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conductor drilling system addresses stability, cost and health & safety issues in the North Sea

LEFT – Upper section of the conductor drilling assembly during interface testing, RIGHT – Dual Bore Centralizer during testing phase

The System

The conductor drilling system comprises a hanger and landing ring which supports the weight of the bottomhole assembly, transfers the mud pressure load to the conductor as well as resisting the torsion generated by the mud motor, and providing an effective seal against the mud pressure. A centralizer was also incorporated lower in the conductor drilling system to reduce deviation of the bottomhole assembly during drilling.

An upper and lower stem act as interfaces between the hanger and the bottomhole assembly/coarse thread safety joint, and a 7 5⁄8″ regular lift tool provides the interface with the upper stem for handling the conductor drilling system–bottomhole assembly.

The conductor drilling system also uses a casing running tool screwed directly into the top of the casing string that forms a seal above the hanger. Mud is then pumped through the casing running tool and forced through the mud motor, thereby generating torque at the drill bit.

As the conductor drilling system bottom hole assembly penetrates the soil, a new joint of conductor is added to the top by removing the casing running tool and torqueing in the new joint. Once the system is at total depth, the coarse thread safety joint is engaged the connection between the landing ring and the hanger is sheared, and the bottom hole assembly retrieved.

Time and Cost Savings

By adding weight above the drill bit, the new system reduced vibrations, enabling Hess to successfully drill to depth (350 m) in one day without incident. Before using this system, drilling speeds had to be limited to minimise vibration and ensure the wellbore was properly cleaned. Charles Youell, senior engineer at Claxton Engineering said:

“Rig costs are very high, so every hour spent not penetrating is very costly. The system also enables Hess to combine two processes by running the casing while drilling. As well as saving time, the system instantly stabilises the top hole and mitigates the risk of it collapsing.”

Follow-On Work

Following the successful delivery of the conductor drilling system, which included design support during the trial and installation phases and supply of tertiary equipment, Hess asked Claxton for additional support. This included providing a dual-bore centralizer, J tool, swage, drilling and running tool interface, installation tool, false rotary table and brushing tool.

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