. In addition, the high density of natural fracture will further enlarge the impact on the fracture geometry. This work is a theoretical study of predicting the hydraulic fracture geometry under complex geologic conditions, which provides the technical guidance for the optimization of the fracturing treatment in Lujiaping shale gas formation.