The objective of this paper is to present a groundbreaking case study for a Novel Articulation Tool utilized by a deepwater Operator to address the significant riserless drilling operations risks associated with extreme environmental conditions off the coast of South Africa.
The Luiperd prospect, located 175 kilometers off the southern coast of South Africa in 1760 m (5774 ft) of water, experiences strong prevailing surface currents and harsh weather year-round. These extreme environmental conditions required careful planning for open water operations to mitigate the associated risks for rig equipment potentially exceeding maximum bending moments or reaching fatigue life limits among other concerns.
For the previously operated offset well, the Operator used drift running techniques during riserless drilling to deploy casing and drilling assemblies in open water to limit their exposure time to strong surface currents. The application of this technique in single derrick mode resulted in safe but slow and costly drilling.
For the Luiperd prospect, one of the measures taken by the Operator to mitigate environmental risks was the use of a Novel Articulation Tool to minimize the bending stresses applied to the subsea wellhead running tools (WHRT) and landing string while running the conductor pipe and the surface casing. This articulation tool is based on a ball-and-socket concept which provides zero rotational stiffness up to 15 degrees in any direction while exceeding operational requirements for through-torque, tensile and working pressure ratings.
The Luiperd well was successfully drilled during Q3 2020 using the Deepsea Stavanger mobile offshore drilling unit (MODU). During the well's riserless drilling operations two Novel Articulation Tools were used, one being made up just above the subsea WHRT and another being placed within the drill pipe landing string in the MODU's moon pool.
Because the Novel Articulation Tool effectively eliminated the highest bending moments that would otherwise act upon the landing string and WHRT, it de-coupled the MODU from the conductor and surface casings run on the Auxiliary Well Center (AWC), enabling dual derrick operations which were not possible for the offset well.
The use of this technology saved multiple drift runs and more than 10 days of rig time for the Luiperd well compared with the offset. A maximum 317 MT (700,000 lbs) of surface casing and landing string was suspended beneath the upper articulation tool. Both articulation tools were in continuous use for 75 hours with 4.3 knots of current and up to 5 m (16 ft) significant wave height (Hs).
Although the Luiperd well was drilled in a unique offshore environment, similar conditions are prevalent across the world's deepwater basins, including the West of Shetland area in the UK and in the Gulf of Mexico where loop currents present a regular challenge. The subject Novel Articulation Tool can reduce operational risks and provide step change improvements in drilling performance for wells which need to contend with strong surface currents and harsh weather environments.
