In Situ CH4–CO2 Dispersion Measurements in Rock Cores

Injection of carbon dioxide (CO2) into a natural gas reservoir is an emerging technology for enhanced natural gas recovery (EGR) realizing increased natural gas production whilst sequestering the injected CO2. However, given that CO2 and natural gas are completely miscible, simulation of potential EGR scenarios is required to determine when breakthrough of CO2 will occur at the natural gas production wells. For such reservoir simulations to be reliable (independent of software used), accurate dispersion data between CO2 and natural gas at relevant reservoir conditions are required. To this end, we apply one-dimensional magnetic resonance imaging (MRI) to quantify this dispersion process in situ in both sandstone and carbonate rock cores. Specifically we apply the SPRITE MRI sequence (Balcom et al. in J Magn Reson Ser A 123(1):131–134, 1996. https://doi.org/10.1006/jmra.1996.0225) to facilitate quantitative axial profiles of methane (CH4) content during core flooding processes between CO2 and CH4. Simultaneously we measure, using infrared, the effluent CO2 and CH4 concentrations enabling ex situ dispersion measurements. Via comparison with the corresponding MRI data, the erroneous contributions to dispersion from entry/exit effects and mixing in piping to and from the rock core holder are quantified. Furthermore, we demonstrate how nuclear magnetic resonance T2 measurements can be uniquely used to probe the pore size occupancy of the CH4 during the core flooding process.