Analysis of CO_2 Migration during Nanofluid-Based Supercritical CO_2 Geological Storage in Saline Aquifers

Carbon dioxide (CO_2) 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 CO_2 effective storage capacities. In this paper, a preliminary model is developed to simulate CO_2 migration during nanofluid-based supercritical CO_2 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 CO_2 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 CO_2 mobility in the flow boundary layer. In addition, nanoparticles increase shear stresses outside the boundary layer and retard CO_2 velocity. These competitive mechanisms result in homogeneous migration of CO_2 in the saline formation. One preliminary suggestion is that nanofluids enhance homogeneous CO_2 transport in the reservoir and mitigate the negative effects of stratigraphic heterogeneity on migration and accumulation of the CO_2 plume. CO_2 effective storage capacity may be greatly elevated by means of nanofluid-based CO_2 geological sequestration. The concept of nanofluid-based CO_2 geological storage may be potentially conducive to large-scale commercial CO_2 geological storage and useful for exploration of geothermal resources in deep-seated hot rocks. The effects of CO_2 solubility and geochemical reactions on nanofluid flows may be considered in a future study.