用J函数提高致密砂岩气层饱和度测井评价精度

低孔渗致密砂岩储层具有孔隙度小、孔隙结构复杂,泥质含量高、束缚水饱和度大等特点。该类储层阿尔奇岩电参数m、n值变化大,电阻率与流体关系复杂,很难用电阻率测井资料据阿尔奇公式求准含气饱和度。通过对致密储层岩样毛管压力曲线形态分类,统计不同毛管压力曲线形态类型的物性特征,最终按孔隙度范围分类建立J函数与饱和度的统计关系。实际应用结果表明,该方法与阿尔奇变m指数法相比计算精度可提高1倍,与孔渗指数方法相比精度也显著提高,且能反映气水界面附近饱和度的变化趋势;为准确求取低孔渗储层饱和度提供了切实可行的测井评价方法,克服了低孔渗储层难以求准饱和度的技术难题。

Improving well log evaluation accuracy of tight sandstone gas saturation using J function

The low porosity and low permeability tight sandstone reservoirs are usually characterized as developed small pores, complex pore structures, high shale content and high bound water saturation. The m and n values of the Archie rock electrical parameters can vary significantly and the relationship between resistivity and fluid is complex of this type of reservoirs, resulting in difficulties in getting accurate gas saturation values when applying the Archie formula to resistivity logging data. The physical properties of different types of capillary pressure curve shapes are obtained by classifying the capillary pressure curve shapes of different rock samples. According to the classification and its porosity range, the statistical relation between the J function and sample saturation is established. The application of the relationship on real samples shows that the spread of the calculated saturation can be improved greatly and is nearly half of that of the "variable m rock electrical parameter" Archie method. This new method is also better than "permeability/porosity ratio parameter" method, and has the ability to show the saturation changing trend near the gas-water interface. The new method is feasible and can give accuracy saturation estimates for low porosity and low permeability tight sandstone reservoirs.