Abstract
Many heavy oil reservoirs contain oil that has some limited mobility under
reservoir conditions. In these reservoirs, a small fraction of the oil-in-place
can be recovered using the internal reservoir energy through heavy oil solution
gas drive (primary production). An integral part of this process is the
so-called 'foamy oil mechanism', whereby oil is produced as a gas-in-oil
dispersion. At the end of primary production, the bulk of the oil is still in
place, while the natural energy of the reservoir has been depleted. This
remaining oil is still mostly continuous and presents a valuable target for
further recovery. Many of these reservoirs are relatively small or thin, or may
be contacted by overlying gas or underlying water. As such, they are poor
candidates for thermal oil recovery methods, so any additional oil recovery
after primary production must be non-thermal. In this work, we present
experimental results of foamy oil depletion at two different length scales and
varying depletion rates. Tests were conducted in the absence of sand
production, and the results from the depletion experiments are interpreted in
terms of viscous forces. At the conclusion of primary recovery, the potential
for further non-thermal exploitation of these reservoirs is explored. Results
for waterflooding and chemical flooding are presented, demonstrating the
viability of these techniques for heavy oil EOR. Several displacement
mechanisms are identified through the secondary and tertiary processes that
contribute to significant (although potentially slow) incremental recovery of
heavy oil.
Introduction
Many countries have heavy oil reservoirs. Canada and Venezuela in particular
contain some of the largest heavy oil and bitumen resources in the world.
Rising energy demands, coupled with a decline in conventional oil reserves, has
led to increased interest in heavy oil recovery in recent years. The size of
these heavy oil deposits is considerable, and with volatile crude oil prices
making it difficult to produce from some higher viscosity bitumen reservoirs,
production of heavy oil could potentially be very important in years to come.
Understanding the mechanisms by which heavy oil can be displaced in reservoirs
is crucial to the successful recovery of this resource base.
Heavy oil can be defined as a class of oils with viscosity ranging from 50
mPa.s up to around 50,000 mPa.s. This oil has limited mobility under reservoir
temperature and pressure, and Darcy's Law predicts that the oil can flow slowly
under high applied pressure gradients. However, it has been observed that in
these reservoirs, solution gas drive leads to significantly higher rates and
recoveries than what was expected by conventional understanding of gas-oil
relative permeability behaviour(1). This behaviour, first reported in Canadian
heavy oil, has since been observed in many other reservoirs around the world
including South America, China and Albania. Investigations into the causes of
this abnormal, but fortuitous, primary production response have been the focus
of many publications in the past 25 years.
The recovery from primary production in heavy oil reservoirs may be as high as
20%(2), but is usually lower.
© 2009. Petroleum Society of Canada (now Society of Petroleum Engineers)
View full textPDF
(
1,198 KB
)
History
- Original manuscript received:
30 March 2006
- Meeting paper published:
12 November 2006
- Revised manuscript received:
4 February 2009
- Manuscript approved:
9 February 2009
View Cart
