Synthesis of hydrophobically modified polyampholyte based on epoxidized soybean oil as shale inhibitor in water-based drilling fluid

Abstract

Developing drilling fluid materials from modified biomass to meet drilling and environmental requirements has always been of concern. This paper reports for the first time the use of polyampholyte hydrophobically modified by epoxidized soybean oil (ESO), as a potential shale inhibitor. It (AADE) was prepared by micellar polymerization of acrylamide (AM), 2-acrylamide-2-methylpropanesulfonic acid (AMPS) and methacrylatoethyl trimethyl ammonium chloride (DMC) with pre-prepared ESO-derived methacrylate monomer (ESO-MA). Its molecular structure was confirmed by Fourier transform infrared spectroscopy and proton nuclear magnetic resonance. A comparative study of obtained AADE and the polyampholyte without hydrophobic modification (AAD) was carried out through thermal properties, rheological properties, inhibition performance and drilling fluid compatibility tests. The results showed that AADE possessed higher thermal stability due to the presence of hydrophobic associative ability and crosslinkable epoxy groups, and the hydrophobic interaction between AADE chains dominated the shear-thinning behavior and lowered the viscosity-temperature and viscosity-salt dependence. Also, AADE at a lower concentration more effectively prevented clay hydration swelling and inhibited shale disintegration than AAD and conventional inhibitors. Meanwhile, AADE was well compatible with bentonite dispersion in both fresh water and brine, and improved rheological properties and decreased API and high temperature high pressure (HTHP) fluid loss before and after hot rolling. The inhibition mechanism of AADE was revealed to be the synergetic actions of physical plugging of hydrophobic associated multipolymer aggregates in micro-pores of shale, chemical film with a hydrophobic shell formed on clay surface, and the surface activity to reduce capillary driven force. This research might provide an insight for the application of hydrophobically modified polymer, particularly plant oil-based, as shale inhibitor in water-based drilling fluid.