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Fundamental study on the effects of heterogeneity on trapping of dissolved CO2 in deep geological formations through intermediate-scale testing and numerical modeling, A
Agartan Karacaer, Elif
Agartan Karacaer, Elif
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2015
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2016-06-01
Abstract
Climate change due to CO2 build up in the atmosphere has been studied for many years. Carbon capture and storage (CCS) is a technology to reduce the atmospheric emissions of CO2 produced from large point sources like power plants. The captured CO2 is deposited into the subsurface formation, such as deep saline aquifers, in the case of geologic sequestration of CO2. The earliest application of CO2 sequestration in subsurface formations was back to the early 1970s in order to increase oil production. Environmental benefits of CO2 storage to reduce greenhouse gas emissions to the atmosphere have been considered since the 1980s and studied in detailed since the 1990s. In deep geologic formations, CO2 is trapped through a number of mechanisms including structural, capillary, dissolution, and mineral trapping to achieve secure and long-term storage which reduces the risk of leakage. The fundamental understanding of these mechanisms should be improved in order to develop strategies on the trapping in the target formation. Heterogeneity of the formation is another factor that plays a key role for the stable trapping at the injection and post-injection periods, and makes it challenging to understand the relative contribution of each mechanism to storage. The main goal of this study is to investigate the role of heterogeneity on the trapping of dissolved CO2 for the secure and long-term storage in the deep saline formations via well-controlled laboratory experiments and numerical modeling. The small and intermediate-scale laboratory experiments were performed using surrogate fluid combinations showing identical density characteristics with dissolved CO2 and brine under ambient pressure and temperature conditions. The more complex packing configurations and field-scale applications were simulated using the numerical model. The results of experimental and numerical modeling studies suggested that the contribution of convective mixing to the stable trapping of dissolved CO2 depends on the geometry, distribution, and hydraulic properties of the geologic features in the formations. In multilayered systems, convective mixing and diffusion controlled trapping contribute to dissolution trapping; however the impact of each mechanisms depends on the permeability and thickness of the low-permeability layers. On the other hand, the intralayer heterogeneity present in low-permeability layers enhances mixing, and the long-term trapping in these layers depends on distribution of the materials. The effective strategies can be developed to enhance trapping by taking the advantage of natural heterogeneity of the formation. These conclusions are relevant when investigating stable trapping of dissolved CO2 in deep saline formations.
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