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An analytical model is presented for the interpretation of pumping tests conducted in a fractured rock aquifer. The solution accommodates multiple horizontal fractures intersecting pumping and observation wells with interconnecting vertical fracture features. The uppermost horizontal fracture is connected via this fracture network to a free surface boundary. Wellbore storage is included at the pumping and observation wells using an approximate superposition technique and the solution is derived using the Laplace transform method. Evaluation is performed by numerical inversion using the Talbot algorithm. Sensitivity of the model to the governing hydraulic parameters for both pumping and observation well data is presented for a realistic range of values for fractured rock. A field example is given to demonstrate the application of the model and to explore the uniqueness of the interpreted values. Based on the results obtained using the present analytical model, estimation of unique values of the vertical hydraulic parameters in a sedimentary rock setting may not be possible using pumping test results. Subsequently, measuring aquifer properties from various testing methods was investigated to explore the significance of fracture heterogeneities relative to tested volumes and to determine which testing methods were capable of producing reliable parameter estimates. The hydrogeological study was performed in a fractured sedimentary rock aquifer using four different field testing methods: constant head tests, pulse interference tests, 12-hour isolated interval pumping tests and 48-hour open-hole pumping tests. Particular emphasis was placed on the reliable estimation of vertical hydraulic parameters in this setting. The evaluation of the pumping test data was performed using the analytical model derived earlier to determine whether the new pumping test model could produce confident estimates of vertical hydraulic parameters. While estimates of horizontal hydraulic conductivity measurements were not affected by test method, open-well pumping tests do not appear able to predict values of vertical hydraulic conductivity and specific yield. Alternatively, pulse interference tests may be a less time-intensive option to constant head injection tests for determining vertical parameters in a sedimentary rock setting. / Thesis (Master, Civil Engineering) -- Queen's University, 2012-09-14 11:28:14.466

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Fractures exert a strong influence on fluid flow in subsurface reservoirs, and hence an adequate understanding of fracture properties could provide useful information on how they may be managed optimally to produce oil and gas or to be used as repositories for carbon dioxide (CO2) to mitigate climate change. Since fractures are commonly aligned by the stress field, seismic anisotropy is a key tool in investigating their properties. Velocity anisotropy is now a well-established technique for determining properties such as fracture orientation and density, but in recent years, attention has focused on quantifying azimuthal variations in Pwave attenuation to provide additional information, especially on the fracture size. However, the practical application of this attribute in geophysical exploration is still limited due to the uncertainty associated with its measurement and the difficulty in its interpretation in terms of rock properties. There is still a lack of proper understanding of the physical processes involved in the mechanisms of attenuation anisotropy. In this thesis, I use the seismic modelling approach to study the effects of attenuation anisotropy in fractured porous media using P-waves with the main aim of improving the understanding of these effects and exploring the physical basis of using attenuation anisotropy as a potential tool for the characterization of fractured reservoirs. Fractures with length on the order of the seismic wavelength in reservoir rocks cause scattering of seismic waves which exhibits characteristic azimuthal variations. I study these scattering effects using complementary seismic physical (scale-model laboratory experiments) and numerical (finite difference) modelling approaches. The results of both approaches are consistent in delineating fracture properties from seismic data. The scattered energy is quantified through estimates of the attenuation factor (the inverse of the seismic quality factor Q) and shown to be anisotropic, with elliptical (cos2θ) variations with respect to the survey azimuth angle θ. The minor axis of the Q ellipse corresponds to the fracture normal. In this direction, i.e. across the material grain, the attenuation is a maximum. The major axis corresponds to the fracture strike direction (parallel to the material grain) where minimum attenuation occurs. Empirically, the magnitude of P-wave attenuation anisotropy is greater in fluid-saturated rocks than in dry rocks. I study the influence of fluid saturation on P-wave attenuation through synthetic modelling and compare the attenuation signature to that of dry fractured rocks. The results of the analysis show that the relaxation time strongly controls the frequency range over which attenuation occurs. The magnitude of the induced attenuation increases with polar angle and also away from the fracture strike direction. The attenuation exhibits elliptical variations with azimuth which are also well fitted with a cos2θ function. The magnitude of the attenuation anisotropy is higher in the case of the fluid-saturated rocks. All of these properties of the numerical model are in agreement with the results of empirical experiments in the laboratory. The same crack density can result from many small cracks, from a few large cracks, or from an equal number of cracks of various sizes with varying thicknesses in the same volume of background material. This makes it difficult to distinguish between the anisotropy caused by micro-cracks and that caused by macro-cracks. I study the effects of fracture thickness or aperture on P-wave scattering attenuation through seismic physical modelling, and find that the induced attenuation has a direct relationship with the fracture thickness or aperture. This result indicates the potential of using P-wave attenuation to get information which might be useful in examining the effects of voids in the rocks, and also provides a basis for further future theoretical development to distinguish the effects caused by thin micro cracks and large open fractures. Finally, I study the effects of two types of fluid saturation (brine and CO2 in the supercritical state) on P-wave attenuation through synthetic modelling, with particular attention to varying CO2 saturation using the CO2 properties at the Sleipner gas Field in the North Sea. The presence of CO2 causes more attenuation in the numerical model output than when the rock is saturated with only brine. The induced attenuation increases with decreasing percentage of CO2 saturation and has a maximum magnitude at 10 % CO2 saturation. Further work is needed to quantify the additional effect of fractures on these results.

