Despite the fact that both depositional and diagenetic processes control pore geometries and hence reservoir complexity, there is a tendency to underestimate the impact of diagenesis on petrophysical reservoir properties. Moreover, there is a lack of published data on the geometry of carbonate pore systems, despite the fact that pore shape and size can highly affect permeability. Seismic and core data of the Shuaiba Formation in northern Oman oil fields highlight the occurrence of large fractures within this formation, yet only few published studies focus on the diagenesis and how it enhances the heterogeneity of the Shuaiba Formation as a reservoir. Integrated depositional and diagenetic study (i.e. petrographic, geochemical, and structural evaluation) is essential if the heterogeneity observed in these carbonate rocks in Oman and elsewhere is to be understood. This thesis presents the first regional, integrated analysis of the upper 10 m – 15 m of the Shuaiba Formation in North Oman, where a noticeable modification in porosity, mostly by solution-enhancement, is documented below the Albian-Aptian unconformity in a number of oil fields. Different hypotheses were tested to justify this modification, including dissolution during sub-aerial exposure, corrosion by burial fluids, and dissolution by fluids sourced from compacted overlying shales of the Nahr Umr Formation. Detailed characterization of the Shuaiba Formation pore system and associated pore- filling cements was accomplished, including classification of pore types and their regional distribution within lithofacies, identification and geochemical characterization of the main diagenetic cement phases and the timing of pore modification relative to the main tectonic events that postdate the deposition of the Shuaiba Formation. Finally, 2D and 3D characterization of the pore system was conducted via multi-scale image analysis. The results of this study show that negligible volumes of porosity were formed at the top of the Shuaiba Formation during sub-aerial exposure. No evidences for clay compaction- related dissolution was found. The majority of the pores are interpreted to have formed from the up-dip migration of fluids during hydrocarbon charge in the Late Cretaceous, largely enhancing microporosity, mainly within the matrix. A phase of dissolution in telogenetic setting possibly occurred at the end of the Late Cretaceous along with precipitation of euhedral, sulphur isotope –depleted pyrite. Breaching of the deeper seals is believed to cause recharge of hydrocarbon in the Late Tertiary which might have contributed to the overall pore system of the Shuaiba Formation in the fields with mixed oils.

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No description available.

There is an urgent need to develop robust tools and policies for stability and hazard risk assessments in order to manage upland peat landslides in locations such as the British Isles where they have frequently occurred and caused harm to the environment. One of the particular difficulties is that reliable values of peat strength are difficult to obtain. The objectives of this research were to establish the nature of any relationships between the strength characteristics and the botanical, physical and chemical properties of the peat, and to determine whether palaeobotanical analyses of samples of the basal peat can provide a reliable indication of potential instability in upland blanket bogs. The research was carried out at the Straduff Townland (Co. Sligo), Slieve Anierin (Co. Leitrim) and Slieve Rushen (Co. Cavan) landslides, all located in northwest Ireland, from the margins of which monolith and core peat samples were collected. Standard and validated paleobotanical, chemical and geotechnical protocols, modified or refined where necessary to suit the nature of the peat, were used in the study. The triaxial, direct shear and tensile strength tests were conducted using experimental very low stress conditions in order to fully replicate in-situ conditions. The reliability of the measured strength parameters was examined by performing deterministic and probabilistic stability analyses of the failed slopes using industry-standard „limit equilibrium‟ software (SLOPE/W). The nature, extent and spatial distribution of the hydrocarbons unexpectedly found in the basal peats during the fieldwork were also investigated. This research found that blanket peat dominated by monocotyledons (with mainly E. vaginatum) is likely to be susceptible to failure because its „effective structural properties‟, specifically the high degree of humification and low fibre content of its basal peat, cause it to have very low strength and also therefore a very low bearing capacity. Furthermore, monocotyledons or its remains in peat have morphological, chemical, biological features that can promote bogflow-type failure. These may include for example (i) their parallel and elongated leaf veinations that promote flow, (ii) the genesis of hydrocarbons such as bitumen from their lignified tissues and (ii) being host to a hydrocarbon-producing aphid Colopha compressa. Laboratory measurements of undrained strength of the weak basal peats were consistently < 3 kPa, and deterministic stability analyses revealed that the value of the tensile strength can be used as an indicator of the undrained shear strength. A new classification (i.e. "the modified fibre content scheme") and a modified procedure for assessing upland peat failure for construction projects has been proposed based on peat fibre and humification characteristics and their apparent influences on peat strength. Deposits of hydrocarbons such as bitumens within the basal peat constitute a previously unrecognised factor that probably contributed to the occurrence of the studied landslides due to their hydrophobic properties.

