Abstract: In order to reduce the reservoir damage caused by foreign fluid during drilling in Chenghai Oilfield,a new film-forming agent LCM-8 had been developed using styrene,butyl acrylate monomer and trigger ammonium persulfate,by emulsion polymerization method based on the film-forming technology.Laboratory tests showed that rheological properties of the drilling fluid could be gotten to carry cuttings after adding LCM-8,which could form a plugging area with low permeability at the polluted end of the core.The plugging rate and flowback permeability recovery rate could be higher than 90%.LCM-8 had been applied in two wells in Chenghai Oilfield,the results showed that the drilling fluid for the upper well section could meet the drilling demand after adding the film-forming agent,resulting in skin factors of -2.31 and -3.11 respectively,while the skin factors of two adjacent wells were -0.27 and 0.23 respectively without adding the film forming agent.It showed that LCM-8 could meet the demand of drilling and reservoir protection in Chenghai Oilfield.