Geophysical company Spectrum Geo (Spectrum) are proposing to undertake the Otway Deep three-dimensional (3D) marine seismic survey (MSS) in the Commonwealth waters of the Otway Basin. The Otway Deep MSS is adjacent to permit areas T30/P and T49/P and predominantly sits over open acreage. The Otway Deep survey area is located entirely within offshore Commonwealth waters, approximately 42 km south of the Victorian mainland and 62 km west of King Island (Tasmania) at its closest points. Water depths within the survey area range from a minimum of 170 m to a maximum of 3,600 m. The survey area encompasses an area of 23,620 km2 and is the area within which the seismic source (airguns) will be operational and seismic data will be acquired, including soft-start procedures and line run-outs (required to obtain full fold coverage). The seismic source will not be operational outside of the survey area. An operational area or ‘buffer’ around the survey area is required for activities including streamer deployment and retrieval, maintenance and recovery, and vessel manoeuvring (line turns). There will be no discharge of the airguns within the operational area.
The duration of the activity is a maximum of 120 days per survey season between 1 October 2018 to end February 2022. The activity will acquire seismic data over a maximum area of 9,200 km2 per survey season, within the total defined survey area of 23,620 km2. The survey season is defined as the window from the beginning of October to end of February, with avoidance of the period from 1 March to end of September. A maximum extent of 9,200 km2 will be acquired during each survey window for the activity (i.e. between October and February in 2019 and again between October and February in 2022). The 120-day survey duration estimate is conservative and allows for some downtime due to weather, avoiding conflicts with other users, marine megafauna, and maintenance.
Spectrum may deploy OBN units on the seabed as an optional component of the Otway Deep MSS to augment the seismic data recorded by streamers. The exact number of these OBN units has not yet been determined but will be no more than 20. The maximum dimensions of each OBN is 1.3 m length, 0.72 m width and 0.75 m height. There will be no seismic operations within the OBN maximum deployment area that lies outside of the survey area. The OBN units will be located on the seabed for at least 30 days and for up to 120 days if weather conditions at the time preclude recovery of the units in a safe manner. Two concrete ballasts, each measuring 0.15 m in diameter and 0.63 m long, will be left on the seabed (per OBN); these will typically degrade within 10 years. The ballasts are composed using only natural components that disintegrate into sand and gravel.