Caldita-Barossa 3D Marine Seismic Survey
|Activity type||Seismic survey|
|Submitted by||ConocoPhillips Australia Exploration Pty Ltd|
|Submission date||09 August, 2016|
|Decision date||08 September, 2016|
|Link to previously accepted EP|
Dr Brenton Chatfield
ConocoPhillips is currently acquiring three dimensional marine seismic data in an area of the Timor Sea, 300 km north of Darwin, Northern Territory. Data is being acquired in Retention Lease Permits NT/RL5 and NT/RL6, known as the Barossa and Caldita fields, as well as some adjacent open acreage. The permit areas are in Commonwealth waters of the Bonaparte Basin. Water depths in the operational area range from approximately 75 m to 550 m. The data acquisition area is a within a larger operational area of 10,448 km2 which allows for most contingencies and for line run‐outs, line turns and line run‐ins.
The accepted EP (accepted by NOPSEMA on 27 July 2016) allows data acquisition from 1 July to 30 September. However, as ConocoPhillips expect to need to continue data collection into October, it is submitting a Revision to extend the operational window until 31 October 2016. All other technical aspects of the data acquisition remain unchanged from that detailed in the previously accepted EP. In response to feedback received during stakeholder consultation for the EP Revision, ConocoPhillips has reduced the size of the acquisition area (as stated in the previously accepted EP) from ~3,186 Sq Kms to ~2,858 Sq Kms by removing approximately 328 Sq Kms (10%) from the northern margin. In doing so, it has reduced the expected duration to complete the survey from 82 days to 73 days which will also reduce the potential impacts from the activity. In addition, ConocoPhillips will acquire the southern and eastern parts of the acquisition area (Area A) first, during July to September, when stakeholder engagement has confirmed that fishing intensity is at its lowest, and then acquire the western portion (Area B), which may require the survey to continue into October.
ConocoPhillips will not acquire data in Area A after 30 September and any data acquired in October will only be within Area B. Area B has low fishing effort (based on publically available catch data) and it is outside (and furthest from) areas in the Timor Reef Fishery (TRF) with higher commercial productivity. This area is also considerably smaller, covering approximately 658 Sq Kms which overlaps approximately 1.2% of the TRF. Consultation with Northern Territory Department of Primary Industry and Fisheries has confirmed that currently there is very limited fishing activity in the part of the TRF overlapped by Area B, and therefore restricting any data acquisition in October to Area B would minimise the impacts to fishing activity and fisheries (e.g. spawning activity). Data is being collected using a purpose‐built seismic vessel towing dual acoustic source arrays and hydrophone cables (streamers). Acoustic emissions from the source arrays are detected by the hydrophone cables and recorded on the vessel. The vessel will tow 16 hydrophone cables, at a length of 6 km at depths between 15‐ 20 m. The distance between the hydrophone cables will be an average 50 m. The total volume of the seismic source proposed for the survey is 4,130 cubic inches. This source size was selected to meet several criteria regarding operational stability, predictable behaviour and fit‐for‐purpose subsurface seismic imaging (vertical focus). The vessel will collect data along a series of pre‐determined sail lines at an average speed of 8‐9 km/hour. There are a total of 109 sail lines in the acquisition area, with a total length of 7,588 km and a separation distance of 400 m. The seismic source will be discharged at a nominal interval of 8 seconds along each sail line. The seismic source will produce peak at source (i.e. within a few metres of the airgun array) sound pulses of zero‐to‐peak sound pressure level of approximately 246 dB re 1 μPa @ 1 m, and sound exposure levels of approximately 223 dB re 1 μPa2.s @ 1 m across a frequency range of 10 Hz to 2 kHz.
The seismic vessel will be accompanied by a support vessel and a chase vessel that ensures other vessels do not come in close proximity. The survey is planned to occur from 1 July to 31 October 2016. Commencement of the survey is subject to gaining the required regulatory approvals and availability of the seismic vessel for conducting the survey.