Laboratory study of the effect of axial compliance on rock penetration of PDC bits

摘要

Drilling field tests and numerical simulations show that there are relationships between Bottom-hole Assembly (BHA) configuration (compliance and mass), BHA vibrations, and the Rate of Penetration (ROP). In recent years sophisticated down-hole tools (e.g. shock sub, Thruster, and Flex Stabilizer) have been designed and fabricated to mitigate unwanted BHA vibrations and increase the ROP. However, utilization of these tools in field tests shows both positive and negative effects on the drilling process. In order to conceptualize the mechanism behind these effects and further investigate the effect of the compliance element on the ROP, a laboratory test rig with a variable compliance feature is developed. Different levels of compliance are achieved by changing the number and pattern of sandwich rubber mounts in the compliance mounting system. Experimental results verify that changing the compliance value can improve the ROP. An optimum compliance value is also investigated in this laboratory study. Additionally, it is investigated that different compliance values alter the relative bit-rock displacement and positively affect bottom hole cleaning, and negatively affect the cutting surface area.