Design Optimization for the Thin-Walled Joint Thread of a Coring Tool Used for Deep Boreholes

Abstract

Threaded joints are key components of core drilling tools. Currently, core drilling tools generally adopt the thread structure designed by the API Spec 7-1 standard. However, fractures easily occur in this thread structure due to high stress concentrations, resulting in downhole accidents. In this paper, according to the needs of large-diameter core drilling, a core barrel joint was designed with an outer diameter of Φ135 mm and a trapezoidal thread profile. Subsequently, a three-dimensional simulation model of the joint was established. The influence of the external load, connection state and thread structure on the stress distribution in the joint was analyzed through simulations, from which the optimal thread structure was determined. Finally, a connection test was carried out on the threaded joint. The stress distribution in the joint thread was indirectly studied by analyzing gas leaks (i.e., the sealing effect) under axial tension. According to the test data and the simulation results, the final joint thread structure was optimized, which lays a good foundation for the design of a core barrel.

Experimental Estimation of Design and Drilling Regime Option Influence on Drilling Tool Dynamics

“…Для покращення експлуатаційних властивостей бурильного інструмента застосовують низку методів. До конструкторських методів відносять удосконалення конфігурації бурильних труб [3,4], нарізних з'єднань [5][6][7], забезпечення точності нарізей [8][9][10] та запобігання самовідгвинчуванню [11], раціональний вибір матеріялів шляхом проведення корозійних досліджень і вивчення структурних змін металів [12][13][14], параметричну оптимізацію озброєння, опор і вузлів промивання доліт [15][16][17] тощо. Серед технологічних методів заслуговують на увагу раціональне армування сталевих деталей [18], оптимізація формоутворення гвинтових поверхонь та поверхонь складної топології [19,20], нанесення гнучких [21,22], металевих [23][24][25] та функціонально ´радієнтних [26][27][28] покриттів, зокрема оксидних [29], а також шліфування і лазерна обробка робочих поверхонь нарізей [30,31].…”

Drill Bit Deformations in Rotary Drilling Systems under Large-Amplitude Stick-Slip Vibrations

“…Oil and gas companies always attempt to combine management of expenses with drilling efficiency (drill efficiently with optimal cost); however, the appearance of vibrations makes this task very difficult to achieve. It is obvious that the drilling process is not perfectly carried out; in other words, there is always contact between the components of the drillstring and the borehole walls on one hand, and strong interaction between the drill bit and the bottom of the borehole on the other hand [17]. The different acting forces on the drillstring, and the complex geological formations, produce irregular and unwanted solicitations, which may promote the appearance of dynamic phenomena.…”

“…The BHA may receive an excitation (perturbation that triggers the whirling) from the bit, as a result of lateral and perpendicular forces to the axis of rotation. According to oil and gas companies, the major problems that are caused by this phenomenon are: widening the hole due to the irregular bit rotation, reduction in drill pipe virtual life due to cyclic variations in vibrations, the instantaneous rupture of drillstring (appearance of micro-cracks which increase as the phenomenon occurs) and severe contacts with the borehole walls [17]. According to the direction in which it occurs, the whirling phenomenon can be divided into two main types: the first type is 'forward whirl', in which the precession of the drillstring turns in the same direction as the bit rotation; the second type is 'backward whirl', which means that the precession takes place in the opposite direction of rotation.…”

Prediction of the Accuracy of the Tapered Thread Profile

“…There are a number of publications that, to some extent, represent the study of high-strength and highprecision tool-joint tapered threads. In paper [1], the connection test was carried out on the threaded joint. According to the test data and the simulation results, the final joint thread structure was optimized, which is fundamental in designing a tool joint.…”