CFD-DEM Simulation on the Main-Controlling Factors Affecting Proppant Transport in Three-Dimensional Rough Fractures of Offshore Unconventional Reservoirs

Hydraulic fracturing is a pivotal technique in the development of offshore unconventional reservoirs. While current research has primarily focused on the longitudinal or transverse roughness of fractures, this study shifts the emphasis to their three-dimensional (3D) roughness characteristics. We present a quantitative analysis of proppant transport within 3D rough fractures of offshore unconventional reservoirs, utilizing computational fluid dynamics (CFD) and the discrete element method (DEM). Our results are validated against experimental data. This study focuses on the main-control factors on the transport of the proppant in rough fractures, including surface roughness, the ratio of lateral to longitudinal forces, the ratio of the proppant diameter to the fracture aperture, and the fracture inclination angle. The results indicate that the rough surface of the fracture has a significant impact on the transport of the proppant, reducing lateral transport distance while increasing the height of the sand dune. Notably, both the lateral transport distance and the height of the sand dune show a quadratic relationship with the fractal dimension of the fractures. In addition, when the ratio of lateral to longitudinal forces is less than one, an increase in fracture roughness significantly reduces the transport efficiency. Once the ratio exceeds one, the effect of fracture roughness on proppant transport becomes negligible. Furthermore, when the ratio of the proppant diameter to the fracture aperture is below 0.25, the roughness has a minimal effect on the lateral transport of the proppant. Our findings, especially the simulation of proppant behavior in realistic 3D fractures, offer a valuable reference point for predicting proppant distribution.