A Novel Grain-Contact Modeling Approach for Enhanced Petro-Elastic Simulations in Digital Rock Physics Applications

Abstract

The characterization of structural and stratigraphic trapping of CO2 at a given storage site depends primarily on CO2 migration in the field. With increased focus on migration-assisted CO2 sequestration in saline aquifers, CO2 solubility, residual CO2 trapping, and process monitoring during CO2 plume migration are areas of growing research and business interest. CO2 solubility trapping, a primary drainage process influenced by pressure, temperature, and brine salinity, leads to pH reduction and promotes reactive geochemical processes. Residual CO2 trapping, a secondary process as water re-imbibes storage volumes, is equally critical. Both mechanisms are vital for safe storage and form the foundation for cost-efficient monitoring and prediction techniques, leveraging pore-scale rock physics experiments, simulations, and field-upscaling workflows. On the pore scale, computational methods such as pore-network modeling and morphological methods simulate capillary pressure, relative permeability saturation functions, and reactive transport to model CO2 trapping functions and their evolution over time. This research advances an efficient methodology to characterize rock properties across pore-to-log-to-seismic scales, enabling computation of specific rock physical properties— especially seismic velocities (Vp and Vs)—for dry, variably saturated, and reactive transport-exposed samples. Enhanced grain mineral configuration identification via a watershed segmentation method is central to this approach. By modeling stiffness reduction at grain-grain contact zones and adjusting for contact area, grain size, and surface area, the algorithm overcomes typical overestimations of effective stiffness in standard microcomputed tomography (µCT) analysis. The presented software developments optimize the need for laboratory measurements, enabling simulation of mixed water-CO2 saturated storage rocks and their acoustic properties under various conditions. These advancements improve the implementation of seismic four- dimensional (4D) monitoring programs, which are often legally required, by facilitating better analysis of physical changes in rock types with time. Furthermore, they enhance understanding of geochemical changes in storage rocks through geomechanical-petrophysical properties, contributing to risk reduction and bolstering social acceptance of carbon capture and storage (CCS) projects. By digitally performing necessary measurements and limiting laboratory work to calibration purposes, the environmental compatibility of CCS storage development improves. This study demonstrates the workflow using OMV data and laboratory measurements on reference and in-situ rock samples from potential CO2 storage sites.