Statistical analysis of drill pipe failures of strength groups S-135 and G-105
Authors:   Ivano-Frankivsk National Technical University of Oil and Gas, Ukraine, Kryzhanivskyi Yevstakhii , Vytyaz Oleg ,   Ivano-Frankivsk National Technical University of Oil and Gas, Ukraine, Hrabovskyi Roman ,   Ivano-Frankivsk National Technical University of Oil and Gas, Ukraine, Tyrlych Volodymyr ,   Ivano-Frankivsk National Technical University of Oil and Gas, Ukraine
Published: July 2022

The characteristic types of operational defects that can form on the inner or outer surface of drill pipes of strength groups S-135 and G-105 (according to API Spec 5DP) are described using the results of technical diagnostics from drilling wells in the Dnipro-Donetsk gas and oil region. In 2018 and 2019, the Ukrburgaz Drilling Department rejected 81 drill pipes of strength group S-135 and 89 drill pipes of strength group G-105 when drilling wells to a depth of 4000 to 6000 m. A statistical evaluation of the operational defects detected during deep drilling of wells (4000–6000 m) was carried out. Potentially dangerous areas were identified: in the drilling pipe upset zone and along the length of the drill string end drill pipes lifetime has been taken into account. It is recommended during defectoscopy of drill string pipes of the selected strength groups to pay close attention to the sections of pipes of strength group S-135 from the end of the coupling or nipple, in the range of 0.45 m to 0.57 m, and for sections of pipes of strength group G-105, in the range of 0.55 m to 0.63 m. In addition, given the depth of drilling (Lmax), when performing diagnostics on drill pipes, special attention should be paid to sections with the most likely defect (Lf ) along the length of the drill string. In particular, taking into account the relative length (Lf /Lmax) of the drill string, for pipes of strength groups S-135 and G-105, segments in the ranges of 0.34 to 0.47 and 0.43 to 0.52, respectively, were identified as having the highest probability of operational defects. The peculiarities of the influence of a drill pipe operating lifespan depending on the strength group were established. In particular, during the long-term deepening of drill pipes in strength group S-135, three stages of drilling were distinguished: Stage I – running-in (from start-up to 2000 hours); Stage II – stable work (2000 to 7000 hours); and Stage III – accelerated destruction (7000 hours and longer). It was found that during defectoscopy of the pipe, special attention should be paid to the drill pipe, the service life of which is 602–998 hours in the first stage, from 3348 to 5344 hours in the second stage, and from 8942 to 10 584 hours in the third stage, because these periods carry the greatest probability of originating an inadmissible defect. For long-term drilling works with pipes of strength group G-105, two stages of drilling were distinguished: the first stage, of stable work (up to 6000 hours), and the second stage, of accelerated destruction (6000 hours and longer). It was found that during defectoscopy of the pipe, special attention should be paid to the drill pipe, the service life of which is from 2692 to 3736 hours in the first stage and from 8744 to 10 983 hours in the second stage, because these periods demonstrate the greatest probability of an inadmissible defect.