The BassGas project includes the development of the Yolla field located in production license T/RL1 of the Bass Strait, offshore of Australia. The field lies in a water depth of 80m, about 147km offshore of southern Victoria.

The project was developed by a joint venture between Origin Energy (42.5%) and AWE Petroleum (35%). Origin Energy is the operator of the project. The joint venture partners invested A$750m in the development of the field.

Toyota Tsusho Gas E&P Trefoil (Toyota Tsusho) and Prize Petroleum, a wholly owned subsidiary of Hindustan Petroleum Corporation (HPCL), each purchased 11.25% of AWE’s share in March 2012 and January 2013 respectively.

First gas from the project was produced in June 2006. The field is currently producing 65 terajoules a day of sales gas, 200t/d of liquefied petroleum gas (LPG) and 445 kilolitres a day of condensate.

Discovery of the Yolla field

The Yolla field was discovered by the Yolla-1 well in 1985. The discovery well was drilled by the Glomar Robert F. Bauer semi submersible drilling rig. It encountered a 30m gas column in five reservoir zones. During flow tests, the well flowed at the rate of 15 million cubic feet of gas per day.

Geology of the Bass Strait area

The field reservoir consists of sandstones of the Eastern View Coal Measures and Intra-Eastern View Coal Measures of the Early Paleocene to Early Eocene age. Hydrocarbon accumulations in the sandstones are sealed by deep and laterally continuous intraformational shales.

Reserves of oil and gas at the Australian field

The Yolla field is estimated to contain proven and probable reserves of 333 petajoules of gas or 28 million barrels of condensate and LPG liquids. These reserves are sufficient to fulfil Victoria’s gas demand for the next 15 years.

Appraisals, exploration drilling and field development at the BassGas project

“The BassGas project includes the development of the Yolla field located in production license T/RL1 of the Bass Strait, offshore of Australia.”

In 1994, a 3D seismic survey over the field was acquired to estimate the reserve potential and identify drilling targets. Based on the survey, the Yolla-2 well was drilled in 1998 to appraise the gas column discovered by Yolla-1.

The BassGas project was initiated by the joint venture partners in 1999 and the development commenced in 2001. The federal government approved the project in December 2002.

The field development plan included the installation of the Yolla A unmanned offshore platform and a pipeline to export the hydrocarbons onshore. It also included the construction of an onshore processing facility at Lang Lang, 70km south of Melbourne in Victoria.

In September 2004, Origin Energy completed the drilling of two production wells – Yolla-3 and Yolla-4. The field was originally scheduled to come on stream in 2004. The commissioning was, however, delayed due to non-compliance by the main contractor Clough with some of the contractual agreements.

In 2009, the mid-life enhancement (MLE) project was approved to meet the increasing demand for gas in southeast Australia. The project will extend the life of the BassGas Project and will be implemented in two phases. The first phase of the project was launched in 2011.

The first phase of the MLE project included the installation of an accommodation module on the Yolla platform, to convert the platform into a manned facility. The $A26.6m module weighs 650t and is 19m high, 33m long and 13m wide. It features bunkrooms, kitchens, offices and power and water utilities. The platform arrived at Port Taranaki in November 2011.

Safety-related facilities, compression facilities and other equipment were also installed on the platform. The first phase was completed in 2012 at an estimated cost of A$550m to A$580m.

Phase two of the MLE project includes drilling of two additional production wells – Yolla-5 and Yolla-6 in 2014.

Safety-related facilities, compression facilities and other equipment will also be installed on the platform. The first phase will be undertaken at a cost of A$360m.

Phase two of the MLE project includes drilling of two additional production wells – Yolla-5 and Yolla-6. This phase will be implemented in 2012/13.

Yolla platform

The Yolla A offshore platform weighs 8,000t and is 120m high. It was built in Singapore. It was towed to the field and installed in 80m of water. The unmanned structure was built at a cost of $210m. It is remotely monitored from the Lang Lang processing plant.

The platform includes facilities to tie-in additional production wells from the Yolla field as well as other fields in the area.

Gas and liquid exportation via pipeline and processing at the Lang Lang facility

The produced gas and liquids are exported from the Yolla platform to the Lang Lang facility through a 180km long pipeline.

“The project was developed by a joint venture between Origin Energy and AWE Petroleum.”

The offshore section of the 14in diameter pipeline is 147.5km long. The pipeline intersects land near the Kilcunda beach.

The Lang Lang facility has a processing capacity of 75 million standard cubic feet per day. It includes a fluids receiver, gas sweetner and dehydrator, LPG recovery unit, fractionator, condensate stabiliser and storage facilities.

It also includes utilities such as power generation, flare systems and heating facilities.

The facility processes the hydrocarbons received from the field and separates the gas from the LPG and condensate. The gas is transported to the Victorian Principal Gas Transmission Pipeline.

The LPG and condensate for sale are transported by road in tankers.

Contracts awarded

Clough was awarded the engineering, construction and procurement contract for the project. The company was responsible for detailed design and construction of the platform, pipeline and onshore processing plant. Uhde was selected by Clough as the main EPC subcontractor for the Lang Lang processing plant.

Dresser-Rand supplied its KG2-3E gas turbine generator packages for the Yolla platform.

Cummins Power Generation supplied five gas generator sets for installation at the Lang Lang processing facility.

ABB was awarded $2.5m worth contracts to supply gas chromatographs and gas sampling systems for the processing facility. The contract also included supply of voltage intelligent motor control centres for the Yolla platform.

Downer Group provided mechanical and electrical services for the onshore processing plant.

BGB Electrical carried out pre-commissioning works for the Lang Lang facility.

Coe Drilling Australia won the contract to install a shore crossing for the onshore section of the pipeline.

CADS Survey was the main surveyor for a section of the pipeline.

Fitzroy Engineering won a $35m contract to build the accommodation module for the Yolla platform.

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