bluuebunny/crossref_metadata_2025_split huggingface dataset:
Geochemical factors in the selection and assessment of sites for the deep disposal of radioactive wastes
Authors: Savage David , Arthur Randolph C. , Saito Shigeyuki 
Published: April 2008

Abstract

Geochemical parameters which are important to waste isolation include (with optimum conditions in parenthesis): groundwater pH (10 > pH > 8), redox (
Eh
< −200 mV),
P

co
2

(<10
−4
bars), and ionic strength (< 0.5 M); the colloid (< 0.01 ppm), organic (< 5 ppm) and inorganic ligand (Cl
−
> HCO
−
3
, low abundances of phosphate) content of groundwaters; and the mineralogical composition and structure of groundwater flowpaths (zeolites, clays, iron oxyhydroxides with appreciable diffusive porosity). pH, redox, and in some environments,
P

co
2

, will be controlled by water-rock reaction; other parameters are influenced more by geological history or environment. pH and redox buffer intensities of likely mineral assemblages and groundwater compositions under possible physical conditions of deep disposal have been calculated. For pH, reactions between aluminosilicates, carbonates and water should dominate over those in the fluid phase alone. The reaction of small amounts of ferrous iron-bearing minerals (≥ 5 vol %) is sufficient to maintain chemically reducing conditions under likely hydraulic conditions at depth. Consideration of laboratory data suggest that pH and redox reactions should not be hindered by kinetics under likely physical conditions for deep disposal, but further field and laboratory experimental data are required to verify these conclusions. The most suitable geochemical environments for waste isolation are basic or intermediate igneous rocks in tectonically stable, low-lying terrain away from sedimentary basins. Geochemical criteria should not be used in isolation of other factors for the selection of sites, but suitable geochemical conditions may help relax the requirements for optimum performance dictated by other geological and hydrogeological factors.
Characterizing the chemical containment properties of the deep geosphere: water-rock interactions in relation to fracture systems within deep crystalline rock in the Tono area, Japan
Authors: Iwatsuki T. , Yoshida H. 
Published: April 2008

Abstract
A water/rock interaction study has been integrated with interpretations of geological structures, in order to understand the geochemical conditions in deep granitic rock at the Tono study site, central Japan. Geological investigations show that fracture systems in the granitic rock can be classified into: intact zones; moderately fractured zones; and intensely fractured zones. This classification is based upon the frequency and width of fractures and fractured zones. Isotopic analyses of the groundwaters indicate that the groundwater at SL 80m (SL: sea level) has recharged within the last 30 years. Petrological and mineralogical observations were undertaken, and coupled with theoretical calculations using the PHREEQE geochemical computer code. The results of this approach suggest that the chemical evolution of the groundwater is generally controlled by water-rock interactions involving plagioclase, clay minerals and ferric hydroxide in the intact zones and moderately fractured zones. The geochemical condition of the groundwater is correlated closely with the nature of the fracture systems, mineral compositions and water-rock interaction processes. Different fractures contain chemically distinct groundwaters, which have differing potential capacities to mobilize radionuclides. The investigation method, based on a comparison between geological structures and groundwater chemistry, can be applied to develop a realistic hydrogeochemical model for deep, fractured granitic rocks. Such an approach is necessary if the chemical containment potential of such lithologies is to be evaluated adequately. The work demonstrates that structural controls on chemical heterogeneities in groundwaters should be understood, before the disposal of redox-sensitive wastes can be undertaken safely in fractured crystalline rocks.
The underground sequestration of carbon dioxide: containment by chemical reactions in the deep geosphere
Authors: Rochelle C. A. , Pearce J. M. , Holloway S. 
Published: April 2008

