Numerical modelling and sensitivity analysis of proppant placement in branch fractures

In complex hydraulic fractures, proppant migration behavior is not fully understood, especially under the factors, such as fracture geometry, roughness, proppant parameters, and fluid properties. This paper conducts a series of numerical simulations to study the proppant placement in branch fractures, aiming to optimize the proppant injection schemes. The results show: ① The rougher the fracture walls are, the more frequently the proppants collide with the walls, which reduces the settling velocity of the proppants but enhances the migration capacity. ② At large included angles between the main and branch fractures, a greater centrifugal force is required for the proppant to change direction, making it harder to enter the branch fracture.③ Smaller proppant particles result in weaker settling tendencies, making effective accumulation difficult. Larger proppant particles settle quickly upon entering the fracture and accumulate significantly at the entrances of both the main and branch fractures. ④ If the proppant density is too low, effective sand dunes cannot form in the main and branch fractures. ⑤ A greater fracturing fluid velocity generates a greater drag force on the proppants, which facilitates proppant entry into the branch fracture and the formation of an effective sand dune. Both the main and branch fractures have relatively high sand concentrations. An appropriate increase in viscosity favors proppant entry into branch fractures. However, a high viscosity increases the flow resistance, causing the proppant-laden fluid to favor the main fracture.