Numerical simulation of proppant transport with multi-stage alternating injection in CO2 hybrid fracturing

Abstract

Effective proppant placement has been one of the key objectives of reservoir stimulation. CO₂ hybrid fracturing is promising for the economic production of unconventional reservoirs, however, there is a lack of understanding of proppant transport within the rough fractures associated with it. In this study, a validated CFD-DEM model is used to simulate proppant transport with multi-stage alternating injection in CO₂ hybrid fracturing, focusing on evaluating the advantages of alternating injection within a rough fracture as well as the influence laws of key parameters. The simulation results show that the use of multi-stage alternating injection of proppant with different fluids in CO₂ hybrid fracturing can obtain better proppant placement than single fluid continuous pumping, with 36.4 % and 4.4 % higher proppant dune lengths, and 3.51 % and 2.3 % higher dune placement rate than single CO₂ pumping and water pumping, respectively. The optimal number of injection stages in multi-stage alternating injection of proppant is 4, while the optimal segment plug length ratio of CO₂ and water is 3:1. The best dune length and placement rate are obtained when the CO₂ segment plug is injected at a velocity of 0.1 m/s, but when the CO₂ segment plug is injected at a velocity of 0.2 m/s, it is favorable for the safety of the pipeline and equipment during fracturing operation.