Rachkevych R. Development of scientific fundamentals for ensuring the operability of columns of drill and pumping pipes in the well sections with geometrical imperfections

Dissertation is about solving of important scientific-technical problem of ensuring the operability of columns of drill and pumping pipes in the directed and horizontally well sections with geometrical imperfections in the form of local curvature (dog-legs) and defects of boreholes wall in the form of cavern. Method of evaluation of influence of dimensions of defects of borehole wall on stress-deformed state of drill string was gotten development. This method considers features of contact between drill string and borehole walls in rectilinear and curvilinear well sections under the tangential and axial loadings. Methods and laboratory equipment for determination of stress-deformed state of columns of drill and pumping pipes in wells with three dimensional curvature is proposed first time. Device for research loads and stresses in the drill pipes during their working in the curvilinear well sections is designed and made. C-criteria of fracture for prediction of drill and pumping pipes fatigue life was developed by the using of local stresses before front of fatigue crack. Also using of equivalent stress that considers normal and tangential stresses, in S-N curve with three parameters is substantiated. Special power mechanism that ensures change between levels of loading block without pause of test for determination of fatigue strength parameters for elements of drill and pumping pipes under the irregular loading was designed and produced.