Numerical Study of Proppant Transport with Supercritical CO₂ in Fracture

Supercritical CO₂ (SC-CO₂) fracturing is one of the new waterless fracturing technologies, which has been drawn much attention because of its environmental friendly and highly efficient advantages. However, the capacity and behavior of proppant transport with SC-CO₂ in fracture have not been figured out yet owing to lower density and viscosity of SC-CO₂. The two-phase flow model of SC-CO₂ and proppant in fracture during SC-CO₂ fracturing was established using computational fluid dynamic method (CFD) considering the particle interaction and the property of SC-CO₂. The effects of proppant density, particle size, sand ratio and displacement were analyzed. The research results indicate that the proppant volume fraction has obvious differences in the vertical profile of fracture. With the injection time increasing, the proppant volume fraction of static granular layer generally remains stable. The proppant volume fraction in contact layer and suspension layer vary gently, but changes dramatically in saltation layer. Under the simulated conditions, proppant density of less than 1 540 kg/m³, proppant size of smaller than 0.25 mm, sand ratio of lower than 8% and injection rate of higher than 4 kg/s are proposed to form uniform proppant bed and avoid sand blocking. The study is expected to provide a theoretical basis for the design of proppant transport with SC-CO₂ in fracture.