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Rotating plane flow distributing pairs have been widely used in engineering. It is very important to reduce the frictional resistance between the pairs to improve the sensitivity and prolong service life. In this paper, the traditional rotating plane flow pair is improved, and the boss is introduced to keep the rotor and the stator in incomplete contact, and then a gap is formed between the flow pairs. The relationship between the pressure distribution and the friction resistance of the flow pairs is established. The theoretical mathematical model of the fluid movement between the gaps of the structure is built. Given the complexity of model analysis, the numerical analysis method is used to analyze the fluid motion in the structure. The height of the boss is proved to be the most important parameter of the structure, the increase of the boss’s height causes the pressure between the flow pairs to increase, and the pressure difference between regions gradually decreases, so the friction between the flow pairs will gradually decrease until reaching a stable value. The change of the boss’s diameter has little influence on the pressure distribution of the clearance, but as the diameter increases, the friction between the flow pairs will increase linearly. Once the opening width of the waist hole on the upper rotor is smaller than the radius of the discharge hole on the lower stator, the smaller the width, the higher the pressure, but when the opening width is larger than the radius of the discharge holes, the change of the width has no obvious influence on the pressure distribution and the friction.

Annular drilling fluid between the drillstring and borehole wall has a great influence on lateral vibration of drillstring and the influence involves the added mass. Assuming the drilling fluid is incompressible, we derive the added mass coefficient that annular drilling fluid influences on lateral vibration of drillstring in the case of axial flow of drilling fluid. When the axial flow of drilling fluid is considered, the added mass coefficient is difficult to solve. We apply CFD method and dynamic mesh technique to establish the calculation model for the flow in the annulus caused by the vibration of drillstring in the annulus. The pressure distribution and velocity distribution of annular drilling fluid are obtained. The added mass force of the drilling fluid acting on the drillstring along the direction of the drillstring is obtained from the pressure distribution, and the added mass coefficient of the lateral vibration of the drillstring is obtained. This paper provides the basis to solve the added mass coefficient of the lateral vibration of drillstring considering axial flow of drilling fluid.

For the increasing well plugging in oilfield development, a new unplugging technology is presented in this paper for the downhole plugging by using high voltage pulse wave. Based on the mechanism analysis, the circuit resistance model and the empirical calculation formula of the pressure shock wave are obtained, and the influence of the same current waveform on the pressure shock wave generated by the wire explosion is preliminarily studied in laboratory experiments under different energy conditions. A corresponding unplugging evaluation test device was designed to simulate the approximate downhole reservoir conditions in the places where the shock wave occurs to test the approximate downhole stress conditions of the core, and to test the permeability changes after different shock waves acted on the core. The results show that the peak value of the pressure shock wave is proportional to the effect of well unplugging, which verifies the feasibility of the unplugging and increasing permeability technology of the electric explosion-controlled shock wave. This technology can quickly dredge the oil seepage channel, increase well permeability, thus increasing the well productivity, which has a broad application prospect and important practical significance.

Rotary-steerable drilling provides unique features such as an extended reach and accurate well trajectory control. These characteristics can notably increase drilling efficiency and safety. One of the main technical difficulties of rotary-steerable drilling is dynamically measuring the spatial attitude at the bottom of the rotating drillstring as the drillstring rotates. We developed a strap-down measurement system, with a triaxial accelerometer and triaxial magnetometers installed near the bit. The inclination and azimuth can be measured in real time even as the drillstring rotates. Although the magnetic system is the norm, we can use this system to achieve continuous measurement while drilling; to achieve this, a novel state-space model is proposed here and the Kalman filter is used to estimate the states. Simulation and experiments show that a continuous-survey system with a Kalman filter approach can improve measurement precision and reduce errors produced by drillstring vibration.

