The Central Area Transmission System (CATS) transports gas from the central UK North Sea to an onshore terminal in Teesside, UK. Image courtesy of SatyaPrem/Pixabay.
The CATS riser platform is connected by a bridge to Harbour Energy-operated North Everest production platform in the UK North Sea. Image courtesy of catmoz/Pixabay.
The CATS terminal processes the gas fed by the CATS pipeline and supplies the sales gas to the UK National Transmission System. Image courtesy of Life-Of-Pix/Pixabay.

The Central Area Transmission System (CATS) comprises a subsea gas gathering and transportation system in the central North Sea, along with an onshore gas treatment and processing facility at Seal Sands, Teesside, UK.

Kellas Midstream operates the integrated gas transmission and processing system through its wholly-owned subsidiary, CATS North Sea. Kellas Midstream owns 98.9982% equity stake in CATS, while the minor shareholders include Harbour Energy (0.6630%) and Eni (0.3388%).

The CATS system handles gas output from more than 30 producing fields in the UK North Sea through as many as 11 production hubs. It includes a fixed offshore riser platform, a 404km-long pipeline, and the onshore gas processing terminal at Teesside.

The pipeline started operations in 1993, followed by the commissioning of the gas processing plant in 1997.

CATS supplied around nine billion cubic metres (bcm) of gas to the UK market in 2020.

CATS riser platform details

Operated by Harbour Energy, the CATS riser platform (CRP) is located in block 22/10a, central North Sea, approximately 230km east of Aberdeen, UK. It is connected through a bridge to the North Everest gas and condensate production platform also operated by Harbour Energy.

The CRP receives natural gas and condensate from Armada, Lomond and Everest production platforms.

A 36in-diameter gas export riser transports gas from the CRP to the CATS pipeline, while the condensate is transported through a 14in-diameter riser to the Everest Liquid System (ELS) subsea pipeline, which further connects to the Forties Pipeline System operated by Ineos.

CATS pipeline details

The 36in-diameter and 404km-long CATS gas pipeline connects the riser platform to the CATS terminal in Teesside, north-east England. The pipeline has a capacity to transport up to 48 million cubic metres (mcm) of gas a day.

The 396km-long offshore section of the CATS pipeline runs from the tie-in point at the subsea isolation valve near the CRP to the landfall at Coatham Sands, Teesside. The onshore section runs for 7.8km from the beach valve station to the CATS terminal located at Seal Sands.

The CATS pipeline consists of six connection points, called tees, along its route to provide subsea gas connections for North Sea producers.

A total of 11 offshore production platforms, namely Andrew, Banff, Culzean, ETAP, Huntington, J- Block, MonArb, Stella, Erskine, Armada and Everest, are connected to the pipeline.

Wood Group is responsible for the operations of the CATS pipeline and the onshore terminal.

CATS terminal details

The CATS terminal is located on a 29ha-site in Teesside and consists of treatment and processing facilities to handle the gas supplied by the CATS pipeline.

The gas received from the CATS pipeline is treated to remove contaminants such as hydrogen sulphide, mercury and particulate contaminants. The gas treatment capacity of the facility is up to 48mcm per day.

The treated gas is later fed either to the CATS gas processing plant or to the adjacent Teesside Gas Processing Plant (TGPP), owned by North Sea Midstream Partners.

The CATS processing plant consists of two gas processing trains of 17mcm per day capacity each. The first processing train started operations in May 1997, while the second train came on stream in February 1998. The processing plant separates propane, butane, and natural gas liquid (NGL) components from the gas.

The CATS system supplies the treated and processed natural gas directly to the UK National Transmission System.

CATS ownership history

Antin Infrastructure Partners initially picked up a 62.78% stake in CATS from BG Group in July 2014. Later, it acquired a 36.22% stake in CATS for £324m ($486m) from BP, which was then its operator, in December 2015.

A consortium of BlackRock’s Global Energy & Power Infrastructure Funds (GEPIF III) and Singapore’s sovereign wealth fund, GIC, acquired Kellas Midstream from Antin Infrastructure Partners in January 2020.

Kellas Midstream, earlier known as CATS Management, holds stakes in other infrastructure assets in the UK North Sea, including a 65% stake in the Esmond Transportation System (ETS) and a 50% stake in the Humber Gathering System (HGS).

Contractors involved

Wood Group was awarded a ten-year duty holder contract, worth $250m (£159m), to provide operating services for the CATS terminal and pipeline from Antin Infrastructure Partners in June 2015. The contract commenced in December 2015.