ORIGINAL ARTICLE Factors affecting CO 2 storage capacity and efficiency with water withdrawal in shallow saline aquifers Fang Yang • Baojun Bai • Shari Dunn-Norman • Runar Nygaard • Andreas Eckert Received: 31 August 2012 / Accepted: 19 March 2013 Ó Springer-Verlag Berlin Heidelberg 2013 Abstract Carbon sequestration in shallow aquifers can be facilitated by water withdrawal. The factors that optimize the injection/withdrawal balance to minimize potential envi- ronmental impacts have been studied, including reservoir size, well pattern, injection rate, reservoir heterogeneity, anisotropy ratio, and permeability sequence. The effects of these factors on CO 2 storage capacity and efficiency were studied using a compositional simulator Computer Modeling Group-General Equation of State Model, which modeled features including residual gas trapping, CO 2 solubility, and mineralization reactions. Two terms, storage efficiency and CO 2 relative breakthrough time, were introduced to better describe the problem. The simulation results show that simultaneous water withdrawal during CO 2 injection greatly improves CO 2 storage capacity and efficiency. A certain degree of heterogeneity or anisotropy benefits CO 2 storage. A high injection rate favors storage capacity, but reduces the storage efficiency and CO 2 breakthrough time, which in turn limits the total amount of CO 2 injected. Keywords CO 2 sequestration  Reservoir heterogeneity  Shallow aquifer  Storage capacity  Storage efficiency  Water withdrawal Introduction Carbon sequestration in saline aquifers is a viable option to reduce the CO 2 concentration in the atmosphere. It has the advantages of large storage capacity and easy access to existing large CO 2 point sources (Baklid et al. 1996; Metz et al. 2005; Bentham and Kirby 2005; Sengul 2006; Yang et al. 2010). Most studies performed thus far have been focused on formations deeper than 800 m to keep CO 2 in its supercritical phase and thus store more CO 2 (Gibson- Poole et al. 2007). Only two field cases studied aquifers less than 800 m, but no gaseous CO 2 occurred in both cases: first, the Utsira Formation at approximately 800 m depth in the Sleipner vest CO 2 disposal project in the Norwegian sector of the North sea, and second, the Stutt- gart Formation at 730 m depth in the European CO2SINK project in Ketzin, Northern Germany (Baklid et al. 1996; Huiter and Berge 2007). The injection of CO 2 in shallow aquifers has been gen- erally ignored due to some perceived concerns. One of the main concerns is that at shallow depths, the amount of CO 2 can be injected is low because CO 2 occurs in a gaseous or less dense liquid phase. Another concern is the CO 2 override at the top of the aquifers and the unstable phase change with depth, both of which increase the leakage risk. A final con- cern is that the injected CO 2 may contaminate shallow groundwater resources. However, with careful site selection, shallow aquifers could still be potential storage sites because of their broad distribution, considerable capacity, and low storage cost associated with the shallow depth. In 2005, the US Department of Energy awarded a shallow carbon sequestration demonstration project that has been investi- gating the feasibility of sequestering CO 2 in a shallow saline aquifer in Missouri (National Energy Technology Labora- tory (NETL) 2010). Los Alamos National Laboratory is also studying a natural analog site to quantify and understand CO 2 migration in a shallow aquifer (McNemar 2009). Many shallow aquifers are part of widespread hydro- logic systems, which can act as closed boundary reservoirs. F. Yang  B. Bai (&)  S. Dunn-Norman  R. Nygaard  A. Eckert Missouri University of Science and Technology, 161 McNutt, 1400 N. Bishop, Rolla, MO 65401, USA e-mail: baib@mst.edu 123 Environ Earth Sci DOI 10.1007/s12665-013-2430-z