Mathematical and experimental investigation of multi-component gas/oil displacements with constant pressure boundaries

Abstract

In this research, for the first time, multi-component gas/oil displacements with con- stant pressure boundaries are investigated mathematically and experimentally. Math- ematically, the minimum miscibility pressure (MMP) is first calculated through an analytical method. Then, a novel extension of the classic Buckley-Leverett theory is applied to solve gas/oil displacement problems under constant pressure boundaries in a one-dimensional, dispersion-free medium. The developed analytical technique is applied to four and five-component systems, where the four-component system is a hypothetical case and the five-component system is a realistic and practical case. Ex- perimentally, the five-component, N₂/CO₂/C₆/C₁₀/C₁₆, gas/oil displacement tests are designed and conducted in a slim tube set up. The MMP is first determined through common constant flux slim tube tests. Then, the analytical solution of sys- tems with constant pressure boundaries is confirmed through corresponding slim tube experiments. However, unlike gas/oil displacements with constant flux boundaries in which the total flux is fixed both in space and time, the total flux varies with time in problems with constant pressure boundaries. Using the analytical technique, the breakthrough time of different waves are determined and the total flux is obtained as a function of time. The results indicate that the analytical solution matches with the experimental results if an appropriate relative permeability model is selected for the gas/oil flow in the slim tube. Finally, a new interpretation method, based on the constant pressure boundary experiments, is applied to obtain the gas/oil relative permeability curves. These independently obtained relative permeabilities are then employed in the analytical simulation and acceptable solutions are achieved.