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1. Splitting tensile strength of shale cores: intact versus fractured and sealed with ureolysis-induced calcium carbonate precipitation (UICP)

   https://doi.org/10.1007/s40948-024-00897-0  

   Bedey, Kayla; Willett, Matthew R; Crandall, Dustin; Rutqvist, Jonny; Matteson, Kirsten; Phillips, Adrienne J; Cunningham, Alfred B; Kirkland, Catherine M (December 2024, Geomechanics and Geophysics for Geo-Energy and Geo-Resources)

   Abstract Ureolysis-induced calcium carbonate precipitation (UICP) is a biomineral solution where the urease enzyme converts urea and calcium into calcium carbonate. The resulting biomineral can bridge gaps in fractured shale, reduce undesired fluid flow, limit fracture propagation, better store carbon dioxide, and potentially enhance well efficiency. The mechanical properties of shale cores were investigated using a modified Brazilian indirect tensile strength test. An investigation of intact shale using Eagle Ford and Wolfcamp cores was conducted at varying temperatures. Results show no significant difference between shale types (average tensile strength = 6.19 MPa). Eagle Ford displayed higher strength at elevated temperature, but temperature did not influence Wolfcamp. Comparatively, cores with a single, lengthwise heterogeneous fracture were sealed with UICP and further tested for tensile strength. UICP was delivered via a flow-through method which injected 20–30 sequential patterns of ureolytic microorganisms and UICP-promoting fluids into the fracture until permeability reduced by three orders of magnitude or with an immersion method which placed cores treated with guar gum and UICP-promoting fluids into a batch reactor, demonstrating that guar gum is a suitable inclusion and may reduce the number of flow-through injections required. Tensile results for both delivery methods were variable (0.15–8 MPa), and in some cores the biomineralized fracture split apart, possibly due to insufficient sealing and/or heterogeneity in the composite UICP-shale cores. 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. 

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2. Mineralogy, morphology, and reaction kinetics of ureolytic bio-cementation in the presence of seawater ions and varying soil materials

   https://doi.org/10.1038/s41598-022-21268-3  

   Burdalski, Robert J.; Ribeiro, Bruna G. O.; Gomez, Michael G.; Gorman-Lewis, Drew (October 2022, Scientific Reports)

   Abstract Microbially-induced calcium carbonate precipitation (MICP) is a bio-cementation process that can improve the engineering properties of granular soils through the precipitation of calcium carbonate (CaCO₃) minerals on soil particle surfaces and contacts. The technology has advanced rapidly as an environmentally conscious soil improvement method, however, our understanding of the effect of changes in field-representative environmental conditions on the physical and chemical properties of resulting precipitates has remained limited. An improved understanding of the effect of subsurface geochemical and soil conditions on process reaction kinetics and the morphology and mineralogy of bio-cementation may be critical towards enabling successful field-scale deployment of the technology and improving our understanding of the long-term chemical permanence of bio-cemented soils in different environments. In this study, thirty-five batch experiments were performed to specifically investigate the influence of seawater ions and varying soil materials on the mineralogy, morphology, and reaction kinetics of ureolytic bio-cementation. During experiments, differences in reaction kinetics were quantified to identify conditions inhibiting CaCO₃precipitation and ureolysis. Following experiments, scanning electron microscopy, x-ray diffraction, and chemical composition analyses were employed to quantify differences in mineralogical compositions and material morphology. Ions present in seawater and variations in soil materials were shown to significantly influence ureolytic activity and precipitate mineralogy and morphology, however, calcite remained the predominant CaCO₃polymorph in all experiments with relative percentages exceeding 80% by mass in all precipitates. 

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3. The impacts of biomineralization and oil contamination on the compressive strength of waste plastic-filled mortar

   https://doi.org/10.1038/s41598-022-25951-3  

   Rux, Kylee; Kane, Seth; Espinal, Michael; Ryan, Cecily; Phillips, Adrienne; Heveran, Chelsea (December 2022, Scientific Reports)

   Abstract Researchers have made headway against challenges of increasing cement infrastructure and low plastic recycling rates by using waste plastic in cementitious materials. Past studies indicate that microbially induced calcium carbonate precipitation (MICP) to coat plastic in calcium carbonate may improve the strength. The objective of this study was to increase the amount of clean and contaminated waste plastic that can be added to mortar and to assess whether MICP treatment enhances the strength. The performance of plastic-filled mortar was investigated at 5%, 10%, and 20% volume replacement for cement. Untreated, clean plastics at a 20% cement replacement produced compressive strengths acceptable for several applications. However, a coating of MICP on clean waste plastic did not improve the strengths. At 10% replacement, both MICP treatment and washing of contaminated plastics recovered compressive strengths by approximately 28%, relative to mortar containing oil-coated plastics. By incorporating greater volumes of waste plastics into mortar, the sustainability of cementitious composites has the potential of being improved by the dual mechanisms of reduced cement production and repurposing plastic waste. 

