This article describes a crosslinking material derived from natural sources
that can be used with a variety of polymers over a broad temperature range to
produce gels for conformance applications. Delayed crosslinked polymer systems
have been used for many years in conformance applications. For the past
decade, the most widely used system has been based on chromium (+3) crosslinked
polyacrylamide. Organic crosslinkers, such as phenol/formaldehyde and
polyethyleneimine, (PEI) have also been used with a variety of polymers.
However, these systems are being scrutinized by regulatory agencies and have
now been scheduled for phase-out in some countries. Because of these issues, a
single, environmentally friendly crosslinker that could be used with a variety
of polymers over a broad temperature range was selected for study.
This article details the laboratory development of an environmentally
friendly, natural polyamine crosslinker system, namely chitosan. This
crosslinker can be used with a variety of polymers, such as polyacrylamide,
AMPS/acrylamide (AMPS/AA), or alkylacrylate polymers. Gels ranging from stiff
and “ringing” type to “lipping” have been obtained. Additionally, this article
summarizes results from recent efforts targeted toward designing chitosan-based
gel compositions with improved environmental rating for potential field use.
These efforts included using chitosan as the base polymer in combination with a
synthetic polymeric crosslinker, as well as developing gels derived completely
from natural polymers.
This study primarily focused on conformance water-based gels designed for
application in wells in which the oil- and water-producing zones were clearly
separated and could be mechanically isolated. Water-based gel systems for
conformance applications included both chromium (+3) crosslinked polyacrylamide
and phenol/formaldehyde crosslinker systems for homo-, co-, and ter-polymer
systems containing acrylamide.
Recently, a less toxic crosslinker tested extensively in field trials
worldwide enjoyed a high success rate. This system is based on PEI
crosslinker and a copolymer of acrylamide and t-butyl acrylate (PA-t-BA). PEI
is a low-toxicity material approved for food contact. Recent test results
indicate that a variety of polymers containing amide pendant groups are
crosslinked by PEI, presumably through a transamidation reaction pathway to
provide gels (Fig. 1).
However, in some countries, PEI is targeted for replacement by systems that
are less corrosive, less toxic, less bioaccumulating, and which show good
biodegradability. Base polymers used in conformance gel systems containing a
carbon/carbon backbone, although of low toxicity, are resistant to
biodegradation and tend to bioaccumulate or persist in the environment for long
© 2005. Society of Petroleum Engineers
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- Original manuscript received:
28 January 2004
- Revised manuscript received:
11 October 2005
- Manuscript approved:
28 October 2005
- Version of record:
15 December 2005