The aim of this dissertation is to determine the spatial and dynamic mechanisms that govern the supply of oil and natural gas. Specifically, the research evaluates how fear of the future affects behavior today and thereby it tests whether non-renewable resource owners behave in the forward-looking manner described by Harold Hotelling in the 1930s. Understanding what governs the supply of oil and natural gas is vital, as these fuels have significant economic and environmental implications for the planet. Integrating original research papers, the dissertation unfolds in seven chapters. The first and second chapters provide the foundation for the following research, by introducing the existing literature on oil and gas management. The subsequent three chapters discuss common pool problems as a method of identifying forward-looking behavior. Retaining this focus on weak property rights, chapter six evaluates the short-term relationship between government stability and oil extraction in authoritarian petro-states. The final chapter summarizes the main findings and outlines key implications. Drawing on new datasets and novel methodological tools, this dissertation demonstrates how fear of common pool problems governs exploration and extraction in the oil and gas industry today. However, contrary to conventional theory, this dissertation does not find that political instability motivates authoritarian regimes to accelerate their extraction.

The link between vegetation and climate change during the Pennsylvanian Subperiod is of significant scientific interest, in part due to the similarities between that time and the present day. These are the only two intervals in Earth's history with comparable levels of polar ice, and widespread tropical vegetation. Extensive coal deposits were formed in areas of wetland vegetation dominated by arborescent lycopsids. A change in composition and westwards decline of these coal swamps across Euramerica, began in the Middle Pennsylvanian. The South Wales Coalfield possesses potentially the most complete terrestrial record of the Middle Pennsylvanian Subperiod and thus a unique resource for the study of this time. Initially changes in atmospheric concentration of CO2 were to be assessed via measurement of stomatal index. Considerable experimentation with various techniques for obtaining cuticle revealed this to be impossible, preservation being variable but consistently too poor for the identification of stomata. Therefore petrographic analysis of coal was utilised to investigate environmental change, principally peat hydrology. Samples were collected through 24 seams across the South Wales Coalfield. Optical analysis of macerals, the plant derived microscopic components of coal, was used to develop a new petrographic technique for defining maceral facies from detrended correspondence analysis of maceral composition data. These changes are compared to group level changes in the palynological assemblages of roof shales which revealed a clear change in dominance from lycopsids to ferns. I interpret a transition, initiated earliest in the West of the basin, from waterlogged environments dominated by rheotrophic peat substrates and lycopsid vegetation, to a better drained environment with expanded areas of clastic substrate and fern dominated vegetation. Signals from petrographic and palynological data are similar, but due to taphonomic factors these diverge from that from macroflora, the former indicating an earlier decline in lycopsid vegetation during the Bolsovian substage. The coeval northwards migration of the Variscan front, and influx of coarse clastic sediment, is presented as the principal driver of the interpreted environmental and vegetational change in South Wales. The present study supports the model proposed as a result of the IGCP 469 project that the role of climate change may have increased globally as the coal swamps contracted, a positive feedback loop being established in which the progressive loss of a significant carbon sink contributed to the establishment of conditions less favourable for the dominant forest vegetation and thereby their further decline.

