Simulation Study of Miscible Displacement Under Gravity Domination
Engineering Honours Degree, 2012
University of Adelaide
The application of miscible flooding has been used across a wide range of industries such as oil and gas, chemical engineering and hydrology. Miscible flooding has been used in enhanced oil recovery and geological sequestration of CO2. Despite the known performance of miscible flooding, there are a number of problems with the stability of miscible displacement. These problems include gravity override and viscous fingering. Density and viscosity differences between the displacing fluid and the in-place fluid and reservoir heterogeneities can cause these issues. Pore level studies are required to capture the influence of each of these mechanisms.
Many simulation-based studies have been performed where the mathematical model and porous arrangements have been tuned to force a fit between the experimental data and the simulation. The objective of this study is to perform pore scale simulations using an experimentally validated simulation model to investigate the effect of fluid properties, angle of tilt and porous arrangement on the stability of a miscible displacement process under gravity domination.
The experimental porous geometry was used instead of an independent pore network model. Exact differential equations such as Navier-Stokes, convection-diffusion and continuity were used to simulate the flow instead of pipe flow equations. The provided experimentally matched model was further validated with simulations performed in a similar study from literature. A sensitivity analysis was performed where the effects of density differences, mobility ratio, angle of tilt and inlet velocity were investigated. Three new porous patterns were generated to investigate the effect of porosity on breakthrough saturation.
The first sensitivity study considered the effect of density difference, mobility ratio and angle of tilt. Plots of breakthrough saturation against cos (θ) could be divided into two regions, where region 1 was for angles of tilt between 0° and 90°, and region 2 for angles of tilt between 90° and 180°. For region 1 it was found that for density differences greater than 200 kg/m3, mobility and density difference have less effect when compared with the angle of tilt. As for density differences less than 200 kg/m3, mobility was more sensitive. For the second sensitivity study it was found that inertial effects within the model were amplified for the higher velocity that was tested. The third sensitivity study, it was found that the loosely packed model followed the trends that were observed in the sensitivity studies, however for tight and moderately packed it was observed that gravity did not have a significant effect in the small section of the pattern that was considered. The results of this study can aid in the understanding of the interplay between different parameters at the pore level.