bluuebunny/crossref_metadata_2025 huggingface dataset:
An integrated ichnological and sedimentological comparison of non-deltaic shoreface and subaqueous delta deposits in Permian reservoir units of Australia
Authors: Bann Kerrie L. , Fielding Christopher R.
Published: April 2008

Permian sequences in the Denison Trough of Queensland, eastern Australia, are productive conventional gas reservoirs. Previous attempts to interpret the reservoir bodies in terms of depositional environments have relied largely on sedimentary facies analysis and palynology. Sequences have been re-evaluated from a detailed, integrated ichnological and sedimentological perspective, resulting in a significant increase in the precision and resolution of the palaeoenvironmental interpretation. Various marine, coastal and upper delta plain deposits are recognized. Ichnological signatures have facilitated the differentiation of subaqueous delta deposits from those deposited in non-deltaic offshore and shoreface environments. Delta front facies are further subdivided by integrating ichnological and sedimentological data. Permian offshore and shoreface successions in the Denison Trough contain ichnological signatures that exhibit high diversities (25 ichnogenera comprising 32 ichnospecies), moderate to intense levels of bioturbation, uniformity of burrowing, and a wide variety of structures representing specialized feeding strategies. Examples from an additional reservoir dataset, the Tern Formation from the offshore Bonaparte Basin in north Western Australia, also clearly demonstrate the ichnological complexity of Permian shoreface successions. In contrast, Permian deltaic deposits contain ichnological signatures that reflect stressed environmental conditions. Assemblage diversity is reduced (16 ichnospecies), bioturbation intensity is significantly reduced, and uniformity of burrowing is sporadic.
The geology of north and central Malaita, Solomon Islands: the thickest and most accessible part of the world’s largest (Ontong Java) ocean plateau
Authors: Petterson Michael G.
Published: April 2008

This paper presents the most complete results yet published of geological surveys in Malaita, north of latitude 9°05′S between 1990 and 1995. The geology of Malaita reflects its position as an obducted part of the Alaska-size Ontong Java Plateau (OJP). The geology comprises a monolithological Cretaceous basalt basement sequence up to 3–4 km thick, termed the Malaita Volcanic Group (MVG), conformably overlain by a 1–2 km-thick Cretaceous-Pliocene pelagic sedimentary cover sequence. Cretaceous-Pliocene pelagic sedimentation was punctuated by alkaline basalt volcanism during the Eocene and by intrusion of alnöites during the Oligocene. Basement and cover sequences were both deformed by an intense, but short, middle Pliocene event. A number of localized, Upper Pliocene-Pleistocene, shallow-marine-subaerial, predominantly clastic formations overlie the middle Pliocene unconformity surface. The MVG comprises a monotonous sequence of pillowed and non-pillowed tholeiitic basalt lavas and sills with a predominant clinopyroxene-plagioclase-glass-opaques ± olivine mineralogy. The basaltic plateau morphology of the MVG is reflected in the presence of trap-like topographic features exposed in numerous river sections. Remarkably little sediment is present between basalt flows (most interlava contacts are basalt-basalt), indicating high to very high effusion rates. When present, inter-lava sediment is laminated pelagic chert or limestone, millimetres to centimetres thick, reflecting emplacement of the basalt in deep water (near or below the calcite compensation depth). Gabbro intrusions, dolerite dykes and an unusual spherulitic dolerite facies are locally present. The deep-water eruptive environment of the MVG probably was defined by the accumulation of voluminous eruptions from a multi-centred, submarine, possibly fissure-fed, volcanic source. The Malaitan cover sequence largely comprises a series of foraminifera-rich, pelagic calcilutites and calcisiltites with chert and, in the younger formations, arc-derived mudstone interbeds at various stratigraphic levels.
Partial melting below the Ontong Java Plateau
Authors: Herzberg Claude
Published: April 2008

Primary magma compositions for Kroenke-type basalts from the Ontong Java Plateau (OJP) have been estimated using a hybrid forward and universe model. For accumulated fractional melting of a fertile peridotite source, the primary magma had 16.8% MgO and lost 18% olivine by fractional crystallization to produce Kroenke-type basalts; the melt fraction was 0.27 and the potential temperature was 1500°C. For equilibrium melting of a fertile peridotite source, the primary magma had 19.3% MgO and lost 25% olivine by fractional crystallization to produce Kroenke-type basalts; the melt fraction was 0.30 and the potential temperature was 1560°C. The model peridotite source composition, melt fraction and potential temperature required to produce the primary OJP magmas are in excellent agreement with those that have been independently estimated from incompatible trace-element concentrations.
Phreatomagmatic eruptions on the Ontong Java Plateau: chemical and isotopic relationship to Ontong Java Plateau basalts
Authors: White Rosalind V. , Castillo Paterno R. , Neal Clive R. , Fitton J. Godfrey , Godard Marguerite
Published: April 2008