Abstract

Anthropogenic emissions of carbon dioxide (CO
2
) have been linked to increasing levels in the atmosphere and to potential global climate change. The capture of CO
2
from large point sources, followed by its sequestration as a supercritical fluid into the deep geosphere, is one potential method for reducing such emissions without a drastic change in our energy-producing technologies. Once emplaced underground, geochemical and hydrogeological processes will act to ‘trap’ the CO
2
as dissolved species and in carbonate minerals. Although dry supercritical CO
2
appears to cause little reaction with the host rocks, once dissolved in water mineral dissolution and precipitation reactions can result. From a geochemical standpoint, sandstones appear to be preferable to carbonates for sequestration operations because fluid-mineral reactions within them have a better capacity for pH buffering. However, individual host lithologies will vary in structure, mineralogy and hydrogeology, and individual sequestration operations will have to take account of local geological, fluid chemical and hydrogeological conditions. This paper summarizes some of the recent laboratory experimental, natural analogue and computer modelling approaches directed at understanding reactions involved in the chemical containment of CO
2
.
The geochemical engineering of landfill liners for active containment
Authors: Thornton S. F. , Bright M. I. , Lerner D. N. , Tellam J. H. 
Published: April 2008

Abstract
The performance of engineered containment barriers presently used to line UK landfills is uncertain over the design lives of most sites. Failure of key components of the barrier technology can be expected within a timescale under which leachate will still present a threat to groundwater resources. Additional environmental control measures are therefore necessary to mitigate the effects of these future impacts. A methodology for the geochemical engineering design of high-attenuation landfill liners using low-cost natural and industrial waste materials which are available in the UK is presented. Anaerobic laboratory column experiments are used to test the performance of various materials as liners in chemically attenuating contaminants in a methanogenic leachate spiked with a suite of heavy metals and organic micropollutants. The basic liner design recipe which maximizes the attenuation of key contaminants in leachate has been confirmed. Variability in material composition does not significantly affect liner performance provided this recipe is used. Important design issues (liner exhaustion and attenuation reversibility effects) are examined in the study. These liners may be routinely constructed from measurements of a limited suite of material properties using standard laboratory procedures. The application of these liners within the current framework of landfill design is outlined.
Radioactive waste containment in indurated shales: comparison between the chemical containment properties of matrix and fractures
Authors: De Windt L. , Cabrera J. , Boisson J. Y. 
Published: April 2008

Abstract

The chemical containment properties of poorly consolidated, plastic clays have received considerable attention, particularly during investigations related to radioactive waste disposal. However, the chemical containment properties of indurated shales have received rather less consideration. This paper summarizes those properties of consolidated shales which make them suitable for the chemical containment of radionuclides, using the example of investigations at the Tournemire research site in the south of France. The problems associated with investigating such low-permeability media are highlighted, and solutions to these problems are presented. At this research site, tectonic processes have induced centimetre-scale fractures and decimetre-scale faults in the shales, whereas excavation of a tunnel has generated metre-scale fracturing. Some low water flows through the fracture networks have been detected. However, the Tournemire shales are characterized by very low matrix pore-water contents, and any limited fluid mobility through the matrix is caused mainly by diffusion. Slowly flowing waters in fractures are chemically analogous to these matrix pore-waters. The hydrochemistry is of Na-Cl-(

HCO
3
−

) type, and the waters are slightly alkaline, strongly reducing and of low ionic strength. The resemblance between the chemistries of pore- and fracture-waters arises from the buffering of the pore-water chemistry by matrix mineral/water interactions, and possible subsequent diffusion of the pore-water into the fractures. The chemical buffering mechanisms controlling the water chemistries (especially pH, alkalinity and
Eh
), are discussed and modelled. The chemical conditions will minimize the mobility of many radionuclides in both shale matrix and in fractures. Chemical evidence from the fracture-filling calcite is consistent with this hypothesis and demonstrates the past immobility of U and Cs. Batch experiments carried out in gloveboxes under a N
2
atmosphere and with synthetic fracture-water show weaker retention of Cs by the calcite fillings than by the shale matrix. Due to its very low porosity, the shale matrix should behave like a membrane filter for colloids, further reducing the mobility of radionuclides. In fractures, interface structures between matrix walls and calcite veins should also hinder colloid migration (except perhaps in occasional centimetre-scale apertures).
Failure envelopes of mudrocks at high confining pressures
Authors: Petley D. N. 
Published: April 2008

