Dissertations / Theses on the topic 'Geological heterogeneity'

Thèse Ecole polytechnique fédérale de Lausanne EPFL, no 4156 (2008), Faculté de l'environnement naturel, architectural et construit ENAC, Programme doctoral Environnement, Institut des infrastructures, des ressources et de l'environnement ICARE (Laboratoire de géologie de l'ingénieur et de l'environnement GEOLEP). Dir.: Aurèle Parriaux, Laurent Tacher.

Thesis (M.S.)--Dept. of Geosciences. University of Missouri--Kansas City, 2006.
"A thesis in urban environmental geology." Typescript. Advisor: Jejung Lee. Vita. Title from "catalog record" of the print edition Description based on contents viewed Jan. 29, 2007. Includes bibliographical references (leaves 60-62). Online version of the print edition.

This work presents model development and model analyses of CO2 storage in deep saline aquifers. The goal has been two-fold, firstly to develop models and address the system behaviour under geological heterogeneity, second to tackle the issues related to problem scale as modelling of the CO2 storage systems can become prohibitively complex when large systems are considered. The work starts from a Monte Carlo analysis of heterogeneous 2D domains with a focus on the sensitivity of two CO2  storage performance measurements, namely, the injectivity index (Iinj) and storage efficiency coefficient (E), on parameters characterizing heterogeneity. It is found that E and Iinj are determined by two different parameter groups which both include correlation length (λ) and standard deviation (σ) of the permeability. Next, the issue of upscaling is addressed by modelling a heterogeneous system with multi-modal heterogeneity and an upscaling scheme of the constitutive relationships is proposed to enable the numerical simulation to be done using a coarser geological mesh built for a larger domain. Finally, in order to better address stochastically heterogeneous systems, a new method for model simulations and uncertainty analysis based on a Gaussian processes emulator is introduced. Instead of conventional point estimates this Bayesian approach can efficiently approximate cumulative distribution functions for the selected outputs which are CO2 breakthrough time and its total mass. After focusing on reservoir behaviour in small domains and modelling the heterogeneity effects in them, the work moves to predictive modelling of large scale CO2  storage systems. To maximize the confidence in the model predictions, a set of different modelling approaches of varying complexity is employed, including a semi-analytical model, a sharp-interface vertical equilibrium (VE) model and a TOUGH2MP / ECO2N model. Based on this approach, the CO2 storage potential of two large scale sites is modelled, namely the South Scania site, Sweden and the Dalders Monocline in the Baltic Sea basin. The methodologies developed and demonstrated in this work enable improved analyses of CO2 geological storage at both small and large scales, including better approaches to address medium heterogeneity. Finally, recommendations for future work are also discussed.

Secondary polymer flooding can significantly improve oil recovery over that obtained by waterflooding. This is achieved principally by improving the water-oil mobility ratio and thus reducing channelling. There are, however, several polymer-specific mechanisms (such as adsorption, mixing, permeability reduction, non-Newtonian flows) that make it more difficult to model numerically compared with waterflooding. Upscaling reservoir properties for reservoir simulation is one of the most important steps in the workflow for building robust dynamic simulation models. It is necessary to reduce computing time and resources when it is not possible to run multiple high resolution models (e.g. as in evaluating the impact of geological uncertainty). This is normally achieved by modifying the inputs to reservoir simulation to represent the influence of sub-grid block heterogeneities on large scale flow and also to compensate for numerical dispersion. At the time of writing there are no accepted methods for upscaling polymer flooding. This study investigates the possibility of creating a methodology to upscale the permeability, the relative permeability, and polymer properties such as adsorption and non-Newtonian flow index. This helps to better represent the secondary polymer flood process by accounting for sub-grid block heterogeneity and compensate for numerical dispersion. The proposed methodology consists of four stages: First, the absolute permeability is upscaled using any of the available upscaling techniques in the literature. This will allow representing the effects of geological heterogeneity on pressure. Second, the effective relative permeability curves are calculated to represent these heterogeneities on the flood front conformance. Third, traditional dynamic pseudo methods are used to compensate for numerical dispersion. Finally, upscale polymer properties to better represent the average polymer concentration distribution in the reservoir. An experimental design has been conducted to identify which polymer property have the most effect in polymer flood simulation. Both the experimental design and the proposed methodology have been demonstrated on a series of 1D and 2D runs with various heterogeneity levels. An alternative method is also presented which is based on volume averaging of properties. This is similar to the pseudoization techniques used for the upscaling the relative permeability with the addition of pseudoizing both adsorption and polymer viscosity in order to accurately represent track the polymer front in the coarse grid model. this method is also tested using several 1D and 2D cases with different permeability distributions.

The demand for large scale storage of carbon dioxide (CO2) grows stronger as incentives to reduce greenhouse gas emissions are introduced. Geological storage sites such as depleted oil and gas reservoirs, unminable coal seams and deep saline water-saturated aquifers are a few of many possible geological storage sites. Geological formations offer large scale storage potential, hidden locations and are naturally occurring world wide. A disadvantage is the difficulty to investigate the properties of storage material over large areas. Reservoir simulation studies addressing issues of heterogeneous reservoirs are growing in number. There is still much to investigate however this study adds to the field by investigating the significance of the heterogeneity in hydraulic conductivity based on core sample data. The data was received from the main CO2 injection site Heletz, Israel in the European Union Seventh Framework Programme for research and technological development (EU FP7) project MUSTANG (CO2MUSTANG, 2011-03-13). By developing models using iTOUGH2/ECO2N, the aim of this study is to contribute to a better understanding of how the average permeability, variance in permeability and spatial correlation of the reservoir properties affect the distribution of CO2 within the deep saline aquifer target layer. In this study a stochastic simulation approach known as the Monte Carlo method is applied. Based on core sample data, geostatistical properties of the data are determined and utilized to create equally probable realizations where properties are described through a probability distribution described by a mean and variance as well as a constructed semivariogram. The results suggest that deep saline aquifers are less storage effective for higher values of average permeability, variance in permeability and spatial correlation. The results also indicate that the Heletz aquifer, with its highly heterogeneous characteristics, in some extreme cases can be just as storage effective as a deep saline aquifer ten times as permeable consisting of homogeneous sandstone.
Incitament för minskningar av växthusgaser har på senare tid ökat efterfrågan för storskalig lagring av koldioxid (CO2). Geologiska lagringsplatser som exploaterade olje- och gasreservoarer, svårutvunna kollager och djupt belägna salina akvifärer är exempel på potentiella lagringsplatser. Sådana geologiska formationer erbjuder storskalig lagring, dold förvaring och är naturligt förekommande världen över. Dock finns det stora svårigheter i att undersöka de materiella egenskaperna för hela lagringsområden. Simuleringsstudier som hantera frågor gällande reservoarers heterogenitet växer i antal. Det finns fortfarande mycket kvar att undersöka och denna studie bidrar till detta forskningsområde genom att undersöka betydelsen av heterogenitet i hydraulisk konduktivitet för spridningen av koldioxid med hjälp av uppmätt brunnsdata. Data erhölls från lagringsplatsen Heletz i Israel som är den huvudsakliga lagringplatsen i projektet MUSTANG är en del av den Europeiska Unionens sjunde ramprogram för forskning och teknisk utveckling (EU FP7), (CO2MUSTANG, 2011/3/13). Genom att utveckla modeller med hjälp av programvaran iTOUGH2/ECO2N är syftet med denna studie att bidra till en bättre förståelse för hur den genomsnittliga permeabilitet, varians i permeabilitet samt rumslig korrelation av reservoaregenskaper påverkar fördelningen av CO2 i den djupa saltvattenakvifären Heletz. Denna studie använde sig av stokastisk simulering genom att tillämpa Monte Carlo-metoden. Med hjälp av tidigare uppmätt brunnsdata kunde geostatistiska egenskaper bestämmas för att skapa ekvivalent sannolika realiseringar. De geostatistiska egenskaperna beskrevs med en sannolikhetsfördelning genom medelvärde och varians samt ett konstruerat semivariogram. Resultaten tyder på att djupa saltvattenakvifärer är mindre lagringseffektiva vid högre värden av genomsnittlig permeabilitet, varians i permeabilitet och rumslig horisontell korrelation. Resultaten visar även att Heletz akvifär, med dess mycket heterogena egenskaper, i extrema fall kan vara lika lagringsineffektiv som en djupt belägen saltvattenakvifär med tio gånger högre genomsnittlig permeabilitet.

