从岩相古地理看柴达木盆地侏罗系的油气前景

HYDROCARBON POTENTIAL OF THE JURASSIC IN QAIDAM BASIN FROM THE VIEWPOINT OF LITHOFACIES PALAEOGEOGRAPHY

在前人研究的基础上,利用20余处露头剖面、150余口钻井剖面和12000 km地震剖面资料,特别是最新的钻探成果,对柴达木盆地侏罗纪的地层和沉积相的展布规律以及岩相古地理进行了重新认识,通过岩相古地理编图,确定了生油凹陷和储集砂体的分布位置,预测了侏罗系油气前景。早、中侏罗世的古气候条件有利于油气的生成,多个古凸起提供的多个物源,有利于储集砂体的形成,确定了辫状河三角洲砂体、滨湖席状砂体、滨浅湖滩坝砂体、河道砂体、浊积扇砂体和近岸水下扇砂体等6种沉积类型和30个有利和较有利的储集砂体。众多半深湖—深湖区提供丰富的油气资源,确定了8个大小不等的生油凹陷,累积面积超过4000 km^2。古地理的演化表明该区发育多套生储盖组合。冷湖地区、昆特依地区、马海尕秀-鱼卡地区等是今后勘探的有利地区。

On the basis of the previous studies and data from over 20 outcrops, over 150 wells and 12 000 km seismic profiles,especially new drilling data, the distribution characteristics of strata and sedimentary facies, and the lithofacies palaeogeography of the Jurassic in the Qaidam Basin was restudied. Based on the lithofacies palaeogeography maps, the position of hydrocarbon-generating sags and sandstone reservoirs was determined, and the hydrocarbon potential of the Jurassic was predicted. In the Early and Middle Jurassic, the humid and warm climate was favourable to the deposition of source rocks,and the supply of clastic materials from several uplifts was advantageous to the formation of the sandstone reservoirs. Six types of the sandbodies,i. e. braided stream delta sandbody,shore lake sheet sandbody,shore and shallow lake beach and bar sandbody,fluvial channel sandbody, turbidity fan sandbody and nearshore submerged fan sandbody, and 30 advantageous sandbodies were determined. The source rocks deposited in a lot of semi-deep and deep lakes supplied abundant hydrocarbons, and the 8 source sags of different sizes totally over 4 000 km2 in area were located. The evolution of the palaeogeography shows that many types of source-reservoir-cap rock assemblages were developed in this area. It was pointed out that the Lenghu.Kunteyi and Mahaigaxiu-Yuka areas are favorable for hydrocarbon exploration in the future.