bluuebunny/crossref_metadata_2025_split huggingface dataset:
Petroleum systems of Alpine-Mediterranean foldbelts and basins
Authors: Ziegler P. A. , Roure F. 
Published: April 2008

Abstract
The Alpine-Mediterranean area hosts a number of large and smaller hydrocarbon provinces in platforms, rifts, foreland basins and the frontal parts of thrust belts. These hydrocarbon provinces are related to a wide range of source rocks occurring in Palaeozoic, Mesozoic and Cenozoic series. Source rocks are alternatively localized in prerift, syn-rift or passive-margin sequences, the age of which is highly variable. Moreover, syn-orogenic foreland basin sequences can contain important source-rocks and are frequently the locus of biogenic gas generation.
Most Mesozoic passive margins of the Western Tethys were destroyed during the Alpine orogenic cycle and were overthrusted by or incorporated into orogenic wedges, the external parts of which host a number of highly diversified petroleum systems. Late Variscan and Alpine compressional intraplate deformation had severe repercussions on the hydrocarbon habitat of some of the Peri-Tethyan platforms. Late Cretaceous and Palaeogene intracratonic and back-arc rifts host some important petroleum provinces; the Euphrates, Abu Gharadig and Sirte basins rely for hydrocarbon charge on syn-rift source rocks whereas post-rift series contain the source rocks of the Black Sea back-arc basin. Oligocene and younger rift systems host the petroleum provinces of the Gulf of Suez, Pelagian Shelf, Valencia Trough and Rhine Graben; these rely variably on pre- and syn-rift source rocks. The Neogene Pannonian system of transtensional back-arc basins relies for hydrocarbon charge mainly on syn-rift source rocks whereas the Vienna Basin is exclusively charged by Mesozoic post-rift source rocks.
The complex evolution of the Western Tethys belt, contrasted thermal regimes and successive episodes of sedimentary and tectonic burial account for the great diversity of its petroleum systems. Each hydrocarbon province is characterized by a very distinct scenario for the accumulation of source rocks, timing of their maturation, hydrocarbon expulsion and migration from effective kitchens to potential trapping domains, and the preservation of hydrocarbon accumulations.
Future exploration in the external parts of the Alpine orogenic belts, their forelands and beneath the Neogene fill of the Pannonian Basin is likely to yield further oil and gas discoveries. In contrast to the Black Sea Basin, the hydrocarbon potential of the Algero-Provençal, Tyrrhenian and Aegean back-arc basins is questionable. The thick sedimentary sequences of the deep East Mediterranean Basin may contain effective source rocks.
Chemical containment of waste in the geosphere
Authors: Metcalfe Richard , Rochelle Christopher A. 
Published: April 2008

Abstract
The aim of this introductory paper is to highlight those underlying chemical principles that are common to all forms of waste management by geological means, and that rely to some extent upon chemical containment. Until recently, chemical processes were usually considered mainly because they can affect the physical performance of engineered containment systems. However, in recent years, many researchers have recognized that chemical processes themselves can offer containment to wastes. Thus, it is no longer possible to view physical and chemical containment processes separately. The containment system can be optimized only if both the engineered and natural barriers are considered together, and if the engineered barrier system is designed taking the features of the geosphere into account. However, there has been relatively little reliance upon the geosphere itself as a chemical barrier. It is concluded that the potential for chemical containment should be considered in all forms of geological waste management. Even if the chemical barrier function of the geosphere is not relied upon to meet safety targets, the confidence of regulators and public alike will be enhanced if it can be demonstrated that the geosphere at the site functions as a chemical barrier.
Regulatory objectives and safety requirements for the disposal of radioactive wastes in Switzerland
Authors: Frank E. 
Published: April 2008

