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# BIBC : Academic collection

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The discovery of a large oil field, the 'Lula oil field' beneath kilometres of sediments, in the deep sea offshore Brazil lead to a bloom in the research on analogue reservoir settings in complex continental carbonates. An analogue reservoir model is a study in which rocks, that are similar to the rocks of an existing oil field, are studied at the earth's surface. In this way, it is possible for geologists to develop a database that helps in finding the most efficient way to drill for oil and gas in the respective rock types and to define the characteristics of the rocks. In this present study, continental carbonates and more specifically, travertine carbonates are studied. These sediments formed when water, rich in carbonate, has ascended to the earth's surface through faults. Upon reaching the surface, the carbonate precipitates, resulting in white rocks, very much like the white precipitates in a water boiler but at a much larger scale. The resulting rocks have a lot of pores in them, which have variable sizes and shapes. When these rocks would be buried and oil would penetrate into these pores, a very interesting oil reservoir will be formed. A travertine body that has been created over >100.000 years ago was analysed in Acquasanta Terme, central Italy. The objectives of this research are to: (i) create an analogue reservoir model, (ii) to determine the chemical composition of the fluids that formed these travertine rocks and to analyse at which depth in the subsurface they have been circulating and (iii) to develop a depositional model of the travertine body. (i) The analogue reservoir model indicates that the variable pore sizes and shapes are well distributed in this travertine body, but that a large fraction (>70%) of the travertine body does not contain a sufficient amount of pores that indicates that it is a good reservoir system. Only about 30% of the rock is of good reservoir quality, especially if the connection of pores to fractures is taken into account. (ii) The fluid characterization indicates that two different fluids are responsible for the formation of the travertine rocks. Both fluids relate to rain water that has found its way through the rocks to ultimately ascend through faults to form travertine. The first fluid did not penetrate deeply into the subsurface. Its temperature was approximately 30°C. The second fluid contains a lot of salts. This indicates that it must have infiltrated up to a depth of 3 km where it reached a temperature of 90°C, and where rock salt (anhydrite) was dissolved that had been formed 220 million years ago. Due to cooling, the water is approximately 60°C when it emerges at the earth's surface, where it formed travertine. (iii) The travertine developed in two stages. In a first stage, there were two point sources from which the water emerged from the subsurface. In the further evolution these points became connected to form a fracture of which the fluids emerged. The travertine rocks also indicate that there were two distinct morphologies along the fracture. The first has very steep slopes, which suggests that water flows fast over these rocks. The second one is flat, which shows that water could be up to 2m deep and where it flows very slowly. This flat morphology is bordered by waterfalls, which are present right next to the Tronto river of Acquasanta Terme.

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Heterogeneity is an inherent characteristic of carbonate reservoir rocks, which is determined by their geological evolution, e.g. sedimentary origin, diagenetic processes and burial history. These processes relate to the economic relevance of reservoir rocks as well as to the degradation of building stones. Different porosity types in sedimentary rocks exist on a spectrum of different spatial scales. An example of the lower end of the spectrum is very fine micro-porosity in mic- ritic textures, characterised by pore diameters on sub-μm scale. On the other hand of the spectrum are the large pores in sedimentary rocks, e.g. karst and shelter porosity with diameters up to meter scale. In this study a unique dataset comprising several orders of spatial scale (from μm till m) is used to develop a new descriptive pore shape classification in order to assess the representativeness of porosity at different spatial scales.^ The major aim of this study was to characterise complex pore systems in 3D in carbonate rocks, framed in a well-established upscaling strategy. Additionally, the aspect of the Representative Elementary Volume (REV) was addressed since in CT-technology sample size is linked to resolution. An up- scaling strategy has been developed in which data on porosity acquired at different resolutions (from micro- to macro-porosity) and sample sizes are aligned. This will help to understand the major controlling factors on pore development, permeability, acoustic properties and other petrophysical characteristics. In order to achieve a 3D interpretation of porosity and mineralogy, samples were scanned using medical and micro-CT. While both systems are non-destructive and pro- vide 3D data, medical and micro-CT scanners have a different hardware set-up and reach different resolutions. The medical CT scans are performed in collaboration with the department of radiology, UZ Leuven.