The compositions of glass clasts in volcaniclastic rocks recovered from drilling at Site 1184 on the eastern salient of the Ontong Java Plateau (OJP) are investigated using microbeam analytical methods for major, minor and trace elements. These data are compared with whole-rock elemental and isotopic data for bulk tuff samples, and with data from basalts on the high plateau of the OJP. Three subunits of Hole 1184A contain blocky glass clasts, thought to represent the juvenile magmatic component of the phreatomagmatic eruptions that generated the volcaniclastic rocks. The glass clasts have unaltered centres, and are all basaltic low-K tholeiites, with flat chondrite-normalized rare earth element (REE) patterns. Their elemental compositions are very similar to the Kwaimbaita-type and Kroenke-type basalts sampled on the high plateau. Each subunit has a distinct glass composition and there is no intermixing of glass compositions between subunits, indicating that each subunit is the result of one eruptive phase, and that the volcaniclastic sequence has not experienced reworking. The relative heterogeneity preserved at Site 1184 contrasts with the uniformity of compositions recovered from individual sites on the high plateau, and suggests that the eastern salient of the OJP had a different type of magma plumbing system. Our data support the hypothesis that the voluminous subaerially erupted volcaniclastic rocks at Site 1184 belong to the same magmatic event as the construction of the main Ontong Java Plateau. Thus, the OJP would have been responsible for volatile fluxes into the atmosphere in addition to chemical fluxes into the oceans, and these factors may have influenced the contemporaneous oceanic anoxic event.
Predicting fracture swarms — the influence of subcritical crack growth and the crack-tip process zone on joint spacing in rock
Authors: Olson Jon E.
Published: April 2008

Swarms or clusters represent an exception to the widely accepted idea that fracture spacing in sedimentary rock should be proportional to mechanical layer thickness. Experimental studies and static stress analysis do not provide adequate explanation for fracture swarm occurrence. The problem is re-examined numerically, accounting for the dynamics of pattern development for large populations of layer-confined fractures. Two crucial aspects of this model are: (1) the inclusion of three-dimensional effects in calculating mechanical interaction between simultaneously propagting fractures; and (2) the use of a subcritical crack-propagation rule, where propagation velocity during stable growth scales with the crack-tip stress intensity factor. Three regimes of fracture spacing are identified according to the magnitude of the subcritical index of the fracturing material. For low subcritical index material (
n
= 5) numerous fractures propagate simultaneously throughout a body resulting in irregular spacing that is, on average, much less than layer thickness. For intermediate subcritical index (
n
= 20) one fracture propagates at a time, fully developing its stress shadow and resulting in a pattern with regular spacing proportional to layer thickness. For high subcritical index cases (
n
= 80) fractures propagate in a fashion analogous to a process zone, leaving a fracture pattern consisting of widely spaced fracture clusters.
The relationship of tilt and twist of fringe cracks in granite plutons
Authors: Bankwitz P. , Bankwitz E.
Published: April 2008

Joint fractography in European plutons frequently shows large fringe-tilt angles connected to small fringe-crack twist angles (type A). In contrast to this first type, fringes of joints that tilt at small angles out of the parent joint plane are often associated with high twist angles of en echelon fringe cracks (type B). The interaction of tilt and twist angles gives evidence for the mode (I, II and III) acting at the advancing crack front during fracture propagation and the formation of fringes. The different fringe types depend on the varying influence of mode II or mode III, which establishes the degree of tilt or twist, in addition to opening-mode I that governs the crack propagation. Fringe types A and B are not randomly distributed. Within several plutons the first joints are characterized by a frequency of type A, and in other plutons by the dominance of type B. A third group of plutons is characterized by low tilt and low angle of twist for early joint fringes. The range of tilt/twist ratios of the earliest joints decreases with increasing depth of pluton emplacement and joint formation. The trend of the ratio approaches a value of between 0.5 and 1.0 at greater depth (
c.
15 km). The ratio seems to be suitable for a prognosis of the possible depth of first joint formation.
Differences between veins and joints using the example of the Jurassic limestones of Somerset
Authors: Peacock D. C. P.
Published: April 2008

Although veins and joints are both extension fractures, they should be treated separately, especially in field analyses. For example, they commonly form at different times and under different conditions. Excellent exposures of the Liassic limestones at Kilve, Somerset, UK, are used as a case study. These rocks show calcite veins related to the Mesozoic extension and Alpine contraction of the Bristol Channel Basin, and joints that appear to have been caused by late- or post-Alpine stress release. The veins at Kilve show the following characteristics that distinguish them from joints. (1) They are mineralized. (2) Veins have measurable widths (up to tens of millimetres wide) and represent measurable strain. En echelon veins are common at Kilve, and indicate shear strains. (3) Vein widths may obey a power-law scaling relationship. (4) The veins were open for long enough and under the correct conditions for calcite to be deposited, indicating high fluid pressures. They are also typically en echelon. (5) Veins form sets with a narrow range of strikes, whereas the joints typically form complex networks. (6) The veins at Kilve are commonly clustered around faults, and are precursors to, or synchronous with, the faults.
Indentation pits: a product of incipient slip on joints with a mesotopography
Authors: Engelder Terry , Schulmann Karel , Lexa Ondrej
Published: April 2008

