2021 - Mines Theses & Dissertationshttp://hdl.handle.net/11124/1222024-03-29T10:45:23Z2024-03-29T10:45:23ZCompositional modeling of gas injection in tight oil reservoirsTian, Yehttp://hdl.handle.net/11124/158412022-12-19T02:11:25Z2021-01-01T00:00:00ZCompositional modeling of gas injection in tight oil reservoirs
Tian, Ye
The commercial development of tight oil reservoirs has reshaped the landscape of the petroleum industry in North America. However, the recovery factor (RF) of tight oil with primary depletion is very low, mostly below 10%. With a large volume of remaining oil in tight oil reservoirs, the successful execution of Improved/Enhanced Oil Recovery (IOR/EOR), even with a minor improvement of 1%, would prompt a substantial production increase. Based on various field pilots, gas injection is by far the most promising IOR/EOR technology for tight oil reservoirs. This work developed an improved compositional model and its associated simulator to understand the complex multiphase and multicomponent behaviors during gas injection into tight oil reservoirs. The model accounts for the key physics in tight oil reservoirs, including nanopore confinement, multicomponent diffusion, and their coupling with geomechanics. Firstly, a hybrid algorithm combining the Successive Substitution and Newton's method was presented to improve the phase equilibrium calculation under confinement. Secondly, a modified formulation of the Maxwell-Stefan equation was presented to better quantify the multicomponent diffusion driven by the chemical potential gradient. A physics-based improvement was then proposed for the advection-diffusion model in fractured reservoirs, where fracture, matrix, and their interface are represented by three different yet interconnected continua to better capture the transient mass exchange between fracture and matrix. Thirdly, the transport is fully coupled with geomechanics during the computation of both primary and secondary variables. The numerical technique of solving the proposed model is also detailed, with special considerations to handle the numerical issues encountered during gas injection modeling. With the more general compositional model presented above, major modifications are implemented in Fortran to update the in-house simulator MSFLOW-COM for better modeling the gas injection processes in tight oil reservoirs. Fourthly, the implemented multicomponent diffusion formulation is validated with both intraphase and interphase diffusion experimental data. For the matrix-fracture mass transfer, the implemented MINC approach with three continua can better match the results of the fine grid model than the conventional double-porosity approach. The developed simulator MSFLOW-COM is validated with a commercial compositional simulator for both primary depletion and gas injection. After validation, the simulator is used to carry out two case studies. The first case study based on the Eagle Ford play investigates the impact of nanopore confinement, geomechanics, and their coupling. The simulation shows that the nanopore confinement has a minimal impact on RF for depletion and the early cycles of gas huff-n-puff (HnP), but in the long run, it reduces RF of the light components and increases RF of the heavy components. Geomechanics is an important factor in production but not always detrimental. The second case study based on the Permian Basin Wolfcamp Shale investigates the effect of multicomponent diffusion within the fractured tight oil reservoir. The simulation reveals that multicomponent diffusion has a minor impact on the performance of depletion as oil is the dominant phase. For gas injection, the simulation neglecting diffusion will underestimate the oil RF. With the diffusion included in the model, gas HnP becomes more sensitive to the soaking time than that without diffusion. Though a longer soaking time will achieve a higher RF after considering diffusion, the incremental oil is not high enough to justify a prolonged soaking time. Simulation using the double-porosity approach leads to a similar cumulative oil RF but overestimates the RF of heavy components compared with the MINC approach with three continua. To the best of the author's knowledge, the above studies cannot be done with any commercial simulators, which neglect fundamental physics, including nanopore confinement, multicomponent diffusion, and their coupling with geomechanics. The developed model and its associated simulator in this work can help researchers better understand the complex multiphase and multicomponent behaviors in tight oil production as well as be of great use for engineers to optimize gas injection parameters in field applications.
2021 Spring.; Includes bibliographical references.
2021-01-01T00:00:00ZNuclear forensics of uranium conversion: investigations of environmentally altered uranium compoundsPastoor, Kevin J.http://hdl.handle.net/11124/153562022-10-01T02:19:08Z2021-01-01T00:00:00ZNuclear forensics of uranium conversion: investigations of environmentally altered uranium compounds
Pastoor, Kevin J.
Uranium conversion, the chemical process used to convert uranium ore concentrates (UOCs) to uranium hexafluoride (UF6), is an essential step in the nuclear fuel cycle. All uranium destined for applications requiring isotopic enrichment must be converted to UF6. Understanding the chemistry of uranium compounds coupled to the conversion process is important to both the nuclear forensics community and nuclear industry. To address a critical knowledge gap, an emerging area of research is investigating environmentally driven changes in fuel cycle relevant uranium compounds. This dissertation focuses on UOCs and uranium tetrafluoride (UF4), important compounds coupled to the uranium conversion process.
The initial work focused on an emerging hardening phenomenon observed in UOCs stored for prolonged periods. Characterization of several free-flowing and hardened UOC samples revealed the hardened material had undergone hydration and oxidation evidenced by elevated moisture content and the presence of various uranium compounds, particularly metaschoepite [(UO2)4O(OH)6](H2O)5 and schoepite [(UO2)4O(OH)6](H2O)6, not found in the parent material. Drying and calcination was shown to be a means of remediating un-processable, hardened UOCs, and identified a compound of potential nuclear forensics interest, dehydrated schoepite (UO2)4O(OH)6. A controlled aging study of three UOC chemical forms found they were stable for up to 9 months in low to moderate (<40%) relative humidity (RH) but higher RH (>67%) drove changes in chemical speciation, primarily forming metaschoepite. Overall, this work determined the hardening phenomenon stems from a chemical transformation in UOCs wherein H2O, either liquid or vapor, is an essential reactant.
