Investigatory Project “ Kaymito Leaves Decoction as Antiseptic Mouthwash ” Essay

Introduction1.1 Problem StatementFractures atomic number 18 prevalent in natural and synthetic structural media, regular(a) in the best engineered materials. We harness betters in bed reel, in sandst cardinal aquifers and oil reservoirs, in body layers and even in unconsolidated materials (Figures 1.1 to 1.4). Fractures argon in addition common in concrete, wasting diseased both as a structural material or as a liner for w atomic number 18ho utilize tanks (Figure 1.5). Clay liners consumptiond in landfills, sludge and salt pissing disposal pits or for under screen background storage tanks washstand burst, releasing their silver contents to the subsurface (Figure 1.6). Even flexible materials much(prenominal) as asphalt fracture with snip (Figure 1.7).The fact that fractures are inevitable has led to using up billions of research dollars to construct safe long-term (10,000 years or much) storage for exalted-level nuclear waste (Savage, 1995 IAEA, 1995), both to de termine which construction techniques are least likely to result in goure and what are the implications of a failure, in term of release to the environment and potential contamination of ground wet sources or exposure of humans to high levels of radioactivity.Why do materials fail? In most(prenominal) cases, the material is flawed from its genesis. In filmy materials, it whitethorn be the inclusion of one different atom or molecule in the structure of the growing crystal, or simply the spliff of two crystal planes. In depositional materials, different element types and sizes whitethorn be laid d aver, resulting in layering which whereforece dumbfounds the initiation plane for the fracture. Most materials fail because of mechanical stresses, for example the weight of the overburden, or heaving (Atkinson, 1989 Heard et al., 1972). several(prenominal) mechanical stresses are applied constantly2 until the material fails, others are delivered in a sudden event. Other causes of failure are thermal stresses, drying and wetting cycles and chemic disintegration.After a material fractures, the two faces of the fracture may be subject to additional stresses which each close or open the fracture, or may subject it to shear. Other materials may temporarily or for good deposit in the fracture, partially or totally blocking it for resultant fluid incline. The fracture may be almost shut for millions of years, that if the material becomes exposed to the surface or near surface environment, the resulting hurt of overburden or weathering may allow the fractures to open. In around cases, we are actually interested in introducing fractures in the subsurface, via hydraulic (Warpinski, 1991) or pneumatic fracturing (Schuring et al., 1995), or more powerful means, to increase fluid ascend in oil reservoirs or at contaminated sites. Our particular focus in this study is the role that fractures play in the black marketment of contaminations in the subsurface. pe eing supply from fractured bedrock aquifers is common in the United States (Mutch and Scott, 1994). With increasing frequency contaminated fractured aquifers are detected (NRC, 1990). In galore(postnominal) cases, the source of the contamination is a Non-Aqueous Phase Liquid (NAPL) which is every in pools or as residual ganglia in the fractures of the porous matrix. Dissolution of the NAPL may occur over several decades, resulting in a growing plume of fade out contaminants which is transported through with(predicate) the fractured aquifer due to natural or imposed hydraulic gradients. Fractures in aquitards may allow the seepage of contaminants, either dissolved or in their own shape, into water sources.Fluid lean in the fractured porous media is of significance not only in the context of contaminant transport, but too in the production of oil from reservoirs, the generation of go for power from geothermal reservoirs, and the prospicience of structural integrity or failure of large geotechnical structures, such as dams or foundations. Thus, the results of this study have a wide range of natural coverings.The conceptual deterrent example of a typical contaminant spill into porous media has been come out forward by Abriola (1989), Mercer and Cohen (1990), Kueper and McWhorter (1991) and Parker et al. (1994). In some cases, the contaminant is dissolved in water and therefrom3 travels in a fractured aquifer or aquitard as a solute. Fractures tender a fast