静态推靠式旋转导向钻井系统的钻压传递效率

Analysis on the weight-on-bit transmission efficiency of the static push-the-bit rotary steerable system

国内研制的静态推靠式旋转导向钻井系统正全面开展现场试验及初步应用,该系统正常钻进时导向翼肋施加到井壁上的静态推靠力会产生较大的摩擦力,有可能影响钻压传递效率和钻井速度。为此,基于该系统的结构及工作原理,考虑井壁无台阶和有台阶两种情况,分别建立了钻压传递效率分析模型,模拟分析了钻压传递效率随名义钻压、井壁摩擦系数,以及导向翼肋推靠力和前倒角的变化规律。研究结果表明:(1)该旋转导向系统对名义钻压有最小值要求,适当提高名义钻压有助于提高钻压传递效率;(2)无论井壁是否有台阶,如果导向翼肋推靠力之和越大、井壁摩擦系数越大,那么钻压传递效率就越低,当井壁有台阶时钻压传递效率明显低于井壁无台阶时的对应值;(3)井壁有台阶时导向翼肋前倒角对钻压传递效率影响明显,前倒角越大则钻压传递效率越低(甚至自锁)。结论认为,该研究成果有助于指导钻井现场合理选择和调控钻压。

Now, the static push-the-bit rotary steerable system （SRSS） developed in China is being put into field tests and primary appli-cations. During its normal drilling, higher frictional forces generated by the static pushing forces of the rotary ribs on the wellbore wall influence the weight-on-bit （WOB） transmission efficiency and the rate of penetration （ROP）. In this paper, analytical models of the WOB transmission efficiency were established for the wellbore wall with and without ladders respectively based on the structure and working principle of the SRSS. And the variation rules of the WOB transmission efficiency with the nominal WOB, the frictional coefficient of well-bore wall, the pushing force and the front chamfer of the steerable rib were analyzed. And the following research results were obtained. First, the nominal WOB of this SRSS has to satisfy the minimum requirement and it is conducive to the increase of WOB transmission efficiency by increasing the nominal WOB appropriately. Second, whether there are ladders on the wellbore wall or not, the WOB transmis-sion efficiency decreases as the total pushing forces of steerable ribs and the frictional coefficient of wellbore wall increase. And the WOB transmission efficiency in the case of wellbore wall with ladders is much lower than that without ladders. Third, if there are ladders on the wellbore wall, the front chamfer of steerable rib has a significant effect on the WOB transmission efficiency. The larger the front chamfer is, the lower the WOB transmission efficiency is （even self-locking）. In conclusion, the research results play an important role in guiding the rational selection and control of the WOB at drilling site.