A Laboratory Study of Gravity Segregation in Frontal Drives

Abstract

Published in Petroleum Transactions, AIME, Volume 210, 1957, pages 275–282. Abstract Scaled reservoir models have been used to study the effect of gravity on oil recovery performance in frontal drive operations, namely, Water, gas, or solvent flooding. The difference in density between the reservoir oil and the inject fluid causes their segregation, resulting in a non-uniform advance of the flood front. In the laboratory flow tests, which simulated both five-spot and end-to-end injection operations in flat reservoirs, the viscous, capillary, and gravity forces present in these operations were scaled. Dyed fluids were used so that the gross movement of the injected fluid could be observed. The studies covered a range of injection rates, formation thicknesses, and rock and fluid properties normally encountered in field operations. The results of the model tests indicate that the volume of the reservoir contacted by the injected fluid at its breakthrough into the producing well is less than that expected based on information which neglects gravity effects. This difference can often be as much as 80 per cent by gas or water injection in uniform sand bodies. Preliminary flow tests on non-uniform sand bodies indicate that the uniformity of the flood front may in some situations be influenced to a much greater degree by permeability variations within the rock body than by gravity effects. The magnitude of fluid segregation due to gravity is controlled by the average injection rate, rather than day to day or week to week variations. Introduction One of the important factors controlling the oil recovery from a frontal drive operation, such as water, gas, or solvent injection, is the volumetric sweep efficiency. This factor is a measure of the gross portion of the reservoir that is contacted by the displacing fluid. The volumetric sweep efficiency is influenced by gravity effects, well arrangements, and variations in rock permeability within the reservoir. The gravity effects are due to the displacing fluid being of different density than the reservoir oil.