Hydrocarbon recovery: Optimized CFD-DEM modeling of proppant transport in rough rock fractures

Proppant distribution in rough rock fractures is a key factor in the evaluation of the effectiveness of a hydraulic fracturing operation. This paper focuses on the study of how fracture roughness influences proppant transport and placement based on improved coupled computational fluid dynamics-discrete element method (CFD-DEM). Laboratory-scale synthetic rough fractures analogous to realistic rock fractures were used to flexibly control fracture geometric parameters. In the numerical model, Magnus force, virtual mass force and Saffman lift force were taken into consideration to precisely describe the interaction between proppant particles and the fracturing fluid. This numerical model was validated by comparison with published experimental results. The distribution of proppant and the transport mechanism in smooth fractures, joint rough fractures and sheared rough fractures were investigated. In addition, the effect of fracture wall’s fractal dimension and fracture inclination on proppant movement and deposition were explored. The study found that proppant settling velocity is slower in fractures with higher fractal dimension. The lateral conveyance of proppant is enhanced by higher fractal dimension of rough fracture walls, and smaller fracture inclination angles. The proppant dune is lower and longer in fractures with greater fractal dimension. When the fracture is close to horizontal, proppant particles show a finger-like distribution instead of generating a sand bed. The results also show that the proppant coverage ratio in fractures increases with increasing fractal dimension, and with decreasing fracture inclination angle. The results provide a better understanding of how fracture roughness and geometry impact proppant transport in rock fractures.