The mechanism for structural damage during incipient slip on joints within the Melechov Granite, Czech Republic, changes with the misalignment of the joint’s mesotopography, largely a plumose surface morphology. Prior to slip, the joint surfaces are well mated so that contact area is organized on a microscopic scale. During the first phase of slip, diffusion-mass transfer is the active deformation mechanism between the sliding surfaces of the joints, as indicated by the extensive growth of crystal-fibre lineations characteristic of slickenside surfaces. After slip of the order of 1 cm or more, the mesotopography becomes mismatched and the contact area is reorganized to form indentation pits aligned on the ridges of hackle plumes. Indentation pits, that are testimony to a brittle process, are generated by the excavation of Hertzian ring cracks that propagate under contact loading of a brittle substrate. The depth of the indentation pits increases with contact width, suggesting that indentation creep is active. Following indentation along Hertzian ring cracks the slip mechanism transforms to a frictional abrasion. The distribution of indentation track lengths is consistent with laboratory wear grooves generated during earthquake-like stick-slip sliding. The elliptical shape of the indentation pits indicates a gradual decrease in contact area, a process that is consistent with a slip-weakening mechanism during a stick-slip cycle.
Geophysical techniques for forensic investigation
Authors: Fenning Peter J. , Donnelly Laurance J.
Published: April 2008

A wide range of geophysical techniques is applied in forensic investigations where the target objects are frequently buried under ground and are often small in size. These include targets which are only a few centimetres in diameter but located within a large search area are often of several hectares. The application of a specific geophysical technique may be governed by the physical properties of the target object and its local surroundings. However, operational and financial costs are important. Topographical and geological variations or presence of man-made structures may hinder the application of the most cost-effective technique. Additionally, site area, logistics and weather conditions are also important factors.

Generally, to overcome these difficulties it is recommended that forensic geophysics be carried out along conventional geophysical guidelines as used in civil-engineering site investigation. On occasion, departure from these conventional guidelines may be beneficial in that field survey data acquisition can be complemented by simultaneous direct invasive assessment of geophysical anomalies instead of waiting until office reporting has been completed. Three case studies are presented: one relates to a search for a buried metal target located using a scanning magnetometer with simultaneous excavation, and two relate to searches for graves and buried wooden coffins
The importance of stratigraphy in forensic investigation
Authors: Hanson Ian D.
Published: April 2008

The laws of stratigraphy, developed in geology, have long been adopted for archaeological use. Archaeological excavation in the UK relies on the application of these principles to define, interpret and understand site history. The adaptation of archaeological methods to forensic settings has recently resulted in successful analysis of stratigraphy-defining complex series of events on murder burial scenes. The breadth of physical evidence that can be recovered through stratigraphic excavation is great, and that which can be lost without due attention to the buried surfaces forming an intrinsic part of the stratified deposits of a site is significant. Recent case examples demonstrate the importance of employing stratigraphical principles in the excavation and interpretation of buried cultural and natural deposits as part of multidisciplinary forensic investigation.
Development of a coastal dune sediment database for England and Wales: forensic applications
Authors: Saye Samantha E. , Pye Kenneth
Published: April 2008

A database of coastal dune sediments in England and Wales has been developed with potential applications in forensic investigations. Coastal dunes are popular sites for criminal-related activities, including burial of drugs, weapons and murder victims. The coastal dunes and associated areas of windblown sand in England and Wales occupy an area of approximately 200 km
2
within 112 individual identified systems. Research has been undertaken to ascertain the spatial variation in sedimentological properties of the coastal dune sediments in England and Wales. Field sediment sampling has been undertaken at each dune system. More than 1500 sediment samples have been analysed by laser diffraction to determine particle size characteristics, and more than 500 have been analysed by inductively coupled plasma atomic emission spectrometry (ICP-AES) to determine chemical composition. Two examples illustrate how the database has been used in criminal investigation.
‘Unique’ particles in soil evidence
Authors: Sugita R. , Marumo Y.
Published: April 2008

Soil is presented as evidence as a mixture of both natural and artificial materials. ‘Unique’ particles found in soil may provide useful information to indicate the origin of the soil and, when found in soil evidence, may provide rapid discrimination between samples. Evidence in poor condition may also be examined for these diagnostic particles. This paper describes some case examples and research, involving geological particles, plant fragments and algae, in which microscopy played an important role.
Forensic examination of rocks, sediments, soils and dusts using scanning electron microscopy and X-ray chemical microanalysis
Authors: Pye Kenneth
Published: April 2008

