MESOZOIC SOURCE-RESERVOIR-SEAL ASSEMBLAGE CHARACTERISTICS IN THE NORTHWEST SHELF OF AUSTRALIA

The Northwest shelf of Australia is rich in gas and poor in oil,and it takes on a wide prospect in recent years' exploration and exploitation.There are four basins and one orogenic zone in the area:North Carnarvon Basin,Roebuck Basin,Browse Basin,Bonaparte Basin and Timor-Banda orogenic zone.It is concluded that most hydrocarbon of Northwest shelf was accumulated during Mesozoic.The petroliferous area of Northwest shelf develops four main hydrocarbon source rocks,such as Triassic lacustrine shale,lower-middle Jurassic marine/paralic carbargilite and coal measure strata,upper Jurassic marine shale and Cretaceous marine shale;the main reservoirs are middle-upper Triassic delta-marginal sea sandstone,lower-middle Jurassic sandstone,upper Jurassic sandstone and Cretaceous sandstone;the main regional seal is lower Cretaceous marine shale.On the basis of depositional environment,source-reservoir-seal assemblages in this area include two main different types,"marine source-marine reservoir-marine seal" and "continental source-continental reservoir-continental seal".The former can be generally found in the Northwest shelf,and it is considered as the most important accumulation form in the area.