Abstract
Identification of operating conditions that have been beneficial or injurious
to overall performance of past waterfloods in heavy oil reservoirs is the first
essential step towards optimization of similar projects in the future.
Comparative analyses of performance of various waterfloods in a given region
(deposited under similar conditions) can be very instructive to identify such
conditions.
Insights on performance of waterfloods in heavy oil reservoirs were derived
from a comparative evaluation of recent performance history of three selected
waterfloods. These waterfloods involved increasing, decreasing and steady water
injection rates.
It was seen that aggressive injection rates lead to increased oil rates, but at
rapidly increasing water cuts. Decreasing water injection rates, on the other
hand, lead to low oil rates, but with water cuts increasing relatively more
gradually. There is, therefore, an economically optimal water injection rate
strategy for each specific situation.
Introduction
In the current environment of volatile oil prices and economic uncertainties,
there is a heightened need for reviewing the cost-effectiveness of ongoing
waterflood and improved oil recovery (IOR) operations within the constraints of
low incremental costs and risks. Some of the options being pursued include
enhanced surveillance, benchmarking of performance against other successful
projects in analogous reservoirs, intense characterization and simulation,
upgrades to facilities, improvement in injection water quality and selective
placement of additional injectors and producers.
In viscous fingering-dominated waterfloods, aggressive water injection
aggravates water channelling. High injection rates (sub-fracture) lead to high
initial oil rates in the short-term, but they subsequently give rise to
excessive water channelling which may result in loss of cost-effectiveness of
the waterflood and, in some cases, premature abandonment. On the other hand,
low injection-production rates (processing rates) in heavy oil waterfloods lead
to relatively low oil rates, long payout periods and a long project life. There
is, therefore, an optimal processing rate/strategy for each specific situation
(based on technical and economic considerations) and, clearly, there is a need
for systematically identifying it.
Since the 1980s, over 70 waterfloods have been operated in the medium and heavy
oil reservoirs of Alberta and Saskatchewan in Western Canada. Waterflooding in
these reservoirs involves adverse mobility ratio and viscous fingering/water
channelling leading to relatively early water breakthrough. Resulting
requirements for handling large amounts of water poses formidable problems.
This study was undertaken to explore whether a judicious scheduling of
injection and production rates could improve cost-effectiveness of similar
operations in the short- and long-term.
We examined performance histories of several ongoing waterfloods, and three
selected waterfloods are reviewed here. We did not have access to many details
on these projects. We believe there is a persuasive case for our hypothesis. It
is understood that the field data examined were, by no means, 'controlled'
(i.e. there may possibly exist factors other than the ones we focused on in
this review, and all cases may not strictly be comparable).
Methodology
We compared the performance of three selected waterfloods in the heavy oil
reservoirs of Southern Alberta; namely, Jenner Upper Mannville O, Jenner Upper
Mannville JJJ and Retlaw Mannville D8D.
© 2009. Petroleum Society of Canada (now Society of Petroleum Engineers)
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History
- Original manuscript received:
11 June 2007
- Meeting paper published:
12 June 2007
- Revised manuscript received:
26 January 2009
- Manuscript approved:
4 February 2009
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