<p>A series of experiments were carried out to gain a better understanding of the mechanisms governing the transport of biological and non-biological particles through single, saturated dolomite fractures at the laboratory scale. Fracture apertures and general roughness were characterized using hydraulic and conservative solute tracer experiments.</p> <p>The effects of particle size, surface characteristics and ionic strength of carrying solution were all evaluated. Particulate material studied included MS2, <em>E. coli</em> and two sizes of carboxylated microspheres. To elucidate the effect of ionic strength on particulate transport, the ionic strength of the carrying solution was altered during each experiment. All particulate experiments were completed at a specific discharge of 15 m/day to facilitate comparisons.</p> <p>Recovery of biological particulate material was found to be much less relative to the carboxylated microspheres, even though the energy profiles predicted similar interactions with the fracture surface. This suggests that the biological surface has a significant impact on retention within the fracture. Further, altering the ionic strength of the carrying solution did not spur significant elution of additional particulate material, regardless of surface characteristics. Therefore, it was determined that retention within the secondary energy minimum was negligible under these operating conditions.</p> <p>With respect to carboxylated microspheres, increased retention was observed within the less variable fracture. This suggests that increased variability within a fracture results in increased eddying within the aperture field. This eddying effectively reduces the aperture region available for particle transport, lessening the particle/fracture interaction. Overall, while mean residence times were similar, recovery of biological particles was poorly replicated by microspheres.</p> / Master of Applied Science (MASc)

Understanding groundwater flow systems and how these control transport is an essential part in assessing the suitability of subsurface environments as hosts for storage of toxic waste. Therefore it is important to be able to integrate knowledge obtained from field characterisation of the subsurface with methods which can be used to evaluate and predict possible impact on surrounding environments.In this thesis I investigate the characteristics of flow and transport in discrete fracture networks by analysing Eulerian and Lagrangian descriptions within a stochastic framework. The analysis is conducted through numerical flow and transport simulations configured according to available field data, combined with independent theoretical analytic and semi-analytic methods which are able to reveal insight to relevant constitutive properties. It is shown that numerical simulations conducted with the discrete fracture network approach can be both conditioned and confirmed against field measurable quantities, and the developed theoretical methods are evaluated against results obtained from simulation. Thereby, a methodology which can provide links between field measurable quantities and tracer discharge is presented, developed and evaluated. It is shown to be robust with respect to underlying assumptions used for flow configurations.In particular, a specific sampling algorithm for obtaining a Lagrangian description of transport based on a Eulerian description of flow is proposed, evaluated and shown to be robust for the cases considered, providing accurate replications. Also a generalisation of both the advection-dispersion solution and the one-sided stable distribution is shown to be able to evaluate advective transport quantities, and combined with a Lagrangian retention model it is shown to be a fairly accurate and robust method for upscaling distributions, enabling