The two-state supply story

The Iona Gas Plant is located 4 km north-east of Port Campbell in Victoria. It is adjacent to the Otway Gas Plant and is connected to the nearby Minerva Gas Plant via the SEA
Gas Pipeline.

Construction and expansion history

Construction on the plant at Iona was originally planned to have started in late 2000, but was brought forward following the Longford Gas crisis in September 1998. Construction began in November 1998 and was completed in stages through to April 2001. At that time it had a storage withdrawal capacity of 200 terajoules per day (TJ/d). First gas flowed from the facility on 6 July 1999.

The plant was expanded to 320 TJ/d in November 2003. The expansion included a new compressor and connection to SEA Gas Pipeline.

From 2005, the Santos offshore fields were connected into the facility.

In January 2004, the Iona Gas Plant’s important place in the network was highlighted when it became the sole gas supplier for South Australia following the Moomba Gas Plant fire.

Another major plant expansion and the development of additional storage fields began in 2007 and were commissioned in 2009. This increased the plant’s capacity to 570 TJ/d and increased storage to 22 petajoules.

Scope of operations

The plant is designed to store gas in offshore reservoirs and process gas from subsea wells Casino, Henry and Netherby, which are owned by Santos, with the capability of tying in future gas fields as they are developed. The plant processes gas from these offshore gas fields and stores it, along with gas received from connected pipelines, in reservoirs for customers. EnergyAustralia owns eight operating storage wells; five on the Iona site, two at North Paaratte and one at Wallaby Creek.

At the site, there are producing and re-injection wells, a two-train gas processing plant, gathering lines and transmission pipeline interconnections. The two discrete gas processing trains each have the capability of removing heavier hydrocarbon and water from the gas stream to meet sales gas hydrocarbon and water dew point specifications. Seven compressors – five reciprocating and two centrifugal – are used to deliver sales gas and inject into storage.

The plant is connected to the South West Pipeline (SWP), which supplies Victoria, and the SEA Gas Pipeline, which supplies South Australia. The plant can also supply the Otway Gas Plant for storage for their customers and supply the Mortlake Electricity Generation Facility.

Processed gas can also be directed into the storage facilities at Iona, North Paaratte and Wallaby Creek. In addition, gas can be withdrawn from all pipelines and directed to and held in storage.

The facility provides seasonal peak sharing capacity to the Victorian gas grid from the western end of the gas distribution system, as well as short-term gas storage and withdrawal. The facility also provides year-round export gas through the SEA Gas Pipeline.

Supplying gas to Victoria and South Australia

Managing the supply of gas to two states

Upon completion of raw gas processing, the Iona gas plant’s compressors are used to deliver sales gas. There are three headers in the compression system – low, intermediate and high pressure.

Gas to the SWP is typically sourced from the intermediate pressure header. Any of the compressors may be configured to flow to this header. Gas to the SEA Gas Pipeline is sourced from either the intermediate or high-pressure header. Two of the reciprocating compressors and one of the centrifugal compressors are available to flow into the high-pressure header.

Day-to-day operations

To deliver customers’ needs, EnergyAustralia is required to assess market signals, and make sure there is sufficient gas in storage and native gas reservoirs to meet market demand.

Each day the Iona Control Room receives nominations for:

Injections into and/or withdrawals from the Victorian Gas Market via the SWP;

Injections into and/or withdrawals from the SEA Gas Pipeline;

Casino Gas flow rates;

Otway Gas Plant Interconnect flow rates; and,

Mortlake Pipeline flow rates.

These pipelines are governed by separate operating rules and contracts.

The Australian Energy Market Operator operates the Victorian Gas Market, and manages the physical transportation of gas in the Victorian gas transmission system.

One of its responsibilities is to schedule the Victorian Gas Market requirements. This includes communicating the Iona Gas Plant’s daily SWP flow requirements to the Iona Control Room.

Maintenance of SWP and SEA Gas pipelines by Iona Gas Plant staff

EnergyAustralia is responsible for maintenance of the pipelines to remote storage sites. These pipelines are bound by the same maintenance schedule and procedures as the rest of the Iona gas plant.

EnergyAustralia employees or external contractors, depending on the hazard category, carry out scheduled external and internal inspections.

APA Group and SEA Gas are responsible for pipeline maintenance of SWP and SEA Gas pipelines respectively. They conduct their own maintenance in accordance with their own policies and procedures.

Unique engineering features

Capacity for flexibility

Unlike a traditional gas plant that runs at maximum capacity, the Iona Gas Plant is required to be available and responsive to market demands and therefore has been engineered in such a way so it can be flexible to meet peak demand.

The plant has two gas processing trains and two compression trains that provide plenty of flexibility in lining up modes of operation, as well as having turbine-driven centrifugal compression ideal for handling base loading, and piston engine-driven reciprocating compression ideal for handling of variable loading. It is also engineered to be a connection hub between SWP and SEA Gas for the national distribution grid.

Storage ability

One of the biggest stand-out features of the Iona Gas Plant and what sets it apart from all other commercial gas plant in Australia is its storage ability.

The Iona facility was originally designed and constructed to operate during the three months of winter peak and summer low demand, with a down-time of up to six months. This supported off-line maintenance. Subsequent expansions of the plant have built on this base design to meet the market demand for more base load. This resulted in the plant expansions for connecting the Casino wells and for managing the declining pressures from the Casino wells.

LOPS Project

One of the most significant engineering achievements was the introduction of the Low Pressure Delivery Service (LOPS) project. The project was implemented to develop a new gas low pressure delivery and process service from the Casino gas field, located about 34 km offshore in 70 m water depth, to the Iona gas processing plant.

The project required a new gas train to be constructed that would increase plant capacity from 320 TJ/d up to 570 TJ/d, and for the new plant to be capable of receiving gas at pressures down to 3,000 kilopascal gauge.

The project required:

Design and implementation to develop a process to boost pressure through the plant while also improving redundancy and reliability;

Development of engineering solutions to integrate the new plant and processes with the existing Iona facilities and to increase the Iona processing and compression capabilities; and,