Scanning electron microscopy (SEM) and energy-dispersive X-ray (EDX) microanalysis are powerful techniques for forensic and wider environmental analysis of a range of materials, including rocks, sediments, soils and dusts. Methods of analysis have evolved rapidly over the past 40 years and computer-controlled, variable pressure SEMs with integrated EDX now provide the opportunity for rapid, automated analysis of large numbers of samples and particulates within individual samples. However, interpretation of the data requires care and experience on the part of the operator, and samples should always be checked by visual inspection. Early SEM work on rocks and sediments mainly used the secondary electron (SE) mode to produce topographical contrast on rough surfaces, but more recent studies have utilized the capacity of backscattered electron (BSE) imaging to image both topographical and atomic number contrast. BSE microscopy, combined with X-ray mapping, provides a rapid means of locating unusual particles and grain coatings, and of mapping their distribution, which may be of diagnostic or discriminatory importance. In the past, much attention has been given to grain surface textural features (mainly of quartz) but many such studies have suffered from a high degree of subjectivity, poor reproducibility, lack of discriminatory power, and high cost both in terms of time and money. The application of digital imaging and statistical data-processing techniques can to some extent reduce these problems but, in general, chemical characterization of particles offers a more powerful approach. This paper provides an overview of these techniques, discusses their limitations and illustrates some of the forensic and wider environmental applications.
The archaeologist as a detective: scientific techniques and the investigation of past societies
Authors: Henderson Julian
Published: April 2008

The use of scientific techniques in the investigation of archaeological sites and artefacts has a long history. These days archaeological science as a discipline has matured to the extent that well-defined questions can be answered in increasingly refined ways. In this paper consideration of specific case studies highlights the kinds of investigations that have been carried out on archaeological materials. The research projects are described in ways that show parallel approaches to more recent types of research in police forensic work. The two case studies focused on are: (1) Islamic glass production — a cross-roads in technology? (eighth to twelfth centuries
ad
); (2) Ottoman Iznik pottery: the state of the art or the art of the State? (fifteenth to seventeenth centuries
ad
). A range of analytical techniques has been used, including electron microprobe analysis, inductively coupled plasma atomic emission spectrometry, scanning electron microscopy and mass spectrometry. Clearly these techniques provide different (and sometimes overlapping) information which help to answer research questions. The characterization of raw materials, production processes and distribution zones of the products all form part of a holistic approach. Ideally the results should be embedded in our knowledge of past societies, just as the interpretation of police forensic work should be.
Comparison of soils and sediments using major and trace element data
Authors: Pye Kenneth , Blott Simon J.
Published: April 2008

Analysis of geochemical data has become an important tool used in forensic comparisons of soils and sediments. The combined use of inductively coupled plasma optical emission spectrometry and mass spectrometry (ICP-OES and ICP-MS) instrumentation allows the abundance of up to 50 elements to be routinely determined in small samples (typically >0.1g). However, key issues concern the extent to which analysed subsamples are representative of the parent material from which they are taken, the best means of comparing datasets for different samples, and interpretation of the significance of the results obtained. ICP measurement precision for most elements is good, but it is important to understand the degree of variation that can arise due to subsampling procedures and selective transfer mechanisms relating to forensic exhibits, as well as the extent of spatial (and sometimes temporal) variability which exists in nature. Although analysis of several different size fractions is often helpful where sufficiently large samples are available, analysis of a standardized <150μm fraction separated from a bulk sample in many cases provides adequate discrimination between samples and provides the most practical method for mass-screening of samples. Where possible, duplicate or triplicate sample preparations should be made, and several analytical determinations made on each prepared subsample. However, the additional time, cost and sample size requirements involved need to be weighed against the benefits of undertaking additional types of analysis of the samples. In order to obtain maximum information from multielement geochemical data, the dataset should be evaluated using a variety of numerical, statistical and graphical procedures. This paper discusses a number of options for such data evaluation using a simple dataset example. Casework experience and experiments have shown that, even in complex situations, multi-element geochemical data can provide very sensitive environmental indicators. However, such data should normally be used in combination with the results of other analyses when making forensic comparisons of soils and sediments.
Investigating multi-element soil geochemical signatures and their potential for use in forensic studies
Authors: Rawlins B. G. , Cave M.
Published: April 2008

