Study on the factors influencing CO2 hydrate sequestration in CH4 hydrate-bearing reservoirs

CO2 sequestration as hydrates beneath the seafloor is a promising strategy to mitigate carbon emissions. However, in marine environments overlapping hydrate stability zones (HSZs) for CO2 and CH4 complicate the process since pre-existing CH4 hydrates can affect outcomes. This study employs the CMG-STARS simulator to compare CO2 sequestration at various stratigraphic positions by evaluating the impacts of geological parameters (porosity, permeability, formation compressibility) and injection parameters (temperature, rate, maximum bottom-hole pressure) on cumulative injection volume and hydrate conversion ratio. Results indicate that sequestering CO2 beneath CH4 reservoirs yields higher sequestration capacity, while injection above CH4 hydrates provides a greater hydrate conversion ratio. For sequestration above CH4 hydrate layers, injection temperature and permeability strongly influence cumulative CO2 injection volume; higher temperatures delay hydrate formation to allow more CO2 flow (correlation: 0.86), and higher permeability enhances fluid migration (correlation: 0.36). Similarly, lower injection temperatures and porosity favor higher hydrate conversion ratios. Lower temperatures promote hydrate formation (correlation: −0.75), while lower porosity improves heat exchange (correlation: −0.46). Formation compressibility, injection rate, and bottom-hole pressure have lesser impacts. These findings provide insights for optimizing CO2 sequestration strategies in CH4 hydrate-bearing reservoirs.