Kellas Midstream fined £175,000 for excessive venting at Teesside gas terminal

KELLAS Midstream has been fined £175,000 (US$239,000) for excessive venting at its CATS gas terminal in Teesside, UK, after the North Sea Transition Authority (NSTA) found the terminal had vented more than double its consented volume in 2024.

According to a sanction notice served last week to the terminal operator, CATS North Sea Limited – a wholly-owned subsidiary of Kellas Midstream – the terminal was found to have exceeded its 4 t limit for 2024 by June. CATS informed the NSTA of issues with vent performance in late August, and in mid-September Kellas told the regulator it had updated its total vent forecast for the year to 9.6 t. However, a week later total venting exceeded 10 t for the year. The NSTA said CATS displayed an “obvious lack of urgency when dealing with the suspected exceedance”.

CATS confirmed the breach was largely caused by an underestimation of venting during a planned shutdown. During the previous planned shutdown in 2016, the leak rate into the double block and bleed valve (DBBV) system was 0.35 bar/15 minutes. This figure was used to calculate the estimated venting for 2024. However, the measured leak rate in 2024 was 1.7 bar/15 minutes. As a result, 4 t of gas was vented through temporary vents during the shutdown – four times the expected volume. CATS told the regulator this error was “made in good faith and based on reasonable historic assumptions”.

The terminal also operates four analyser vents used during normal operations but had only accounted for one in its vent consent calculations. The expected volume vented from the analyser vents was 3 t but by September 2024 the actual volume had reached 8.4 t.

Operators have since increased monitoring of vent emissions by including them with the monthly flare reporting process and plan to perform additional maintenance on the DBBV system ahead of the next planned shutdown in 2032.

The NSTA said CATS cooperated fully with their investigation. A spokesperson for CATS and Kellas Midstream said: “CATS is committed to maintaining high standards of safety and environmental compliance…improvements in vent estimating, monitoring, and reporting were swiftly identified and corrective measures implemented.”

The spokesperson also highlighted that the volume of gas vented in 2024 amounted to 0.65% of CATS’ total greenhouse gas emissions of 46,919 tCO2e – down from 54,240 tCO2e in 2023.

Venting penalties

Opened in 1993, the CATS terminal is a significant midstream asset, processing gas from around 30 central North Sea fields and delivering around 7.3 bcm annually into the UK system. Of the fine issued to CATS, NSTA director of regulation Jane de Lozey said: “Operators must understand that we will not tolerate breaches of regulatory obligations, which weaken the industry’s reputation in the eyes of the public and investors, and, in the case of venting, undermines wider efforts to cut emissions.”

In January 2025, NSTA announced that any future breaches of venting consents would carry a minimum fine of £500,000.