Abstract Geological storage of carbon dioxide (CO 2 ) is perceived to be one of the most promising methods to provide significant reduction in CO 2 emissions. During CO 2 injected into cold saline aquifers, CO 2 hydrate may generate under these temperature and pressure conditions. In the displacement process, the CO 2 hydrate formed at the interphase of CO 2 and brine could therefore affect the CO 2 injection characteristics and the pore structure properties of the aquifers. A multi-phase flow displacement model coupled CO 2 hydrate formation process is established in this paper. We use numerical simulations to study characteristics of CO 2 hydrate formation during CO 2 injection and the displacement process and the permeability evolution of saline aquifers as well. To describe the hydrate formation process, based on the model of hydrate formation kinetics, we employ an improved kinetics model of hydrate formation and derive a thermal energy balance equation for the displacement process, with the thermal effect during the formation of hydrate taken into consideration. The commercial software package COMSOL Multiphysics is used to solve the proposed model numerically. Through numerical simulations, we investigate the CO 2 hydrate formation process during the displacement process in the saline aquifer and the impact of hydrate formation on the porosity characteristics and the injection pressure. The results indicate that the formation of CO 2 hydrate reduces the porosity of saline aquifers and the velocity of CO 2 injected, and the pressure of the wellbore rises gradually, which will impede the CO 2 injection and displacement process. During CO 2 injection, the process of hydrate formation changes the local temperature and pressure. The remarkable rise in temperature as a result of the exothermic reaction of hydrate formation leads to the reduction of the local hydrate formation rate. In this paper, the simulation and analysis of hydrate formation during CO 2 injection into cold saline aquifers will provide references for the optimization of operating conditions and the prediction of CO 2 storage in saline aquifers.
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