下扬子区古生界油气地质条件及勘探选区

下扬子区发育海相上震旦统至上奥陶统烃源岩（大部分已进入过成熟干气阶段，经历过两期生油过程，仍有一定生烃能力）和上石炭统至二叠系烃源岩（其本处于生油晚期阶段）；成岩后生作用大大改善了古生界碳酸盐岩及碎屑岩的储集性能和渗滤性；古生界露头区已发现背斜逾２００个（许多面积大于４０ｋｍ２），预计覆盖区构造型及其它类型圈闭同样很多，具有优越的圈闭条件；广泛分布３套有效区域盖层（下志留统高家边组，上二叠统龙潭组，上白垩统浦口组），以浦口组盖层最重要。下扬子区上震旦统至二叠系的油气显示（油、气和固体沥青）多达４２４处，多赋存于洞、缝，反映该区经历过广泛的成油过程。印支期至燕山期的构造运动对古生界原生油气藏改造相当严重，但构造相对稳定的区块仍有勘探远景，综合分析认为，泰州—泰兴、南通—无锡、句容—南陵、射阳—大丰和无为—望江地区最有勘探前景。图３表２参４（王孝陵摘）

Palaeozoic oil and gas geological conditions and exploration area screening in Lower Yangzi region.

In Lower Yangzi region, Upper Simian Upper Ordovician marine hydrocarbon source rocks (most of which have entered into their overmature gas stage, underwent two oil generation stages but still had certain hydrocarbon generation capacity) and Upper Carboniferous Permian hydrocarbon source rocks (which are basically at their late oil generation stage) are developed. Epidiagenesis improved greatly the storage and percolation characters of carbonate and clastic rocks. Over 200 anticlinal traps (many of which are larger than 40km 2 in area) are found in Palaeozoic outcrop area. It is predicted that structural or other types of traps may be also many in the covered region, which provides very favourable conditions for trapping with the help of widely distributed three sets of effective regional cap rocks (i. e. Lower Silurian Gaojiabian Formation, Upper Permian Longtan Formation and Upper Cretaceous Pukou Formation), of which the Pukou Formationis the most important. There are 424 oil and gas shows from the Upper Sinian Permian system in Lower Yangzi region, which are mostly in fractures and caves, indicating this region has underwent a full oil generation and accumulation process. The Indosinian Yanshan tectonic movement modified greatly the primary Palaeozoic oil and gas pools, but those areas structurally stable still have an exploration potential. An integrate analysis indicates that the Taizhou Taixing, Nantong Wuxi, Jurong Nanling, Sheyang Dafeng and Welwei Wangjiang areas are most potential for exploration.