Synthesis of polyacrylamide copolymers cross-linked by chitosan hydrogels with potential application for conformance control of petroleum reservoirs

Abstract

Conformance control treatment of oil reservoirs is one of the techniques that can bring improvements in both sweep efficiency and reduction of excessive co-production of oily water. In this work, the chemical treatment of conformance control was studied through the development of gelling systems for in situ hydrogel formation to act as blocking agents in the more permeable regions. For this purpose, copolymers based on acrylamide were used, containing the co-monomers of acrylic acid (AA), partially hydrolyzed polyacrylamide (PHPA), or 2-acrylamide-methylpropane-sulfonic acid (AMPS), as well as the terpolymer containing these three types of co-monomers (AA, PHPA, and AMPS), and chitosan as a cross-linking agent. The systems were preliminarily evaluated using Sydansk gel strength codes, which classify the behavior of hydrogels using codes from “A” to “J” according to their fluidity. In these tests, scans of polymer and cross-linker concentration were performed, the formation of hydrogels was verified, and mechanistic proposals were considered. Subsequently, the viscoelastic properties of the materials were evaluated, followed by an experimental design consisting of a central composite experimental design (CCD), where the variables, temperature and aging time of the hydrogels, showed statistical relevance directly to the gel strength. The systems had optimal injection viscosity values and low tan(delta) values, demonstrating a desirable gel strength to act as blocking agents, and a critical stability time of 15 days. Graphical Abstract: [Figure not available: see fulltext.].