Quoll 3D Marine Seismic Survey
|Activity type||Seismic survey|
|Submitted by||Searcher Seismic Pty Ltd|
|Submission date||01 May, 2015|
|Decision date||16 June, 2015|
|Link to previously accepted EP|
1.0 Project Description
1.1 Introduction Searcher Seismic Pty Ltd (Searcher) proposes to undertake the Quoll 3D MSS permit area AC/P 55 in the Timor Sea off northern Western Australia. The following project description outlines the basis of the activity as shown in the Environment Plan under assessment by NOPSEMA.
1.2.1 Project Area The area over which seismic data will be acquired (the “project area”) covers approximately 419 km2 located entirely within permit area AC/P 55, which lies in the Timor Sea off northern Western Australia. Water depths in the project area range from approximately 60 to 120 m.
Searcher will apply a buffer around the area of full power data acquisition, referred to as the “operational area”. The operational area represents the outer bounds within which the activity will be conducted; it does not include transit routes to and from the area. The operational area will be restricted to the minimum area required for routine seismic survey activities, including streamer deployment, maintenance and recovery. All vessel turns at the end of acquisition lines, streamer maintenance, soft start procedures and vessel manoeuvres will be contained within the operational area (Figure A). The operational area will cover approximately 1,632 km2 and intersect petroleum permit blocks AC/P 55, AC/P 45, AC/RL 7 and AC/L 6. Searcher will ensure that valid AAs are in place prior to commencing the activity. The operational area is located entirely in Commonwealth waters (coordinates shown in Table 1-2); there will be no seismic data acquisition within the buffer surrounding the project area.
There are no islands or emergent land within the operational area. At its nearest point, the operational area is located approximately 50 km north-east of Cartier Island. The nearest settlement on the Australian mainland is Derby, approximately 540 km south of the operational area.
1.3 Description of the Activity
1.3.1 Survey Vessel
Searcher proposes to conduct the Quoll 3D MSS using a purpose built seismic survey vessel, the BGP Explorer. The BGP Explorer has current certification/registration consistent with International Maritime Organisation (IMO) requirements for a vessel of this size and purpose, including International Convention for the Safety of Life at Sea (SOLAS) and the International Convention for the Prevention of Pollution from Ships 1973, as modified by the Protocol of 1978 (MARPOL) requirements. The vessel has implemented and tested the Shipboard Oil Pollution Emergency Plan (SOPEP), in accordance with Regulation 37 of Annex 1 of MARPOL. The vessel carries a maximum number of 49 people on-board.
The BGP Explorer proposes to use a Marine Gas Oil (MGO) fuel and does not utilise heavy fuel oil. MGO is produced through distillation and as such, it contains a higher proportion of lighter hydrocarbons than other marine fuel types such as intermediate fuel oil or heavy fuel oil. Helicopter transfers of crew and vessel refuelling at sea will not occur as the planned length of the activity is 16 days (not including any potential downtime). The deployment of a support vessel will not be undertaken for this activity. The survey vessel is equipped with a fast rescue craft (rescue boat, DSB-3.9 SR / IRB).
1.3.2 Seismic Data Acquisition
The BGP Explorer will traverse a series of predetermined sail lines at speed between four and five knots. As the vessel travels along the survey lines, a series of acoustic pulses, generated by an airgun array, will be directed down through the water column and seabed. The released sound is attenuated and reflected at geological boundaries and the reflected signals are detected using sensitive hydrophones arranged along a number of cables (streamers) towed behind the seismic vessel. The reflected sound is then processed to provide information about the structure and composition of geological formations below the seabed in an attempt to identify hydrocarbon reservoirs. At the end of each survey line, the vessel will turn with a sufficiently large arc to avoid letting the streamers sink to a depth where there is a risk of entanglement with seabed features. The seismic source will be powered down to the lowest power setting when not collecting data (i.e. on line turns) and will fire a single airgun for line turns of less than two hours duration. For longer line turns in excess of two hours, the source will be shut down and soft start procedures would be followed once the vessel reaches the next new line. The seismic array will comprise two air gun arrays operating alternatively (i.e. flip-flop), with each array having a total volume of 3,480 cubic inch. Under no circumstances will the arrays be discharged simultaneously. The two air gun arrays will be towed behind the vessel at a depth of 6 m (± 1 m). Acquisition will take place at a speed of approximately 4.5 knots with a shot point interval of 25 m linear distance travelled, resulting in a period of approximately 10 seconds between consecutive shots. The operating pressure of the air gun arrays will be approximately 2,000 psi. The total power output for the array will have a sound pressure level (SPL) of 247.5 dB re 1 μPa (at 1 m) peak to peak. Sound energy of the seismic impulse generated by the array is low frequency (1 to 1,000 Hz). The characteristics of the seismic array are summarised in Table 1-4. Hydrophones used to detect reflected sound energy impulses will be mounted in an array of four solid streamers that will be towed behind the survey vessel. The streamers will have a maximum active length of 4,500 m and they will be towed with a separation of 100 m between each streamer, resulting in a total streamer spread of 300 m plus paravanes and floats. The streamers will be towed at a depth of between 6 and 9 m. Each streamer will be fitted with a clearly visible tail buoy to maintain depth and facilitate identification of the streamer. All tail buoys will be fitted with turtle guards to reduce the risk of entanglement of marine fauna. The streamers will be fitted with selfinflating Streamer Recovery Devices (SRDs) at regular distance intervals along each streamer that will return them to the surface in the event they sink below a predefined, user selectable water depth setting.
1.4 Timing of the Activity
1.4.1 Survey Design and Schedule
The proposed activity has an expected duration of 16 days and it will take place between July and December 2015, pending vessel availability. Seismic data will be acquired over a 24-hour period, with shut-downs as required for routine and reactive maintenance, repairs, transit and line turns, and marine fauna / stakeholder avoidance and adverse weather. All relevant stakeholders, including NOPSEMA NOPTA and AMSA will be notified prior to the start of the activity. Service Layer Credits: Esri, DeLorme, GEBCO, NOAA NGDC, and other contributors.