西藏羌塘盆地的深部结构特征与含油气远景评价

羌塘盆地是目前国内石油勘探的热点地区之一,本文综合研究了羌塘盆地的地球物理、石油地质调查资料及INDEPTH-3深部调查结果,得出:①盆地内烃源层、储集层、盖层及其组合条件很好,局部构造发育,有利于形成和保存油气藏,断裂不会成为致命问题,提出了今后工作的主要目的层上三叠统—中侏罗统组成的中构造层;②对盆地二级、三级构造作了新的划分,否定羌中隆起,提出盆地表层的主要构造方向为北西—南东向,成“三凹三隆”及“一深凹”的地壳结构特征,其中主沉降带内部及其两侧是最有利的找油气远景地带;③本区壳幔之间的相互作用较强,盆地北部火山及热活动多,对油气远景评价有较大影响,而盆地南部沉积厚度大,受深层热影响相对较小,是找油气的更有利地段;④强调查明深部地层物性、油气赋存状况,烃类物质的来源和上下构造符合情况是当务之急,重点是加强点上的调查和评价研究;⑤提出不能轻视伦坡拉陆相古近—新近系盆地找油前景,它可能汇聚有两侧海相地层的油气。

Deep structure and petroleum prospect evaluation of the Qiangtang basin, Tibet

The Qiangtang basin is now one of the hot areas of petroleum exploration in China. Recent geophysical and petroleum geological survey and INDEPTH-3 deep exploration have revealed the following points: (1) In the basin, hydrocarbon source rocks, reservoir rocks and seal rocks, as well as their association are quite good, with local structures well developed, which is favorable for the formation and preservation of petroleum accumulations, and faults will not constitute a vital problem; the main target in the future work will be the Upper Triassic-Middle Jurassic intermediate tectonic layer.(2)A new tectonic division into the second- and third-order structures in the basin has been made and the existence of the Central Qiangtang uplift has been negated; the main structures at the surface of the basin are oriented in a NW-SE direction and characterized by the form of "three subbasins and three rises" and "a deep subbasin", among which the main subsidence zone and its two sides are the most favorable areas. (3)The intense interaction between crust and mantle in the area led to repeated volcanic and thermal activities, which has significant influence on petroleum prospect evaluation in the northern part of the basin; whereas the southern part of the basin has been subjected to less deep-seated thermal influence because of its thick sediments and therefore is more favorable for petroleum finding. (4)It is a task of top priority to ascertain the physical parameters of deep-seated rocks, mode of occurrence of petroleum, sources of hydrocarbon and coincidence between the upper and lower structures. The focus should be on intensifying the investigation and evaluation of sites of interest.(5)The petroleum prospects in the Tertiary Lunpola continental basin should not be ignored because petroleum might be accumulated in marine rocks on its two sides.