辽东湾海域天然气分布特点及其控制因素

Distribution Characteristics and Main Controlling Factors of Natural Gases in Liaodong Bay,East China

辽东湾海域天然气可分为油型气、煤成气和生物成因气3种类型。除JZ31-6气田为生物成因干气外,其余主要气田中天然气均为湿气。研究区天然气的分布具有北多南少,深部沙河街组多,浅部东营组和新近系少的特点。这一特点主要受到烃源岩有机质类型与热演化程度、盖层厚度、超压等因素的影响。辽东湾北部气藏主力烃源岩有机质类型偏Ⅱ2型,而南部偏Ⅱ1型,且热演化程度北高南低。同时,东三段区域盖层北厚南薄,且在北部广泛发育欠压实成因的超压。超压和泥岩盖层的双重封堵为北部天然气藏提供了良好的保存条件。此外,辽中凹陷北洼沙三段烃源岩通过生烃产生的超压,为天然气由洼陷向辽西凸起带运移成藏提供了充足的动力。

Three types of natural gases,including coal-derived gas, oil-derived gas and biogenic gas have been found in the Liaodong Bay. All of the natural gases in the main gas fields of the Liaodong Bay are wet gas except those in JZ31-6 which are dry biogenie gas. The natural gas mainly distributes in the northern part of the Liaodong Bay with only a small part in the southern part. In the deep,it mainly distributes in the Shahejie Formation with little in the lower Dongying Formation and the Neogene. The distribution characteristics of the natural gas is controlled by the types and thermal maturity of the organic matters, the thickness of the cap rocks and the formation mechanisms of the overpressure. The organic matter in the northern part are type 112-prone which mainly generates natural gas with a higher maturity while those in the northern part are type II 1- prone which mainly generates oil with a lower maturity. The thickness of the cap rocks in the 3rd member of the Dongying Formation（E3da） decreases from the north to the south. The overpressure which evolves in the 3rd member of the Dongying Formation（E3d3） is caused by the uncompaction,providing a good condition for the gas preservation in cooperation with the huge-thick cap rocks, while the overpressure which evolves in the 3rd member of the Shahejie Formation（E3s3） is caused by the expansion of the hydrocarbon, providing a strong power for the natural gas which migrates from the sag to the Liaoxi Salient.