Eliminating Buoyant Migration of Sequestered CO2 Through Surface Dissolution: Implementation Costs and Technical Challenges

Abstract

Summary Sequestration of carbon dioxide (CO2) in geologic formations will be part of any substantive campaign to mitigate greenhouse gas emissions. The risk of leakage from the target formation must be weighed against economic feasibilities for this technology to gain stakeholder acceptance. The standard approach to large-scale geologic sequestration into saline aquifers assumes that CO2 will be injected as a bulk phase. In this case, the primary driver for leakage is the buoyancy of CO2 under typical deep-reservoir conditions (depths > 2,600 ft or 800 m). Investigating alternative approaches that use inherently safe trapping mechanisms can help to characterize the price of reducing the risk of leakage. In this paper, we examine a process in which CO2 is dissolved in brine before injection into deep subsurface formations. The CO2-laden brine is slightly denser than brine containing no CO2, so the complete dissolution of all CO2 into brine at the surface before injection will eliminate the risk of buoyancy-driven leakage. The process considered here involves dissolving CO2 at surface facilities. We determine the capital costs for the additional facilities and compare them the capital costs for injecting bulk-phase CO2. We also estimate the power requirements to determine the additional operating costs. The additional capital and operating costs can be regarded as the price of this form of risk reduction. Comparing this alternative to the standard, we find that an additional power consumption of 3 to 9% of the power plant capacity will be required, and the capital costs will increase by approximately 60%. Brine is required at rates of millions of barrels per day and would be lifted from the target aquifer. The bulk volume of the aquifer is on the order of a hundred million acre-ft for reasonable power plant sizes (250 to 1,000 MW) and for reasonable injection periods (30 to 50 years). Although this alternative results in higher costs, surface dissolution may be attractive when the costs of monitoring or ensuring against buoyancy-driven CO2 leakage exceed these additional costs.