Experimental and simulation studies of water-alternating-enriched gas injection for San Francisco Field, Colombia

Abstract

This thesis presents a complete investigation involving experimental and compositional reservoir simulation studies into enriched gas injection as a method to enhance oil recovery from the San Francisco field in Colombia. In enriched gas floods, the objective is to achieve a multicontact miscible displacement by taking advantage of the high local displacement efficiency that is possible when the injection gas is sufficiently enriched with intermediate hydrocarbon components. To evaluate the most optimum WAG process using enriched gas, the following tasks were performed. First, slim-tube experiments at the current reservoir pressure were made using a set of three gases, San Francisco, Balcon, and a mixture of 50:50 San Francisco and Balcon gases. For these experiments four propane:gas mass ratios were used with San Francisco gas, namely, 0:100, 5:100, 7.5:100, and 10:100, and two propane:gas mass ratios, 0:100 and 5:100, were used with the other two gases. Second, a 1D compositional simulation for each of the slim-tube experiments was conducted, and the minimum miscibility pressure, MMP, was estimated for each gas. Third, a 3D compositional reservoir simulation study of the WAG pilot in Block 8 of the San Francisco field was performed and 48 production forecasting runs were carried out using the set of enriched gases. From MMP consideration, the displacement process in the reservoir is immiscible when lean San Francisco gas is used. The level of miscibility increases from immiscible to partially miscible when gas is enriched with propane and also when rich Balcon gas is used. Results from compositional reservoir simulation show that the oil recovery is not significantly improved when San Francisco gas is injected, even when it is enriched with propane. On the other hand, a more efficient injection process is achieved with Balcon gas, giving 2.78% OOIP more recovery than that estimated using San Francisco lean gas. This value of recovery is obtained from Block 8 of San Francisco field after 9 years of production using a WAG cycle of 20:60 (20 days injecting water followed by 60 days injecting gas) when 2MMSCF/D per well of 5:100 mass ratio of propane:Balcon gas is injected.