BORETHIN® is a zwitterionic polymer viscosity reducer used in water-based drilling fluid systems. The cations can be quickly adsorbed on the surface of negatively charged clay particles in an electrostatic way, neutralizing part of the negative charge on clay surface to form dense coating, thus thickening the coating film, weakening the flocculation trend of clay particles and enhancing the stability of the system. BORETHIN® can be preferentially adsorbed due to its low molecular weight and performs as highly inhibitive and high viscosity reduction. BORETHIN® is suitable for use in any freshwater or brine drilling fluid systems and works well with a variety of polymer additives.