鄂尔多斯盆地延长探区陆相页岩气储层特征

Characteristics of terrestrial shale gas reservoir in Yanchang exploration area of Ordos basin

结合我国陆相页岩分布特征,以鄂尔多斯盆地延长探区为例,对钻孔岩心样品进行有机地球化学、X射线衍射、孔隙度测定、扫描电镜、气体吸附等多种实验分析,研究陆相页岩气储层特征。结果表明,延长探区延长组陆相页岩厚度较大(平均50 m),有机质丰度高(平均TOC为4.86%),有机质类型主要为Ⅱ型,热演化程度处于成熟阶段(Rran为0.84%~1.10%);页岩中黏土矿物质量分数高(21.8%~71.5%,平均47.3%),石英质量分数较低(10.8%~44.9%,平均22.3%),脆性指数相对较小(27.1%~77.2%,平均49.6%),表明页岩储层具有脆性和可压裂性;延长组页岩孔隙度主要分布在1%~3%,孔隙类型多样,以粒间孔和粒内孔为主,其次是晶间孔、微裂缝、溶蚀孔和有机质孔,为页岩气赋存提供了储集空间;延长组页岩总含气量为1.60~6.67 m3/t,显示出较好的含气性。

Taking Yanchang Formation in Yanchang exploration area as an example and combining with the distribution characteristics of continental shale in China, the authors investigated the accumulation conditions and the reservoir characteristics of continental shale gas using many experimental methods, such as organic geochemical analyses, X-ray diffraction（XRD）, determination of porosity, scanning electron microscope（SEM）, gas adsorption, etc. The results show that the thickness of Yanchang Formation shale in Yanchang exploration area is large（average 50 m）, the organic carbon content is relatively high（average TOC is 4.86%）, the main types of organic matter are typeⅡ, and the thermal evolution degree of organic matter is of the mature stage（Rran=0.84%-1.1%）; the mass fraction of clay minerals is high（21.8%-71.5%, average 47.3%）, and the mass fraction of quartz is low（10.8%-44.9%, average 22.3%）, brittleness index is relatively small（27.1%-77.2%, average 49.6%）, indicating that the shale reservoir is brittle and can be fractured. The porosity of Yanchang Formation shale in Yanchang exploration area is mainly between 1%-3%, and the pore types are diversiform. The intergranular pores and the inner pores are dominant, followed by intergranular pores, microcracks, dissolved pores and the organic pores, which provide reservoir space for the accumulation of shale gas. The gas content of Yanchang Formation shale is between 1.60-6.67 m^3/t, showing a better gas generation capability.