柴达木盆地西部地区古近系下干柴沟组咸化湖相泥页岩储集层特征

Reservoir characteristics of salt-water lacustrine shale of the Paleogene Xiaganchaigou Formation in western Qaidam Basin

中国已获得湖相页岩气勘探开发的重要突破，但对于咸化湖盆环境泥页岩储集层特征的研究较少。作者对柴达木盆地西部地区古近系下干柴沟组湖相泥页岩储集层开展有机地化、岩矿组成、储集层孔隙结构等特征的研究。（1）研究区泥页岩有机质丰度在0.12％～1.35％之间，具有强烈的非均质性，有机质类型以Ⅱ型为主，氯仿沥青“A”含量较高。（2）泥页岩中碳酸盐岩矿物含量最高，平均27.8％，黏土矿物和石英含量次之，有38.2％的样品检测出硬石膏，反映典型的咸化环境特征。（3）扫描电镜观察有机质孔隙发育较少，形状不规则且孔径较大，粒（晶）间孔隙直径多以微米级为主，微裂缝宽多小于1μm；低温气体吸附测试显示，中孔提供了主要的孔比表面积和孔隙体积，氯仿沥青“A”的存在对样品孔隙结构产生影响。（4）研究区泥页岩储集层中黏土矿物含量低而脆性矿物含量高，与北美页岩气产层及四川盆地龙马溪组页岩储集层岩矿特征类似，易于产生裂缝，有利于页岩气的后期开采。

Great breakthrough has been made in the exploration of lacustrine shale gas in China,but little research on reservoir of salt-water lacustrine shale was carried out.Organic geochemical analysis, mineral composition analysis and pore structure analysis of reservoir of the Palaeogene Xiaganchaigou For-mation lacustrine shale in western Qaidam Basin has been done by the authors.（1 ） The organic content has intense heterogeneity in the 0.1 2%~1 .35% range,the content of chloroform bitumen “A” is high and the organic matter is mainly of type Ⅱ.（2） The content of carbonate is the highest with an average of 27.8%,and then clay minerals and quartz.There are 38.2% of the samples have anhydrite,which re-flects the typical salt-water lacustrine environments.（3）The organic matter micro-pores observed in the SEM are less developed,the shape is irregular and pore size is large.Intergranular pores are mainly mi-cronl-sized in diameter,while micro-fractures are mainly less than 1 μm in width.Mesopores have most of specific surface area and pore volume of shale pores,and are main places for gas adsorption and storage. The chloroform bitumen “A” influenced the pore structure of the samples.（4） The content of clay min-erals is low and brittle minerals is high in research area,which is comparable with the series of gas-contai-ning shales in U.S.and with the Lower Paleozoic shale in the Sichuan Basin,are conducive to creating cracks,and are easy for fracturing.