Abstract
According to Swiss Law the producers of radioactive waste are responsible for management and safe disposal of all types of radioactive waste. Therefore, in 1972, the electricity utilities involved in nuclear power production formed the National Cooperative for the Disposal of Radioactive Waste (NAGRA) which is responsible for final disposal and related work. The general disposal strategy includes two repository siting programmes, a deep repository for high-level waste in Northern Switzerland (crystalline basement or Opalinus claystone) and a repository with horizontal access for low- and intermediate-level waste in the Alps (marls and shales of the Wellenberg-site).
The safety of waste disposal is assessed on the basis of specific protection objectives formulated by the Swiss regulatory authority. The protection objectives limit the annual dose equivalent or the radiological risk to an individual and they require that post-closure safety must not depend on long-term monitoring or any other interventions to ensure safety. After a final repository has been sealed, it must be possible to dispense with safety and surveillance measures.
The chemical basis of near-field containment in the Swiss high-level radioactive waste disposal concept
Authors: Alexander W. R. , McKinley I. G. 
Published: April 2008

Abstract
Concepts for the disposal of high-level radioactive waste (HLW) vary from country to country but, in Switzerland, a key contribution to safety is the chemistry of the near-field. In this paper, the development of the Swiss repository design is discussed as a basis for explaining the chemical confinement of radionuclides within the engineered barrier system (EBS). The expected performance of the EBS is described and the chemistry of the system explained. Potential perturbations to the EBS are examined and the methodology of assessing the long-term behaviour of the EBS is briefly described. The relevance of HLW near-field design to chemo-toxic wastes is discussed and an extensive reference list on the chemical aspects of the EBS is provided.
Experimental simulation of the alkaline disturbed zone around a cementitious radioactive waste repository: numerical modelling and column experiments
Authors: Bateman K. , Coombs P. , Noy D. J. , Pearce J. M. , Wetton P. , Haworth A. , Linklater C. 
Published: April 2008

Abstract
One approach to describe the migration of an alkaline plume from the cementitious engineered barriers of a geological disposal facility for radioactive wastes is to employ coupled chemistry and flow computer models. Although evidence from natural systems is useful to constrain reaction mechanisms and minerals to be incorporated into such models, time-dependent information is generally lacking. A series of laboratory column experiments has been conducted in order to test the capabilities of two of the currently available, coupled models to predict product solids and output fluid compositions with time. The coupled models PRECIP and CHEQMATE were used to provide predictive calculations based upon known experimental parameters and data available from the literature. The predictions did not replicate all the variations in mineralogy observed in the experiments, primarily due to restrictions in the availability of kinetic and thermdynamic data for the range of secondary phases of interest. However, the model predictions did reproduce the general variation of secondary phases with time and distance along the columns.
What is the porosity of a mudrock?
Authors: Pearson F. J. 
Published: April 2008

Abstract
Several types of porosity (total or physical, advective flow, advective and diffusive transport, and geochemical) can be distinguished in a mudrock. Each may have a different value. Physical porosity is the volume not occupied by mineral grains. Interconnected physical porosity can be found using injection techniques and water-content measurements. Advective and diffusive flow and transport porosities are used when describing the movement of fluids and solutes. Advective porosity relates the average linear velocity of a fluid to its Darcy flux (velocity), and in mudrock is relevant principally to fractures. Diffusive porosity relates diffusion in rock to diffusion in pure water and depends on the diffusing substance and the medium. In mudrock, water diffusion porosities equal water content porosities but solute diffusion porosities are smaller because solutes do not have access to the entire water content of a rock. Inaccessible water may be in pores too small to admit solutes, or present as interlayer or surface-layer water. Geochemical porosity is required to model pore-water composition and reactive transport. It represents the fluid volume in which reactions occur, and for mudrocks, seems equivalent to solute-diffusion porosity. Review of studies of several mudrocks shows halide geochemical porosities from 0.3 to 0.7 of other porosity values. Uncertainties of this size are unimportant for transport calculations, but lead to significant uncertainties in modelled pore-water compositions. To make acceptably accurate calculations of water-rock reactions and transport in mudrock, it is important to define the geochemical porosity.
Permeability and fluid flow in natural mudstones
Authors: Dewhurst David N. , Yang Yunlai , Aplin Andrew C. 
Published: April 2008

