点物源扇三角洲的岩相与构型特征:以希里沟湖现代扇三角洲为例

Sedimentary facies and architecture of point-provenance fan deltas:A case study of modern lacus fan delta in the Xiligou Lake

扇三角洲沉积体具有良好的储集性能,是重要的油气储层。为了阐明扇三角洲储层的岩相与构型特征,定量表征构型单元的几何属性,明确构型分布规律,应用探地雷达技术和野外剖面观察技术,采用露头实测、精细构型解释等方法,对青海省乌兰县希里沟湖现代点物源扇三角洲进行了系统研究,共识别出16种岩相类型、8种垂向序列和8种构型单元。点物源扇三角洲主要发育主水道(MCH)、分支辫状水道(DCH)、片状洪流沉积(SF)、辫流坝(CB)、洪漫沉积(OF)、水下分流河道(UCH)、河口坝(RMB)以及间湾/席状砂(SS)共计8种典型构型单元,以分支辫状水道和辫流坝构型单元为主。分支辫状水道构型单元厚度1.5~2.0m,宽厚比30~70。辫流坝厚度2.0~3.0m,宽厚比50~70。同一沉积时期,点物源扇三角洲发育5种基本构型单元组合,分别为SF-MCH-SF、OF-DCH-CB-DCH-OF、SS-UCH-RMB-UCH-SS、SS-RMB-SS和SS-UCH-SS。不同沉积时期的构型单元分布表现为4种基本组合类型在横向上的重复和垂向上的叠加。

Fan delta deposits are important reservoirs for oil and gas.To illustrate the sedimentary facies and architecture of lacustrine fan delta deposits,we have quantitatively characterized the geometric attributes of different architecture units and clarified the regularity of their distribution.Based on detailed outcrop measurements and architecture interpretations using ground penetrating radar,we have recognized 16 sedimentary facies,eight vertical sequences,and eight architecture units,including main channel(MCH),distributary channel(DCH),sheet flood(SF),braided bar(CB),overbank flow(OF),subaqueous distributary(UCH),river mouth bar(RMB),and sheet sand(SS).The thickness of the distributary braided channels varies from 1.5 m to 2.0 m,with a width-to-thickness ratio of 30 to 70.The thickness of the braided bar varies from 2.0 m to 3.0 m,with a width-to-thickness ratio of 50 to 70.During the same sedimentary period,lacustrine fan delta developed five basic architectural unit combinations,namely,SF-MCH-SF,OF-DCH-CB-DCH-OF,SS-UCH-RMB-UCH-SS,SS-RMB-SS,and SS-UCH-SS.The distribution of architecture units in different depositional periods shows lateral repetition of the five basic combinations and vertical superposition.