阿克库勒地区三叠系层序地层学及储集砂体成因类型

Sequence Stratigraphy and Sandbody Genetic Types of Triassic System in Akekule Area

通过钻测井资料、地震资料的地质综合研究,以及地面露头观察与实验分析,研究区内三叠纪反映湖平面变化的地层旋回性非常清楚。按层序划分的基本原则,在三叠纪地层中可识别出7个Ⅰ型层序边界,相应地划分出6个Ⅰ型层序。总体来说,在层序内部,低位体系域发育,它们构成了区内储集砂体的主体;而高位及湖侵体系域往往被上覆层序侵蚀,甚至剥缺。储集砂体的分布受层序格架的严格控制,主要储集砂体的成因类型包括低位早期的湖底扇沉积、低位晚期侵蚀沟谷的河流充填与滨湖沉积,以及高位期三角洲及滨湖滩、坝沉积。区域盆地格架研究表明,研究区三叠纪时期是位于库车前陆盆地系统的前隆及前隆后缘盆地的边缘,因此,湖平面相对升降变化导致了区内十分明显的地层旋回,这种旋回性直接控制了砂体的成因类型及其分布规律。

Based on comprehensive geological analysis of log data and seismic data, integrated with outcrop observation and experimental analysis, stratigraphic cyclicity reflecting lake level change of Triassic Period in the studied area is very clear. According to the dividing criterion of sequence, seven type I sequence boundaries could be identified, and six type I sequences are divided correspondingly. Generally, Lowstand Systems Tracts （LST） are well developed, and they constitute the main reservoir sandstone bodies of the studied area. Whereas, the sandstones of highstand System Tracts （HST） and Transgressive Systems Tracts （TST） are eroded, or sometimes lost. The distribution of reservoir is strictly controlled by sequence framework. The genetic types of sandstone bodies have sublacustrine-fan deposit during early stage of LST, fluvial deposit in eroded valley and shore lake deposit during later stage of LST, and delta deposit, beach and dam deposition of shore lake during HST. The study of regional basin framework has demonstrated that the studied area lied on fore-upfold and back-edge basin edge of Kuche foreland system during Triassic Period. So the relative change of lacustrine level result in prominent stratigraphic cyclicity which control sandstone body type and distribution.