Abstract
Mudstone permeabilities vary by ten orders of magnitude and by three orders of magnitude at a single porosity. Much of the range at a given porosity can be explained by differences in grain size; at a given effective stress, coarser-grained mudstones are more permeable than finer-grained mudstones, although the difference diminishes with increased burial. Pore size distributions illustrate why more silt-rich mudstones are more permeable than finer mudstones and also show that the loss of porosity and permeability with increasing effective stress is driven primarily by the preferential collapse of large pores. Pore size distributions can also be used to estimate permeability rapidly. None of the existing models are ideal and need to be adjusted and validated through the acquisition of a much larger permeability database of well-characterized mudstones. We also examine the role of faults and fractures as fluid conduits in mudstones. The occurrence of microscopic hydrofractures is inferred from the observation that fluid pressures in sedimentary basins rarely exceed minimum leak-off pressures. The extent to which microfractures enhance mudstone permeability, both instantaneously and over longer periods of geological time, is poorly constrained. Although fault zones in mudstones have generally low permeability, there is abundant evidence for episodic flow along faults in tectonically active regions. The role of faults as fluid conduits during periods of tectonic quiescence is less certain, and the timing and extent of any enhanced permeability and enhanced flow are not well known. In general, conditions conducive to fluid flow along muddy faults include an increase in the activity of the fault, high fluid pressures within the fault zone and the extent of overconsolidation and lithification of the mudstones.
Permeability anisotropy of consolidated clays
Authors: Clennell M. B. , Dewhurst D. N. , Brown K. M. , Westbrook G. K. 
Published: April 2008

Abstract
Consolidation of clays tends to result in changes in particle orientation and pore size distribution as well as progressive reduction of porosity and permeability with increasing effective stress. Clay particles are expected to rotate normal to an axial load, thus decreasing flow path tortuosity parallel to the particle alignment direction and increasing tortuosity normal to the particle alignment. This results in the development of anisotropic permeability, such that the horizontal permeability of a consolidated sediment is greater than the vertical permeability at any given porosity. Within any uniform layer, levels of permeability anisotropy are modest. Typically, permeability anisotropy produced by consolidation of natural clays is in the range 1.1–3 and does not reach the high levels predicted by simple models of clay particle reorientation. The discrepancy arises from particle clustering and irregularities in particle packing. Although somewhat higher levels of anisotropy may exist as a consequence of lamination within individual beds, values > 10 that are known to exist on the formation scale are produced by strong contrasts between the permeabilities of interlayered beds. As argillaceous sediments have permeability ranges of many orders of magnitude, apparently subtle lithological layering in a shale unit may lead to a highly anisotropic flow behaviour.
Top-seal leakage through faults and fractures: the role of mudrock properties
Authors: Ingram Gary M. , Urai Janos L. 
Published: April 2008

