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Formation dry-out from CO2 injection into saline acquifers: Part 2, Analytical model for salt precipitation

Description: From a mass balance for water dissolved into the flowing CO{sub 2} stream, and a consideration of saturation profiles from the Buckley-Leverett (1942) fractional flow theory, we derive an equation that directly relates gas saturation S{sub g,d} at the dry-out front to temperature, pressure and salinity dependence of fluid properties. The equation is easily solved by iteration or interpolation. From gas saturation at the front we derive the average gas saturation in the dry-out region, from which we obtain the 'solid saturation' S{sub S}, i.e., the fraction of pore space filled with solid precipitate. Values of S{sub S} derived from this theory show excellent agreement with numerical simulations presented in the preceding companion paper ('Part 1'). Thus, from relative permeabilities and fluid properties at in situ conditions prior to CO{sub 2} injection, it is possible to directly make an accurate estimate of solids precipitation, without having to perform a numerical simulation of the injection process.
Date: February 1, 2009
Creator: Pruess, Karsten
Partner: UNT Libraries Government Documents Department

Geologic carbon sequestration as a global strategy to mitigate CO2 emissions: Sustainability and environmental risk

Description: Fossil fuels are abundant, inexpensive to produce, and are easily converted to usable energy by combustion as demonstrated by mankind's dependence on fossil fuels for over 80% of its primary energy supply (13). This reliance on fossil fuels comes with the cost of carbon dioxide (CO{sub 2}) emissions that exceed the rate at which CO{sub 2} can be absorbed by terrestrial and oceanic systems worldwide resulting in increases in atmospheric CO{sub 2} concentration as recorded by direct measurements over more than five decades (14). Carbon dioxide is the main greenhouse gas linked to global warming and associated climate change, the impacts of which are currently being observed around the world, and projections of which include alarming consequences such as water and food shortages, sea level rise, and social disruptions associated with resource scarcity (15). The current situation of a world that derives the bulk of its energy from fossil fuel in a manner that directly causes climate change equates to an energy-climate crisis. Although governments around the world have only recently begun to consider policies to avoid the direst projections of climate change and its impacts, sustainable approaches to addressing the crisis are available. The common thread of feasible strategies to the energy climate crisis is the simultaneous use of multiple approaches based on available technologies (e.g., 16). Efficiency improvements (e.g., in building energy use), increased use of natural gas relative to coal, and increased development of renewables such as solar, wind, and geothermal, along with nuclear energy, are all available options that will reduce net CO{sub 2} emissions. While improvements in efficiency can be made rapidly and will pay for themselves, the slower pace of change and greater monetary costs associated with increased use of renewables and nuclear energy suggests an additional approach is needed to help bridge the ...
Date: April 1, 2011
Creator: Oldenburg, C.M.
Partner: UNT Libraries Government Documents Department

Numerical simulation experiments on the long-term evolution of a CO2 plume under a sloping caprock

Description: We have used the TOUGH2-MP/ECO2N code to perform numerical simulation studies of the long-term behavior of CO{sub 2} stored in an aquifer with a sloping caprock. This problem is of great practical interest, and is very challenging due to the importance of multi-scale processes. We find that the mechanism of plume advance is different from what is seen in a forced immiscible displacement, such as gas injection into a water-saturated medium. Instead of pushing the water forward, the plume advances because the vertical pressure gradients within the plume are smaller than hydrostatic, causing the water column to collapse at the plume tip. Gas saturations and updip CO{sub 2} fluxes are nearly constant, independent of time and position, in the upper, mobile portions of the plume. The CO{sub 2} plume becomes thinner as it advances, yet the speed of advancement remains constant over the entire simulation period of up to 400 years, with migration distances of more than 80 km. Our simulation includes dissolution of CO{sub 2} into the aqueous phase and associated density increase, and molecular diffusion. However, no convection develops in the aqueous phase because it is suppressed by the relatively coarse (sub-)horizontal gridding required in a regional-scale model. A first crude sub-grid-scale model was implemented to represent convective enhancement of CO{sub 2} dissolution. This process is found to greatly reduce the thickness of the CO{sub 2} plume, but does not affect the speed of plume advancement.
Date: August 15, 2009
Creator: Pruess, Karsten
Partner: UNT Libraries Government Documents Department