Numerous gas field developments worldwide have maximised profitability by utilising high productivity, large-bore horizontal completions. However, this production strategy is associated with significant risk in reservoirs with a large component of water-drive, particularly if the gas column is thin, the structural relief is small, and the reservoir is producing from only one or two wells. Rapid water influx ('cresting') can lead to early water breakthrough which effectively 'kills' the well. Predicting the time to breakthrough requires proper consideration of the interaction between reservoir properties and production strategy. We present an integrated geoscience and engineering study to quantify the impact of depositional heterogeneity on gas-water fluid flow behaviour when horizontal wells are produced at high rates in the presence of a bottom water aquifer. Gas production is simulated from a reservoir model of a single shoreface-shelf parasequence, that is conditioned to' high-resolution outcrop data. Novel surface-based modelling techniques ensure that cr\rical heterogeneities are captured without recourse to upscaling. The model is representative of gas reservoirs in the Columbus Basin, offshore Trinidad and Tobago, which are currently being developed using a small number of high rate horizontal wells. We find that an understanding of well location with respect to the spatial distribution of non-reservoir. units is critical to managing production rate and delaying water break1hrough. This is because enhanced recovery occurs when heterogeneity is suppressing cresting, rather than because production is 'outrunning' the aquifer. Furthermore, when the well is protected from water cresting, aquifer support is actually observed to improve ultimate recovery. Simulation models should possess sufficient geological detail to describe the location and 3D architecture of baffles to flow. Other aspects of the reservoir description, such as permeability contrasts between facies, are much less significant. Our results explain how material balance approaches can be interpreted to improve predictions of production performance when there is a significant risk of water cresting, or the aquifer response is modified by depositional heterogeneity.

A model is developed to describe solute transport and retention in fractured rocks. It accounts for the fact that solutes not only can diffuse directly from the flowing channel into the adjacent rock matrix composed of different geological layers but can also at first diffuse into the stagnant water zone occupied in part of the fracture and then from there into the rock matrix adjacent to it. Moreover, the effect of radioactive decay-chain has also been studied in the presence of matrix comprising different geological layers. In spite of the complexities of the system, the analytical solution obtained for the Laplace-transformed concentration at the outlet of the flowing channel can conveniently be transformed back to the time domainby use of e.g. De Hoog algorithm. This allows one to readily include it into a fracture network modelorachannelnetwork model to predictnuclide transport through channels in heterogeneous fracturedmedia consisting of an arbitrary number of rock units withpiecewise constant properties. Simulations made in this study indicate that, in addition to the intact wall rock adjacent to the flowing channel, the stagnant water zone and the rock matrix adjacent to it may also lead to a considerable retardation of solute in cases with a narrow channel. The results further suggest that it is necessary to account for decay-chain and also rock matrix comprising at least two different geological layers in safety and performance assessment of the repositories for spent nuclear fuel. The altered zone may cause a great decrease of the nuclide concentration at the outlet of the flowing channel. The radionuclide decay, when accounted for, will drastically decrease the concentration of nuclides, while neglecting radioactive ingrowth would underestimate the concentration of daughter nuclides.

QC 20140224

One of the main concerns in reservoir studies is to accurately define the internal architecture and the geological characteristics of the reservoir so as to estimate the amount of hydrocarbons that could be recovered for a given development strategy. This can represent a major challenge especially during the appraisal stage of a reservoir, because the information available is still very limited, or in the presence of geological heterogeneities, which increase the architectural complexity and the uncertainty associated to the internal description, such as in channelized depositional settings. At the appraisal stage of a reservoir study, all the uncertainties affecting the quantity and distribution of hydrocarbons in the reservoir should be captured and accounted for in the evaluation of the final hydrocarbon recovery to properly assess the viability of any development plan. A typical modeling workflow accounting for geological uncertainties consists in creating a large set of 3-D stochastic geological (static) models from a set of geological input parameters. Subsequently, a few representative reservoir realizations are selected out of this set based on the calculated hydrocarbons originally in place and simulated to estimate future production so as to propagate the uncertainty onto the final recovery factors. However, even in homogeneous reservoirs, the estimation of the hydrocarbon stored in the reservoir can be affected by uncertainties because it is calculated mostly from local petrophysical parameters, which might not be representative of the rock properties at the reservoir scale. This especially applies to channelized reservoirs characterized by depositional elements with high geological heterogeneity, both in the lateral and in the vertical directions. Thus for these depositional settings a more attractive criterion for the model selection is offered by the study of the connectivity layout of the reservoir elements. In the technical literature, connectivity is defined through numerical indexes that account for geological connectivity between reservoir elements, which might not be indicative of reservoir production performance. In fact, the latter is influenced by the degree of connectivity among sand bodies and only deep merging of the channels guarantees that the reservoir can be efficiently drained by just a few wells. Therefore, in the first place, the present study was aimed at thoroughly investigating the validity of the indexes previously proposed in the technical literature by evaluating the reservoir production uncertainty associated to sets of synthetic equi-probable models of channelized oil reservoirs. Secondly, the goal of the research was to develop new indexes to express the channel connectivity, capable of incorporating information on the quality of the connectivity through the evaluation of channel amalgamation. When applied to the same set of reservoir equi-probable realizations, these indexes proved that a more effective selection of the geological realizations can be made to capture the uncertainty affecting the forecasted reservoir production performance.

