Works on the Dampier to Bunbury Natural Gas Pipeline (DBNGP) Stage 5B Expansion were completed at the end of April 2010. Stage 5B involved the installation of 440 km of 26 inch diameter parallel pipe in sections along the 1,530 km length of the DBNGP, increasing the pipeline's full haul capacity by approximately 110 terajoules per day (TJ/d).

Built in the early 1980s by the State Energy Commission of Western Australia, the pipeline extends from the Pilbara Region in the state's northwest to Bunbury, located approximately 180 km south of Perth.

Stage 5B was the most recent of three expansion projects undertaken on the pipeline by owner DBP Transmission since it took ownership in 2004. DBP Transmission is jointly held by Diversified Utility and Energy Trusts (DUET) Group with a 60 per cent interest, and Alcoa and Prime Infrastructure, each with a 20 per cent interest.

The project was undertaken in response to the increased demand for gas for power generation and industrial processes in the southwest region of the state.

Construction

Construction on the Stage 5B expansion began in January 2009. The project extended on 812 km of looping undertaken in stages 4 and 5A, this time installing 11 loops along the pipeline route. Following the completion of Stage 5B 1,252 km – or 83 per cent – of the pipeline's length has been duplicated.

DBP General Manager Commercial Mark Cooper says that Stage 5B was probably the most challenging of the three expansions. He says that some of the issues to be addressed were very different to issues than they had faced before.

McConnell Dowell undertook the Stage 5B looping construction work. Logistics proved to be a key issue, Project Manager Rob Harris said, as the project was not a standard continuous pipeline construction project but 11 separate projects. Individual loops were on average 100 km apart, meaning that moving people and equipment, and organising accommodation facilities between projects was a major challenge.

Looping sections 0 through 8 were located in remote areas between Karratha and Gin Gin that did not have appropriate pre-existing accommodation. Construction teams instead lived at temporary base camps, which had to be moved with each looping project.

One of the major challenges was undertaking construction in Ellenbrook, a suburb in Perth's northeast. In order to minimise dust issues and ensure there were no trenches open at night, pipe lengths were reduced from 18 m to 12 m and trenches were open for only up to 300 m at a time. Working hours were also reduced in order to minimise noise impact.

Construction of Loop 0, in the state's north, required three river crossings. Loop 10, in the state's south, also included a crossing of the Murray River. McConnell Dowell used horizontal directional drilling to install 480 m of pipeline under the river, as well as several other road, rail and channel crossings.

Stage 5B was also to include the crossing of Fortescue River, also in northern Western Australia; however this has been delayed as the bed of the river has been moving with each cyclone season over the last five years.

The project was completed on schedule and within the budget of $690 million. Over two million man hours were worked and over ten million kilometres driven during the course of the project without any significant injury or vehicle incident.

Compressor stations

The project also involved upgrades to compressor stations, notably CS1 and CS10. There are ten compressor stations along the pipeline, spaced at intervals of approximately 140 km.

The most complex upgrade works occurred at CS1, located 137 km southeast of Dampier. This involved replacing the existing compressor with a larger one. Valves and blank flanges were used to stop the gas entering the compressor, which was then disconnected and removed, allowing the new compressor to be put in its place and reconnected.

In order to upgrade CS10, the pipeline feeding gas to the Rockingham and Mandurah areas needed to be relocated as it was situated in the location of the new compressor. Following the relocation, civil foundation works were carried out on the site and the new Solar Taurus Gas Turbine Compressor was installed. The equipment was then connected to the operating system in a second station outage, which had to be planned around a large gas consumer coming offline.

Gas supply

Natural gas transported by the DBNGP is produced in the offshore Carnarvon Basin, located in the North West Shelf. The gas is sourced from the Karratha Gas Plant and facilities at Varanus Island.

Woodside Petroleum operates the Karratha Gas Plant, producing gas for joint venture partners Shell, BP, BHP Billiton, Chevron and Mitsubishi /Mitsui.

The Varanus Island facilities process gas from, among others, the Harriet, East Spar, Griffith and John Brookes developments, which are various joint ventures involving Apache, Tap Oil, Kuwait Foreign Petroleum Exploration Company and Santos.

Currently under construction, Apache's Devil Creek production facilities will process gas from the Reindeer fields, located southeast of the North West Shelf Joint Venture. Apache is planning to tie in the Devil Creek processing facilities to the DBNGP.

The onshore component of the Devil Creek Development Project is located approximately 45 km southwest of Karratha, on the Pilbara coast. It will comprise of gas treatment/dehydration, condensate liquid stablisation, storage and road loadout facilities, gas compression and metering. An onshore single three-phase 16 inch raw sales gas pipeline will link to the shore crossing and tie-in to the DBNGP.

In addition, BHP Billiton is expecting to sanction its Macedon Gas Field development during 2010. Gas from the subsea Macedon Field will be piped via a 20 inch, 81 km offshore pipeline and 15 km onshore pipeline to a gas plant at Ashburton North. The DBNGP will connect to the Ashburton North plant via the 67 km Macedon tie-in. BHP Billiton expects first gas from the project in 2013.

Supplying gas

The pipeline currently has five gas receipt points, at which ownership of the gas transfers from shippers to DBP. At gas delivery points, of which there are 55, ownership of gas transfers back to shippers. Over 30 customers purchase gas transported by the DBNGP.

Approximately 60 per cent of the gas is used for industrial purposes, notably alumina, while 25 per cent is used for power generation, and the remaining 15 per cent for retail distribution. Gas for retail usage is mostly fed into the WA Gas Networks Distribution Systems.

The pipeline delivers 50 per cent of the transported gas to the Perth/Kwinana area, 35 per cent to the state's South West and the remainder to Pilbara and the Mid West region.