Abstract
Whereas models for the mechanical behaviour of many types of sedimentary rocks at high mean effective stresses (2–50 MPa) are now reasonably well developed, few attempts have been made to generate models for mudrocks in the same way. This paper combines a new set of undrained shear experiments on London Clay with a summary of other mudrock datasets as described in the literature, including Kimmeridge Clay, London Clay, Boom Clay and clay from mud volcanoes. It has been demonstrated previously that at low mean effective stresses, most undisturbed mudrocks behave in a brittle manner, showing a distinct peak strength before undergoing failure and strain weakening to a residual strength. At very high mean effective stresses they tend to behave in a ductile manner, with the maintenance of peak strength to large strains. This paper shows for the first time that a ‘transitional’ regime can be defined for most mudrocks. In this transitional regime, undrained shear deformation leads to the maintenance of peak strength to a given axial strain in a manner that is similar to ductile deformation, before the initiation of strain weakening to a residual strength. Detailed analysis has demonstrated that during the maintenance of peak strength the sample is undergoing pervasive micro-fracturing and is thus behaving in a ductile manner on the macro-scale and in a brittle manner on the micro-scale. As a result of this study it has been possible to construct a model for the form of the failure envelopes of most mudrocks, with two fundamentally important envelopes being defined: (1) a linear residual strength envelope: at low and medium mean effective stresses the stress path will tend towards this envelope after brittle failure; (2) a peak strength envelope: at low mean effective stresses this envelope has a linear form, but once the transitional regime is attained it reduces in gradient, eventually intercepting the residual strength envelope at the boundary of the ductile regime. This new framework for the behaviour of mudrocks during undrained shear deformation is generally consistent with those developed for other sedimentary rocks.
Insights into the hydraulic performance of landfill-lining clays during deformation
Authors: Peters M. G. , Maltman A. J. 
Published: April 2008

Abstract

The low hydraulic conductivities of mudrocks are widely utilized in the waste disposal industry, where clays are commonly employed as a lining to landfill sites. The hydraulic conductivity of these clays is well characterized, but only under steady-state conditions. In reality, as with many situations in geology, landfills are dynamic environments and the lining materials are subject to temporal and spatial stress variations. These fluctuating stress conditions are likely to lead to deformation of the liner, which may in turn lead to changes in its hydraulic performance. To assess the behaviour of clay lining materials under operational stresses, samples of actual liner clays have been subjected to anisotropic loading in a triaxial cell while monitoring their hydraulic performance with a constant-rate-of-flow permeameter. The clays show marked changes in hydraulic conductivity during deformation, with increases and decreases being seen in different samples. However, the measured changes are probably not large enough to breach the minimum performance specification for landfill linings (current legislation calls for a maximum saturated hydraulic conductivity of 1 × 10
−9
m s
−1
). The fluctuations in hydraulic conductivity can be linked to the consolidation state and changes in the pore volume of the samples during deformation. The results and interpretations detailed here for three representative tests provide models of the hydrological behaviour of clays during deformation that may be applicable to poorly lithified mudrocks in other dynamic situations.
Gas transport properties of clays and mudrocks
Authors: Harrington J. F. , Horseman S. T. 
Published: April 2008

