Polarcus Seismic Limited (Polarcus) is proposing to undertake the Petrelex three-dimensional (3D) marine seismic survey (MSS) in Commonwealth waters of the Bonaparte Basin. The purpose of the Petrelex 3D MSS is to collect high quality geophysical data about rock formations and structures beneath the seabed and assess potential for new oil and gas discoveries.
The Petrelex 3D MSS is a typical 3D survey using methods and procedures similar to others conducted in Australian waters. No unique or unusual equipment or operations are proposed.
The Acquisition Area comprises the area within which 3D seismic acquisition will be undertaken and covers approximately 2,900 km2. The Acquisition Area is surrounded by a larger Operational Area (~7,150 km2), for the purpose of line turns, run-ins, run-outs, seismic testing and support activities. The Operational Area at its closest is approximately 90 km north-west of the Northern Territory coastline and 140 km north-east of the Kimberley coastline. The seismic survey will be undertaken in water depths between approximately 73 m to 107 m.
The survey will involve a single seismic survey vessel towing a seismic source array with a total volume of 2,495 cubic inches (in3), at a water depth of approximately 6 m. The seismic source will use compressed air to emit regular pulses of sound that reflect off the seabed and underlying rock formations. The reflected sound wave will be received by up to ten hydrophone streamers. Each streamer will be up to 8,100 m in length, spaced 112.5 m apart and towed at a depth of approximately 15 m. During the survey, the seismic survey vessel will travel at a speed of approximately 4-5 knots, discharging the seismic source approximately every 5-8 seconds. The survey vessel will typically acquire seismic data along a series of adjacent and parallel lines in a “racetrack” pattern. When the vessel completes the line, it will turn again to follow another line offset approximately 562.5 m from the first. This pattern is repeated until the required coverage is completed.
The Petrel 3D MSS may commence as early as October 2019 and will be completed before 31 December 2020, with the provision that the survey will not be undertaken during the period 1 August – 30 September 2020 (subject to change), due the Department of Defence undertaking a major military exercise within the Northern Australia Exercise Area (NAXA). The survey will take a maximum of 64 days to acquire, with eight days’ deployment/retrieval and two days’ local transit to and from port. The precise timing of the survey is subject to weather conditions, vessel availability and other operational considerations, and will take into account the seasonality of environmental sensitivities, where practicable.
