Migration and sedimentation of proppant and its influencing factors in a visual plate fracture model

Hydraulic fracturing technology is the main method used to form high-conductivity fracture networks in unconventional oil and gas reservoirs, and the effective filling of quartz sand proppant in the fracture network is key to its successful implementation. Conventional experiments on the evaluation of sand carrying migration are mainly based on the migration and sedimentation law of a single-mesh proppant in the main fracture; the results obtained are inconsistent with the field observations. To improve our understanding of the migration and sedimentation law of the proppant in the main and branch fractures, in this study, the influences of injection time, injection rate, fracturing fluid viscosity, and proppant combination type on the migration and sedimentation law of a proppant in single and branch fractures were analyzed based on the injection parameters of the sand-carrying fracturing fluid obtained using a similarity criterion through a visual large-scale parallel-plate fracture model system built indoors. The results showed that the rapid accumulation stage of the proppant in the fracture is during the injection time of 5–10 min; the injection rate affected the accumulation area and height of the proppant to a certain extent but had little effect on the final sand dike morphology. A low viscosity of the fracturing fluid was not conducive to the sedimentation of the proppant in the branch fractures; an excessively high fracturing fluid viscosity was not conducive to the sedimentation of the proppant in both the main and branch fractures. When the fracture morphology is single, the viscosity of the fracturing fluid is recommended to be between 30 and 60 mPa·s. When the fracture morphology is complex, the recommended value is between 40 and 50 mPa·s. Taking the migration and sedimentation laws of the proppant in the main fracture as an example, the flow of fracturing fluid in the fracture after the formation of a stable sand dike could be divided into five regions: ① inlet scour zone; ② buffer zone; ③ sand dike stable transition zone; ④ sand dike stability zone; and ⑤ outlet scour zone. The higher the large mesh proppant ratio used in the fracturing fluid, the lower the total area ratio of the corresponding sand dike; however, the proppant sedimentation ratio in the branch fracture increases. This study enriches and improves the relevant theoretical research on the migration and sedimentation of proppants and has a certain effect on improving the success rate of the hydraulic fracturing technology applied to unconventional oil and gas reservoirs.