Purpose. To develop a probabilistic model of PDC drill bit wearing estimation according to the drilling time, drill solids and instrument design. Methodology. The method is based on the experimental data of drill bit cutter run. Drill bit cutter wear rate can be described with a probabilistic function, parameters of this function have to be defined experimentally for particular cutters and drilling conditions. For wear rate probabilistic parameters, 3 types of the models are proposed to analyze: reliability of cutters and their failure due to margin wear rate caused by one type rock drilling; reliability of cutters and their failure due to margin wear rate caused by drilling different rocks; drill bit reliability and its failure due to the margin wear rate of its cutters. Drilling practice shows that wearing of the cutters is unbalanced: central cutters are the most worn out, while the peripheral ones are not worn out, as a rule. Blunting criterion of drill bit is proposed. Findings. The article analyses the problems of estimation of the wear rate of PDC drill bit cutters and their remaining life. Technical guaranties of PDC drill bit cutters are developed with different drilling conditions considered. The blunting criteria of single bit cutters and whole PDC drill bit were reasoned considering cut rock characteristics, total drilling time and drill bit construction. Based on the experimental data, wearing probabilistic function was developed. The drill bit construction requirements, which provide total drilling time optimization, were defined. Originality. The research advances of the method proposed in the paper include cutter and drill bit wearing process rationalization, as well as the development of drill bit wear criterion which allows enhancing efficiency of drill bit construction. Practical value. A method of bit wearing probability determination depending on the drilling time, drilled rocks and bit construction was proposed. Drill bit blunting criterion was suggested.

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