Analysis of U‐tube sampling data based on modeling of CO 2 injection into CH 4 saturated aquifers

When CO 2 is injected into aquifers in a hydrocarbon basin, either for CO 2 geological storage or enhanced oil recovery (EOR), these aquifers are most likely saturated with CH 4 . Dissolving CO 2 into the aqueous phase will cause CH 4 to come out of the aqueous phase and partitioning into the CO 2 ‐rich non‐aqueous phase under static conditions. It is not well understood how this process develops under flow conditions, which is the subject of this paper. Although CH 4 solubility in brine is low under the subsurface conditions, the effects of CH 4 dissolved in saline aquifers cannot be ignored for CO 2 sequestration projects. This is due to the changes of the phase behavior, capillary pressure, and relative permeability which has already been recognized by previous studies. This work couples a recently developed thermodynamic model of CO 2 ‐CH 4 ‐brine system with an industrial reservoir simulator and applies it in the simulation of CO 2 injection into a CH 4 saturated aquifer. Simulation results are compared to field observations from U‐tube sampling and used to provide reasonable explanations. From the simulations, the compositions in U‐tube samples are influenced by U‐tube inlet position, perforation and the reservoir (geological) properties. With the explanations, the U‐tube observations of gas samples can be well matched by numerical simulation results.© 2014 Society of Chemical Industry and John Wiley & Sons, Ltd