The Outeniqua basin off South Africa is exposed to high winds and huge waves. What’s more, it lies in the path of the Agulhas Current, one of the most powerful currents in the world. In these extreme conditions, new operating solutions were needed to drill our Brulpadda-1AX exploration well on Block 11B/12B. These innovations allowed us to push back the industry’s technical limits and carry out this type of development without cost overruns.
Drilling in Almost Impossible Conditions
In this particular offshore environment, drilling was virtually impossible using the standard equipment available in the industry. The Agulhas Current is often too powerful for the riser and drilling rig to remain stable in the water column, creating uncertainty that compromises the integrity of operations. We had already experienced a failed drilling attempt in 2014.
After four years of intensive engineering and design work, we managed to push back the exploration limits in 2018, drilling a 3,633-meter well in a water depth of 1,432 meters. This was one of the most difficult drilling operations ever carried out at TotalEnergies, and we did it with help from our contractor Odfjell.
An Innovation Showcase
To achieve this breakthrough, three innovative systems were crucial to the drilling campaign’s success. These solutions also generated significant savings in relation to initial budget estimates.
- A lateral riser retention system (LRRS) - a world first. A riser is used to connect the rig to the subsea wellhead during drilling. Its stability cannot be guaranteed if surface current velocity exceeds 1.7 meters per second. In such an environment, the riser can break and seriously threaten the installation’s integrity. The Agulhas Current exceeds that threshold half of the time, but unpredictably, compromising drilling deadlines and success. The riser was therefore modified to allow for drilling in a current velocity of more than 1.7 meters per second. A lateral riser retention system (LRRS) was added to enhance the riser’s stability in the water column and control its movement more effectively. This simple, robust solution developed with Odfjell comprises four tensioners attached to the drilling rig that transmit the retention force applied by four cables connected to the riser, in accordance with real-time measurements and numerical simulations. The versatile LRRS concept can be adapted for use on other drilling rigs in areas with difficult metocean conditions.
- A tug for added stability. No drilling rig is strong enough to remain in place with such difficult seas and currents using only its own dynamic positioning propellers and thrusters. In another world first, a tug was attached to the rig to ensure its stability and secure its position. The force transferred by the tug increased the rig’s capacity to remain stationary by 25%. The difficult part was managing cable tension and the interactions between the tug and the rig connected to the wellhead. The tug assist helped us avoid disconnecting the rig at least twice, which would have put us five to ten days behind schedule each time.
- High frequency radar (HFR) for current forecasting. The Agulhas Current is not only powerful, but it also creates meanders and eddies moving from east to west, all of which disturbs drilling operations. These phenomena cannot be effectively forecast by satellite observation or numerical modeling. To track them in real time and improve forecasting, an onshore network of three HFR stations was deployed along the coast. The system was designed to monitor surface ocean currents up to 250 kilometers offshore and provide a six-kilometer-by-six-kilometer grid covering 80% of the operated block, with refreshed data every 30 minutes. These devices gave us two days of visibility for currents and eddies compared with the previous 12-hour forecasts, making it easier to plan drilling operations. Deployed on an industrial scale for the first time, the system could be used at other sites with complex surface currents, such as the mouth of the Congo River.
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