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Item Biofilm enhanced subsurface sequestration of supercritical CO2(2009-01) Mitchell, Andrew C.; Phillips, Adrienne J.; Hiebert, Dwight Randall; Gerlach, Robin; Cunningham, Alfred B.In order to develop subsurface CO2 storage as a viable engineered mechanism to reduce the emission of CO2 into the atmosphere, any potential leakage of injected supercritical CO2 (SC-CO2) from the deep subsurface to the atmosphere must be reduced. Here, we investigate the utility of biofilms, which are microorganism assemblages firmly attached to a surface, as a means of reducing the permeability of deep subsurface porous geological matrices under high pressure and in the presence of SC-CO2, using a unique high pressure (8.9 MPa), moderate temperature (32 °C) flow reactor containing 40 millidarcy Berea sandstone cores. The flow reactor containing the sandstone core was inoculated with the biofilm forming organism Shewanella fridgidimarina. Electron microscopy of the rock core revealed substantial biofilm growth and accumulation under high-pressure conditions in the rock pore space which caused >95% reduction in core permeability. Permeability increased only slightly in response to SC-CO2 challenges of up to 71 h and starvation for up to 363 h in length. Viable population assays of microorganisms in the effluent indicated survival of the cells following SC-CO2 challenges and starvation, although S. fridgidimarina was succeeded by Bacillus mojavensis and Citrobacter sp. which were native in the core. These observations suggest that engineered biofilm barriers may be used to enhance the geologic sequestration of atmospheric CO2.Item Microbially enhanced carbonate mineralization and the geologic containment of CO2(2008) Mitchell, Andrew C.; Phillips, Adrienne J.; Kaszuba, John P.; Hollis, W. Kirk; Cunningham, Alfred B.; Gerlach, RobinGeologic sequestration of CO2 involves injection into deep underground formations including oil beds, un-minable coal seams, and saline aquifers with temperature and pressure conditions such that CO2 will likely be in the supercritical state. Supercritical CO2 injection into the receiving formation will result in elevated pressure in the region surrounding the point of injection, and may result in an upward hydrodynamic pressure gradient and associated “leakage†of supercritical to gaseous CO2. Therefore mechanisms to reduce leakage and to mineralize CO2 in a solid form are extremely advantageous for the long-term geologic containment of CO2.This paper will focus on microbially-based strategies for controlling leakage and sequestrating supercritical CO2 during geologic injection. We will examine the concept of using engineered microbial barriers (Cunningham et al., in review; Mitchell et al., in review) which are capable of precipitating calcium carbonate (Mitchell and Ferris, 2005; 2006) under high-pressure subsurface conditions. These “biomineralization barriers†may provide a method for plugging preferential flow pathways in the vicinity of CO2 injection, thereby reducing the potential for unwanted upward migration of CO2, as well as mineralizing injected CO2. A summary of experiments investigating biofilm and associated calcium carbonate formation in porous media using a unique high pressure (8.9 MPa), moderate temperature (≥ 32 °C) flow reactor will be presented, and the potential for biomineralization enhanced CO2 sequestration discussed.Item Resilience of planktonic and biofilm cultures to supercritical CO2(2008-12) Mitchell, Andrew C.; Phillips, Adrienne J.; Hamilton, Martin A.; Gerlach, Robin; Hollis, W. Kirk; Kaszuba, John P.; Cunningham, Alfred B.Supercritical CO2 has been shown to act as a disinfectant against microorganisms. These organisms have most often been tested in vegetative or spore form. Since biofilm organisms are typically more resilient to physical, chemical, and biological stresses than the same organisms in planktonic form, they are often considered more difficult to eradicate. It is therefore hypothesized that supercritical CO2 (SC–CO2) induced inactivation of biofilm organisms would be less effective than against planktonic (suspended) growth cultures of the same organism. Six-day old biofilm cultures as well as suspended planktonic cultures of Bacillus mojavensis were exposed to flowing SC–CO2 at 136 atm and 35 ◦C for 19 min and slowly depressurized after treatment. After SC–CO2 exposure, B. mojavensis samples were analyzed