Mechanisms for CO2 Sequestration in Geological Formations and Enhanced Gas Recovery (Bookzcity)

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Carbon dioxide storage in geological formations (porous media) has received
increased interest because it is considered one of the options to reduce greenhouse
gas emission. Even though there is a vast literature available on the subjects, some
aspects deserve special attention. In the thesis, Dr. Khosrokhavar has focussed his
interest on various mechanisms that explain and enhance the storage capacity of the
reservoir and enhance the methane recovery from nearby or solitary shale
formations.

In the first part of this work, CO2-reservoir characteristics are observed: Injected
carbon dioxide is partitioned between the injected gas cap and the underlying
aquifer. The transfer rate between the gas cap and the aquifer requires enhanced
mixing in the aquifer, which occurs due to the formation of unstable fingers of high
density carbonated brine in the lower density initial brine. The same mechanism
also occurs for carbon dioxide flooding in enhanced oil recovery. This fingering
process is indeed a likely mechanism but has never been visualized. The following
chapter uses an optical technique to visualize the occurrence and effect fingers
which, thanks to natural convection, greatly enhance the transfer from the gas cap to
the aquifer. To our knowledge there are no visual data in the literature for natural
convection flow of super critical CO2 in the aqueous and the oleic phase. There are
no experiments that deal with visualization of the CO2–Oil system. The visualization
shows a number of features that characterize the enhanced transfer, even if,
admittedly, it is only feasible in bulk flow. First it shows a small transition region
between the gas/fluid interface into the fluid, with a steep concentration gradient,
leading to a high transfer rate. The fingers emanate from the bottom of the small
transition region. The visual cell can not only be used to prove the fingering
mechanism but also to show that enhanced transfer does not only occur in fresh
water but also in brine of various concentrations and oil.