Ratnanabha Sain

Digital rock physics benchmarks-part II: Computing effective properties

This is the second and final part of our digital rock physics (DRP) benchmarking study. We use segmented 3-D images (one for Fontainebleau, three for Berea, three for a carbonate, and one for a sphere pack) to directly compute the absolute permeability, the electrical resistivity, and elastic moduli. The numerical methods tested include a finite-element solver (elastic moduli and electrical conductivity), two finite-difference solvers (elastic moduli and electrical conductivity), a Fourier-based Lippmann-Schwinger solver (elastic moduli), a lattice-Boltzmann solver (hydraulic permeability), and the explicit-jump method (hydraulic permeability and electrical conductivity). The set-ups for these numerical experiments, including the boundary conditions and the total model size, varied as well. The results thus produced vary from each other. For example, the highest computed permeability value may differ from the lowest one by a factor of 1.5. Nevertheless, all these results fall within the ranges consistent with the relevant laboratory data. Our analysis provides the DRP community with a range of possible outcomes which can be expected depending on the solver and its setup.

Numerical simulation of pore-scale heterogeneity and its effects on elastic, electrical, and transport properties

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Effect of Diagenesis On Elastic And Transport Properties Using Computational Rock Physics In Realistic Pore Microstructure

Summary We present evolution of elastic and transport properties due to di agenetic effects in realistic pore microstructure using computational rock physics tools. We generate compacted spherical random packs using Granular Dynamics simulation. The output from this process based simulation is gridded at fine scale resolution (5 microns) and used for diagenesis modeling. Different diagenetic methods are employed to recreate the effects of cementation on the initial compacted pack. The microstructures obtained after diagenetic modeling are used for estimating elastic and transport properties. A Finite Element based model is used for elastic properties, while Lattice Boltzmann method is used for estimating permeability. The bulk and shear moduli from the reconstructed microstructures are compared to clean sandstone samples and are found to be reasonably close. We present different diagenetic trends in the elastic, transport and cross-property domains.

Computing rock physics trends using sandstone micro‐CT images and digital mineral precipitation

Modern imaging technology provides high-resolution x-ray computer tomographies of Fontainebleau sandstone on the microscale. The 3-D images of the true rock microgeometries allow hydraulic and elastic rock properties to be estimated accurately and efficiently with the help of digital rock physics. Furthermore, image processing algorithms allow to add an additional material phase to the pore space, thus making it possible to compute porosity-permeability trends which reflect the effects of mineral precipitation. Based on the distance of individual pore voxels to the grain walls, three different precipitation patterns are generated. It turns out that at permeabilities around 0.15, the permeability is insensitive to the distribution of precipitated solid material in the pore space. At low porosities close to the percolation threshold, material in small pores may close flowpaths and may create a significant amount of disconnected porosity, which effectively reduces hydraulic permeability. The computer simulations are in agreement with laboratory measurement of permeability changes associated with salt precipitation.

Evolution of Elastic Properties And Fabric Tensor In a Deposition Model Using Granular Dynamics Simulation

In this work, we present elastic property computations on a rock microstructure obtained by using granular dynamics simulation. The granular dynamics simulation in this case models gravity sedimentation and compaction of spherical quartz grains. We focus on studying the interrelationship of elastic and fabric properties in the regime just above critical porosity, which is difficult to model in a laboratory experiment. We find that the elastic properties near the critical porosity depend more on the grain rearrangements and less on the pressure. We also investigate the relation between fabric anisotropy and coordination number. The final fabric tensor shows transverse isotropy symmetry for the simulated pack.