Deformation bands in high-porosity sandstones: do they help or hinder CO2 migration and storage in geological formations?

Azadeh Pourmalek, Andrew Newell, Seyed M. Shariatipour, Andrew Butcher , Adrian Wood, Antoni Milodowski, Mohammadreza Bagheri

Research output: Contribution to journalArticlepeer-review


Small-scale deformation bands in Penrith Sandstone are used for CO2 flow simulation to assess the extent to which these features can act as effective mini-traps and contribute to long term, secure CO2 geological storage. A comprehensive set of simulation scenarios is applied to one zone of conjugate deformation bands and also to the deformation band clusters to evaluate the effects of: i) deformation band density; ii) the contrast in host rock/deformation band permeability and; iii) the effect of deformation band geometry, orientation and distribution on fluid movement and its significance on CO2 storage capacity and security.
The findings of this study show that conjugate deformation bands can improve CO2 storage security, depending upon the plunge angle of the hinge. It has also been demonstrated that a high contrast in permeability between the host rock and a deformation band can influence the CO2 distribution extensively. While a permeability contrast of one to two orders of magnitude affects the flow, a permeability contrast of at least three orders of magnitude is necessary for the CO2 to be effectively trapped by the deformation bands.
The long term CO2 storage security of such systems depends on the amount of free gas that reaches the transmissible faults or the caprock, as any free gas accumulating in the proximity fault and under the caprock increases the risk of leakage. This study shows that this is not only controlled by the contrast in permeability, but also by the permeability of the host rock. Furthermore, the modelling shows that clusters alone may not augment CO2 storage. The implication is that there needs to be an optimum number of deformation bands that do not excessively damage reservoir communication, reduce reservoir porosity and allow the vertical movement of CO2. This study demonstrates that the highest deformation band density modelled for Penrith Sandstone is still a sufficient number to contribute to the secure storage of CO2 without causing an injectivity issue. The amount of mobile CO2 that reaches the caprock or leaky faults is not only governed by contrast in the permeability, but also by the geometrical architecture of the deformation bands. Therefore, some types of deformation band may contribute to storage security, while others may compromise it. To improve storage capacity and security, for the types of reservoir studied herein, the results demonstrate the importance of accounting for the optimum injection rate and well placement. High injection rates may limit storage effectiveness and compromise injection security.
Original languageEnglish
JournalInternational Journal of Greenhouse Gas Control
Publication statusSubmitted - 2020

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