Data from a regional soil survey in eastern England have been used to determine whether samples over the same parent material can be discriminated on the basis of both individual and multielement geochemistry. Discrimination was based on estimates of measurement uncertainty, which were calculated from the analysis of a series of duplicates and subsamples. In the multivariate analysis we estimated a covariance matrix for the two sources of uncertainty and compared this to Mahalanobis distances calculated for pairs of samples within each parent material group. For 12 of the 19 individual elements, it was possible on average to discriminate between more than 80% of the samples within parent material groups and typically between 15 and 17 of the 19 elements discriminated individual samples. In the multi-element analysis, typically more than 99.8% of samples within the same parent material group were discriminated from one another. Hence, the geochemistry of a natural soil sample, when collected and analysed according to a strict protocol, and compared to a database that adopted the same methods, could be used to help establish provenance within bedrock-derived soil types. However, there are significant differences between the nature of soil samples and the way they are collected or derived in soil surveys and forensic investigations. These questions need to be addressed thoroughly before any practical application to forensic cases in which an investigator is attempting to link a suspect to a location based on soil geochemical signatures.
Defining ‘local signature’ in terms of Sr isotope composition using a tenth- to twelfth-century Anglo-Saxon population living on a Jurassic clay-carbonate terrain, Rutland, UK
Authors: Evans J. A. , Tatham S.
Published: April 2008

The Sr isotope ratios and Sr concentration in tooth enamel from a rural tenth-twelfth century Anglo-Saxon population living on a Jurassic clay-carbonate terrain in eastern England gives the following mean values:
87
Sr/
86
Sr=0.7098±0.0018 (2σ,
n
=22) and Sr concentrations = 74±62 p.p.m. (2σ). The isotope data are taken to be representative of Anglo-Saxon biosphere values in the area of study. The Sr isotope composition of soil leachates, plant material, riverwaters and animal tooth enamel associated with the burial site were all analysed to see which gave the best approximation to these local Anglo-Saxon values, the aim being to define the best method of predicting the local Sr signature of areas for archaeological purposes. The Sr isotope composition of acetic acid soil leachates were dominated by the carbonate soil component and gave 0.7085±0.0020 water leachates gave 0.7090±0.0014 and plant material gave 0.7092±0.0018 (all at 2σ,
n
=12). All of these materials were less radiogenic that those of the Anglo-Saxon population. Riverwater gave the same result as the plants at 0.7092±0.0012 (2σ,
n
=3). The Anglo-Saxon animal tooth enamel gave the best match with a value of 0.7099±0.0017 (2σ,
n
=13). Analysis of variance (ANOVA) tests show that there is a high probability (>70% probability, 2SD) that the animals and the humans sampled were from the same population with respect to Sr isotope composition. Thus animal tooth enamel proved to be the best proxy, in this study, for the local human population.
Why do we need to consider geological storage of CO
2
Authors: Gale John
Published: April 2008

To meet targets for greenhouse gas emission reduction set by the Kyoto Protocol, many countries are considering a range of near-term options such as, fuel switching, energy efficiency improvements and use of renewable sources of energy, to reduce their greenhouse gas emissions. However, to meet the goal of the UN Framework Convention on Climate Change, namely stabilization of greenhouse gas concentrations in the atmosphere, it is likely that deeper reductions in emissions will be needed. This will require additional measures such as the geological storage of CO
2
. Geological storage of CO
2
would be used to sequester CO
2
captured from large anthropogenic sources, such as power and large industrial plants. There are a number of reservoirs suitable for geological storage of CO
2
including depleted oil and gas fields and deep saline aquifers. Many of these reservoirs have stored hydrocarbons and fluids for million of years, which gives confidence that CO
2
can be stored for similar durations, but research is needed to confirm this.
Analysis of CO
2
leakage through ‘low-permeability’ faults from natural reservoirs in the Colorado Plateau, east-central Utah
Authors: Shipton Z. K. , Evans J. P. , Kirschner D. , Kolesar P. T. , Williams A. P. , Heath J.
Published: April 2008

The numerous CO
2
reservoirs in the Colorado Plateau region of the United States are natural analogues for potential geological CO
2
sequestration repositories. To understand better the risk of leakage from reservoirs used for long-term underground CO
2
storage, we examine evidence for CO
2
migration along two normal faults that cut a reservoir in east-central Utah. CO
2
-charged springs, geysers, and a hydrocarbon seep are localized along these faults. These include natural springs that have been active for long periods of time, and springs that were induced by recent drilling. The CO
2
-charged spring waters have deposited travertine mounds and carbonate veins. The faults cut siltstones, shales, and sandstones and the fault rocks are fine-grained, clay-rich gouge, generally thought to be barriers to fluid flow. The geological and geochemical data are consistent with these faults being conduits for CO
2
moving to the surface. Consequently, the injection of CO
2
into faulted geological reservoirs, including faults with clay gouge, must be carefully designed and monitored to avoid slow seepage or fast rupture to the biosphere.
The impact of chemical reactions on CO
2
storage in geological formations: a brief review
Authors: Rochelle C. A. , Czernichowski-Lauriol I. , Milodowski A. E.
Published: April 2008