^ For the micro-CT scans a GE Nanotom of the Material Engineering Department, KU Leu- ven is used. Samples scanned with a medical CT scanner have a resolution around 250 μm while with a micro-CT scanner resolutions between 20 and 1 μm can be obtained. The first aim of the project was to develop an objective description of pore shapes based on 3D data. This is achieved by analysing the ratios of the longest, intermediate, shortest dimensions and compactness of the pore shapes, based on an approximating ellipsoid, in order to obtain a thorough and objective description of pore shapes. This classification differs from traditional pore classifications because it is based on 3D data and uses solely the shape of the pores. In the traditional classifications of Choquette and Pray (1970), Lucia (1999) and Lønøy (2006), the parameters that are used are descriptive and relative to each other. They describe the rock, i.e.^ the solid constituents, to extract information about the porosity type rather than describing the pore itself, e.g. intercrystal or interparticle porosity. By using intrinsic properties, the classification based on CT data can be used at every resolution scale. Five shape classes are defined: i.e. rod, blade, plate, cuboid and cube. An additional advantage of this classification is that the data provide information about the orientation of the pores. This permits the assessment of the anisotropy of the porosity parameter. The new 3D classification (Claes et al., 2015b) allows a better understanding of the influence of the porosity parameter on other petrophysical parameters, e.g. the acoustic properties of rock samples (Soete et al., 2015). In this study it was shown that rod and cuboid shaped pores increase compressional wave velocities, while flattened pore shapes such as blade and plate-like shaped pores decrease the acoustic wave propagations.^ These observations help us to understand more accurately acoustic properties of reservoir rocks. Additionally, the surface area of the pore is an important parameter since it plays a crucial role in the connectivity of pores as well as the reactive surface. Addressing the shape of the surface area is highly dependent on the resolution of the dataset. Hence the voxel representation of smooth continuous surfaces is generally jagged, so the total area of exposed voxel faces is usually greater than that of the original continuous surface. This can be solved by a triangulation of the surface but literature indicates this is not the ideal solution. When using the marching cubes algorithm to create the triangulated representation, topological ambiguities may occur and holes may be generated due to the complex shapes of the pores.^ Secondly, the surface area estimate, produced by summing up the area of the resulting triangles, does not converge to the true surface area as the resolution increases due to the locality of the marching cubes algorithm. The extension of Fourier series to 3D results in the definition of spherical harmonic surfaces. Based on this new iterative approach, additional parameters such as surface area and circularity are calculated. Moreover the accuracy of the calculated parameters is sufficiently increased compared to other estimating methods. In a second research step the aspect of Representative Elementary Volume (REV) was studied. This is an important parameter in several research fields such as reservoir properties and structural property determination. In the former the porosity parameter will be the most crucial.^ High-resolution LIDAR data of quarry walls were used to assess the porosity on the upper end of the spatial spectrum, while medical CT, micro-CT scans and thin- sections are used to cover the middle and lower end of the spectrum. For each spatial scale the REV is calculated (i.e. the smallest value that can be taken as a representation for the entire sample area/volume that does not respond to small changes in volume or location).
In this study two approaches to calculate the REV were developed and compared. Both methods are applicable to 2D as well as 3D datasets. This is important for linking the results of the new 3D approach with data of traditional studies. The first method uses the chi-square criterion to measure how much a single randomly chosen sub-sample diverges from the mean value of all realisations. This method is closely related to the original definition proposed by Bear. The second method uses the relationship between the REV and geo- statistical interpretations.^ A volume Vi falls within the REV domain if Y(x,Vi) can be treated as a stationary random function for any x in the domain. The advantage of both methods is that they allow to calculate 95 % confidence bounds for the REV parameter. The results of both methods are in the same order of magnitude and vary depending on the scale of the sample. Nevertheless the geostatistical method provides additional information on the shape of the REV based on the spatial distribution of the porosity parameter, i.e. the anisotropy. Additionally both approaches can be used on 2D as well as 3D datasets. This is an important feature because CT only allows to obtain 3D information of samples, which have a sample size between mm and m. In order to be able to perform further down- scaling or upscaling, 2D datasets are more common such as scanning electron microscopy images and LiDAR datasets. This study illustrates the complexity of the application of the REV parameter in geo- logical studies.