Coupled heat and mass transfer model of gas migration during well cementing through a hydrate layer in deep-water regions

Abstract

During well cementing through a hydrate layer, hydrate dissociation occurs because of the heat generated during the cement hydration reaction, which causes gas migration into the wellbore. Given the shortcomings of extant studies, the present study proposes a coupled heat and mass transfer model to investigate the gas migration occurring during well cementing through a hydrate layer. The coupled model considers the complex interactions among the cement sheath thermal model, the hydrate layer thermal model, the multiphase flow in the hydrate layer, and the gas migration model in the cement sheath. The proposed models are validated through three experiments from literature, which exhibit good agreement with the proposed model. In addition, numerical simulations are conducted using a simulation well. According to the simulation results, the heat exchange between the cement sheath and hydrate layer leads to hydrate dissociation, which is the primary cause of gas migration. Gas migration results in a high casing pressure, which poses a serious threat to the safety of the workers in the future. Conclusions and suggestions are drawn from the case study, which can assist engineers to improve the safety of workers.