Experimental investigation of carbon dioxide trapping due to capillary retention in deep saline aquifers.

摘要

Carbon dioxide (CO2) is by far the most significant greenhouse gas released by human activities through fossil fuel combustion. In order to minimize CO2 emissions to the atmosphere, sequestration of CO 2 in underground geological formations has been considered the most promising alternative to control greenhouse effects. In particular, deep saline aquifers are prime candidates for CO2 sequestration due to their large potential storage capacity and common occurrence. CO2 sequestration in deep saline aquifers can be achieved by several trapping mechanisms which are generally categorized as structural, dissolution, mineral and capillary trapping. Capillary trapping is a physical mechanism by which CO2 is naturally immobilized in the pore spaces of aquifer rocks during geologic carbon sequestration operations, and thus a key aspect of estimating geologic storage potential. It is an important, yet poorly understood trapping mechanism, primarily because of the lack of well characterized, laboratory or field data that could lead to a better understanding of the physical mechanism associated with capillary retention of CO2 in geological media.;Here, we studied capillary trapping of supercritical carbon dioxide (scCO 2), and the effect of initial scCO2 saturation and flow rate on the storage/trapping potential of Berea sandstone. We performed two-phase, scCO2-brine displacements in two sequential drainage-imbibition core flood cycles to quantify end saturations of scCO2 with the aid of micro-computed tomography imaging. Drainage I led to an average initial scCO2 saturation of 45% after scCO2 injection, and Imbibition I resulted in an average residual scCO2 saturation of 26% after brine injection. In comparison, Drainage II and Imbibition II were performed at higher flow rates and yielded average initial and residual scCO2 saturations of 61% and 31%, respectively. We also analyzed pore size distribution to estimate primary capillary pressure characteristics of the samples under investigation. Overall, we concluded that the initial scCO2 saturation influences the residual scCO2 saturation to a greater extent than the rate of imbibition and therefore, it is a dominant factor in determining the amount of CO2 that can be geologically stored.;Our study contributes to the research of CO2 capillary trapping in saline aquifers by proposing experimental methods that can mimic deep saline aquifers conditions in the lab, by investigating pore size distribution with high resolution X-ray imaging and, most important, by quantifying the capacity of capillary trapping of CO2 in a brine-CO2-rock system.