Coupling Mechanisms between Cement Hydration and Permafrost During Well Construction in the Arctic Region

During well construction in the Arctic region, the coupling mechanisms between cement hydration and permafrost may lead to unpredictable thaw of permafrost, thereby threatening the wellbore stability and ecological environment in the Arctic. In the present study, thermal kinetics of cement hydration under different temperatures are studied experimentally, and the hydration kinetics model is proposed. Then the coupled model is proposed considering the complicated physicochemical interactions between cement and permafrost. In the proposed model, the hydration reaction of cement, phase change of the permafrost, and the water migration in permafrost are considered. Moreover, the coupling mechanisms between cement and permafrost are studied by numerical simulations. Temporal and spatial distribution of properties in permafrost are obtained including the temperature, and the water/ice content. The obtained results shows an obvious temperature increase and permafrost thaw due to cement hydration heat. Moreover, it is found that low-temperature ambient in permafrost slows down the cement hydration process. During the permafrost thaw, dissociated water migrates from the warm area near the cement to the far cold area. Compared with the hydration process, heat diffusion in permafrost takes a much longer period. Thus, continuous attention should be paid to threaten posed by permafrost thaw for a long period after well cementing.