Sequoia 3D survey

ConocoPhillips files for Sequoia 3D survey

ConocoPhillips Australia and 3D Oil are proposing to undertake the Sequoia 3D marine seismic survey within exploration permit T/49P in the Otway Basin, west of Tasmania’s King Island.

Courtesy: NOPSEMA/ConocoPhillips

The purpose of the Sequoia 3D survey is to acquire geophysical data to provide a 3D image of the subsurface geology within the T/49P permit area in order to identify prospective commercially viable gas reservoirs for future development.

The acquisition area covers 2,840 square kilometres. It is 129 kilometres long at its longest and 25 kilometres wide at its widest.

Operational area is 153 kilometres long and 26.5 kilometres wide, covering an area of 4,089 square kilometres.

Water depths in the survey area range from 70 metres to 1,000 metres, with 91 per cent of the survey area being in water depths of less than 150 metres. At its nearest points, the survey area is located 23.5 kilometres from the west coast of King Island and 26 kilometres from the Victorian coast.

The Sequoia survey should take place during the window of 1 August to 31 October 2021.

The survey would take approximately 60 days, though the vessel may be present on location for longer than this (but not acquire outside the months of August and October) depending on factors such as sea state conditions, whale-instigated shutdowns and technical issues. The actual number of days of active seismic acquisition will be approximately 31 days.

The survey vessel will acquire the seismic data by towing three acoustic source sub-arrays operating alternatively, one discharging as the others recompress. There will be 12 to 18 hydrophone ‘streamer’ cables approximately 6,100 m long.

CSI technology

The survey will use ConocoPhillips’ Compressive Seismic Imaging (CSI) technology. This means that while the overall width of the streamer configuration remains consistent, the internal streamer separation will vary between 25 metres and 100 metres with a non-uniform interval distribution. Using the CSI technology means that the survey can sail fewer line kilometres and use fewer streamers and acquire the seismic data quicker than a conventional seismic survey.