Oil Recovery by Hydrocarbon Slugs Driven by a Hot Water Bank
Authors: Alikhan Abbas A. , Ali S.M. Farouq 
Published: December 2007

Abstract
An experimented study was conducted of the recovery of oil from as porous medium overlain and underlain by heat-conducting formations and containing a residual oil or connate water saturation by injection of a small slug of a light hydrocarbon followed by 1/2 PV of hot water driven by a conventional waterflood.
The fluid production histories and the temperature distribution obtained showed that a light hydrocarbon sag injected ahead of a hot water slug leads to a considerable increase in oil recovery. The net oil recovery was found to depend on the original oil viscosity, hydrocarbon slug viscosity, and the injection rate. The process was more effective in a previously waterflooded core rather than in one containing connate water. The over-all ratio of the total hydrocarbon produced to the hydrocarbon injected ranged from 1.10 to 3.96, the variation corresponding to the viscosity of the hydrocarbon slug employed.

Introduction
Numerous methods have been proposed for recovering oil from previously waterflooded porous media. Some methods involve the application of heat in one form or another, while others utilize miscible displacement processes. The proposed method involves a combination of the two, employing a small hydrocarbon slug followed by a slug of hot water, which is driven by a conventional waterflood. An attempt was made to investigate the conditions (residual oil saturation, viscosity, etc.) under which such a method would yield a sizable oil recovery.
Use of a solvent dug followed by a heat-carrying agent was earlier considered by Pirela and Farouq Ali. The process was designed to take advantage of the improved ternary-phase equilibrium behavior at elevated temperatures in the alcohol slug process. The experimental runs were conducted under isothermal conditions. In another study, Avendano found that injection of a light crude oil into a core containing a highly viscous oil prior to steam injection led to a large improvement in oil recovery.
A number of investigators have studied the effect of water-driven hydrocarbon slugs on oil recovery from waterflooded porous media. Csaszar and Holm employed slugs of propane in waterflood cores containing oils with viscosities ranging from 3 to 9 cp. The volume of the oil recovered was 2 to 3 times the propane injected, the efficiency of the process depending on the amount of mobile oil process depending on the amount of mobile oil near the point of injection and the viscosity of the in-place oil. Wiesenthal used gasoline as an intermediate slug when waterflooding cores containing oils having viscosities of 1.28 to 324 cp. He found that the process was effective in waterflooded porous media, especially in the case of viscous oils. Fitzgerald conducted similar experiments using gasoline and arrived at more or less the same conclusions.
The process under consideration involves a combination of miscible displacement and hot waterflooding, both of which have been amply discussed in the literature. A comprehensive survey of miscible displacement has been presented by Perkins and Johnston, while a description of hot Perkins and Johnston, while a description of hot waterflooding may be found elsewhere. In the following, only the most important features of the two processes operating in the combination process will be considered.