ISSN: 2410-9649 Amadi and Ukpaka / Chemistry International 2(2) (2016) 103-114 iscientic.org. 103 Article type: Research article Article history: Received June 2015 Accepted September 2015 April 2016 Issue Keywords: Molecular diffusion Residual oil Waterflood Recovery Carbon dioxide Traditionally, carbon dioxide (CO 2 ) injection has been considered an inefficient method for enhancing oil recovery from naturally fractured reservoirs. Obviously, it would be useful to experimentally investigate the efficiency of waterflooding naturally fractured reservoirs followed by carbon dioxide (CO 2 ) injection. This issue was investigated by performing water imbibition followed by CO 2 gravity drainage experiments on artificially fractured cores at reservoir conditions. The experiments were designed to illustrate the actual process of waterflooding and CO 2 gravity drainage in a naturally fractured reservoir in the Brass Area, Bayelsa. The results demonstrate that CO 2 gravity drainage could significantly increase oil recovery after a waterflood. During the experiments, the effects of different parameters such as permeability, initial water saturation and injection scheme was also examined. It was found that the efficiency of the CO 2 gravity drainage decrease as the rock permeability decreases and the initial water saturation increases. Cyclic CO 2 injection helped to improve oil recovery during the CO 2 gravity drainage process which alters the water imbibition. Oil samples produced in the experiment were analyzed using gas chromatography to determine the mechanism of CO 2 -improved oil production from tight matrix blocks. The results show that lighter components are extracted and produced early in the test. The results of these experiments validate the premises that CO 2 could be used to recover oil from a tight and unconfined matrix efficiently. © 2015 International Scientific Organization: All rights reserved. Capsule Summary: The efficiency of water flooding naturally fractured reservoirs followed by carbon dioxide (CO 2 ) injection, for the recovery of oil residues was investigated and it was found that CO 2 gravity drainage could significantly increase oil recovery and has may play a considerable role in oil residue recovery. Cite This Article As: S. A Amadi and C. P. Ukpaka. 2016. Role of molecular diffusion in the recovery of water flood residual oil. Chemistry International 2(1) 103-114 INTRODUCTION The displacement of oil by CO 2 has been the subjects of numerous studies, and a considerable volume of experimental data now exists for the process. In these studies, CO 2 usually displaces oil from a fully saturated slim tube or test core in a secondary displacement under conditions where phase behavior favors the development of miscibility. Foe these conditions, recoveries are observed high and rate-insensitive, provided that the effects of gravity segregation, viscous fingering, and bypassing are minimized. In direct contrast, for tertiary recovery experiments, CO 2 is injected into a previously watered-out test core, recoveries of residual oil which observed to be considerably lower, dependent on both flood rate and core length, and different for water-wet and oil-wet systems. A CO 2 pilot test is now being conducted in various fields in different parts of the world for naturally fractured oil reservoirs. Traditionally, in Chemistry International 2(2) (2016) 103-114 Role of molecular diffusion in the recovery of water flood residual oil S. A Amadi and C. P. Ukpaka * Department of Chemical/Petrochemical Engineering Rivers State University of Science and Technology Nkpolu P.M.B. 5080, Port Harcourt, Nigeria * Corresponding Author E-mail: chukwuemeka24@yahoo.com ARTICLE INFO A B S T R A C T