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Item Comparing the mechanical properties of shale cores: intact vs. fractured and sealed with UICP(Montana State University - Bozeman, College of Engineering, 2023) Bedey, Kayla Marjorie; Chairperson, Graduate Committee: Catherine Kirkland; This is a manuscript style paper that includes co-authored chapters.Fractures in subsurface shale formations are instrumental in the recovery of hydrocarbon resources. A result of hydraulic fracturing, these fractures have the potential to become harmful leakage pathways that may contribute undesired fluids to the atmosphere and functional groundwater aquifers. Ureolysis-induced calcium carbonate precipitation (UICP) is a biomineral solution where the urease enzyme converts urea and calcium into calcium carbonate mineral. The resulting biomineral can bridge gaps in fractured shale, reduce undesired fluid flow through leakage pathways, limit fracture propagation, better store carbon dioxide, and potentially extend the efficiency of future and existing wells. The mechanical properties of fractured shale sealed with UICP was investigated using a modified Brazilian indirect tensile strength test. Part one of this study investigated the tensile strength of shale rock using intact Eagle Ford (EF) and Wolfcamp (WC) shale cores (5.08 cm long by 2.54 cm diameter) tested at room temperature (RT) and 60°C. Results show no significant difference between shale types (average tensile strength = 6.19 MPa). EF cores displayed a higher strength at RT versus 60°C, but no difference was seen between temperatures for WC cores. Part two used UICP to seal shale cores (5.08 cm long by 2.54 cm diameter) with a single, heterogeneous fracture spanning the core length. UICP was delivered two ways: 1) the flow-through method injected 20-30 sequential patterns of microbes and UICP-promoting fluids into the fracture until fracture permeability reduced by three orders of magnitude and 2) the immersion method placed cores treated with guar gum and UICP-promoting solutions into a batch reactor, demonstrating that guar gum is a suitable inclusion to UICP-technology and may be capable of reducing the number of injections required in flow-through methodology. Tensile results for both flow-through and immersion methods were widely variable (0.15 - 8 MPa), and in some cores the biomineralized fracture split apart. Notably in other cores the biomineralized fracture remained intact, demonstrating more cohesion than the surrounding shale, indicating that UICP may produce a strong seal for subsurface application.Item Feasibility study for field-scale use of Ureolysis-Induced Calcite Precipitation (UICP) for roadbed improvement(Montana State University - Bozeman, College of Engineering, 2023) Dorian, Hudson Thomas; Chairperson, Graduate Committee: Mohammad Khosravi; Adrienne J. Phillips (co-chair); This is a manuscript style paper that includes co-authored chapters.A series of tests were conducted to evaluate the feasibility of using ureolysis-induced calcium carbonate precipitation (UICP) to improve the strength of the soil layers used to in the construction of roads. This process involved three series of tests conducted on soil specimens of gradually increasing volume. The first series regarded the relative effect of treatment direction, comparing top-down treatment to bottom-upwards and alternating treatment methods on 50-by-100-millimeter soil columns. This was evaluated through unconfined compressive strength (UCS) and the calcium carbonate distribution over the length of the soil, finding that all methods generated a reliable increase in the strength of the soil specimen. This phase of research also included a batch study, evaluating the growth of the ureolytic bacteria Sporosarcina pasteurii in a solution composed of commercially available ingredients, showing that the bacteria could be cultured at a far lower cost (as low as 20 cents per liter) than with lab-grade ingredients ($2.66 per liter). The next series of tests compared the effect of applying treatment solutions to the soil surface directly and using a probe to inject solutions beneath the surface. This was done with 15-centimeter, cylindrical specimens, evaluated through the California bearing ratio (CBR) test. It was determined that the treatment process had the capacity to increase the CBR value substantially (from ~11% up to 188%), and it was suggested that each treatment mechanism resulted in a predictable distribution of calcium carbonate. There was also success in using alternative, commercially-sourced ingredients to facilitate the treatment and improve the CBR value. The last tests centered on the treatment of a 30-centimeter-by-30-centimeter mock road section, combining the treatment mechanisms used at the 15-centimeter-scale to facilitate an increase in the CBR of a soil layer under pavement. Through UICP, the CBR value of this layer was successfully increased.