Mechanisms of Efficient Proppant Placement in Fractures via Proppant-Fiber Cluster Transport

Summary

To address the problems of limited proppant transport distance and insufficient placement height in unconventional reservoir hydraulic fracturing, a visualized experimental study of fiber-assisted proppant transport in slit fractures was conducted to investigate the formation, transport, and deposition mechanisms of proppant-fiber clusters. The effects of key operational parameters, including fluid viscosity, sand/liquid ratio, proppant particle size, fiber length, fiber concentration, and structural stabilizer concentration, on cluster characteristic size, packing porosity, and placement height were systematically analyzed. The results show that proppant-fiber clusters are mainly formed during the post-shut-in sedimentation stage through orthokinetic flocculation under the effect of intermaterial adhesion interactions. Compared with conventional proppant transport, the porous cluster structure changes the sedimentation and packing behavior of proppants, thereby improving fracture placement range and effective propped volume. High sand/liquid ratio and high fiber concentration are beneficial for enlarging cluster characteristic size and increasing placement height, whereas moderate fluid viscosity (9–12 mPa·s), short fibers (3 mm), and the addition of structural stabilizer promote the formation of high-porosity accumulation structures. Although increasing fiber concentration can significantly improve placement performance, the enhancement efficiency gradually decreases at high concentration conditions. For main fractures, the favorable parameter combination for efficient placement is as follows: a sand/liquid ratio of 20%, a slickwater viscosity of 9–12 mPa·s, a fiber concentration of 0.5–0.7%, a fiber length of 3 mm, 70/140-mesh proppant, and a structural stabilizer concentration of 0.3%. For multiscale fracture networks, the introduction of fracture-stimulating agents enables the formation of deformable cluster-sand plugs, which improves the entry capability of cluster units into branch fractures and enhances fracture support effectiveness. The technology was successfully applied in shale gas wells of the Wujiaping Formation D1 platform and the Qiongzhusi Formation Z2 platform. On the D1 platform, Well 1 achieved 36.9% higher gas production per unit pressure drop and 7.8% lower per-kilometer fracturing cost than the fiber-free Well 3, demonstrating its strong potential for field-scale application.