channel for widely distributing the contaminant throughout the aquifer and to a fault result in contaminant transport in somewhat unorthodox directions, depending on the fracture planes that are intersected (Hsieh et al., 1985).More typically a contaminant enters the subsurface as a liquid frame sort out from the gassy or aqueous phases present (Figure 1.8). The NAPL may be leaking from a dishonored or decaying storage vessel (e.g. in a gasoline broadcast or a refinery) or a disposal pond, or may be spilt during transport and use in a manufacturing process (e.g. during degreasing of coat parts, in the electronics industry to clean semiconductors, or in an notefield for modify jet engines). The NAPL travels first through the un virginal zone, under three-phase conflate conditions, displacing air and water. The variations in matrix permeability, due to the heterogeneity of the porous medium, result in additional deviations from vertical hunt.If the NAPL encounters layers of slightly less permeable materials (e.g. silt or clay lenses, or even tightly packed sand), or materials with small pores and thus a higher hairlike entry pressure (e.g. NAPL entranceway a tight, water-filled porous medium), it get out tend to flow mostly in the horizontal direction until it encounters a path of less resistance, either more permeable or with larger pores. Microfractures in the matrix are also important in allowing the NAPL to flow through these lowpermeability lenses. When the N APL reaches the capillary fringe, two scenarios may arise. First, if the NAPL is less dense than water (LNAPL, e.g. gasoline, most hydrocarbons), then buoyancy forces depart allow it to float on top of the water table.The NAPL first forms a small mound, which quickly penetrates horizontally over the water table (Figure 1.9). When the water table rises due to recharge of the aquifer, it displaces the NAPL pool upward, but by that term the saturation of NAPL may be so low that it becomes disconnected. Disconnected NAPL entrust usually not flow under two-phase (water and NAPL) conditions.Connected NAPL will move up and down with the movements of the water table, being smeared until becomes disconnected. If the water table goes higher up the disconnected NAPL, it will begin to slowly dissolve. NAPL in the unsaturated zone will4 slowly volatilize. The rates of dissolution and volatilization are controlled by the flow of water or air, respectively (Powers et al., 1991 Miller et al., 1990 Wilkins et al., 1995 Gierke et al, 1990). A plume of dissolved NAPL will form in the ground water, as fountainhead as a plume of volatilized NAPL in the unsaturated zone.If the NAPL is denser than water (DNAPL, e.g. chlorinated organic solvents, polychlorinated biphenyls, tars and creosotes), then once it reaches the water table it begins to form a mound and spread horizontally until either there is enough mass to overcome the capillary entry pressure (DNAPL into a water saturated matrix) or it finds a path of less resistance into the water-saturated matrix, either a fracture or a more porous/permeable region. Once in the saturated zone, the DNAPL travels downward until either it reaches a low enough saturation to become disconnected (forming drops or ganglia) and immobile, or it finds a low-permeability layer. If the layer does not expire really far, the DNAPL will flow horizontally around it.In many cases, the DNAPL reaches bedrock (Figure 1.10). The rock usually contains f ractures into which the DNAPL flows readily, displacing water. The capillary entry pressure into most fractures is quite low, on the order of a few centimeters of DNAPL head (Kueper and McWhorter, 1991). draw into the fractures continues until either the fracture becomes highly DNAPL saturated, or the fracture is filled or closed below, or the DNAPL spreads thin enough to become disconnected. The DNAPL may flow into horizontal fractures within the fracture net action.In terms of remediation strategies, DNAPLs in fractured bedrock are probably one of the most intractable problems (National research Council, 1994). They are a continuous source of dissolved contaminants for years or decades, making any pumping or active bioremediation alternative a very long term and costly proposition. Excavation down to the fractured bedrock is very expensive in most cases, and removal of the contaminated bedrock even more so.Potential remediation alternatives for sellation, include dewatering th e contaminated zone via high-rate pumping