Carbon Capture, Storage and Utilization (CCUS) on a large scale is one of the possible solutions to mitigate CO2 emission into the atmosphere. Potential escape of CO2 due to leaking faults and seals in subsurface formations poses a safety risk. Therefore, it is important to investigate CO2 trapping mechanisms in the formation: structural and stratigraphic trapping, residual trapping, solubility trapping and mineral trapping (Benson et al. 2012). Trapping occurs at the interface of rock-CO2, and rock-CO2 dissolved in water. This dissertation studies wettability of rock surfaces at a micro scale to understand rock-fluid interaction along CO2 pathways in the formation. The methods utilized are gas adsorption, surface free energy, and X-ray Photoelectron Spectroscopy (XPS).
In the first part of the thesis, shales rich in calcite, clay and organic matter are investigated. The analysis of CO2 with calcite-rich shale suggests presence of chemisorbed water in calcite that permanently traps CO2 in the ultra-micropore region (0.2-0.4 nm) at reservoir conditions. Such trapping is not observed in clay- and organic-rich shales; removal of soluble organic matter leads to a gradual but reversible increase in CO2 adsorption in the micropore region (<2 nm).
In the second part of the thesis, rock surface forces are studied by determining their surface free energy. The prominent component governing the interactions on shale surfaces is van der Waals forces. The surface free energy of individual pure minerals does not contribute to the effective surface free energy of the shale in an additive manner. However, a validation of surface free energy is not possible because the existing theoretical inversion models are not comparable to each other.
I explored the usability of X-ray Photoelectron Spectroscopy (XPS) to characterize chemical compositions and reactions on the surface. Literature review of XPS shows that XPS has been successfully used to evaluate oil wettability through identification and quantification of organic carbon content, sulfur and nitrogen elements on the rock surface. In this work, I present a workflow to use near-ambient pressure capability of XPS to study mineral carbonation while dosing with gases such as CO2, H2O and CH4. Preliminary sample characterizations are conducted in this study using XRD, ESEM/EDS and TGA.
Finally, the results from this thesis are used to estimate CO2 storage capacity in calcite-rich and organic-rich shale formations. Permanent storage of CO2 is observed in pore structures of calcite-rich shales. An increase in CO2 storage capacity is observed in the pores of insoluble kerogen as soluble organic matter is removed, due to increasing micro-porosity and affinity of kerogen to CO2.
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|Advisor:||Prasad, Manika, Pylypenko, Svitlana|
|Commitee:||Koh, Carolyn, Yin, Xiaolong|
|School:||Colorado School of Mines|
|School Location:||United States -- Colorado|
|Source:||MAI 58/06M(E), Masters Abstracts International|
|Subjects:||Climate Change, Chemistry, Petroleum engineering|
|Keywords:||CCUS, Organic matter, Shales, Storage capacity, Surface free energy, XPS|
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