Abstract

Mudrocks are effective top seals for hydrocarbon accumulations because they possess very low permeabilities, high capillary entry pressures, and are often laterally continuous basin-wide. For leakage through the seal to take place, an additional mechanism must provide enhanced permeability in mudrocks. Tectonically induced, dilatant faulting and fracturing in brittle rocks is such a mechanism. The effectiveness of mudrocks as seals may be compromised by a number of other factors, such as tectonic fault displacements in excess of the seal thickness; tensile fracturing under extreme fluid pressure conditions; and leakage via a network of juxtaposed thin leaky beds across sub-seismic faults within the seal. Before hydrocarbon trap integrity analysis, seismic interpretations should honour the fundamental geometry of the trap as closely as possible because top seals can be reliably appraised only when basic geometries are accurately determined. Fluid pressure is a proven risk in many exploration provinces, in terms of mudrock top-seal leakage via opening mode fractures. This natural hydrofracturing can take place if buoyancy pressures, combined with fluid overpressures, exceed the minimum
in situ
horizontal stress, plus the tensile strenght of the seal, an occurrence that leads to mechanical failure of the seal rock. The rheology of a seal is another important factor as it determines the failure mode, i.e. whether the rocks are ductile and remain sealing after deformation or whether they deform in a brittle manner to create permeable leak paths. Several techniques have been developed to predict rock rheology; these rely on uplift, sonic velocity and clay content data. Burial curves can be used to determine overconsolidation of mudrocks. Sonic velocity data can be used to estimate unconfined compressive strength in mudrocks. The most direct method utilizes relationships between mudrock friction angle, swelling clay content and mudrock surface area to determine ductility. The effect on trap integrity of sub-seismic faults is also quantifiable because advances in structural geological technology now permit predictions of the numbers of sub-seismic faults in a trap. This information, combined with detailed top-seal stratigraphic data, provides the power to screen traps for the risk of top-seal leakage via sub-seismic fault juxtapositions within the seal. A simple strategy incorporating these factors and linking them to other structural and stratigraphic information can contribute to reducing uncertainty about top-seal leakage caused by tectonic deformation.
Porosity characteristics of Cambrian mudrocks (Oak Ridge, East Tennessee, USA) and their implications for contaminant transport
Authors: Dorsch J. , Katsube T. J. 
Published: April 2008

Abstract

Thirty-eight mudrock samples from the Cambrian Conasauga Group were analysed by immersion, helium and mercury porosimetry. The data generated from these techniques include effective porosities, pore throat size distributions and sample densities. The purpose of these analyses was to obtain information required to evaluate the capacity of the Conasauga Group mudrock to retard transport of and to store contaminants on the Oak Ridge Reservation (East Tennessee, USA). Results indicate that the three porosities were 9.90±2.61%, 3.8±0.7% and 8.1±4.3% for immersion (φ
I
), mercury (φ
Hg
) and helium porosity (φ
he
), respectively. These values are considerably higher than those previously reported for these rocks (0.1–3.4%). The φ
Hg
values are commonly the smallest of the three. Although the three porosities generally show little change with depth, an expected trend as a result of the maximum burial depth of the Conasauga Group of >4 km, a decrease with depth is seen in some of the coreholes for only φ
I
. Furthermore, inconsistencies between the different porosity types provide an insight into the mudrock pore structure and related geochemical characteristics. For example, they indicate the existence of considerable pore space accessed only through <3 nm pore throats and the possibility of meteoric cement having replaced original diagenetic cement for some mudrock samples, which would lead to a possible instability to immersion with contaminated water. These characteristics have significant implications for the evaluation of the mudrock retardation and storage capacity for contaminants, and the design of remediation measures.
Preferential pathways in an Eocene clay: hydrogeological and hydrogeochemical evidence
Authors: Walraevens K. , Cardenal J. 
Published: April 2008

Abstract

This study was initiated to test the extent to which the cation exchange capacity of marine clay-rich units, through which fresh water has been recharged, controls the composition of pore waters in an aquifer. The semi-confined Ledo-Paniselian (Eocene) aquifer in Flanders is recharged in elevated regions, where it is covered by Bartonian Clay. These sediments were initially laid down in marine conditions. The effects of recharging fresh CaHCO
3
water by downward flow through the overlying clay within the aquifer were modelled using PHREEQM. In the aquifer, progressively fresh waters are found in an upstream direction, which indicates a reduced influence of the initial marine conditions. Different stages of cation exchange produce a chromatographic sequence of groundwater types. Hydrogeological and hydrogeochemical evidence suggests the existence of preferential, faster flow pathways for recharge groundwater flow through the Bartonian Clay overlying the aquifer. These conclusions are indicated by differences between the observed and predicted features of the aquifer. It is necessary to invoke hydraulic conductivity values of 10
−9
m s
−1
rather than 10
−10
m s
−1
(measured values) for the Bartonian Clay so that the predicted head distributions in the aquifer match the observed heads. Furthermore, the measured exchangeable cations in clay collected from cores in the recharge area show less freshening than is predicted from the model to produce either the observed groundwater type within the aquifer in the recharge area or the overall distribution of groundwater types in the aquifer. Given the discrepancy between the observed and calculated state of freshening it is assumed that the analysed flow line in the core must be part of a slower flow pathway.
Methodologies for multi-well sequence analysis using borehole image and dipmeter data
Authors: Prosser Jeremy , Buck Stuart , Saddler Shaun , Hilton Vince 
Published: April 2008