Ocean Thermal Energy Conversion: An Overall Environmental Assessment

Description: Significant acccrmplishments in Ocean Thermal Energy Conversion (OTEC) technology have increased the probability of producing OTEC-derived power within this decade with subsequent large scale commercialization following by the turn of the century. Under U.S. Department of Energy funding, the Oceanic Engineering Operations of Interstate Electronics Corporation has prepared several OTEC Environmental Assessments over the past years, in particular, the OTEC Programmatic Environmental Assessment. The Programmatic EA considers several technological designs (open- and closed-cycle), plant configuratlons (land-based, moored, and plant-ship), and power usages (baseload electricity, ammonia and aluminum production). Potential environmental impacts, health and safetv issues and a status update of the institutional issues as they influence OTEC deployments, are included.
Date: August 1, 1980
Creator: Sands, M.Dale
Partner: UNT Libraries Government Documents Department

Ocean Thermal Energy Conversion Programmatic Environmental Assessment

Description: Significant achievements in Ocean Thermal Energy Conversion (OTEC) technology have increased the probability of producing OTEC-derived power in this decade with subsequent large-scale commercialization to follow by the turn of the century. Under U.S. Department of Energy funding, Interstate Electronics has prepared an OTEC Programmatic Environmental Assessment (EA) that considers tne development, demonstration, and commercialization of OTEC power systems. The EA considers several tecnnological designs (open cycle and closed cycle), plant configurations (land-based, moored, and plantship), and power usages (baseload electricity and production of ammonia and aluminum). Potencial environmental impacts, health and safety issues, and a status update of international, federal, and state plans and policies, as they may influence OTEC deployments, are included.
Date: August 1, 1980
Creator: Sands, M.Dale
Partner: UNT Libraries Government Documents Department

On carbon footprints and growing energy use

Description: Could fractional reductions in the carbon footprint of a growing organization lead to a corresponding real reduction in atmospheric CO{sub 2} emissions in the next ten years? Curtis M. Oldenburg, head of the Geologic Carbon Sequestration Program of LBNL’s Earth Sciences Division, considers his own organization's carbon footprint and answers this critical question? In addressing the problem of energy-related greenhouse gas (GHG) emissions and climate change, it is essential that we understand which activities are producing GHGs and the scale of emission for each activity, so that reduction efforts can be efficiently targeted. The GHG emissions to the atmosphere of an individual or group are referred to as the ‘carbon footprint’. This terminology is entirely appropriate, because 85% of the global marketed energy supply comes from carbon-rich fossil fuel sources whose combustion produces CO{sub 2}, the main GHG causing global climate change. Furthermore, the direct relation between CO2 emissions and fossil fuels as they are used today makes energy consumption a useful proxy for carbon footprint. It would seem to be a simple matter to reduce energy consumption across the board, both individually and collectively, to help reduce our carbon footprints and therefore solve the energyclimate crisis. But just how much can we reduce carbon footprints when broader forces, such as growth in energy use, cause the total footprint to simultaneously expand? In this feature, I present a calculation of the carbon footprint of the Earth Sciences Division (ESD), the division in which I work at Lawrence Berkeley National Laboratory (LBNL), and discuss the potential for reducing this carbon footprint. It will be apparent that in terms of potential future carbon footprint reductions under projections of expected growth, ESD may be thought of as a microcosm of the situation of the world as a whole, in which alternatives to the ...
Date: June 1, 2011
Creator: Oldenburg, C.M.
Partner: UNT Libraries Government Documents Department

