Investigating the Potential for Large-Scale Carbon Dioxide Sequestration in Shale Gas Formations

Abstract:

Recent studies [Godec et al., Int. J. Coal. Geol., 2013; Liu et al., IJGGC, 2013; Tao and Clarens, ES&T, 2013] have suggested the possibility of geological CO₂ sequestration in depleted shale gas formations, motivated by large storage capacity estimates in these formations. The kinetics and practicality of injecting large amounts of CO₂ into shale gas wells at the appropriate scale remain as open questions. To further investigate the feasibility of CO₂ sequestration, models of gas flow and storage in a horizontal shale gas well were developed based on observed behavior of gas production data and the associated models that are consistent with those observations [Patzek et al., PNAS, 2013]. Both analytical and numerical models were used to investigate the well-scale kinetics of CO₂ injection into a typical shale gas well. It was found that relatively low rates could be injected into individual wells compared with CO₂ emissions from large industrial sources, and that injection rates would rapidly decline with time. Based on typical well parameters, 170 wells would be required to inject the emissions from one large coal-fired power plant over a 15 year period. Significant practical and logistical challenges to industrial-scale CO₂ sequestration in depleted shale gas formations arise due to the relatively low injection rates, low storage capacity of individual wells and large numbers of wells required. These challenges include the difficulty of managing the required large, ever-changing networks of injection wells, potentially prohibitive energy requirements, and leakage concerns in hydraulically fractured wells. The combination of these factors, and the fact that they are all likely less of an issue for other potential geological sequestration targets such as deep saline aquifers, mean that targets in conventional formations are more likely to be suitable for industrial-scale CO₂ sequestration.