La démarche d’intégration des hétérogénéités dans les modèles réservoirs en est à ses prémices dans le domaine du stockage géologique de CO2. C’est dans ce contexte que s’inscrivent ces travaux de thèse. Un protocole d’analyse depuis l’étude de terrain jusqu’aux simulations réservoirs a été établi. La caractérisation du Minjur Sandstone (formation Triasique d’Arabie Centrale) met en avant le caractère crucial de la connectivité des corps dans l’architecture du réservoir, notamment en liant génétiquement leur nature, leur connectivité et leur position dans la séquence de dépôt. S’appuyant sur la connaissance de cette formation, un modèle conceptuel est construit, puis reproduit stochastiquement par un algorithme permettant l’élaboration de modèles conditionnés par une histoire sédimentaire. Le protocole prévoit la création de 50 scénarios illustrant divers degrés de connectivité ; chaque scénario étant composé de deux modèles de même architecture mais à remplissage sédimentaire différent. Cette approche permet d’appréhender (a) l’impact de la connectivité et (b) des hétérogénéités sédimentaires sur les performances réservoirs. L’estimation de capacité par l’approche statique des volumes disponibles estime une capacité moyenne d’environ 13Mt (aquifère semi-infini de 25 km par 25 km et 60m d’épaisseur à 1000 m de profondeur). Les hétérogénéités internes (sédiments argileux appelés oxbow lakes) entraînent une différence de capacité de 30%. Les simulations dynamiques confirment ces résultats et révèle une variabilité de capacité de 23% liée la connectivité des corps. De plus les hétérogénéités réduisent la migration verticale du gaz ce qui peut augmenter l’intégrité du stockage
In the CO2 storage context, heterogeneity has only been rarely considered in reservoir models to date. To address this key issue, the project aims at developing a workflow that manages the heterogeneity from the field observations up to the reservoir simulation. The characterisation of the Minjur Sandstone (a Triassic formation from Central Saudi Arabia) shows the crucial role of connectivity in the reservoir architecture, and the genetic link between the nature, location and connectivity of the sedimentary bodies in the sequence. Stemming from this study, a conceptual model was established and stochastically reproduced through an algorithm simulating models conditioned to a sedimentary history. Fifty scenarios were simulated, representing various connectivity degrees. Each of these scenarios is composed of two models, identical by their architecture but different in their internal sedimentary fill. This approach allows the study of the impact of the (a) reservoir bodies’ connectivity and (b) their internal sedimentary heterogeneity on the reservoir’s performances. The capacity estimates using a static calculation based on the available pore volumes reveals a mean capacity of 13 Mt (for a 25 x 25 km x 60 m semi finite aquifer at 1000m deep). The sedimentary heterogeneity (shaly deposits called oxbow lakes) is responsible for a 30% difference of capacity. The flow simulations confirm these results and show that the connectivity of the reservoir bodies creates a 23% capacity variation. Moreover, the heterogeneities tend to reduce the amount of CO2 able to reach the uppermost reservoir which may enhance the storage integrity

Geological Carbon Storage (GCS) is considered as one of the key techniques to reduce the rate of atmospheric emissions of CO2 and thereby to contribute to controlling the global warming. A successful application of a GCS project requires the capability of the formation to trap CO2 for a long term. In this context, processes related to CO2 trapping and also possible leakage of CO2 to the near surface environment need to be understood. The overall aim of this thesis is to understand the flow and transport of CO2 through porous media in the context of geological storage of CO2. The entire range of scales, including the pore scale, the laboratory scale, the field experiment scale and the industrial scale of CO2 injection operation are addressed, and some of the key processes investigated by means of experiments and modeling.  First, a numerical model and laboratory experimental setup were developed to investigate the CO2 gas flow, mimicking the system in the near-surface conditions in case a leak from the storage formation should occur. The system specifically addressed the coupled flow and mass transport of gaseous CO2 both in the porous domain as well as the free flow domain above it. The comparison of experiments and modelling results showed a very good agreement indicating that the model developed can be applied to evaluate monitoring and surface detection of potential CO2 leakage. Second, the field scale CO2 injection test carried out in a shallow aquifer in Maguelone, France was analyzed and modeled. The results showed that Monte Carlo simulations accounting for the heterogeneity effects of the permeability field did capture the key observations of the monitoring data, while a homogeneous model could not represent them. Third, a numerical model based on phase-field method was developed and model simulations carried out addressing the effect of wettability on CO2-brine displacement at the pore-scale. The results show that strongly water-wet reservoirs provide a better potential for the dissolution trapping, due to the increase of interface between CO2 and brine with very low contact angles. The results further showed that strong water-wet conditions also imply a strong capillary effect, which is important for residual trapping of CO2. Finally, numerical model development and model simulations were carried out to address the large scale geological storage of CO2 in the presence of impurity gases in the CO2 rich phase. The results showed that impurity gases N2 and CH4 affected the spatial distribution of the gas (the supercritical CO2 rich phase), and a larger volume of reservoir is needed in comparison to the pure CO2 injection scenario. In addition, the solubility trapping significantly increased in the presence of N2 and CH4.

