Research on Hydrate Formation Risk in the Wellbore of Deepwater Dual-Source Co-production

Hydrate reservoirs with underlying natural gas are currently considered to be the most promising hydrate reservoirs for commercial exploitation. However, during the production process, the temperature-pressure conditions and multiphase flow conditions after mixing are complex due to the differences in the physical parameters of each layer of fluid, and it is much more difficult to predict the secondary formation of hydrates. In order to accurately calculate the hydrate generation regions, a new prediction model of wellbore temperature and pressure field under the conditions of deepwater dual-source co-production was proposed, and the distribution pattern of the hydrate generation region in the wellbore was investigated based on this model. The results revealed that in the process of deepwater dual-source co-production, due to the influence of deepwater low-temperature environment, the section of gas line above the mudline had an extremely higher risk of hydrate formation. For the section of wellbore below the mudline, the inflow of relatively low-temperature fluid from the hydrate layer caused a sudden temperature drop in the wellbore, resulting in a corresponding increase in the risk of hydrate formation. Meanwhile, the larger the production rate of hydrate layer, the more obvious the temperature drop was. Hydrate production increased from 2 thousand m3/d to 300 thousand m3/d, temperature drop increased from 2.8 ℃ to 7.1 ℃, the hydrate generation region expanded from 200 m–1780 m to 20m-1900m. With the increase of shallow gas production rate, the temperature in the wellbore rose, the cooling effect of hydrate layer fluid weakened, and the risk of hydrate formation decreased accordingly. Shallow gas production increased from 10 thousand m3/d to 600 thousand m3/d, temperature drop decreased from 3.1 ℃ to 1.5 ℃, no hydrate generation below the mudline, and hydrate generation area above the mudline shifted upward from 180 m–1770 m to 0 m–690 m. The increased in shallow gas water content removed hydrate generation risk from wellbores below the mudline, but had little effect above the mudline. Reduced gas-liquid separation efficiency resulted in increased liquid production in the gas pipeline, a shift in the phase equilibrium curve toward lower temperatures, and a slight reduction in the risk of hydrate generation. The results of this paper can provide a reference for the prevention of secondary hydrate generation in the wellbore of deepwater dual-source co-production.