Browsing by Author "Hommel, Johannes"

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Field-scale modeling of microbially induced calcite precipitation
(2018-11) Cunningham, Alfred B.; Class, Holger; Ebigbo, Anozie; Gerlach, Robin; Phillips, Adrienne J.; Hommel, Johannes
The biogeochemical process known as microbially induced calcite precipitation (MICP) is being investigated for engineering and material science applications. To model MICP process behavior in porous media, computational simulators must couple flow, transport, and relevant biogeochemical reactions. Changes in media porosity and permeability due to biomass growth and calcite precipitation, as well as their effects on one another must be considered. A comprehensive Darcy-scale model has been developed by Ebigbo et al. (Water Resour. Res. 48(7), W07519, 2012) and Hommel et al. (Water Resour. Res. 51, 3695–3715, 2015) and validated at different scales of observation using laboratory experimental systems at the Center for Biofilm Engineering (CBE), Montana State University (MSU). This investigation clearly demonstrates that a close synergy between laboratory experimentation at different scales and corresponding simulation model development is necessary to advance MICP application to the field scale. Ultimately, model predictions of MICP sealing of a fractured sandstone formation, located 340.8 m below ground surface, were made and compared with corresponding field observations. Modeling MICP at the field scale poses special challenges, including choosing a reasonable model-domain size, initial and boundary conditions, and determining the initial distribution of porosity and permeability. In the presented study, model predictions of deposited calcite volume agree favorably with corresponding field observations of increased injection pressure during the MICP fracture sealing test in the field. Results indicate that the current status of our MICP model now allows its use for further subsurface engineering applications, including well-bore cement sealing and certain fracture-related applications in unconventional oil and gas production.
Finding a Balance between Accuracy and Effort For Modeling Biomineralization
(2016-11) Hommel, Johannes; Ebigbo, Anozie; Gerlach, Robin; Cunningham, Alfred B.; Helmig, Rainer; Class, Holger
Microbially induced calcite precipitation (MICP) is a technology aiming at the mitigation of potential leakage from underground gas storage sites. A numerical model for MICP was previously developed and validated. The model complexity leads to high computation times, prohibiting at the moment the use of the model for designing field-scale MICP applications. This study investigates savings of the computational time by well-chosen model simplifications. Additionally, this approach is motivated by the high uncertainty of relevant input-parameters. Excessively detailed equations are unnecessary burdens to the MICP model, whose reliability is influenced by the input-parameter uncertainty.
Investigating the influence of the initial biomass distribution and injection strategies on biofilm-mediated calcite precipitation in porous media
(2016-09) Hommel, Johannes; Lauchnor, Ellen G.; Gerlach, Robin; Cunningham, Alfred B.; Ebigbo, Anozie; Helmig, Rainer; Class, Holger
Attachment of bacteria in porous media is a complex mixture of processes resulting in the transfer and immobilization of suspended cells onto a solid surface within the porous medium. Quantifying the rate of attachment is difficult due to the many simultaneous processes possibly involved in attachment, including straining, sorption, and sedimentation, and the difficulties in measuring metabolically active cells attached to porous media. Preliminary experiments confirmed the difficulty associated with measuring active Sporosarcina pasteurii cells attached to porous media. However, attachment is a key process in applications of biofilm-mediated reactions in the subsurface such as microbially induced calcite precipitation. Independent of the exact processes involved, attachment determines both the distribution and the initial amount of attached biomass and as such the initial reaction rate. As direct experimental investigations are difficult, this study is limited to a numerical investigation of the effect of various initial biomass distributions and initial amounts of attached biomass. This is performed for various injection strategies, changing the injection rate as well as alternating between continuous and pulsed injections. The results of this study indicate that, for the selected scenarios, both the initial amount and the distribution of attached biomass have minor influence on the Ca2+2+ precipitation efficiency as well as the distribution of the precipitates compared to the influence of the injection strategy. The influence of the initial biomass distribution on the resulting final distribution of the precipitated calcite is limited, except for the continuous injection at intermediate injection rate. But even for this injection strategy, the Ca2+2+ precipitation efficiency shows no significant dependence on the initial biomass distribution.
A Numerical Model for Enzymatically Induced Calcium Carbonate Precipitation
(MDPI, 2020-06) Hommel, Johannes; Akyel, Arda; Frieling, Zachary; Phillips, Adrienne J.; Gerlach, Robin; Cunningham, Alfred B.; Class, Holger
Enzymatically induced calcium carbonate precipitation (EICP) is an emerging engineered mineralization method similar to others such as microbially induced calcium carbonate precipitation (MICP). EICP is advantageous compared to MICP as the enzyme is still active at conditions where microbes, e.g., Sporosarcina pasteurii, commonly used for MICP, cannot grow. Especially, EICP expands the applicability of ureolysis-induced calcium carbonate mineral precipitation to higher temperatures, enabling its use in leakage mitigation deeper in the subsurface than previously thought to be possible with MICP. A new conceptual and numerical model for EICP is presented. The model was calibrated and validated using quasi-1D column experiments designed to provide the necessary data for model calibration and can now be used to assess the potential of EICP applications for leakage mitigation and other subsurface modifications.
A revised model for microbially induced calcite precipitation: Improvements and new insights based on recent experiments
(2015-05) Hommel, Johannes; Lauchnor, Ellen G.; Phillips, Adrienne J.; Gerlach, Robin; Cunningham, Alfred B.; Helmig, Rainer; Ebigbo, Anozie; Class, Holger
The model for microbially induced calcite precipitation (MICP) published by Ebigbo et al. (2012) has been improved based on new insights obtained from experiments and model calibration. The challenge in constructing a predictive model for permeability reduction in the underground with MICP is the quantification of the complex interaction between flow, transport, biofilm growth, and reaction kinetics. New data from Lauchnor et al. (2015) on whole-cell ureolysis kinetics from batch experiments were incorporated into the model, which has allowed for a more precise quantification of the relevant parameters as well as a simplification of the reaction kinetics in the equations of the model. Further, the model has been calibrated objectively by inverse modeling using quasi-1D column experiments and a radial flow experiment. From the postprocessing of the inverse modeling, a comprehensive sensitivity analysis has been performed with focus on the model input parameters that were fitted in the course of the model calibration. It reveals that calcite precipitation and concentrations of inline image and inline image are particularly sensitive to parameters associated with the ureolysis rate and the attachment behavior of biomass. Based on the determined sensitivities and the ranges of values for the estimated parameters in the inversion, it is possible to identify focal areas where further research can have a high impact toward improving the understanding and engineering of MICP.