Leveraging Digital Rock Physics Workflows in Unconventional Petrophysics: A Review of Opportunities, Challenges, and Benchmarking
- Ayaz Mehmani (The University of Texas at Austin) | Shaina Kelly (ConocoPhillips) | Carlos Torres-Verdín (The University of Texas at Austin)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- SPWLA 60th Annual Logging Symposium, 15-19 June, The Woodlands, Texas, USA
- Publication Date
- Document Type
- Conference Paper
- 2019. held jointly by the Society of Petrophysicists and Well Log Analysts (SPWLA) and the submitting authors
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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 modeling, 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 permeability will greatly help reduce variables. Finally, this paper offers a technical roadmap for the robust application of unconventional DRP for the petrophysics and general subsurface community.
Rock diagenesis can generate complex pore-lining and pore-filling textures beyond the idealized sedimentary “spherical grain pack” that greatly influence pore size distributions and transport properties including permeability, capillary trapping, diffusion, and relative permeability. Compaction, cementation, dissolution, and microporosity are examples of such geometric complexity. Meanwhile, mineralogical composition and organic matter content can lead to multiple surfaces of potentially varying wettability. Petrophysically-speaking, dispersed shale, laminated shale, and structural shale grains are categories of complexity as well. These various configurations often necessitate the need for visualization of rock pore systems, a practice that has been done for years via thin section and SEM imaging as well as computed tomography. Traditionally, imaging techniques have been used for validation of a model or assumption (such as laminated sands in shaly sand analysis), but, as computing power and microscopy technologies have increased, many researchers and vendors have leveraged these technologies to create digital laboratories where petrophysical properties can be directly calculated. This intriguing field of study is called digital rock physics (DRP) and is a potential addition to the petrophysical toolkit.
|File Size||16 MB||Number of Pages||18|