The present invention relates to core-shell type
polymer microspheres, preparation and applications thereof. The preparation comprises: adding deionized water, an emulsifier and a dispersing agent to a reaction kettle, slowly stirring and dissolving, adding a
styrene base
monomer, a
vinyl polymer cross-linking agent and an initiator, introducing
nitrogen to replace air of the reaction kettle, heating to a temperature of 70-85 DEG C, reacting to form a core structure, adding a reaction solution containing
acrylate, a
styrene base
monomer, a
vinyl polymer cross-linking agent and an initiator in a dropwise manner, forming a shell structure on the core structure surface, cooling to a
room temperature, discharging the material, and filtering to obtain the product. According to the core-shell type
polymer microspheres of the present invention, the internal core structure is formed by the reaction of the styryl
monomer and the
vinyl polymer cross-linking agent, the shell layer of the microspheres is formed through the copolymerization of the
acrylate, the
styrene base monomer and the vinyl
polymer cross-linking agent, and produces
volume expansion under the downhole oil-gas effect so as to bond and seal the micro-crack in the
cement sheath or the interface micro-gap, and the sufficient strength of the microspheres after expanding is ensured through the core portion of the microspheres.