Carbon-capture and sequestration (CCS) in geologic reservoirs is one strategy for reducing anthropogenic CO2 emissions from large-scale point source emitters. Recent developments have shown that basalt reservoirs are highly effective for permanent mineral trapping on the basis of CO2-water-rock interactions, which result in the formation of carbonate minerals. However, the injection of super-critical CO2 into the subsurface causes a disturbance in the pressure, temperature, and chemical systems within the target reservoir. How the ambient conditions change in response to a CO2 injection ultimately affects the transport and fate of the injected CO2. Understanding the behavior and transport of CO2 within a geologic reservoir is a difficult problem that is only exacerbated by heterogeneities within the reservoir; for example, permeability can be highly heterogeneous and exhibits significant control on the movement of CO2. This work is focused on constraining the permeability uncertainty within a flood basalt reservoir, specifically the Columbia River Basalt Group (CRBG). In order to do so, this dissertation is a culmination of four projects: (1) a geostatistical analysis resulting in a spatial correlation model of regional scale permeability within the CRBG, (2) a Monte Carlo-type modeling studying investigating the effects that permeability uncertainty has on the injectivity and storativity of the CRBG as a storage reservoir, (3) a modeling study utilizing 1-, 2-, and 3-D numerical models to investigate how the thermal signature of the CO2-water system evolves during a CO2 injection, and (4) a Monte Carlo-type modeling study focused on the integrity of the CRBG as a CO2 storage reservoir through a probabilistic assessment of static threshold criteria.
Doctor of Philosophy
The process of capturing CO2 from point-source emitters, such as power plants and injecting that CO2 into a geologic formation is one way to reduce anthropogenic CO2 emissions. Recent field studies have shown that basalt reservoirs may be very effective at permanently storing the injected CO2 making them a secure geologic formation to store the CO2. However, basalt reservoirs can be highly fractured, which causes the properties of the reservoir (e.g. permeability, porosity, etc.) to be nonuniform. Having nonuniform reservoir properties creates uncertainty when planning a large-scale CO2 injection. This research is focused on understanding and constraining the uncertainty of nonuniform reservoir properties associated with a large-scale CO2 injection. The work presented utilizes a geostatistical analysis of permeability to inform a variety of numerical models to study how nonuniform reservoir properties affect CO2 injection rate, how much CO2 can be stored, how the pressure and temperature of the reservoir changes, and how secure the storage reservoir is during a CO2 injection.

Slow slip and tectonic tremor in subduction zones take place at depths (~20 - 50 km) where there is abundant evidence for distributed shear over broad zones (~10 - 10^3 m) composed of rocks with marked differences in mechanical properties and for near lithostatic pore pressures along the plate interface where the main source of fluids must be attributed to chemical dehydration reactions. In Chapter II, I model quasi-dynamic rupture along faults composed of material mixtures characterized by different rate-and-state-dependent frictional properties to determine the parameter regime capable of producing slow slip in an idealized subduction zone setting. Keeping other parameters fixed, the relative proportions of velocity-weakening (VW) and velocity-strengthening (VS) materials control the sliding character (stable, slow, or dynamic) along the fault. The stability boundary between slow and dynamic is accurately described by linear analysis of a double spring-slider system with VW and VS blocks. In Chapter III, I model viscoelastic compaction of material subducting through the slow slip and tremor zone in the presence of pressure and temperature-dependent dehydration reactions. A dehydration fluid source is included using 1) a generalized basalt dehydration reaction in subducting oceanic crust or 2) a general nonlinear kinetic reaction rate law parameterized for an antigorite dehydration reaction. Pore pressures in excess of lithostatic values are a robust feature of simulations that employ parameters consistent with the geometry of the Cascadia subduction margin. Simulations that include viscous deformation uniformly generate traveling porosity waves that transport increased fluid pressures within the slow slip region. Slow slip and tremor also occur in shallow (< 10 km depth) accretionary prism sections of subduction zones. In Chapter IV, I examine how geologic heterogeneities affect the mechanics of accretionary prisms in subduction zones by showing how spatial variations in pore pressure, porosity, and internal friction coefficient affect predictions of basal shear stress, taper angle, and internal slip surface geometry. My results suggest that assuming average porosity throughout the prism may be a good approximation in many cases, but assuming an average value for the pore pressure can cause significant errors. This dissertation includes previously published and unpublished coauthored material.

This dissertation focuses on two different types of responses of Earth; that is, seismic and electromagnetic, and aims to better understand Earth processes at a wider range of scales than those conventional approaches offer. Electromagnetic responses resulting from the subsurface diffusion of applied electromagnetic fields through heterogeneous geoelectrical structures are utilized to characterize the underlying geology. Geology exhibits multiscale hierarchical structure which brought about by almost all geological processes operating across multiple length scales and the relationship between multiscale electrical properties of underlying geology and the observed electromagnetic response has not yet been fully understood. To quantify this relationship, the electromagnetic responses of textured and spatially correlated, stochastic geologic media are herein presented. The modelling results demonstrate that the resulting electromagnetic responses present a power law distribution, rather than a smooth response polluted with random, incoherent noise as commonly assumed; moreover, they are examples of fractional Brownian motion. Furthermore, the results indicate that the fractal behavior of electromagnetic responses is correlated with the degree of the spatial correlation, the contrasts in ground electrical conductivity, and the preferred orientation of small-scale heterogeneity. In addition, these inferences are also supported by the observed electromagnetic responses from a fault zone comprising different lithological units and varying wavelengths of geologic heterogeneity. Seismic signals generated by aftershocks are generally recorded by local aftershock networks consisted of insufficient number of stations which result in strongly spatially-aliased aftershock data. This limits aftershock detections and locations at smaller magnitudes. Following the 23 August 2011 Mineral, Virginia earthquake, to drastically reduce spatial aliasing, a temporary dense array (AIDA) consisting of ~200 stations at 200-400 m spacing was deployed near the epicenter to record the 12 days of the aftershocks. The backprojection imaging method is applied to the entire AIDA dataset to detect and locate aftershocks. The method takes advantage of staking of many seismograms and improves the signal-to-noise ratio for detection. The catalog obtained from the co-deployed, unusually large temporal traditional network of 36 stations enabled a quantitative comparison. The aftershock catalog derived from the dense AIDA array and the backprojection indicates event detection an order of magnitude smaller including events as small as M–1.8. The catalog is complete to magnitude –1.0 while the traditional network catalog was complete to M–0.27 for the same time period. The AIDA backprojection catalog indicate the same major patterns of seismicity in the epicentral region, but additional details are revealed indicating a more complex fault zone and a new shallow cluster. The b-value or the temporal decay constant were not changed by inclusion of the small events; however, they are different for two completeness periods and are different at shallow depth than greater depth.
Ph. D.

Three-dimensional fluid-flow simulation models provide attractive tools for understanding the potential behavior of the subsurface. Retention of high-resolution geologic heterogeneity in the characterization of large volumes presents significant challenges to this modeling.

A 2D dataset donated by Industry constrains a hierarchical stratigraphic framework based on 30,000 wells with log curves, 60 surfaces crossing the 70,000 cubic-kilometer Powder River Basin from Precambrian basement to top of the Cretaceous Lewis Shale. Five sedimentary systems subdivided into 25 stratigraphic intervals make up the 3D representation of 70 discrete modeling areas. These sedimentation regions group distinct sedimentary attributes (e.g., porosity, thickness, sedimentary architecture). These attributes relate to suites of rock properties, such as porosity, percentage of thickness with porosity and well log shape, which were compiled from 4000 wells with donated/purchased log ascii files, 15 cores, 300 wells with public core plug data, 115 published oil field reports, and basin rimming outcrops.

