Residual Trapping in Simultaneous Injection of CO2 and Brine in Saline Aquifers

Abstract

Disposal of carbon dioxide (CO2) into saline aquifers appears to be one of the best CO2 sequestration options in terms of capacity and technology. Injected CO2 migrates invariably upwards due to buoyancy forces. In most common aquifer settings, the density difference between CO2 and brine is sufficiently high that gravity force is a pre-dominant factor that controls the upward migration of a CO2 plume. Any scheme that can retard the vertical movement of the plume can enhance the entrapment of the injected CO2 and reduce the risk of potential leakage back into the atmosphere. An appealing scheme for sequestration projects in aquifers involves simultaneous injection of brine and CO2 from vertical wells, where brine is injected in the upper part of injection well(s) and CO2 is injected in the lower portion of the well(s). This scheme inhibits the rapid upward migration of CO2, since the injected CO2 is forced to move horizontally during the injection period. The horizontal displacement increases the volume of the aquifer that is contacted by the injected CO2, and hence, the residual entrapment of the CO2-rich phase can be increased significantly. The upward migration of CO2 away from the injector occurs predominantly in a counter-current flow mode. In this study, we compare residual entrapment of CO2 for the simultaneous injection of CO2 and brine in four different aquifer settings. The four aquifer settings are selected from the classification scheme proposed by Kopp et al. (2009). It is shown that for large gravity numbers, there is a significant difference between the four aquifer settings in terms of storage capacity with warm aquifers having the least storage capacity and cold aquifers providing the largest storage capacity. The distance at which segregation of brine and CO2 is complete, not only depends on the gravity number, but also on the aquifer setting. It is indicated that residual entrapment of CO2 depends on brine injection rate and higher rates of brine (lower gravity number) increase the fraction of CO2 that is trapped in a residual phase. Finally, we demonstrate that the reduction in the relative permeability of both phases, due to counter-current flow, has a major impact on the sweep efficiency of the injected CO2 and hence impact both the distance traveled before full segregation and the level of residual entrapment.

A review of developments in carbon dioxide storage

“…CO2 storage in saline aquifers is considered as one of the most feasible technology deployment options [37][38][39][40], probably because it provides the largest potential storage volume [36]. In addition, the majority of saline aquifers are currently not suitable for other synergic or conflicting applications [41], particularly in the framework of densely populated countries [42].…”

Interfacial tension and wettability alteration during hydrogen and carbon dioxide storage in depleted gas reservoirs

“…Storing CO 2 in saline aquifers is effective due to its high storage potential and limited conflicting uses. However, the lack of infrastructure makes many such aquifers economically unattractive for water storage [29][30][31][32][33][34][35][36][37] .…”

A Comprehensive Review on Carbon Dioxide Sequestration Methods

“…Several researchers have acknowledged that storing CO 2 in deep salty aquifers represents one of the most successful strategies for reducing CO 2 in the atmosphere (Li et al, [19]) (Javaheri et al, [20]), (Yang et al, [21]), (Frerichs et al, [22]), and (Burnol et al, [23]), due to its already available technological and significant possible storage capacity, (Bachu et al, [14]). However, most saline aquifers are presently unsuitable for other synergistic or competing uses (Trémosa et al,[24]), especially in highly populated nations (Procesi et al,[25]; Quattrocchi et al, [26]).…”