巴西东缘桑托斯盆地盐上碎屑岩系沉积特征及其演化规律

巴西东缘桑托斯盆地是近年来油气勘探的热点地区之一，其盐上碎屑岩系油气主要分布于晚白垩世森诺曼-土伦期、科尼亚克-马斯特里赫特期和古近纪等3个期次的地层中。基于区域沉积背景分析，通过调研盆地周缘水系发育及物源供给特征，利用现有的钻井、地震、测井及分析化验数据等，对盐上3个砂岩储层发育期次的主要沉积特征及其演化规律进行系统分析。研究表明，晚白垩世森诺曼-土伦沉积期在桑托斯盆地南部主要以浅海-半深海泥质沉积为主，在盆地中北部发育小规模三角洲及浊积水道；晚白垩世科尼亚克-马斯特里赫特沉积期，区域抬升导致物源供应充足，在浅水陆架区，发育多支大规模三角洲沉积，并持续向海进积，在陆坡区主要发育海底扇，具有“早期水道为主、晚期朵叶为主”的特点，深水区的盐岩起限制作用；古近纪沉积期，受区域水系迁移影响，物源供应减弱，整体以泥质沉积为主，三角洲规模明显萎缩，在深水区发育小型朵叶（或水道化朵叶）。

SEDIMENTARY CHARACTERISTICS AND EVOLUTION OF POST-SALT CLASTIC DEPOSITS OF SANTOS BASIN,EASTERN MARGIN OF BRAZIL

The Santos Basin on the eastern margin of Brazil is one of the hot spots for oil and gas exploration in recent years. Hydrocarbon discoveries in the post salt clastic series are mainly distributed in the Late Cretaceous Cenomanian-Turonian period, Late Cretaceous Coniacian-Maastrichtian period and Paleocene period. Based on the analysis of regional depositional settings, provenance characteristics of the surrounding drainages with the drilling, seismic, logging data, this paper makes a systematic study on the main depositional characteristics and the evolution of the three post salt sandstone reservoirs. The results suggest that the south part of the Santos Basin is dominated by shallow-bathyal argillaceous sediments in the Cenomanian-Turonian period, while the small deltas and turbidite channels dominate the middle and northern part of the basin. In the Coniacian-Maastrichtian period, sufficient sediment supply made larger scale deltas continuously prograded seaward into the shallow water shelf area, leaving submarine fans developed on the slope, forming a pattern of "channels dominating the early stage, lobes dominating the later stage". During the period of Paleogene, due to the migration of regional drainage system, sediment supply was reduced, and argillaceous sediments increased. As the results, the scale of delta was obviously reduced, and small channels or channelized lobes dominate the deep-water areas.