Field-Scale Numerical Investigation of Proppant Transport among Multicluster Hydraulic Fractures

Abstract

Summary Plug-and-perforation (P-n-P) completion has been widely used in horizontal wells for the development of unconventional reservoirs. In the field, uneven proppant distribution among different fractures within a fracturing stage has been frequently observed in P-n-P treatments, leaving a large portion of reservoir volume understimulated. In this paper, an efficient 3D multiphase particle-in-cell (MP-PIC) method has been used to simulate proppant transport among multiple fractures (fracture near the heel, middle fracture, fracture near the toe) at the field scale. This work studies the fundamental physics of the proppant transport process and reveals the mechanisms of uneven proppant placement, giving strategies to improve the proppant placement. Before applying the MP-PIC method to field-scale problems, we conducted indoor experiments to validate the model. The simulation results show an excellent agreement with the vertical slot experimental results. After model validation, we used the MP-PIC method to directly simulate the field process of proppant transport, involving slurry transport from the wellbore through perforation holes and finally into fractures. A base case with three fractures in a stage was first established to calculate the percentage of proppant mass distribution in each fracture. Then, we performed the sensitivity analysis of both proppant size and injection rate to investigate their effects on proppant placement. The results reveal that all the cases tend to have a heel-biased proppant distribution among three fractures, which agrees with the field observations. There are two reasons for the heel-biased proppant distribution. First, at the very beginning of the injection, more proppants tend to flow toward the toe side because of large momentum. As more and more proppants move to the toe side, the concentration near the toe side gradually increases, which adds flow resistance to the newly injected proppants. Therefore, most newly injected proppants will go to the first fracture. The second reason comes from the fracture geometry. Because the first fracture has the largest fracture width among three fractures, it has the smallest flow resistance for proppant transport. More slurry will flow into the first fracture. Apart from giving explanations for the heel-biased distribution, we also suggest some strategies to improve the proppant distribution. The sensitivity analysis shows that the strong heel-biased proppant distribution can be mitigated by optimizing the proppant size and injection rate. Our study for the first time conducts a field-scale numerical investigation of proppant transport in the wellbore-fracture system during P-n-P treatments. The results can provide us with more insights into the optimization of fracture design in field practice.