山东东营凹陷沙四段盐下层油气成藏条件分析

东营凹陷是渤海湾含油气区中最重要的含油气凹陷之一,历经40多年的勘探开发,沙河街组四段上亚段及其以上层系已达到较高勘探程度。为确保油田的可持续发展,寻找有利的勘探接替领域已成为该凹陷勘探中面临的重要问题。应用地化指标、包裹体均一温度测试等手段,分析了盐下层暗色泥岩埋藏生烃史,结合沉积相、成岩相和高压封存箱等对储层储集性能的控制作用进行研究,综合分析了盐下层成藏条件与主控因素,指出北部陡坡带盐膏层之间及盐膏层之下的暗色泥岩已进入有机质演化的成熟?高成熟期,可生产大量的油气;同时,盐膏层具有良好的封隔性,使盐下层形成了单独的含油气系统,以发育自生自储型的岩性油气藏为主。油气成藏主要受沉积相带、成岩作用及高压封存箱等因素所控制,尤其是盐下高压封存箱的存在,既可延缓烃类和成岩演化,同时又为原生孔隙和裂缝的保存创造了良好的条件,十分有利于油气的生成、运移和保存。

Background for Oil and Gas Accumulation of Es4 Sub-salt Reservoir in Dongying Sag,Shandong

Dongying Sag is one of the major hydrocarbon bearing sags in Bohaibay Basin.After 40-year exploration and development,the upper part of the fourth section of Shahejie Formation(Es4) as well as those above the sequence have been highly explored.To ensure the sustainable development of Shengli oilfield,it is very urgent to explore favorable prospects.The article analyzed the background for oil and gas accumulation in Es4 sub-salt reservoir by the tests of geochemistry targets and organic inclusion homogenization temperature,combined with the study of the reservoir capability controls of sedimentary facies,diagenetic facies and high-pressure sealed boxes.It is indicated that in the northern slope belt of Dongying Sag,the lower part of Es4 develops semi-deep lake facies to intermittent brine lake facies,leading to thick glutenite and dark mudstone deposit in and below evaporate layers,among which the dark mudstone has experienced high-degree organic matter evolution and can yield large amounts of hydrocarbon.Evaporate layers may act as a favorable barrier bed for sub-salt layers to form independent hydrocarbon bearing system which is mainly self-generating and self-storage lithologic hydrocarbon reservoir.The sedimentary facies,diagenesis and high-pressure sealed boxes control the generation of hydrocarbon reservoir,and especially sub-salt high-pressure sealed boxes may slow down the process of hydrocarbon and diagenetic evolution as well as may provide conditions for the preservation of primary pore and fracture,which are in favor of hydrocarbon generation,migration and preservation.