Stones field is an offshore oil and gas project located in the US Gulf of Mexico. The Shell-owned and operated field is located at a water depth of around 9,500ft (2,900m) making it one of the deepest oil and gas projects in the world.

The field was discovered in 2005 and the final investment decision to develop the asset was taken in May 2013.

In September 2016, production commenced using a floating production, storage and offloading (FPSO) facility.

At peak, Stones is designed to produce 50,000 barrels of oil equivalent per day (boe/d).

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Site and location details

The Stones field is located offshore around 320km south west of New Orleans, Louisiana, in the Gulf of Mexico’s lower tertiary geologic trend.

The water depth in the region is around 9,500ft, while the reservoir is situated at a depth of approximately 26,500ft below sea level.

Project details

Stones is Shell’s second producing field in the Lower Tertiary geologic frontier in the Gulf of Mexico. The company achieved its first commercial production in this ultra-deepwater region with Perdido in 2010.

Stones project development consists of a FPSO vessel named Turritella which is connected to subsea infrastructure to extract oil and gas from hydrocarbon-bearing reservoirs.

Tankers are used to transport oil from the Stones FPSO to US refineries, while the recovered gas is exported by a pipeline.

In the first phase, a total of eight wells were tied back to Turritella to produce from more than 250 million barrel of oil equivalent (boe) of recoverable resources.

In future, Shell plans a multiphase seafloor pumping to extract oil and gas from the seabed to the vessel as Stones field is estimated to host more than 2 billion boe of oil.

Stones FPSO details

Turritella is a converted Suezmax FPSO with a turret featuring a disconnectable buoy (Buoyant Turret Mooring or BTM) weighing 3,150 metric tonnes and nearly 18m high. This disconnectable buoy carries mooring lines and risers from the well system.

The turret and buoy are designed to enable the vessel to safely disconnect and sail to safer waters when a heavy storm or hurricane approaches.

Additionally, Stones uses a steel lazy wave riser flexible pipe to transport oil and gas to Turritella for processing.

According to Shell, the steel lazy wave risers have additional buoyancy which creates an arched bend in the pipes between the seafloor and the surface to absorb the motion of the FPSO and support production.

Stones is the first project to see the use of a disconnectable buoy with steel lazy wave risers to recover oil from ultra-deep waters.

The FPSO has a processing facility capacity of 60,000 barrels of oil equivalent per day (boe/d) and 15mmscf/d of gas treatment and export. The hull is capable of storing 800,000 barrels of crude oil.

The Stones project also uses an In-Line Mooring Connector (ILMC) to gain direct access to the mooring line. This allowed readjusting of the mooring line tension without any device installed on the FPSO.

Contractors involved

The FPSO vessel was engineered and built by SBM Offshore. The contract was the first project to be awarded to SBM Offshore by Shell under the Enterprise Framework Agreement (EFA) concerning the supply of medium and small FPSOs on a lease and operate basis.

A joint venture company comprising SBM Offshore (55%), Mitsubishi Corporation (30%), and Nippon Yusen Kabushiki Kaisha (NYK Line) (15%) owns the FPSO.

Engineering firm Cronus Technology secured the project management services contract for the installation of the piles, moorings, riser, Buoy Turret Module, and commissioning activities. The company also served as the primary interface for mooring and Buoy Turret Module installation during fabrication and installation as well as offered technical assistance during offshore installation.

Additionally, Cronus Technology supported and monitored health, environment, and safety (HES) compliance along with logistics for personnel and vessels used during the installation phase.

Other entities such as Acteon’s Engineering, Moorings, and Foundations division brand InterMoor, Mirage and UTEC were also associated with the project.