Studies have shown that CO2 under conditions of high pressure often develops miscibility with oil, thus making it a good agent for improving the sweep efficiencies of reservoirs. A critical question is; at what pressures does CO2 develop a miscible mixture? This paper examines the optimal reservoir pressure for CO 2flooding to be performed on Farnsworth Unit (FWU) oil in reservoir core to achieve the optimum sweep efficiency and also determines the minimum miscibility pressure (MMP) for pure CO2 and FWU crude oil.

A core flooding apparatus was built and used with materials from the Farnsworth Field in the Texas panhandle as a case study. The research involved the use of three reservoir pay zone cores obtained from depths of about 7687 ft. subsurface. These were placed sequentially in the apparatus to undergo core flooding at reservoir conditions using FWU crude oil. Tests were performed at pressures from 400 psi to 5400 psi and reservoir temperature of 168°F. In each test the core was flooded with eight pore volumes of CO2 while gas cut, recovery factor, residual oil, working pressures and pressure differentials were determined.

It was observed that the recovery factor remained steady and was highest at pressures above 3900 psi while recording the lowest gas cut at pressures of 3900 psi to 5400 psi. The lowest oil production and highest gas cut was recorded at 400 psi with minimum miscibility of approximately 3900 psi.

From the results it can be concluded that CO2flooding should be performed at or above the minimum miscibility pressure of 3900 psi to obtain the highest oil recovery. This research is providing guidance for Farnsworth field operations and can aid in other projects.

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