Affecting Parameters in Density Driven Convection Mixing in CO2 Storage in Brine
- Mansour Soroush (Norwegian U. of Science & Tech) | Dag Wessel-Berg (SINTEF Petroleum Research) | Ole Torsaeter (Norwegian U. of Science & Tech) | Amir Taheri (Norwegian U. of Science & Tech) | Jon Kleppe (Norwegian U. of Science & Tech)
- Document ID
- Society of Petroleum Engineers
- SPE Europec/EAGE Annual Conference, 4-7 June, Copenhagen, Denmark
- Publication Date
- Document Type
- Conference Paper
- 2012. Society of Petroleum Engineers
- 5.1.1 Exploration, Development, Structural Geology, 5.2 Reservoir Fluid Dynamics, 5.3.2 Multiphase Flow, 5.1 Reservoir Characterisation, 4.1.5 Processing Equipment, 5.5.8 History Matching, 1.6.9 Coring, Fishing, 1.14 Casing and Cementing, 4.1.2 Separation and Treating, 6.5.3 Waste Management, 5.4 Enhanced Recovery, 5.1.5 Geologic Modeling, 5.4.2 Gas Injection Methods
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After injecting CO2 into subsurface brine for storage, it will be trapped in the reservoir through various mechanisms. In the beginning, the geological trapping mechanism dominates and the CO2 plume is moving upward below a cap rock. Then brine will imbibe the formation and some parts of the CO2 will be trapped in the pore paces. Later on injected CO2 will dissolve in the brine and increases its density. As a result, the heavier brine will move into deeper parts of the reservoir and density driven convection mixing will occur. This is known as the solubility trapping mechanism.
Here in this study, density driven phenomena in CO2 storage in brine and the influencing parameters are the prime targets. We find particularly interesting results for this through Hele-Shaw cell experiments and numerical simulations. Hele-Shaw flow is defined to occur between two parallel flat plates separated by a small gap. In each experiment the cell is filled with fresh water and a shim prevents it to leak. Then liquid with higher density is placed on top. Several tests including water of varying salinity at the top of the cell have been conducted, and the results are interpreted separately and compared with the base experiment.
More extensive studies and sensitivity analysis is done based on a simulation model constructed on the reservoir properties of a brine formation, with wide range of affecting parameters, including density differences, permeability variations and the effect of diffusion coefficients. It has been also attempted to investigate the effect of anisotropy and heterogeneity on the CO2 state after injection.
Possible risks of increasing greenhouse gases in the atmosphere have motivated feasibility studies of geological storage of CO2 that is produced by different industrial sources including power plants, refineries, cement factories and other sources. This study deals with processes that occur during CO2 storage in brine formations. There are other potential storage sites including depleted oil and gas reservoirs, coal beds, but the main motivation for using brine formation as storage site for CO2 is availability and possible larger volume that will results in reduction in transmission cost (Benion and Bachu, 2005). The main challenge is how to use these brine formations that provide the largest potential capacity to store CO2 (Benson, 2008).
In CO2 storage, after injecting CO2 into the brine it will trap in to the reservoir through various mechanisms. Each trapping mechanism has different timescale. In the beginning the structural and geological trapping mechanism dominates, which is the trapping of the CO2 plume moving upward below a cap rock (IPCC report, 2005).
After CO2 injection and movement of CO2 upward, brine will imbibe the formation bearing the injected CO2 and some fraction of the gas will be trapped in the pore spaces. Capillary forces prevent complete drainage of CO2 and this residual saturation remains trapped in the pores. Depending on the salinity, pressure and temperature range and heterogeneities of brine formation, and other reservoir parameters, injected CO2 will dissolve more and more in the brine and increases its density. As a result, the heavier brine will move into deeper parts of the reservoir and convection driven movement will be activated. This mechanism is called the solubility trapping mechanism. Finally, a fraction of the CO2 may be converted to stable carbonate minerals. This process is called mineral trapping. Mineral trapping is believed to be a comparatively slow process, potentially taking thousand years or longer (IPCC report, 2005).
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