Effect Of Geometry And Fluid Viscosity On Dynamics Of Fluid-Filled Cracks: Insights From Analog Experimental Observations

Fluid-filled volumes in geological systems can change the local stress field in the host rock and may induce brittle deformation as well as crack propagation. Although the mechanisms relating fluid pressure perturbations and seismicity have been widely studied, the fluid-solid interaction inside the crack of a host rock is still not well understood. An analog experimental model of fluid intrusion in cracks between planar layers has been developed to study stress conditions at the margins and tips. A combined high-speed shadowgraph and a photoelasticity imaging system is used to visualize the fluid dynamics and induced stresses on the solid matrix. Cavitation, as well as bubble growth and collapse, occurs along the sawtooth crack margins, which produces a highly localized stress concentration to initiate new subcrack systems. The presence of the bubbles at the crack tip during fluid pressure perturbation can enhance crack propagation.Plain Language Summary Cracks serve as important fluid pathways in the crust, so their characteristics and density strongly influence fluid flow. At the same time, crack properties are also affected by fluid flow, as their dimensions and connectivity might change under pressures from fluids. Many analytical and experimental studies have been conducted to investigate the effect of subsurface flow on crack dynamics. However, some complexities of crack geometries and fluid properties, in particular when bubbles are present, remain poorly understood. We developed a laboratory analog experiment using an optical imaging system to visualize the induced stresses on a crack. Fluid cavitation and collapse occurring at the margins of a rough crack boundary are observed. In addition, gas bubbles at crack tips significantly contribute to the crack opening. Both observations may help explain crack propagation in underground geological systems.