北京地区中元古界下马岭组页岩气形成条件

Forming Conditions and Characteristics of the Shale Gas within the Mesoproterozoic Xiamaling Formation,Beijing Area

以野外露头与地热井的岩屑样品为基础,以岩石学、有机地球化学和储层物性实验测试分析为手段,对北京地区中元古界下马岭组页岩进行了页岩气形成条件研究。结果表明,中元古界下马岭组页岩分布广泛,沉积厚度大,有机碳含量高,有机质类型好,以Ⅱ型为主、兼有少量的Ⅰ型,具有良好的页岩气形成条件。中元古界下马岭组页岩矿物组成主要为石英和黏土矿物,石英平均质量分数为60%,黏土矿物平均质量分数为31.5%,黏土矿物中伊利石含量最高,占黏土矿物总组成的77.54%;页岩中微孔隙与微裂缝发育,具备良好的页岩气赋存条件,等温吸附实验也证明了这一点。北京地区经历了多期构造变动,但页岩气藏具有较强的抗构造破坏能力,使得研究区具有较好的页岩气保存条件。总体认为北京地区中元古界下马岭组是较理想的页岩气勘探目的层系。

On the basis of field outcrops and geothermal well samples, this paper studies the forming condi- tions and characteristics of the shale gas within the Mesoproterozoic Xiamaling Formation shale by means of the petrology, organic geochemistry and physical properties of reservoir. The shale is widely distributed with great thickness, high total organic carbon content, and good organic types which is dominated by type Ⅱ and slightly type Ⅰ, and high organic thermal evolution degree, which offers sufficient conditions for shale gas formation. The shale is mainly composed of quartz and clay minerals. The average contents of quartz and clay minerals are 60% and 31.5% respectively. Illite is the most dominant constituent of the clay minerals with an averaging content of 77.54%. Large quantity of micropores and microfractures developed in the shale, which is available for shale gas accumulation. The isothermal adsorption test showed that the shale has strong potential of gas adsorption. Although there were many tectonic movements after the deposition of the Xia- maling Formation, shale gas has strong resistance from being destroyed. We think that the shale within the Meso- proterozoic Xiamahng Formation in Beiiing area is a good exploration formation.