Configuration of slim tube apparatus for consistent determination of minimum miscibility pressure (MMP) data

摘要

Gas flooding is one of the most widely used techniques of Enhanced Oil Recovery (EOR) especially for light to medium API oils. It involves displacing reservoir oil with gas such as nitrogen, carbon dioxide, flue gas or hydrocarbon gas, in either miscible or immiscible mode. Due to the fact that immiscible gas flooding is often characterized by pre-mature gas breakthrough and hence low recovery efficiency resulting from flooding fronts instabilities, gravity override and reservoir heterogeneity, miscible flooding has become the order of the day.;Gas-oil miscibility is achieved, either through vaporizing drive mechanism or condensing drive mechanism or a combination of both, at the reservoir temperature when the operating pressure is equal to or greater than a threshold known as the minimum miscibility pressure (MMP). MMP is thus one of the most important parameter in designing miscible displacement projects.;MMP is most commonly measured using the slim-tube apparatus, whose characteristic large length and relatively small diameter often help to eliminate the inherent problems associated with the immiscible flooding. To earnest this characteristic benefit of the slim-tube apparatus, the length must be considerately large enough to allow the miscibility of the solvent with the oil being displaced, and hence improve the oil recovery efficiency beyond the immiscible region.;In this research project, the effects of coil length and injection rate on the laboratory measured MMP using slim tube apparatus were investigated. Three injection rates and three coil lengths were used for the same reservoir fluid and injection gas (lean gas). Although the results obtained showed that the measured MMP did not really exhibit any known trend with the injection rates used, the lowest rate tested achieved a slightly lower value of MMP and better performances that each of the other rates. As for the coil lengths, the measured MMP decreased with increased coil length. The curved trend observed suggests that as the coil length increases, the measured MMP will at a time maintain a constant value so that the curve becomes asymptotic to the horizontal axis. This implies that beyond the investigated lengths, there might exist an optimum coil length at which MMP is best measured for the given reservoir fluid-injection gas system, although not proven in this work.;Besides, contrary to the common believe that miscibility is achieved by vaporizing mechanism for a system of light oil and lean gas, analysis of the effluent gas compositions shown in this report revealed that multi-contact miscibility was achieved by the combined effects of both the vaporizing and the condensing gas drives.;MMP measurement is very significant to the economics of a gas flooding project and as such, accurate measurement of this parameter is imperative. It is our belief that this research project will give the foundation for further investigations to develop the optimum design criteria for MMP measurement with slim tube experiment to provide representative MMP data for field implementation.