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碳酸盐岩地层的主要特征是孔隙结构比较复杂,因此利用电阻率测井资料估算含水饱和度的传统方法将会导致很大的误差。本文阐述了饱含流体混合物的双孔隙度碳酸盐岩地层的有效电导率的模拟结果。采用的是“有效介质近似法”来进行计算。碳酸盐岩可看作由矿物骨架、少量的原生孔隙以及大量的次生孔隙所组成。在这种模型中,所有的组分都可以用三轴的椭球体来近似表示。地层水和非导电流体在原生孔隙和次生孔隙中的分布状态是不相同的。岩石的孔隙系统可看作由三种类型所组成,即完全饱含地层水或非导电流体的孔隙;用层状椭球体近似的孔隙;以上两种组成的混合型孔隙。建立了层状椭球体模型来描述地层水在次生孔隙中的分布状态,其中水占据椭球体的外层。已经证明,对于不同的次生孔隙类型和孔隙度,有效电阻率与原生孔隙和次生孔隙的饱和度之间存在一定的函数关系。计算结果表明,只适用于单孔隙地层的阿尔奇公式在估算双孔隙碳酸盐岩地层的含水饱和度时会导致偏高或偏低的计算结果。对于原生孔隙度为0.08～0.1而次生孔隙度为0.01～0.02的地层,计算含水饱和度的相对误差可达25～30%。在模拟的基础上,提出了一种确定双孔隙碳酸盐岩地层含水饱和度的方法。试验数据表明,这种评价含水饱和度的方法是切实可行的。
The main feature of carbonate formations is the complex pore structure, so that the traditional method of estimating water saturation using resistivity logs will result in large errors. This article describes the simulation of the effective conductivity of a dual porosity carbonate formation saturated with a fluid mixture. Using the “effective medium approximation ” to calculate. Carbonates can be thought of as consisting of a mineral skeleton, a small number of primary pores, and a large number of secondary pores. In this model, all the components can be approximated by a triaxial ellipsoid. The distribution of formation water and non-conductive fluids in primary and secondary pores is not the same. The rock pore system can be thought of as consisting of three types, namely, pores that are completely saturated with formation water or non-conductive fluids; pores that are approximated by layered ellipsoids; and mixed pores of the above two types. A layered ellipsoid model was established to describe the distribution of formation water in secondary pores, where water occupies the outer layer of the ellipsoid. It has been shown that there is a certain functional relationship between the effective resistivity and the saturation of the primary and secondary pores for different secondary pore types and porosities. The calculation results show that Archie’s formula, which is only applicable to single-porosity formation, can lead to high or low calculation results when estimating the water saturation of double-porosity carbonate formations. For the formation with the primary porosity of 0.08-0.1 and the secondary porosity of 0.01-0.02, the relative error of calculating the water saturation can reach 25-30%. Based on the simulation, a method to determine the water saturation of double-porosity carbonate rocks is proposed. Experimental data show that this method of evaluating water saturation is feasible.