Pressurisation and Brine Displacement – Issues for Deep Saline Formation CO₂ Storage

Publication Overview

Worldwide, deep saline formations are expected to store gigatonnes of CO₂ over the coming decades, making a significant contribution to greenhouse gas mitigation. At present, our experience of deep saline formation storage is limited to a small number of demonstration projects that have successfully injected megatonnes of captured CO₂. However, concerns have been raised over pressurization, and related brine displacement within and around deep saline formations, given the anticipated scale of future storage operations. This report aims to address these concerns and their origins in computational and analytical flow models. The report does not address the related impact of brine displacement on shallow potable groundwater, which is the subject of a separate IEAGHG study, to follow in 2011.

Publication Summary

In summary, recent concerns regarding pressurization appear to be largely model driven. The scarcity of pressure data for megatonne storage projects has meant that pressure prediction models have been hypothetical in nature. Chief amongst the hypothetical constraints have been assumptions concerning the likely boundary conditions of deep saline formations. In the absence of sufficient calibration data (which will presumably emerge over the coming decade), modeling is at best a sensitivity analysis. As such, the ‘no-flow’ assumption for shales is a poor approximation. The analysis presented here suggests that the flow contribution of shale boundaries to pressure dissipation via brine displacement is significant with respect to CO₂ storage, in accord with long established principles for basin-scale flow dynamics in both the fields of regional hydrology and petroleum systems analysis. The model results suggest that, while pressurization may remain an issue for small restricted storage compartments, future storage operations in regional deep saline formations are unlikely to encounter significant pressurization issues