| dc.description.abstract | In recent decades, the demand in energy has continuously escalated due to the growing world population. In order to meet these ever-growing energy needs, many avenues have been explored. In the oil and gas industry, in particular, shale production has appeared as a convenient solution to energy concerns and has upended the industry, especially in the United States. Unfortunately, increasing the energy output with fossil fuel sources like shales has also increased the strain on the environment. In order to responsibly tackle energy challenges created by the population increase, underground injection of CO2 for purposes of enhanced recovery and geologic sequestration have been proposed and studied. Despite previous documentation and research, the implementation of these methods in shales remains a very complex process due to their delicate and complicated pore structure, convoluted fracture network, and intricate geology. This thesis thus aims to investigate the chemically and/or stress-induced changes in shales during their interaction with CO2-enriched brine.
Eagle Ford and Wolfcamp shales were used in this study and were subjected to a comprehensive experimental program to identify porosity changes and chemical and mechanical alterations in shale constituents. The mechanical evaluation of shales involved microscale property analyses like nanoindentation and microtomography while the chemical assessment was realized through energy dispersive X-ray spectrometry, inductively coupled plasma mass spectrometry and reactive transport modeling. These analyses showed the existence of three regions of different behavior after CO2 attack: (1) a dissolution zone, (2) a precipitation zone and (3) an unaltered zone. The dissolution region is characterized by high porosity and low indentation modulus and hardness whereas the precipitation region’s defining characteristics are low porosity and high mechanical properties. The unaltered zone presents similar petrophysical and mechanical properties as untouched shales. Evaluation of the micromechanical results also suggests that CO2 infiltration into shales depends on the alignment between flow direction and laminations’ orientation. In addition, the new understanding developed in this thesis can potentially be used to predict macroscale effects on rock strength based on the relative extents of the identified dissolution and precipitation regions. | en |
