东海盆地某油气田A井P层沉积体系研究

Study on Sedimentary System of P Formation in Well A in Oil and Gas Field of East China Sea

金艳 傅强

JIN Yan FU Qiang

上海石油天然气有限公司, 上海 200041; 同济大学海洋与地球科学学院, 上海 200092

Shanghai Petroleum Co. Ltd., Shanghai 200041, China; School of Ocean and Earth Sciences, Tongji University, Shanghai 200092, China

东海盆地某油气田A井钻遇古近系平湖组P层为一套灰绿色含砾细砂岩。对此层中的微量元素、古生物资料、粒度特征以及测井资料的分析表明:沉积物中的硼元素含量较低, Sr/Ba比值小于1, Fe/Mn比值远大于5, 这些指标反映沉积水体为淡水;同时, Ni/Co比值大多数介于2.5~5之间, 而V/Ni比值大于1, 指示研究层位沉积于还原环境中。该层沉积物中, 蕨类孢子含量极高, 花粉组合以阔叶类木本为主, 且含较多喜暖湿针叶类花粉, 说明当时盆地周边区域气候大致相当于现代亚热带气候, 较温暖且偏湿润。A井P层中, 砾石具近源快速堆积特征, 泥岩属较深水沉积, 岩层粒度具浊积岩特征;结合空间岩性展布状况可以判断, P层沉积相属于温暖湿润气候下的淡水近岸水下扇相。

Pinghu formation in Paleogene, consisting mainly of grayish green pebbly fine sandstone, was penetrated in A well in Xihu sag, East China Sea. Through analysis of trace elements, paleontological data, grain size characteristics and logging data, it is indicated that the content of boron is low, Sr/Ba ratio is less than 1, and Fe/Mn ration is far higher than 5, indicating that the sediments were deposited in fresh water. Meanwhile, the Ni/Co ratio is between 2.5 ~5 and the V/Ni ratio is higher than 1,indicating that sedimentary environment was reducing environment. In the sediments, spores are quite abundant, while the pollen of broad-leaved trees and warm/humid-preferring conifers dominates the pollen assemblages, that suggests the the regional climate was close to modern subtropical climate, it was warm and quite humid then. In the P formation of A well, the gravels are characterized by proximal and fast accumulation; the mudstones are relatively deep water deposits. The grain sizes have typical turbidite characteristic. Combined with the spatial distribution pattern of different rocks, it can be determinated that P formation is nearshore subsea fan sedimentary facies.

https://doi.org/10.3969/j.issn.1008-2336.2013.04.019