南鄱阳盆地东部乐平组老山段沉积环境及油气地质意义

Sedimentary environment and oil-gas geological significance of Laoshan Member of Leping Formation in eastern part of South Poyang Basin

开展南鄱阳盆地东部页岩气重点勘探层位岩相古地理研究。根据野外露头和钻井资料,综合岩性特征、沉积构造、古生物化石、剖面结构及地球化学等相标志,分析上二叠统乐平组老山段沉积环境、沉积相类型及空间展布特征,识别出3类主要的沉积体系,包括6种亚相和9种微相;结合物源分析,恢复了老山段三角洲-有障壁海岸相沉积模式。结果表明,在南东高北西低的古地貌背景下,物源由南东—北西方向注入,顺物源方向依次发育三角洲前缘、潮坪、潟湖、障壁岛沉积。受海平面变化影响,相序横向变迁及垂向连续叠置,有利于形成完整的生储盖组合。潮坪、潟湖相为烃源岩发育和页岩气储集的有利相带。

The lithofacies paleogeography of key shale gas exploration layers in eastern part of South Poyang Basin is studied based on outcrop and drilling data.The sedimentary environment,sedimentary facies types and spatial distribution characteristics of Laoshan Member of Leping Formation of Upper Permian are analyzed by analysis of lithology,sedimentary structure,paleontological fossils,profile structure and geochemistry.Three types of sedimentary systems are identified in Laoshan Member,including 6 subfacies and 9 microfacies,and the delta-barrier coastal facies sedimentary model of Laoshan section is recognized and constructed through source analysis.The research results show that under the paleogeomorphic background of high in the southeast and low in the northwest,the provenance is considered to be originated from the southeast to the northwest,and the delta front,tidal flat,lagoon and barrier islands sediments developed successively along the provenance direction.Under the influence of sea level change,the horizontal transition and vertical continuous superposition of phase sequences are conducive to forming a complete source-reservoir-cap association.It is considered that the tidal flat and lagoon facies are favorable zones for source rock development and shale gas reservoir.