Preparation and evaluation of amine terminated polyether shale inhibitor for water-based drilling fluid

Facing the problems of shale hydration, swelling and borehole wall instability in shale gas drilling, a new type of amine terminated polyether (ATPE) shale inhibitor used in water-based drilling fluid is successfully synthesized through the method of leaving group. Using the yield of ATPE as index, orthogonal experiments are designed to determine the optimal reaction conditions. When the mole ratio of polyethylene glycol tosylate (PEG-OTs)/ethylenediamine is 1/3.6, mole ratio of PEG-OTs/triethylamine (acid binding agent) is 1/4, reaction time is 3.5 h and reaction temperature is 60 degrees C, the yield of ATPE is 91.12%. The structure and molecular weight of polyethylene glycol (PEG-400, a kind of oligomer), PEG-OTs and ATPE are characterized by Fourier transform infrared spectroscopy, nuclear magnetic resonance hydrogen spectroscopy (H-1-NMR) and time of flight mass spectrometer. The characterization results show that the ATPE has a reasonable molecular weight, and the both hydroxyls of PEG-400 have been replaced by ethylenediamine. The inhibition property of ATPE, potassium chloride (KCI), potassium formate (KCOOH), methane-siliconic acid (FMS-1) and polymeric alcohol (JLX-B) are comparatively evaluated through shale rolling dispersion experiment, linear expansion experiment and laser particle size test.The results show that the ATPE has a better shale inhibition property than traditional inhibitors. The drilling fluid system performance evaluation results show that the system has good engineering application value with excellent rheological property, low fluid loss and good shale inhibition property, which guarantee the well-bore stability in shale gas drilling.