- Email: [email protected]
Estimation of aquifer parameters by least-squares method under linear flow conditions in fractured rocks
198A
HYDROGEOLOGY:FLUID FLOW
Unsaturated flow systems were studied which consisted of two-dimensional doublets embedded in a porous medium. The isolated flow regions formed around the doublets (source-sink combinations) were called Rankine bodies as a generalization of the classical geometries used in fluid mechanics for solutions to Laplace's equation. The motivation was to simulate unsaturated flow around subterranean objects, such as cavities and rock inclusions. (from Authors) 965O43 Parametric studies on the advancing interface in coastal aquifers due to linear variation of the freshwater level A. Mahesha, Water Resources Research, 31(10), 1995, pp 2437-2442. The transient motion of the freshwater seawater interface in coastal aquifers due to a constant lowering of freshwater levels at inland locations is simulated using a sharp-interface, finite-element model. The advancement of the interface was found to be dependent on the rate, location, and period of freshwater level variations. A seaward moving freshwater divide is formed by the lowering of the freshwater level. When the advancing interface crosses the seaward moving divide, aggressive intrusion is likely because of the reversed freshwater gradient existing landwater of the divide. A safe zone for the freshwater extraction can be determined based on the movement of the interface and the freshwater divide. (from Author) 965O44 Plume-scale dependent dispersion in aquifers with a wide range of scales of heterogeneity H. Rajaram & L. W. Gelhar, Water Resources Research, 31(10), 1995, pp 2469-2482. Dispersivity computations are developed for heterogeneous aquifers which exhibit structured variability across a wide range of scales. Multiscale, fractional Gaussian and selfsimilar random field models are used to describe the statistical structure of hydraulic conductivity variations. The concept of a relative dispersivity (A~) is introduced, following a similar concept introduced earlier in the context of turbulent diffusion. Dispersivities associated with the ensemble average concentration will tend to overestimate the degree of dilution and spreading in an aquifer, and this error can be very large in media with a wide range of scales of heterogeneity. (from Authors) 965045 Temporal moments for nonergodic solute transport in heterogeneous aquifers J.-O. Selroos, Water Resources Research, 31(7), 1995, pp 1705-1712. The first two temporal moments, iv, mean value and variance of residence time, are used to characterize nonergodic transport in heterogeneous porous media. The expected value and variance of the first temporal moment and the expected value of the second temporal moment are derived for both conservative solute and solute subject to sorption governed by linear kinetics. The methodology is exemplified for a twodimensional aquifer using first-order results for the velocity statistics. The results indicate that the relative difference between nonergodic and ergodic conditions, expressed through the second temporal moment, clearly is diminished for a kinetically sorbing solute as compared to a conservative one. (from Author) 965046 A stochastic approach to the characterization of lithofacies from surface seismic and well data N. Copty & Y. Rubin, Water Resources Research, 31(7), 1995, pp 1673-1686. This study presents a formal stochastic approach for the integration of surface seismic data and well data into the identification of the spatial arrangement of lithofacies and incorporating this information in the estimation of the log permeability probability density function (pdf). The effective-
ness of the proposed procedure is shown to depend on the quality of the seismic data and the degree of correlation between seismic and hydrogeologic soil properties. (from Authors) 965047 Effect of solute size on transport in structured porous media Qinhong Hu & M. L. Brusseau, Water Resources Research, 31(7), 1995, pp 1637-1646. The purpose of this work was to investigate the effect of solute size on transport in structured porous media. Miscible displacement experiments were performed with tracers of different sizes in aggregated, stratified, and macroporous media. The breakthrough curves exhibited both early breakthrough and tailing, indicative of nonideal transport in these structured media. Comparison of breakthrough curves revealed that the extent of nonideality was HPCD > PFBA, 2,4-D > 3H20. This behavior is consistent with the impact of solute size on the relative degree of 'nonequilibrium' experienced by solutes whose transport is constrained by