连续管可控偏心垫块BHA滑动钻进导向性能分析

针对小井眼连续管水平钻井过程中导向控制的要求,提出采用可控偏心垫块控制井眼轨迹的方法。在下部钻具组合(BHA)中按照一定的分布规律安装可独立控制的偏心垫块,通过控制偏心垫块的伸出与缩回,使BHA产生相对于井眼轴线的偏心位移,从而改变钻具组合的力学特性;对该钻具组合形式采用纵横弯曲连续梁法,建立了连续管可控偏心垫块BHA滑动钻进导向性能的力学模型与控制方程,并针对具体算例采用控制方程进行了求解。计算结果表明,在不同钻压条件下,钻头井斜力、钻头方位力、井斜平面内钻头转角和方位平面内钻头转角均随偏心稳定器在井斜平面与方位平面内的偏心位移呈线性变化;钻铤内径增大,钻头井斜力、方位力均表现为先缓慢减小后快速降低,钻头转角的变化很小。研究表明,控制钻具组合偏心垫块的伸出与缩回可以改变BHA的力学性能,使BHA产生相对于井眼轴线的偏心位移,达到控制井眼轨迹的目的。 

Steering Performance Analysis on BHA with Controllable Eccentric Telescopic Blocks in Coiled Tubing Drilling

In order to meet the requirement of steering control during drilling horizontal slim hole by coiled-tubing, a new method was proposed to control the wellbore trajectory by using controllable eccentric telescopic blocks. The bottom hole assembly (BHA) was equipped with independently controllable eccentric telescopic blocks that can be controlled for extension and retraction to generate displacement of BHA against the borehole axis, so as to change the mechanical properties of BHA. Based on the proposed BHA, a mechanical model and control equation were established to analyze steering performance of the coiled-tubing BHA with eccentric telescopic blocks by means of beam-column theory, and the solution for the specific cases was given by using the control equation. The calculation results showed that the bit drift force, azimuth force and its rotation angle within the inclination plane and azimuth plane are linearly related to the eccentric displacement of eccentric stabilizers at different WOBs. With the increase of the inner diameter of drill collars, the drift force and the azimuth force of bits decreased in cubic polynomial form, but the angle of bit rotation changed very slightly. It is shown that the mechanical properties of BHA can be changed by controlling the extension or retraction of the eccentric blocks by which the eccentric displacement of BHA produced against the borehole axis, so as to control the well trajectory.