Analytical model for prediction of volumetric fracture propagation morphology considering elastoplasticity

Abstract

Characterization of fracture propagation morphology of multi-stage fracturing in horizontal wells in shale reservoirs is a challenging task, especially for complex volumetric fractures. Experimental conditions limit the applicability of experimental methods, so numerical simulation methods are often used to study fracture propagation. The numerical model has a slow simulation speed under the condition of engineering scale, and considering the complex fracture morphology and plasticity at the same time will increase the modeling difficulty and simulation computational cost. Therefore, it is urgent to propose a fast analytical model to predict the fracture propagation characteristics. In this study, the average fracture length and average fracture density were used to equivalently simplify the complex volumetric fracture morphology. Based on energy conservation and material balance, combined with the minimum action principle, an analytical model for rapid prediction of volumetric fracture propagation morphology considering elastoplasticity is established. The results showed that the average fracture length and average fracture density increase as a power exponential function with time, and their growth rate decreases with time. Through the orthogonal test analysis method, it is clarified that the net pressure in fracture is the main controlling factor affecting the fracture propagation morphology. The net pressure increased from 2 to 8 MPa, the dimensionless average fracture length increased from 3.2 to 4, and the average fracture density decreased from 4.3 to 2 after 200 s of fracture propagation.