Fault-zones significantly influence the migration of fluids in the subsurface and can be important controls on the local as well as regional hydrogeology. Hence, understanding the evolution of fault porosity-permeability is critical for many engineering applications (like geologic carbon sequestration, enhanced geothermal systems, groundwater remediation, etc.) as well as geological studies (like sediment diagenesis, seismic activities, hydrothermal ore deposition, etc.). The highly heterogeneous pore structure of fault-zones along with the wide range of hydrogeochemical heterogeneity that a fault-zone can cut through make conduit fault-zones a dynamic reactive transport environment that can be highly complex to accurately model. In this paper, we present a critical review of the possible ways of modeling reactive fluid flow through fault-zones, particularly from the perspective of chemically driven “self-sealing” or “self-enhancing” of fault-zones. Along with an in-depth review of the literature, we consider key issues related to different conceptual models (e.g. fault-zone as a network of fractures or as a combination of damaged zone and fault core), modeling approaches (e.g. multiple continua, discrete fracture networks, pore-scale models) and kinetics of water-rock interactions. Inherent modeling aspects related to dimensionality (e.g. 1D vs 2D) and the dimensionless Damköhler number are explored. Moreover, we use a case-study of the Little Grand Wash Fault-zone from central Utah as an example in the review. Finally, critical aspects of reactive transport modeling 2 like multiscale approaches and chemo-mechanical coupling are also addressed in the context of fault-zones.

Although geologic carbon sequestration projects have yet to induce – or may never induce – a damaging earthquake, experiences from other deep injection industries such as hydraulic fracturing, enhanced geothermal systems, and saltwater disposal suggest that effective quantitative seismic risk assessment is necessary for deep saline carbon capture and sequestration (CCS) projects. One such imminent CCS project is the San Juan Basin CarbonSAFE Phase III program. The study detailed in this paper utilizes Monte Carlo probabilistic geomechanical analyses combined with observations of the geological and operational parameters of the San Juan Basin site and suggests that this project is of low induced seismic risk. The primary analysis is split into four sections. First, we assessed the literature for faults and past seismicity, and at least five faulting scenarios are directly relevant. Second, we developed and calibrated an integrated earth model for the project site. Third, we performed Monte Carlo simulations that considered reasonable uncertainties of the geomechanical parameters. Only the Hogback flexural faulting scenario presented high Coulomb failure functions, but fourth, we determined the risk to be low based on the combined lack of historical seismicity, the geological framework of the flexural faults, and the presence of saltwater injection at the same depth as the proposed supercritical carbon dioxide injection. The most sensitive parameters in the geomechanical calculations were the fault dip and the coefficient of friction. The least sensitive were the fault strike and the orientation of the maximum horizontal principal stress.

Surface tension controls all aspects of fluid flow in porous media. Through measurements of surface tension interaction under multiphase conditions, a relative permeability relationship can be determined. Relative permeability is a numerical description of the interplay between two or more fluids and the porous media they flow through. It is a critical parameter for various tools used to characterized subsurface multiphase flow systems, such as numerical simulation for oil and gas development, carbon sequestration, and groundwater contamination remediation. Therefore, it is critical to get a good statistic distribution of relative permeability in the porous media under study. Empirical relationships for determining relative permeability from capillary pressure are already well established but do not provide the needed flexibility in that is required to match laboratory derive relative permeability relationships. By expanding the existing methods for calculating relative permeability from capillary pressure data it is possible to create both two and three-phase relative permeability relationship. Existing laboratory measured relative permeability data along with mercury intrusion capillary (MICP) data coupled with interfacial tension and contact angle measurements were used to determine the efficacy of this approach to relative permeability curve creation. The relative permeability relationships determined with this method were fit to the existing laboratory data to elucidate common fitting parameters that were then used to create relative permeability relationships from MICP data that does not have an associated laboratory measured relative permeability relationship. The study was undertaken as part of the Southwest Regional Partnership on Carbon Sequestration (SWP) under Award No. DE-FC26-05NT42591.

Although carbon sequestration projects have yet to induce – or may never induce – a damaging earthquake, experiences from other deep injection industries such as hydraulic fracturing, enhanced geothermal systems, and saltwater disposal suggest that effective quantitative seismic risk assessment is appropriate for deep saline carbon sequestration (CCS) projects. One such imminent CCS project is the San Juan Basin CarbonSAFE Phase III program. The study detailed in this paper utilizes probabilistic geomechanical analyses combined with observations of the geological and operational parameters of the San Juan Basin to show that this project is of low induced seismic risk. The primary analysis is split into four sections. First, we assessed the literature for faults and past seismicity, and at least five faulting scenarios are directly relevant. Second, we developed and calibrated a mechanical earth model for the project site. Third, we performed Monte Carlo simulations considering reasonable uncertainties of the geomechanical parameters. Only the Hogback flexural faulting scenario presented high Coulomb failure functions, but fourth, we determined the risk to be low based on the combined lack of historical seismicity, geological framework of the flexural faults, and the presence of saltwater injection at the same depth as the proposed supercritical carbon dioxide injection. In order to assess the likelihood of inducing slip on the basement faults, an analytical treatment of the poroelastic stress perturbations from the proposed injection was considered, and this also suggested a low chance for triggering or inducing earthquakes at this depth. The most sensitive parameters in the geomechanical calculations were the dip and the coefficient of friction. The least sensitive were the strike and the orientation of the maximum horizontal principal stress. In summary, results of this study suggest that the San Juan Basin CarbonSAFE project is unlikely to induce a medium- or large-scale event.