predictions of transport in terms of tracer discharge. Evaluation of transport is also conducted against the advective-dispersion assumption, where results indicate advective transport is generally non-Fickian for the fracture networks and domain scales considered, but not necessarily anomalous. Additionally, the impact certain model assumptions have on tracer discharge are analysed. For example, transport is evaluated for assumptions regarding injection mode, fracture network heterogeneity, relationship between aperture and transmissivity, relationship between transmissivity and size, as well as scale and modelling dimension. In relation to hydraulic testing and flow analysis, a method for conditioning fracture transmissivity from field measurements of flow by simulation is developed and evaluated against homogenisation assumptions commonly used in field applications. Results indicate the homogenisation assumption generally fails for current interpretations of field data. / Miljökonsekvensbedömningar av toxiskt avfall i djupt bergförvar kräver engrundläggande förståelse av grundvattenströmning samt hur detta påverkartransportfenomet. Därför är det viktigt att kunna integrerafältundersökningsdata från berggrundsmätningar med metoder som kan användas föratt utvärdera och förutsäga potentiella konsekvenser på omgivningen.I denna avhandling undersöker jag flödes- och transportegenskaper i diskretaspricknätverk genom stokastisk analys av eulerska och lagrangeskafältbeskrivningar. Analysen sker genom en kombination av dels numeriska flödes-och transportsimuleringar som är konfigurerade enligt tillgänglig fältdata, samtdels med oberoende teoretiska analytiska och semi-analytiska metoder som gerdjupare insyn i relevanta konstitutiva egenskaper. Resultat visar att dennumeriska simuleringsmetoden för diskreta spricknätverk kan både konditionerastill fältdata och bestyrkas gentemot mätbara kvantiter. Detta är av betydelse dåde teoretiska metoderna i sin tur är främst evaluerade gentemotsimuleringsresultat. Därmed utvecklas en bestyrkt metodik som kansammanlänka och i viss mån omvandla fältdata till uppskattningar av mängdenspårämnen i ett utflöde. Resultat indikerar att denna metodik är robust avseendeflera antaganden som har används i simuleringskonfigurationen.En särskild urvalsalgoritm introduceras som kan erhålla en lagrangesktransportbeskrivning utifrån ett eulerskt strömningsfält. även denna utvärderasavseende vissa simuleringsantaganden och resultat tyder på att den är robust förde undersökta fallen. Vidare föreslås en viss generalisering av lösningen tillden advektiva-dispersionsekvationen samt av ensidigt stabila (one-sided stable)sannolikhetsfördelningar som metod för att prediktera advektiva kvantitetergenom upskalning av transportfördelningar i rummet. Denna modell kombineras meden tidigare utvecklad metod för transportretention för att uppskatta reaktivagenombrottsfördelningar. Således blir det möjligt att prediktera reaktivtransport d v s rumslig upskalning av genombrottstider för spårämnestransport.Metoden används också för att evaluera ett linärt dispersionsantagande, därresultat indikerar att även advektiv transport kan påvisa icke-linärt beteende.Transport i spricknätverk utvärderas bland annat för modellantaganden avseendeinjektionsmetod, heterogenitet i spricknätverk, konstitutiva relationer mellanapertur och transmissivitet samt mellan transmissivitet och spricklängd, ochmodelleringsskala samt dimension. Beträffande hydrauliska testmetoder ochflödesanalys introduceras en simuleringsmetod för att konditioneraspricktransmissivitet från flödesmätningar. Detta jämförs med etthomogeniseringsantaganden som inte sällan används i fältundersökningar för atttolka flödesmätningar till spricktransmissivitet, och resultat tyder på attdetta antagande kan betydligt undervärdera transmissivitet.