The sequestration of CO
2
in the deep geosphere is one potential method for reducing anthropogenic emissions to the atmosphere without a drastic change in our energy-producing technologies. Immediately after injection, the CO
2
will be stored as a free phase within the host rock. Over time it will dissolve into the local formation water and initiate a variety of geochemical reactions. Some of these reactions could be beneficial, helping to chemically contain or ‘trap’ the CO
2
as dissolved species and by the formation of new carbonate minerals; others may be deleterious, and actually aid the migration of CO
2
. It will be important to understand the overall impact of these competing processes. However, these processes will also be dependent upon the structure, mineralogy and hydrogeology of the specific lithologies concerned and the chemical stability of the engineered features (principally, the cement and steel components in the well completions). Therefore, individual storage operations will have to take account of local geological, fluid chemical and hydrogeological conditions. The aim of this paper is to review some of the possible chemical reactions that might occur once CO
2
is injected underground, and to highlight their possible impacts on long-term CO
2
storage.
The impact of geological heterogeneity on CO
2
storage in brine formations: a case study from the Texas Gulf Coast
Authors: Hovorka Susan D. , Doughty Christine , Benson Sally M. , Pruess Karsten , Knox Paul R.
Published: April 2008

Geological complexities such as variable permeability and structure (folds and faults) exist to a greater or lesser extent in all subsurface environments. In order to identify safe and effective sites in which to inject CO
2
for sequestration, it is necessary to predict the effect of these heterogeneities on the short- and long-term distribution of CO
2
.

Sequestration
capacity
, the volume fraction of the subsurface available for CO
2
storage, can be increased by geological heterogeneity. Numerical models demonstrate that in a homogeneous rock volume, CO
2
flowpaths are dominated by buoyancy, bypassing much of the rock volume. Flow through a more heterogeneous rock volume disperses the flow paths, contacting a larger percentage of the rock volume, and thereby increasing sequestration capacity.

Sequestration
effectiveness
, how much CO
2
will be sequestered for how long in how much space, can also be enhanced by heterogeneity. A given volume of CO
2
distributed over a larger rock volume may decrease leakage risk by shortening the continuous column of buoyant gas acting on a capillary seal and inhibiting seal failure. However, where structural heterogeneity predominates over stratigraphic heterogeneity, large columns of CO
2
may accumulate below a sealing layer, increasing the risk of seal failure and leakage.
Geological sequestration of CO
2
in the subsurface: lessons from CO
2
injection enhanced oil recovery projects in oilfields
Authors: Worden Richard H. , Smith Leta K.
Published: April 2008

In this paper production geochemical data from oil fields where CO
2
has been injected to enhance oil recovery (CO
2
-EOR) and experimental simulations of this process are reviewed. These data show that over the timescale of days to many years, CO
2
injected into the subsurface typically results in the bulk dissolution of carbonate minerals. There is little evidence for the sequestration of the injected greenhouse gas as a solid phase carbonate mineral on the timescale of the CO
2
-EOR projects or experiments. There is extensive aqueous geochemical, petrographic and core analysis evidence that supports the conclusion that CO
2
, injected into oil fields to enhance secondary recovery, leads to the bulk dissolution of calcite, dolomite and siderite. Although carbonate dissolution leads to enhanced porosity, the expected commensurate increase in permeability may be offset by the migration of clays, liberated by the action of the acidic water on the rock, with consequent blocking of pore throats. Additionally, injection of CO
2
into oil fields can result in asphaltene deposition on mineral surfaces. Such a bitumen coat could ultimately isolate the mineral matrix from injected fluids and insulate the rock to the injected greenhouse gas. Localized precipitation of calcite scale has been reported in the topside facilities of CO
2
-EOR projects and in the low-pressure region of experimental simulations.
Monitoring experience associated with nuclear waste disposal and its application to CO
2
sequestration projects
Authors: Stenhouse Michael J. , Savage David
Published: April 2008

Monitoring is a key component of the development and operation of nuclear waste repositories, and some of the underlying considerations and lessons learned can benefit projects involving the geological storage of CO
2
. Before reviewing the general monitoring objectives for nuclear waste repositories, the key differences between nuclear waste disposal and CO
2
storage projects are emphasized. The philosophy underlying monitoring after closing/sealing a repository is discussed. Important aspects of this philosophy include the need to collect adequate baseline data representative of the unperturbed site, and the desire to engender public confidence, but not at the expense of compromising the protective barriers of the repository itself. Pre-operational and operational monitoring provide important data that feed into safety assessment calculations, either as input data or as information that can be used to confirm, and/or refine, predictions. Using a specific example of a deep (geological) repository, monitoring experience at the WIPP site in New Mexico is discussed, focusing on methods and techniques that are relevant to CO
2
sequestration projects. Such monitoring includes geotechnical (characterization of the evolving behaviour of underground facilities), groundwater (quality and quantity), environmental (impacts on ecosystems), and subsidence (to support subsidence predictions for the WIPP site located in bedded salt formations).
Peperitic lava lake-fed sills at Ság-hegy, western Hungary: A complex interaction of a wet tephra ring and lava
Authors: Martin Ulrike , Németh Károly
Published: April 2008

