Abstract:

Due to intense tectonic compression,the massive sandstone of the Bashijiqike Formation in the Cretaceous within the piedmont belt of the Kuqa Depression exhibit severe deformation,complex seismic imaging,and high ambiguity,resulting in limited methods and even fewer achievements in the detailed study of provenance transport pathway in the Keshen natural gas accumulation area. In response to this issue,a comprehensive study was conducted on the heavy mineral assemblages of over 400 sandstone samples from more than 40 wells in the Bashijiqike Formation of the Keshen area,as well as experimental analyses including sandstone clastic components and cathodoluminescence on over 600 samples from 26 wells. The results show that: (1)Zircon,tourmaline,garnet,and magnetite are consistently present as heavy minerals in the wells of this area. The presence and variations in the content of stable heavy minerals such as rutile,apatite,and titanite,along with unstable heavy minerals like epidote,chlorite,and mica,lead to differences in heavy mineral assemblages across well zones. Combined with the ZTR index,these variations can help determine the differences in sedimentary provenance pathways among the well zones. (2)The sedimentary source rocks of the thick sandstone mainly come from pre Carboniferous high-grade metamorphic rocks,low-grade metamorphic rocks,intermediate acidic igneous rocks,basic igneous rocks,and sedimentary rocks,which can be subdivided into nine heavy mineral combination zones from east to west. (3)Due to the control of the content of sandstone debris components by primitive sedimentation,the planar variation characteristics of the average content of potassium feldspar,plagioclase,and metamorphic rock debris in sandstone debris components indicate the existence of 5-7 source transport pathways. (4)Based on a comprehensive analysis of the characteristics of source pathways indicated by heavy mineral assemblages and sandstone debris components,it is believed that there were at least seven source transport pathways from east to west during the sedimentation period of the Bashijiqike Formation,among which Zone Ⅱ and Zone Ⅴ may have been channels with longer river extensions. The above understanding provides a basis for the analysis of large-scale sedimentary microfacies and favorable sand body distribution in the Keshen area,supporting the fine research and evaluation of gas reservoirs in this area.

Key words: Kuqa Depression, Keshen area, deep thick sandstone, heavy mineral assemblage, sandstone detrital component, provenance transport pathway

摘要：

由于受强烈构造挤压作用,库车坳陷山前带白垩系巴什基奇克组巨厚砂岩变形强烈、地震成像复杂且多解性强,导致克深天然气富集区沉积物源通道精细研究的方法少、成果更少。针对此问题,开展了克深地区巴什基奇克组40余口钻井400多块砂岩样品的重矿物组合分析,26口钻井600余块样品的砂岩碎屑组分与阴极发光等实验分析,结果表明: (1)该区各井中锆石、电气石、石榴子石、磁铁矿等重矿物稳定存在,金红石、磷灰石、榍石等稳定重矿物与绿帘石、绿泥石、云母等不稳定重矿物是否存在及含量的差异导致各井区重矿物组合不同,辅以ZTR指数大小可判断各井区物源输送通道的差异; (2)巨厚砂岩的沉积物源母岩主要来自于前石炭系高级变质岩、低级变质岩、中酸性火成岩、基性火成岩与沉积岩,自东向西可细分为9个重矿物组合区; (3)由于砂岩碎屑组分的含量受原始沉积作用控制,砂岩碎屑组分中钾长石、斜长石及变质岩岩屑平均含量平面变化特征显示存在5~7个物源输送通道; (4)综合分析重矿物组合与砂岩碎屑组分分别指示的物源通道特征,认为巴什基奇克组沉积时期自东向西至少存在7条物源输送通道,其中Ⅱ区和Ⅴ区可能是河道延伸较远的通道。以上认识为克深地区大比例尺沉积微相及有利砂体展布分析提供依据,支撑了该区气藏精细研究与评价。

关键词: 库车坳陷, 克深地区, 深层厚层砂岩, 重矿物组合, 砂岩碎屑组分, 物源输送通道

CLC Number: 

• P588.21