Determination of the oil saturation coefficient according to Dakhnov–Archi using a new methodological approach when studying core samples

Abstract

Background. Predisposition of the rock to wetting by water (hydrophilicity) or oil (hydrophobicity) has a significant influence on the results of determining the oil saturation coefficient according to Dakhnov–Archi. Carbonate reservoir rocks in most cases are characterized by a complex type of wettability: heterogeneous (selective), mixed or neutral wettability. Collectively, the surface properties of such rocks can be defined by the term “nonhydrophilic wettability”. Studying rocks with nonhydrophilic wettability using standard core research methods can lead to subsequent errors in calculating oil reserves using the volumetric method. Objective. To eliminate the risk of such errors by adapting standard research methods, in particular the centrifugation method, to the results of experiments in reservoir conditions. Materials and methods. Capillarimetric method (semipermeable membrane method), centrifugation method, core “aging”. Results. The results of core studies necessary for calculating the oil saturation coefficient of nonhydrophilic reservoirs using formation resistivity data using the Dakhnov–Archi method are presented. A methodological approach is proposed for adapting the centrifugation method to reservoir conditions. Conclusions. The applied methodological approach makes it possible to increase the volume of statistical data and calculate an adequate value of the oil saturation coefficient according to Dakhnov–Archi for nonhydrophilic reservoirs.