Characterization of karst systems, especially the assessment of structure and geometry of conduits along with forecast of state-variables, are essential for groundwater quality/quantity management and implementation/rehabilitation of large-scale engineering projects in karst regions. These objectives can be fully met by utilizing process-based discrete-continuum models, such as MODFLOW-2005 CFPv2, as employed here. However, such tools should be used with the caveat of the potential non-uniqueness of results. This research focuses on the joint-inversion of discharge, water temperature, and solute concentration signatures of Freiheit Spring in Minnesota, USA, in response to a spatiotemporally small-scale hydraulic and transport experiment. Adopting the multi-model concept to address conceptual uncertainty, seven distinctive model variants were considered. Spring hydro-chemo-thermo-graphs for all variants were simultaneously simulated, employing joint-inversion by PEST. Subsequently, calibrated models were compared in terms of calibration performance, parameter uncertainties and reasonableness, as well as forecast capability. Overall, results reveal the reliability of the discrete-continuum flow and transport modeling, even at a spatiotemporally small-scale, on the order of meters and seconds. All conceptualized variants suggest almost identical conduit tracer passage sizes which are close to the flood-pulse method estimates. In addition, the significance of immobile conduit-associated-drainable storages in karst hydrodynamic modeling, which is uniquely provided in our model code, was highlighted. Moreover, it was demonstrated that the spring thermograph and hydrograph carry more information about the aquifer characteristics than the chemograph. However, this last result can be site-specific and depends on the scale of the experiment and the conceptualized variants of the respective hydrological state.

This poster presents field-scale numerical compositional simulations of CO2 storage mechanisms in the Morrow B sandstone of the Farnsworth Unit (FWU) located in Ochiltree County, Texas. The study examines structural-stratigraphic, residual, solubility and mineral trapping mechanisms. The reactive transport modeling incorporated evaluates the field’s potential for long-term CO2 sequestration and predicts the CO2 injection effects on the pore fluid composition, mineralogy, porosity and permeability. The dynamic CO2 sequestration simulation model was built from an upscaled geocellar model for the Morrow B. This model incorporated geological, geophysical, and engineering data including well logs, core, 3D surface seismic and fluid analysis. We calibrated the model with historical CO2-WAG miscible flood data and used it to evaluate the feasibility and mechanisms for CO2 sequestration. We used the maximum residual phase saturations to estimate the effect of gas trapped due to hysteresis. In addition, gas solubility in the aqueous phase was modelled as function of pressure, temperature and salinity. Lastly, the coupled geochemical reactions, i.e., the characteristic intra-aqueous and mineral dissolution/precipitation reactions were assimilated numerically as chemical equilibrium and rate-dependent reactions respectively. Additional scenarios that involve shut-in of wells were performed and the reservoir monitored for over 1000 years to understand possible mineralization. Changes in permeability as a function of changes in porosity caused by mineral precipitation/dissolution were calibrated to the laboratory chemo-mechanical responses. The study validates the effects of Morrow B petrophysical properties on CO2 storage potential within the FWU. Study results shows: EOR at the tertiary stage of field operations, total amount of CO2 stored in aqueous-gaseous-mineral phases, evolution and dissolution/precipitation of the principal accessory minerals and the time scale over which mineral sequestration took place in the FWU. This study relates the important physics and mechanisms for CO2 storage in the FWU and illustrates the use of the coupled reactive flow. The study serves as a is benchmark for future field-scale reactive transport CO2-EOR projects in similar fields throughout the world.