Sedimentary system analysis considered regional controls on the depositional setting from the craton-scale to the pore-scale and it employed techniques to group information and replicate the effect of fine-scale geologic heterogeneity in a static reservoir model. This process highlights the importance of understanding the role of tectonic anisotropy on the preservation of stratigraphic sequences when interpreting the depositional environment. Subdivision into the 70 sedimentation regions permitted calculation of the gross pore volume in each sedimentary system, using total porosity and a percentage of the vertical thickness for each modeling volume. The total volume calculated depended on the method; stratigraphic layering and sedimentation regions provided 600 cubic kilometers and equating to storage capability of over 250 gigatons of supercritical carbon dioxide, whereas using factors and no stratigraphy, the total volume was calculated at 460 cubic kilometers.

Pore volume distribution in the subsurface is more accurately characterized with high-resolution stratigraphic and sedimentation region analysis. Integrated tectonic analysis provides context that better constrains the application of outcrop analogs and depositional models, which guide sedimentation region analysis. This dissertation addresses the impact of geologic heterogeneity from crustal anisotropy to distributions of porosity and permeability and provides a tool to assess feasibility of gigaton-scale carbon dioxide sequestration.

Excess of arsenic in groundwater is a worldwide problem threatening the health of the millions of people directly exposed to Arsenic-rich water intake. The problem is particularly acute in naturally occurring unconsolidated aquifers where Arsenic-rich groundwater is an easily accessible resource of drinking water, such arsenic in India, Bangladesh and Vietnam. In Italy, arsenic is found in aquifers from north to south and it is associated to different geological settings (i.e. volcanic areas and alluvial plains). The shallow aquifer of Venetian Alluvial Plain (VAP) is notoriously affected by arsenic contamination, characterized by a patchy distribution with variable extensions and concentrations. With concentrations exceeding the WHO limit of 10 μg/L, this metal poses a risk for locals, arsenic the aquifer is exploited for agricultural purposes. Although empirical evidences exist about the relationship between arsenic occurrence and other factors, several aspects regarding the physical and geochemical processes controlling arsenic in the VAP aquifers remain unclear. In this line, the present study aims to elucidate both the geochemical processes fostering arsenic mobility and their correlation with the subsurface heterogeneity, in order to improve the knowledge about arsenic-controlling processes and use them arsenic aid for the environmental management. To this end, we focused in detail on an agricultural zone nearby the Venice lagoon, affected by arsenic contamination (called “Western Agricultural Areas”, WAA). The available data, collected by several hydrogeological surveys, show a spatial and temporal variability of arsenic concentration, which can be associated to a variety of hydro-geochemical processes such arsenic redox variations, sorption or reductive dissolution of Arsenic-rich iron oxy-hydroxides. In order to point out the consistency and the importance of these processes, we structured the study in two main phases: 1) evaluation of geochemical processes by means of a PHREEQC batch-like reactive model and 2) creation of a 3D reactive transport model based on previous results. The former allows us for testing whether the supposed geochemical processes are able to fit the geochemical conditions of the study system, identifying the main actors for arsenic mobility. The latter couples the obtained reactive processes with a 3D flow model, in order to evaluate the spatial and temporal distribution of dissolved arsenic as function of the subsurface heterogeneity. The results highlighted a strong effect of oxy-reductive potential on arsenic mobility, and it seems to be strictly correlated to organic matter degradation. The uprising of reduced condition, then, affects other mechanism such arsenic reductive dissolution of iron hydroxides, ion exchange and sorption processes, causing arsenic mobilization. Moreover, this study shaded light on the existence of oxygen ingress arsenic function of local water recharge events, which seems to be responsible of space/time redox variation. The 3D reactive transport model showed a strong dependence between the aforementioned processes and subsurface heterogeneity. The material distribution, indeed, plays an import role affecting the arising of the main chemical reactions.

The need to consider groundwater and surface water as a single resource has fostered the interest of the scientific community on the interactions between surface water and groundwater. The region below and alongside rivers where surface hydrology and subsurface hydrology concur is the hyporheic zone. This is the region where water exchange determines many biogeochemical and ecological processes of great impact on the functioning of rivers. However, the complex processes taking place in the hyporheic zone require a multidisciplinary approach. The combination of innovative point and distributed techniques originally developed in separated disciplines is of great advantage for the indirect identification of water exchange in the hyporheic zone. Distributed techniques using temperature as a tracer such as fiber-optic distributed temperature sensing can identify the different components of groundwater-surface water interactions based on their spatial and temporal thermal patterns at the sediment-water interface. In particular, groundwater, interflow discharge and local hyporheic exchange flows can be differentiated based on the distinct size, duration and sign of the temperature anomalies. The scale range and resolution of fiber-optic distributed temperature sensing are well complemented by geophysics providing subsurface structures with a similar resolution and scale. Thus, the use of fiber-optic distributed temperature sensing to trace flux patterns supported by the exploration of subsurface structures with geophysics enables spatial and temporal investigation of groundwater-surface water interactions with an unprecedented level of accuracy and resolution. In contrast to the aforementioned methods that can be used for pattern identification at the interface, other methods such as point techniques are required to quantify hyporheic exchange fluxes. In the present PhD thesis, point methods based on hydraulic gradients and thermal profiles are used to quantify hyporheic exchange flows. However, both methods are one-dimensional methods and assume that only vertical flow occurs while the reality is much more complex. The study evaluates the accuracy of the available methods and the factors that impact their reliability. The applied methods allow not only to quantify hyporheic exchange flows but they are also the basis for an interpretation of the sediment layering in the hyporheic zone. For upscaling of the previous results three-dimensional modelling of flow and heat transport in the hyporheic zone combines pattern identification and quantification of fluxes into a single framework. Modelling can evaluate the influence of factors governing groundwater-surface water interactions as well as assess the impact of multiple aspects of model design and calibration of high impact on the reliability of the simulations. But more importantly, this modelling approach enables accurate estimation of water exchange at any location of the domain with unparalleled resolution. Despite the challenges in 3D modelling of the hyporheic zone and in the integration of point and distributed data in models, the benefits should encourage the hyporheic community to adopt an integrative approach comprising from the measurement to the upscaling of hyporheic processes.