Abstract
Borehole image logs provide high-resolution directional data sets, in addition to a wealth of information concerning sedimentary fabric and texture. The data derived from these images are typically used for lithofacies characterization, palaeotransport analyses, and fault and unconformity recognition. These data are ideal input variables to the development of correlative models, particularly within a sequence stratigraphical context. However, in field settings characterized by low structural dip (less than 15°), unconformity recognition can be very difficult within shallow marine sediments, which would have had very low depositional or sedimentary dip. In the study described, integration of borehole image data with core sedimentological and ichnofabric analyses has enabled calibration of images for lithofacies recognition, identification of bioturbation fabrics, and the degree of bioturbation present. In particular, comparison of the results of dip trend analyses with the results of ichnofabric analyses has indicated that subtle, though consistent variations in shale bed dip azimuth correspond closely with the locations of sequence boundaries. This has provided increased confidence in unconformity recognition in un-cored well sections, and enabled correlations to be developed. Lessons learned from interpretation and calibration of high sample density borehole image logs (FMI) within cored well sections has enabled interpretive methodologies to be transferred to lower density FMS and SHDT data sets. Similarly, examination of core-photographs as a continuous ‘photographic image log’ in the workstation environment has revealed that when displayed at appropriate scales, even vintage core photographic plates contain a phenomenal amount of data. This is obviously useful for calibration of dipmeter data where, due to climate etc., cores are poorly if at all preserved. Perhaps more surprisingly, comparison of core-photographic data with existing cores has revealed that when displayed on a workstation, core photographs are suitable for detailed ichnofabric analysis. This has allowed reinterpretation of effectively ‘lost’ data within the context of recent advances in sedimentology. The procedures described constitute an innovative approach to the integration of different data types gathered using existing, proven techniques.
Stratigraphic relationships in the upper Rotliegend: interpretations from horizontal and vertical well borehole images, core and logs in the Lancelot area, Southern North Sea, UK
Authors: Went David J. , Fisher William C. 
Published: April 2008

Abstract
Interpretation of data from core and borehole images in horizontal and vertical wells in Lancelot area fields has resulted in a clearer understanding of the stratigraphic relationships in the upper section of the Rotliegend reservoir. The complex stratigraphy of the upper Rotliegend stems from the reworking and marine inundation of an erg margin. Extensive erosion, fluidization and reworking of the erg occurred but a remnant aeolian topography was retained. The remnant aeolian dune sequence (Unit 3) shows a mounded geometry with a relief up to 40 m and an estimated wavelength of 2 km. Sets of aeolian dune cross bedding are heterogeneous with low permeability layers associated with foresets and set boundaries. Cross bed set orientation and sizes affect upscaled permeability. Differences in set size may relate to a mixture of dune and draa slipfaces or variously sized dunes migrating over draa without slipfaces. The reworked sequence (Unit 4) is a variably thick, commonly erosively-based interval of slightly to heavily cemented sandstone. It is commonly structureless but locally contains slumped aeolian dune foreset beds, dewatering structures, deformed bedding, and sequences featuring repeated intervals of marine shale (Kupferschiefer). The distribution of the various subfacies is related to a model of remnant aeolian dune relief which influenced the style of sediment reworking. The geometric attributes and heterogeneity distributions associated with Units 3 and 4 have important implications for successful targetting of horizontal wells, particularly those planned for close to the top of the reservoir (ensuring maximum standoff from the field gas water contact), for volumetric estimates and reservoir simulations.