Martsynkiv O. Enhancement of operation reliability of casings in directional wells.

Thesis is devoted to the enhancement of operation reliability of casings in directional wells by taking into consideration the curve influence on the out-of-roundness of casing pipes and on the magnitude of ambient critical pressure. The factors have been analyzed that influence on the operation reliability of casing strings during the fixing process of directional wells. There have been observed the methods for solution of the above-mentioned problem. The classification of reasons of low quality casing of directional wells has been specified. Theoretical investigations have been conducted to analyze the influence of casing string curve on the out-of-roundness and durability of casing pipes under the influence of ambient excess pressure. To evaluate the stress state of casing pipes and forms of their cross sections at curve, experimental research has been conducted. The latter has confirmed the results of theoretical investigations devoted to the influence of pipes’ curve on form of their cross sections and necessity to specify the calculation methods of casing strings for fixing of directional wells. The methods have been improved for the calculation of casing as to their reliability during lining of directional wells by the introduction of correction coefficient to the value of external critical pressure depending on the intensity of curve, wall thickness, diameter of pipes and group of steel strength. The recommendations have been developed for the enhancement of operation reliability of casing strings to fix directional wells, which are based on the improved methods of their calculation depending on the degree of well crookedness.