柴达木盆地干柴沟地区古近系下干柴沟组上段页岩层系优势岩相及其控储因素

Dominant lithofacies and factors controlling reservoir formation of the shale sequence in the upper member of the Paleogene Lower Ganchaigou Formation， Ganchaigou area， Qaidam Basin

张洪 冯有良 刘畅 杨智 伍坤宇 龙国徽 姚健欢 孟博文 邢浩婷 蒋文琦 王小妮 魏琪钊

Hong ZHANG Youliang FENG Chang LIU Zhi YANG Kunyu WU Guohui LONG Jianhuan YAO Bowen MENG Haoting XING Wenqi JIANG Xiaoni WANG Qizhao WEI

柴达木盆地干柴沟地区页岩油勘探近年获得重要突破，研究高原咸化湖盆岩相与储层特征对甜点识别具有重要意义。通过岩心和薄片观察、全岩矿物组成和原位微量元素分布测试、大面积视域扫描拼接成像、高压压汞与氮气吸附实验以及一维核磁共振分析，判识了岩相类型，系统研究了页岩储集性和含油性差异，提出了优势岩相和控储主因。研究结果表明：研究区储层有块状灰云岩（碳酸盐矿物含量>70 %）、层状灰云岩（碳酸盐矿物含量50 % ~ 70 %）、纹层状混积岩（碳酸盐矿物含量10 % ~ 50 %）和断续状水平层理混积岩（碳酸盐矿物含量10 % ~ 50 %）4种岩相。块状灰云岩和层状灰云岩孔隙以晶间孔为主，储集空间大且连通性好，孔隙中含油指数高，为优势岩相；纹层状混积岩基质孔隙发育较差，纹层密集发育的混积岩渗透性较好；断续状水平层理混积岩孔、缝不发育，储集性较差。优势岩相成储过程受3方面因素控制：①碳酸盐矿物组构决定宏孔发育程度；②陆源长英质细粒沉积物和黏土矿物含量控制比表面吸附性；③纹层发育程度最终改善储层渗透性能。

In recent years， major breakthroughs in shale oil exploration have been achieved in the Ganchaigou area of the Qaidam Basin， highlighting the significance of investigating the lithofacies and reservoir characteristics of the plateau saline lacustrine basin for sweet spot identification. Focusing on shale oil reservoirs in the Ganchaigou area， we identify the lithofacies types and systematically examine the differences in the reservoir and oil-bearing properties of shales with varying lithofacies. Furthermore， we determine dominant lithofacies and primary factors controlling the reservoir formation. The methods employed in this study include core and thin section identification， whole-rock mineralogy and in-situ trace-element distribution testing， large-field splicing scanning electron microscopy （MAPS）， high pressure mercury injection （HPMI） and nitrogen adsorption experiments， along with one-dimensional nuclear magnetic resonance （NMR） measurements. The results indicate that the reservoirs in the study area exhibit four lithofacies： massive limy dolomite （carbonate mineral content： above 70 %）， laminated limy dolomite （carbonate mineral content： 50 %-70 %）， lamellar mixed siliciclastic-carbonate rock （carbonate mineral content： 10 %-50 %）， and mixed siliciclastic-carbonate rock with intermittent horizontal beddings （carbonate mineral content： 10 %-50 %）. The massive and laminated limy dolomites， among others， exhibit the predominance of intercrystalline pores， large reservoir spaces with high connectivity， and pores with large oil saturation index （）， thus serving as dominant lithofacies； The lamellar mixed siliciclastic-carbonate rock manifest poorly developed matrix pores but high permeability due to intensively developed laminae； The mixed siliciclastic-carbonate rock with intermittent horizontal beddings， lacking pores and fractures， display poor reservoir properties. The reservoir formation process of the dominant lithofacies is governed by three factors： （1） carbonate fabrics， which determine the degree of macropore development； （2） the contents of terrigenous felsic fine-grained sediments and clay minerals， which dictate the specific surface adsorptivity； and （3） the developmental degree of laminae， which can ultimately enhance the reservoir permeability.

10.11743/ogg20240508