No abstract

Previous studies have shown that bulk CO 2 injection in deep saline aquifers supplies insufficient aquifer storage efficiency and causes excessive risk due to aquifer pressurization. To avoid pressurization, we propose to produce the same volume of brine as is injected as CO 2 in a CO 2 -brine displacement. Previous work showed that this increases the storage efficiency from 2% to 8%. However, this transforms the CO 2 storage problem into a brine disposal problem. Therefore, we propose to desalinate the native brine and inject the saturated brine into the same aquifer while producing additional brine to maintain voidage balance.A hypothetical case study using documented aquifer properties of the Woodbine aquifer in Texas indicates that the available volume is insufficient volume to store all of the CO 2 being generated by power plants in the vicinity for more than 14 years. However, the CO 2 -brine displacement increases storage efficiency enough to store the CO 2 produced for 84 years at the current rate of coal fired electric power generation. Using the reported brine salinity of the Woodbine aquifer, the energy requirements for CO 2 transport and injection, brine production and transport, desalination, and saturated brine injection are estimated consistent with assumptions about the location of injection and production wells, the desalination unit or units, and whether desalinated water can be used by the power plant or for other uses.While this approach may enable CO 2 storage, the high energy cost ranging from 7.5% to 16% of the total power generation capacity is not insignificant, and comes with significant land use implications for injection and production wells, pipelines, etc. The importance of these results cannot be overstated.

Previous studies have shown that bulk carbon dioxide (CO 2 ) injection in deep saline aquifers supplies insufficient aquifer storage efficiency and causes excessive risk because of aquifer pressurization. To avoid pressurization, we propose to produce the same volume of brine as is injected as CO 2 in a CO 2 /brine displacement. Two approaches to CO 2 /brine displacement are considered-an external brine-disposal strategy in which brine is disposed of into another formation such as oilfield brine and an internal saturated brine-injection strategy with which the produced brine is desalinated and reinjected into the same formation. The displacement strategies increase the storage efficiency from 0.48% for the bulk-injection case to more than 7%. A conceptual case study with documented aquifer properties of the Woodbine aquifer in Texas indicates that the available volume is sufficient to store all the CO 2 being generated by power plants in the vicinity for approximately 20 years only. However, the CO 2 /brine displacement increases storage efficiency enough to store the CO 2 produced for at least 240 years at the current rate of coal-fired electric-power generation. Sensitivity analyses on relative permeability, permeability, and temperature were conducted to see the effects of these reservoir parameters on storage efficiency.For bulk injection, increased permeability resulted in increased storage efficiency, but for the CO 2 /brine-displacement strategies, decreased permeability increased storage efficiency because this resulted in higher average pressure that increased CO 2 storage per unit of pore volume (PV) and increased CO 2 viscosity. Also, storage efficiencies for the displacement strategies were highly sensitive to relative permeability. There is an optimal CO 2 -injection temperature below which the formation-fracturing pressure is lowered and above which CO 2 breakthrough occurs for a smaller injection mass. The CO 2 /brine-displacement approach increased capital expenditures for additional wells and an operating expense for produced-brine disposal, but these additional costs are offset by increased CO 2 -storage efficiency at least 12 times that achieved by the bulk-injection strategy.

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