鄂尔多斯盆地七里村油田延长组长62油层沉积相特征及沉积模式

本文通过钻井、测井资料及露头地质剖面研究,对鄂尔多斯盆地三叠系延长组长62油层沉积相进行了系统分析。研究表明,研究区目的层发育三角洲前缘亚相沉积,其不具备吉尔伯特式三角洲模式的顶积层、前积层、底积层三层结构。沉积结构上,三角洲单体厚度薄、分布广,具有"毯状"沉积结构、水下分流河道砂体优势发育等特征。沉积微相发育是以分流河道砂体为骨架,河口坝一般不发育,分流河道遭受不同程度的席状化改造。一方面,当河道入湖后迅速扩展,形成面状流向湖盆中央推进,后期河道扩展后对前期沉积物进行冲刷及改造;另一方面,湖水波浪改造使河口处形成的河口坝沉积物难以保存。沉积微相组合具有以水下分流河道优势发育,水下分流河道砂体与水下分流间湾微相互层发育等特征。研究区三角洲沉积受构造演化、气候、水平面变化及供给体系等因素控制。长62油层沉积时期地形平缓,沉降速率缓慢,气候温湿,当河道携带细粒沉积物进入湖盆时,河道迅速扩展,水流分散形成面状流并向湖盆中央推进,形成"毯式"结构。总体呈水下分流河道砂体与泥岩互层发育。

Sedimentary facies and sedimentary model for the Chang 62 oil measures of the Triassic Yanchang Formation in the Qilicun Oil Field, Ordos Basin

Sedimentary facies and sedimentary model are constructed according to well logs and section examination of the Chang-62 oil measures of the Triassic Yanchang Formation in the Qilicun Oil Field, Ordos Basin. The delta front subfacies deposits predominate in the target beds in the study area, and has the ＂blanket＂ structure instead of the three-layer structure of topsets, foresets and bottom sets indicated by the Gilbert-type delta model. Sedimentary microfacies consists of the subaqueous distributary channel and interdistributary bay microfacies in the delta front subfaeies. The controlling factors include tectonic evolution, palaeoclimates, lake-level changes and sediment supply systems. During the deposition of the Chang-62 oil measures of the Triassic Yanehang Formation, the broad channels facilitated the wide spreading of water-carried fine-grained sediments and progradation toward the center of the basin, and resulted in the formation of the ＂blanket＂ structure composed of the sandstone-mudstone couplets in the subaqueous distributary channel facies.