Seismic shift

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Woodside’s 4D seismic survey over the Pluto gas field – Australia’s first-ever such survey over a gas field – has proved a great success, generating invaluable data for the management of the reservoir.

Chief reservoir engineer Lupo Guerrera says it’s given Woodside a comprehensive view of the current state of the reservoir across its whole volume. “When we know better what we don’t know, we can plan our future operations around those uncertainties,” Lupo says.

A 4D survey adds the dimension of time to 3D surveys by repeating the survey at the same place at a different time. “It shows how the area of the reservoir has changed in the time it’s been producing,” explains principal geophysicist Jeremy Fitzpatrick.

Chief science and technology manager Neil Kavanagh adds: “It’s especially useful when we want to accelerate studies because 4D allows us to work in an agile style and fine tune a reservoir’s potential as we go.”

Neil notes Woodside has been an early adopter of 4D seismic over oil fields but the method has never been used in Australia over gas fields because of the interpretation difficulty in identifying water encroachment into gas fields.

The Pluto 4D data was acquired by seismic specialist PGS and processed by geophysical company CGG over 12 months.

“The Woodside planning was characteristically thorough, and communication with PGS throughout the project execution was very good,” says Andrew Long, chief scientist and technology analyst at PGS.

Myuran Pathmanathan, studies and integrated modelling manager, adds: “It also took significant interaction between our geoscientists and CGG to incorporate insights into ongoing interpretation before the processing was finished.”

Principal geophysicist Larry Tilbury says internal collaboration has been vital with geotechnical operations, geoscience technology, development geoscience and reservoir engineering being some of the teams involved. “It’s been a great example of how several departments across the business have come together to create incredible value for the company,” Larry says.

Larry has been advocating for a 4D survey for several years, arguing it would better map water encroachment while also highlighting where wells could maximise gas recovery and identify bypassed reserves.

Lupo says an integrated way of working cut the time to interpret what was probably the largest data set Woodside has ever had on an asset.
“Collaborative work enabled us to accelerate studies by about six months,” he says.

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Trunkline Q2 2018