The irreducible water saturation (S_wir) is a significant parameter for relative permeability prediction and initial hydrocarbon reserves estimation. However, the complex pore structures of the tight rocks and multiple factors of the formation conditions make the parameter difficult to be accurately predicted by the conventional methods in tight gas reservoirs. In this study, a new model was derived to calculate S_wir based on the capillary model and the fractal theory. The model incorporated different types of immobile water and considered the stress effect. The dead or stationary water (DSW) was considered in this model, which described the phenomena of water trapped in the dead-end pores due to detour flow and complex pore structures. The water film, stress effect and formation temperature were also considered in the proposed model. The results calculated by the proposed model are in a good agreement with the experimental data. This proves that for tight sandstone gas reservoirs the S_wir calculated from the new model is more accurate. The irreducible water saturation calculated from the new model reveals that S_wir is controlled by the critical capillary radius, DSW coefficient, effective stress and formation temperature.

中文翻译：

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致密气藏中不可还原水饱和度预测的新模型

不可减水饱和度（S _wir）是相对渗透率预测和初始油气储量估算的重要参数。然而，致密气藏的复杂孔隙结构和形成条件的多种因素使得致密气藏难以通过常规方法准确预测该参数。在这项研究中，导出了一个新模型来计算 S _wir 基于毛细模型和分形理论 该模型结合了不同类型的固定水并考虑了应力效应。在该模型中考虑了死水或固定水（DSW），该水描述了由于tour回流动和复杂的孔结构而在死角孔中捕获水的现象。在模型中还考虑了水膜，应力效应和地层温度。提出的模型计算结果与实验数据吻合良好。这证明了对于致密砂岩气藏而言，根据新模型计算出的S _wir更为准确。根据新模型计算得出的不可约水饱和度表明，S _wir 由临界毛细管半径，DSW系数，有效应力和地层温度控制。