鄂尔多斯盆地上古生界山西组泥页岩地质特征与勘探对策

Geological characteristics and exploration countermeasures of the Upper Paleozoic Shanxi Formation mudstone/shale in Ordos Basin

借助X衍射分析、扫描探针显微镜、扫描电镜、高压压汞实验及页岩现场含气量测试等技术手段,并结合山西组泥岩沉积相、地球化学特征,研究了鄂尔多斯盆地山西组页岩地质特征和含气性特征。结果表明:鄂尔多斯盆地上古生界山西组海陆过渡相和陆相页岩单层厚度薄,泥页岩与煤层、砂岩互层分布;泥页岩分选较差,结构成熟度低,孔喉以纳米级孔喉为主,孔隙类型以无机质孔为主,有机质孔为辅;泥页岩的含气性主要受有机碳含量的影响,与美国巴尼特页岩和四川盆地龙马溪组海相页岩相比,鄂尔多斯盆地山西组泥页岩具有连续厚度小、有机碳含量低、脆性矿物含量低、改造难度大的特点,难以单独开采。建议在鄂尔多斯盆地山西组页岩气勘探开发中同时对泥页岩与邻层的致密细砂岩和粉砂岩进行综合评价,系统评价勘探潜力。

Combined with depositional facies and geochemical characteristics of the Upper Paleozoic Shanxi Formation mudstone in Ordos Basin,the sedimentary,reservoir and gas-bearing characteristics of the shale gas in Shanxi Formation was studied by means of technical measures such as x-ray diffraction,scanning probe microscopy,scanning electron micrograph (SEM),experiment of mercury injection at high pressure,and on-site measurement of gas content in the shale.The results show that the monolayered thickness of the marine-continental transitional facies and continental-facies shale of the Upper Paleozoic Shanxi Formation in the Ordos Basin is thin,and coal seams and/or sandstone are interbedded with the shale.The shale is poorly sorted.The structural maturity is low,and the pore-throats are nano scale-dominated.The pore types are with un-OM-hosted pores remaining dominant while OM-hosted pores as accessorial.The gas-bearing of the shale is mainly affected by the organic carbon content.Compared with the US Barnett shale and the marine shale of Longmaxi Formation in the Sichuan Basin,the shale of the Shanxi Formation in the Ordos Basin has the characteristics of small continuous thickness,low organic carbon content,low brittle mineral content,and being difficult to be stimulated.So it is difficult to be recovered separately.It is suggested that they need to conduct comprehensive evaluation and to systematically evaluate the exploration potential of the shale and the adjacent tight fine sandstone and siltstone layers simultaneously,during the exploration and development of the Shanxi Formationshale gas in the Ordos Basin.