Investigation of hydraulic fracture propagation patterns and hydro-mechanical coupling mechanisms through DEM analysis

Abstract

Accurate prediction of fracture propagation morphology contributes to the success of hydraulic fracturing operations and the estimation of oil and gas production capacity. Various factors, including fluid injection characteristics, in-situ stresses, and pre-existing natural fractures, exert significant influence on the fracture morphology. The discrete element method (DEM) captures inter-particle interactions and exhibits distinct advantages in handling the propagation and interaction of multiple fractures. In this study, we employ a simulation approach that combines DEM with the pipe network flow model. Initially, a comprehensive coupling enhancement of the pressure-updating equation is implemented, ensuring the constant satisfaction of the principle of flow conservation. This leads to an accurate fluid pressure distribution during the process of fracture propagation, which serves as the driving force for fracture development. Building upon this foundation, an analysis is conducted regarding the fracture propagation patterns and underlying microscopic mechanisms under varying fluid viscosities, pre-existing natural fractures, and gas fracturing. The findings reveal that low-viscosity fluids exhibit higher penetration as fractures extend, promoting the propensity for complex branching of fractures. When interacting with pre-existing natural fractures, the model effectively simulates interactions such as cross, offset, and capture types for different interaction angles and in-situ stress ratios. During gas fracturing, the high compressibility of gas prominently leads to the occurrence of complex multiple fractures within the particle assembly, and the effects of burn rate, duration, and the in-situ stress ratio on the morphology of gas fracturing are conducted.