Competition between dry-out and hydrate formation during cold CO₂ injection into depleted reservoirs

Abstract

CO₂ injection into depleted reservoirs is a promising strategy for carbon storage, but it poses operational risks from hydrate formation, which can result in injectivity impairment. Concurrently, the injection of dry CO₂ drives a reservoir dry-out process by vaporizing formation water, which is counteracting the hydrate formation. This study uses numerical simulation to systematically investigate the competition between these two phenomena and to determine the conditions under which dry-out can mitigate or prevent hydrate formation. A five-phase, thermal-compositional model was developed to analyze the interplay between the advancing dry-out front and the thermal (cold) front. The results reveal two distinct regimes. A rapid and extensive leading dry-out front that outpaces the cold front and completely removes water before the reservoir cools. Conversely, a slow trailing dry-out front , where dry-out occurs within the already-cooled region. The leading dry-out front completely prevents hydrate formation. Even in the trailing-front scenario, the partial water removal ahead of the cold front significantly reduces the resulting hydrate saturation. Sensitivity analysis identifies initial reservoir temperature and initial water saturation as the most critical parameters governing this behavior. This work demonstrates that reservoir dry-out is an inherent mechanism for mitigating hydrate risk.