长江三角洲晚第四纪地层沉积特征与生物气成藏条件分析  

Sedimentary Characteristics and Accumulation Conditions of Shallow-biogenic Gas for the Late Quaternary Sediments in the Changjiang River Delta Area

作　　者：林春明[1] 张霞[1] 徐振宇 邓程文 殷勇[3] 承秋泉[4] 

机构地区：[1]内生金属矿床成矿机制研究国家重点实验室,南京大学地球科学与工程学院,江苏南京210046 [2]南京地调中心石油勘察研究院,江苏南京210016 [3]南京大学地理与海洋科学学院,江苏南京210046 [4]中国石化石油勘探开发研究院无锡石油地质研究所,江苏无锡214151

出　　处：《地球科学进展》2015年第5期589-601,共13页Advances in Earth Science

基　　金：国家自然科学基金项目“杭州湾地区全新世古河口湾沉积物源示踪”(编号:41402092);江苏省自然科学基金项目“末次盛冰期以来钱塘江下切河谷充填物物源特征”(编号:BK20140604)资助

摘　　要：对长江三角洲晚第四纪地层沉积特征进行了精细研究,探讨了研究区层序地层格架,在此基础上分析了浅层生物气成藏条件、特征和分布规律。研究表明,长江三角洲晚第四纪发育3期下切河谷,形成了3套沉积层序;因后期河流的强烈下切破坏,早期沉积层序往往被剥蚀殆尽,仅残留下部的河床相粗粒沉积,造成不同期河床相的叠置;相对而言,末次冰期以来形成的下切河谷沉积层序以相对完整的沉积相组合被保存下来。长江三角洲浅层天然气是未经运移的原生生物气,其主要富集于末次冰期以来的沉积层序内,气藏为自生自储同生型的岩性圈闭。河口湾—河漫滩和浅海相泥质沉积物既是气源岩,又是盖层,后者可作为良好的区域盖层;河口湾—河漫滩和河床相砂质沉积物为主要储集层。因此,研究区晚第四纪多期下切河谷沉积层序有利于浅层生物气藏的形成,特别是晚期下切河谷内河口湾—河漫滩相砂质透镜体以及河床相砂体可作为优先勘探目标。This paper deals with the characteristics, distribution pattern, and accumulation features of the late Quaternary shallow-biogenic gas in the Changjiang River delta area based on the detailed analysis of sedimentarycharacteristics, facies, and sequence stratigraphic framework, and organic geochemistry. The results show that there are three episodes of inciseA valley developing in the study area, resulting in the formation of distinct sedi- mentary sequences. The early two systems are incomplete due to the late strong incision and erosion, and are char- acterized by the superposition of fluvial sediments; while the last postglacial sequence is relatively complete with different sedimentary facies assemblages. The shallow gas in the study area has a biogenic origin, and the gas reser- voir belongs to a syngenetic type of self-generating and self-reservoir. The muddy clay and silty clay of estuary- floodplain and shallow marine facies occur as both gas source and cap sediments, and the muddy clay of the shallow marine facies can be used as good regional cap beds. As main biogenic gas reservoirs, the sand sediments of estuar- y-floodplain and fluvial channel facies distributed within the incised valleys. The study area and its adjacent area are characterized by several times of incised valleys, in favor of the development of gas source, cap and reservoir sediments. As a consequence, the incised valley is the most favorable zone for the shallow-biogenic gas exploration, and the sand bodies of estuary-floodplain and fluvial channels especially the former within the incised valleys have the high priority of exploration.

关 键 词：沉积特征 成藏特征 浅层生物气 长江三角洲 晚第四纪 

分 类 号：P62[天文地球—地质矿产勘探]