Potential application of oxygen containing gases to enhance gravity drainage in heavy oil bearing reservoirs

In the frame of laboratory studies the effect of air/ natural CO 2 mixtures on chemical composition of crude oil and gas phase, the rheological and interfacial properties, the flow mechanism and the safety measures were analyzed. The tests were performed at reservoir conditions (200 bar and 109 °C) using natural rock, oil and gas samples. The oxygen content of the gas phase and the gas/oil ratio varied within wide limits. Both crude and asphaltene-free oil were used to determine the consequences of the low temperature oxidation. On the basis ofthe experimental results it was found that the oxygen content of the cap gas had completely consumed by the chemical reactions (oxidation, condensation and water formation) before the asphaltene content set in equilibrium. Nearly 9 % excess asphaltene formation was observed in both the crude and the asphaltene-free oils. The substantial increase in asphaltene content and the presence of colloidal water results in a measurable change in rheological and interfacial properties. Despite these factors the flow and displacement mechanism is only slightly influenced if the reservoir is offractured character. On the other hand the in-situ oxidation ofthis heavy crude oil improves the efficiency ofbitumen production and the quality of product used mostly for road construction. As a final statement, it was concluded that replacing the CO 2 with oxygen containing inert gas, the chemical reactions can be in-situ regulated without jeopardizing the recovery efficiency. Application of the artificial gas cap concept opens new perspectives in EOR technology of karstic and fractured reservoirs containing medium and heavy crude oils in those cases where CO 2 or CH gas is not available. Thus, the application of air and oxygen containing pillow (cap) gas aimed at improving the gravitational segregation in offshore production technology may offer appropriate alternative to increase the recovery factor even in heavy oil bearing reservoirs.