5:15 PM - 6:45 PM
[SCG46-P14] Hydro-mechanical-chemical coupled modeling revealing fracture flow alteration and its impact on rock physical properties
Keywords:Chemical erosion, Precipitation, Permeability, Resistivity, Elastic wave velocity, Fault-valve model
Fluid flow in faults dominates subsurface heat and mass transport, owing to its high permeability and heterogeneity. Numerous previous studies have reported the channeling behavior of fracture flow, which is the formation of preferential flow pathways. Flow channeling becomes significant as the fracture closes owing to the large number of contacts. Because of non-uniform flow, mineral dissolution is accelerated where the flow rate is high. Meanwhile, the stagnant flow area will be dominated by mineral precipitation, which will be related to the fault healing process based on the idea of the fault-valve model. In this model, the seismic cycle is often interpreted as mineral precipitation or perturbation of the pore pressure. Although some geological observations have estimated the time scale of fault healing based on quartz veins, the quantitative correlation between geophysical and geological observations remains unclear. Because geophysical properties (e.g., seismic velocity and electrical resistivity) are highly sensitive to the fracture surface condition and pore pressure, it would be beneficial to evaluate the pore pressure and degree of chemical alteration through geophysical observations that can be remotely monitored. To this point, this study established hydro-mechanical-chemical coupled modeling to investigate the evolution of the fracture flow and rock physical properties as elevated stress and reactions
Synthetic faults were first generated as input to the simulation based on fractional Brownian motion and natural rough surfaces of granitic fractures. Various fracture models with different fractal characteristics were prepared. For each fracture model, normal loading up to 100 MPa was applied using a half-space-based dry contact model. Based on deformed rough surfacers, the fracture flow was calculated using the modified local cubic law, which enables us to simulate larger-scale faults while maintaining both low computational cost and high precision. The chemical reactions were solved using the level-set method. The geophysical properties were estimated using the resistor network model based on an analogy with the modified local cubic law.
Consequently, the results demonstrate that chemical erosion preferentially occurred in the critical neck of the dominant flow pathways, whereas precipitation occurred in a wider flow area. Interestingly, the permeability changed significantly with the degree of chemical erosion, whereas the resistivity and elastic properties were almost constant. These results indicate that the permeability is highly sensitive to the aperture in the critical neck, whereas the electrical and elastic properties are more sensitive to the contact area. As mineral precipitation enhances the contact area, the results also show that the elastic properties are correlated to the precipitation rate.
Synthetic faults were first generated as input to the simulation based on fractional Brownian motion and natural rough surfaces of granitic fractures. Various fracture models with different fractal characteristics were prepared. For each fracture model, normal loading up to 100 MPa was applied using a half-space-based dry contact model. Based on deformed rough surfacers, the fracture flow was calculated using the modified local cubic law, which enables us to simulate larger-scale faults while maintaining both low computational cost and high precision. The chemical reactions were solved using the level-set method. The geophysical properties were estimated using the resistor network model based on an analogy with the modified local cubic law.
Consequently, the results demonstrate that chemical erosion preferentially occurred in the critical neck of the dominant flow pathways, whereas precipitation occurred in a wider flow area. Interestingly, the permeability changed significantly with the degree of chemical erosion, whereas the resistivity and elastic properties were almost constant. These results indicate that the permeability is highly sensitive to the aperture in the critical neck, whereas the electrical and elastic properties are more sensitive to the contact area. As mineral precipitation enhances the contact area, the results also show that the elastic properties are correlated to the precipitation rate.