Rachkevych I. Prognosis of the drill string elements fatigue longevity with consideration of complicate deformable state.

ANNOTATION Rachkevych I.O. Prognosis of the drill string elements fatigue longevity with consideration of complicate deformable state. – Academic qualification scientific work on the rights of a manuscript. Dissertation for obtaining the academic degree of the Philosophy Doctor in specialty 133 – «Industrial machinery engineering». The dissertation is prepared in the Ivano-Frankivsk national technical university of oil and gas, 2021. The dissertation solves important scientific-technical problem of prognosis of the drill string elements fatigue longevity with consideration of normal and shear stresses in its cross section. Method of estimation of stress-strain state of the drill string section in the arbitrarily curved well is developed. Results of well survey are used as parameters of curved well. Axial force, bending moment and torque are taken in to account during calculations. 3D modeling of the system «drill string section – well section» is used for calculations by the finite elements method. It gives possibility to calculate with consideration of geometrical parameters of drill pipes screw joints and their positions according to well walls. There is additional possibility to take in to account of physical and mechanical parameters of rock. Methodic of determination of the critical compression load of the device for managing of the well trajectory using 3D modeling of elastic shells packet is gotten refinement. It gives possibility to set more accurately axial load that acts on the device with purpose of more effective managing of the well trajectory. Laboratory equipment for research of deformations and stresses in the pipe string models in the arbitrarily curved wells is improved. In particular, loading unit is upgraded by the purpose of realization of axial tension and compression force. It gives possibility of physical modeling of the drill pipes that are located higher and lower of drill string neutral cross section. Method of prognosis of the drill string elements fatigue longevity is developed using fracture mechanics. In particular, 3D model of the upset end of the drill pipe with semi elliptical crack in its cross section is developed. The 3D model is loaded by the axial force, bending moment and torque. It gives possibility to determine stress intensity factor for opening model and in-plane shear model of crack growth with take in to account normal and shear stresses in to dangerous cross section. Consequently, it gives possibility to calculate quantity of load cycles to critical condition. Key words: drill string; directional well; axial load; bending moment and torque; stress-strain state; normal and shear stress; fatigue longevity; semi elliptical crack; stress intensity factor.