Effect of proppant sizes and injection modes on proppant transportation and distribution in the tortuous fracture model

Particle-fluid transport and placement mechanism in tortuous fracture played a crucial role in unconventional reservoirs. Currently, most studies focused on mono-size proppant with fluid transport processes in tortuous fractures. However, the mixture-size proppant with fluid movement mechanism in tortuous fracture was still uncommon. Therefore, this study designed and applied a series of experiments with a physical analog model of a tortuous fracture with 120° and 90°-angled bends and combined high-speed camera-based equipment. This experimental system was used to track different-mixture-sized proppant particle motion trajectories for a series of proppant injection schemes; The following conclusions were drawn from this study:1. The pile-up processes mechanism in all investigated schemes were similar and could be reduced to four main stages. 2. The packing structure at both sides of the fracture wall had different variation rates, which were controlled by the mix ratio (change from 1:1–1:5) of proppant size. 3. Some new packing patterns, such as Zebra Stripe, had occurred, controlled by the different proppant injection sequences. 4. Small-sized mono-proppant (30/50 mesh) had the highest transport efficiency in the tortuous fracture, followed by the mixed-sized multi-proppant (10/20 mesh:30/50 mesh), large-sized proppant (10/20 mesh) was the worst. 5. An optimized alternating injection mode was recommended as injecting small-sized proppant first (30/50 mesh) and followed by mixed-sized multi-proppant (10/20 mesh:30/50 mesh), which could contribute to obtaining the optimal both proppant packing height and travel distance in tortuous fracture.6. Two correlations were developed for predicting the proppant packing height and transportation distance.