Biomedical subjects

Russell L Detwiler

Publications and source records attributed to Russell L Detwiler.

3 recordsLinked to original sources

PubMed2005

Satiated relative permeability of variable-aperture fractures.

Experimental studies of capillary-dominated displacements in variable-aperture fractures have demonstrated the occurrence of a satiated state at the end of invasion, where significant entrapment of the displaced phase occurs. The structure of this entrapped phase controls the behavior of flow and transport processes in the flowing phase. Recent studies have shown that the areal saturation of the flowing phase at satiation (S(f) ) is largely controlled by a single parameter C/delta , where C , the curvature number, weighs the mean in-plane interfacial curvature relative to the mean out-of-plane interfacial curvature, and delta , the coefficient of variation of the aperture field, represents the strength of interface roughening induced by aperture variations. Here we consider the satiated relative permeability (k(rs)) to the flowing phase, which is defined as the relative permeability when the defending phase is fully entrapped. The satiated relative permeability is shown to be a well-defined function of S(f) over a wide range of C/delta , ranging from capillary fingering with significant entrapment (C/delta-->0) to smooth invasion with very little entrapment (C/delta > 1) . We develop a relationship for k(rs) as a function of S(f), by combining theoretical results for the effective permeability in a spatially correlated random permeability field, with results from continuum percolation theory for quantifying the influence of the entrapped phase. The resulting model for k(rs) also involves a dependence on delta . The predicted relative permeability values are accurate across the entire range of phase structures representative of capillary-dominated displacements in variable-aperture fractures.

Journal Article↗

PubMed2003

Immiscible displacements in rough-walled fractures: competition between roughening by random aperture variations and smoothing by in-plane curvature.

Phase structure during capillary displacement of fluid phases within rough-walled fractures is controlled by the competition between random aperture variability which tends to roughen the interface and in-plane curvature which tends to smooth it. We show that the phase structure and corresponding areal saturation at the end of displacement depend primarily on the ratio of two dimensionless parameters: one that controls roughening (the coefficient of variation of the aperture field, delta) and another that controls smoothing (the curvature number C, which weighs the mean influences of aperture induced and in-plane curvature). Interestingly, for C/delta above approximately 0.5, areal saturation for wetting and nonwetting invasion first diverges and then converges to create an envelope, whose width increases with delta. This nonunique behavior with respect to wettability is fundamental to capillary displacements in rough-walled fractures and is due to an asymmetry in capillary competition in wetting versus nonwetting invasions.

Journal Article↗

PubMedDate not supplied

Comparison of an algebraic multigrid algorithm to two iterative solvers used for modeling ground water flow and transport.

Numerical solution of large-scale ground water flow and transport problems is often constrained by the convergence behavior of the iterative solvers used to solve the resulting systems of equations. We demonstrate the ability of an algebraic multigrid algorithm (AMG) to efficiently solve the large, sparse systems of equations that result from computational models of ground water flow and transport in large and complex domains. Unlike geometric multigrid methods, this algorithm is applicable to problems in complex flow geometries, such as those encountered in pore-scale modeling of two-phase flow and transport. We integrated AMG into MODFLOW 2000 to compare two- and three-dimensional flow simulations using AMG to simulations using PCG2, a preconditioned conjugate gradient solver that uses the modified incomplete Cholesky preconditioner and is included with MODFLOW 2000. CPU times required for convergence with AMG were up to 140 times faster than those for PCG2. The cost of this increased speed was up to a nine-fold increase in required random access memory (RAM) for the three-dimensional problems and up to a four-fold increase in required RAM for the two-dimensional problems. We also compared two-dimensional numerical simulations of steady-state transport using AMG and the generalized minimum residual method with an incomplete LU-decomposition preconditioner. For these transport simulations, AMG yielded increased speeds of up to 17 times with only a 20% increase in required RAM. The ability of AMG to solve flow and transport problems in large, complex flow systems and its ready availability make it an ideal solver for use in both field-scale and pore-scale modeling.

Forecasting↗