Department of Earth and Environmental Sciences
http://hdl.handle.net/10106/25156
2024-03-29T10:11:24ZExperimental and theoretical studies of fluid-solid coupling processes of tight rock media
http://hdl.handle.net/10106/31775
Experimental and theoretical studies of fluid-solid coupling processes of tight rock media
**Please note that the full text is embargoed until 8/1/2025** ABSTRACT: This study covers the application of continuum mechanics in the realm of rock work in geological studies. Continuum mechanics encompasses two major branches: fluid mechanics that deals with fluid behavior, and solid mechanics pertaining to the behavior of rock media. The research focuses on comprehending the mechanical behavior of rocks as a continuous mass, offering a comprehensive perspective for analyzing geological structures, fluid flow, and rock mechanics. Under the framework of continuum mechanics applied to rock media, following the sequence of the rock/solid properties, fluid flow properties, and the fluid-solid coupling behavior, this dissertation is divided into four sections, each addressing a unique aspect of the subject matter stated above.
The dissertation presents an analysis of true-triaxial hydraulic fracturing of granite samples for fluid-solid coupling processes during the rock failure, followed by an integrated technique for rapid gas permeability measurement of tight rock media. Then, this works elucidates shale wettability using a contrast-matching technique of Small Angle Neutron Scattering (SANS), investigating the heterogeneity and overturning of wettability at different pore intervals. This research is significant in the field of geo-energy stewardship, which involve fluid-solid coupling phenomena in poromechanics, includes shale petroleum development, enhanced geothermal stimulation, CO2 sequestration, H2 storage, nuclear waste repository, and underground water management.
2023-08-24T00:00:00ZLiquid Flow and Gas Diffusion in Natural Rocks: Experimental and Simulation Studies
http://hdl.handle.net/10106/31749
Liquid Flow and Gas Diffusion in Natural Rocks: Experimental and Simulation Studies
Natural rocks, as key components in energy and environmental geosciences, play crucial roles in groundwater extraction, geological storage of high-level nuclear waste, geothermal energy mining, and petroleum exploration in both conventional and unconventional reservoirs. Unconventional reservoirs, specifically the tight shale formations, have seen a significant usage in petroleum production in recent decades, largely due to advances in fracturing stimulation techniques which counter the inherently low permeability and connectivity of shale reservoirs by expanding natural fractures and creating artificial ones for an enhanced petroleum production. However, the low mobility (liquid flow and gas diffusion) of stored fluids in naturally fractured formations with tight matrix blocks presents a challenge; consequently, understanding liquid flow and gas diffusion in fractured low-permeability media has become a paramount issue in porous media studies.
This research combines integrated methodologies of experimental and simulation studies (numerical and machine learning regression models) to delve into the processes of spontaneous imbibition and gas diffusion, respectively, within various porous natural rocks such as shales, sandstones and carbonate rocks.
For the imbibition analysis, several Barnett Shale samples with fractures were examined with flow direction oriented either parallel (P) or transverse (T) to the bedding plane. A newly developed model, integrating concepts of percolation theory implemented via MATLAB, allows for capturing 3D porous media imbibed with 2D fractures, an innovation over previous piston-like or multiply-sized pore models. The model incorporates the complex interplay of factors, such as porosity, fracture distribution, and pore connectivity. Results demonstrate a sensitivity of imbibed water mass to the number of fractures directly connected to the water source, importing a novel parameter for understanding the wetting-front progression in fractured tight shale.
Subsequently, we utilize machine learning regression techniques, specifically linear regression, Gradient Boosting regression, Decision Tree regression, and Random Forest regression, to predict gas diffusion across 15 different types of rocks with both heterogenous and homogeneous structures. We prioritize attributes such as rock type, sample radius, sample height, porosity, permeability, and tracer concentration difference for their impacts on diffusion velocity and the feature importance. Notably, the Random Forest model identifies the tested gas concentration difference as the most significant factor in affecting gas diffusion.
Our dual-method (experimental and simulation) approach offers valuable insights into liquid flow and gas diffusion behavior in natural rocks, providing a platform for their targeted usage in energy and environmental geosciences. Machine learning models can expedite and economize the testing process, highlighting their potential to enhance operational efficiency in the studies of porous media.
This dissertation is structured into five chapters. The first chapter (Chapter I) provides an overview and succinct introduction to the contents of the subsequent chapters. Chapter II features a paper that has already been published, showcasing the liquid imbibition into fractured Barnett Shale. In Chapter II, the research elucidates the intricate imbibition mechanism prevalent in fractured shale formations. Additionally, it offers a versatile model suitable for Barnett Shale lithology, delineating the spatial-temporal dynamics during fluid imbibition within porous substrates. Chapter III scrutinizes the impact of pore throat distribution and mineralogical constitution on the velocity and amplitude of spontaneous fluid imbibition across a diverse range of natural lithologies. Chapter IV elucidates the proficiency and precision of machine learning models in predicting the gas diffusion process within natural rock matrices. The findings underscore the Random Forest model's aptitude in delineating feature significance and quantifying the contributing attributes for gas diffusion. Chapter V draws conclusions by synthesizing the findings and implications of this research during the duration of this PhD program.