diffusive mass transfer. (from Authors) 965048 On the relationship between mechanical and hydraulic apertures in rough-walled fractures C. E. Renshaw, Journal of Geophysical Research, 100(B12), 1995, pp 24,629-24,636. Recent investigations on the distribution of apertures in natural fractures suggest that the cubic law can accurately predict the fluid flux through rough-walled fractures as long as the appropriate average fracture aperture is used. Combining the stochastic cubic law with a simple deformation model results in a nonlinear relationship between fracture hydraulic and mechanical aperture. This relationship is shown to be consistent with published experimental and numerical data above a critical minimum aperture. Below this minimum aperture, the transmissivity of the fracture is approximately constant. Results have implications for the interpretation of laboratory fracture flow data and raise important questions pertaining to the mechanics of fracture deformation below the critical minimum aperture. (from Author) 965049 Multiphase nonisothermal transport of systems of reacting chemicals S. P. Wl~te, Water Resources Research, 31(7), 1995, pp 17611772. A mathematical model of muitiphase transport of heat, mass, and reacting chemical species in a porous media is developed. The model is appropriate for describing many of the reactions that take place in a geothermal reservoir. This model leads to the separation of transport terms from reaction terms in the equations for chemical species concentration. A numerical method for the solution of the transport equations is developed based on the integrated finite difference method. (from Author) 965O5O Estimation of aquifer parameters by least-squares method under Hnear flow conditions in fractured rocks M. L. Jat, M. S. Acharya & J. Singh, Nordic Hydrology, 26(2), 1995, pp 111-124. Pumping and recovery test data in phyllite formations were analysed under linear flow conditions by incorporating modification in the method proposed by Sen (1986). The results obtained were compared with SeEs graphical method. lower values of root mean-square error were obtained by least-squares method. The estimated values of transmissivity and storage coefficient were acceptable at 1% level of significance. An advantage of the least-squares method is the automization, which is lacking in the graphical method utilising curve-matching technique. (from Authors)
HYDROGEOLOGY:FLUID FLOW
Unsaturated flow systems were studied which consisted of two-dimensional doublets embedded in a porous medium. The isolated flow regions formed around the doublets (source-sink combinations) were called Rankine bodies as a generalization of the classical geometries used in fluid mechanics for solutions to Laplace's equation. The motivation was to simulate unsaturated flow around subterranean objects, such as cavities and rock inclusions. (from Authors) 965O43 Parametric studies on the advancing interface in coastal aquifers due to linear variation of the freshwater level A. Mahesha, Water Resources Research, 31(10), 1995, pp 2437-2442. The transient motion of the freshwater seawater interface in coastal aquifers due to a constant lowering of freshwater levels at inland locations is simulated using a sharp-interface, finite-element model. The advancement of the interface was found to be dependent on the rate, location, and period of freshwater level variations. A seaward moving freshwater divide is formed by the lowering of the freshwater level. When the advancing interface crosses the seaward moving divide, aggressive intrusion is likely because of the reversed freshwater gradient existing landwater of the divide. A safe zone for the freshwater extraction can be determined based on the movement of the interface and the freshwater divide. (from Author) 965O44 Plume-scale dependent dispersion in aquifers with a wide range of scales of heterogeneity H. Rajaram & L. W. Gelhar, Water Resources Research, 31(10), 1995, pp 2469-2482. Dispersivity computations are developed for heterogeneous aquifers which exhibit structured variability across a wide range of scales. Multiscale, fractional Gaussian and selfsimilar random field models are used to describe the statistical structure of hydraulic conductivity variations. The concept of a relative dispersivity (A~) is introduced, following a similar concept introduced earlier in the context of turbulent diffusion. Dispersivities associated with the ensemble average concentration will tend to overestimate the degree of dilution and spreading in an aquifer, and this error can be very large in media with a wide range of scales of heterogeneity. (from Authors) 965045 Temporal moments for nonergodic solute transport in heterogeneous aquifers J.