下扬子区中生界构造特征及油气远景

STRUCTURAL FEATURES AND DIL AND GAS POTENTIAL OF THE MESOZOIC IN XIAYANGZI REGION OF CHINA

下扬子区中生界包括海相和陆相沉积，中生代演化分为6个地质阶段：①早、中三叠世稳定沉积；②晚三叠世推覆运动；③早、中侏罗世前陆盆地；④晚侏罗世走滑作用；⑤早白垩世挤叠盆地；⑥晚白垩世拗陷盆地。下扬子区中生代发育的陆相叠合盆地中，存在多层系生储盖组合，具有一定油气远景。上古生界和下三叠统烃源岩是下扬子区最有利的烃源岩，浦口组沉积后处于晚期大量生烃阶段，生成的烃类可被中生界圈闭捕获成藏。构造运动对该区油气的影响利大于弊。印支末期的推覆运动使局部地区烃源岩堆叠加厚，形成独立的生烃中心；区内北北东向走滑断裂在晚侏罗世再次明显活动，控制了火山岩的喷发，火山岩既可加速烃源岩热演化，又可作为储集岩，断裂自身则可成为烃类纵向运移的通道。

The Mesozoic strata in Xiayangzi region consist marine and continental sediments. The evolution of the Mesozoic can beclassified into six geological stages: ①Early and Middle Triassic stable deposition stage, ② Late Triassic napping movementstage, ③ Early.and Middle Jurassic foreland basin forming stage, ④ Late Jurassic striking-slipping stage, ⑤ foeing stage ofEarly Cretaceous compressional and superimposed basin, and ⑥ the forming stage for Late Cretaceous depressional basins.There exist multiple source-reservoir-cap assemblages in the Mesozoic continental superimposed basins of Xiaysngzi region,which pocess a certain oil and gas potential. The Upper Paleozoic and Lower Triassic hydrocarbon source rocks are the mostfavourable source rocks in the Xiayangzi region. The Pukou Formation, after deposition, was at the late peak hydrocarbongeneration stage, the oil and gas generated from it could be trapped in the Mesozoic and formed oil and gas pools. Thepositive effect of the tectonic movement on oil and gas in the region is stronger than its negative effect. The Late Indosiniannapping made local source rock overlapped and thickened, and forming independent hydrocarbon generation center. The NNEstrike-ship fault reactivated during Late Jurassic, controlling the eruption of volcanic rocks which could accelerate the thermalevolution of hydrocarbon source rocks and also be the reservoir for hydrocarbon, and the faults themselves could become thevertical migration paths of hydrocarbon.