Water-based drilling fluid base slurry additive and water-based drilling fluid

The invention relates to a water-based drilling fluid base slurry additive and a water-based drilling fluid, and belongs to the technical field of drilling fluids. The water-based drilling fluid base slurry additive is mainly composed of a vinyl monomer multipolymer, a zwitterionic polymer coating agent, a filtrate reducer, an anti-collapse agent, a liquid lubricant and a hydrocarbon reservoir protective agent. The mass ratio of the vinyl monomer multipolymer to the zwitterionic polymer coating agent to the filtrate reducer to the anti-collapse agent to the liquid lubricant to the hydrocarbon reservoir protective agent is (0.2-0.4): (0.3-0.5): (0.5-1): (1-2): (4-8): (2-3); the hydrocarbon reservoir protective agent is composed of nanoscale cross-linked starch microspheres and fibers with nanoscale diameters, and the mass ratio of the nanoscale cross-linked starch microspheres to the fibers is (2-4): 1. The water-based drilling fluid adopting the slurry additive is good in compatibility and rheological propert