Quantification of clay mineral microporosity and its application to water saturation and effective porosity estimation: A case study from Upper Ordovician reservoir, Libya

Abstract

The relative volume of clay minerals contributing to the microporosity is the main feature that influences the estimation of water saturation in hydrocarbon reservoirs. For developing a genuine understanding of reservoir quality, the present study elucidated the petrography, quantification of clay minerals, and microporosity, besides their effect on the petrophysical parameters. The ratified method is an integration of core data, SEM (Scanning Electron Microscopy), XRD, and thin section. The most identified clay minerals in order of decreasing abundance are kaolinite (45%), Illite (35%), a mixed layer (10%), smectite (5%) and others are 5%. The estimation of clay mineral microporosity was based on the SEM photomicrographs. Mixed clay minerals have a variety of textures with microporosity values that range from 10 to 55%. In this regard, the clay microporosity data was used to calculate the effective clay volume; the clay bound water, the effective water saturation and porosity. As a result, the estimated values are decreased when the microporosity is considered, except for the effective volume of clay minerals which is approximately twice (52.5%) as the original dry mineral volume. Moreover, the microporosity based water saturation decreased dramatically when compared to log values up to 22. 37%. The above-estimated values correlated with both core and log readings using linear regression. The derived relationships with a high correlation coefficient (R2) were used to extrapolate microporosity, clay bound water, effective saturation and effective porosity in the uncored well interval. The correlation coefficient R2 is higher than 90%. Keywords: Clay minerals, Microporosity, Effective porosity, Effective saturation, Effective clay volume, Solid clay mineral volume