^ Only by calculating the REV at different scales, reservoir properties in complex carbonate rocks can be evaluated correctly. In order to link results from LIDAR, medical CT, micro-CT and thin-sections and to accurately predict adequate REV sizes, a new upscaling strategy to incorporate 3D CT data was developed. Hence the necessity to establish a link between different datasets, acquired at different resolutions is required. This can be achieved by using a workflow derived from multiple point geostatistical studies. This approach combines the strengths of pixel-based and object-based techniques. The shape of the pores is re- produced, while retaining the flexibility of a pixel-based method. Scans of the 2.5 cm diameter plugs are used as a training image while data from 10 cm diameter cores are used for conditioning.^ The quality of the simulated datasets is determined by com- paring pore shape distributions and the simulated permeability values of a corresponding part of both the original dataset and the simulated dataset. The simulated samples provide further information about the size of the REV over the studied scale range and bridge the gap between 10 cm and 2.5 cm diameter samples. This upscaling approach allows us to counter one of the main disadvantages of using CT data. To achieve μm resolutions only small samples (7 mm diameter) can be scanned. The technique described above allows to artificially improve the resolution of CT datasets as long as a representative training image of the desired resolution is present. This again proves the importance of an accurate calculation of the REV. An extra research topic that was added to the project was the use of the developed techniques to establish a workflow in order to simulate rock volumes based on a single thin-section.^ It is important that these simulated “numerical-rock” volumes have the same petrophysical characteristics as the original rock from which the thin-section was made. In this project, the used work- flow can be best described as a 2.5D approach, where 2D slices are simulated using some selected pore centres as conditioning data for the next slice. Because of this simplified approach, less computation time is needed compared to other pure 3D techniques. Heterogeneity is an inherent characteristic of carbonate reservoir rocks, which is determined by their geological evolution, e.g. sedimentary origin, diagenetic processes and burial history. These processes relate to the economic relevance of reservoir rocks as well as to the degradation of buildi

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The importance of fault-damage zones in reservoir performance including fluid flow and production have been highlighted in several studies (e.g. Aydin, 2000; Sibson, 2000; Kim et al., 2004; Mitchel and Faulkner, 2009; Bense et al., 2013; Agar and Geiger, 2015). Fault-damage zones may act as fluid barriers in high porosity rocks by forming deformational bands (compaction bands) while they can enhance porosity in intrinsically low-permeable rocks (Sibson, 1987; Cox, 2007; Agosta et al., 2010; Laubach et al., 2010; Bense et al., 2013). They can be key components of hydrocarbon traps when they are sealing barriers or when they juxtapose the reservoirs with sealing intervals (Sibson, 2000). Furthermore, they can function as cross-formational corridors distributing large volumes of fluids when they are conductive (Burley et al., 1989). In the later situation, they are considered to be directional permeability zones influencing fluid migration.^ Moreover, the fluids distributing along these zones can increase or decrease the porosity and permeability of host rock matrix by dissolution or further cementation, respectively. Syn-tectonic veins can be used as proxies to obtain valuable information regarding the extent of fluid flow and faults conductivity. In addition, pristine diagenetic properties of the host rock should be investigated to be able to pinpoint the possible interactions between the host rock and the fluids potentially introduced to them by faults. In this research outcrops of the Jabal Qusaybah Anticline were used as an analogue to study the behaviour of fault-damage zones in relation to migration of fluids on local and regional scale. In this study, both the diagenesis of host rocks and the physico-chemical properties of precipitated fluids in relation to fault-damage zones and their structural evolution are addressed.^ This required a comprehensive multi-disciplinary approach including detailed structural analysis (performed by Prof. Dr. F. Storti and his team from Parma University, Italy) and systematic sampling on one hand and petrography, geochemistry and study of fluid inclusions as well as computer modelling on the other hand. The Jabal Qusaybah Anticline is an 8 kilometer long anticline located at the toe-thrust of the North Oman Mountains in the Adam Foothills. The formation of this anticline took place during the first (Late Cretaceous) and the second Alpine events (Oligocene to Pliocene). During the former event the Adam Foothills experienced an extensional regime due to downbending as a result of the Semail Ophiolite obduction. This period was synchronous with formation of the Aruma Foredeep and development of normal fault zones.