Summary
Matrix acidizing and water control are usually addressed as two separate
issues. Associative polymers can be used to simultaneously achieve effective
acidizing and water control during a single treatment. A polymer-based
treatment was applied in an offshore, perforated vertical well with two sets of
perforations in a carbonate reservoir in Saudi Arabia. The acid treatment was
needed to restore the productivity of the upper set of perforations and reduce
water production from the lower set of perforations.
Experimental studies were carried out to investigate the potential use of
associative polymers to control water mobility and act as an acid diverter.
Coreflood experiments were conducted on reservoir cores at downhole conditions
(temperature of 200°F and pressure of 3,500 psi). Extensive laboratory testing
showed that associative polymers had no significant effect on the relative
permeability to oil. However, the relative permeability to water was
significantly reduced.
This paper presents a case history where an associative polymer was applied
during matrix acid treatment of a damaged well. The treatment included two
stages of associative polymer solutions and 20 wt% HCl with additives.
Post-stimulation treatment production data showed that oil rate increased
11.18-fold, whereas water rate decreased 1.7-fold, resulting in a reduction in
the water cut from 75 to 14 vol%.
The production logging tool (PLT) results indicated that the associative
polymer was effective in diverting the acid into the oil producing zone. The
upper set of perforations was producing most of the fluid, which further
confirmed that the associative polymer significantly reduced water production
from the lower zone.
Introduction
Matrix acidizing and water control are two important treatments conducted to
enhance well performance. These treatments are commonly addressed as two
separate issues. Associative polymers can be used to simultaneously achieve
effective acidizing and water control utilizing a single treatment (Eoff et al.
2005).
Acid diversion is an important issue contributing to the success of any
matrix acid stimulation treatment. For this reason, extensive laboratory
studies and field applications have been performed on several acid diverting
agents as reported in the literature. Among the techniques that have been
applied to improve acid coverage are: mechanical (packers, ball sealers, and
particulate diverting agents) and chemicals (foam, polymers, and in-situ-gelled
fluids). More recently, viscoelastic surfactants have been used extensively for
diversion during matrix acid treatments, and have shown a tendency to reduce
water production as reported by Nasr-El-Din et al. (2006).
Relative permeability modifiers, commonly used for water control, can also
be utilized for acid diversion. They can act simultaneously to enhance
diversion during matrix acid treatments and impair water mobility. Eoff et al.
(2005) presented laboratory and field tests, which showed that associative
polymers could provide both goals in sandstone reservoirs. However, a few
studies considered application of associative polymers to divert and control
water production in carbonate formations. Therefore, the objectives of the
present study are to: (1) assess the effectiveness of associative polymers in
reducing brine permeability in carbonate cores, (2) design a polymer-based
treatment to control water and divert acid in matrix treatments, and (3)
evaluate the use of associative polymers based on field application.
This paper presents laboratory data that support the use of this new
technology in carbonate reservoirs. It will also give for the first time field
results on the application of associative polymers in a carbonate reservoir in
Saudi Arabia. Field data were in good agreement with laboratory results.
© 2008. Society of Petroleum Engineers
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History
- Original manuscript received:
27 February 2007
- Meeting paper published:
11 June 2007
- Revised manuscript received:
12 May 2008
- Manuscript approved:
23 May 2008
- Version of record:
25 October 2008
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