On fluid flow in a heterogeneous medium under nonisothermal conditions

Description: An asymptotic technique, valid in the presence of smoothly-varying heterogeneity, provides explicit expressions for the velocity of a propagating pressure and temperature disturbance. The governing equations contain nonlinear terms due to the presence of temperature-dependent coefficients and due to the advection of fluids with differing temperatures. Two cases give well-defined expressions in terms of the parameters of the porous medium: the uncoupled propagation of a pressure disturbance and the propagation of a fully coupled temperature and pressure disturbance. The velocity of the coupled disturbance or front, depends upon the medium parameters and upon the change in temperature and pressure across the front. For uncoupled flow, the semi-analytic expression for the front velocity reduces to that associated with a linear diffusion equation. A comparison of the asymptotic travel time estimates with calculations from a numerical simulator indicates reasonably good agreement for both uncoupled and coupled disturbances.
Date: November 1, 2010
Creator: D.W., Vasco
Partner: UNT Libraries Government Documents Department

ON""GENERAL CONSERVATION EQUATIONS FOR MULTIPHASE SYSTEMS: 1. AVERAGING PROCEDURE"" BY M. HASSANIZADEH AND W.G. GRAY.

Description: The author comments upon a point made in the referenced paper on general conservation equations. The author directs attention to the fact that the referenced paper's authors correctly point out that when an averaging operation involves integration, the integrand multiplied by the infinitesimal volume must be an additive quantity. The importance of this requirement is emphasized.
Date: December 1, 1979
Creator: Narasimhan, T.N.
Partner: UNT Libraries Government Documents Department

On the propagation of a coupled saturation and pressure front

Description: Using an asymptotic technique, valid for a medium with smoothly varying heterogeneity, I derive an expression for the velocity of a propagating, coupled saturation and pressure front. Due to the nonlinearity of the governing equations, the velocity of the propagating front depends upon the magnitude of the saturation and pressure changes across the front in addition to the properties of the medium. Thus, the expression must be evaluated in conjunction with numerical reservoir simulation. The propagation of the two-phase front is governed by the background saturation distribution, the saturation-dependent component of the fluid mobility, the porosity, the permeability, the capillary pressure function, the medium compressibility, and the ratio of the slopes of the relative permeability curves. Numerical simulation of water injection into a porous layer saturated with a nonaqueous phase liquid indicates that two modes of propagation are important. The fastest mode of propagation is a pressure-dominated disturbance that travels through the saturated layer. This is followed, much later, by a coupled mode with a large saturation change. These two modes are also observed in a simulation using a heterogeneous porous layer. A comparison between the propagation times estimated from the results of the numerical simulation and predictions from the asymptotic expression indicates overall agreement.
Date: December 1, 2010
Creator: Vasco, D. W.
Partner: UNT Libraries Government Documents Department

Natural nanoparticle structure, properties and reactivity from X-ray studies

Description: Synthetic analogs of naturally occurring nanoparticles have been studied by a range of X-ray techniques to determine their structure and chemistry, and relate these to their novel chemical properties and physical behavior. ZnS nanoparticles, formed in large concentrations naturally bymicrobial action, have an interesting core-shell structure with a highly distorted and strained outer layer. The strain propagates through the particles and produces unusual stiffness but can be relieved by changing the nature of the surface ligand binding. Weaker bound ligands allow high surface distortion, but strongly bound ligands relax this structure and reduce the overall strain. Only small amounts of ligand exchange causes transformations from the strained to the relaxed state. Most remarkably, minor point contacts between strained nanoparticles also relax the strain. Fe oxyhydroxide nanoparticles appear to go through structural transformations dependent on their size and formation conditions, and display a crystallographically oriented form of aggregation at the nanoscale that alters growth kinetics. At least one Fe oxyhydroxide mineral may only be stable on the nanoscale, and nonstoichiometry observed on the hematite surface suggests that for this phase and possibly other natural metal oxides, chemistry may be size dependent. Numerous questions exist on nanominerals formed in acid mine drainage sites and by reactions at interfaces.
Date: October 1, 2009
Creator: Waychunas, Glenn A.
Partner: UNT Libraries Government Documents Department

