Successful Hole Enlargement Operations Utilizing Reaming While Drilling Techniques and Combining LWD operations in a Deep Water Drilling Environment

Abstract

Hole enlargement tools are often required in deep water drilling operations because of the necessity of running additional casing strings. At the same time, logging while drilling (LWD) tools are required depending on the drilling purpose even in large hole sections. When LWD and hole enlargement operations are required opening the hole and drilling with LWD at the same time offers an effective solution to save time and drilling costs. Deepwater drilling, hole enlargement and LWD operations are well established technologies individually. However, it becomes very challenging once these three factors are combined together. The main reasons of complication are hydraulics and vibration issues. Additional factors including deep water, large diameter hole, heavy LWD BHA's and reduction of flow to LWD tools by diversion at hole enlargement tools, may require a higher flow rate and higher pump pressure than the rig is capable of providing. Sonic LWD sensors are also sensitive to noise and vibration which are often caused by hole enlargement tools. In these most challenging of circumstances the operator decided to open the hole to 20? while simultaneously logging with LWD. This paper describes the procedures used at pre-drilling stage and actual operations such as the positive indication of the hole enlargement tool's activation and comparisons between surface weight on bit (WOB) / torque (TRQ) and downhole WOB / TRQ. The hole enlargement system selection and hydraulic optimization were the key points at the engineering stage. During the actual operation, it was crucial to monitor various drilling parameters and to keep the hole in good condition because of unstable formations. Although the hole enlargement service and LWD service providers were selected from different companies, detailed engineering and close communications were achieved for the common goal. The challenge ended successfully with hole enlargement to 20? while acquiring satisfactory LWD data for over a 1,100m section.