Sulfonated lignin modified with silane coupling agent as biodegradable shale inhibitor in water-based drilling fluid

A series of sulfonated lignin (SL) samples modified with a silane coupling agent (Si–SL) was investigated as a biodegradable shale inhibitor for water-based drilling fluid (WBDF). Cutting dispersion, linear swelling, bentonite inhibition, and mud ball tests were used to evaluate the inhibition performance of the Si–SL series of and compared with conventional shale inhibitors including potassium formate (HCOOK), polyethylene alycol (PEA), Ultrahib polymer, and polyacrylamide potassium salt (K-PAM). The results showed that the inhibition performance of a series of Si–SL was similar to that of Ultrahib and was significantly better than that of HCOOK, PEA and K-PAM at normal temperature. In addition, compared with other inhibitors, Si–SL showed optimal temperature resistance. The inhibition mechanism of Si–SL was studied by particle distribution, rock compressive strength measurement, shale micro-fracture propagation synthesis, X-ray diffraction (XRD) measurement, adsorption measurement, contact angle measurement, scanning electron microscopy (SEM) observation and atomic force microscopy observation. At high temperature, Si–SL can be strongly adsorbed on the surface of clay particles, while phenyl in molecular chain of Si–SL is conducive to improving the temperature resistance and reducing the hydrophilicity of the surface of clay particles, thus effectively preventing the migration of water molecules to the clay layer. More importantly, through biotoxicity and biodegradability test, the results showed that Si–SL had no toxicity and was easy to be biodegraded. In field application of Bei 213-21HF well, the Si–SL effectively inhibits the hydration of water-sensitive cuttings and maintains the wellbore stability of the shale formation, providing a guarantee for safe and fast drilling.