Estimating Plume Volume for Geologic Storage of CO2 in Saline Aquifers

Description: Typically, when a new subsurface flow and transport problem is first being considered, very simple models with a minimal number of parameters are used to get a rough idea of how the system will evolve. For a hydrogeologist considering the spreading of a contaminant plume in an aquifer, the aquifer thickness, porosity, and permeability might be enough to get started. If the plume is buoyant, aquifer dip comes into play. If regional groundwater flow is significant or there are nearby wells pumping, these features need to be included. Generally, the required parameters tend to be known from pre-existing studies, are parameters that people working in the field are familiar with, and represent features that are easy to explain to potential funding agencies, regulators, stakeholders, and the public. The situation for geologic storage of carbon dioxide (CO{sub 2}) in saline aquifers is quite different. It is certainly desirable to do preliminary modeling in advance of any field work since geologic storage of CO{sub 2} is a novel concept that few people have much experience with or intuition about. But the parameters that control CO{sub 2} plume behavior are a little more daunting to assemble and explain than those for a groundwater flow problem. Even the most basic question of how much volume a given mass of injected CO{sub 2} will occupy in the subsurface is non-trivial. However, with a number of simplifying assumptions, some preliminary estimates can be made, as described below. To make efficient use of the subsurface storage volume available, CO{sub 2} density should be large, which means choosing a storage formation at depths below about 800 m, where pressure and temperature conditions are above the critical point of CO{sub 2} (P = 73.8 bars, T = 31 C). Then CO{sub 2} will exist primarily as a free-phase supercritical ...
Date: July 11, 2008
Creator: Doughty, Christine
Partner: UNT Libraries Government Documents Department

Evaluating Bounds and Estimators for Constants of Random Polycrystals Composed of Orthotropic Elastic Materials

Description: While the well-known Voigt and Reuss (VR) bounds, and the Voigt-Reuss-Hill (VRH) elastic constant estimators for random polycrystals are all straightforwardly calculated once the elastic constants of anisotropic crystals are known, the Hashin-Shtrikman (HS) bounds and related self-consistent (SC) estimators for the same constants are, by comparison, more difficult to compute. Recent work has shown how to simplify (to some extent) these harder to compute HS bounds and SC estimators. An overview and analysis of a subsampling of these results is presented here with the main point being to show whether or not this extra work (i.e., in calculating both the HS bounds and the SC estimates) does provide added value since, in particular, the VRH estimators often do not fall within the HS bounds, while the SC estimators (for good reasons) have always been found to do so. The quantitative differences between the SC and the VRH estimators in the eight cases considered are often quite small however, being on the order of ±1%. These quantitative results hold true even though these polycrystal Voigt-Reuss-Hill estimators more typically (but not always) fall outside the Hashin-Shtrikman bounds, while the self-consistent estimators always fall inside (or on the boundaries of) these same bounds.
Date: March 1, 2012
Creator: Berryman, J. G.
Partner: UNT Libraries Government Documents Department

Finite Size Effects on the Real-Space Pair Distribution Function of Nanoparticles

Description: The pair distribution function (PDF) method is a powerful approach for the analysis of the structure of nanoparticles. An important approximation used in nanoparticle PDF simulations is the incorporation of a form factor describing nanoparticle size and shape. The precise effect of the form factor on the PDF is determined by both particle shape and structure if these characteristics are both anisotropic and correlated. The correct incorporation of finite size effects is important for distinguishing and quantifying the structural consequences of small particle size in nanomaterials.
Date: October 1, 2008
Creator: Gilbert, Benjamin
Partner: UNT Libraries Government Documents Department

