Minimum Miscibility Pressure, Rising Bubble Apparatus, and Phase Behavior

Abstract

Abstract The objective of this study was to determine the minimum miscibility pressure (MMP) as a function of temperature using the rising bubble apparatus for a ternary system consisting of CO2, normal pentane, and normal hexadecane. The MMP's were compared and interpreted with the phase behavior of the ternary system. In addition, the MMP was determined for a dead oil of 41.7° API gravity and a live oil having a bubble point pressure of 2266 psia at a reservoir temperature of 240°F for CO2 and CO2 enriched with normal butane. The MMP's as a function of temperature were determined using a modified rising bubble apparatus (RBA). Bubble behavior was monitored using a motion tracking optical system (MTOS) and a cell pressure data acquisition and monitoring system (CPMS). The MTOS consists of a video camera mounted on a rail table parallel to the path of the rising bubble in the sight gauge (or cell). The magnified bubble image is monitored on a screen and recorded on a video cassette for subsequent viewing. The VCR can playback the recorded image frame-by-frame or at any desired speed for detailed study of bubble behavior and shape. An image processor installed on the computer captures and digitizes selected bubble images that are printed out on a laser printer with high resolution. The CPMS records the pressure behavior in the cell as a function of time as the bubble rises in the oil column and aids in the determination of the MMP. The MMP measured with the RBA for the ternary system agreed with the MMP as determined from the phase behavior of the ternary system. For the dead oil and the ternary system the MMP measured as a function of temperature terminates at a low temperature at the critical temperature and pressure of the injected gas for both the vaporizing and condensing systems. For the ternary system the MMP as a function of temperature for an enriched gas goes from a multiple contact condensing system to a multiple contact vaporizing system at the temperature where the enriched gas ternary system MMP curve crosses the CO2 -Ternary System MMP curve. At the cross-over temperature and pressure both the liquid composition and the enriched gas composition lie on the termini of the limiting tie line of the ternary system and thus the enriched gas is single contact miscible with the liquid.