Editor's note: This Subsea Systems column first appeared in the March-April 2024 issue of Offshore magazine. Click here to view the full issue.
By Ariana Hurtado, Editor and Director of Special Reports
Chevron and its partners have maintained progress of the Jansz-Io compression project over the last few years, and they are meeting each of the targets on schedule.
The Jansz-Io gas Field is about 200 km (124 miles) offshore northwestern Australia, and it is part of the wider Chevron-operated Gorgon development. Gorgon comprises offshore production wells and pipeline infrastructure that gathers natural gas from the Jansz-Io and Gorgon gas fields and transports it to a facility on Barrow Island for processing. The Gorgon project is a joint venture between the Australian subsidiaries of Chevron (47.3%), Exxon Mobil (25%), Shell (25%), Osaka Gas (1.25%), Tokyo Gas (1%) and JERA (0.417%).
The Jansz-Io Field has been supplying gas to the Gorgon gas processing facilities on Barrow Island since 2015. According to Chevron, after about 10 years of production, the reservoir pressure at Jansz-Io will decline, requiring modification of the existing subsea gas gathering network to maintain long-term natural gas supply.
In July 2021, Chevron announced that as modification of the existing Gorgon development, the Jansz-Io compression project will involve the construction and installation of a 27,000-tonne normally unattended floating field control station, about 6,500 tonnes of subsea compression infrastructure and a 135-km submarine power cable linked to Barrow Island. At the time, the operator said construction and installation activities would take about five years to complete.
The field control station provides power and control, and a subsea cable from Barrow Island powers the field control station. In addition, a subsea compression station 1,360 m below sea level increases gas pressure, and the increased pressure pushes gas to the Gorgon gas plant.
ABB secured the order to supply the overall electrical power system for the Jansz-Io compression project. The order, which included contracts with Chevron Australia Pty Ltd. and Aker Solutions, was booked in third-quarter 2021 and work began immediately. ABB will provide the majority of the electrical equipment, both topside and subsea. The project will combine two ABB technologies, power from shore and variable speed drive long step-out subsea power, for the first time. The company said the electrical system will be able to transmit 100 megavolt-amperes over a distance of about 140 km and at depths of 1,400 m. The contract was awarded following concept development and a FEED study. ABB said the subsea compression system is expected to be in operation in 2025.
Chevron awarded Daewoo Shipbuilding & Marine Engineering (DSME) a contract in early 2022 to build the field control station for the Jansz-Io compression project. The station will be built at the Okpo Shipyard in Geoje. At the time, DSME said the station is expected to be completed by third-quarter 2025.
Last year the Jansz-Io project continued its progress as Chevron secured contracts for marine warranty survey services and telecoms system integration.
In February 2023, Chevron contracted ABL Group to provide marine warranty survey services for the Jansz-Io compression project. ABL’s Australian operation will oversee the delivery of transportation and installation operations for four work packages related to the offshore installation; construction and marine transportation operation of the field control station and high-voltage power and communication transmission system; and marine transportation of other project cargo.
In July 2023, DSME commissioned Kent to perform detailed engineering, procurement, integration and testing of the telecoms infrastructure/systems for the Jansz-Io compression project. The contract relates to the new offshore field control station. The company’s team in Perth will manage the program, monitoring the multiple vendors to ensure its equipment supplies are correctly integrated to safeguard communications and security for the normally unattended offshore station.
Installation timeline
Chevron said Jansz-Io subsea compression installation is scheduled to occur from mid-2024 to mid-2026. The timeline of installation milestones includes:
- The electric-powered subsea compression station for the Jansz-Io Field is scheduled to receive power via the field control station in late 2025 to late 2026;
- The manifold station required for the operation of the subsea compression station has an installtion timing of late 2025 to mid-2026;
- For the field control station, the moored floating facility will accommodate electrical equipment and will be normally unattended. Mooring suction piles are scheduled for mid/late 2024 and the field control station for mid/late 2025;
- The subsea compression station, subsea compression manifold station and existing subsea infrastructure will be connected by spools, umbilicals and flying leads by mid/late 2025 to mid-2026;
- A new umbilical to supply power from Barrow Island to the field control station and
subsea structures is scheduled for mid/late 2025 to mid-2026. The umbilical will run adjacent to the existing feed gas pipeline; and - Concrete mattresses and rock stabilization will be installed in late 2025 over existing pipelines and umbilicals to allow for installation of the Jansz-Io compression infrastructure. Rock stabilization will also be installed on the new Jansz-Io umbilical.
Gorgon Stage 2 development
In June 2023, Chevron Australia and its partners in the Gorgon joint venture produced first gas from the Gorgon Stage Two development offshore Western Australia’s northwest coast. The development involves expanding the Gorgon project’s existing subsea gas gathering network, which produces gas for the Western Australia domestic market and exports LNG to buyers in the Asia-Pacific region.
For Gorgon Stage 2, 11 new wells were drilled on the Gorgon and Jansz-Io fields and extra offshore production pipelines and subsea structures were installed to maintain feed gas supply for the processing complex on Barrow Island.
