Polymer viscosity reducer for water-based drilling fluid and preparation method thereof

A polymer viscosity reducer for a water-based drilling fluid, which is prepared from raw materials consisting of, in parts by mass:

• 100 parts to 150 parts of water, 30 parts to 50 parts of acrylic acid, 10 parts to 20 parts of maleic anhydride, 40 parts to 60 parts of allyl polyethylene glycol, 3 parts to 6 parts of an initiator, 1 part to 3 parts of a pH regulator, 10 parts to 20 parts of a diamine, and 5 parts to 10 parts of a saturated organic acid,
• wherein the polymer viscosity reducer for the water-based drilling fluid is prepared by a method comprising the following steps:
• mixing the diamine and the maleic anhydride to obtain a mixture, and subjecting the mixture to amidation to obtain an amidation product, wherein the amidation is conducted at a temperature of 60° C. to 80° C. for 1 h to 2 h;
• mixing the amidation product, the water, the acrylic acid, the allyl polyethylene glycol, the pH regulator, and the initiator to obtain a mixed material, and subjecting the mixed material to polymerization to obtain a polymerization product;
• and
• mixing the polymerization product and the saturated organic acid to obtain a mixed solution, and subjecting the mixed solution to neutralization to obtain the polymer viscosity reducer for the water-based drilling fluid.