Fluid effects on seismic waves in hard rocks with fractures and in soft granular media

Description: When fractures in otherwise hard rocks are filled with fluids (oil, gas, water, CO{sub 2}), the type and physical state of the fluid (liquid or gas) can make a large difference in the wave speeds and attenuation properties of seismic waves. The present work summarizes methods of deconstructing theses effects of fractures, together with any fluids contained within them, on wave propagation as observed in reflection seismic data. Additional studies of waves in fluid-saturated granular media show that the behavior can be quite different from that for fractured media, since these materials are typically much softer mechanically than are the fractured rocks (i.e., having a very small drained moduli). Important fluid effects in such media are often governed as much by fluid viscosity as by fluid bulk modulus.
Date: March 1, 2009
Creator: Berryman, James G.
Partner: UNT Libraries Government Documents Department

Modeling quasi-static poroelastic propagation using an asymptotic approach

Description: Since the formulation of poroelasticity (Biot(1941)) and its reformulation (Rice & Cleary(1976)), there have been many efforts to solve the coupled system of equations. Perhaps because of the complexity of the governing equations, most of the work has been directed towards finding numerical solutions. For example, Lewis and co-workers published early papers (Lewis & Schrefler(1978); Lewis et al.(1991)Lewis, Schrefler, & Simoni) concerned with finite-element methods for computing consolidation, subsidence, and examining the importance of coupling. Other early work dealt with flow in a deformable fractured medium (Narasimhan & Witherspoon 1976); Noorishad et al.(1984)Noorishad, Tsang, & Witherspoon. This effort eventually evolved into a general numerical approach for modeling fluid flow and deformation (Rutqvist et al.(2002)Rutqvist, Wu, Tsang, & Bodvarsson). As a result of this and other work, numerous coupled, computer-based algorithms have emerged, typically falling into one of three categories: one-way coupling, loose coupling, and full coupling (Minkoff et al.(2003)Minkoff, Stone, Bryant, Peszynska, & Wheeler). In one-way coupling the fluid flow is modeled using a conventional numerical simulator and the resulting change in fluid pressures simply drives the deformation. In loosely coupled modeling distinct geomechanical and fluid flow simulators are run for a sequence of time steps and at the conclusion of each step information is passed between the simulators. In full coupling, the fluid flow and geomechanics equations are solved simultaneously at each time step (Lewis & Sukirman(1993); Lewis & Ghafouri(1997); Gutierrez & Lewis(2002)). One disadvantage of a purely numerical approach to solving the governing equations of poroelasticity is that it is not clear how the various parameters interact and influence the solution. Analytic solutions have an advantage in that respect; the relationship between the medium and fluid properties is clear from the form of the solution. Unfortunately, analytic solutions are only available for highly idealized conditions, such as a ...
Date: November 1, 2007
Creator: Vasco, D.W.
Partner: UNT Libraries Government Documents Department

Modeling broadband poroelastic propagation using an asymptotic approach

Description: An asymptotic method, valid in the presence of smoothly-varying heterogeneity, is used to derive a semi-analytic solution to the equations for fluid and solid displacements in a poroelastic medium. The solution is defined along trajectories through the porous medium model, in the manner of ray theory. The lowest order expression in the asymptotic expansion provides an eikonal equation for the phase. There are three modes of propagation, two modes of longitudinal displacement and a single mode of transverse displacement. The two longitudinal modes define the Biot fast and slow waves which have very different propagation characteristics. In the limit of low frequency, the Biot slow wave propagates as a diffusive disturbance, in essence a transient pressure pulse. Conversely, at low frequencies the Biot fast wave and the transverse mode are modified elastic waves. At intermediate frequencies the wave characteristics of the longitudinal modes are mixed. A comparison of the asymptotic solution with analytic and numerical solutions shows reasonably good agreement for both homogeneous and heterogeneous Earth models.
Date: May 1, 2009
Creator: Vasco, Donald W.
Partner: UNT Libraries Government Documents Department

