Prion 3D Marine Seismic Survey

Overview

Beach Energy (Operations) Limited (‘Beach’) is the Operator of Retention Leases T/RL2, T/RL4 and T/RL5 in the Commonwealth waters of Bass Strait and is proposing to undertake the Prion three-dimensional (3D) marine seismic survey (MSS) over these leases.

The purpose of the Prion 3DMSS is to acquire geophysical data to gain deeper knowledge of the subsurface geology in order to identify commercially viable gas reservoirs for future development.

The proposed Prion 3DMSS comprises two areas, these being the:
• ‘Acquisition area’ – the physical area in which the seismic source will operate (i.e., acquire data), covering an area of 880 km2. The acquisition area measures 39 km long (northeast-southwest orientation) at its longest and 24 km wide (west-east orientation) at its widest.

• ‘Operational area’ – the physical area in which operations ancillary to achieving survey coverage will take place. This includes vessel approach, vessel line turns (15 km allowance), ‘soft starts’ of the seismic source, run-ins and run-outs of the seismic source and miscellaneous maintenance operations. The operational area measures 71 km long (northeast-southwest orientation) and 32 km wide (west-east orientation), covering an area of 2,272 km2.
The acquisition and operational areas combined are referred to as the ‘survey area’. Water depths in the survey area range from 50 m to 80 m. At its nearest points, the survey area is located 75 km east of King Island and 57 km from Stanley in Tasmania.

The Prion 3DMSS is scheduled to commence between July 2021 and June 2022, but may not commence until June 2023. This EP is therefore valid for a survey start date of any time up until June 2023. The preferred windows of opportunity are listed below in order of preference, noting that timing of survey commencement is dependent on vessel contracting and weather/sea state conditions:

• October to December 2021 (or 2022) – favourable sea state, avoids the peak blue whale migration period;
• January to April 2022 (or 2023) – favourable sea state, but overlaps the peak and shoulder blue whale migration periods; or
• April to July 2022 (or 2023) – less favourable sea state, streamers would need to be towed lower in the water column to mitigate for weather-related downtime and minimise
acquiring poor data.

The survey is expected to take up to 40 days, though the vessel may be present on location for longer than this depending on factors such as sea state conditions, whale-instigated shutdowns and technical issues.

The survey vessel will acquire the seismic data by towing three acoustic source sub-arrays operating alternatively, one discharging as the others recompress. The lateral distance between each of the sources will be 100 m. The source volume will be a maximum of 2,495 cubic inches with an operating pressure of 2,000 pounds per square inch. There will be 10 to 12 hydrophone ‘streamer’ cables approximately 8,000 m long towed behind the survey vessel. The vessel will sail back and forth across the acquisition area along 76 sail lines (nominally) that will be spaced 300 m apart.

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