合川地区低孔低渗砂岩储层含水饱和度的评价方法

Evaluation methods for water saturation of low porosity and low permeability sandstone reservoirs in the Hechuan area,middle Sichuan Basin

合川地区上三叠统须家河组二段气藏属低孔低渗气藏,其储层孔喉结构复杂,造成了含水饱和度计算不准的问题。为此,研究了储层岩性、物性、孔喉结构和地层水特征对含水饱和度的影响,认为储层特征致使含水饱和度复杂多变,增加了储层含水饱和度的定量评价难度;以测井地质应用技术为指导,用核磁共振测井资料检验所求取的含水饱和度精度,探讨了Archie公式、Simandoux公式和印度尼西亚公式所建立的3种含水饱和度模型在合川地区复杂地质条件下的应用效果和影响因素。实践表明:Simandoux公式的解释结果与核磁测井含水饱和度值误差在-6.1%～2.6%,更加适合于研究区复杂地质条件下泥质砂岩含水饱和度的求取,为该区低孔低渗砂岩气藏勘探开发提供了技术支持;在没有适合于所有储层的含水饱和度模型情况下,油气田勘探开发时尽可能结合油气藏的储层特征多选用几种含水饱和度模型进行试算与分析,然后选取其中最适合的来应用。

Gas reservoirs in the second member of the Upper Triassic Xujiahe Formation in the Hechuan area are characterized by low porosity,low permeability,and complex pore throat structures,which results in the inaccuracy of water saturation calculation.The impacts of lithology,petrophysical properties,pore throat structures,and formation water properties on water saturation are studied in this paper.It is believed that reservoir features can cause large complexity and variability of water saturation,making it difficult to quantitatively evaluate reservoir water saturation.Three water saturation models are built by using the Archie,Simandoux and Indonesia formula respectively.They are used to calculate the water saturation of reservoirs in the Hechuan area with complex geologic conditions.The calculation results are compared with the interpretation results of NMR log data,and the influential factors of these models are discussed.The error between the water saturation calculated with the Simandoux formula and that measured by the NMR log is-6.1%-2.6%,indicating that this formula is more suitable for calculating water saturation of the argillaceous sandstone reservoirs with complex geologic conditions.If there is not a universal water saturation model that can be applied to all reservoirs,different types of water saturation models should be built for trial according to reservoir features,so as to identify the most suitable one for use.