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This research is addressing the fundamental behavior of carbon dioxide (CO₂) sequestration into water aquifers, with a specific examination of the joint effects of relative permeability and gas dissolution into and evolution from the water phase.  The interaction of solubility effects with hydrodynamic effects is not currently well understood, and there is good potential to enhance the effectiveness of carbon dioxide sequestration if these fundamental issues are investigated.  The work is making use of experimental observations of carbon dioxide displacements in rock cores and in micromodel visualization cells.  These observations have been used to develop and verify conceptual models based on statistical thermodynamics.  The concepts of solubility sequestration have been investigated by others, however the importance of the interaction between dissolution and relative permeability seems to have been missed.  We refer to this interaction as “active phase change”, and have been investigating its influence on the displacement and storage of CO₂ in aquifers.  Experimental observations of the differences between N₂-water and CO₂-water flow in our preliminary research have shown that apparent relative permeability is affected strongly by CO₂ dissolution – the consequences of these phenomena on sequestration are unknown but are likely to be of considerable significance. The overall goal of this project has been to investigate the importance of active phase change and mass transfer on CO₂-water two-phase flow and determine the impacts this phenomenon has on CO₂ sequestration. Importantly, the issue of dissolution phenomena in CO₂-water systems may allow for improved sequestration of CO₂ without needing to go to the extreme depths required to achieve supercriticality, while reducing the risk of CO₂ escaping to the atmosphere.

During the 2009-2010 academic year, research student Sarah Pistone took over the work begun on this project by Robert Stacey in the previous year.  Her first objective was to replicate the results shown by Stacey with regard to his discovery of a carbon sequestration mechanism that takes advantage of the active phase change phenomenon.  The purposes in replicating Stacey’s results were two, firstly to demonstrate repeatability in the scientific context, and secondly to come up to speed on the experimental apparatus and procedures.  The focus during the year was on bringing the coreholder apparatus into operation, and also on running experiments in the micromodel.  We also spent some time investigating the feasibility of using the active phase change mechanism to sequester CO₂ in geothermal reservoirs, where the higher temperature and possibility of using CO₂ as a working fluid for the power generation cycle have been discussed in the literature.

The project is running behind schedule in time, mainly due to the substitution of Pistone for Stacey in the middle of the work.  Nonetheless, the project is on track with regard to expenditure, and having been granted a no-cost extension by ACS we expect to complete the work within budget but delayed in time.