The need to consider groundwater and surface water as a single resource has fostered the interest of the scientific community on the interactions between surface water and groundwater. The region below and alongside rivers where surface hydrology and subsurface hydrology concur is the hyporheic zone. This is the region where water exchange determines many biogeochemical and ecological processes of great impact on the functioning of rivers. However, the complex processes taking place in the hyporheic zone require a multidisciplinary approach. The combination of innovative point and distributed techniques originally developed in separated disciplines is of great advantage for the indirect identification of water exchange in the hyporheic zone. Distributed techniques using temperature as a tracer such as fiber-optic distributed temperature sensing can identify the different components of groundwater-surface water interactions based on their spatial and temporal thermal patterns at the sediment-water interface. In particular, groundwater, interflow discharge and local hyporheic exchange flows can be differentiated based on the distinct size, duration and sign of the temperature anomalies. The scale range and resolution of fiber-optic distributed temperature sensing are well complemented by geophysics providing subsurface structures with a similar resolution and scale. Thus, the use of fiber-optic distributed temperature sensing to trace flux patterns supported by the exploration of subsurface structures with geophysics enables spatial and temporal investigation of groundwater-surface water interactions with an unprecedented level of accuracy and resolution. In contrast to the aforementioned methods that can be used for pattern identification at the interface, other methods such as point techniques are required to quantify hyporheic exchange fluxes. In the present PhD thesis, point methods based on hydraulic gradients and thermal profiles are used to quantify hyporheic exchange flows. However, both methods are one-dimensional methods and assume that only vertical flow occurs while the reality is much more complex. The study evaluates the accuracy of the available methods and the factors that impact their reliability. The applied methods allow not only to quantify hyporheic exchange flows but they are also the basis for an interpretation of the sediment layering in the hyporheic zone. For upscaling of the previous results three-dimensional modelling of flow and heat transport in the hyporheic zone combines pattern identification and quantification of fluxes into a single framework. Modelling can evaluate the influence of factors governing groundwater-surface water interactions as well as assess the impact of multiple aspects of model design and calibration of high impact on the reliability of the simulations. But more importantly, this modelling approach enables accurate estimation of water exchange at any location of the domain with unparalleled resolution. Despite the challenges in 3D modelling of the hyporheic zone and in the integration of point and distributed data in models, the benefits should encourage the hyporheic community to adopt an integrative approach comprising from the measurement to the upscaling of hyporheic processes.

Pore type variations account for complex velocity-porosity relationship and intensive permeability heterogeneity and consequently low oil and gas recovery in carbonate reservoir. However, it is a challenge for geologist and geophysicist to quantitatively estimate the influences of pore type complexity on velocity variation at a given porosity and porosity-permeability relationship. A new rock physics-based integrated approach in this study was proposed to quantitatively characterize the diversity of pore types and its influences on wave propagation in carbonate reservoir. Based on above knowledge, permeability prediction accuracy from petrophysical data can be improved compared to conventional approach. Two carbonate reservoirs with different reservoir features, one is a shallow carbonate reservoir with average high porosity (>10%) and another one is a supper-deep carbonate reservoir with average low porosity (<5%), are used to test the proposed approach. Paleokarst is a major event to complicate carbonate reservoir pore structure. Because of limited data and lack of appropriate study methods, it is a difficulty to characterize subsurface paleokarst 3D distribution and estimate its influences on reservoir heterogeneity. A method by integrated seismic characterization is applied to delineate a complex subsurface paleokarst system in the Upper San Andres Formation, Permian basin, West Texas. Meanwhile, the complex paleokarst system is explained by using a carbonate platform hydrological model, similar to modern marine hydrological environments within carbonate islands. How to evaluate carbonate reservoir permeability heterogeneity from 3D seismic data has been a dream for reservoir geoscientists, which is a key factor to optimize reservoir development strategy and enhance reservoir recovery. A two-step seismic inversions approach by integrating angle-stack seismic data and rock physics model is proposed to characterize pore-types complexity and further to identify the relative high permeability gas-bearing zones in low porosity reservoir (< 5%) using ChangXing super-deep carbonate reservoir as an example. Compared to the conventional permeability calculation method by best-fit function between porosity and permeability, the results in this study demonstrate that gas zones and non-gas zones in low porosity reservoir can be differentiated by using above integrated permeability characterization method.