Abstract
Controlled flow rate gas injection experiments have been performed on clay and mudrock samples using helium as a permeant. By simultaneously applying a confining stress and back-pressure, specimens were isotropically consolidated and fully water saturated under predetermined effective stress conditions, before injecting gas at a very slow rate using a syringe pump. Ingoing and outgoing gas fluxes were monitored. All tests exhibit a conspicuous threshold pressure for gas breakthrough. All tests showed a post-peak negative transient leading to steady-state gas flow. On the basis of a stepped history of flow rate, the flow law was shown to be nonlinear (i.e. non-Darcian). With the injection pump stationary (i.e. zero flow rate), gas pressure declined with time to a finite value. No gas flow was ever detected at excess gas pressures less than this lower threshold. When gas flow was re-established, the threshold for gas breakthrough was found to be significantly lower than in the virgin clay. There is strong evidence to suggest that the capillarity restrictions on gas penetration of the intergranular pores of saturated clays and mudrocks are of such a magnitude that normal two-phase flow is impossible. Gas therefore does not occupy, or flow through, the intergranular porosity of the clay matrix. In the absence of pressure-induced cracks, water-saturated clays and mudrocks are totally impermeable to gas. The measured gas permeability of a clay-rich medium is a dependent variable rather than a material property, as it depends on the number of pressure-induced pathways in the plane normal to the flow, together with the width and aperture distributions of these pathways. The experiments suggest that the flow pathways open under high gas pressure conditions and partially close if gas pressure falls, thus providing a possible explanation of the nonlinearity of the flow law. Reliance on conventional two-phase flow theory is inadvisable when attempting to quantify gas transport in initially water-saturated clay-rich materials.
Origin of overpressures on the Halten Terrace, offshore mid-Norway: the potential role of mechanical compaction, pressure transfer and stress
Authors: Skar T. , Van Balen R. T. , Arnesen L. , Cloetingh S. 
Published: April 2008

Abstract
The Halten Terrace, a structural element on the mid-Norwegian margin, is characterized by distinct spatial variations in subsurface fluid pressure. Jurassic formations on the western part of the Halten Terrace are highly overpressured (> 30 MPa), whereas the same formations have fluid pressures close to hydrostatic in the central and eastern parts of the terrace. The cretaceous formations are moderately overpressured in the whole area. The porosities in the overpressured middle Jurassic formations and lower Cretaceous shales are only slightly influenced by the present-day overpressures, suggesting that most of the overpressure development was recent. Overpressure generation as a result of mechanical compaction, induced by the weight of the Plio-Pleistocene sediments, is not sufficient to explain the overpressure magnitudes in the Jurassic and Cretaceous formations. Results from forward modelling of mechanical compaction suggest that the deep Rås Basin adjacent to the Halten Terrace has been highly overpressured since Cretaceous time. Pressure transfer from this basin to the western part of the Halten Terrace is therefore a possible explanation for the observed overpressures. Migration of the overpressured fluids may have occurred through the Klakk Fault Complex separating the basin from the terrace, during an event related to a basinal stress reorientation in early Pliocene time.
The recognition of artefacts from acoustic and resistivity borehole imaging devices
Authors: Lofts J. C. , Bourke L. T. 
Published: April 2008

Abstract
Image artefacts, that is, non-geological features present on acoustic or micro-resistivity borehole image logs are a fact of life. In poor quality image logs, they can constitute the bulk of the data-set although fortunately, such features generally constitute the minority of a data-set. The recognition of artefact features must form part of the log quality control process and should also form part of the interpretation process. By applying sound log quality control principles, these artefacts can be identified systematically and the remaining image data will be geologically related. This paper provides an up-to-date summary of borehole image artefacts, their cause and recognition. It also, for the first time, considers artefacts arising from acoustic (ultrasonic) as well as micro-resistivity images. Four main artefact image categories related to data acquisition, borehole wall condition, post processing of data and measurement physics form the basis for the systematic identification procedure. These are discussed and developed herein.
A methodology for applying a non unique, morphological classification to sine wave events picked from borehole image log data
Authors: Trice Robert 
Published: April 2008

