Leakage dynamics of fault zones: experimental and analytical study with application to CO2 storage.

The injected brine solutions had an initial dye concentration of Graph $c 0 = 3.00 \pm 0.05$ g l Graph $^{-1}$ and an initial density Graph $\rho 0 = 1.030$ or 1.070 g cm Graph $^{-3}$, assuming a water temperature of 20 Graph $^{\circ }$ C (Green & Southard 2019). The injected fluid spreads below an impermeable horizontal baffle containing a fault of gap width Graph $d f$, thickness Graph $h f$, permeability Graph $k f$ and porosity Graph $\phi f$ which abuts the boundary. Less dense CO Graph $ 2$ is injected at a constant rate of 0.1 Mt yr Graph $^{-1}$ at the bottom of layer 1, and assumed to have constant density Graph $\rho = 790$ kg m Graph $^{-3}$ and dynamic viscosity Graph $\mu = 6.9 \times 10^{-5}$ Pa s, calculated at typical storage reservoir conditions of 15 MPa and 40 Graph $^{\circ }$ C (Dubacq, Bickle & Evans 2013). Figure 2( I b i ) shows three height profiles at Graph $\tilde {t}=0.5$, Graph $\tilde {t}=5$ and Graph $\tilde {t}=50$ (solid lines), where the extent and height of the profiles have been normalised by the maximum extent Graph $\tilde {x} N$ and the thickness of the current at Graph $\tilde {x}=0$, Graph $\tilde {h} 0$. In diffusion dominated flows, where Graph ${\textit {Pe}} \ll 1$, the transport coefficient Graph $D\simeq D d/\tau$ is constant whereas in advection dominated flows, where Graph ${\textit {Pe}} \gg 1$, Graph $D\simeq d 0U$ is dependent on the flow speed. [Extracted from the article]