Multiphase flow and transport in fractured rock is of importance to many practical and engineering applications. In the field of groundwater hydrology an issue of significant environmental concern is the release of dense non-aqueous phase liquids (DNAPLs) which can cause long-term groundwater contamination in fractured aquifers. This study deals with two fundamental processes – fluid displacement and interphase mass transfer – concerning the behavior of the multiphase contaminants in fractured media. The focus of this work has been placed on improving the current understanding of small-scale (single fracture) physics by a combined effort of numerical modeling analysis, laboratory experiments and model development. This thesis contributes to the improved understanding through several aspects. Firstly, the effect of aperture variability, as characterized by geostatistical parameters such as standard deviation and correlation length, on the DNAPL entrapment, dissolution and source-depletion behaviors in single fractures was revealed. Secondly, a novel, generalized approach (adaptive circle fitting approach) to account for the effect of in-plane curvature of fluid-fluid interfaces on immiscible fluid displacement was developed; the new approach has demonstrated good performance when applied to simulate previously published experimental data. Thirdly, the performance of a continuum-based two-phase flow model and an invasion percolation model was compared for modeling fluid displacement in a variable-aperture fracture and the dependence of fracture-scale capillary pressure – saturation relationships on aperture variability was studied. Lastly, through experimental studies and mechanistic numerical modeling of DNAPL dissolution, kinetic mass transfer characteristics of two different entrapment configurations (residual blobs and dead-end pools) were investigated. The obtained understanding from this thesis will be useful for predictive modeling of multiphase contaminant behavior at a larger (fracture network) scale. / Flerfasflöde och ämnestransport i sprickigt berg är av betydelse för många praktiska och tekniska problem. Tunga, svårlösliga organiska vätskor (engelska: dense non-aqueous phase liquids: DNAPLs; t.ex. klorerade lösningsmedel) kan orsaka långvarig förorening av vattenresurser, inklusive akviferer i sprickigt berg, och utgör ett viktigt miljöproblem inom grundvattenhydrologin. Denna studie behandlar två fundamentala processer för spridning av flerfasföroreningar i sprickiga medier – utbredning av den organiska vätskan och massöverföring mellan organisk vätska och vatten. Arbetet har fokuserat på att förbättra nuvarande kunskap om de fysikaliska processerna på liten skala (enskilda sprickor) genom en kombination av numerisk modellering, laboratorieexperiment och modellutveckling. Avhandlingen har bidragit till utökad processförståelse i flera avseenden. För det första har arbetet belyst effekterna av sprickaperturens variabilitet, uttryckt med geostatistiska parametrar som standardavvikelse och rumslig korrelationslängd, på fastläggning och lösning av organiska vätskor i enskilda sprickor, samt utmattningsbeteendet hos dessa källor till grundvattenförorening. För det andra har en ny, generell metod (adaptiva cirkelpassningsmetoden) för att ta hänsyn till effekten av krökningen av gränsytan mellan organisk vätska och vatten i sprickplanet utvecklats; denna metod har visats fungera väl i simuleringar av tidigare publicerade experimentella data. För det tredje, har en jämförelse gjorts mellan en kontinuumbaserad tvåfasflödesmodell och en invasions-perkolationsmodell med avseende på hur väl de kan simulera tvåfasflöde i en spricka med varierande apertur. Här studerades även hur relationen mellan kapillärtryck och mättnadsgrad på sprickplansskala beror av variabiliteten i sprickapertur. Till sist undersöktes lösning av den organiska vätskan i grundvatten för två fastläggningsscenarier (fastläggning i immobila droppar och ansamling i fällor – ”återvändssprickor”) både genom experiment och mekanistisk numerisk modellering. Kunskapen som tagits fram i denna avhandling bedöms vara användbar även för att modellera spridningen av flerfasföroreningar på större (spricknätverks-) skalor.

