Main control factor of hydrate generation during overflow well control period of deepwater drilling

At present, most scholars judge the hydrate generation based on the thermodynamic characteristics. However, in order to make a more accurate judgment, the characteristics of molecular dynamics should be considered. The hydrate formation in the wellhole is relatively slow. Even if the thermodynamic conditions for hydrate formation are met, it is inevitable to go through the hydrate nucleation and growth processes. Based on the wellhole multi-phase flow law during the overflow well control period of deepwater drilling, characteristics of thermodynamics and dynamics of hydrate, as well as micro-pore plate theory of hydrate membrane, this paper has researched the hydrate generation mechanism in the circulation, well shut-in and well killing during the overflow well control period, and analyzed the effects of different flow patterns on the hydrate generation. According to the research results, when the deepwater drilling overflow occurs, no hydrate will be generated if the throttle device is installed at the wellhead during the circulation period; during the well shut-in period, no hydrate blocking will be formed under bubble flow conditions, but formed at the wellhead under the slug flow conditions; during the well killing period, the hydrate generation will not pose great hazards to the wellhole.