for total and viable cells. Suspended cultures revealed a 3 log10 reduction while biofilm cultures showed a 1 log10 reduction in viable cell numbers. These data demonstrate that biofilm cultures of B. mojavensis are more resilient to SC–CO2 than suspended planktonic communities. It is hypothesized that the small reduction in the viability of biofilm microorganisms reflects the protective effects of extracellular polymeric substances (EPS) which make up the biofilm matrix, which offer mass transport resistance, a large surface area, and a number of functional groups for interaction with and immobilization of CO2. The resistance of biofilm suggests that higher pressures, longer durations of SC–CO2 exposure, and a quicker depressurization rate may be required to eradicate biofilms during the sterilization of heat-sensitive materials in medical and industrial applications. However, the observed resilience of biofilms to SC–CO2 is particularly promising for the prospective application of subsurface biofilms in the subsurface geologic sequestration of CO2.Item Detecting Microbially Induced Calcite Precipitation in a Model Well-Bore Using Downhole Low-Field NMR(2017-02) Kirkland, Catherine M.; Zanetti, Sam; Grunewald, Elliot; Walsh, David O.; Codd, Sarah L.; Phillips, Adrienne J.Microbially induced calcite precipitation (MICP) has been widely researched recently due to its relevance for subsurface engineering applications including sealing leakage pathways and permeability modification. These applications of MICP are inherently difficult to monitor nondestructively in time and space. Nuclear magnetic resonance (NMR) can characterize the pore size distributions, porosity, and permeability of subsurface formations. This investigation used a low-field NMR well-logging probe to monitor MICP in a sand-filled bioreactor, measuring NMR signal amplitude and T2 relaxation over an 8 day experimental period. Following inoculation with the ureolytic bacteria, Sporosarcina pasteurii, and pulsed injections of urea and calcium substrate, the NMR measured water content in the reactor decreased to 76% of its initial value. T2 relaxation distributions bifurcated from a single mode centered about approximately 650 ms into a fast decaying population (T2 less than 10 ms) and a larger population with T2 greater than 1000 ms. The combination of changes in pore volume and surface minerology accounts for the changes in the T2 distributions. Destructive sampling confirmed final porosity was approximately 88% of the original value. These results indicate the low-field NMR well-logging probe is sensitive to the physical and chemical changes caused by MICP in a laboratory bioreactor.Item NMR relaxation measurements of biofouling in model and geological porous media(2011-09) Codd, Sarah L.; Vogt, Sarah J.; Hornemann, Jennifer A.; Phillips, Adrienne J.; Maneval, James E.; Romanenko, K. R.; Hansen, L.; Cunningham, Alfred B.; Seymour, Joseph D.Recently 2D nuclear magnetic resonance (NMR) relaxation techniques have been able to access changes in pore structures through surface and diffusion based relaxation measurements. This research investigates the applicability of these methods for measuring pore and surface changes due to biofilm growth in various model porous systems and natural geological media. Model bead packs of various construction containing 100 lm borosilicate and soda lime glass beads were used to demonstrate how changes in the measured relaxation rates can be used to non-invasively verify and quantify biofilm growth in porous media. However significant challenges are shown to arise when trying to implement the same techniques to verify biofilm growth in a natural geological media.Item Reducing the risk of well bore leakage using engineered biomineralization barriers(2011-04) Cunningham, Alfred B.; Gerlach, Robin; Spangler, Lee H.; Mitchell, Andrew C.; Park, Saehan; Phillips, Adrienne J.If CO2 is injected in deep geological formations it is important that the receiving formation hassufficient porosity and permeability for storage and transmission and be overlain by a suitable low-permeability cap rock formation. When the resulting CO2 plume encounters a well bore, leakage may occur through various pathways in the “disturbed zone†surrounding the well casing. Gasda et al.