Seventy three petroleum accumulations have been found to 30 June 1992 in the Carnarvon Basin. Most accumulations occur offshore in the northern part of the basin, in Triassic to Cretaceous sedimentary rocks. This Mesozoic sequence was deposited in a series of sub-basins associated with the rifting of the Australian and Indian plates. Petroleum accumulations are found in the Barrow, Dampier and Exmouth Sub-basins, the Exmouth Plateau, and the Peedamullah/Onslow Shelf.
Trapping mechanisms include structural and stratigraphic traps at several levels in the Mesozoic sequence. The largest known gas and oil fields in the basin are reservoired in pre-rift Triassic fluvio-deltaic sands and post-rift Cretaceous marginal marine sandstones. Several significant accumulations, including the Wanaea and Cossack oil accumulations, occur in the Jurassic syn-rift sequence, which includes marine shelf, slope and basin floor sandstones.
Source and seal for many accumulations are provided by marine prodelta shales and by restricted occurrences of deep marine shales, both of Jurassic age. Cretaceous marine claystones also act as seals, often by juxtaposition of these impermeable sediments against reservoirs across faults.
Thirteen developments were in place, as at 30 June 1992, to produce petroleum from the Carnarvon Basin and a further nine were planned, not including the planned Wandoo production test. Development infrastructure offshore consists of manned and unmanned platforms and monopods, seapoles and pipelines, while onshore facilities include the gas processing facilities and LNG plant at Karratha, the Tubridgi gas plant, the Harriet gas gathering facility on Varanus Island, oil processing or storage plants on Varanus, Thevenard, Airlie and Barrow Islands and offloading facilities at these islands. The Talisman development using a floating production facility ceased production in August 1992 and was decommissioned in October 1992.
