Waterflooding Oil Reservoirs With Bottom Water
Authors: Islam M. Rafiqul , Ali S.M. Farouq 
Published: March 2010

Abstract
This research addresses the problem of waterflooding a medium gravity oil-bearing formation with a water leg, and offers recommendations/ or process selection. Many oil reservoirs in Alberta and Saskatchewan have some type of a high water saturation zone below the oil layer. The presence of a bottom-water zone results in very poor areal and vertical sweep efficiencies. However, waterflooding still remains the most widely used oil recovery technique for reservoirs with a bottom-water zone. The performance in such reservoirs can be improved greatly if an effective method of partially plugging the bottom-water zone can be developed. A possible means of accomplishing this would be to precede the waterflood with a slug of a mobility control agent. Recently(1) this possibility was investigated using a large flow model, for a series of mobility control agents, such as polymer, emulsion, air, biopolymer, and foam. The present study complements that investigation for a wider range of mobility control agent slug sizes, oil-to-water zone permeability and thickness ratios, etc. Also presented is a qualitative comparison of various mobility control agents to show their relative merits. The flow stability and displacement pattern are discussed jar each mobility control agent. It is shown that the choice of one agent over others depends on variables such as permeability contrast, relative oil-water layer thickness, etc.

Introduction
The problem of controlling mobility of water or gas has received attention for more than two decades(2–9). However, very few studies report a systematic comparative evaluation of various mobility control agents. In fact, some of these techniques have not been specifically tested for bottom-water cases. Only recently, slam and Farouq Ali(1) reported a systematic study of various mobility control agents available for improving oil recovery from a reservoir with a bottom-water zone. The present study complements the authors' previous study and gives new interpretation to various mechanisms involved in the process.

Experimental Set-up and Procedure
The experimental apparatus for the displacement tests consisted of a pump and an especially designed rectangular core holder. A constant rate, computer-controlled, positive displacement syringe pump was used along with floating pistons. The rectangular core holder had one inlet and one outlet at the inlet/outlet faces. Figure 1 shows a schematic of the experimental set-up. The core holder had a cover plate along the bottom side. This enabled one to pack several layers along the length. The chemicals used for different runs are listed in Table 1. Further details f the experimental procedure are available in References 1 and 10.

Experimental Results and Discussion
Displacement tests were carried out with water and different mobility control agents, viz. polymer, emulsion, air, foam, glycerine, etc. A total of 21 different runs were conducted to test the effectiveness of each of the mobility control agents with permeability, relative thickness and slug size as variables. These runs will be discussed under different sections according to the mobility control agent used. Table 2 lists major characteristics of different runs.
FIGURE 1. Schematic of the experimental set-up. FIGURE 1. Available In Full Paper
TABLE 1. Properties of chemicals used. Table 1 Available In Full Paper.