Planning for Success; Acquiring Australia’s First 4D Time Lapse Survey Over a Gas Field, Pluto Reservoir, North West Shelf

The Pluto & Xena giant gas fields (offshore Western Australia) were discovered in 2005 and contain approximately 5 trillion cubic feet of dry gas combined.

Production started in 2012 and after 4 years the subsurface team needed to better understand the impact of hydrocarbon extraction and changes in fluid distribution within the reservoir. To provide this information a 4D or time lapse seismic survey was proposed, with the expectation that a comparison back to the original 3D image would enable the mapping of movements of hydrocarbons and the associated changes in the gas water contact.

There are few successful examples worldwide of acquiring time lapse data over gas reservoirs, due to the difficulty in identifying a reliable 4D signal caused by a weak acoustic impedance contrast associated with a fairly indistinct gas / water interface.

Detailed and careful survey planning carried out prior to acquisition have made it possible to deliver a high quality dual purpose seismic data over a complex field.

In a wider context, the use of new 4D seismic acquisition design and techniques has created significant new and transferable knowledge, processes, techniques and systems that can be applied for time lapse monitoring of other gas producing reservoirs.