Migration and settlement laws of proppant in multi-scale fractures during the fracturing in the unconventional reservoirs

The effective proppant packing in fractures is crucial to the formation of high-conductivity fracture channels during hydraulic fracturing. At present, the researches on proppant migration and settlement laws in fractures are mainly performed by means of physical experiment or numerical simulation, and mainly focus on the results of proppant settlement, but with less emphasis on the mechanisms of proppant migration and settlement. To gain further insights into proppant migration and settlement laws in fractures, this paper combines experiment with numerical simulation to study the influences of proppant size, injection velocity and fracturing fluid viscosity on the migration and settlement behaviors of proppant in single and cross fractures. The following research results are obtained. First, proppant size controls the distribution of particle migration mainly by influencing settlement angles. The larger the proppant size, the larger the settlement angle and the shorter the migration distance. Second, injection velocity has a great influence on the shape of the sand dune. When the injection velocity increases from 0.2 m/s to 1.0 m/s, the effective supporting area ratio and maximum height of sand dune in a single fracture decrease significantly, while the effective supporting area ratio of sand dune in a branch fracture increases by 34.3%, showing an opposite trend to that in a single fracture. Third, fracturing fluid viscosity mainly affects the sand-carrying capacity of the fluid. With the increase of fracturing fluid viscosity, the effective supporting area ratio and maximum height of sand dune decrease by 8.4% and 6.1 cm in the main fracture, but increases first and then decreases in the branch fracture. In conclusion, proppant migration in branch fractures and main fractures often shows different laws under the influence of operation factors. The research results will further improve the theoretical understanding of hydraulic fracturing and provide theoretical support for the optimization of fracturing operation design. © 2024 Natural Gas Industry Journal Agency. All rights reserved.