Abstract: When infill wells were drilled and massively upscaled within cluster well groups in the artificial island B of the Bohai Sea,it was difficult with low efficiency in the design of anti-collision and obstacle-bypassing systems.According to the analysis of the overall anti-collision situation and characteristics of the infill wells,the data of previously drilled wells were accurately calibrated;the principles for cluster well group platform optimization and anti-collision design which were specified in the industrial standard were used to formulate the specific workflow for anti-collision trajectory design in order to massively upscale the infill wells,and thus form an overall optimal design method and optimized the drilling sequence,slot matching relations,as well as anti-collision trajectory design parameters.Through multiple rounds of slots adjustment and trajectory optimization,trajectory design and anti-collision analysis were conducted in 45 infilling wells in a limited well platform space.The lowest separation coefficient values of all wells met the minimum limit of 1.5 specified by the industrial standard,and 70% of such values concentrated at more than 1.7,reducing the risk of borehole collision on the whole.The research results showed that the anti-collision optimization design technology can effectively solve the anti-collision design problem in large-scale infilling adjustment of well cluster groups,and improve the design quality and efficiency.