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

Abstract：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.