# Experimental Investigation on the Development of Environmentally Friendly Chitosan Quaternary Shale Inhibitor

## TL;DR

This paper develops a new eco-friendly shale inhibitor using modified chitosan that outperforms traditional chemicals in preventing clay swelling during drilling.

## Contribution

A novel chitosan-based quaternary ammonium compound is developed with superior shale inhibition and environmental benefits.

## Key findings

- 1% QASC reduced bentonite swelling to 28.1% after 16 h, outperforming 5% KCl and 1% polyetheramine.
- QASC achieved 88.4% shale recovery at 150 °C, significantly higher than polyetheramine and pure water.
- QASC inhibits clay hydration through electrostatic adsorption and intercalation into clay interlayers.

## Abstract

With the increasingly stringent environmental regulations, the development of high-performance and eco-friendly shale inhibitors for water-sensitive formations has become an urgent priority. Chitosan, a renewable biopolymer derived from chitin, has inherent potential as a shale inhibitor but is limited by low water solubility and suboptimal inhibition efficiency. To overcome these limitations, cationic quaternary ammonium groups were grafted onto chitosan through etherification with 3-chloro-2-hydroxypropyltrimethylammonium chloride (CHA), yielding chitosan quaternary ammonium chloride (QASC). Systematic evaluation through linear swelling, rolling recovery, and bentonite inhibition tests revealed QASC’s superior performance. Notably, 1% QASC reduced bentonite swelling to 28.1% after 16 h, outperforming 5% KCl (48.2%) and 1% polyetheramine (41.1%). Remarkably, QASC achieved 88.4% shale recovery at 150 °C significantly exceeding the values for polyetheramine (52%) and pure water (13.2%). Mechanistic analysis revealed that QASC inhibits clay hydration through dual mechanisms: (1) electrostatic and hydrogen-bond mediated adsorption on clay surfaces, effectively neutralizing surface charges and diminishing hydration films; (2) intercalation into clay interlayers to create a physical barrier against water invasion. This synergistic combination ensures stable inhibitory performance under elevated temperatures. Given its enhanced biodegradability, QASC emerges as a sustainable alternative to conventional inhibitors, effectively addressing the dual challenges of technical performance and environmental compatibility in shale gas drilling operations.