and then applying begrime Vapor Extraction to remove volatile DNAPLs, or applying steam to mobilize and volatilize the DNAPL towards a collection well. An additional option is to use5 surfactants, either to increase the dissolution of DNAPL or to reduce its interfacial tension and thus remobilize it (Abdul et al., 1992). An issue with remobilizing via surfactants is the potential to come the DNAPLs further down in the aquifer or bedrock, complicating the removal.If an effective remediation scheme is to be engineered, such as Soil Vapor Extraction, steam injection or surfactant-enhanced dissolution or mobilization, we study to escort how DNAPLs flow through fractures. Flow may be either as a solute in the aqueous phase, as two separate phases (DNAPL-water) or as three phases (DNAPL, water and gas, either air or steam). Another complication in any remediation scheme, not intercommunicate in this study, is how to characterize the fracture network. Which are the fractures that carry most of the flow? What is their aperture and direction? What is the density of fracturing in a particular medium? be the fractures connected to other fractures, probably in other planes?How does one exemplification enough of the subsurface to generate a good idea of the complexness involved? Some techniques are beginning to emerge to determine some of the most important parameters. For example, pumping and tracer tests (McKay et al., 1993 Hsieh et al., 1983) may provide enough training to determine the mean mechanical and hydraulic aperture of a fracture, as well as its main orientation. Geo physiological techniques like seismic imaging, ground-penetrating radar and galvanic conductivity tests are being improved to assist in the object of fracture zones (National question Council, 1996).However, there is room for significant improvement in our current ability to characterize fractures in the subsurface. Even if we come to understand how single and multiphase flow occurs in a fracture, and the interactions between the fracture and the porous matrix surrounding it, how do we describe all these phenomena in a modeling manakin? Clearly, we cannot describe every fracture in a model that may consider scales of tens, hundreds or thousands of meters in one or more directions. One approach is to consider the medium as an equivalent continuum (Long, 1985), where the small-scale properties are somehow averaged in the macroscopic scale. probably the best solution for averaging properties is to use a stochastic description of properties such as permeability (or6 hydraulic conductivity) including the effect of fractures on overall permeability, diffusivity, sorption capacity, grain size, wettability, etc. Another approach, first developed in the petroleum industry, is to consider a dual porosity/dual permeability medium (Bai et al., 1993 Zimmerman et al., 1993 fundaments and Roberts, 1991 warren and Root, 1963), referring to the porosity and permeability of the matrix and the fracture. Diffusive or capillary forces drive the contaminants, or the oil and its components, into or out of the matrix, and most advective flow occurs in the fractures. None of these models has yet been validated through controlled experiments.1.2 Research ObjectivesThe objectives of this research are To characterize the fracture aperture dissemination of several fractured porous media at high resolution To study the transport of a contaminant dissolved in water through fractured media, via experimental observation To study the physical processes involved in two- and three-phase displacements at the pore scale To find out two- and three-phase displacements in real fractured porous media To bring the experimental observations into a modeling framework for cryive purposes.1.3 Approach7To understand single and multiphase flow and transport processes in fractures, I first decided to characterize at a high level of resolution t he fracture aperture distribution of a number of fractured rock cores using CAT-scanning. With this information, I determined the geometry and permeability of the fractures, which I then use to construct a numeric flow model. I also use this information to test the validity of predictive models that are based on the assumed statistics of the aperture distribution.For example, stochastic models (Gelhar, 1986) use the geometric mean of the aperture distribution to predict the transmissivity of a fracture, and show that the aperture variance and correlation length can be used to