鄂尔多斯盆地东部石炭系本溪组页岩气地质特征及富集规律

鄂尔多斯盆地东部石炭系本溪组广泛发育富有机质泥页岩，具有良好的资源勘探前景。通过对本溪组泥页岩的有机地球化学特征、孔隙分布特征、含气性等一系列页岩气成藏条件研究，查明了本溪组页岩气地质特征及成藏富集规律，提出晋祠段富有机质泥页岩为本溪组页岩气有利层段，具有四大地质特征：①有机质含量高（平均TOC值为3.06%），且普遍处于成熟—高成熟阶段（R_O值平均为1.84%），有机质类型主要为Ⅲ型，生气能力强；②发育微纳米级孔缝，以无机孔为主，部分有机质发育有机质孔，微孔和介孔为页岩气提供了主要的赋存空间，平均孔体积为0.024 m³/g，平均比表面积为11.05 m²/g，具备较好的储集能力，页岩气主要以吸附态存在于孔隙之中，其中压力和有机碳含量是影响泥页岩吸附气含量的重要因素；③硅质页岩段脆性矿物含量较高，大于40%，表明储层的可压性较大，有利于后期的压裂开采；④具有理想的成藏组合特征，以8^#、9^#煤层分别为顶、底板，煤层与泥页岩间较大的烃浓度差提供了良好的保存条件，2套煤层之间发育炭质页岩和硅质页岩，高TOC的炭质页岩与煤层含气性较好，紧邻9^#煤层的硅质页岩层段压裂开采中容易产生裂缝，为相邻煤系气的补充提供了一定的运移通道。结合地质特征总结出本溪组成藏富集规律：潟湖相沉积环境控烃、页岩孔隙发育控储、成藏有利组合控富以及硅质页岩可压裂性控产。研究结果为鄂尔多斯盆地本溪组页岩气有利区的确定和下一步勘探开发提供有益参考。

Study on geological characteristics and enrichment law of shale gas of Carboniferous Benxi Formation in eastern Ordos Basin

Organic-rich shale is widely developed in Carboniferous Benxi Formation in Ordos Basin, which has a good resource exploration prospect. Based on a series of studies on the organic geochemical characteristics, pore distribution characteristics and gas-bearing properties of shale in the Benxi Formation, the geological characteristics and accumulation laws of shale gas in the Benxi Formation were revealed. Jinci Member is the favorable zone in the Benxi Formation, with the following four geological characteristics: (1) the shale is characterized by high organic matter abundance (average TOC is 3.06%) and high thermal maturity (average R_O is 1.84%) , its kerogen belongs to type Ⅲ; (2) micro and nanoscale pores are mainly inorganic pores, with a little organic pores, the micropores and mesoporous pores provide the main storage space, the average pore volume is 0.024 m³/g, and the average specific surface area is 11.05 m²/g. Shale gas mainly exists as adsorbed gas, and the pressure and TOC are important factors affecting the adsorbed gas volume; (3) brittle mineral content of siliceous shale is higher than 40%, indicating that the reservoir is more compressible; (4) the ideal combination accumulation characteristics provide a good preservation condition. Carbonaceous shale and siliceous shale developed between the two sets of coal, the former has good gas-bearing property, and the latter is easy to be fractured. The rules of accumulation and enrichment are summarized: Lagoon facies controls the development of source rocks; pores control the storage; favorable combination controls the accumulation and the fracturing ability of siliceous shale controls the exploration of shale gas. The results can provide a useful reference for determining favorable shale gas areas and further exploration and development of the Benxi Formation in Ordos Basin.