The Mechanical Properties of Stripa Granite

Description: The mechanical properties of Stripa granite are presented as determined from small (laboratory size), oven-dried specimens, The properties determined include Young's modulus, Poisson's ratio, unaxial compressive fracture stress, and the expansion coefficient, all as a function of temperature, In addition the Brazilian tensile fracture stress, residual shear strength as a function of a normal stress and the rock's anisotropy ratios are presented, Finally ultrasonic determinations at 1 MHz of the rock's dilatational wave velocity are given and the deduced Young's modulus is compared with the static value for room temperature. This report is one of a series documenting the results of the Swedish-American cooperative research program in which the cooperating scientists explore the geological, geophysical, hydrological, geochemical, and structural effects anticipated from the use of a large crystalline rock mass as a geologic repository for nuclear waste.
Date: August 1, 1978
Creator: Swan, G.
Partner: UNT Libraries Government Documents Department

Mechanics of layered anisotropic poroelastic media with applications to effective stress for fluid permeability

Description: The mechanics of vertically layered porous media has some similarities to and some differences from the more typical layered analysis for purely elastic media. Assuming welded solid contact at the solid-solid interfaces implies the usual continuity conditions, which are continuity of the vertical (layering direction) stress components and the horizontal strain components. These conditions are valid for both elastic and poroelastic media. Differences arise through the conditions for the pore pressure and the increment of fluid content in the context of fluid-saturated porous media. The two distinct conditions most often considered between any pair of contiguous layers are: (1) an undrained fluid condition at the interface, meaning that the increment of fluid content is zero (i.e., {delta}{zeta} = 0), or (2) fluid pressure continuity at the interface, implying that the change in fluid pressure is zero across the interface (i.e., {delta}p{sub f} = 0). Depending on the types of measurements being made on the system and the pertinent boundary conditions for these measurements, either (or neither) of these two conditions might be directly pertinent. But these conditions are sufficient nevertheless to be used as thought experiments to determine the expected values of all the poroelastic coefficients. For quasi-static mechanical changes over long time periods, we expect drained conditions to hold, so the pressure must then be continuous. For high frequency wave propagation, the pore-fluid typically acts as if it were undrained (or very nearly so), with vanishing of the fluid increment at the boundaries being appropriate. Poroelastic analysis of both these end-member cases is discussed, and the general equations for a variety of applications to heterogeneous porous media are developed. In particular, effective stress for the fluid permeability of such poroelastic systems is considered; fluid permeabilities characteristic of granular media or tubular pore shapes are treated in some detail, as ...
Date: June 1, 2010
Creator: Berryman, J. G.
Partner: UNT Libraries Government Documents Department

Resonant seismic emission of subsurface objects

Description: Numerical modeling results and field data indicate that some contrasting subsurface objects (such as tunnels, caves, pipes, filled pits, and fluid-filled fractures) are capable of generating durable resonant oscillations after trapping seismic energy. These oscillations consist of surface types of circumferential waves that repeatedly propagate around the object. The resonant emission of such trapped energy occurs primarily in the form of shear body waves that can be detected by remotely placed receivers. Resonant emission reveals itself in the form of sharp resonant peaks for the late parts of the records, when all strong direct and primary reflected waves are gone. These peaks were observed in field data for a buried barrel filled with water, in 2D finite-difference modeling results, and in the exact canonical solution for a fluid-filled sphere. A computed animation for the diffraction of a plane wave upon a low-velocity elastic sphere confirms the generation of resonances by durable surface waves. Resonant emission has characteristic quasi-hyperbolic traveltime patterns on shot gathers. The inversion of these patterns can be performed in the frequency domain after muting the strong direct and primary scattered waves. Subsurface objects can be detected and imaged at a single resonance frequency without an accurate knowledge of source trigger time. The imaging of subsurface objects requires information about the shear velocity distribution in an embedding medium, which can be done interactively during inversion.
Date: April 15, 2009
Creator: Korneev, Valeri A.
Partner: UNT Libraries Government Documents Department