As a kind of superhard material, the polycrystalline diamond compact (PDC) has been extensively used in engineering with its high strength and high wear resistance. Meanwhile, PDC has been increasingly used in bearing design to improve bearing capacity and service life. However, as a bearing material, its friction coefficient under different working conditions is not clear although it is a very important parameter. In this paper, the authors proposed a theoretical model of friction measurement and design a set of measurement rig to investigate the friction characteristics of the PDC bearing. The measurement equipment is developed based on the Coulomb friction model, with the three measurement environments taken into consideration: dry, water and drilling mud. A pair of thrust ball bearing was used in the measurement equipment to equilibrium axial load. But the friction coefficient of thrust ball bearing is proved far less than that of the PDC bearing in the experiment. The frictional coefficient of PDC bearings can be stabilized at about 0.12 under dry friction or water lubrication conditions and increase to 0.2 when tested under drilling fluid environment. Measuring the friction coefficient of PDC bearing -especially under drilling fluid environment can not only provide support for the design of the downhole tool where the bearing friction coefficient obviously affects the feasibility and agility of the tool but also help people to deepen the understanding of PDC materials.

Automatic vertical drilling tools are the key technologies to achieve vertical drilling in deep & super-deep wells, and are also the core for deviation control and well straightening. Based on a self-development automatic vertical drilling tool with electronic closed loop control system (EVDT) designed by the research team, straightening behavior is analyzed in this paper. The mechanical analysis model of the BHA (bottom hole assembly) equipped with the EVDT is developed by using the beam-column theory. The formulas are deduced for calculating the bit lateral forces, bit tilt angle and trend angle of deviation. The influence laws of the push-out force, WOB (weight on bit), deviation angle and wellbore curvature on the straightening behavior of drilling tools are discussed. The results show that when the counterforce of the push-out force is pointing to the low side of borehole wall, the bit lateral force is inclination-drop force and the drilling tendency is straightening. The absolute values of bit lateral force and trend angle of deviation decrease with the increase of WOB but increase with the increase of push-out force, deviation angle and wellbore curvature. The push-out force and wellbore curvature have great influence on both bit lateral force and trend angle of deviation. WOB has major influence on trend angle of deviation, but minor influence on bit lateral force. The deviation angle has little influence on both bit lateral force and trend angle of deviation. This provides basis for predicting and controlling wellbore trajectory.

In the study of drilling dynamics, many investigations are limited to laboratory systems and simple mathematical models. Using field measurement data and a new dynamical model in a rotary steerable drilling system, we demonstrate the existence of low-dimensional chaos in drilling. The behaviors of the mathematical model and actual measurement are shown to be consistent. The revealing of chaos provides a new way to detect early fatigue cracks as weak signals in a noisy environment to reduce engineering cost and the possibility of disaster.

In present, the drilling industry have to face the reality of low oil and gas prices, fully mechanical vertical drilling tool is likely to become the best choice for vertical drilling in the future. Without electric measurement and control system, the mechanical vertical drilling tool has a mechanically stable platform with gravity sensitivity. The stable platform included an eccentric block which is not only sensitive to gravity but also severely affected by torsional vibration. In this article, we reveal the dynamics of eccentric block under the effect of torsional vibration, which is the key element of the well deviation control accuracy in mechanical vertical drilling tool. The dynamic model of eccentric block is established using Lagrangian equation and Coulomb friction, and the law of dynamic characteristics under the effect of different amplitudes and period of torsional vibration is found. The results show that, with the deviation angle and eccentric torsion moment of eccentric block is increased, the resistance to torsional vibration increases. While the frequency of torsional vibration decreases, a subordinate period gradually appears after the rotation speed value of ω is less than 1 rad/s, the torsional vibration with large amplitude and high frequency is detrimental to the stability of the eccentric block. In addition, the largest Lyapunov exponent is estimated using the time series of simulation, the dynamics of eccentric block under the effect of torsional vibration can be switched four types, and the maximum and minimum values of largest Lyapunov exponent are 3.99 × 10 −2 and −2.98 × 10 −2 , which means with the state of torsional vibration changes and the response of eccentric block would be transformed to chaos.