Summary
For stratified reservoirs with free crossflow and where fractures do not
cause severe channeling, improved sweep is often needed after water
breakthrough. For moderately viscous oils, polymer flooding is an option for
this type of reservoir. However, in recent years, an in-depth
profile-modification method has been commercialized in which a block is placed
in the high-permeability zone(s). This sophisticated idea requires that (1) the
blocking agent have a low viscosity (ideally a unit-mobility displacement)
during placement, that (2) the rear of the blocking-agent bank in the
high-permeability zone(s) outrun the front of the blocking-agent bank in
adjacent less-permeable zones, and that (3) an effective block to flow form at
the appropriate location in the high-permeability zone(s). Achieving these
objectives is challenging but has been accomplished in at least one field test.
This paper investigates when this in-depth profile-modification process is a
superior choice over conventional polymer flooding.
Using simulation and analytical studies, we examined oil-recovery efficiency
for the two processes as a function of (1) permeability contrast, (2) relative
zone thickness, (3) oil viscosity, (4) polymer-solution viscosity, (5) polymer-
or blocking-agent-bank size, and (6) relative costs for polymer vs. blocking
agent. The results reveal that in-depth profile modification is most
appropriate for high permeability contrasts (e.g., 10:1), high thickness ratios
(e.g., less-permeable zones being 10 times thicker than high-permeability
zones), and relatively low oil viscosities. Because of the high cost of the
blocking agent relative to conventional polymers, economics favors small
blocking-agent-bank sizes (e.g., 5% of the pore volume in the high-permeability
layer). Even though short-term economics may favor in-depth profile
modification, ultimate recovery may be considerably less than from a
traditional polymer flood.
© 2012. Society of Petroleum Engineers
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History
- Original manuscript received:
1 July 2011
- Meeting paper published:
16 November 2011
- Revised manuscript received:
24 November 2011
- Manuscript approved:
11 January 2012
- Published online:
31 July 2012
- Version of record:
5 September 2012
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