Effect of Salinity Changes of the Injected Water on Water Flooding Performance In Carbonate Reserviors

Abstract

ABSTRACT Water flooding is a promising oil recovery mechanism, which has inherent potentials to recover more oil from the reservoir. Quite unfortunately, the mechanism has been under utilized due to improper consideration of quality of water to be injected. The quantity of water injected into the reservoir has always been of interest to the Engineer, until recently when they became interested in the quality. They soon discovered that if proper consideration is given to the quality of the ionic composition of the injected water by lowering its TDS, oil recovery can be greatly enhanced, and residual oil saturation immensely reduced (Tang and Morrow 1999). Its evidences in the literature are undisputable. Lowering the salinity or TDS of injected water results in lowering the oil-rock capillary pressure, reduction in oil-water interfacial tension, and finally a change in the relative permeability, which results into a wettability change, usually to a mixed-wet or water-wet state. This project aims at determining the impact of low salinity water flooding on oil recovery in a carbonate reservoir in the Middle East. It was decided to use ECLIPSE and an analytical solution as methodologies for solving the problem. Quite interestingly, ECLIPSE was not able to predict increase in oil recovery due to non- dependence of salt concentration on relative permeability in the model. The analytical solution predicted an oil recovery of about 9% FOE, with an additional oil volume of three million and seventy-six thousand barrels (3,076,000 STB) to be recovered at the surface. This increased the worth of the company by one hundred and twenty three million, and sixty-four thousand Dollars ($123,064,000), when a pessimistic oil price of $40/barrel is used. Indeed, it is a cost effective oil recovery mechanism with little or no investment cost. It is however recommended to inject water in the range of 1500ppm or lower.