珠江口盆地白云凹陷沉降特征分析

Analysis of Subsidence Characteristics of Baiyun Sag,Pearl River Mouth Basin

白云凹陷位于南中国海北部珠江口盆地的深水区域,由多个洼陷组成。以白云西洼、白云主洼和白云东洼三个次级构造单元为研究重点。埋藏史恢复过程中,要进行地层压实回剥、海平面和古水深校正。在白云凹陷中选取有代表性的2口钻井和1口虚拟井,并对其进行埋藏史恢复,计算各井每个时期的沉降量和沉降速率。结果表明,白云西洼早中新世珠江晚期、白云主洼始新世文昌期、白云东洼渐新世珠海期沉降异常高。结合区域构造运动和沉积相资料,表明白云西洼珠江组上段发育海相陆架斜坡深水扇沉积,白云主洼文昌组发育河湖相三角洲、冲积扇,白云东洼珠海组发育浅水陆架三角洲相、滨岸相。

Baiyun Sag,located in the deep-water area of the Pearl River Mouth Basin in the northern part of South China Sea,consists of several sub-sags.This paper focused on three secondary-level structural units including the west sub-sag,the primary sub-sag and the east sub-sag.In the study of the burial history,the data,such as the compaction backstripping of stratum and the correction of ancient water depth and sea level were necessary.Out of the existing three drilling wells and seven virtual wells in Baiyun Sag,three wells representing each sub-sag were chosen to recover their burial histories and calculate their subsidence amounts and subsidence rates during each period of the structural evolution.The results show that the subsidence of the west sub-sag in the early Miocene late Zhujiang period,the subsidence of the primary sub-sag in the Eocene Wenchang period,and the subsidence of the east sub-sag in the Oligocene Zhuhai period are violent.Combined with regional tectonic movement and sedimentary facies data,the results also shows that the uppersegment of the Zhujiang formation developed marine shelf slope deep-water fans in the west sub-sag;the Wenchang formation developed fluvial lake delta and alluvial fan in the primary sub-sag;and the Zhuhai formation developed shallow shelf delta and shore fancies in the east sub-sag.