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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。
The natural gas in the Liaodong Bay can be divided into three types: oil gas, coal gas and biogenic gas. Except for the JZ31-6 gas field, which is a biogenic dry gas, most of the other major gas fields are wet gas. The distribution of natural gas in the study area has the characteristics of less north and south, more deep Shahejie formation, shallow Dongying formation and less Neogene. This feature is mainly affected by the source rock organic matter types and thermal evolution, cover thickness, overpressure and other factors. In the northern part of Liaodong Bay, the main source rocks of the gas reservoirs are partial type Ⅱ2, while the south part is Ⅱ1 type, and the degree of thermal evolution is high in the north and low in the south. In the meantime, the north-south and north-south cap rocks of the East Third Member area are underdeveloped, and overpressures due to under-compaction are widely developed in the north. The double plugging of overpressure and mudstone cap provides good preservation conditions for the northern gas reservoir. In addition, the overpressure produced by hydrocarbon generation in the third member of Beiwa sandstone in the central part of Liaozhong sag provides sufficient motivation for natural gas migration from the depression to the Liaoxi uplift zone.