predict the dispersivity of a solute through a fracture. These models have not been, to my knowledge, been tested experimentally prior to this study. I compare these theoretical predictions of fracture transmissivity and dispersivity of a contaminant, with experimental results, both from the interpretation of the breakthrough curve of a non-sorbing tracer and from CAT-scans of the tracer movement through the fr actured cores.To study multiphase displacements at the pore scale, we use a physical micromodel, which is a simile of a real pore space in two dimensions, etched onto a silicon substrate. The advantage of having a realistic pore space, which for the first time has the correct pore body and pore throat dimensions in a micromodel, is that we can observe multiphase displacements under realistic conditions in terms of the balance between capillary and viscous forces. I conduct two- and three-phase displacements to observe the role that water and NAPL layers play in the mobilization of the various phases.The micromodels are also used to study the possible combinations of double displacements, where one phase displaces another which displaces a third phase. The pore scale observations have been captured by Fenwick and Blunt (1996) in a threedimensional, three-phase network model which considers flow in layers and allows for double displacements. This network model then can produce three-p hase congener permeabilities as a function of phase saturation(s) and the displacement path ( drainage, drunkenness or a series of drainage and imbibition steps).8In addition, I use the fracture aperture information to construct capillary pressuresaturation curves for two phase (Pruess and Tsang, 1990) and three phases (Parker and Lenhard, 1987), as well as three-phase proportional permeabilities (Parker and Lenhard, 1990). The fracture aperture distribution is also an input to a fracture network model which I use to study two-phase displacements (drainage and imbibition) under the assumption of capillary-dominated flow.To observe two- and three-phase displacements at a larger scale, in real fractured cores, I use the CAT-scanner. I can observe the displacements at various time steps, in permeable (e.g. sandstones) and impermeable (e.g. granites) fractured media, determining the paths that the different phases follow. These observations are then compared with the results of the n etwork model as well as with more conventional numerical simulation.1.4 Dissertation OverviewThe work is presented in self-contained chapters. Chapter 2 deals with the high resolution measurement and resultant statistical characterization of fracture aperture. Chapter 3 uses the fracture aperture geostatistics to predict transmissivity and diffusivity of a solute in single-phase flow through a fracture, which is then tested experimentally. We also observe the flow of a tracer inside the fracture using the CAT-scanner, and relate the observations to numerical modeling results.Chapter 4 presents the speculation behind the flow characteristics at the pore scale as well as the micromodel observations of two- and three-phase flow. In Chapter 5, twophase flow in fractured and unfractured porous media is presented, comparing CATscanned observations of various two-phase flow combinations (imbibition, drainage and water flooding) against numerical modeling results. Chapter 6 presents three -phase flow9 in fractures, comparing numerical results against CAT-scanner observations. Finally, Chapter 7 considers the engineering relevance of these studies.1.5 ReferencesAtkinson, B. K., 1989 Fracture Mechanics of joggle, Academic Press, reinvigorated York, pp. 548 Abdul, A. S., T. L. Gibson, C. C. Ang, J. C. Smith and R. E. Sobczynski, 1992 Pilot test of in situ surfactant washing of polychlorinated biphenyls and oils from a contaminated site, Ground body of water, 302, 219-231Abriola, L., 1989 Modeling multiphase migration of organic chemicals in groundwater systems A review and assessment, Environmental Health Perspectives, 83, 117-143 Bai, M., D. Elsworth, J-C. Roegiers, 1993 Multiporosity/multipermeability approach to the simulation of naturally fractured reservoirs, Water Resources Research, 296, 1621-1633 Fenwick, D. H. and M. J. Blunt 1996, third Dimensional Modeling of Three Phase Imbibition and Drainage, Advances in Water Resources, (in press)Gelhar, L. W., 1986 Stochastic subsurface hydrology From theory to applications., Water Resources Res., 22(9), 1355-1455.Gierke, J. S., N. J. Hutzler