Effect of flexible fibers for preventing proppant flowback after fracture closure by CFD-DEM method

Proppant flowback can lead to blockages in the wellbore and surface pipelines. Adding fibers during the hydraulic fracturing process has been proven to be an effective method to control proppant flowback. Proppant flowback involves interactions between proppant-proppant, proppant-wall, proppant-flexible fiber, and solid phase-fluid. To study this issue, this paper employs a multi-node structural modeling method, overcoming the limitations of a single-node cylindrical rigid fiber, and establishes flexible fibers that can undergo arbitrary deformations. To analyze the movement of fibers-proppant under fluid action, the Gidaspow model is used for proppants, and the Marheineke&Wegener model is used for fibers, coupling fluids and solids to achieve a simulation of fiber-proppant flowback under fluid action. Simulation results indicate that the average flowback velocity of proppant is lower after adding fibers than without them. The longer the fiber length and the higher the mass concentration, the better the effect of the fibers in controlling the flowback of the proppant. The velocity of proppant flowback is positively correlated with the fracture width to particle size ratio and negatively correlated with the closing pressure. Under conditions of low fracture width to particle size ratio or high closing pressure, the contact force between particles are large and the proppants are not prone to flowback, so fibers can be used less or not at all. In addition, the proppant flowback velocity is directly proportional to the fracture fluid viscosity and velocity. This study provides new insights into the interaction between fiber and proppant after fracture closure.