INPEX Browse E&P Pty Ltd (INPEX) is proposing to undertake a three-dimensional (3D) marine seismic survey (MSS) in the greenhouse gas (GHG) assessment permit G-7-AP, located offshore in the Bonaparte Basin off northern Australia. The G-7-AP permit area is wholly located within Commonwealth waters to the north of the Joseph Bonaparte Gulf and approximately 100 km west of Darwin Harbour.
The 3D MSS will be undertaken by a seismic survey vessel towing the seismic source and a series of streamers behind it. The seismic source is expected to be a conventional triple or a dual source with individual arrays discharged alternately approximately every 12.5 m (approximately every 5.4 seconds) or approximately every 18.75 m (approximately every 8 seconds), respectively.
The seismic source will be towed behind the seismic survey vessel at a depth of approximately 6 – 8m below sea level. The seismic source will emit regular pulses of sound which reflect off the seabed and underlying geological rock formations. The reflected sound is recorded by hydrophones or similar devices installed on the streamers.
The seismic survey vessel and towed equipment will traverse a series of pre-determined, parallel sail lines within the Acquisition Area and Active Source Area, spaced approximately 375 – 675 m apart, at a speed of approximately 4.5 knots (8.3 km/hr). The seismic survey vessel will typically complete the lines in a “racetrack” (loop) formation.
The 3D MSS will comprise approximately 40 days of seismic data acquisition. To allow for equipment deployment and recovery, potential adverse weather and operational downtime, the survey may occur over a longer period, and so the survey vessel may be present in the Operational Area for up to a total of 65 days. Operations will occur 24 hours per day.
The seismic survey vessel will be accompanied by one to two support vessels, which will assist with on the water communication with other marine users, refuelling, re-supply and other support functions.
One or two small work-boats (typically 5-10 m in length deployed from the seismic survey vessel) may also assist the seismic survey vessel within the Operational Area during deployment and recovery of the seismic source and streamers. Refuelling and re-supply will occur approximately every 35 days (5 weeks), either at sea or in port. Crew changes may also occur approximately every 5 weeks, which will involve either the vessels returning to port or personnel transfers via helicopter or supply vessels.
An exact start date that the 3D MSS may commence is subject to vessel availability, operational efficiencies, other site survey and drilling activities that INPEX plan to undertake within the permit area, potential Department of Defence exercises that may occur, and weather. For contingency purposes, this Environment Plan allows for the activities to occur within the calendar years 2023-2024.