[9], propose a method for determining effective well bore permeability from a field pressure test. If permeability results from such tests prove unacceptably large, strategies for in situ mitigation of potential leakage pathways become important. To be effective, leakage mitigation methods must block leakage pathways on timescales longer than the plume will be mobile, be able to be delivered without causing well screen plugging, and be resistant to supercritical CO2 (ScCO2) challenges. Traditional mitigation uses cement, a viscous fluid that requires a large enough aperture for delivery and that also must bond to the surrounding surfaces in order to be effective. Technologies that can be delivered via low viscosity fluids and that can effectively plug small aperture pathways, or even the porous rock surrounding the well could have significant advantages for some leakage scenarios.We propose a microbially mediated method for plugging preferential leakage pathways and/or porous media, thereby lowering the risk of unwanted upward migration of CO2, similar to thatdiscussed by Mitchell et al.[12].We examine the concept of using engineered microbial biofilms which are capable of precipitating crystalline calcium carbonate using the process of ureolysis. The resulting combination of biofilm plus mineral deposits, if targeted near points of CO2 injection, may result in the long-term sealing of preferential leakage pathways. Successful development of these biologically-based concepts could result in a CO2 leakage mitigation technology which can be applied either before CO2 injection or as a remedial measure. Results from laboratory column studies are presented which illustrate how biomineralization deposits can be developed along packed sand columns at length scales of 2.54 cm and 61 cm. Strategies for controlling mineral deposition of uniform thickness along the axis of flow are also discussed.Item Darcy-scale modeling of microbially induced carbonate mineral precipitation in sand columns(2012-07) Ebigbo, Anozie; Phillips, Adrienne J.; Gerlach, Robin; Helmig, Rainer; Cunningham, Alfred B.; Class, Holger; Spangler, Lee H.This investigation focuses on the use of microbially induced calcium carbonate precipitation (MICP) to set up subsurface hydraulic barriers to potentially increase storage security near wellbores of CO2 storage sites. A numerical model is developed, capable of accounting for carbonate precipitation due to ureolytic bacterial activity as well as the flow of two fluid phases in the subsurface. The model is compared to experiments involving saturated flow through sand-packed columns to understand and optimize the processes involved as well as to validate the numerical model. It is then used to predict the effect of dense-phase CO2 and CO2-saturated water on carbonate precipitates in a porous medium.Item Potential CO2 leakage reduction through biofilm-induced calcium carbonate precipitation(2013-01) Phillips, Adrienne J.; Lauchnor, Ellen G.; Eldring, Joseph; Esposito, R.; Mitchell, Andrew C.; Gerlach, Robin; Cunningham, Alfred B.; Spangler, Lee H.Mitigation strategies for sealing high permeability regions in cap rocks, such as fractures or improperly abandoned wells, are important considerations in the long term security of geologically stored carbon dioxide (CO2). Sealing technologies using low-viscosity fluids are advantageous in this context since they potentially reduce the necessary injection pressures and increase the radius of influence around injection wells. Using aqueous solutions and suspensions that can effectively promote microbially induced mineral precipitation is one such technology. Here we describe a strategy to homogenously distribute biofilm-induced calcium carbonate (CaCO3) precipitates in a 61 cm long sandfilled column and to seal a hydraulically fractured, 74 cm diameter Boyles Sandstone core. Sporosarcina pasteurii biofilms were established and an injection strategy developed to optimize CaCO3 precipitation induced via microbial urea hydrolysis. Over the duration of the experiments, permeability decreased between 2 and 4 orders of magnitude in sand column and fractured core experiments, respectively. Additionally, after fracture sealing, the sandstone core withstood three times higher well bore pressure than during the initial fracturing event, which occurred prior to biofilm-induced CaCO3 mineralization. These studies suggest biofilm-induced CaCO3 precipitation technologies may potentially seal and strengthen fractures to mitigate CO2 leakage potential.Item Microbial CaCO3 mineral formation and stability in an experimentally simulated high