Supercritical CO2 sweeping efficiency in shale for enhanced oil recovery and CO2 storage

We conducted in-depth investigation of the process and controls of CO₂ injection for scCO₂/oil miscible displacement for enhanced oil recovery and CO₂ storage in shale samples with different wettability. An integrated multiscale imaging and injection under different boundary conditions technique was used. Results of this study filled the knowledge gap on how injected CO₂ flows in the shale matrix and how the geological and petrophysical properties, including pore wettability, pore network distribution, connectivity, and heterogeneity, controls the flow. We gained important insights on specific mechanisms of scCO₂ oil recovery, the impact of boundary conditions on the CO₂/oil displacement, and the effect of heterogeneity of pore wettability on the formation of preferential scCO₂ flow paths. These observations and findings have important implications on the challenges and opportunities for optimal engineering design for further enhancement of oil recovery and CO₂ storage through CO₂ injection in unconventional reservoirs.

Depleted unconventional reservoirs after EOR can also provide a valuable addition to the carbon storage capacities in saline aquifers and depleted conventional reservoirs. The current rate of CO₂ storage is only around 56 Megatons (MT), which is far below the global target of ~170 Gigatons (GT) by 2050, requiring storage of 5 – 8 GT per annum to reach net-zero by 2050. As a result, all potential options must be explored. Our recent study indicates a significant storage capacity potential in unconventional reservoirs in the US. Another expected benefit is the ability to reuse existing infrastructure for CO₂ injection and monitoring, which can greatly reduce upfront investment costs. We proposed a new injection mode of "huff-and-huff" and a rotational pattern that can be used in many adjacent wells (e.g., 10-100) during the same time window in unconventional reservoirs. This injection pattern can be combined with direct air capture or other transportation methods. Further investigation on the CO₂ injectivity, the effect of heterogeneity on CO₂-gas, water or oil displacement, CO₂ adsorption, and well integrity for CO₂ injection is needed for field application and deployment.