Improving the drilling performance of hole enlargement via optimized operation

The severe vibration experienced by the bottom hole assembly (BHA) in the process of hole enlargement when drilling (HEWD) is the major cause for deteriorated drilling performance. A dynamic model of the system of reamer near pilot bit (RNB)-HEWD-BHA including the drillstring and drill collar is formulated with the finite element method. Based on the dynamic analysis and some project cases of hole enlargement, the relationship between operating rotation speed and dynamic characteristics of RNB-HEWD-BHA is discussed. The results show that “the optimum operating rotation speed” exists to this kind of BHA, and the dynamic characteristics of this BHA such as the rate of penetration (ROP), vibration, and safety can be improved effectively when the optimum operating rotation speed works. Furthermore, this paper offers a more scientific and objective method, the Fuzzy Synthetic Evaluation Model, to make a comprehensive evaluation of drilling performance of RNB-HEWD-BHA at different operating rotation speeds. These evaluation results will guide the operator to make more reasonable drilling operation plan to enlarge the hole efficiently and safely.