Transp Porous Med (2012) 94:795–815 DOI 10.1007/s11242-012-0025-x Analytical Model for CO 2 Injection into Brine Aquifers-Containing Residual CH 4 Seyyed Abolfazl Hosseini · Simon A. Mathias · Farzam Javadpour Received: 15 February 2012 / Accepted: 18 May 2012 / Published online: 12 June 2012 © Springer Science+Business Media B.V. 2012 Abstract During CO 2 injection into brine aquifers-containing residual and/or dissolved CH 4 , three distinct regions develop: (1) a single-phase, dry-out region around the well-bore filled with pure supercritical CO 2 ; (2) a two-phase, two-component system containing CO 2 and brine; and (3) a two-phase, two-component system containing CH 4 , and brine. This article extends an existing analytical solution, for pressure buildup during CO 2 injection into brine aquifers, by incorporating dissolved and/or residual CH 4 . In this way, the solution additionally accounts for partial miscibility of the CO 2 –CH 4 –brine system and the relative permeability hysteresis associated with historic imbibition of brine and current drainage due to CO 2 injection and CH 4 bank development. Comparison of the analytical solution results with commercial simulator, CMG-GEM, shows excellent agreement among a range of different scenarios. The presence of residual CH 4 in a brine aquifer summons two compet- ing phenomena, (1) reduction in relative permeability (phase interference), which increases pressure buildup by reducing total mobility, and (2) increase in bulk compressibility which decreases pressure buildup of the system. If initial CH 4 is dissolved (no free CH 4 ), these effects are not as important as they are in the residual gas scenario. Relative permeability hysteresis increased the CH 4 bank length (compared to non-hysteretic relative permeability), which led to further reduction in pressure buildup. The nature of relative permeability func- tions controls whether residual CH 4 is beneficial or disadvantageous to CO 2 storage capacity and injectivity in a candid brine aquifer. Keywords Pressure buildup · Residual methane · Hysteresis · Fractional flow · CMG-GEM S. A. Hosseini (B ) · F. Javadpour Bureau of Economic Geology, Jackson School of Geosciences, The University of Texas at Austin, Austin, TX, USA e-mail: seyyed.hosseini@beg.utexas.edu S. A. Mathias Department of Earth Sciences, Durham University, Durham, UK 123