西藏羌塘盆地动力学演化与油气前景探讨

西藏羌塘盆地是特提斯构造域巨型油气富集带中一个大型晚古生代—中生代海相残留盆地。盆地盖层厚度可达万米,其中侏罗系浅海相地层占50%以上。盆地经历了晚古生代大陆边缘沉积阶段、三叠纪陆间裂谷阶段、侏罗纪大陆边缘沉积阶段和侏罗纪末班公湖—怒江缝合带闭合以来的构造反转挤压、长期剥蚀改造阶段。盆地中三叠系与侏罗系广泛发育良好的烃源岩,而且形成多套生储盖组合;但储集层、盖层及保存条件相对较差。与同一构造的波斯湾等大型含油气盆地相比,它只具备多期大陆边缘发育时期,缺少后期,特别是第三纪以来的前陆发育时期。盆地内部生储盖组合具全,构造变形较弱,发现中小型油气田的可能性较大。

DISCUSSION ON GEODYNAMIC EVOLUTION AND OIL-GAS PROSPECT OF QIANGTANG BASIN

Qiangtang Basin is a large latePaleozoicMesozoic era residual basin in Tethys tectonic region and has a thick sediment from upper Paleozoic to Cenozoic,up to 10,000m.The basin has an area of 200,000km2.It underwent continental margin stage in latePaleozoic era,intracontinental rift stage in Triassic period,continental margin stage in Jurassic period,and tectonic inversioncompression and erosion stage since lateJurassic.Based on analyses of oilproducing basins in Tethys tectonic region,these basins almost underwent continental margin basin and foreland basin stages.But Qiangtang Basin only underwent continental margin except conversion in LateJurassic.There is good oilgeneration condition in the basin,but reservoir rock,cap rock and preservation condition are not good.Jurassic stratigraphic sequence which is the main source rock,and cap rock was exposed to air.Therefore,it seems impossible to find large oilgas fields.But it is possible that middlesmall size oilgas fields can be found because there are good matured source rocks and large structural tarps.