Sealing Ability of Expansive Consolidation Materials in Centimeter-Level Width Fractures

To address the severe lost circulation challenges in shallow fractured formations with centimeter-scale fracture widths and vuggy structures, this study developed a novel gel plugging material (CPM series) composed of water-absorbing/swelling components (e.g., polyacrylamide), a glyoxal cross-linker, and inert skeleton materials. The sealing performance of the material was systematically evaluated. The plugging mechanism under high-pressure flushing conditions was investigated with a custom-designed simulation device capable of replicating centimeter-scale fractures. The results showed that the optimized formula CPM-2 (water absorption component at 50%, cross-linking agent at 15%, and inert material at 35%) had the best comprehensive performance. The material demonstrated a water absorption rate of 700%, retaining a swelling ratio of 580% even in a 5% brine solution. The shear strength was 2.13 MPa (5 MPa normal stress). The maximum pressure-bearing capacity of the plugging body formed by the material in the simulated wedge seam and step seam was 5.1 MPa, and the pressure-bearing capacity increased with the increase of the temperature. The plugging body formed an interpenetrating network skeleton through water absorption and swelling, exhibiting a three-stage evolution of water absorption expansion–plastic–densification strengthening during compaction. Failure in wedge-shaped fractures primarily occurred via extrusion at the outlet, while stepped fractures experienced multi-stage, step-by-step breakdown at the fracture tips. In comparison to traditional bridging materials, this gel material solves the problems of particle size mismatch and scouring failure in centimeter-scale fractures through a rapid phase transition (achieving 85% expansion within 20 min) and adaptive filling capability. The new gel material provides a new solution for managing severe lost circulation in shallow fractured reservoirs, demonstrating a significant value for engineering applications. Furthermore, with laboratory plugging experiments conducted specifically for centimeter-scale fracture widths, this study provides a theoretical basis for the engineering design of plugging operations targeting fractures of centimeter-scale width.