RIASSUNTO
Summary
This article describes a crosslinking material derived from natural sourcesthat can be used with a variety of polymers over a broad temperature range toproduce gels for conformance applications. Delayed crosslinked polymer systemshave been used for many years in conformance applications.For the pastdecade, the most widely used system has been based on chromium (+3) crosslinkedpolyacrylamide. Organic crosslinkers, such as phenol/formaldehyde andpolyethyleneimine, (PEI) have also been used with a variety of polymers.However, these systems are being scrutinized by regulatory agencies and havenow been scheduled for phase-out in some countries. Because of these issues, asingle, environmentally friendly crosslinker that could be used with a varietyof polymers over a broad temperature range was selected for study.
This article details the laboratory development of an environmentallyfriendly, natural polyamine crosslinker system, namely chitosan.Thiscrosslinker can be used with a variety of polymers, such as polyacrylamide,AMPS/acrylamide (AMPS/AA), or alkylacrylate polymers. Gels ranging from stiffand ""ringing"" type to ""lipping"" have been obtained. Additionally, this articlesummarizes results from recent efforts targeted toward designing chitosan-basedgel compositions with improved environmental rating for potential field use.These efforts included using chitosan as the base polymer in combination with asynthetic polymeric crosslinker, as well as developing gels derived completelyfrom natural polymers.
Introduction
This study primarily focused on conformance water-based gels designed forapplication in wells in which the oil- and water-producing zones were clearlyseparated and could be mechanically isolated. Water-based gel systems forconformance applications included both chromium (+3) crosslinked polyacrylamideand phenol/formaldehyde crosslinker systems for homo-, co-, and ter-polymersystems containing acrylamide.
Recently, a less toxic crosslinker tested extensively in field trialsworldwide enjoyed a high success rate.This system is based on PEIcrosslinker and a copolymer of acrylamide and t-butyl acrylate (PA-t-BA). PEIis a low-toxicity material approved for food contact. Recent test resultsindicate that a variety of polymers containing amide pendant groups arecrosslinked by PEI, presumably through a transamidation reaction pathway toprovide gels (Fig. 1).
However, in some countries, PEI is targeted for replacement by systems thatare less corrosive, less toxic, less bioaccumulating, and which show goodbiodegradability. Base polymers used in conformance gel systems containing acarbon/carbon backbone, although of low toxicity, are resistant tobiodegradation and tend to bioaccumulate or persist in the environment for longperiods.