Factors affecting self‐sealing of geological faults due to CO₂‐leakage

Abstract

Injecting anthropogenic CO2 into the subsurface is suggested for climate change mitigation. However, leakage of CO2 from its target storage formation is a concern. In the event of leakage, permeability in leakage pathways such as faults may get altered due to mineral reactions induced by CO2‐enriched water, thus influencing the migration and fate of the CO2. An example of such fault permeability alteration is found in the Little Grand Wash Fault zone (LGWF), where the fault outcrops show fractures filled with calcium carbonate. To test the nature, extent, and time‐frame of such fault ‘self‐sealing’, we developed reactive flow simulations based on hydrogeological conditions of the LGWF. We measured LGWF water chemistry and conducted an x‐ray powder diffraction (XRD) analysis of the fault‐rock to constrain the model geochemistry. We hypothesized that the choice of parameters for relative permeability, capillary pressure, and reaction kinetics will have a huge impact on the fault sealing predictions. Simulation results showed that precipitation of calcite in the top portion of the fault led to a decrease in porosity of the damage zone from a value of 40% to ∼2%. Over a simulation time of 1000 years, porosity in the damage zone showed self‐enhancing behavior in the bottom portion and self‐sealing behavior in the top portion of the fault. We found that the results were most sensitive to the relative permeability parameters and the fault architecture. A major conclusion from this analysis is that, under similar conditions, some faults are likely to seal over time. © 2017 Society of Chemical Industry and John Wiley & Sons, Ltd.

420,000 year assessment of fault leakage rates shows geological carbon storage is secure

“…However, the considerably larger volumes of travertines located at the tip of the Coyote Wash Fault and along the Buttes Fault illustrate that the majority of CO 2 leakage occurred at fault induced fracture networks. The long lifespan of the studied travertine mounds highlights that CO 2 flow through fracture networks does not necessarily lead to self-sealing due to mineral precipitation as observed elsewhere 24,42 and high rates of flow can be sustained over geological times. Factors governing fluid flow through fracture networks at the study site could be of geomechanical nature as the continuous influx of magmatic CO 2 into the shallow reservoir, which is needed to sustain the high leakage rates, could increase pore pressure and potentially bring fractures closer to failure and increase the fracture permeability 5,43 .…”

Identifying Hydrogeochemical Conditions for Fault Self‐Sealing in Geological Storage

“…The effective fault porosity‐permeability was 0.21 and m , respectively. The effect of varying fault architecture on fault self‐sealing rates was analyzed in detail in Patil et al ()…”

“…To investigate these hypotheses, we tested three typical end‐member composition types and one mixed geologic mineral composition at shallow and deep subsurface conditions to represent a reasonable range of hydrogeochemical conditions. We also compared this analysis with a real fault system, the Little Grand Wash Fault zone (LGWF) in Utah that has shown self‐sealing behavior (Patil et al, ). These reactive transport results are expressed in terms of spatiotemporally evolving dimensionless Damköhler numbers.…”

Hydraulic and Mechanical Impacts of Pore Space Alterations within a Sandstone Quantified by a Flow Velocity-Dependent Precipitation Approach

“…The prediction of the resulting changes in effective hydraulic and mechanical rock properties is of paramount importance for numerous natural geochemical systems and commercial applications such as geothermal energy production [ 1 , 2 ], hydrocarbon exploration and exploitation [ 3 , 4 ], nuclear waste disposal [ 5 , 6 ] as well as energy and gas storage [ 7 , 8 , 9 ]. Within the context of subsurface utilisation, the interaction of hydraulic, mechanical and chemical processes may be triggered or preferably prevented depending on the geological application: Precipitation of minerals reduces the permeability, what could negatively impact the injectivity and productivity of a reservoir [ 10 , 11 ], but on the other hand mineral growth can seal potential leakage pathways, e.g., in the context of CO 2 storage [ 12 , 13 ]. Regarding changes in mechanical properties, an effective stiffening of rocks due to their cementation [ 14 , 15 ] may be of particular relevance for the integrity of a reservoir or fault systems.…”