ФІЗИЧНІ Й КОНСТРУКТИВНІ ОСОБЛИВОCТІ КОМПОНУВАННЯ НИЗУ БУРИЛЬНОЇ КОЛОНИ З ОБВАЖНЕНИХ БУРИЛЬНИХ ТРУБ ЗМІННОГО МОМЕНТУ ІНЕРЦІЇ

• Дата: 2023
• Автори: Чернова, Мирослава, Кунцяк, Ярослав
• Формат: Стаття
• Мова: Ukrainian
• Опубліковано: Институт сверхтвердых материалов им. В. Н. Бакуля Национальной академии наук Украины 2023
• Теми: бурение; момент инерции; КНБК; УБТ
• Онлайн доступ: http://altis-ism.org.ua/index.php/ALTIS/article/view/329
• Назва журналу: Tooling materials science

The task of the research considered in this article is the ways to improve and increase the speed of well drilling processes. The methodology for achieving this goal is based on the selection and application of a mathematical model that takes into account the physical and mechanical loads that the drill string perceives in its lower part. The use of variable stiffness drill collars (VSDC) in the bottom hole assembly (BHA), which leads to a smooth change in the moment of inertia of the structure, partially solves this problem. The results obtained by carrying out theoretical and industrial studies confirmed the feasibility of using drill collars with variable moment of inertia (DCVMI) due to the smooth redistribution of stresses in the transition zone of their joints. This technological approach provides a reduction in the construction and commissioning of wells by 30÷60%. During the construction process of oil and gas wells, the drill string is subjected to a complex of constant and alternating loads, the combined effect of which leads to the occurrence of significant stresses, the accumulation of fatigue cracks and, ultimately, to the fatigue failure of the drill string elements. To create the required axial force on the bit and provide greater rigidity of the bottom of the layout, weighted drill pipes are used, the number and dimensions of which depend on the structural and technological characteristics of the well. Weighted drill pipes (WDP), which are produced serially according to technical conditions (TU 39-076-74), are characterized by a constant axial moment of inertia of the cross section along the pipe, since their outer and inner diameters remain unchanged. During the assembly of candles in a column to connect pipe sections of different sizes in the countries of the former secular union, adapters are usually used, the length of which is 0.3÷0.7 m. In such structures, due to a sharp change in stiffness in the transition from drill to weighted drill pipes stresses increase significantly, which shortens the period of critical growth of fatigue cracks. To prevent this in the USA, according to the recommendations of ARIA, when assembling the layout, instead of the adapter, an intermediate heavy pipe 121, which consists of three sections, is used. The middle part has a thickened wall, compared to ordinary pipes, and is 6 m long. Two thick-walled sections are welded to the joint to its planted ends: the lower one, which is 0.6 m long and the upper one with a groove under the elevator and up to 2.4 m long. The thicknesses of the walls of the lower and upper parts of the pipe are the same. Such an intermediate pipe fits more smoothly into the profile of the well, but does not completely solve the problem, as it only slightly reduces the stress concentration in the zone directly adjacent to the weighted drill pipes. Based on the analysis of the work of existing drill pipes and weighted drill pipes, as well as on the theoretical and experimental studies, we developed constructions of weighted drill pipes of variable moment of inertia (WDPVMI). Their use provides: a significant reduction of stresses in the transition zone from drill pipes (DP) to weighted drill pipes (WDP); increasing the stability and reliability of the drill string; facilitation of lowering and lifting operations and fishing operations. During the assembly of the candle in the arrangement of the bottom of the drill string from the well-known pipes, there are ledges along it, which are used for fastening in the elevator during lowering and lifting operations. Under the condition of operation of the drill pipe column at the place of installation of weighted drill pipes of variable moment of inertia, a smooth change in stiffness from the heavy bottom to the drill pipes is ensured, which is associated with a gradual decrease in the diameters of the sections of the proposed structure. If the bottom of the drill string is caught, the uncaught part is unscrewed in the upper threaded connection of the candle. Since the upper part of the variable moment of inertia weighted drill pipe has a smaller diameter, compared to a conventional weighted drill pipe, there is an additional possibility of placing fishing tools from the outside of the pipe in the gap formed with the well wall. On the basis of selected mathematical models for the operation of a drill string made of weighted drill pipes of a variable moment of inertia, the nature of stress changes, their permissible level and optimal values were studied. A weighted variable moment of inertia drill pipe is exponentially shaped (like the Eiffel Tower), has a variable cross-section and a constant-diameter internal bore, the elastic line of which is subjected to axial and centrifugal forces, torque, pressure, and moving flushing fluid.