A Study of CO₂ Storage Capacity Estimation under Supercritical Conditions

CO₂ sequestration in abandoned coal seams is regarded as an effective potential approach to mitigate the ever-increasing CO₂ levels in the atmosphere. The injection of CO₂ into abandoned coal mines not only provides a solution for the long-term storage of CO₂ but it also has the added advantage of using coal bed methane as an energy source. Adsorption is the main criterion for storage in coal seams, where it constitutes to about 95–98% of total storage. The coal matrix is heterogeneous and consists of three porosity systems: micropores, mesopores and macropores. Therefore, the inherent mechanical properties such as permeability and other in-situ attributes such as fractures complicate storage capacity estimation. Earlier studies have shown that the injection of supercritical CO₂ offers higher storage capacity. However, there is a lack of experimentally verified storage capacity estimation methodologies, especially for supercritical CO₂. In this paper, various parameters such as coal rank, carbon content, pressure, moisture and temperature found in earlier studies for supercritical CO₂ are presented for clarification of the estimation of supercritical CO₂ storage capacity in coal seams. Methodologies suggested by earlier studies as better suited for supercritical conditions are also reviewed.