For some polymer gels applied in reservoirs to control water flow, a
favorable disproportionate permeability reduction (DPR) occurs in which
permeability to water is reduced to a much greater extent than it is to oil.
Permeability reduction in sandpacks by partially hydrolyzed
polyacrylamide-chromium acetate gels was studied as functions of gel
composition and the pressure gradients imposed on the gels. For the range of
parameters studied, increased gel composition increased the factors by which
the permeabilities to water and oil were reduced. Increased gel composition
also increased selectivity, a measure of the water-permeability reduction with
respect to oil-permeability reduction. Applied pressure gradients during
steady-state flows had little effect on oil permeability and a moderate effect
on water permeability. Material balances on phases and components in the
sandpacks provided insights into mechanisms responsible for the development of
flow channels through gelled sandpacks and mechanisms contributing to favorable
DPR. Increased pressure gradient during channel development decreased the
selectivity of the treatment.
High water production is a major concern in mature hydrocarbon reservoirs.
Costs of handling and disposing of water produced from oil reservoirs often
shorten the life of a production well. Disposal of the water is also an
environmental concern. In order to reduce water production, polymer gels have
been used to modify the mobility of water and oil in petroleum reservoirs.
When some gels are placed in a petroleum reservoir, permeability reduction
occurs to a much greater extent for water than for oil. This phenomenon is
known as favorable DPR. Reduced permeability to water can lead to decreased
production of water, and sometimes increased oil production, thereby prolonging
the useful life of the reservoir. Results reported in the literature have shown
that the application of several polymer gel systems can result in DPR.
Mechanisms for DPR have been debated, and the magnitude of the effect has been
unpredictable from one application to another. Mechanisms for DPR that have
been proposed and studied by several researchers are shown in Table 1. The
usual method to study DPR is to saturate a porous medium with gelant, allow
time for gelation to occur, and then inject oil and water to steady-state
conditions and determine permeabilities at 100% fractional flow of each fluid.
One aspect of this procedure that most of these experimental works do not
describe or examine is the process that occurs when oil or water is first
injected into the gel-treated porous media. It is our experience that the
medium has very little permeability at the start of injection and that
considerable time is required for the injected fluid to develop channels or
flow paths through the system before a steady state is approached.
© 2006. Society of Petroleum Engineers
View full textPDF
- Original manuscript received:
12 January 2004
- Revised manuscript received:
9 September 2005
- Manuscript approved:
11 September 2005
- Version of record:
20 June 2006