Influence of polymer structure on the gelation kinetics and gel strength of acrylamide‐based copolymers, bentonite and polyethylenimine systems for conformance control of oil reservoirs

Abstract

ABSTRACTIn oil reservoirs with conformance problems, the sweep and oil recovery efficiencies tend to be low because the injected oil‐recovery drive fluids channel through high‐permeability zones and/or anomalies, leaving behind part of the displaceable oil in unswept low‐permeability zones. In these scenarios, conformance improvement treatments with crosslinked polymers can be used to plug the main paths of the reservoir, improving the overall sweep efficiency. This study aimed to investigate the influence of the polymer structure [molecular weight, acrylate, 2‐acrylamido‐2‐methylpropane sulfonic acid (AMPS), and/or N‐vinyl‐2‐pyrrolidone (NVP) moieties] on the gelation kinetics of gelling systems based on homopolymers and copolymers of acrylamide, natural bentonite and polyethylenimine for the conformance control of reservoirs with harsh conditions of temperature and salinity/hardness. The correspondence between the gelation time and gel strength obtained from bottle tests and dynamic shear tests was evaluated. Samples with higher AMPS and NVP moieties formed strong composite hydrogels (equilibrium complex modulus = 20–40 Pa) with low syneresis, and good long‐term stability (∼3–6 months) under harsh conditions (90 °C, 56,012 mg L−1 total dissolved solids and 2100 mg L−1 of divalent ions). © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47556.HIGHLIGHTS Acrylamide‐based copolymers, bentonite and polyethylenimine systems showed controllable gelation time and gel strength Addition of clay into the formulation increased the gelation time and syneresis resistance of the systems, and slightly improved the final strength of the composite hydrogels Polyacrylamide (PAM) and partially hydrolyzed polyacrylamide (PHPA) samples formed heterogeneous composite hydrogels that suffered strong syneresis and thermal degradation, precipitating during aging after approximately 2 months, independently of the initial acrylate moieties of the sample Acrylamide and 2‐acrylamide‐2‐methylpropane sulfonic acid copolymer (PAM–AMPS) and acrylamide, 2‐acrylamido‐2‐methylpropane sulfonic acid, and N‐vinyl‐2‐pyrrolidone (PAM–AMPS–NVP) samples presented higher salt tolerance and formed composite hydrogels with lower syneresis and good long‐term stability (∼3–6 months). Furthermore, samples with sulfonation degree greater than 10% improved the dispersion of clay particles within the hydrogels' structure