Utilization of depleted heavy oil reservoirs for carbon dioxide storage and sequestration: A molecular level assessment

Abstract

Hydrocarbon-bearing formations have a life cycle that starts with initial development and ends with abandoning the formation once depleted. The number of abandoned reservoirs is increasing and is expected to do so over the foreseeable future. These reservoirs offer a sustainable solution to mitigate the negative impact of oil and gas industry on the environment. The abandoned reservoirs could serve as natural compartments to store greenhouse gasses, such as carbon dioxide, owing to their geological sealing features, the well-established understanding of their development, and the abundance of drilled wells that could serve as potential carbon dioxide injectors. Among other oil compounds, the abandoned oil phase is enriched with heavy oil components, such as asphaltene. The asphaltene deposition increases with an increased depletion rate and is mostly found as layers coating the rock grains. Owing to their molecular structure, asphaltene can host carbon dioxide in the sorbed form. In this study, realistic asphaltene structures are recreated on a molecular simulation platform and assessed for their carbon dioxide storage capacity. The findings substantiate asphaltene for its carbon dioxide storage capacity as absorbed (dissolved) and adsorbed phases. The presence of asphaltene increases the storage capacity of pore spaces by a factor up to 4 for the considered cases in this study. Furthermore, the sorption capacity has hysteresis favoring the retention of the sorbed phase. This study casts some light on the potential utilization of depleted heavy oil reservoirs for long-term carbon dioxide storage and sequestration.