Effect of gas content in macropores on hydraulic fracturing in rocks using a fully coupled DEM/CFD approach

Abstract

Abstract The paper focuses on the effect of the gas content in rock macropores on a hydraulic fracturing process. The process was simulated by combining the discrete element method (DEM) with computational fluid dynamics (CFD) under two‐dimensional (2D) isothermal conditions. The mechanical behavior of the rock matrix was simulated with DEM, and CFD was used for describing the behavior of laminar two‐phase fracturing fluid (liquid and gas) flow in pre‐existing and newly developed fractures. Geometry changes of pores and fractures in the rock matrix were precisely reproduced. Fully coupled hydro‐mechanical simulation tests were carried out with a rock segment of simplified particulate mesostructure under plane strain compression. The rock segment contained one or two injection slots. The effect of the initial gas‐phase content in macropores on the propagation of hydraulic fractures was estimated in numbers for different initial rock porosities. In addition, the influence of different pre‐existing discontinuities in the rock segment was studied. The main characteristics of a fractured rock segment due to a high‐pressure fluid injection were realistically reproduced with a proposed approach. The initial gas‐phase fraction in macropores and pre‐existing discontinuities were found to be strongly influential in the course of hydraulic fracturing.