Research on Cementable Prefluid to Improve Cementing Quality at Coalbed Methane Well Interfaces

In the context of coalbed methane development, the boreholes within coal and rock strata exhibit irregularities, and it is challenging to ensure the centralization of casings. As a result, it is arduous to guarantee the displacement efficiency. Additionally, the coal and rock segments possess a strong lipophilic property, which poses a significant obstacle to enhancing the cementing quality at the secondary interface. To address these issues, this study is grounded in the multi-component synergistic hydration mechanism of silico-alumino based cementitious materials and the penetration and wetting mechanism of surfactants. By developing key additives such as novel prefluid enhancement materials and highly efficient wetting and flushing agents, a cementable prefluid system integrating multiple functions, including inter-layer isolation, high-efficiency flushing, and improved cementation, has been formulated. Performance evaluation experiments demonstrate that the cementable prefluid exhibits excellent construction safety. The flushing efficiency for on-site drilling fluids can reach up to 98%. When compared with conventional prefluid, after being mixed with cement slurries and drilling fluids, it can effectively increase the strength of the mixed slurry. Specifically, the interface cementing strength is enhanced by more than twofold. Microscopic mechanism analysis reveals that the cementable prefluid facilitates the improvement of the microscopic morphology of hydration products at the interface between cement and coal-rock cores, and promotes the formation of C-S-H gel products. This cementable prefluid can effectively enhance the cementing quality at the secondary interface during well cementing, thereby providing technical support for the high- quality development of coalbed methane.