Abstract: In this study, a new FDEM-flow method is developed by considering the permeability of rock matrix, and it fully utilises the unique topological connection between joint elements and triangular elements in the original combined finite-discrete element method (FDEM). First, the joint elements were used as a natural channel for fluid flow, and the fluid flow in rock matrix and fissures were characterized by fluid flow in joint elements based on the cubic law. While the permeability of rock matrix was determined by calibrating the appropriate aperture of the joint element. Then, a numerical example of the free surface steady flow with the analytical solution was employed to validate the proposed seepage algorithm and the calibration method for rock matrix permeability. Finally, a hydraulic fracturing example was conducted to demonstrate that the permeability of rock matrix and fracture was considered simultaneously in the modified FDEM-flow method. Moreover, by using simple pure fracture seepage this method solved the complex issues of hydraulic fracturing. Therefore, the application scope of the new FDEM-flow method is broader than that of the original FDEM-flow method. This method provides a new solve tool for simulating hydraulic fracturing in shale gas exploration and geothermal exploration in hot dry rock.

Key words: FEMDEM, FDEM-flow, fluid-solid coupling, hydraulic fracturing, fluid viscosity, seepage