基于动态物源演变的“源-汇”分析——以琼东南盆地松南地区陵水组为例

Source-sink analysis based on dynamic provenance evolution:taking Lingshui Formation in Songnan area of Qiongdongnan Basin as an example

琼东南盆地作为中国重点含油气盆地,其勘探重点逐渐向盆内深水区拓展。作为盆内重要物源的松南地区,其构造地貌存在典型的坡控特点,与盆缘断控地区具有明显差异。海平面的周期性旋回变化,致使油气勘探过程中可能忽视早期局部物源存在,制约了松南地区规模性储集体的寻找工作。本文以物源的动态演化为核心,认为松南地区主要发育“动态多期型”和“动态淹没型”2大动态物源体系。前者在陵水组沉积时期实际成扇的有效供源面积呈递减趋势,于陵三段低位期、高位期及陵二段低位期形成近源扇三角洲沉积;后者在陵三段低位域时期存在规模性局部物源,发育扇三角洲沉积体系。松南地区动态物源体系受海平面旋回变化与构造地貌共同影响,隆起区整体呈现“早期供源成扇,晚期作为水下隆起控坝”的沉积规律。对动态物源体系“源-汇”要素的定量分析显示,源区规模、渠道深度及古水系组合样式是松南地区动态物源体系砂体沉积的主控因素,即低水位期规模性物源、高陡地形强下切沟道、平缓背景下多级复合古水系,有利于汇水区规模性扇体发育。

Qiongdongnan Basin,a key oil-bearing basin in China,has been gradually expanded the exploration to the deep-water area.The Songnan area,an important provenance in the basin,has typical slope control characteristics in tectonic geomorphology,which is obviously different from the basin margin fault-control area.Due to the sea level fluctuation,the existence of early local provenance was often neglected during oil and gas exploration,which restricts the search for large-scale reservoir in the Songnan area.Based on the dynamic evolution of provenance,we found that two dynamic provenance systems,“dynamic multi-phase type”and“dynamic submergence type”,were mainly developed in the area.During the deposition period of Lingshui Formation(LF)(Oligocene),the effective material supply area of actual fan decreased,and the near-source fan delta deposition was formed in the low and high stages of the third member of LF and the low stage of the second member of LF.The latter had large-scale local provenance with well-developed fan delta sedimentary system in the lower area of the third member of LF.The dynamic provenance system in the Songnan area was influenced by the sea level fluctuation and paleo-geomorphology.The uplift area as a whole evolved from a material supply source forming fans in early period,to an underwater high as a dam in late period.Quantitative analysis on the source-sink components of the dynamic provenance system showed that the size of the source area,the depth of the channel,and their combination pattern were the main controlling factors of sand body formation in the dynamic provenance system in the Songnan area.Therefore,the large-scale provenance in low water level period,the strong downcut channel in the high and steep terrain,and the multiclass complex water system in a gentle terrain background are conducive to the large-scale fan development in the catchment of the study area.