Poroelastic modeling of fracture-seismic wave interaction

Description: Rock containing a compliant, fluid-filled fracture can be viewed as one case of heterogeneous poroelastic media. When this fracture is subjected to seismic waves, a strong contrast in the elastic stiffness between the fracture itself and the background can result in enhanced grain-scale local fluid flow. Because this flow--relaxing the pressure building up within the fracture--can increase the dynamic compliance of the fracture and change energy dissipation (attenuation), the scattering of seismic waves can be enhanced. Previously, for a flat, infinite fracture, we derived poroelastic seismic boundary conditions that describe the relationship between a finite jump in the stress and displacement across a fracture, expressed as a function of the stress and displacement at the boundaries. In this paper, we use these boundary conditions to determine frequency-dependent seismic wave transmission and reflection coefficients. Fluid-filled fractures with a range of mechanical and hydraulic properties are examined. From parametric studies, we found that the hydraulic permeability of a fracture fully saturated with water has little impact on seismic wave scattering. In contrast, the seismic response of a partially water-saturated fracture and a heterogeneous fracture filled with compliant liquid (e.g., supercritical CO{sub 2}) depended on the fracture permeability.
Date: August 15, 2008
Creator: Nakagawa, Seiji
Partner: UNT Libraries Government Documents Department

Poroelastic response of orthotropic fractured porous media

Description: An algorithm is presented for inverting either laboratory or field poroelastic data for all the drained constants of an anisotropic (specifically orthotropic) fractured poroelastic system. While fractures normally weaken the system by increasing the mechanical compliance, any liquids present in these fractures are expected to increase the stiffness somewhat, thus negating to some extent the mechanical weakening influence of the fractures themselves. The analysis presented quantifies these effects and shows that the key physical variable needed to account for the pore-fluid effects is a factor of (1 - B), where B is Skempton's second coe#14;fficient and satisfies 0 {<=} #20; B < 1. This scalar factor uniformly reduces the increase in compliance due to the presence of communicating fractures, thereby stiffening the fractured composite medium by a predictable amount. One further goal of the discussion is to determine how many of the poroelastic constants need to be known by other means in order to determine the rest from remote measurements, such as seismic wave propagation data in the field. Quantitative examples arising in the analysis show that, if the fracture aspect ratio a{sub f} ~ 0.1 and the pore fluid is liquid water, then for several cases considered Skempton's B ~ 0:9, so the stiffening effect of the pore-liquid reduces the change in compliance due to the fractures by a factor 1-B ~ 0.1, in these examples. The results do however depend on the actual moduli of the unfractured elastic material, as well as on the pore-liquid bulk modulus, so these quantitative predictions are just examples, and should not be treated as universal results. Attention is also given to two previously unremarked poroelastic identities, both being useful variants of Gassmann's equations for homogeneous -- but anisotropic -- poroelasticity. Relationships to Skempton's analysis of saturated soils are also noted. The paper ...
Date: December 1, 2010
Creator: Berryman, J.G.
Partner: UNT Libraries Government Documents Department

Probabilistic Simulation of Subsurface Fluid Flow: A Study Using a Numerical Scheme

