Anti-sloughing viscosity-reducing filtrate reducer for drilling fluid as well as preparation method and application of anti-sloughing viscosity-reducing filtrate reducer

The preparation method comprises the following steps: firstly, adding water into a reaction kettle, stirring, adding humic acid, then adding sodium hydroxide, heating to 75-80 DEG C, reacting for 50-70 minutes, carrying out precipitation separation on the obtained liquid, then removing sedimentation residues, adding hydrolyzed polyacrylonitrile salt into the residual liquid, then adding phenolic resin and AMPS (2-acrylamido-2-methylpropanesulfonic acid), and carrying out stirring, so as to obtain the anti-sloughing, viscosity-reducing and filtrate-loss-reducing agent for the drilling fluid and the preparation method of the anti-sloughing, viscosity-reducing and filtrate-loss-reducing agent for the drilling fluid. And finally, adding high-temperature defoaming oil, stirring and reacting at 80-85 DEG C for 90-120 minutes, and drying to obtain the black brown spherical fine particle anti-sloughing viscosity-reducing filtrate reducer for the drilling fluid. The phenolic resin is directly adopted, secondary sulfon