pressure saline aquifer with supercritical CO2(2013-07) Mitchell, Andrew C.; Phillips, Adrienne J.; Schultz, Logan N.; Parks, Stacy L.; Spangler, Lee H.; Cunningham, Alfred B.; Gerlach, RobinThe use of microbiologically induced mineralization to plug pore spaces is a novel biotechnology to mitigate the potential leakage of geologically sequestered carbon dioxide from preferential leakage pathways. The bacterial hydrolysis of urea (ureolysis) which can induce calcium carbonate precipitation, via a pH increase and the production of carbonate ions, was investigated under conditions that approximate subsurface storage environments, using a unique high pressure (∼7.5 MPa) moderate temperature (32 °C) flow reactor housing a synthetic porous media core. The synthetic core was inoculated with the ureolytic organism Sporosarcina pasteurii and pulse-flow of a urea inclusive saline growth medium was established through the core. The system was gradually pressurized to 7.5 MPa over the first 29 days. Concentrations of NH4+, a by-product of urea hydrolysis, increased in the flow reactor effluent over the first 20 days, and then stabilized at a maximum concentration consistent with the hydrolysis of all the available urea. pH increased over the first 6 days from 7 to 9.1, consistent with buffering by NH4+ ⇔ NH3 + H+. Ureolytic colony forming units were consistently detected in the reactor effluent, indicating a biofilm developed in the high pressure system and maintained viability at pressures up to 7.5 MPa. All available calcium was precipitated as calcite. Calcite precipitates were exposed to dry supercritical CO2 (scCO2), water-saturated scCO2, scCO2-saturated brine, and atmospheric pressure brine. Calcite precipitates were resilient to dry scCO2, but suffered some mass loss in water-saturated scCO2 (mass loss 17 ± 3.6% after 48 h, 36 ± 7.5% after 2 h). Observations in the presence of scCO2 saturated brine were ambiguous due to an artifact associated with the depressurization of the scCO2 saturated brine before sampling. The degassing of pressurized brine resulted in significant abrasion of calcite crystals and resulted in a mass loss of approximately 92 ± 50% after 48 h. However dissolution of calcite crystals in brine at atmospheric pressure, but at the pH of the scCO2 saturated brine, accounted for only approximately 7.8 ± 2.2% of the mass loss over the 48 h period. These data suggest that microbially induced mineralization, with the purpose of reducing the permeability of preferential leakage pathways during the operation of GCS, can occur under high pressure scCO2 injection conditions.Item Design of a meso-scale high pressure vessel for the laboratory examination of biogeochemical subsurface processes(2015-02) Phillips, Adrienne J.; Eldring, Joseph; Hiebert, Dwight Randall; Lauchnor, Ellen G.; Mitchell, Andrew C.; Cunningham, Alfred B.; Spangler, Lee H.; Gerlach, RobinBiocides are critical components of hydraulic fracturing (“fracking†) fluids used for unconventional shale gas development. Bacteria may cause bioclogging and inhibit gas extraction, produce toxic hydrogen sulfide, and induce corrosion leading to downhole equipment failure. The use of biocides such as glutaraldehyde and quaternary ammonium compounds has spurred a public concern and debate among regulators regarding the impact of inadvertent releases into the environment on ecosystem and human health. This work provides a critical review of the potential fate and toxicity of biocides used in hydraulic fracturing operations. We identified the following physicochemical and toxicological aspects as well as knowledge gaps that should be considered when selecting biocides: (1) uncharged species will dominate in the aqueous phase and be subject to degradation and transport whereas charged species will sorb to soils and be less bioavailable; (2) many biocides are short-lived or degradable through abiotic and biotic processes, but some may transform into more toxic or persistent compounds; (3) understanding of biocides’ fate under downhole conditions (high pressure, temperature, and salt and organic matter concentrations) is limited; (4) several biocidal alternatives exist, but high cost, high energy demands, and/or formation of disinfection byproducts limits their use. This review may serve as a guide for environmental risk assessment and identification of microbial control strategies to help develop a sustainable path for managing hydraulic fracturing fluids.