Technical complications that arose during the construction of underwater crossings of main pipelines by directional drilling method caused the need for a detailed study of the processes of the drilling tools. Breakage the drilling tool during the underreaming of the pilot well occurred as a result of fastening of the drilling tool and the fatigue failure of metal in the body of the drill pipes. This required the development of a simulation model of the stress-strain state of drill pipes near the reamer.
The article presents the design scheme of the structure, established dangerous cross-sections and determining the effect of bending stresses on the strength of the section of the drill string. The coefficients of safety margin and endurance limit of the pipes material are determined.
The performed work allowed to form limitations on the application of technologies for underreaming the pilot wells to the drilling rig ("on yourself") and from the drilling rig ("from itself"). On the basis of calculations conclusions are drawn that if it is necessary to carry out operation of underreaming of a well by a method "from itself", there is no sufficient resource of work of a drill string in the course of underreaming. The most preferred method is to expand "on yourself", in the process of which the magnitude of the stresses in the dangerous cross-section become much smaller. For dangerous cross-section in the layout of the drill tool, the critical operation time of drill pipes is determined, at loads implemented in practice. For drill pipes operating in the hazardous area, set the service life to 520 h at a rotational speed of 32 rpm and 300 h at a rotational speed of 56 rpm.
References
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