Simulation of Proppant Transport in 2D Discrete Fracture Networks

Abstract

We developed a modeling approach to describe proppant transport in two-dimensional discrete fracture networks models. We implemented our approach into the two-dimensional version of the discrete fracture network (DFN) simulator Complex Fracturing ReseArch Code (CFRAC). Conventionally, proppant is not used in Enhanced Geothermal Systems (EGS), though it is widely used in hydraulic fracturing for hydrocarbon recovery. It is believed in the EGS community that slip on preexisting fractures (shear stimulation) is the only important mechanism of stimulation and so proppant is not necessary. In this paper, based on the idea that newly forming hydraulic fractures can propagate and play a key role in EGS, we discuss proppant transport in natural and hydraulic fractures and its impact on stress, aperture, and transmissivity. To model the process of proppant settling with a two-dimensional model, we split each fracture element into two sections: a proppant bed at the bottom of the fracture and a slurry (mixture of fluid and proppant) above the proppant bed. The model takes into account fracture closure around the proppant and the effect of closure on fracture properties. The results demonstrate that our formulation can describe proppant transport, proppant settling, proppant erosion, and fracture closure in a fully consistent way.