Potential for Alkali-Surfactant Flooding in Heavy Oil Reservoirs Through Oil-in-Water Emulsification

ABSTRACT

Alkali-surfactant flooding is an established enhanced oil recovery technique in conventional oil reservoirs, whereby the injected chemical lowers the oil/water interfacial tension, leading to reduced trapping of oil ganglia. In the past, there have been some studies of alkali and alkali-surfactant flooding of heavy oil systems as well, and it has been observed that chemical injection can lead to improved oil recovery. The heavy oil recovery mechanism proposed in this work is the creation of oil-in-water emulsions, which may form under conditions of low interfacial tension and shear due to flow through rock pores. Oil may either be produced in the water (emulsification and entrainment) or the droplets may coalesce or plug the rock pores, leading to improved sweep efficiency (emulsification and entrapment). Both of these mechanisms are investigated in laboratory systems of varying rock permeability, using a heavy oil with a viscosity of 11,500 mPa.s. When oil-in-water emulsions form, the oil recovery can be improved significantly, even without the addition of polymer for mobility control. The effect of permeability and varying injection rates are considered, to understand how different ranges of shear affect the efficiency of these emulsion systems.

Introduction

Several countries in the world, notably Canada and Venezuela, contain significant deposits of heavy oil and bitumen. As Canadian conventional oil reserves continue to decline, the industry interest is now shifting rapidly towards the recovery of this unconventional crude. The immensity of this resource base is exciting, but heavy oil reservoirs pose unique challenges when designing recovery strategies.

The Canadian oil sands are unconsolidated, high porosity and high permeability reservoirs. Ease of flow is therefore not an issue, as it is in many conventional oil reservoirs. Rather, the single biggest impediment to the successful recovery of heavy oil and bitumen is the high oil viscosity. Heavy oil reservoirs are a special subset of our oil sands, whereby the oil viscosity at reservoir temperature varies from around 50 mPa.s up to around 50,000 mPa.s. At reservoir conditions, the oil requires high pressure draw downs in order for it to flow even through the permeable sands, after which point the reservoir has been depleted of all of its natural energy. In order to recover additional heavy oil, energy has to be injected into the reservoir. Often, this takes the form of a fluid that displaces the oil, meaning that the oil must be made to flow to production wells. Most improved/enhanced oil recovery schemes focus on reduction of the oil viscosity through the application of heat or miscible solvents. However, many of the Canadian heavy oil reservoirs are relatively small and thin, and have been disturbed to an unknown extent during primary production. Therefore, the development of injection strategies that are not energy intensive (i.e. non-thermal) and easy to control will be of considerable benefit to heavy oil producers.

In this work, alkali-surfactant solution is investigated as a potential non-thermal injection fluid. It is demonstrated that through the injection of low concentrations of alkali and preformed surfactant solution, oil recovery can be increased significantly above that of waterflooding.

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