This paper presents technical features and associated benefits of a recently developed under reamer technology and its applications in the offshore Norway Oseberg South field to drill 12 ¼″ × 13 ½″ and 8 ½″ × 9 ½″ sections. It discusses the results of the operations and demonstrates how the operations benefited from the new technology.

In today's drilling operations, expandable reamers are broadly used to support optimized casing and completion programs and to reduce operational risks such as high Equivalent Circulating Density (ECD), drilling troublesome formations and reaming well path conformities. The currently available hole enlargement technologies, such as ball drop and hydraulically activated reamers, carry intrinsic risks and limitations.

To address the challenges associated with currently available under reamer technologies, expandable reamer technology was recently developed jointly by a service company and a major operator, and was field tested offshore Norway. The under reamer, which is fully integrated with the company's existing Rotary Steerable System (RSS) Bottom Hole Assembly (BHA), provides unlimited, on-command activation cycles, optimal placement within the BHA in multiple configurations and real-time feedback via mud-pulse telemetry. The feedback from the reamer includes confirmation of blade activation status, health of the tool, and vibration and stick-slip measurements. Because of the flexibility of its placement in the BHA, the reamer can reduce the length of the rat hole to a minimum of 4 m compared to the standard 30 to 70 m in the same drilling run, eliminating the need for a dedicated clean-out run. The reamer also enables reliable and unlimited activation / deactivation cycles with each cycle taking less than 5 minutes, saving operational costs for the operators.

The under reamer was successfully deployed to drill challenging 12 ¼″ × 13 ½″ and 8 ½″ × 9 ½″ sections in the offshore Norway Oseberg South field. The 2497 m long 12 ¼″ × 13 ½″ section and 900 m long 8 ½″ × 9 ½″ section were both drilled to Total Depth (TD) in one run, with all requirements on directional control and Measurement While Drilling (MWD) / Logging While Drilling (LWD) met. The technology was proven to be a reliable and flexible hole enlargement while drilling solution that elevates drilling performance, reduces operational risks and lowers operational costs.

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