Unstable, Super Critical CO2–Water Displacement in Fine Grained Porous Media under Geologic Carbon Sequestration Conditions

Abstract

In this study we investigated fluid displacement water with supercritical (sc) CO 2 in chalk under conditions close to those used for geologic CO 2 sequestration (GCS), to answer two main questions: How much volume is available for scCO 2 injection? And what is the main mechanism of displacement over a range of temperatures? Characterization of immiscible scCO 2 displacement, at the pore scale in the complex microstructure in chalk reservoirs, offers a pathway to better understand the macroscopic processes at the continuum scale. Fluid behavior was simulated by solving the Navier-Stokes equations, using finite-volume methods within a pore network. The pore network was extracted from a high resolution 3D image of chalk, obtained using X-ray nanotomography. Viscous fingering dominates scCO 2 infiltration and pores remain only partially saturated. The unstable front, developed with high capillary number, causes filling of pores aligned with the flow direction, reaching a maximum of 70% scCO 2 saturation. The saturation rate increases with temperature but the final saturation state is the same for all investigated temperatures. The higher the saturation rate, the higher the dynamic capillary pressure coefficient. A higher dynamic capillary pressure coefficient indicates that scCO 2 needs more time to reach capillary equilibrium in the porous medium.

Influences of Dead‐End Pores in Porous Media on Viscous Fingering Instabilities and Cleanup of NAPLs in Miscible Displacements

“…It can be extended to the case considering concentration-dependent diffusion and/or velocity-induced, anisotropic dispersion (Yuan et al, 2017), depending on different scenarios and applications. Previous studies indicate that the dispersion anisotropy does not affect the qualitative features of flow dynamics (Ghesmat & Azaiez, 2008;Jha et al, 2011;Sabet et al, 2020;Zimmerman & Homsy, 1991). Therefore, in this work, we use a constant 𝐴𝐴 𝐴𝐴 and will solve the equations in dimensionless form.…”

“…We also plot the concentration fields and 𝐴𝐴 𝐴𝐴 -averaged concentration profiles at 𝐴𝐴 𝐴𝐴= 2000 as shown in Figure 4. In the classic studies on VF without dead-end pore effects (Chen & Eckart, 1998;Ghesmat & Azaiez, 2008;Islam & Azaiez, 2005;Norouzi & Shoghi, 2014;Sajjadi & Azaiez, 2014;Tan & Homsy, 1988), there is no need to study the variations of fluids (NAPLs in this case) behind the finger trailing fronts as they are completely cleaned up, that is, their concentration is 0 in this region. However, when dead-end pores are incorporated, a certain concentration of NAPLs remains behind the finger trailing fronts as shown in the 𝐴𝐴 𝐴𝐴 -averaged concentration profile in Figure 4b.…”

“…Miscible displacement processes in porous media, where the interfacial tension between two fluids is zero, are of particular interest in a wide spectrum of applications such as soil and water contaminate remediation (Ali et al., 1995), sequestration (Gooya et al., 2019; Riaz et al., 2006), enhanced oil recovery (Orr & Taber, 1984), geothermal recovery (Vasilyeva et al., 2006), drug delivery (Escala et al., 2019), and chromatographic separation (Mayfield et al., 2005). However, one of the major challenges is that miscible displacements usually suffer from low displacement efficiency, which results from two broad reasons (Lake, 1989): (a) macroscopically , the displacing fluids with less viscosity tend to bypass the displaced fluids with high viscosity, resulting in the viscous fingering (VF) instability; and (b) microscopically , the displaced fluids that are trapped in stagnant pockets or dead‐end pores in swept area in porous media cannot be directly flooded by the injected fluids.…”