Real-time structural integrity monitoring enhances jackup drilling operations

With high-specification jackups drilling development wells through steel jackets in deep water, structural integrity between the jackup and the jacket is critical.

Jackup rigs are increasingly being used to drill wells in ever greater water depths, HP/HT and harsher environments. Real-time structural integrity monitoring can ensure on-going safety of operations as well as validate and calibrate simulation models of the drilling and well equipment used in the planning of operations.
New generation jackup rigs are capable of operations in water depths of 150m (492 ft), raising new challenges to drilling equipment and well systems. The increased deflections of the jackups and the higher loading this generates on equipment is a key challenge to the industry. This is more so where high pressures and temperatures require heavy-duty drilling equipment with significant mass and stiffness.

Developing Valemon field
The decision to use the West Elara (CJ-70) jackup rig to drill the HP/HT Valemon field in 135-m (443-ft) water depth raised particular challenges for the operator, Statoil. The gas and condensate field is located on the Norwegian Continental Shelf, and is one of the biggest undeveloped gas fields in the North Sea.
The field is being developed using the 9,000 metric-ton, 20-slot capacity Valemon platform. The steel jacket was installed in June 2012 and the two-year pre-drilling phase with the West Elara began in September 2012. In 2014 the jacket topsides are to be installed, after which the main-drilling phase will commence with the West Elara until completion.

Choosing integrity monitoring
Simulations completed before operations began predicted high loading in the drilling and well equipment, primarily due to high lateral motions of the West Elara jackup (up to 1.5m {4.9 ft}). The increased height of the West Elara during main drilling to accommodate the Valemon topsides was the more critical phase. The simulation models demonstrated that long-term fatigue and extreme loading performance of the system was acceptable for both drilling phases.
However, a range of assumptions had to be made in the simulation models. Due to the sensitivity of the West Elara motions to these assumptions, integrity monitoring was chosen to confirm the validity of the simulation models and as a means to confirm safe operations on an on-going basis.

Real-time monitoring system
The real-time integrity monitoring system deployed on the West Elara jackup and Valemon jacket had three main objectives:

• During the pre-drilling phase monitor the deflections of the West Elara and the Valemon jacket as well as the bending loads and fatigue damage accumulation to the conductor, high-pressure riser, and overshot;
• Confirm that the deflections of the West Elara and Valemon platform remained within expected levels and that the loading and fatigue damage accrued during drilling operations remained within the allowable safe design limits; and
• Compare the measured responses to the simulation models for pre-drilling to verify simulation model accuracy and calibrate to improve predictions. Using the improved model, re-evaluate main drilling predicted responses.

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06 Sep 2013
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