Summary
An idealistic goal of water-shutoff technology is that of identifying
materials that can be injected into any production well (without zone
isolation) and that will substantially reduce the water productivity without
significantly impairing hydrocarbon productivity. Although many polymers and
gels reduce permeability to water more than to oil or gas, several factors
currently limit widespread field applications of this disproportionate
permeability-reduction property. Chromium (III)-acetate-hydrolyzed
polyacrylamide [Cr(III)-acetate-HPAM] pore-filling gels were investigated to
overcome these limitations. For porous media with pregel kw
(at Sor) ranging from 120 to 6,500 md, one pore-filling gel
consistently reduced kw to about 0.24 md (ranging from 0.12 to 0.37 md). In
contrast, in Berea sandstone with kw (at
Sor) ranging from 222 to 363 md, a commercially available
relative-permeability modifier (i.e., a suspension of gel particles) exhibited
a much wider range of post-polymer kw values--from 0.75 to
202 md.
Thus, pore-filling gels can provide greater reliability and behavior that is
insensitive to the initial rock permeability.
With sufficient oil throughput, Cr(III)-acetate-HPAM pore-filling gels
dehydrate, thus increasing permeability to oil. Several gel formulations
provided water residual-resistance factors (permeability-reduction factors)
greater than 2,000 and ultimate oil residual-resistance factors
(Frro) values of 2 or less. These results provide hope that
our current approach will identify gels that can treat either fractured or
unfractured production wells successfully and reliably without zone isolation.
Significant oil throughput was required to achieve low Frro
values, suggesting that gelant penetration into porous rock must be small (a
few feet or less) for existing Cr(III)-acetate-HPAM pore-filling gels to
provide effective disproportionate permeability reduction.
Introduction
Many polymers and gels can reduce permeability to water more than that to
oil or gas (Liang et al. 1995; Seright 1995; Zaitoun et al. 1998; Al-Sharji et
al. 1999; Willhite et al. 2002). This disproportionate permeability reduction
(or relative-permeability modification) is essential if polymers or gelants are
placed in production wells without protecting hydrocarbon-productive zones
(Liang et al. 1993). With existing polymers, gels, and technology,
disproportionate permeability reduction may have its greatest value when
treating production wells that intersect a fracture or fracture-like features
(Seright et al. 1998, 1993; Marin et al. 2002). Nonetheless, many people are
very interested in exploiting this property to reduce excess water production
from unfractured wells (i.e., radial flow into porous rock or sand). The
idealistic goal of this technology is to develop a material that can be
injected into any production well (without zone isolation) and that will
substantially reduce the water-productivity index without significantly
impairing hydrocarbon productivity. Several obstacles must be overcome before
this ideal can be achieved. This paper discusses these obstacles and offers an
approach toward a solution using pore-filling gels (i.e., gels that fill all of
the aqueous pore space). It also examines the issue of the time and oil
throughput required to recover productivity in oil zones after a gel treatment
has been applied.
© 2009. Society of Petroleum Engineers
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History
- Original manuscript received:
9 February 2006
- Meeting paper published:
22 April 2006
- Revised manuscript received:
18 April 2008
- Manuscript approved:
7 May 2008
- Published online:
16 March 2009
- Version of record:
1 March 2009
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