鄂尔多斯盆地东部大面积致密碳酸盐岩气地质特征及成藏条件分析

Geological characteristics and reservoir forming conditions of large area tight carbonate gas in eastern Ordos Basin,China

基于非常规气理念,以鄂尔多斯盆地东部奥陶系马家沟组马五_(1+2)亚段碳酸盐岩储层为例,采用露头、岩心、铸体薄片、孔隙度、渗透率、同位素和试气成果资料综合分析的方法,重新认识和评价其含气潜力。结果表明,储层以泥粉晶—粗粉晶白云岩为主,渗透率小于0.1×10^(-3)μm^2的储层占80%以上,孔隙类型主要为裂缝—溶孔、裂缝—晶间孔,非均质性强,属于致密碳酸盐岩储层。气藏具有低丰度大面积分布、异常低压、无边底水、无自然产能、产水少等特点,属于碳酸盐岩致密气藏。天然气分布主要受控于大范围稳定分布的特殊的镶嵌式源储组合和平缓的单斜构造背景,勘探潜力较大,是海相碳酸盐岩天然气勘探的一种新类型。

Based on the concept of unconventional gas,a case study was performed on the Ordovieian Majiagou Formation M51＋a carbonate reservoir in the eastern Ordos Basin.According to the comprehensive analysis of outcrop, core, casting thin sections, porosity, permeability, isotope, test analysis results of gas, the gas potential was evaluated, Results show,the reservoir is dominated by mud powder and coarse powder dolomite;Reservoirs with permeability less than 0.1 × 10^-3μm^2 account for more than 80% ;The pore types are mainly composed of fracture-dissolution pore and the fracture-intergranular pore; Strong heterogeneity, which belong to tight carbonate reservoir, gas reservoir has the characteristics of low abundance and wide distribution, subnormal pressure, no border and bottom water, low natural production ; Produce less water, which belong to tight carbonate gas reservoir.The distribution of natural gas is mainly controlled by a wide range of stable distribution of special mosaic type source reservoir combination and gentle slope structure background.It is expected to have great exploration potential and will be a new type of marine carbonate exploration.