Hydrate prevention based on convection and diffusion in alternate injection wells of carbon dioxide and water

To prevent the formation of frozen hydrate blocks with the alternative injection of supercritical carbon dioxide and water after shut-in, the upper and lower interfaces of the frozen block sections in the injection well bore are calculated based on the temperature–pressure curves of the injection well and the hydrate phase equilibrium. The results show that for wells in which water and carbon dioxide are injected alternately, hydrate will be produced in the well bore after shut-in. the lower interfaces of the hydrate freeze plug in the well bore is above 141.36 m. Hydrate inhibitors can effectively prevent hydrate formation in wellbores, and the limit concentrations of methanol, ethanol, and ethylene glycol to inhibit hydrate freezing and blockage are 40%, 60%, 60%, respectively. In the initial state, there is a interface between the inhibitor and the formation water. The two-phase interface is blurred, and the inhibitor concentration in the upper part decreases when the wells have been shut for days. As the close-in time increased, the effective distance of action of the inhibitor decreased. The range of shut-in was 50–300 days, and the safety distance of the inhibitor should be controlled from 54 to 127 m below the frozen and blocked sections.