The dynamics of eccentric block in a fully mechanical vertical drilling tool under the effect of torsional vibration

Abstract

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 v 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 3 10 22 and 22.98 3 10 22 , which means with the state of torsional vibration changes and the response of eccentric block would be transformed to chaos.

Dynamic Characteristics and Key Parameter Optimization of Mechanical Automatic Vertical Drilling Tools

“…When the inclination angle exists, the gravity block will produce a restoring torque that always points to the low side of the wellbore. Li et al [9] proved that, as shown in Figure 2, when the included angle of the heavy block is π, the largest restoring torque T E produced is as shown in the following equation:…”

“…More important, the all-metal structural design can withstand higher temperatures and high temperature environments such as ultra-deep wells and vertical wells with abnormal geothermal gradients. So, it becomes the only way to achieve active correction during drilling in high temperature and ultra-deep wells [9][10][11].…”

“…erefore, the working performance of the tool will eventually change dynamically. Li et al [9] introduce a kind of MAVDT which has a mechanically sensing mechanism with gravity sensitivity and revealed the dynamics of gravity block under the effect of torsional vibration and found that while the frequency of torsional vibration decreases, a subordinate period gradually appears after the rotation speed value less than 1 rad/s. However, the static design is still used in the design process of the sensing mechanism.…”

Integral Modeling for Deviation Correction Trajectory of the Mechanical Vertical Drilling System

“…Since the eccentric block is usually symmetrical, the center of gravity is located on the Y axis (as shown in Figure 5a). The Y coordinate value of the gravity center can be obtained by using Equation ( 5) [13].…”

“…For the stable platform, Wang et al have used experimental methods to study the variation of friction performance between the upper and lower plate valves under different working conditions [12]. Li et al have derived the stable position model of the eccentric block and investigated the dynamic characteristics of it under the effect of torsional vibration by using multi-body dynamics simulation method [13]. For the actuator, Zhang have studied the output characteristics of the pushing force through experimental methods [14].…”