Ság-hegy is the remnant of a complex volcano consisting of several phreatomagmatic pyroclastic sequences preserved in immediate contact with a thick (
c.
50 m) coherent lava body. Due to the intensive quarrying, the inner part of the lava has been removed, leaving behind a castle-like architecture of pyroclastic rocks. The outcrop walls thus demonstrate the irregular morphology of the lava, which was emplaced in a NW-SE-trending ellipsoidal vent zone in a phreatomagmatic volcano. Pyroclastic beds in the quarry wall are cross-cut by dykes and sills, inferred to have been fed from a central magma zone. Thin (<10 cm) strongly chilled, black, angularly jointed aphanitic basaltic lava mantles the pyroclastic sequence, and has a corrugated margin as a consequence of sudden chilling against the cold and wet phreatomagmatic tephra in the inner wall of the tuff ring crater. These corrugated zones are inferred to be a characteristic textural feature, indicating extensive mixing of lava and host tephra which led to peperite formation along the outer rim lava lake. A spectrum of peperite formed along the lake margin, and fluid oscillation, due to fluidization of the wet tephra, disrupted a steam envelope formed around the lava, causing basaltic magma to invade and mix with the phreatomagmatic tephra. The presence of unconformities in the tephra ring facilitated the formation of sills fed from the central lava body.
Depth, geometry and emplacement of sills to laccoliths and their host-rock relationships: Montecampione group, Southern Alps, Italy
Authors: Corazzato Claudia , Groppelli Gianluca
Published: April 2008

This study focused on a set of shallow subvolcanic bodies, mainly laccoliths and sills, that intruded the Upper Permian-Lower Triassic sedimentary sequence of the central Southern Alps, in the area of Montecampione (Val Camonica, Italy). These intrusions represented a shallow magmatic reservoir probably associated with Triassic volcanism. Based on a detailed stratigraphic reconstruction, this paper presents results dealing with the evaluation of the emplacement depth, the estimated volume of the subvolcanic bodies, a description of their geometries, and their relation to the host rock and response of the sedimentary units to the intrusions. The emplacement depth was estimated using the thickness of the sedimentary overburden at the time of emplacement, and by applying simple equations involving laccolith dimensions. The results are comparable, and support an average emplacement depth of about 1300 m. The minimum volume of the intrusions was obtained using a GIS, and is about 1 km
3
. Concerning the relationship between the intrusive bodies and the host rock, we observed that sills are mainly emplaced into the Servino Formation, while the laccoliths are emplaced near the contact between the Verrucano Lombardo and the Servino Formation. The two sedimentary units show a different response to the intrusion: the Verrucano Lombardo always appearing fractured and tilted, while the Servino Formation shows a range of deformation patterns, from light ductilization at the contact, to folding, brecciation and foliation. These different responses reflect the mechanics of emplacement and geometry of the intrusions, and local heterogeneities in the host rock. Both units show a local thermal effect close to the contact.
Reservoir properties of Arab carbonates, Al Rayyan Field, offshore Qatar
Authors: Clark David , Heaviside John , Habib Kassim
Published: April 2008

Oil is present in the Upper Jurassic Arab A and Arab C carbonates of the Al Rayyan Field. The Arab A consists of porous limestone with thin units of tight dolomite at the top and bottom. Two reservoir intervals can be distinguished, separated by a slightly less permeable unit. The upper reservoir consists of stromatolites and cross-bedded peloidal-grainstones, whereas the lower reservoir consists predominantly of ooliticgrainstones. The less permeable unit comprises moderately cemented, cross-bedded peloidal-grainstones. Higher porosity and permeability generally occurs in the coarser grained, cross-bedded grainstones, where pores are mostly primary and intergranular; lower permeability is characteristic of grainstones with moderately developed early cement. Porosity is enhanced at some levels by the presence of leached intragranular pores, but these have little effect on permeability. The Arab C is strongly stratified and completely dolomitized. Three reservoir intervals can be recognized, separated by less permeable layers of poorer quality rock. The upper reservoir consists of partially leached and moderately cemented, cross-bedded bioclastic-peloidal-grainstones. Porosity is high because of the presence of leached intragranular pores in addition to primary intergranular pores but permeability is relatively low because of the presence of early cement. The main reservoir comprises loosely compacted and lightly cemented, cross-bedded peloidal-grainstones. Porosity is lower than that in the upper reservoir because leached intragranular pores are generally absent, but permeability is higher because cementation is relatively light. The lower reservoir is made up of peloidal-grainstones and coarse-grained bioclastic-grainstones. The upper and main reservoirs are separated by a thick interval of relatively tight, thinly bedded, strongly cemented peloidal-grainstones, whereas the main and lower reservoirs are separated only by a thin bed of tight, nodular anhydrite. The pore types and cements observed in the Arab C are similar to those of the Arab A, but dolomitization has resulted in an enhancement of permeability and capillary pressure properties compared to those of the Arab A. Thus, the overall water saturation of the Arab C is lower than that of the Arab A, and the displacement pressures and irreducible water saturations are also significantly lower than those of Arab A carbonates.
The geochemical behaviour of Tc, Np and Pu in spent nuclear fuel in an oxidizing environment
Authors: Buck Edgar C. , Hanson Brady D. , McNamara Bruce K.
Published: April 2008

