Abstract: From the study of depositional setting of Holocene ultra shallow biogas,sedimentary facies and its distribution at Hangzhou Bay area are analyzed,and the forming and evolution regularity of the sedimentary facies in close relationship with space time distribution of the biogas in the former river valley are pointed out.Jiazao biogas pool which is the most typical is analyzed and then some typical features of ultra shallow biogas pool are discussed.The study shows that the river downcutted and then the Qiantangjiang old channel with depth of 40 100 meters was formed during the last Glaciation at low sea level,and the old channel was infilled and covered during sea level rising in post glacial period.Muddy sediments of flood plain facies and shallow sea facies are not only gas source rocks,but also cap rocks,the latter may be regional cap rocks.Sandy lenticular body of flood plain facies distributing in the old channel is the sole gas bearing reservoir which has industrial value.The gas pool is of lithologic trap and of authigenic and autostoring and syngenetic type.On shallow S wave seismic profiles,top interface of gas bearing sand layer shows stronger reflecting boundary,and this reflection wave will sharply decline when gas bearing sand layer pinches out in transverse.Thus,gas bearing sand body can be outlined based on this result.

Key words: Hangzhou Bay, Holography, biogenic gas, geologic feature

摘要： 从杭州湾地区全新世超浅层生物气所赋存的沉积背景入手,分析了该区沉积相及其展布,并恢复了与生物气时空分布密切相关的沉积相在古河谷形成演变规律.在此基础上,重点解剖最具代表性的夹灶生物气藏,探讨了超浅层生物气藏典型特征.研究表明:末次盛冰期低海面,河流下切形成40～100m深的钱塘江古河谷,冰后期海平面上升,古河谷被充填和覆盖.河漫滩和浅海泥质沉积物既是气源岩,又是盖层,后者可作为区域盖层;分布在古河谷的河漫滩砂质透镜体为唯一具工业价值的储气层,气藏为岩性圈闭,属自生自储同生型.含气砂层顶界面在浅层横波地震剖面上表现出强的反射面,当含气砂体横向尖灭,反射波急剧减弱,据此可圈定含气砂体的边界.

关键词: 杭州湾, 全新世, 生物气, 地质特征