Managing Losses with Controlled Mud Level Drilling

Abstract

Since 2016, Lundin Norway has used Enhanced Drilling's EC-Drill System to enable Controlled Mud Level (CML) drilling in the Barents Sea. The CML process allows control of the mud level in the riser in order to mitigate and manage losses while drilling, coring, tripping, cementing casing/liner, wireline operations, and well abandonment operations. With a sub-sea pump module (SPM) docked to a modified riser joint, pressure sensors on the riser and mud return line connected to the top-side, the EC-Drill equipment was able to precisely control the fluid level in the riser and manage the bottom hole pressure while drilling through potential loss zones in naturally fractured and potentially karstified carbonate formations. This paper discusses the CML system used during the project, as well as the drilling, tripping, and cementing strategy, examples of how the system was used to reduce wellbore ballooning, reduce losses during drilling, cementing and well abandonment, and several key lessons learned over the the past seven exploration and appraisal well operations. The ability to raise and lower the riser level to manage the loss rate allowed the CML process to be used during drilling / coring operations, cementing of 7" liners and 9 5/8" casing, as well as wireline operations and well abandonment. Once the SPM and modified riser joint were deployed with the marine drilling riser and SS BOP, the system is ready for use. This allowed using the CML process in hole sections as large as 17 ½" with minimal modification of conventional drilling practices, or sacrificing ROP due to restricted flow rates. The accuracy of the riser pressure sensors on the modified riser joint allowed the system to be used while tripping to reduce surge pressures while running in hole. The system also added value during cement jobs by managing the wellbore pressure profile and return flow throughout the cement circulation and displacement. During plug and abandonment operations critical path time and cost have been reduced by managing losses to an acceptable rate during casing retrieval. The CML process has become an integral part of the operation from start to finish for Barents Sea operations for Lundin.