Open Access

ARTICLE

Synthesis of Hyperbranched Polyethyleneimine-Propylene Oxide-N-isopropylacrylamide (HPEI-co-PO-co-NIPAM) Terpolymer as a Shale Inhibitor

Wenjun Hu, Liquan Zhang^*
Oilfield Chemistry Department, China Oilfield Services Limited, Langfang, 065201, China
* Corresponding Author: Liquan Zhang. Email:

Journal of Polymer Materials https://doi.org/10.32604/jpm.2025.072450

Received 27 August 2025; Accepted 30 October 2025; Published online 27 November 2025

Abstract

Addressing the persistent challenge of shale hydration and swelling in water-based drilling fluids (WBDFs), this study developed a smart thermo-responsive shale inhibitor, Hyperbranched Polyethyleneimine-Propylene Oxide-N-isopropylacrylamide (HPN). It was synthesized by grafting hyperbranched polyethyleneimine (HPEI) with propylene oxide (PO) and N-isopropylacrylamide (NIPAM), creating a synergistic hydration barrier through hydrophobic association and temperature-triggered pore plugging. Structural characterization by Fourier-Transform Infrared (FTIR) spectroscopy and gel permeation chromatography (GPC) confirmed the successful formation of the HPN terpolymer, revealing a unique “cationic–nonionic” amphiphilic architecture with temperature-responsive properties. Performance evaluation demonstrated that HPN significantly outperforms conventional inhibitors, including potassium chloride (KCl), cationic polyacrylamide (C-PAM), polyethylene glycol (PEG), polyetheramine (PEA), and HPEI. It achieved a superior performance profile: a low yield point of 14.6 Pa, a maximum linear expansion of only 3.1 mm, and a high shale recovery rate of 62.8% at 20% bentonite content. The inhibition mechanism is attributed to a powerful synergy of electrostatic adsorption, hydrophobic association, and thermally induced aggregation, which provides robust performance under demanding conditions such as high salinity (200,000 mg/L NaCl) and high temperature (120°C). Thermogravimetric analysis confirmed excellent thermal stability, and the inhibitor exhibited low biological toxicity, complying with stringent environmental standards. These results establish HPN as an efficient, eco-friendly, and field-ready shale inhibitor well-suited for challenging drilling operations.

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Keywords

Hyperbranched polyethyleneimine; propylene oxide; water-based drilling fluids; shale inhibitor; temperature-responsive polymer

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