Spent fuel from commercial nuclear reactors consists mainly of uranium oxide. However, the changes that occur during reactor operations have a profound effect on chemical and physical properties of this material. Heat build-up in the fuel pellet during reactor operations can cause redistribution of fission products. The fission products may aggregate in one of three types of precipitates; gaseous, metallic, or oxide, depending on the burn-up and in-core treatment. Radiation damage and variations in fission and neutron capture yields across the fuel pellets lead to Pu enrichment and increased porosity with increasing burn-up. A more porous surface may make the fuel more susceptible to oxidative dissolution. As the level of actinides and fission products increases, the fuel may become more resistant to oxidation. These changes may limit the usefulness of natural uraninite (UO
2
) analogues for predicting the geological behaviour of spent fuel disposed in a high-level waste (HLW) repository. In this Chapter, an overview of spent fuel microstructure, radiolytic effects, and alteration processes is presented. Evidence for Np incorporation into U
6+
phases, the nature of Pu surface precipitates on spent fuel, and evidence for the preferential removal of 4d-metals from ε-particles in corroded spent fuel is discussed. Understanding the potential mechanisms of radionuclide attenuation through sorption and/or incorporation requires techniques with both high spatial resolution and excellent elemental sensitivity.
Geochemical behaviour of host phases for actinides and fission products in crystalline ceramic nuclear waste forms
Authors: Lumpkin Gregory R. , Smith Katherine L. , Gieré Reto , Williams C. Terry
Published: April 2008

A number of polyphase or single-phase ceramic waste forms have been considered as options for the disposal of nuclear waste in geological repositories. Of critical concern in the scientific evaluation of these materials is their performance in natural systems over long periods of time (e.g., 10
3
to 10
6
years). This paper gives an overview of the aqueous durability of the major titanate host phases for actinides (e.g., Th, U, Np, Pu, Cm) and important fission products (e.g., Sr and Cs) in alternative crystalline ceramic waste forms. These host phases are compared with reference to some basic acceptance criteria, including the long-term behaviour determined from studies of natural samples. The available data indicate that zirconolite and pyrochlore are excellent candidate host phases for actinides. These structures exhibit excellent aqueous durability, crystal chemical flexibility, high waste loadings, and well-known processing conditions. Although both pyrochlore and zirconolite become amorphous due to alpha-decay processes, the total volume swelling is only 5–6% and there is no significant effect of radiation damage on aqueous durability. Hollandite also appears to be an excellent candidate host phase for radioactive Cs isotopes. Brannerite and perovskite, on the other hand, are more prone to alteration in aqueous fluids and have a lower degree of chemical flexibility. With the exception of hollandite, many of the properties of these potential host phases have been confirmed through studies of natural samples.
Special cases of natural analogues: The Gabon and Cigar Lake U ore deposits
Authors: Gauthier-Lafaye F. , Stille P. , Bros R.
Published: April 2008

The Gabon and Cigar Lake uranium deposits may be used as natural analogues for nuclear waste because they both provide information on actinide immobilization in a geological system over a very long period of time. These deposits contain high-grade uranium ores (40–60% UO
2
) embedded in a clay matrix. Futhermore, the Oklo and Bangombé uranium deposits in Gabon were natural nuclear fission reactors that operated 2000 Ma ago. This offers the unique opportunity to study the behaviour of fission products and actinides in a geological environment. The geological stability of the sites is one of the most important parameters that can explain the preservation of the natural reactors of Gabon and of the Cigar Lake deposit. The mineralogy of the hosted rocks and the chemical composition of the fluids are likewise important parameters. It can be shown that clays, Fe-sulphides and organic matters provide effective redox buffering and consequently play an important role in the long-term preservation of the ores. Adsorption of actinides and fission products on clays and Ti-oxides is also an important process for retention of these elements. This process is even more efficient when it is followed by the formation of coffinite, USiO
4
·
n
H
2
O. Coffinitization is common at the Cigar Lake deposit and in the natural reactors of Gabon. Coffinitization may be related to hydrothermal alteration (Cigar Lake) and to weathering (Bangombé).