Hydrophobic Small-Molecule Polymers as High-Temperature-Resistant Inhibitors in Water-Based Drilling Fluids

Water-based drilling fluids can cause hydration of the wellbore rocks, thereby leading to instability. This study aimed to synthesize a hydrophobic small-molecule polymer (HLMP) as an inhibitor to suppress mud shale hydration. An infrared spectral method and a thermogravimetric technique were used to characterize the chemical composition of the HLMP and evaluate its heat stability. Experiments were conducted to measure the linear swelling, rolling recovery rate, and bentonite inhibition rate and evaluate accordingly the inhibition performance of the HLMP. Moreover, the HLMP was characterized through measurements of the zeta potential, particle size distribution, contact angles, and interlayer space testing. As confirmed by the results, the HLMP could successfully be synthesized with a favorable heat stability. Furthermore, favorable results were found for the inhibitory processes of the HLMP on swelling and dispersed hydration during mud shale hydration. The positively charged HLMP could be electrically neutralized with clay particles, thereby inhibiting diffusion in the double electron clay layers. The hydrophobic group in the HLMP molecular structure resulted in the formation of a hydrophobic membrane on the rock surface, enhancing the hydrophobicity of the rock. In addition, the small molecules of the HLMP could plug the spaces between the layers of bentonite crystals, thereby reducing the entry of water molecules and inhibiting shale hydration.