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.
© 2009. Petroleum Society of Canada (now Society of Petroleum Engineers)
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History
- Original manuscript received:
2 April 2007
- Meeting paper published:
9 June 2007
- Revised manuscript received:
23 December 2008
- Manuscript approved:
8 January 2009
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