Moving forward in the uranium conversion process, the next effort investigated UF4. A controlled aging study found UF4 was stable for up to 9 months for a wide range of environmentally relevant conditions (20 and 35 °C, and ≤75% RH). However, exposure to higher RH conditions (>90%) drove changes in chemical speciation. Specifically, UF4 hydrate formed within 30 days for UF4 aged at 20 °C and 95% RH and within 180 days for UF4 aged at 35 °C and 91% RH. Investigation of the surface composition of unaged and aged UF4 samples revealed degradation of the surface consistent with the degradation observed for the bulk UF4. This work determined UF4 may persist in the environment for several months unless exposed to very high RH conditions, driving formation of UF4 hydrates.
Finally, UF4·2.5H2O, recently identified as a relevant compound for nuclear forensics, nuclear fuel cycle science, and environmental concerns, was structurally characterized using density functional theory (DFT) and neutron powder diffraction. Complete elucidation of the structure revealed an extensive hydrogen bonding network involving water-fluorine and water-water interactions. Low temperature experiments and thermal analysis showed UF4·2.5H2O is thermally stable from 10 to 358 K, undergoes dehydration at higher temperatures and is nearly dehydrated at 473 K. This work determined UF4·2.5H2O is thermally stable at environmentally relevant temperatures, indicating it may persist in the environment.
Overall, this work demonstrates the importance of understanding environmentally driven changes in relevant nuclear materials. It has shown that uranium compounds, including compounds previously considered stable, may undergo changes in chemical speciation when exposed to certain environmental conditions. These chemical speciation changes can be problematic for the nuclear industry, but the resulting compounds may be useful to the nuclear forensics and nuclear nonproliferation community as indicators of UOCs and UF4 exposed to very high RH or liquid H2O during storage. Future work should consider the role of minor impurities, additional uranium compounds, and other fuel cycle relevant nuclear materials.
Includes bibliographical references.; 2021 Fall.
2021-01-01T00:00:00ZSoil burn severity and climatic analysis of post-wildfire soil hydraulic properties from across the western continental United StatesBedwell, Caroline J.http://hdl.handle.net/11124/143152022-08-11T02:16:15Z2021-01-01T00:00:00ZSoil burn severity and climatic analysis of post-wildfire soil hydraulic properties from across the western continental United States
Bedwell, Caroline J.
Rainfall infiltration into soil is a key factor in both landscape development and generation of rainfall-runoff hazards like flash flooding and debris flows in recently burned areas. However, infiltration capacity is spatially and temporally variable, which makes its prediction challenging, particularly in burned environments. The extent of fire-prone areas in the western United States is growing, and locations where historically wildfires were rare are burning more frequently, highlighting a need for additional study of post-wildfire soil hydrology and associated hazards.
In this work, I have compiled and re-analyzed new and existing post-wildfire Mini Disk infiltration datasets from two dozen wildfires across the western United States. This compilation contains field saturated hydraulic conductivity (KFS) estimates from different soil burn severity classes and collection times post-burn. I quantified the impact of three common methodologies for KFS estimation on the re-processed compilation, and assessed the overall fit of burned KFS estimates to normal family statistical distributions. To test if the observed variability in post-wildfire infiltration behavior can be explained by other landscape and climatological factors, I analyzed these datasets in conjunction with soil burn severity, climatological, and environmental data from each site. My results show that cumulative infiltration (CI), cumulative linearization (CL), and differentiated linearization (DL) methods for KFS estimation produce significantly different outcomes at different spatial and temporal scales, and estimates produced using these methods should not be directly compared if precision is required. Additionally, KFS estimates from burned environments do not show strong linear correlations with climatic and other environmental variables; however, the average change in KFS estimates between burn severity classes does show an inverse linear relationship with both 15-minute duration rainfall intensity for a 2-year recurrence interval storm, and pre-wildfire soil moisture. Better understanding of how post-wildfire infiltration behavior relates to regional climatic variables and burn conditions will be valuable in post-wildfire hazard prediction and modeling under the current regime of rapidly changing wildfire behavior.
Includes bibliographical references.; 2021 Fall.
2021-01-01T00:00:00ZDesign and development of a hybrid near field and far field antenna measurement system, TheVelasco, Andreshttp://hdl.handle.net/11124/143142022-08-11T02:15:29Z2021-01-01T00:00:00ZDesign and development of a hybrid near field and far field antenna measurement system, The
Velasco, Andres
In this thesis, a dual-purpose antenna chamber measurement system is presented. The measurement system is an anechoic chamber where the near-fields or far-fields of an antenna can be measured with the same equipment. A custom software was developed to perform either type of measurement. This antenna chamber is a much more cost-effective solution compared to conventional antenna chambers, where separate chambers are used for different types of measurements. This thesis presents the developed software and hardware for a custom-made chamber design that produces accurate results.
Both mechanical and software capabilities are introduced, but emphasis is put on the development of the software capabilities throughout this thesis. Both theoretical, numerical, and experimental analysis is introduced to verify the performance of the chamber. The necessary methods to perform the near-field to far-field transformations are presented and discussed in detail. A circular patch antenna is designed, simulated and tested to verify the accuracy of the far fields measured in the chamber, and a broadband horn antenna is measured to verify the accuracy of the near field measurements. The measured results for these two types of antennas matched the expected results, verifying the accuracy of each measurement type. Lastly, an antenna array is tested using both far field and near field systems, and the results from both measurement system were compared with each other. Good agreement is obtained, but due to the physical limitations related to the equipment used in the chamber and the size of the antenna some differences in the far field patterns are observed.
Includes bibliographical references.; 2021 Fall.
2021-01-01T00:00:00Z