Analysis of CO2 Migration during Nanofluid-Based Supercritical CO2 Geological Storage in Saline Aquifers

Carbon dioxide (CO2) geological storage in deep saline aquifers is a key measure to mitigate global warming. However, it still faces a variety of technical challenges such as enhancing CO2 effective storage capacities. In this paper, a preliminary model is developed to simulate CO2 migration during nanofluid-based supercritical CO2 geological storage in saline aquifers. The main mechanisms, including Brownian motion, thermophoresis, thermal energy transfer, and interfacial tension, are included in the proposed conceptual model. Based on the high-resolution space-time conservation element and solution element (CE/SE) method, the model is used to simulate CO2 migration and distribution in the in-situ heterogeneous saline aquifer. It can be inferred that the involvement of nanoparticles decreases shear stresses opposing flow and enhances CO2 mobility in the flow boundary layer. In addition, nanoparticles increase shear stresses outside the boundary layer and retard CO2 velocity. These competitive mechanisms result in homogeneous migration of CO2 in the saline formation. One preliminary suggestion is that nanofluids enhance homogeneous CO2 transport in the reservoir and mitigate the negative effects of stratigraphic heterogeneity on migration and accumulation of the CO2 plume. CO2 effective storage capacity may be greatly elevated by means of nanofluid-based CO2 geological sequestration. The concept of nanofluid-based CO2 geological storage may be potentially conducive to large-scale commercial CO2 geological storage and useful for exploration of geothermal resources in deep-seated hot rocks. The effects of CO2 solubility and geochemical reactions on nanofluid flows may be considered in a future study.