Elastic and tough modifier composition for well cementation of oil and gas well, preparation method of elastic and tough modifier composition and elastic and tough cement paste system

The invention belongs to the field of oil-gas well cementation, and particularly relates to an elastic and tough modifier composition for oil-gas well cementation, a preparation method of the elastic and tough modifier composition and an elastic and tough cement paste system. The elastic and tough modifier composition mainly comprises the following components in parts by weight: 1 part of mixed fiber, 45-75 parts of epoxy resin coated rubber particles and 0.5-5 parts of nano silicon dioxide. According to the invention, the epoxy resin coated rubber particles are used as elastic particles to play a buffering role, absorb part of energy and improve the impact resistance of set cement; the mixed fibers are uniformly distributed in the set cement to form a compact net-shaped structure, so that when the set cement is broken, the tendon pulling effect of the fibers can be formed, and the fracture toughness of the set cement is improved; the nano silicon dioxide has a filling effect on micropores in the set cement b