Numerical Simulation of CO2 Hydrate Formation in Subsea Sand When Salinity is Considered

Abstract The objective of this study is to develop a mathematical CO2 phase equilibrium model for saline condition to integrate its effects within the numerical simulation framework for CO2 hydrate formation in undersea sand layers at the reservoir scale. Also, we evaluate the potential of CO2 hydrate storage under saline conditions for practical requirements. A salinity-dependent phase equilibrium curve for CO2 hydrate was created by fitting the experimental results of previous studies in the literature. An advection-diffusion equation solver was added in the reservoir-scale simulation method to account for salinity transfer, because salinity is increased when pure water is used to form hydrate. The model simulates CO2 storage with injecting liquid CO2 into the subsurface at specified depths on the reservoir scale. Since salinity works as an inhibitor for hydrate formation, the simulation has variations in parameters such as absolute permeability, gravel porosity etc. to perform as successful shielding of liquid CO2. After incorporating the salinity-dependent phase equilibrium curve, we found that the conditions for CO2 hydrate formation to store CO2 safely become more limited. Specifically, it requires lower temperatures and higher pressures when the other conditions are the same, meaning deeper storage point and lower seafloor temperatures. Additionally, the formation rate of CO2 hydrate was also affected. After verifying the impact of salinity on CO2 hydrate storage, we conducted a series of simulations under various conditions under saline conditions. It was observed that CO2 could be successfully stored under certain conditions, while under the others, it could not achieve the safe storage.