Investigation of the scale effect and the concept of a representative volume element of rocks in relation to porosity

Abstract

© 2020 The Authors. The article discusses the concepts of upscaling, the representative volume element (RVE) of the geological environment in relation to porosity from the point of view of the theory of structured continuum. The manifestation of the large-scale effect of porosity in terrigenous and carbonate reservoirs has been studied. The analysis of domestic and foreign methods of core sampling was carried out using the example of the Schlumberger company to study the porosity and permeability of the core in petrophysical laboratories and calculate the RVE of rock samples according to the porosity values determined by analyzing the pore-network model, liquid saturation, nuclear magnetic resonance and X-ray computed tomography, as well as the gas-volumetric method. The features and reasons for the manifestation of the large-scale effect of porosity in heterogeneous carbonate reservoirs have been studied. Methods for quantitative assessment of the anisotropy of rocks in the study of heterogeneity of rocks are considered. The necessity of taking into account the scale effect of porosity in the analysis of the correlation dependence “core - geophysical well logging”, established from the porosity data for both terrigenous and carbonate sections. The feasibility of using a core with a diameter of 60-100 mm and standard-size samples is considered when comparing laboratory values of porosity and porosity values determined from logging data. A study of direct and indirect petrophysical methods for determining the porosity of core samples was carried out when solving the same problems to identify the minimum representative volume of a core sample. It has been established that direct methods are the most effective in terms of time and financial costs for the prompt calculation of porosity coefficients for specimens with a diameter and height of 30-100 mm. The analysis of the porosity data ultimately made it possible to study the manifestation of the scale effect of porosity with a change in the sample size. A detailed analysis of published works will allow in the future to develop our own effective sampling technique for determining the RVE of the core interval as applied to porosity.