-O. Selroos, Water Resources Research, 31(7), 1995, pp 1705-1712. The first two temporal moments, iv, mean value and variance of residence time, are used to characterize nonergodic transport in heterogeneous porous media. The expected value and variance of the first temporal moment and the expected value of the second temporal moment are derived for both conservative solute and solute subject to sorption governed by linear kinetics. The methodology is exemplified for a twodimensional aquifer using first-order results for the velocity statistics. The results indicate that the relative difference between nonergodic and ergodic conditions, expressed through the second temporal moment, clearly is diminished for a kinetically sorbing solute as compared to a conservative one. (from Author) 965046 A stochastic approach to the characterization of lithofacies from surface seismic and well data N. Copty & Y. Rubin, Water Resources Research, 31(7), 1995, pp 1673-1686. This study presents a formal stochastic approach for the integration of surface seismic data and well data into the identification of the spatial arrangement of lithofacies and incorporating this information in the estimation of the log permeability probability density function (pdf). The effective-
ness of the proposed procedure is shown to depend on the quality of the seismic data and the degree of correlation between seismic and hydrogeologic soil properties. (from Authors) 965047 Effect of solute size on transport in structured porous media Qinhong Hu & M. L. Brusseau, Water Resources Research, 31(7), 1995, pp 1637-1646. The purpose of this work was to investigate the effect of solute size on transport in structured porous media. Miscible displacement experiments were performed with tracers of different sizes in aggregated, stratified, and macroporous media. The breakthrough curves exhibited both early breakthrough and tailing, indicative of nonideal transport in these structured media. Comparison of breakthrough curves revealed that the extent of nonideality was HPCD > PFBA, 2,4-D > 3H20. This behavior is consistent with the impact of solute size on the relative degree of 'nonequilibrium' experienced by solutes whose transport is constrained by diffusive mass transfer. (from Authors) 965048 On the relationship between mechanical and hydraulic apertures in rough-walled fractures C. E. Renshaw, Journal of Geophysical Research, 100(B12), 1995, pp 24,629-24,636. Recent investigations on the distribution of apertures in natural fractures suggest that the cubic law can accurately predict the fluid flux through rough-walled fractures as long as the appropriate average fracture aperture is used. Combining the stochastic cubic law with a simple deformation model results in a nonlinear relationship between fracture hydraulic and mechanical aperture. This relationship is shown to be consistent with published experimental and numerical data above a critical minimum aperture. Below this minimum aperture, the transmissivity of the fracture is approximately constant. Results have implications for the interpretation of laboratory fracture flow data and raise important questions pertaining to the mechanics of fracture deformation below the critical minimum aperture. (from Author) 965049 Multiphase nonisothermal transport of systems of reacting chemicals S. P. Wl~te, Water Resources Research, 31(7), 1995, pp 17611772. A mathematical model of muitiphase transport of heat, mass, and reacting chemical species in a porous media is developed. The model is appropriate for describing many of the reactions that take place in a geothermal reservoir. This model leads to the separation of transport terms from reaction terms in the equations for chemical species concentration. A numerical method for the solution of the transport equations is developed based on the integrated finite difference method. (from Author) 965O5O Estimation of aquifer parameters by least-squares method under Hnear flow conditions in fractured rocks M. L. Jat, M. S. Acharya & J. Singh, Nordic Hydrology, 26(2), 1995, pp 111-124. Pumping and recovery test data in phyllite formations were analysed under linear flow conditions by incorporating modification in the method proposed by Sen (1986). The results obtained were compared with SeEs graphical method. lower values of root mean-square error were obtained by least-squares method. The estimated values of transmissivity and storage coefficient were acceptable at 1% level of significance. An advantage of the least-squares method is the automization, which is lacking in the graphical method utilising curve-matching technique. (from Authors)