Gravity-driven controls on fluid and carbonate precipitation distributions in fractures

Abstract

Many challenges related to carbon-dioxide ($$\hbox {CO}_2$$ CO 2 ) sequestration in subsurface rock are linked to the injection of fluids through induced or existing fracture networks and how these fluids are altered through geochemical interactions. Here, we demonstrate that fluid mixing and carbonate mineral distributions in fractures are controlled by gravity-driven chemical dynamics. Using optical imaging and numerical simulations, we show that a density contrast between two miscible fluids causes the formation of a low-density fluid runlet that increases in areal extent as the fracture inclination decreases from 90$$^\circ$$ ∘ (vertical fracture plane) to 30$$^\circ$$ ∘ . The runlet is sustained over time and the stability of the runlet is controlled by the gravity-driven formation of 3D vortices that arise in a laminar flow regime. When homogeneous precipitation was induced, calcium carbonate covered the entire surface for horizontal fractures (0$$^\circ$$ ∘ ). However, for fracture inclinations greater than 10$$^\circ$$ ∘ , the runlet formation limited the areal extent of the precipitation to less than 15% of the fracture surface. These insights suggest that the ability to sequester $$\hbox {CO}_2$$ CO 2 through mineralization along fractures will depend on the fracture orientation relative to gravity, with horizontal fractures more likely to seal uniformly.

Emergence of Unstable Focused Flow Induced by Variable‐Density Flows in Vertical Fractures

“…From the concentration distributions (Figure 13e) of Case 11, although the inertial force is smaller, the lower part of the runlet is still straight due to the inertial force. Further, the upper part of the runlet is unstable in both cases but the wavelength in Case 11 is significantly shorter than that in the reference case, which is consistent with what is observed in laboratory experiments (Xu et al, 2023). Studies on confined laminar impinging slot-jet also reported that the size of a vortex increases with increasing Reynolds number (Sexton et al, 2018;Sivasamy et al, 2007).…”

“…The denser fluid (Fluid 1) also contained a dye (Brocresol green) to enable the imaging of fluid distributions, and a RaspberryPi spy camera was used for digital imaging. Readers are referred to Xu et al (2023) for additional experimental details.…”