^ The second Alpine event is characterised by a compressional tectonic regime and layer parallel shortening which resulted in uplift and inversion of the pre-existing normal faults in the Aruma Foredeep and development of the Adam Foothills including Jabal Qusaybah. The second Alpine event is interpreted to be responsible for the present-day topography of Jabal Qusaybah (Loosveld et al., 1996; Storti et al., 2015). The axial plane of this anticline strikes nearly E-W while affected by networks of strike-slip and normal faults. The majority of strike-slip faults are left-lateral and have a NE-SW direction. Only one N-S right-lateral strike-slip fault occurs at the western flank of the anticline. The normal faults are generally N-S trending with exception of two faults that show an E-W trend.^ Left-lateral strike-slip fault zones have an oblique trend with respect to the anticline strike and N-S extensional fault zones are confined within strike-slip-bounded compartments characterising the central part of the fold (Storti et al., 2015). Therefore, N-S extensional fault zones terminate within the anticline. The regional tectonic framework used in this study is based on the model proposed by Loosveld et al. (1996) while the detailed structural studies of the fault-damage zones and evolution of Jabal Qusaybah as an anticline are based on the co-authored paper of Storti et al. (2015). The sedimentary successions exposed in this anticline belong to the upper intervals of the Natih Formation (Middle Cenomanian to Early Turonian). The sediments corresponding to this formation were part of shallow water carbonate successions that accumulated along the Neo-Tethys passive margins prior to the onset of the first Alpine event.^ The stratigraphy and the characterisation of depositional systems of this formation used in this study are mainly the ones proposed by Van Buchem et al. (1996; 2002), Homewood et al. (2008) and Grélaud et al. (2010) and is based on the work from Glennie et al. (1974). The first part of this research mostly focused on unravelling the cement petrography, relative timing and parental fluids encountered during diagenesis of the Natih C, B and A members exposed in the study area. This part of the study aims toprovide evidences to ascertain whether the fracture-controlled fluids could affect the geochemical properties of surrounding host rocks whithin and outside of the fault-damage zones. In addition, it provides information to understand if the host rocks were already tight at the stage of fault-damage zone formation.^ The results provide indications confirming that the studied intervals were cemented early in their diagenetic history (Middle Cenomanian to Early Turonian) prior to significant burial, creating relatively tight host rocks. The cement phases are generally calcite, and consist of bladed, mosaic to blocky and syntaxial overgrowths. No evidence of fracture-led cements and/or consistent trend between geochemical properties of host rocks and including veins was detected. In addition to early diagenetic modifications, the migration of fluids during major deformational events (i.e. the first and second Alpine event) has been recorded in Jabal Qusaybah by several generations of calcite veins and localised dolomite cementation in the fault-damage zones. Based on the structural framework, fault systems and geochemical analysis, three groups of veins were distinguished.^ The first group of veins are interpreted to be linked to burial and early‑tectonic deformation in association with E‑W extensional fault zones and incipient strike-slip faults which commenced at the first Alpine event. The δ13C values of these veins are in agreement with the known δ13C values of the Middle to Upper Cretaceous marine carbonates, and δ18O values vary from -10.3 to -8.1‰ V‑PDB. Based on further geochemical analyses including trace elements and 87Sr/86Sr ratios (0.70744 to 0.70752), which are in good agreement with the Middle to Upper Cretaceous marine carbonates, the intra‑formational low salinity fluids (< 3.5 eq. wt. % NaCl) with an H2O‑NaCl composition were responsible for calcite cementation in these veins. The formation of this group of veins can be linked to the first stages of fracture formation when their conductivity was not developed enough to introduce extra-formational fluid circulation to the studied intervals.^ The vein formation was therefore controlled by diffusional mass transfer or short-range advection. These veins contain hydrocarbon inclusions which are considered to be derived from local source rocks (i.e. Natih B) or be secondary in origin. The second group of veins are related to syn‑tectonic deformation along NE-SW strike‑slip and incipient N‑S extensional faults linked to bulging of the Jabal Qusaybah Anticline. The cements that precipitated during this stage show δ13C values in agreement with the known δ13C values of the Middle to Upper Cretaceous marine carbonates, but the δ18O values display a wide range varying between significantly depleted to less depleted (‑11.2 to +0.3‰ V-PDB) compared to the Middle to Upper Cretaceous marine carbonates with a relative correlation with the salinity of the fluid inclusions.^ They are also characterised by a relatively broad range of temperatures (65-97oC) and salinity values that evolve from seawater to moderately saline fluids (3.4 to 12.8 eq.wt% NaCl) with an H2O‑NaCl composition. The geochemical analyses (e.g. trace elements and 87Sr/86Sr ratios) confirm that from this stage onward, fluids correspond to progressive fault connectivity and dilation related to interaction of fault‑folding systems as the cements are generaly ferroan to non-ferroan and their 87Sr/86Sr ratios are higher than the values known for the Middle to Upper Cretaceous marine carbonates. Based on the calculated δ18OV-SMOW value of their parental fluids (+2.0 to +8.5‰ V-SMOW), in addition to their salinity values as measured from fluid inclusions, the fluid source is inferred to be evaporitic brines and the large range of salinity values is interpreted as the result of mixing between those brines and modified seawater taking place within a broad range of burial settings, i.e.