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

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.