The geological repository for final storage of spent nuclear fuel, envisioned by the Swedish Nuclear Fuel and Management Company (SKB), relies on several barriers: copper canisters deposited in holes in the floor of underground tunnels in deep bedrock, embedded in a buffer of compacted bentonite. The initially unsaturated buffer would take up water from the surrounding rock mass and swell to seal any potential gap. This initial two-phase (gas and liquid) regime with two components (air and water) may impact the final density, swelling pressure and biogeochemical conditions in the buffer. A main objective of this work is to identify factors and mechanisms that govern deposition hole inflow and bentonite wetting under the prevailing two-phase flow conditions in sparsely fractured bedrock. For this purpose, we use the numerical code TOUGH2 to perform two-phase flow simulations, conditioned by a companion field experiment (the Bentonite Rock Interaction Experiment or BRIE) performed in a 417 m deep tunnel of the Äspö Hard Rock Laboratory in southeastern Sweden. The models predict a significant de-saturation of the rock wall, which was confirmed by field data. To predict the early buffer wetting rates and patterns, the position of local flowing fractures and estimates of local rock matrix permeability appear more important than the total open hole groundwater inflow. A global sensitivity analysis showed that the buffer wetting time and the persistence of unsaturated conditions over extended periods of time in the rock depend primarily on the local fracture positions, rock matrix permeability, ventilation conditions in the tunnel and pressure far in the rock. Dismantling photographs from BRIE were used to reconstruct a fine-scale snapshot of saturation at the bentonite/rock interface, showing tremendous spatial variability. The high level of heterogeneity in the rock generates complex two-phase flow phenomena (air trapping, dissolution), which need to be accounted for in buffer design and rock suitability criteria. In particular, results suggest that uncertainties regarding two-phase flow behavior are relatively high close to residual air saturation, which may also have important implications for other applications involving two-phase flows, such as geological storage of carbon dioxide. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 1: Manuscript. Paper 4: Manuscript.</p>

<p>One of many applications of geohydraulic modelling is assessing the suitability of a site to host a nuclear waste repository. This modelling task is complicated by scale-dependent heterogeneity and coupled thermo-hydro-mechanical (THM) processes. The objective here was to develop methods for (i) upscaling flow and transport in fractured media from detailed-scale data and (ii) accounting for THM-induced effects on regional-scale transport. An example field data set was used for demonstration.</p><p>A systematic framework was developed where equivalent properties of flow, transport, and stress-effects were estimated with discrete fracture network (DFN) modelling, at some block scale, and then transferred to a regional-scale stochastic continuum (SC) model. The selected block scale allowed a continuum approximation of flow, but not of transport. Instead, block-scale transport was quantified by transit time distributions and modelled with a particle random walk method at the regional scale.</p><p>An enhanced SC-upscaling approach was developed to reproduce the DFN flow results more simply. This required: (i) weighting of the input well-test data by their conductivity-dependent test volumes and (ii) conductivity-dependent correlation structure. Interestingly, the best-fitting correlation structure resembled the density function of DFN transmissivities. </p><p>Channelized transport, over distances exceeding the block scale, was modelled with a transport persistence length. A linear relationship was found between this persistence length and the macroscale dispersion coefficient, with a slope equal to a representative mean block-scale dispersion coefficient.</p><p>A method was also developed to combine well-test data and rock-mechanical data in estimating fracture transmissivities, and its application was demonstrated.</p><p>Finally, an overall sequential THM analysis was introduced allowing the estimation of the significance of waste-related thermo-mechanical (TM) effects on regional transport; here TM effects are calculated separately and their impact on fracture transmissivities were incorporated into the hybrid framework. For the particular case, their effects on regional-scale transport were small.</p>

One of many applications of geohydraulic modelling is assessing the suitability of a site to host a nuclear waste repository. This modelling task is complicated by scale-dependent heterogeneity and coupled thermo-hydro-mechanical (THM) processes. The objective here was to develop methods for (i) upscaling flow and transport in fractured media from detailed-scale data and (ii) accounting for THM-induced effects on regional-scale transport. An example field data set was used for demonstration. A systematic framework was developed where equivalent properties of flow, transport, and stress-effects were estimated with discrete fracture network (DFN) modelling, at some block scale, and then transferred to a regional-scale stochastic continuum (SC) model. The selected block scale allowed a continuum approximation of flow, but not of transport. Instead, block-scale transport was quantified by transit time distributions and modelled with a particle random walk method at the regional scale. An enhanced SC-upscaling approach was developed to reproduce the DFN flow results more simply. This required: (i) weighting of the input well-test data by their conductivity-dependent test volumes and (ii) conductivity-dependent correlation structure. Interestingly, the best-fitting correlation structure resembled the density function of DFN transmissivities. Channelized transport, over distances exceeding the block scale, was modelled with a transport persistence length. A linear relationship was found between this persistence length and the macroscale dispersion coefficient, with a slope equal to a representative mean block-scale dispersion coefficient. A method was also developed to combine well-test data and rock-mechanical data in estimating fracture transmissivities, and its application was demonstrated. Finally, an overall sequential THM analysis was introduced allowing the estimation of the significance of waste-related thermo-mechanical (TM) effects on regional transport; here TM effects are calculated separately and their impact on fracture transmissivities were incorporated into the hybrid framework. For the particular case, their effects on regional-scale transport were small.