Abstract
Sine wave events are interactively picked as a representation of planar and pseudo-planar events within a borehole. This paper presents a logic and terminology by which sine wave features can be assigned a classification based on their morphological character. This morphological classification is non unique with respect to geological interpretation but can act as a template from which geological interpretations can be applied. The methodology presented has been written as a result of working on problematic image interpretations from a range of sedimentological, structural and petrophysical case studies. Application of the technique is considered of specific benefit to geoscientists with limited practical experience in image log analysis, to practising image log specialists when dealing with problematic data sets and as a methodology by which a base case interpretation can be derived in equity or shared data sets. An application of the technique is provided as a short case study.
Geology and reservoir description of 1Y1 reservoir, Oso Field, Nigeria using FMS and dipmeter
Authors: Thompson Laird B. , Snedden J. W. 
Published: April 2008

Abstract
Mobil Producing Nigeria’s Oso Field produces 120 000 barrels of oil per day from late Tertiary sands in the Niger Delta offshore. The reservoir consists of anastomozing fluvial deltaic sands which are difficult to correlate from well to well using traditional log correlation techniques. Image log data from Formation MicroScanner (FMS) logs and dipmeter data tied directly to cores permit detailed analysis of channel thickness, orientation, and distribution. This geographic understanding of the sand bodies enables geoscientists to construct a detailed ‘plumbing’ diagram of this complex reservoir, thus allowing for better exploitation.
Fault visualization from borehole images for sidetrack optimization
Authors: Grace L. M. , Newberry B. M. , Harper J. H. 
Published: April 2008

Abstract
Missing pay sections in faulted areas is a common occurrence. An accurate measurement of the fault plane and surrounding bed distortion can substantially reduce the risk involved in the sidetrack decision. The measurement of the fault plane includes the dip and strike as well as the sealing nature of the fault plane. Our experience indicates mineral-filled fault planes are always sealing. This has lead to several interesting sidetracks, many of which are against conventional wisdom. Case studies included show an extensional fault sidetrack to the downthrown block; a perforating determination based on the location of the actual sealing fault; an extensional fault sidetrack based on the non-sealing properties of the fault plane. In these cases the distortion of the surrounding blocks are modeled using enhanced computer techniques (Etchecopar 1992). The input of the actual fault plane dip and strike is shown to be the key to an accurate cross-sectional projection. The visualization of the fault model is critical to the resolution of the sidetrack azimuth and distance. Whether a fault plane is sealing is also an important contribution to any sidetrack analysis. This technique has accurately predicted the sidetrack location for many successful wells.
Manganiferous ironstones in the early Ordovician Manx Group, Isle of Man: a protolith of coticule?
Authors: Kennan P. S. , Morris J. H. 
Published: April 2008

Abstract

Spessartine-garnet quartzites (coticule) are now widely recognized as extremely useful marker horizons throughout the Appalachian-Caledonian Orogen. In many instances, they appear to be of early Ordovician age. They reflect a syn-sedimentary, volcanic exhalative origin and in many areas, e.g. the Leinster region in southeast Ireland, they are intimately associated with,
inter alia
, base metal mineralization and with tourmalinite. However, though the metamorphic coticule is common, the pre-metamorphic coticule precursor has proved difficult to recognize.

Manganiferous ironstone rocks of coticule aspect are a distinctive feature in parts of the Manx Group exposed along the west coast of the Isle of Man. Though they lack any trace of the characteristic manganese garnet, perhaps reflecting a relatively low metamorphic grade, they do bear a strong morphological resemblance in outcrop to the typical coticule lithology of the Ribband Group in southeast Ireland. In both places, tourmaline-rich rocks occur nearby. On the Isle of Man, a major tourmalinite occurrence is linked to an important shear zone.
In briefly reviewing the field occurrence, petrography and chemistry of the manganiferous ironstone beds, and by comparison with coticule elsewhere, the possibility that these ironstones are a coticule precursor or a coticule facies variant is introduced. That a lithology now termed coticule might be a significant component in the Manx Group (‘Slates’) was noted no less than 70 years ago. Any recognition of coticule rock would have an important bearing on the understanding of the stratigraphy, metamorphism and mineralization of the Manx Group.