Robust NMR Examination of the Three-Phase Flow Dynamics of Carbon Geosequestration Combined with Enhanced Oil Recovery in Carbonate Formations

A net-zero strategy for counterbalancing anthropogenic carbon dioxide (CO2) emissions has become a key aspect in achieving the global decarbonization initiative by 2050. In particular, carbon geosequestration and enhanced oil recovery (EOR) in hydrocarbon reservoirs is a cost-effective strategy for attaining net-zero emissions. However, EOR and the ability to capture residual CO2 are greatly affected by the presence or absence of oil layers along with the pore size distribution and fluid displacement, which drastically impact the reservoir-scale flow. Thus, the present study makes systematic use of the versatile in situ two-dimensional (2D) nuclear magnetic resonance (NMR) T1–T2 imaging technique to visualize the fluid occupancy of the pore network in dolomite rock and uses the T1/T2 ratios to assess the physicochemical properties thereof, including the microscopic wettability with respect to the pore-space fluids, after each process step. Specifically, the T2 relaxation time is measured to demonstrate the displacement processes and to evaluate the trapping behavior and associated rock/fluid interactions at the pore level, which are closely correlated with the fluid flow behavior. Thus, in the tested water-wet dolomite, the strongest-wetting phase (i.e., water) is shown to occupy the smallest pores, where it is held by strong capillary forces, while the nonwetting CO2 phase occupies the large pores and the intermediate-wetting oil reside in the intermediate-sized pores. As a result, 16% of the residual CO2 trapped in large pores, while 71% of the oil is recovered, which is comparable to previous results obtained for analogue two-phase flow in water-wet dolomite samples, although some details differ and the displacements are noticeably complex. These findings have significant impacts on net-zero emissions, the budgets and storage capacities of CO2-EOR project schemes, and CO2 geosequestration. In the latter context, the present findings also greatly increase the geo-storage integrity over reservoir-scale implementations.