A sustainable chitin nanocrystal-stabilised emulsions to enhance the conformance control in porous media

Abstract

The presence of high permeability zones causes the injected fluid/gas to bypass the low permeability pores, initiating an early breakthrough. One of the most influential and promising methods to control fluid bypass is fluid diversion using an emulsion/chemical agent placed at the highly permeable zone, which eventually diverts the injected fluids to a less permeable region. Chitin Nanocrystal (ChiNCs), a naturally abundant nanomaterial with high oil-water interfacial adsorption, has attracted significant interest as an emulsion stabiliser in various applications. Unlike traditional surfactants, ChiNCs offer a sustainable alternative by stabilising the emulsion, providing long-term stability and enhanced viscoelasticity. This study presents a novel, eco-friendly solution by exploring ChiNCs as pickering emulsions stabilisers for conformance control in porous media. The ChiNCs were prepared through acid hydrolysis of chitin powder derived from crab shells. ChiNCs and their emulsions were analysed using Transmission Electron Microscopy (TEM), Dynamic Light Scattering (DLS), Zeta (ζ)-Potential, Cross-Polarised Microscopy (CPM), and rheometer. The presence of ChiNCs in the emulsion resulted in shear-thinning behaviour, making it suitable for conformance control. Core-flood experiment results confirmed the effectiveness of ChiNCs-stabilised emulsions for permeability reduction. Pressure drops and permeability reductions increased with larger emulsion slug sizes, indicating successful pore plugging and improved fluid diversion. The highest-permeability reduction with 85.6% were obtained with 0.7 pore volume (PV) of emulsion injection for a short time. In contrast, injecting 0.5 PV of the emulsion led to a significant and sustained permeability reduction of 80.8%. To the best of the authors' knowledge, this is the first application of chitin nanocrystals in fluid diversion and conformance control. The ζ-potential over +20 mV within the pH range 3–6 was sufficient to achieve the highest colloidal stability via electrostatic effect and good ChiNCs suspension transparency. The microstructure observed under the CPM correlates with the rheological behaviour, showing that the ChiNCs provide a significant steric barrier to coalescence, thus enhancing the emulsion's resistance to flow and deformation.