鄂尔多斯盆地上三叠统延长组长7油层组沉积相分析

SEDIMENTARY FACIES ANALYSIS OF THE CHANG 7 MEMBER OF THE UPPER TRIASSIC YANCHANG FORMATION IN THE ORDOS BASIN, NW CHINA

本文为精细刻画鄂尔多斯盆地上三叠统延长组长7油层组沉积相类型及分布特征,开展了详细的野外露头剖面、岩芯岩性观察、古水流方向实测、重矿物分析、岩石薄片分析和测井岩电关系分析。研究表明:①受NE(东北)、NW(西北)、SW(西南)和S(南)四大方向的物源供给,鄂尔多斯盆地长7油层组划分为Ⅰ区(东北部)、Ⅱ区(西北部)、Ⅲ区(西南部)、Ⅳ区(南部)和Ⅴ区(中部)五个物源沉积区;②长7油层组沉积相、亚相和微相分别划分为3类、5类和15类,其中曲流河三角洲相主要位于盆地东北、西北地区,辫状河三角洲相主要位于盆地西南、南部地区,湖泊相主要位于盆地中部地区;③长7油层组总体为一套"湖退进积"沉积,砂质碎屑流微相和浊积岩微相砂体在中部湖泊相十分发育。上述研究对鄂尔多斯盆地长7油层组页岩油的勘探与开发具有参考意义。

This paper focuses on the type and distribution of sedimentary facies of the Chang 7 Member of the Upper Triassic Yanchang Formation in Ordos Basin, NW China. In order to gain a detailed understanding of this issue, the authors made a detailed lithological observation of the outcrops and drilling cores, a heavy minerals analysis of sandstones from boreholes, a thin section analysis of rocks from outcrops and boreholes and a log rock-electricity relationship analysis, combined with measurements of the paleocurrent direction on typical outcrops. The results show that: 1) the Chang 7 Member had a sediment source derived from the northeast, northwest, southwest and south, respectively, of this basin, and accordingly can be divided into five depositional areas including Area Ⅰ(in the northeast of the Ordos Basin), Area Ⅱ(in the northwest), Area Ⅲ(in the southwest), Area Ⅳ(in the south) and Area Ⅴ(in the middle);2) three types of sedimentary facies are recognized from the Chang 7 Member including the meandering river delta facies developed in the northeast and northwest of the basin, the braided river delta facies in the southwest and south, and the lacustrine facies in the middle, and they can be further divided into five types of subfacies and fifteen types of microfacies;3) and the Chang 7 Member was generally deposited during the paleolake regression, with sandy debris-flow and turbidite sandstone bodies well developed in the lacustrine facies in the middle of the basin. The above results will be valuable for the further exploration and development of shale oil from the Chang 7 Member in the Ordos Basin.