Core-to-Core property upscaling: case study for Berea Sandstone

Efficient development of hydrocarbon reservoirs requires accurate aggregation of information on the petrophysical, electromagnetic, and elastic properties of reservoir rocks, obtained through various research methods at different scales. Modern methods such as micro-computed tomography enable detailed investigation of rock samples down to the microporosity level. However, transferring properties between scales requires careful consideration of scale effects and is closely related to the problem of representative element volume (REV). In this paper, we focus on the scale effect in the transfer of rock properties between "micro-core-to-core" levels, using Berea Sandstone as an example. A numerical homogenization method, based on solving direct problems via the finite element method on mesh models of the samples is applied. The mesh models of the rock subsamples are constructed so as to accurately describe the intricate internal geological structure and topology of the pore space. The representative volume is obtained by analyzing the stability of properties such as porosity, connectivity factor, and effective electrical conductivity throughout the sequence of gradually increasing subsamples. The results demonstrate that the size of the representative volume element varies depending on the property considered. For the Berea Sandstone sample, the REV size for electrical conductivity nearly matches the full size of the core. A nonlinear relationship between porosity and specific electrical conductivity was established through studies on random micro-subsamples of varying sizes. The proposed approaches and results emphasize the importance of studying scale effects to accurately describe reservoir rock properties. They also highlight the potential of digital rock framework and micro-CT methods in addressing challenges related to hydrocarbon field development.