Investigation of concentration‐dependent diffusion on frontal instabilities and mass transfer in homogeneous porous media

Abstract

Mass transfer plays an important role in influencing the efficiency of miscible displacements in solvent-based processes in enhanced oil recovery. The mass transfer rate because of the pure molecular diffusion is very slow. However, this process can be greatly enhanced by the appearance of frontal instabilities called viscous fingering mechanisms, which are beneficial for improving the mixing and mass transfer between the injected solvent and oil. Instead of a piston-like displacement, the interface between solvent and oil is very convoluted with intricate finger-like patterns of the less viscous solvent intruding into the highly viscous oil. This intrusion significantly increases the surface area of contact of the two fluids and leads to more efficient mass transfer and mixing. Experimental measurements on the diffusion coefficients of two miscible fluids indicate that, instead of a constant diffusion coefficient (CDC), a concentration-dependent diffusion coefficient (CDDC) is more realistic. In the present study, a CDDC relation in which the diffusion coefficient is exponentially proportional to concentration is adopted. Its effect on the development of frontal instabilities is examined through highly accurate nonlinear numerical simulations. The differences between the CDDC case and the widely assumed CDC case are discussed. Furthermore, the enhancement of frontal instabilities on mass transfer when the CDDC is considered is investigated at various mobility ratios and Peclet numbers. The special characteristics for the CDDC case indicate its important role in miscible displacements. Eventually, the relation of breakthrough time to parameters is correlated to accurately predict the breakthrough time in any CDDC scenario.

Control of viscous fingering and mixing in miscible displacements with time‐dependent rates

“…Further increase of T results in larger value of mixing degree, earlier start of convection‐dominated regime and more unstable displacements. The critical value of period T c which leads to the least unstable displacement is therefore around . These findings are also quite different with our previous research in which the increase of T in E/I processes can always lead to less unstable displacements monotonically when the dispersion is not considered .…”

“…We developed our own simulator which runs on the WestGrid clusters. It has been successfully used in our previous studies on constant displacement rate . It should be noted that our present research is more focused on the physical problems and the insights which can be obtained for such cyclic time‐dependent displacement scenario.…”

“…It should be noted that our present research is more focused on the physical problems and the insights which can be obtained for such cyclic time‐dependent displacement scenario. A detailed description of the similar implementations and modeling process can be found in previous studies …”

“…More practically, the diffusion coefficient is concentration‐dependent (CDC) for a binary miscible system, proved by a series of experiments . The different diffusion–concentration relations have been previously examined . Different with the diffusion, the dispersion is however strongly velocity‐induced (VID) .…”

Numerical Simulation Study on Steam-Assisted Gravity Drainage Performance in a Heavy Oil Reservoir with a Bottom Water Zone

“…Consequently, a lower oil recovery factor is obtained when solution gas exists in the heavy oil, as shown in Figure 6. The negative effects of the existence of the initial solution gas were briefly reported in the previous literature [56][57][58][59][60][61][62][63][64][65][66][67][68][69]. In this study, more details are investigated.…”