Misciblc gas flooding using carbon dioxide and natural hydrocarbon gases is currently being investigated as possible EOR process in a number of Libyan reservoirs. The major reason for selecting miscible gas flooding as an EOR process was because of the adaptability and possible gas availability at reasonable cost. C02 and hydrocarbon gases could achieve miscibility with a number of reservoir oils at current conditions [pressure] through a multi-contact miscibility process.

The main disadvantages of miscible gas flooding is the high mobility ratio so that the gases have the tendency to channel through the oil which results in by-passing much of the oil in the reservoir and low sweep efficiency. To solve this problem, a technique was tested consisting of alternately injecting small solvent [hydrocarbon gas or CO2] and water slugs. The slug of water reduces the speed of the solvent which results in reducing the chance of solvent fingering and improving the mobility of the system.

The main objective of this study is to investigate the effect of WAO RATIO on overall reovery of tertiary miscible flooding. Laboratory tests were conducted on three stacks of composite cores arranged in permeability descending order. The effects of lithology on overall performance was also tested.. The system studied in this work was an oil wet system. Tests were conducted in 3 ft. oil wet sandstone and carbonate rock cores. Cores utilized in this projcct were obtained from two Libyan reservoirs and arranged in desending order to form three composite stacks. Water and solvent were iinjected separately.

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