Simulations and analysis of hydrate formation during CO2 injection into cold saline aquifers

Abstract

Abstract Geological storage of carbon dioxide (CO2) is perceived to be one of the most promising methods to provide significant reduction in CO2 emissions. During CO2 injected into cold saline aquifers, CO2 hydrate may generate under these temperature and pressure conditions. In the displacement process, the CO2 hydrate formed at the interphase of CO2 and brine could therefore affect the CO2 injection characteristics and the pore structure properties of the aquifers. A multi-phase flow displacement model coupled CO2 hydrate formation process is established in this paper. We use numerical simulations to study characteristics of CO2 hydrate formation during CO2 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 CO2 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 CO2 hydrate reduces the porosity of saline aquifers and the velocity of CO2 injected, and the pressure of the wellbore rises gradually, which will impede the CO2 injection and displacement process. During CO2 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 CO2 injection into cold saline aquifers will provide references for the optimization of operating conditions and the prediction of CO2 storage in saline aquifers.