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4. Fracture Characteristics of Shale: Unraveling CO2-Driven Mechanical Metamorphosis at Microscale

   https://doi.org/10.56952/ARMA-2024-0162  

   Mahgoub, S A; Abedi, S (June 2024, ARMA)

   ABSTRACT:This study investigates the distinction between unreacted shale samples and those exposed to CO2-rich brine under elevated temperature (100°C) and pressure (1800 psi) conditions over 28 days. Samples underwent scratch testing under constant loading to ensure independent penetration depth, circumventing variability associated with load-dependent outcomes prevalent in progressive loading methodologies. Vertical hardness profiles revealed significant variations between reacted and unreacted regions, influenced by differential dissolution and precipitation characteristics, while horizontal hardness provided limited insights, particularly in the reacted region where higher tangential forces and deeper scratches indicated greater material compressibility. Distinct scratch path variations were observed, with fractures absent in the ductile reacted region at lower testing forces. The shale samples were sourced from the Eagle Ford Formation, providing insights into the mechanical response of carbonate-rich shale rocks in extreme environments. This research enhances understanding of shale's mechanical properties and material responses under diverse operational conditions, elucidating interactions with influential environmental factors, particularly in CO2-exposed scenarios. Conducted at a microscale level, this study offers detailed insights into material behavior, crucial for predicting long-term stability of geostructures exposed to reactive brine and potential CO2 leakage in subsurface reservoirs. 1. INTRODUCTIONThe investigation into chemical interactions between carbonate rocks and acidic brine is cruical for understanding complex mechanical and microstructural transformations essential for applications like geostructure stability, CO2 storage, and energy exploitation. Under elevated pressure and temperature conditions, the equilibrium between injected fluids and rocks undergoes alterations, leading to geochemical responses, especially with the presence of CO2 as a supercritical phase or in aqueous form (Prakash et al. 2023a; Prakash et al. 2022). In this context, investigating fracture properties becomes essential, aiming to comprehend the development and propagation of fractures within reacted formations to evaluate structural integrity and potential pathways for fluid migration.Prior geochemical investigations have explored the localized repercussions of CO2 attacks on rock permeability, shedding light on alterations attributed to carbonate precipitation sealing fractures and pores or the dissolution of diverse minerals (Burnside et al. 2013; Minardi et al. 2021). Shale rocks exposed to acidic brine predominantly undergo carbonate reactions, particularly carbonates dissolution and precipitation (Prakash et al., 2022; Prakash et al. 2023b). Experimental studies on fracture mechanics and mechanical properties have utilized conventional methods such as single edge notched bend, chevron notched beam, three-point bending, and semi-circular bending tests, acknowledging their inherent limitations (Smith & Chowdary, 1975; Bazant and Kazemi, 1990; Helmer et al. 2014; Dubey et al., 2020). 

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5. Biotrapping Ureolytic Bacteria on Sand to Improve the Efficiency of Biocementation

   Ugur, Gizem E; Rux, Kylee; Boone, John C; Seaman, Rachel; Avci, Recep; Gerlach, Robin; Phillips, Adrienne; Heveran, Chelsea (January 2024, ACS applied materials interfaces)

   Microbially induced calcium carbonate precipitation (MICP) has emerged as a novel technology with the potential to produce building materials through lower-temperature processes. The formation of calcium carbonate bridges in MICP allows the biocementation of aggregate particles to produce biobricks. Current approaches require several pulses of microbes and mineralization media to increase the quantity of calcium carbonate minerals and improve the strength of the material, thus leading to a reduction in sustainability. One potential technique to improve the efficiency of strength development involves trapping the bacteria on the aggregate surfaces using silane coupling agents such as positively charged 3-aminopropyl-methyl-diethoxysilane (APMDES). This treatment traps bacteria on sand through electrostatic interactions that attract negatively charged walls of bacteria to positively charged amine groups. The APMDES treatment promoted an abundant and immediate association of bacteria with sand, increasing the spatial density of ureolytic microbes on sand and promoting efficient initial calcium carbonate precipitation. Though microbial viability was compromised by treatment, urea hydrolysis was minimally affected. Strength was gained much more rapidly for the APMDES-treated sand than for the untreated sand. Three injections of bacteria and biomineralization media using APMDES-treated sand led to the same strength gain as seven injections using untreated sand. The higher strength with APMDES treatment was not explained by increased calcium carbonate accrual in the structure and may be influenced by additional factors such as differences in the microstructure of calcium carbonate bridges between sand particles. Overall, incorporating pretreatment methods, such as amine silane coupling agents, opens a new avenue in biomineralization research by producing materials with an improved efficiency and sustainability. 

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