Hydraulic Fracture Simulation Based on Discrete Element Method and Lattice Boltzmann Method

Abstract

One of the challenges in geothermal energy extraction is how to stimulate and sustain the flow of fluid through the geothermal field and how to generate an efficient hydraulic subsurface heat exchanger system. Understanding the characteristics of hydraulic fracture, porous flow and heat transfer in fractured rock is an important step to achieve this goal, and numerical simulation can provide a powerful approach for systematically and thoroughly investigating these problems. In this paper, we present a fully coupled solid-fluid code using Discrete Element Method and Lattice Boltzmann Method The DEM with bonded particles is used to model the deformation and fracture in solid, while the LBM is used to model the fluid flow. The two methods are two-way coupled, i.e., the solid part provides a moving boundary condition and transfers momentum to fluid, while the fluid exerts a dragging force to the solid. Two widely used open source codes, the ESyS_Particle and the OpenLB, are integrated into one code and paralleled with Message Passing Interface library. Several 2-D simulations are carried out to validate the integrated code, including hydraulic fracturing induced by injection of fluid into a borehole, and fluid flow inside the cracks. The preliminary results indicate that the new code is capable of reproducing the basic features of hydraulic fracture without too much assumptions on how the cracks start and propagate in solids and how fluid flow in the narrow cracks. This study is the first step towards developing a fully coupled thermal– hydraulic - mechanical code. Our next step is to implement thermal effect into the code which thus offers a promising tool for simulation of the whole process of geothermal extraction, including hydraulic fracture, fluid and heat flow and heat exchange between rocks and fluid.