Leveraging digital rock physics workflows in unconventional petrophysics: A review of opportunities, challenges, and benchmarking

Abstract

Digital rock physics (DRP), via both direct numerical simulation and pore-network modeling, holds great promise in terms of probing such pore-scale controls on transport, particularly with multiphase flow and sensitivity analysis of time-intensive measurements such as relative permeability. However, despite advances in micro-computed tomography (microCT) and scanning electron microscopy (SEM) techniques, obtaining cost-effective representative elementary volumes (REV) at sufficient resolution that capture dual-scale porosity and surface textures remains a formidable challenge in establishing digital rock physics as a predictive toolset. Furthermore, implementers are faced with several options of numerical solvers such as finite element method, lattice Boltzmann method, and mass balance-based pore-network modeling. This paper reviews the current status of establishing an REV and upscaling techniques for DRP in tight and/or diagenetically-altered rocks, highlighting successful and unsuccessful pore-to-core data benchmarking examples by the authors and the greater literature in terms of static and dynamic properties.The review finds that performing DRP on a single image modality is not sufficient, even for many conventional rocks, and that it is crucial to interface with experimental data, be it core analysis deliverables or subpore-scale and Darcy-scale microfluidics. In unconventional rocks, the majority of work does not leverage mesoscale simulations, instead zooming in to a discrete pore-scale scenario that is often not benchmarked with SCAL data. Even when a simulation domain is benchmarked, the matching of a discrete case with a multivariable situation is non-unique. Benchmarking with dynamic or pseudo-dynamic core data such as MICP and single phase perm will greatly help reduce variables. Finally, this paper offers a technical roadmap for the robust application of unconventional DRP for the petrophysical and general subsurface community.