One-Dimensional Numerical Simulation on Removal of CO2 Hydrate Blockage around Wellbore by N2 Injection

Abstract

CO2 sequestration in sediments as solid hydrate is considered a potential way to capture and store anthropogenic CO2. When CO2 hydrate is formed in front of CO2 migration, the injection channel will be blocked, and the removal of hydrate blockage becomes the first problem that must be faced. This work proposed an N2 injection method to remove CO2 hydrate blockage. Based on numerical simulation, a study was conducted using TOUGH+MIXHYD v.1.0 to confirm the feasibility of N2 injection and compare it to depressurization. The spatial and temporal distribution characteristics of pressure, temperature, hydrate saturation, and gas saturation were investigated. Under the combined effects of temperature, pressure, and gas composition, secondary CO2-N2 hydrate can form far from the injection point, causing an increase in local temperature and hydrate saturation. The rate of CO2 hydrate dissociation using direct depressurization is significantly slower compared to N2 injection methods. As the pressure of N2 injection increases, the rate of CO2 hydrate dissociation notably accelerates, which does not show a significant increase with increasing injection temperature. This work introduced a novel approach to addressing the issue of CO2 hydrate blockage, which holds prominent significance for the advancement of hydrate-based CO2 geological sequestration.