^ temperature. The most likely origin for the evaporitic brines is considered to be the Ara evaporites (the Huqf Supergroup; Pre-Cambrian-Cambrian). These veins contain hydrocarbon inclusions which by taking the high conductivity of faults into account and considering the fact that the study area was located in regional hydrocarbon migration pathways (Terken, pers. comm.), they could have been originated form regional and/or local source rocks. Since the microthermometric analysis can only indicate the minimum trapping temperature of fluid inclusions, the procedure of Thiéry et al. (2000, 2002) and Pironon (2004) was used to obtain a more precise trapping temperature for the cement populations that contain both oil and aqueous inclusions. Accordingly, the correction for Group 1 veins and the earliest population of Group 2 veins is approximately 8 and 6°C, respectively while for younger populations of Group 2 veins is 13°C.^ The third group of veins are considered to be related to late‑tectonic deformation linked to late axial bulging of th

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Industrial waste containing significant amounts of Potentially Toxic Elements (PTEs) can represent a risk to the environment or an opportunity providing a valuable resource for metal recovery. Hence, a detailed understanding of the characteristics of waste materials is crucial for a better management of these materials. The main objective of this study was to characterize waste collected from different industrial processing facilities in Vietnam (blasted copper slag, bottom ash, and industrial sludge) and investigate the PTE leaching behavior. In addition a case study was performed which assessed the PTE contamination status of sediments and soils from site affected by the dumping of blasted copper slag. To achieve the research objectives, many different methods were applied in this project such as X-ray diffraction (XRD) in combination with Field Emission Gun Electron Probe Micro Analysis (FEG-EPMA) for the solid phase characterization, a series of leaching/extraction tests including pH dependent and pHstat leaching tests, cascade leaching tests, ammonium-EDTA-extractions, as well as the performance of an oxidation test under atmospheric conditions and a resuspension test to assess the implications of land disposal and re-suspension on selected sludge samples. Moreover, PTE contamination of sediments and soils in Ninh Hoa district (Khanh Hoa province) were assessed based on Enrichment Factors (EF) calculated with the local background concentrations of PTEs derived from sediment/soil core analysis. The investigated waste were chemically and mineralogically distinct, which was also reflected in the PTE leaching behavior and the resulting potential environmental scenarios. FEG-EPMA was useful in complement with XRD for the solid phase characterization since it provided information on phases containing PTEs that were not detected by XRD analysis. Understanding the matrices composition in which PTEs are incorporated was helpful for the interpretation of the leaching behavior of PTEs in some of the studied samples (e.g., Co-Ni associated with Fe-alloy and Fe-oxide phases in the bottom ash and Ni associated with Zn-rich phases in the industrial sludge). The pH dependent leaching test showed that PTE release increased with decreasing pH, except for As, Mo and Cu (sludge and ash) in the alkaline pH range. Cascade leaching tests and pHstat leaching tests allow to assess the kinetic release of PTEs which is important for predicting the environmental risks associated with these elements over time. Moreover, the potential leachability of PTEs under mildly acidic conditions of waste also was investigated. Recovery of metals from the investigated waste could be a promising option due to the high release of metals under acidic conditions. The exposure of the investigated sludges to atmospheric oxidation indicated a risk to the environment due to the important release of some elements (Fe, Mn, Cu, Ni, and Zn). The dissolved concentrations of Fe, Mn, Cu, and Zn in pore water highly exceeded the National Technical Regulation on Underground Water Quality. Hence, these elements may negatively affect water quality if these sludges are disposed off near a water body. Through the investigation of sediments and soils collected near the dump site of blasted copper slag and shipyard in Ninh Hoa district (Khanh Hoa province) contamination of surface soils and surface marine sediments was recognized (mainly with As, Cu, and Zn). This study also demonstrates that it is important to use local background values of PTEs in sediments and soils for a correct estimation of the degree of PTE contamination. The findings of this doctoral research and the applied methodology can be helpful to develop appropriate management options for industrial waste and contribute to the assessment of sites contaminated by PTEs from industrial activities for the purpose of environmental protection.