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Shale gas production has become the main driver of global gas production growth. Deep shale gas is difficult to extract, which puts forward higher requirements for drilling speed increase. The downhole power drilling tools are mainly screw drilling tools. Conventional screw drill tool stator bushing has poor heat dissipation, which is prone to thermal hysteresis failure, shortening drilling tool life, and is not suitable for high temperature and high pressure environment of deep shale gas wells. Equal wall thickness screw drilling tools and hydrogenated nitrile rubber have better high temperature resistance. Therefore, based on the thermal aging experiment and constitutive model of the rubber changes the displacement of the inner cavity of the stator bushing and the difference between the front and the back is up to 21.6%. The increase of the interference and eccentricity between rotor and motor leads to the increase of the maximum von Mises stress of the stator bushing and the thermal hysteresis temperature. The influence of the interference is greater than the influence of the eccentricity so that the interference should be given priority in the design. This paper provides a theoretical reference for the design and optimization of equal wall thickness bushing of positive displacement motor.

Double shoulder drill pipe joint (DSJ) is a novel thread structure which appears in recent years. Its strength reduced efficiently while the structure design is not appropriately, for the DSJ’s mechanical behaviors weren’t well studied. In this paper a 3D whole structure finite element model of DSJ was established based on the Principle of Virtual Work, and validated the model’s computing results by experimental results. The authors analyzed the stress and strain distribution with the 3D whole structure finite element model’s computing results under torque moment, compression force, tension load, and bend moment. And then acquired the DSJ’s mechanical behaviors under each load. The research works of this paper refer accordance to recognize and design the DSJ. Key words: Double shoulder, Drill pipe joint, Thread, Mechanical behavior

Horizontal wells show better affect and higher success rate in low water ratio cement, complex fracture zone, crevice and heavy oil blocks, it is the main measures to expand control area of a single well. Hydraulic fracturing technology is the most financial way to improve the penetration of the reservoir to increase the production. However, compare with the vertical wells, the fracture of Horizontal wells are more complex, and lead to the initiation crack pressure is much higher than vertical wells. In this paper, defined the crack judging basis, and established the finite element model which could compute the initial crack pressure, to research the affection mechanism of perforation azimuth angle, density, diameter and depth, to provide references of perforation project's design and optimize. The research of this paper has significances on further understanding the affection mechanism of perforation parameters.

Stick-slip vibration presents one of the major causes of drilling problems, such as premature tool failures, low drilling efficiency and poor wellbore quality. The objective of this work is to investigate the influences of rotary table speed (RTS) on stick-slip phenomenon of the drilling system. In this study, the drilling system is treated as a lumped torsional pendulum model of which the bit/rock interaction is regarded as Coulomb friction. By analyzing cases with different RTS, two types of vibrations on the bit are found: stick-slip vibration and uniform motion. With an increase in the RTS, the stick-slip vibration on the drill bit disappears once the RTS arrives at its critical value. For the cases that stick-slip vibrations occur, the phase trajectories converge toward a limit cycle. For the cases that stick-slip vibration does not appear, the drill bit tends to stabilize at a uniform motion and the phase trajectories correspond to contracting spirals observed in the phase plane.

In this paper, the stick-slip vibration in oilwell drillstring is studied. The drilling system is modelled as a lumped-parameter torsional pendulum and the interaction between the drill bit and the rock is treated as Coulomb friction. Equation of motion of the drill bit is established and the dynamic responses of the drill bit are obtained. A drilling system with the drillstring length 3000 m is analysed, in which the system parameters are selected by reference to the actual drilling situation. After the slip vibrations in the initial stage, final state of the drill bit is a stable stick-slip vibration of which the limit cycle is a closed loop. In order to find the stability of the limit cycle corresponds to the periodically stick-slip vibration, different initial conditions for the drill bit are studied. Results show that the drill bit will lead to a periodic motion and the phase trajectories ultimately converge to the same limit cycle corresponds to stable stick-slip vibration.