Improving Reliability of Under Reaming While Drilling Operations by Advancing Understanding in Drilling Dynamics

Abstract

Under reaming while drilling operations have become a common practice in the oil and gas industry to address drilling challenges, e.g. reactive and swelling formation, equivalent circulation density (ECD), tight casing tolerance, and to increase production. However, the reliability of the operation remains a challenge, largely due to the lack of understanding in drilling dynamics brought by the additional active cutting element, i.e. the under reamer blades, in the bottom-hole-assembly (BHA) and the lack of standard work practices to mitigate the associated risks. This thesis aims to improve the reliability of under reaming while drilling operations by advancing understanding in drilling dynamics associated with under reamer BHA. Focuses were put on better predicting lateral vibration of the BHA and optimizing BHA design to minimize vibration related failures. These learnings were then applied to evaluate and improve the recently developed Baker Hughes pre-job planning procedures and best drilling practices guideline for under reaming while drilling operations. It is expected that the improved procedures will incorporate better understanding of downhole drilling dynamics and improve quality of service delivery for under reaming while drilling operations. Through detailed static and dynamic analyses performed with a Baker Hughes proprietary Finite Element Analysis software program, this thesis specifically examined how the well path and mud property impact drilling dynamics with an under reamer BHA, identified ways to optimize BHA design to mitigate risks associated with drilling dynamics induced failures for under reaming while drilling applications, and explored the recommended work flow to eliminate rat hole with a dual reamer BHA.