Palaeocene high-latitude coals from the Todalen Mbr. Central Tertiary Basin, Svalbard present an opportunity to understand the processes which controlled Arctic peat formation. Coals from this region have produced sub-economic quantities of bitumen during the 1920’s. Previous palaeogeographic models show significant variation between studies favouring deltaic and tidal wetland conditions. In addition, coal geochemistry studies have been limited to characterisation with little integration with palaeogeographic studies. This study utilises a large database of drill-logs to create cross sections and coal isopach maps to examine the spatial relation between seam thickness and palaeotopography. Palaeotopography is defined by mapping a ‘valley indicator’; the Grønfjorden bed, a fluvial conglomerate representing the first Palaeocene sedimentation. In addition, organic petrology organic and inorganic geochemistry were applied to samples from two mine sections and two boreholes to examine how coal quality and oil potential changed both within and between seams. The cross sections and isopach maps reveal that landscape had a significant but diminishing control upon peat accumulation. Thickest peats consistently formed at the break-in slope whilst topographic lows acted as areas of preferential channel formation and conduits for clastic sedimentation. Evolution of the landscape control had a significant control upon groundwater supply. As landscape control decreased the coals moved from isolated, raised bogs (Svea Seam) to laterally expansive minerotrophic fens (Svarteper and Askeladden Seams). Evidence of increasing marine influence and higher groundwater input was also observed from the Svea Seams to the Askeladden seam. In the Svea Nord and Longyear seam, supply of lithophile elements (Al, Ti, Na, K) is shown to be controlled by dust supply controlled by orbital cyclicity. By the Svarteper/Askeladden period lithophile element concentrations are controlled by clastic supply. Ca, Mg and Fe appear to be derived from groundwater. Sulfur concentration primarily reflects the supply of marine sulfur. Upper Todalen coals (Longyear, Svarteper and Askeladden) have significantly more oil potential than the Svea Seams with estimated retorting yields of 170-190kg/ton vs. 50kg/ton respectively. The Longyear seam exhibits relatively high HI values (ca. 300-400 mg/g TOC) consistent with a mixed Type II/III kerogen source. Greatest oil potential is shown to be favoured by formation within a fen environment, with high bacterial degradation (>100μg/g TOC hopanes), marine influence (>0.5wt% sulfur, Fe/S <0.9) and the unique temperate high lattitude Palaeocene climate of Svalbard, leading to preservation of hydrogen rich organic matter via organo-sulfur bond formation.

In addition to its role as moderator within British nuclear reactors, polycrystalline graphite is also a major structural component of the core, enabling access for control rods, coolant gas and fuel. Aging processes, primarily fast neutron irradiation and radiolytic oxidation lead to distortion of the graphite components and property changes which ultimately reduce the material's effectiveness and can lead to component failure.Despite much research into the material, graphite behaviour under irradiation conditions is not fully understood and has resulted in an overestimation of the extent of component failures in Magnox reactors, and a subsequent underestimation of component failures in the following generation Advanced Gas-cooled Reactors (AGRs). A greater understanding of the material is therefore required in order to make more informed evaluations as part of on-going safety cases. Young's modulus is one property which varies as a complex function of radiolytic oxidation and fast neutron irradiation dose; this work investigates investigate the Young's modulus behaviour of nuclear grade graphites through property measurement and microstructural characterisation. Physical properties are dependent on microstructure, which is in turn a result of the manufacturing processes and raw materials used in its fabrication. Because of this, this thesis begins with a microstructural study of AGR graphite artefacts from varying points during the manufacturing process and post-irradiation, utilising X-ray diffraction to observe changes in crystallinity, microscopy to directly observe the microstructure and pycnometry to gauge porosity variations. Increases in crystallinity towards graphitisation are seen, with a subsequent decrease after irradiation; and significant changes are observed from inspection of optical and scanning electron micrographs. Young's modulus property data are obtained using a combination of static and dynamic techniques to accumulate data from a variety of techniques. An experiment designed to track changes to the speed of sound under compressive load was carried out on Magnox and AGR graphite, showing different behaviour between the grades, and variation with irradiation.A final series of tests combine compressive testing with in-situ microscopy to try and better understand the reasons behind this varied in behaviour and relate microstructural changes to graphite behaviour under compressive loading.