and J. C. Crittenden, Modeling the movement of volatile organic chemicals in columns of unsaturated soil, Water Resources Research, 267, 1529-1547 Heard, H. C., I. Y. Borg, N. L. Carter and C. B. Raleigh, 1972 Flow and fracture of rocks, geophysical Monograph 16, American Geophysical Union, Washington, D. C. Hsieh, P. A., S. P. Neuman, G. K. Stiles and E. S. Simpson, 1985 Field determination of the threedimensional hydraulic conductivity of anisotropic media 2. Methodology and application to fracture rocks, Water Resources Research, 2111, 1667-1676Hsieh, P. A., S. P. Neuman and E. S. Simpson, 1983 Pressure testing offractured rocks- A methodology employing three-dimensional cross-hole tests, Report NUREG/CR-3213 RW, Dept. of Hydrology and Water Resources, University of Arizona, Tucson, AZ 85721 IAEA, 1995 The principles of radioactive waste management, internationalistic Atomic Energy Agency, ViennaJohns, R. A. and P. V. Roberts, 1991 A solute transport model for channelized flow in a fracture. Water Resources Res. 27(8) 1797-1808.Kueper, B. H. and D. B. McWhorter, 1991 The port of dense, nonaqueous phase liquids in fractured clay and rock, Ground Water, 295, 716-728Long, J. C. S., 1985 Verification and characterization of continuum behavior of fractured rock at AECL Underground Research science lab, Report BMI/OCRD-17, LBL-14975, Batelle Memorial Institute, OhioMcKay, L. D., J. A. Cherry and R. W. Gillham, 1993 Field experiments in a fractured clay till, 1. Hydraulic conductivity and fracture aperture, Water Resources Research, 294, 1149-1162 Mercer, J. W. and R. M. Cohen, 1990 A review of immiscible fluids in the subsurface properties, models, characterization and remediation, J. of contaminant Hydrology, 6, 107-163 Miller, C. T., M. M. Poirier-McNeill and A. S. Mayer, 1990 Dissolution of trapped nonaqueous phase liquids mas s transfer characteristics, Water Resources Research, 2611, 2783-2796 Mutch, R. D. and J. I. Scott, 1994 Problems with the damages of Diffusion-Limited Fractured Rock Systems. Hazardous Waste Site Soil Remediation Theory and Application of Innovative Technologies. New York, Marcel Dekker, Inc.National Research Council, 1994 Alternatives for ground water cleanup, National Academy Press, Washington, D. C.National Research Council, 1996 Rock Fracture and Fracture Flow Contemporary Understanding and Applications, Committee on Fracture Characterization and Fluid Flow, National Academy Press, Washington, D. C. (in press).Parker, J. C. and R. J. Lenhard, 1987 A model for hysteretic constitutive relations governing multiphase flow 1. Saturation-pressure relations, Water Resources Research, 2312, 2187-219610 Parker, J. C. and R. J. Lenhard,1990 Determining three-phase permeability-saturation-pressure relations from two-phase system measurements, J. Pet. Sci. and Eng., 4, 57-65 Parker, B. L. , R. W. Gillham and J. A. Cherry, 1994 Diffusive disappearance of immiscible-phase organic liquids in fractured geologic media, Ground Water, 325, 805-820 Powers, S. E., C. O. Loureiro, L. M. Abriola and W. J. Weber, Jr., 1991 Theoretical study of the significance of nonequilibrium dissolution of nonaqueous phase liquids in subsurface systems, Water Resources Research, 274, 463-477Pruess, K. and Y. W. Tsang, 1990 On two-phase relative permeability and capillary pressure of roughwalled rock fractures, Water Resources Research, 269, 1915-1926 Reitsma, S. and B. H. Kueper, 1994 Laboratory measurement of capillary pressure-saturation relationships in a rock fracture, Water Resources Research, 304, 865-878 Savage, D., 1995 The scientific and regulatory basis for the geological disposal of radioactive waste, John Wiley, New YorkSchuring, J. R., P. C. Chan and T. M. Boland, 1995 Using pneumatic fracturing for in-situ remediation of contaminated sites, Remediation, 52, 77-90Norman R. Warpin ski, 1991 Hydraulic fracturing in tight, fissured media, SPE 20154, J. Petroleum Technology, 432, 146-209Warren , J. E. and P. J. Root, 1963 The behavior of naturally fractured reservoirs, Soc. Pet. Eng. J., 3, 245-255Wilkins, M. D., L. M. Abriola and K. D. Pennell, 1995 An experimental investigation of rate-limited nonaqueous phase liquid volatilization in unsaturated porous media Steady state mass transfer, Water Resources Research, 319, 2159-2172Zimmerman, R. W., G. Chen, T. Hadgu and G S. Bodvarsson, 1993 A numerical dual-porosity model with semianalytical treatment of fracture/matrix flow, Water Resources Research, 297, 2127-2137