Optimal Emulsion Design For The Recovery Of A Saskatchewan Crude
Authors: Fiori M. , Ali S.M. Farouq 
Published: March 2010

This paper presents macroemulsion flooding as all alternative secondary recovery technique for moderately viscous oils in reservoirs unsuitable for thermal recovery applications.

In laboratory experiments, wellhead Eyehill crude oil samples were employed directly in the tailoring and systematic development of all emulsion. A unique feature of this research is the use of solvents in adjusting the emulsion characteristics for increased oil displacement efficiency. Emulsion slugs were then injected into partially water flooded cores resulting in incremental recoveries of up to 70%.

Introduction

This paper deals with designing water-in-oil (W/O) macroemulsions prepared with the Eyehill crude produced in the province of Saskatchewan, and laboratory testing of these emulsions as secondary recovery agents. Previous studies(1–4) concentrated on the flow properties of macroemulsions in porous media and the emulsions used were oil-in-water (O/W) type. No systematic study of W/O petroleum macroemulsions and their flow properties is known for the present fluid system.

Carefully designed crude oil emulsions can offer an alternative recovery technique for heavy oil reservoirs with low primary productivity, poor response to waterflooding and low potential for thermal recovery applications(5–9). As reported by Jameson (1973)(10), primary production of a Saskatchewan crude yields between 2% and 8% of the oil-in-place. Because of an adverse mobility ratio, waterflooding is not effective and recovers only an additional 2% to 5% of the oil-in-place.

In this study, cost was always kept in perspective because the objective was to formulate a procedure that was simple, effective and practical. Cost was also the reason why sodium hydroxide was preferred to commercial emulsifiers. Wellhead samples of the Eyehill crude oil-water emulsion referred to as "crude" in this paper were used as the basic material in this study. The crude contained already 59% water as dispersed drops. Wellhead crude was thus already a W/O emulsion.

The first stage was to examine the parameters affecting interfacial tension. The goal was to determine under what conditions interfacial tension could be lowered sufficiently to obtain homogeneous mixtures. Eyehill crude is an acidic crude containing a wide array of fatty acids which can react with NaOH to give a soap (i.e. surfactant). This, in turn, lowers the interfacial tension and provides the necessary environment for emulsification. The lower the interfacial tension, the smaller the energy required to create new interfaces between the crude and the NaOH solution. The NaOH concentration which provided the lowest interfacial tension was selected.

The second stage was to prepare and observe mixtures of Eyehill wellhead crude and of the selected NaOH solution. The goal was to find a mixture that remained homogeneous for a very long period of time. That mixture was then blended with distilled water and/or wellhead crude to determine how well it retained its homogeneity. In the reservoir, an emulsion bank could encounter varying saturations of water and crude. It is important to predict how combinations of these three fluids (i.e. emulsion, distilled water and crude) behaved. If the emulsion broke down, efficiency of displacement would drop. If the viscosity of the emulsion increased drastically, the porous medium would become plugged.