下扬子海相中—古生界烃源岩发育的控制因素

下扬子沉积了巨厚的海相中—古生界,主要发育了上震旦统陡山陀组、下寒武统荷塘组、下奥陶统、上奥陶统五峰组—下志留统高家边组、下二叠统栖霞组和上二叠统—下三叠统下段6套烃源岩层系,具有较大油气勘探潜力。烃源岩的发育主要受沉积相类型、古地貌格局及构造演化控制。烃源岩沉积相类型以陆棚相、台地相及沼泽相为主,陆棚相以深水陆棚相为最有利的烃源岩相带。下扬子南北海槽是震旦纪—中奥陶世最有利的烃源岩发育区。受区域构造拉张的影响,下扬子曾发生多期较大规模海侵,在海侵期发育了有利烃源岩层段,主要集中在下寒武统荷塘组、下奥陶统—中奥陶统下段、下二叠统栖霞组和上二叠统大隆组—下三叠统下段。受华南板块在加里东运动晚期的向北挤压的影响,下扬子板块发生挤压挠曲,使得南部抬升、北部沉降,上奥陶统五峰组—下志留统高家边组在北部沉降区发育有利的烃源岩。

CONTROLLING FACTORS ON THE MESOZOIC-PALEOZOIC MARINE SOURCE ROCKS IN THE LOWER YANGTZE PLATFORM

In the thick sequence of the marine Mesozoic-Paleozoic in the Lower Yangtze Area, there are six sets of hydrocarbon source rocks, i.e. the Lower Ordovician, the Wufeng Formation of the Upper Ordovician, the Gaojiabian Formation of the Lower Silurian, the Qixia Formation of the Lower Permian, the lower section of the Upper Permian, and the Lower Qinglong Formation of the Lower Triassic. Therefore, there is great potential for oil and gas accumulation in the Area. The hydrocarbon source rocks are mainly controlled by the types of sedimentary facies, ancient landform patterns and tectonic evolution. The facies types favorable for deposition of hydrocarbon source rocks mainly include the continental shelf facies, carbonate platform facies and swamp facies. The deep shelf facies is the most favorable for hydrocarbon generation. In the time range from Sinian to Middle Ordovician, the North Trough and the South Trough were the most favorable areas for the deposition of source rocks. Influenced by the pulling-apart effect of the regional tectonism, several times of large-scale transgressions happened in the Lower Yangtze Area. Deposition of hydrocarbon source rocks were thus happened during the transgressive phase, for examples, in the Hetang Formation of Early Cambrian, the lower Ordovician and the lower part of the middle Ordovician, the Qixia Formation of Lower Permian and the Dalong Formation of the Upper Permian, the lower part of the Lower Triassic. The Late Caledonian movement drove the South China plate drifting toward the north, the Lower Yangtze plate had suffered under a compression stress, and the north of the lower Yangtze plate subsided, while the south was uplifting. As the result, the northern part of the area, which was subsiding, became a favorable area for hydrocarbon source rocks of the Wufeng Formation of upper Ordovician and the Gaojiabian Formation of the lower Silurian to form.