In the last decades digital modelling applied to geological research is getting increasing attention (Alaei, 2012; Tomassetti et al., 2018; Trippetta et al., 2020; De Franco et al., 2019; Mascolo and Lecomte, 2021). Indeed, relevant implications both in scientific and economic terms could be inferred by using this technique. In particular, the application of digital models in complex geologic scenarios is critical for the understanding of potentially exploitable systems from multiple perspectives. Starting from the most classical model application for the exploitation of oil and gas fields passing through the implementation of extraction strategies - by reducing uncertainties (Macgregor & Moody, 1998; Racey 2001) - digital models find new place in latest applications such as natural gas storage. Recently, models are also applied for the study of geological bodies, potential reservoirs for the CO2 or hydrogen injection (Dockrill and Shipton, 2010; Trippetta et al., 2013; Aminu et al., 2017; Heinemann et al., 2018). Modelling contribute and facilitate to capture and store gases in the subsurface, balancing their release into the atmosphere. Digital modelling represents one of the major innovative strategies in the control of greenhouse gases concentration in atmosphere, a currently trending topic from media, public opinion, and political points of view. Another possible application of digital models for subsurface gas storage involves the monitoring of reservoirs in order to ascertain and quantify gas leakage through fault or fracture systems (Wang et al., 2018). Moreover, radioactive waste storage could be integrated as current and powerful employment of digital models (Malvić et al., 2020). In particular, the technological tools used for these purposes are called forward models since their outcomes gives predictive results on the processes happened in the past and protracted towards the future. They appear extremely suitable for the study of geological subsurface formations that can be also applied to an emerging field such as the development of geothermal energy power plants (De Franco et al., 2019). All these are topics of great actuality since world governments' plans are1 directed towards the total replacement of classic energy sources from hydrocarbons with green energies. However, digital modelling needs input data such as geometries and rock properties that should be well constrained. Seismic exploration is probably the most powerful tool for investigating subsurface rock formations (Avseth et al., 2010). Important progress has been made in recent years, but significant problems remain in the geologic interpretation of seismic data. The reflections that can be read in seismic data depend on the Acoustic Impedance (AI) contrast in the transit of the P-wave between layers in the subsurface. AI depends on the density (ϼ) and the P-wave velocity (Vp) of the medium through which wave propagates (AI= ϼ Vp). These petrophysical characteristics, in turn, are controlled by structure, texture, porosity, and boundary conditions of the rocks (Dvorkin et al., 2014; Tomassetti et al., 2018; Trippetta et al., 2020; Brandano et al., 2020). These two links, one between rock structure and its elasticity and the other between elasticity and signal propagation, form the physical basis of seismic interpretation (Anselmetti and Eberli, 1993; Eberli et al. 2003; Weger et al. 2009; Hairabian et al. 2014; Dvorkin et al., 2014). Dealing with these relationships, we are facing the so- called inverse problem. We see from seismic sections the resulting seismic images of rock formations where the same signal can be the result of a combination of different features. It should be, thus, very useful to well understand what are the features that lead to a certain seismic image. Synthetic seismic modelling (or forward modelling) is a fundamental prospecting method for understanding the features leading to the corresponding seismic images of subsurface structures and reservoir architectures (Alaei, 2012). Forward modelling methodology, as approach to the interpretation of seismic data, involves the detailed characterization of lithology, density, porosity, seismic velocity and fluid in the rock, as well as the reservoir geometry. As a result, the corresponding seismic properties are calculated, and then synthetic seismic traces are generated. These issues became essential for lithologies characterized by a complex seismic interpretation (Al-Salmi et al., 2019). In addition, synthetic seismic forward models allow accurate analysis of fault zones. The study of seismic response in fault zones is crucial since the2 fracturing or compaction that faults create strongly modifies the petrophysical characteristics of rocks by affecting their properties (Botter et al., 2017; Kolyukhin et al., 2017). Synthetic seismic forward models are, therefore, mandatory for the comprehension of faults behaviour through seismic imaging. Faults play a key role in reservoirs by increasing or limiting fluid flow. Even if interpretation of seismic data is a pivotal method for studying the subsurface, the internal structure and properties of fault zones are often below the limit imposed by seismic resolution (Botter et al., 2017). Despite the impact of faults on reservoir permeability, modelling tools and workflows still lack for realistic representation of fault zones in models (Tveranger et al., 2005; Braathen et al., 2009; Manzocchi et al., 2010). With facies analysis and petrophysical data it is possible to build field-based digital models fundamental in understanding architectures of carbonate sedimentary bodies which often constitute reservoir surface analogues of buried world-wide petroleum systems, CO2, hydrogen, radioactive waste storage sites and geothermal fields. Surface analogues are rocks with depositional, textural, and petrophysical characteristics similar to those constituting the petroleum system, but they outcrop on the surface. Starting from petrophysical characteristics of facies, forward models can be built. In this thesis, as a case study for the development of a forward model, rocks belonging to the carbonate realm, more specifically carbonate ramps, were analyzed. Carbonate ramps constitute important hydrocarbon deposits in North Africa (Macgregor & Moody, 1998), Venezuela, and many other regions of the World (Racey, 2001) due to their excellent porosity and permeability characteristics. However, the depositional model that is the basis for a proper interpretation produces many uncertainties arising from the difficulty in attributing different facies to a depositional environment and process due to the poor occurrence of sedimentary structures (Buxton and Pedley, 1989; Pomar and Kendall, 2008; Burchette, 2012; Bassi et al., 2013; Tomassetti et al., 2018; Tomassetti et al., 2022). In addition, strong lateral heterogeneity in terms of petrophysical characteristics, components, structure, and texture leads to complex distinction of facies belts (Tomassetti et al., 2018; Trippetta et al., 2020; Brandano et al., 2020). To overcome these issues, quantification of3 petrophysical characteristics can be crucial in understanding facies heterogeneity from a physical perspective to be incorporated in synthetic seismic forward models building. Carbonate rocks are often difficult to interpret seismically because the slight acoustic impedance contrast at the interface between carbonate facies in subsurface does not allow a clear resolution of major reflectors and reservoir formations. Strong constraints are often imposed by geophysical survey techniques characterized by low resolution especially in carbonates and interpretation capabilities that depend on the interpreter skill (Tomassetti et al., 2018; Trippetta and Geremia, 2019; Faleide et al., 2021). These constraints can be overtaken through the modelling of surface analogues allowing a detailed analysis on the facies association but also their petrophysical characteristics and seismic properties such as acoustic impedance (Tomassetti et al., 2018; Lipparini et al., 2018; Trippetta and Geremia, 2019; Brandano et al., 2020). In order to analyse the petrophysical characteristics and seismic response of the carbonate realm through modelling two carbonate ramps both belonging to the Adria plate were considered as case studies. The first is the Chattian carbonate ramp of the Porto Badisco calcarenite outcropping in the southern Salento peninsula, the southernmost portion of the Apulian carbonate platform. The Porto Badisco carbonate ramp is an excellent surface analogue of exploited oil and gas field in the offshore Venezuela, Philippine and South China Sea (Zampetti et al., 2005; Sattler et al.,2004; Fournier and Borgomano, 2007; Lallier et al., 2012; Marini and Spadafora, 2014; Pomar et al., 2015; Valencia and Laya, 2020) as well as fields in offshore Adriatic Sea such as Ombrina Mare field (Campagnoni et al., 2013). In this carbonate system firstly the analysis of outcropping facies was carried out observing over 100 thin sections produced. Consequently facies association modelling was performed through Petrel software (mark of Schlumberger) using TGSim stochastic approach algorithm adopting the depositional model based on field data. This model is useful for qualitatively understand the broad facies spacial distribution which reflects the abrupt heterogeneity from a sedimentary point of view. To physically quantify the lateral facies heterogeneity the petrophysical characteristics such as porosity, density and seismic velocity were measured and analyzed through a multi-analytical approach. Density4 measurements were carried out with the helium pycnometer. Porosity was firstly calculated from the density data and then was additionally measured through image analysis and point counting to cross-correlate the values. Seismic velocity was measured by using an ultrasonic generator connected to piezoelectic transducers and to an oscilloscope. The analysis performed on the carbonate ramp outcropping in Porto Badisco offers the opportunity to analyze facies heterogeneity, modeling its distribution and physically quantifying it through petrophysical characterization. From the petrophysical data, it was possible to construct 2D models of the distribution of porosity and P-wave seismic velocity along the depositional model. This study, which can be applied globally to carbonate platforms, emphasizes with the modelling exercise how facies heterogeneity is an intrinsic feature of these systems. The petrophysical characterization which provides quantitative values to the heterogeneity allow to build more complex models such as seismic forward models discussed in the second chapter. The other case study is represented by the Cenozoic carbonate ramp outcropping on the Majella Massif in Abruzzi, the northernmost portion of the Apulian carbonate platform which gives the opportunity to study a carbonate ramp surface analogue of a buried reservoir. Also in Majella the Oligo- Miocene stratigraphic interval represented by the Bolognano Formation which is the reservoir of the system is considered an excellent surface analogue of the productive fields in the Adriatic Sea, offshore Venezuela, Philippines and many others worldwide (Tomassetti et al., 2021). Specifically, this system offers the opportunity to integrate the facies heterogeneity in the synthetic seismic forward modelling and understand its seismic response without the introduction of artificial noise to obtain additional information. On the Majella Massif a model of the facies heterogeneity to understand their seismic response was performed. After analyzing the facies and measuring their petrophysical characteristics, the data obtained were used as input for build a 3D property modelling in Petrel software representing the entire carbonate ramp from the topographic surface to the Upper Cretaceous from the platform top going towards the basin located northward from the Majella Massif. From the 3D model was cut a section whose data were used as input in Matlab (mark of Mathworks) in order to perform the synthetic seismic forward model5 with the geophysical codes provided by the CREWES consortium. The resulting forward model represent the seismic response of the facies heterogeneity of carbonate rocks. In addition, from the obtained seismic images it is possible to evaluate the presence of hydrocarbons and to identify how the presence of important bituminous impregnations – that can be appreciated in the field in Majella – modify the seismic response. The workflow developed to quantify the signature of the facies heterogeneity of carbonate rocks and the presence of infilling hydrocarbons is applicable to other systems worldwide, which is a large issue that is still open and can help in the problems relative to seismic interpretation associated with these systems. Given the presence of a buried normal fault system in the study area, a forward modelling in the fault zones was performed as well. By measuring the petrophysical characteristics of the fault rocks characterized by both fracturing or compaction, fault zones were modeled. Two end member scenarios with two opposite behaviors of the rocks belonging to the damage zone were modeled in Matlab. A scenario in which the damage zone is characterized by fracturing and therefore rocks affected by greater porosity than the host rock. In the other scenario was modeled a damage zone with lower porosity than the host rock caused by the presence of compaction bands. Consequently, the seismic response of these end members was compared to understand how faults affect the seismic response of carbonate ramp systems. Notoriously, fault systems globally characterize carbonate ramps, and understanding their seismic response facilitates interpretation of the deformation behavior that a fault can assume under different boundary conditions. This can lead to an understanding of whether faults behave as barriers or conduits for fluids with the important implications for the study of fluid leakage from reservoirs.