This thesis describes a study of reactive transport processes in fractured rock in response to high pressure gas injection and displacement. This is achieved through the development and application of a theoretical and numerical modelling platform. A dual porosity, dual permeability framework has been formulated based on a mechanistic approach, which considers the coupled hydraulic, gas/chemical and deformation behaviour of fractured rock. The fracture network and porous rock matrix were treated as overlapping continua with distinct transport and storage properties. Flow in each continuum was considered by advection, diffusion and dispersion mechanisms, and a sink/source term was included for the kinetically controlled sorption of multicomponent gas. A mass exchange term was introduced to couple the continua and allow pressure and concentration differences to develop. The transport properties of non-ideal gas mixtures at high pressure were characterised by appropriate constitutive relationships. The developed model has been incorporated in an existing coupled thermal, hydraulic, chemical and mechanical framework. A numerical solution was obtained using the finite element method for spatial discretisation and the finite difference method for temporal discretisation. Verification of the approach proposed has been addressed via a series of benchmark tests. The results obtained provide confidence in the accuracy of the numerical implementation of the dual porosity governing equations, including a time splitting approach used to couple the transport module with the mass exchange and geochemical reaction modules. Key theoretical features have been included to enhance the model capabilities and enable application of the model to study species dependent coal-gas behaviour, especially in relation to carbon dioxide sequestration in coal and enhanced coal bed methane displacement. The development of constitutive relationships describing the feedback of dual porosity physico- and chemo-mechanical deformation on gas transport in coal was considered in detail. Furthermore, a combination of two first-order rate models was used to include the specific gas sorption behaviour in coal. A detailed validation of the model using high resolution experimental data on gas interactions, transport and displacement in coal has been included. The theoretical models developed for coal-gas interactions were first evaluated, providing a platform to facilitate numerical simulations of gas injection and displacement experiments, performed on intact samples of anthracite coal from the South Wales coalfield. Under the conditions considered and for two injection scenarios, namely, nitrogen and subcritical carbon dioxide injection, it was demonstrated that the model is capable of simulating the salient physical and chemical phenomena involved in gas transport and methane displacement in coal. More advanced simulations have been performed to study the behaviour for a larger sample size and different gas injection pressures and compositions. The injection of supercritical carbon dioxide and two carbon dioxide-rich gas mixtures at high pressure was considered. It is claimed that a substantive insight has been gained into the coupled behaviour of the material at the laboratory scale. Overall, the analysis carried out in this research indicated that species dependent chemo-mechanical deformation was the dominant factor in smaller core samples. Fracture-matrix exchange and preferential methane desorption by carbon dioxide only became more apparent in larger samples. An appreciation of the effects of sample size on the behaviour observed is therefore important when interpreting experimental data, and implies that due care must be taken in interpreting laboratory scale results towards larger scale applications. In this work, the capabilities of the new model have been showcased with regards to the study of coal-gas systems. Importantly, the developments presented are more generally relevant and thus enable the study of a broad new range of applications involving multiphase, multicomponent gas/chemical transport in fractured rock.

At the boundary between the Paleocene and Eocene epochs (ca. 56 Ma) a significant global warming event, termed the Paleocene-Eocene Thermal Maximum (PETM), occurred. Records of this event are characterised by a negative carbon isotope excursion (CIE) which has been associated with the release of thousands of petagrams of isotopically light carbon into the ocean-atmosphere system, initiating changes in the carbon cycle, the climate system, ocean chemistry and the marine and continental ecosystems. The amount of isotopically light carbon that was required to cause the event, its source and the rapidity of its release are, however, are still debated. This study uses δ13CTOC, δ13Cn-alkane, δ13CCARB and palynological data to evaluate the PETM CIE in terms of the magnitude of the CIE in both continental and marine settings, rapidity of release and drawdown of carbon, and mobilisation of different organic matter (OM) pools as a response to the climate change. The sections studied span a continental to marine transect in northern Spain. This represents the first organic geochemical study of these PETM sections, one of the first comparisons of CIE magnitude between continental and marine sections within the same sediment routing system, and one of the first comparisons of the same OM proxies within different depositional environments. The data suggest that different OM pools were mobilised in response to the PETM, with reworking of older material, soil residence times, and contemporaneous vegetation all contributing. CIE profile shapes predominantly suggest a rapid onset and recovery from the event. The magnitude of the CIE was also assessed. The current resolution of the data suggests that the differences between continental and marine CIE magnitudes could be minimal within a single sediment routing system, perhaps establishing a realistic CIE magnitude for the PETM, for use in future modelling scenarios.