Hydrophobically modified cationic oligoacrylamide as a potential shale hydration inhibitor in water-based drilling fluid and mechanism study

Abstract

Inhibiting shale hydration is crucial for wellbore stability in oil and gas drilling operations when using water-based drilling fluids (WBDFs). In the study, a hydrophobically modified cationic oligoacrylamide (HCOA) was employed as a potential shale hydration inhibitor. It was prepared by precipitation polymerization of acrylamide (AAm), methylacrylethyl trimethylammonium chloride (DMC) and octadecyl acrylate (SA) in anhydrous ethanol. Characterizations were conducted by fourier transform infrared spectroscopy (FT-IR), proton nuclear magnetic resonance spectroscopy (1HNMR), fluorescence spectrophotometer (FR) and gel permeation chromatography (GPC). The results revealed the molecular weight of HCOA was 1.432 × 103 g/mol, and confirmed the hydrophobic association behavior in aqueous solution. The performance of HCOA on inhibiting shale hydration was evaluated by shale cuttings hot-rolling dispersion test, relative inhibition ratio and linear swelling measurements. The results showed that HCOA can perform as an effective shale hydration inhibitor. The rheological and filtration tests of WBDF demonstrated that HCOA can considerably decrease the high temperature high pressure filtration loss (FLHTHP) of WBDF and had no negative effect on the WBDF's rheological property. The inhibition mechanism study revealed that HCOA could adsorb on the clay surface via electrostatic binding and form a hydrophobic layer to prevent contact between water molecules and clay particles, rather than intercalating into clay interlayers to inhibit shale hydration. This study might provide a basis for the design of permanent shale inhibitors for drilling fluids.