Study On Shaly Sand Irreducible Water Saturation Calculation Method

The log interpretation of shaly sands with complicated configuration, such as low-resistivity oil/gas reservoirs and high-resistivity water reservoirs, is always in the regard of the log analysts owing to the influences of the complex lithology and porosity structure on the calculation of the formation parameters. Thus water-bearing reservoir and oil-bearing reservoir are difficult to distinguish with the log data. The same problem exists in Daqing oil field, especially in its periphery. In order to solve the problem, many three-porosity electrical conduction models aiming to describe the effect of the complex porous structure on the shaly sands conductivity have been presented In the application of the models, the calculation of three porosities, including free porosity, microporosity and clay porosity, are involved. Usually, the three porosities are calculated with irreducible saturation, clay saturation and bulk porosity. But the irreducible saturation, of the three parameters, is difficult to exactly estimated, and some studies on the determination of the irreducible saturation are presented in the paper.These studies are held in Hailaer basin of Daqing oil field. Firstly, the relations of the irreducible saturation with shaly content, porosity, granularity and the content of clay are analysed. The porosity structure of rock is thought as the main factor in affecting the irreducible saturation according to the analysis.Secondly, from three aspects of theories, experiments and practices, microporosity has been deeply reviewed to clarify the limit among free...