鄂尔多斯盆地致密砂岩气储层饱和度测井评价方法

Saturation log evaluation method in the Ordos Basin tight sandstone gas reservoir

以鄂尔多斯盆地某区域石盒子组致密砂岩气储层为例,研究了其饱和度测井评价方法。宏观上基于岩屑石英砂岩及岩屑砂岩,微观上基于残余粒间孔及溶蚀-粒间孔,结合岩样薄片显微分析资料、岩电试验资料以及网络模型数值模拟结果,分析获得致密气储层的导电规律:地层因素F、孔隙度φ与电阻率指数I、含水饱和度Sw的关系由于岩性及孔隙类型的不同而存在差异,岩屑砂岩因其岩屑成分及孔隙类型的复杂性,增加了岩石的导电难度,在同等条件下,地层因素及电阻率指数均高于岩屑石英砂岩;电阻率指数与含水饱和度呈现指数关系,而非Archie模型的乘幂关系。在此基础上,分类型建立了可变胶结指数(m)的改进Archie模型,并应用于石盒子组致密气储层饱和度测井评价,结果显示饱和度计算值的绝对误差小于5%,验证了该测井评价方法的实用性。

As a saturation logging evaluation problem, the conductance mechanism is studied with a tight gas reservoir in the Shihezi formation in Ordos Basin as an example, based macroscopically on the lithic quartz sandstone and the lithic sandstone, microscopically on the remnant intergranular pore and the corrosion intergranular pore, and combined with the thin section analysis data and the litho-electric experiment data. The relationships between the formation factor（F） and the porosity（~p）, the resistivity index（I） and the water saturation （Sw） are affected by the lithology and the pore type. The conductance of the lithic sandstone is decreased because of the complexity of the mineral and pore type. Under the same condition, the formation factor and the resistivity index of the lithic sandstone are greater than those of the lithic quartz sandstone. The relationship between the resistivity index and the water saturation is exponential rather than as a specific power relation based on the numerical simulation of the network model. On the basis of the conductance mechanism, a modified Archie model of changeable cementation index is built for different lithologies and pore types. Applying the saturation model to this area, its practicability is confirmed.