Micro- and nano-scale investigation of rock behavior in subsurface environments and implications for carbon storage

Abstract

It is challenging to capture the internal transformation and deformation of a rock in common basin-scale/field-scale studies because of the heterogeneity of subsurface rocks, especially fine-grained argillaceous rocks. As a powerful supplement to large-scale studies, micro- and nano-scale characterisation techniques, such as scanning electron microscopy (SEM), X-ray computed tomography (XCT), transmission X-ray microscopy (TXM), nanoindentation and atomic force microscopy-based infrared spectroscopy (AFM-IR), are used in this research to provide an understanding of micro-scale rock behavior in response to heating, swelling and fluid-rock reaction. Five different sets of experiments were undertaken in this thesis. Time-lapse TXM imaging was performed on Kimmeridge Clay and Akrabou Shale samples. At increasing temperature, a major expansion of pore volume was observed between 300-350 °C, where microfractures expanded rapidly along the organic-rich bedding plane. The configurations of organic matter, mineral components, pores and connectivity impact elastic deformation during shale pyrolysis. Subsequent Akrabou Shale swelling experiments in the presence of water further revealed that the higher strains were localized to the boundary between brittle minerals and organic matter/clays. Considering the important role of organic matter within shales, nanoscale chemical characteristics of individual organic particles were measured on Baltic Shale and Bowland Shale using AFM-IR. Compared with the Bowland Shale, organic matter grains in the Baltic Shale sample show relatively higher O/C and hydroxylic and carboxylic groups which implies a higher gas adsorption capacity. Finally, samples from potential carbon storage sites were investigated. A combined reservoir-caprock system using Mancos Shale and Sherwood Sandstone was created to investigate of CO2 transport and associated hydro-mechanical effects. Mercia Mudstone samples were used in a CO2-brine soaking experiment to provide insight into caprock stability for this rock. The results suggest that clay particle changes, such as dispersion in brine, migration as fines, and swelling induced by synergistic effects of CO2 and water, play an important role in the opening and closing of pores/fractures. The concentrated strains around the main fracture in mudstone and web-like strains around the contact boundary of granular minerals in sandstone in the presence of flowing ScCO2 show different reservoir and caprock behavior. Furthermore, despite a weakening of mechanical strength during a short CO2-brine-rock reaction time, interlayered phases of Mercia Mudstone with different mechanical properties can support each other to maintain stability during long-term CO2 sequestration. For the understanding of long-term carbon sequestration, mineralogical characteristics, interactions between rock-rock and fluid-rock, and the impacts following CO2 phase transition are all important concerns. The combined imaging, mechanical and chemical characterization presented in this thesis further our overall understanding of micro- and nano-scale rock behavior, and can be also linked to the macro-scale behaviors. The findings have opened an avenue for applications in both safe carbon sequestration and other similar energy systems, such as enhanced gas recovery, underground hydrogen storage and nuclear waste disposal.

Date of Award	29 Mar 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Kevin Taylor (Main Supervisor) & Lin Ma (Co Supervisor)