A method of preparing a polymer composite includes dispersing a nanosheet filler within a polymer matrix by dissolving a monomer in water to form a first solution, dispersing the nanosheet filler in an organic solvent in the presence of an emulsifying agent to form a second solution, combining the first solution and the second solution, and adding a polymerization initiator to initiate a polymerization reaction of the monomer to form a polymer composite precursor comprising the nanosheet filler dispersed in the polymer matrix. The method further includes quenching the polymerization reaction and then filtering, washing, grinding, and drying the polymer composite precursor to form the polymer composite. A method of preparing a polymer composite hydrogel for water shutoff applications and the associated method of forming a barrier to shut off or reduce unwanted production of water in a subterranean formation utilizing the polymer composite hydrogel is also provided.