2023-08-24T00:00:00ZPETROGRAPHY AND GEOCHEMISTRY OF CONTINENTAL CARBONATES IN SOUTH TEXAS: IMPLICATIONS FOR OLIGOCENE-MIOCENE PALEOCLIMATE AND PALEOENVIRONMENT NEAR SEA LEVEL
http://hdl.handle.net/10106/31688
PETROGRAPHY AND GEOCHEMISTRY OF CONTINENTAL CARBONATES IN SOUTH TEXAS: IMPLICATIONS FOR OLIGOCENE-MIOCENE PALEOCLIMATE AND PALEOENVIRONMENT NEAR SEA LEVEL
The Oligocene-Miocene Catahoula, Oakville, and Goliad formations in south Texas contain abundant continental carbonates which are useful in reconstructing paleoclimate and paleoenvironment in a near sea level region. Field observations and thin section characterizations identify three types of pedogenic carbonates, including rhizoliths, carbonate nodules, and platy horizons, and two types of groundwater carbonates, including cemented beds and carbonate concretions. The pedogenic carbonates display sharp upper contacts and diffuse lower contacts, and contain soil structural elements and biogenic elements related to root action. Under microscope, the pedogenic carbonates are micritic with clotted micrite, micrite laminations, and alveolar-septal structures and display dull cathodoluminescence. The groundwater carbonates display sharp lower contacts and preferential cementation within permeable units, and lack pedogenic profiles that destroy original beddings. Under microscope, the groundwater carbonates contain equant, blocky and sometime drusy and poikilotopic spars, and the spars often display dull to bright orange concentrically-zoned cathodoluminescence. Based on the preservation of microfabrics and the variabilities of carbon and oxygen stable isotopic compostion, we suggest that all the studied carbonates experienced minimal diagenesis, and their isotopic compositions reflect paleoclimate and paleoenviornment in south Texas during the Oligocene and Miocene. The δ18O values of the continental carbonates decreased ~3 ‰ after the earliest Oligocene, which is interpretted to reflect at least a 6° C drop in mean annual temperature in south Texas. The δ13C values of the pedogenic carbonates increased ~4.4 ‰ from the late Oligocene to the middle Miocene, suggesting an expansion of C4 plants in south Texas as early as the early Miocene. This early Miocene expansion of C4 plants is ~16 myr older than what has been documented in Asia, possibly as a result of local climate change rather than global climate change.
Petrophysical Studies on Woodford Shale in Oklahoma and Wolfcamp Shale in Texas: A Multiple-Approach Methodology
http://hdl.handle.net/10106/31388
Petrophysical Studies on Woodford Shale in Oklahoma and Wolfcamp Shale in Texas: A Multiple-Approach Methodology
The successful development of oil and gas from unconventional reservoirs in the United States proves the high petroleum potential that shale rock reserves. Petrophysical studies on shale rocks are an important part of reservoir characterization. Petrophysical studies investigate the basic properties and pore structures of the shale rock, including porosity, density, pore size distribution, specific surface area, wettability, pore connectivity, and permeability, to understand the storage and movement of oil and gas in shale rocks. Multiple experimental approaches were applied onto both outcrop and well-core samples from several U.S. shale plays. A range of complementary methodologies of X-ray diffraction, polarized optical microscopy, mercury intrusion porosimetry, gas physisorption, small-angle X-ray scattering, liquid immersion porosimetry, scanning electronic microscopy, and tracer gas diffusion were designed to measure the basic properties and pore structure of these shale samples. This Ph.D. dissertation is divided into three chapters for three different but coherent projects: 1) The first one is by applying multiple approaches mentioned above on Woodford Shale outcrop samples to study the limitations of each approach and find a good combination for pore structure studies; the fluid-rock interactions and pore structures were also investigated in this project; 2) The second one is by using mercury intrusion porosimetry, gas physisorption, small angle X-ray scattering, scanning electronic microscopy, and spontaneous imbibition to study the effects of sedimentary features and mineralogy on pore structure and fluid-rock interaction of Wolfcamp Shale core samples; and 3) The third is to measure the porosity of granular rock samples by using a modified bulk density method for obtaining size-dependent effective porosity in conjunction with particle density analyses. In summary, this dissertation aims to understand and assess the limitations of laboratory experimental approaches, the effect of mineralogy on pore structure, and fluid-rock interaction on shale.
2022-05-09T00:00:00Z