南沙海域方安盆地地震相解释及沉积相分析

SEISMIC FACIES INTERPRETATION AND SEDIMENTAL FACIES ANALYSIS OF WAN'AN BASIN, SOUTH CHINA SEA

本文按地震地层学原理，利用万安盆地大量的地震反射剖面，对其地震相特征作了综合解释。在此基础上，结合前人工作成果和少量钻井资料，分析了三个勘探目的层（Ｅ２＾３（？）－Ｅ３，Ｎ１＾１－Ｎ１＾２，Ｎ１＾３）的沉积特征，进而推测沉积相对油气分布的控制。

Several thousand kilometers of continuous seismic profiles have shown that there are over ten thousands thick clastic sediments and limestones deposited in Wan'an Basin since late Eocene. The features of the seismic facies and the sedimental facies of the three explorat- ing target strata (E_2~3-E_3,N_1 ~1-N_1~2,N_1~3) have been interpreted and analysed in this paper based on the seismic stratigraphy principle. 1. During Paleogene, the deposition of this basin was characterized by fluvial-lacustrine depositional system. The gradation of sedimental facies from west to east are plain-fluvial fa- cies and shoreface lacustrine-swamp, littoral-neritic marine facies, etc. The shoreface lacus- trine-swamp facies occupies greater part of the basin. 2. In early-mid Miocene, a lot of clastic materials transfered from northwesten area de- posit in the west and center parts of this basin, forming some larger delta system; foresets of which are coastal depositional system. The eastern shelf deposition spread gradually towards western area. 3. Since mid-Miocene, the carbonate platforms and reefs thrived at the basin's southern area in an environment of clean and shallow water and warm climate. In late Miocene, the sedimentation of the carbonate platforms and reefs ceased, but at the same time, shelf de- posits spread westward and the slop-bathyal deposition came to sediment because of the sub- sidence of the basin's eastern area in this basin.