Deep Structure of the Joint Development Zone and Adjacent Areas, Timor Sea : Survey 116 Post-cruise Report

The primary objective of AGSO Survey 116 was the acquisition of high-quality deepseismic data and other geophysical data over the Indonesian - Australian JointDevelopment Zone (JDZ) and adjacent areas of the Timor Sea. The cruise was partof a program being undertaken by AGSO, to determine the structural architecture ofthe north western margin of Australia and the influence of structuring on the location,migration and trapping of hydrocarbons in the region.

The survey vessel R.V. Rig Seismic left Darwin on 22 January 1993 but returned toport on 30 January due to equipment problems and poor weather conditions. Theship again departed Darwin on 3 February and began seismic acquisition on 5February. The survey was completed on 7 March and finished in Darwin on 8 March.

During the survey, 16 seismic lines were completed for a total of 3595 km at anaverage of 119 km per day. All of the proposed Timor Sea Tie lines were completed,however lines across Zone of Cooperation C of the JDZ and the Timor Trough inIndonesian waters were not collected because an agreement between AGSO andIndonesian authorities had not been finalised. In addition to the proposed program,the survey included 5 lines of the Malita Graben program, totalling 1028 km. TheseN-S lines were shot when marginal weather conditions prevented seismic acquisitionin an E-W direction. The Timor Sea Tie lines were tied to 17 exploration wells.

Acquisition within the Joint Development Zone was undertaken on behalf of NOPEC,who have been authorised by the Joint Development Authority to research this area.All seismic lines were collected to specifications agreed upon by NOPEC and AGSO.

The seismic data were recorded from a 4800 m streamer, configured with 192 x 25 mactive groups. The record length was 16 seconds, and the sample interval 2 ms.The seismic source consisted of dual sleeve gun arrays with a capacity of 50 litres.Navigation for the survey was provided by differential Global Positioning System(dGPS), using shore reference stations Darwin and Broome.

The seismic acquisition system was inoperable during the first week at sea duringwhich time weather conditions also prevented acquisition. After repairs to thesystem, both the seismic and non-seismic acquisition systems ran without majorproblems. Navigational data were of good quality, with differential GPS beingavailable at least 95% of the survey time.

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