Abstract
Many countries in the world contain significant heavy oil deposits. In
reservoirs with viscosity over several hundred mPa?s, waterflooding is not
expected to be successful due to the extremely high oil viscosity. However, in
many smaller, thinner reservoirs, or reservoirs at the conclusion of cold
production, thermal enhanced oil recovery methods will not be economic.
Waterfloods are relatively inexpensive and easy to control; therefore, they
will still often be employed in high viscosity heavy oil fields. This paper
presents experimental findings of waterflooding in laboratory sandpacks for two
high viscosity heavy oils of 4,650 mPa.s and 11,500 mPa.s at varying water
injection rates. The results of this work show that capillary forces, which are
often neglected due to the high oil viscosity, are important even in heavy oil
systems. At low injection rates, water imbibition can be used to stabilize the
waterflood and improve oil recovery. Waterflooding can therefore be a viable
non-thermal enhanced oil recovery technology, even in fields with very high oil
viscosity.
Introduction
Although conventional oil reserves are declining in many countries, the global
energy demand is still increasing. As a result, the industry focus is now
shifting towards unconventional oil resources, such as the oil sands in
countries like Canada and Venezuela. The size of this resource base is immense,
but the production of high viscosity crude oil carries its own unique
challenges.
Heavy oil is a special class of this unconventional oil, and has viscosities
ranging from 50 to 50,000 mPa.s. Heavy oil reservoirs are often found in highly
porous, highly permeable, unconsolidated sand deposits. At reservoir
conditions, the oil may contain dissolved solution gas; thus, some oil can be
initially recovered using the energy from heavy oil solution gas drive. At the
end of primary production, however, a significant amount of oil still exists
for potential secondary recovery. Many of these reservoirs are small and thin
or were disturbed during primary production, making them poor candidates for
expensive thermal enhanced oil recovery strategies. In times of uncertain
commodity pricing, it is beneficial to examine the potential for relatively
inexpensive, non-thermal oil recovery techniques.
Waterflooding is often employed, at least initially, in heavy oil reservoirs,
both along with or after primary recovery in order to re-pressurize the
reservoir and displace oil to producing wells. In these applications, it is
very important to understand the forces that are present in the reservoir and
how they can be used to properly design the waterflood. Specifically, proper
design and maintenance of waterfloods requires comprehension of how viscous oil
can be displaced by water, and how oil recovery can be optimized. This work
presents the results for water injection into laboratory sandpacks containing
gas-free heavy oil of varying viscosity. The responses for different
waterfloods are compared in order to investigate the mechanisms by which heavy
oil can be recovered by water injection.
Theory
Waterflooding of oil reservoirs is a well-recognized technique for oil recovery
after primary production. In conventional oil, waterflooding theory has been
well documented(1).
© 2009. Petroleum Society of Canada (now Society of Petroleum Engineers)
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History
- Original manuscript received:
2 April 2007
- Meeting paper published:
12 June 2007
- Revised manuscript received:
19 January 2009
- Manuscript approved:
3 February 2009
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