A Numerical Study on CO2 Seepage from Offshore Geologic Storage Site

Abstract

The objective of the present study is to gain a fundamental understanding on CO2 behavior during the seepage from the geologic carbon sequestration site. To elucidate the seepage behavior in the marine sediment, CO2 bubble dynamics in partially saturated porous media was studied. Force balance on a CO2 bubble in porous media was calculated by considering buoyancy force, surface tension effect and drag force. To consider the effect of porosity, permeability and wetting fluid saturation on ascent of CO2 in porous media, a new surface tension force model was studied. Based on the calculation results, the bubble rising velocity showed strong dependency on porosity and grain diameter. But there was negligible permeability effect. The developed model showed different calculation results with correction factor of force balance. There is no agreement in previous researches whether the escaped CO2 bubble from the marine sediment can be released to the atmosphere or not. To understand the CO2 bubble behavior in the water column, we calculated the dissolution of CO2 bubble in sea water. A molecular diffusion and a convective mass transfer of CO2 bubble were calculated by considering offshore environmental conditions during the dissolution. Based on the calculation results, the bubble dissolution rate showed strong dependency on the initial bubble diameter and bubble rising velocity.