Pore-scale simulation of density-driven convection in fractured porous media during geological CO2 sequestration

Cheng Chen, Dongxiao Zhang

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Abstract

Global warming is attributed to the excessive emission of greenhouse gases, one of whose main components is carbon dioxide (CO2). A promising long-term solution for mitigating global warming is geological CO2 sequestration, which is the capture and storage of enormous amounts of CO 2 in underground reservoirs in order to reduce CO2 build up in the atmosphere. In this study, a pore-scale lattice Boltzmann method was used to simulate density-driven convection in a porous medium with a fracture, to study geological CO2 sequestration in deep saline aquifers. The CO2-brine interface was located at the top of the domain. Both fracture width and body force were varied to generate different Ra numbers in order to investigate the effect of Ra on the convection. All simulated data can be fitted by the same trend, implying that the characteristic length of the system was dominated by the fracture width. When Ra was high enough, increasing Ra did not reduce the critical time for the onset of instability apparently. Also, it did not increase the maximum peak vertical velocity noticeably. Therefore, there existed asymptotic values for the critical time and maximum peak vertical velocity. With high Ra numbers, the high-frequency oscillation of turbulence greatly enhanced the dissolution of CO2 into brine. After the onset of convective instability, the brine with a high CO2 concentration intruded into the underlying unaffected brine, which increased the interfacial area between the CO2-rich brine and unaffected brine, and consequently favored the migration of CO2 into the fracture and porous medium. This study is the first pore-scale one investigating density-driven convection during geological CO2 sequestration in deep saline aquifers, whereas most existing research is focused on the field scale and the dissolved CO2 concentration at the top boundary is usually assumed to be saturated.

Original languageEnglish
Article numberW11527
JournalWater Resources Research
Volume46
Issue number11
DOIs
StatePublished - 2010

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