Description: There has been an increasing interest in probabilistic modeling of hydrogeologic systems. The classical approach to groundwater modeling has been deterministic in nature, where individual layers and formations are assumed to be uniformly homogeneous. Even in the case of complex heterogeneous systems, the heterogeneities describe the differences in parameter values between various layers, but not within any individual layer. In a deterministic model a single-number is assigned to each hydrogeologic parameter, given a particular scale of interest. However, physically there is no such entity as a truly uniform and homogeneous unit. Single-number representations or deterministic predictions are subject to uncertainties. The approach used in this work models such uncertainties with probabilistic parameters. The resulting statistical distributions of output variables are analyzed. A numerical algorithm, based on axiomatic principles of probability theory, performs arithmetic operations between probability distributions. Two subroutines are developed from the algorithm and incorporated into the computer program TERZAGI, which solves groundwater flow problems in saturated, multi-dimensional systems. The probabilistic computer program is given the name, PROGRES. The algorithm has been applied to study the following problems: one-dimensional flow through homogeneous media, steady-state and transient flow conditions, one-dimensional flow through heterogeneous media, steady-state and transient flow conditions, and two-dimensional steady-stte flow through heterogeneous media. The results are compared with those available in the literature.
Date: March 1, 1980
Creator: Buscheck, Timothy Eric
Partner: UNT Libraries Government Documents Department

Physicochemical controls on absorbed water film thickness in unsaturated geological media

Description: Adsorbed water films commonly coat mineral surfaces in unsaturated soils and rocks, reducing flow and transport rates. Therefore, it is important to understand how adsorbed film thickness depends on matric potential, surface chemistry, and solution chemistry. Here, the problem of adsorbed water film thickness is examined through combining capillary scaling with the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. Novel aspects of this analysis include determining capillary influences on film thicknesses, and incorporating solution chemistry-dependent electrostatic potential at air-water interfaces. Capillary analysis of monodisperse packings of spherical grains provided estimated ranges of matric potentials where adsorbed films are stable, and showed that pendular rings within drained porous media retain most of the 'residual' water except under very low matric potentials. Within drained pores, capillary contributions to thinning of adsorbed films on spherical grains are shown to be small, such that DLVO calculations for flat surfaces are suitable approximations. Hamaker constants of common soil minerals were obtained to determine ranges of the dispersion component to matric potential-dependent film thickness. The pressure component associated with electrical double layer forces was estimated using the compression and linear superposition approximations. The pH-dependent electrical double layer pressure component is the dominant contribution to film thicknesses at intermediate values of matric potential, especially in lower ionic strength solutions (&lt; 10 mol m{sup -3}) on surfaces with higher magnitude electrostatic potentials (more negative than - 50 mV). Adsorbed water films are predicted to usually range in thickness from 1 to 20 nm in drained pores and fractures of unsaturated environments.
Date: June 14, 2011
Creator: Tokunaga, T.
Partner: UNT Libraries Government Documents Department

Pore-fluid effects on seismic waves in vertically fractured earth with orthotropic symmetry

Description: For elastically noninteracting vertical-fracture sets at arbitrary orientation angles to each other, a detailed model is presented in which the resulting anisotropic fractured medium generally has orthorhombic symmetry overall. Some of the analysis methods and ideas of Schoenberg are emphasized, together with their connections to other similarly motivated and conceptually related methods by Sayers and Kachanov, among others. Examples show how parallel vertical-fracture sets having HTI (horizontal transversely isotropic) symmetry transform into orthotropic fractured media if some subsets of the vertical fractures are misaligned with the others, and then the fractured system can have VTI (vertical transversely isotropic) symmetry if all of the fractures are aligned randomly or half parallel and half perpendicular to a given vertical plane. An orthotropic example having vertical fractures in an otherwise VTI earth system (studied previously by Schoenberg and Helbig) is compared with the other examples treated and it is finally shown how fluids in the fractures affect the orthotropic poroelastic system response to seismic waves. The key result is that fracture-influence parameters are multiplied by a factor of (1-B), where 0 {le} B &lt; 1 is Skempton's second coefficient for poroelastic media. Skempton's B coefficient is itself a measurable characteristic of fluid-saturated porous rocks, depending on porosity, solid moduli, and the pore-fluid bulk modulus. For heterogeneous porous media, connections between the present work and earlier related results of Brown and Korringa are also established.
Date: May 15, 2010
Creator: Berryman, J.G.
Partner: UNT Libraries Government Documents Department