William J. Bosl

A study of porosity and permeability using a lattice Boltzmann simulation

We explicitly calculate the absolute (single-phase) permeability of simulated granular rocks as the pore space is evolved by various diagenetic schemes. Our goal is to match our computed curves to laboratory measurements of porosity-permeability relationships in real rocks. To achieve this goal we model rock as a dense random pack of identical spherical grains with diagenetic cement deposited in the pore space. The positions of the sphere centers in our numerical model are taken from experimental measurements (the Finney pack). The diagenesis is simulated in various ways: uniform cement deposition on the surface of each grain (uniform growth of the grains); cement deposition at grain contacts; cement deposition away from grain contacts; random filling of the pore spaces; and various combinations of these. Permeability is computed by explicitly modeling Stokes flow in the simulated pore space using a lattice Boltzmann method. Our simulations produce distinctively different porosity-permeability relationships which are characteristic of the cement deposition pattern. The distinctive porosity-permeability relationships found in laboratory measurements of real rocks are matched by certain simulation schemes.

Analysis of subsurface contaminant migration and remediation using high performance computing

Abstract Highly resolved simulations of groundwater flow, chemical migration and contaminant recovery processes are used to test the applicability of stochastic models of flow and transport in a typical field setting. A simulation domain encompassing a portion of the upper saturated aquifer materials beneath the Lawrence Livermore National Laboratory was developed to hierarchically represent known hydrostratigraphic units and more detailed stochastic representations of geologic heterogeneity within them. Within each unit, Gaussian random field models were used to represent hydraulic conductivity variation, as parameterized from well test data and geologic interpretation of spatial variability. Groundwater flow, transport and remedial extraction of two hypothetical contaminants were made in six different statistical realizations of the system. The effective flow and transport behavior observed in the simulations compared reasonably with the predictions of stochastic theories based upon the Gaussian models, even though more exacting comparisons were prevented by inherent nonidealities of the geologic model and flow system. More importantly, however, biases and limitations in the hydraulic data appear to have reduced the applicability of the Gaussian representations and clouded the utility of the simulations and effective behavior based upon them. This suggests a need for better and unbiased methods for delineating the spatial distribution and structure of geologic materials and hydraulic properties in field systems. High performance computing can be of critical importance in these endeavors, especially with respect to resolving transport processes within highly variable media.©1998 Elsevier Science Limited. All rights reserved

Permeability-porosity transforms from small sandstone fragments

Numerical simulation of laboratory experiments on rocks, or digital rock physics, is an emerging field that may eventually benefit the petroleum industry. For numerical experimentation to find its way into the mainstream, it must be practical and easily repeatable — i.e., implemented on standard hardware and in real time. This condition reduces the size of a digital sample to just a few grains across. Also, small physical fragments of rock, such as cuttings, may be the only material available to produce digital images. Will the results be meaningful for a larger rock volume? To address this question, we use a number of natural and artificial medium- to high-porosity, well-sorted sandstones. The 3D microtomography volumes are obtained from each physical sample. Then, analogous to making thin sections of drill cuttings, we select a large number of small 2D slices from a 3D scan. As a result, a single physical sample produces hundreds of 2D virtual-drill-cuttings images. Corresponding 3D pore-space realizati...

A Numerical Simulation of Groundwater Flow and Contaminant Transport on the CRAY T3D and C90 Supercomputers

Numerical simulations of groundwater flow and chemical transport through three-dimensional heterogeneous porous media are described. The authors employ two CRAY supercomputers for different parts of the decoupled calculation: the flow field is computed on the T3D massively parallel computer, and the contaminant migration is simulated on the C90 vector supercomputer. The authors compare simulation results for subsurface models based on homogeneous and heterogeneous conceptual models and find that the heterogeneities have a profound impact on the character of contaminant migration.