Leakage of stored bulk phase CO₂ is one risk for sequestration in deep saline aquifers. As the less dense CO₂ migrates upward within a storage formation or in layers above the formation, the security of its storage depends upon the trapping mechanisms that counteract the migration. The trapping mechanism motivating this research is local capillary trapping (LCT), which occurs during buoyancy-driven migration of bulk phase CO₂ within a saline aquifer with spatially heterogeneous petrophysical properties. When a CO₂ plume rising by buoyancy encounters a region where capillary entry pressure is locally larger than average, CO₂ accumulates beneath the region. One benefit of LCT, applied specifically to CO₂ sequestration and storage, is that saturation of stored CO₂ phase is larger than the saturation for other permanent trapping mechanisms. Another potential benefit is security: CO₂ that occupies local capillary traps remains there, even if the overlying formation that provides primary containment were to be compromised and allow leakage. Most work on LCT has involved numerical simulation (Saadatpoor 2010, Ganesh 2012); the research work presented here is a step toward understanding local capillary trapping at the bench scale. An apparatus and set of fluids are described which allow examining the extent of local capillary trapping, i.e. buoyant nonwetting phase immobilization beneath small-scale capillary barriers, which can be expected in typical heterogeneous storage formation. The bench scale environment analogous to CO₂ and brine in a saline aquifer is created in a quasi-two dimensional experimental apparatus with dimension of 63 cm by 63 cm by 5 cm, which allows for observation of plume migration with physically representative properties but at experimentally convenient ambient conditions. A surrogate fluid pair is developed to mimic the density, viscosity and interfacial tension relationship found at pressure and temperature typical of storage aquifers. Porous media heterogeneity, pressure boundary conditions, migration modes of uprising nonwetting phase, and presence of fracture/breach in the capillary barrier are studied in series of experiments for their influences on LCT. A variety of heterogeneous porous media made of a range of sizes of loosely packed silica beads are used to validate and test the persistence of local capillary trapping mechanism. By adjusting the boundary conditions (fluid levels in reservoirs attached to top and to bottom ports of the apparatus), the capillary pressure gradient across the domain was manipulated. Experiments were conducted with and without the presence of fracture/potential leakage pathway in the capillary seal. The trapped buoyant phase remained secure beneath the local capillary barriers, as long as the effective capillary pressure exerted by the trapped phase (proportional to column height of the phase) is smaller than the capillary entry pressure of the barrier. The local capillary trapping mechanism remained persistent even under forced imbibition, in which a significantly higher hydraulic potential gradient, and therefore a larger gradient in capillary pressure, was applied to the system. The column height of buoyant fluid that remained beneath the local capillary barrier was smaller by a factor corresponding to the increase in capillary pressure gradient. Mimicking a breach of the caprock by opening valves at the top of the apparatus allowed buoyant mobile phase held beneath the valves to escape, but buoyant phase held in local traps at saturations above residual, and therefore potentially mobile, was undisturbed. This work provides systematic validation of a novel concept, namely the long-term security of CO₂ that fills local (small-scale) capillary traps in heterogeneous storage formations. Results from this work reveal the first ever unequivocal experimental evidence on persistence of local capillary trapping mechanism. Attempts to quantify the nonwetting phase saturation and extent of LCT persistence serve as the initial steps to potentially reduce the risks associated with long-term storage security.
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The purpose of this study was to evaluate the effectiveness of traditional hydrogeologic characterization approaches in a highly heterogeneous glaciofluvial aquifer at the North Campus Research Site (NCRS), situated on the University of Waterloo campus. Continuous soil cores to a depth of approximately 18 m were collected during the installation of the CMT monitoring wells and the multi-screen pumping well. K estimates were obtained for the core by obtaining 471 samples and testing them with a falling head permeameter, as well as by utilizing empirical equations developed to estimate K. A geostatistical analysis performed on the K datasets yielded strongly heterogeneous kriged K fields for the site. K and Ss were also estimated via type curve analysis of slug and pumping test data collected at the site. The various K and Ss estimates were then evaluated by simulating the transient drawdown data using a 3D forward numerical model constructed using Hydrogeosphere (Therrien et al., 2005). Results showed that, while drawdown predictions generally improved as more complexity was introduced into the model, the ability to make accurate drawdown predictions at all of the CMT ports was inconsistent. These results suggest that new techniques may be required to accurately capture subsurface heterogeneity for improved predictions of flow in similar systems.