石油および環境バイオテクノロジージャーナル

概要

Analytical Study of Viscosity Effects on Waterflooding Performance to Predict Oil Recovery in a Linear System

Abbas Mamudu1*, Olafuyi Olalekan2 and Giegbefumwen Peter Uyi3

Waterflood displacement efficiency is affected by the viscosity ratio of the displaced to the displacing fluid. Therefore, the oil recovered in a water flooding process is largely determined by the viscosity ratio. This paper presents a quantitative analysis of the viscosity effects on oil recovery in a linear system using Buckley-Leverett equation and other related mathematical models to simulate the effects on two stages: Case one, when the viscosity of the displaced fluid was varied from 5cp to 300cp and that of the displacing fluid remained constant at 1cp. And case two, when the viscosity of the displaced fluid was at 2cp and that of the displacing fluid varied from 2cp to 10cp with the assumption of miscibility between the viscous water and the interstitial water or previously injected water. With the aid of the fractional flow curves, the value for the average water saturations, w s behind the shock front associated with each change in the viscosity ratio was obtained and the corresponding recoveries were predicted. The results show appreciable recovery at a viscosity ratio as high as 100, however, the S-shape of the fractional flow curve diminishes with increasing viscosity ratio. At 200cp and above, the S-shape totally disappears. Viscous fluid appreciably improves oil recovery particularly in reservoirs containing viscous oil. The difference between Swf and w s is constant at various viscosity ratios till the disappearance of the S-shape of the fractional flow curve. Recovery increases with decreasing viscosity ratio and decreases with increasing viscosity ratio. At a very low viscosity ratio, o w μ μ of 0.4, w s equals the end point water saturation, and this gives the highest possible oil recovery (the optimum). The oil produced, Np and the average water saturation, w S in an immiscible displacement system are linearly related.