bluuebunny/crossref_metadata_2025_split huggingface dataset:
Quartz cement volumes across oil-water contacts in oil fields from petrography and wireline logs: preliminary results from the Magnus Field, Northern North Sea
Authors: Barclay S. A. , Worden R. H. 
Published: April 2008

Abstract
Quartz cement is a significant porosity-reducing mineral cement in many sandstones and thus affects economically significant reserves calculations and flow-rate (through its effect on permeability). The presence of oil in a reservoir is commonly assumed to retard quartz cement precipitation and thus early oil emplacement is often thought to preserve porosity and permeability. A combined petrographic and wireline log approach was utilized to investigate whether quartz cement volumes and the total quantity of quartz do indeed vary across the oil-water contact in a sandstone reservoir. Thin-section point-count data and bulk density, neutron porosity and sonic transit time wireline log data were obtained across the oil-water contact from three wells in the Magnus field, an Upper Jurassic turbidite sandstone reservoir in the Northern North Sea. Reported oil filled inclusions in quartz overgrowths in this reservoir show that quartz cementation occurred either during or after oil emplacement. Point count data were used to determine quartz cement and total quartz volumes across the oil-water contact, whilst wireline data were transformed to reveal the total quantity of quartz across the oil-water contact. Preliminary results seem to show that the volume of quartz cement and the total volume of quartz show little or no variation across the oil-water contact. These data seem to imply that the presence of oil in the reservoir had no appreciable effect on the component processes involved in quartz cementation in this field: a paradox that will be further investigated.
Physical signature of basaltic volcanics drilled on the northeast Atlantic volcanic rifted margins
Authors: Bücker C. J. , Delius H. , Wohlenberg J. 
Published: April 2008

Abstract
During several DSDP and ODP Legs in the NE Atlantic, basaltic lava flows of the early rifting and break-up phase in the Tertiary have been drilled and logged. The lava flows were deposited subaerially with characteristic variations in their physical and magnetic properties and it is possible to distinguish different intraflow zones (I–IV) by evaluating downhole and core measurements. The physical and magnetic properties are mainly influenced by the degree of vesicularity and alteration, especially in the top and bottom parts of the flows. The pattern of the magnetic properties susceptibility and remanence seems to be helpful in distinguishing different flow types (aa and pahoehoe) as well as intraflow structures.
These zonal characterizations of subaerial basaltic lava flows can be seen frequently in core as well as in downhole measurements. This holds true not only for one hole but also for holes at different locations in the NE Atlantic with an exceptional high correlation down to fine scale variations, pointing to comparable genetic mechanisms during the initial phase of rifting.
The comparison of core and geophysical log measurements obtained in the Nirex investigation of the Sellafield region
Authors: Kingdon A. , Rogers S. F. , Evans C. J. , Brereton N. R. 
Published: April 2008

Abstract
The Sellafield region, west Cumbria, is the focus of one of the most thorough geological investigations in the United Kingdom. The Sellafield Site is defined as an area immediately around the potential repository, extending 6.5 km north-south by 8 km eastwest. Twenty six deep boreholes were drilled within the area up to the end of 1995, with a total depth of approximately 28 km. Most of these boreholes have been continuously cored, a total of over 17 kilometres of core, with average core recovery well in excess of 90%. All boreholes were logged with a comprehensive suite of geophysical logs, including many state of the art tools. Laboratory physical property analysis of hundreds of sample cores has been carried out.
Pilot studies were carried out to compare and contrast datasets and to investigate the relationships between the different data scales. Various techniques, including fractal analysis and Artificial Neural Networks, were tried in order to explore the relationships of these data at a variety of measurement scales.

The pilot study was conducted in two stages:

(1)
evaluation of the primary controlling factors of the physical properties;

(2)
testing the validity of ‘Up-scaling’.

The rocks of the Borrowdale Volcanic Group provided the most challenging problems due to the physical properties being dominated by fracturing and associated alteration zones.
Relationships between data types at different scales were established suggesting that the extrapolation of properties derived from core and wireline logs across three-dimensional seismic grids would allow an understanding of the properties throughout a three-dimensional volume.
In situ
characterization of suspended particles using focused-beam, laser reflectance particle sizing
Authors: Law D. J. , Bale A. J. 
Published: April 2008

Abstract

Measurements of the size distribution of suspended particles were made as part of the LISP (UK) experiment using a novel,
in situ
instrument which employs focused-beam, laser reflectance. Data were acquired over three complete, ebb-flood tidal cycles at two stations possessing different elevations on the intertidal mudflat. The reflectance method, which employs a physical arrangement similar to optical back-scatter sensors for measuring the concentration of suspended particulate matter (SPM), measures sediment particles in the size range 2–1000 µm with negligible disruption to fragile aggregates and can operate over the wide range of SPM concentrations found in estuaries. The results indicated that the median sizes (
D
50
) of particle populations over the intertidal mud flats were relatively constant at 60–100 µm even during mild erosion and resuspension events caused by ebb and flood tides. However, populations with
D
50
values of up to 300 μm were seen at one station within the ridge-runnel systems during resuspension. These large aggregates were attributed to the particularly ‘mobile’ sediment in that environment and to increased biodeposition. In general, variations in the size characteristics of particles measured
in situ
were consistent with the properties of the underlying substrate. Measured sizes compared well with values determined by direct video-microscope observation.
Use of
in situ
flume to quantify particle flux (biodeposition rates and sediment erosion) for an intertidal mudflat in relation to changes in current velocity and benthic macrofauna
Authors: Widdows John , Brinsley Mary , Elliott Mike 
Published: April 2008

Abstract

A portable
in situ
annular flume was deployed on eight occasions at five stations along a shore normal transect from immediately below the saltmarsh to the mid-tide level of the Skeffling mudflat in the Humber estuary. Both large scale (km) and small scale (m) spatial differences (i.e. between ridges, gullies and pools on ridges) were examined. Biodeposition rates were measured at low current velocities (5 cm s
−1
), while sediment resuspension and erosion rates were determined in response to step-wise increases in current velocities between 10 and 50 cm s
−1
(equivalent to a range in shear stress from 0.02 to 1.6 Pa). Maximum biodeposition rates (6.6 g m
−2
h
−1
) were more than an order of magnitude higher than the mean sedimentation rate in the absence of sediment and biota. There was a significant correlation between biodeposition rate and the density of the suspension feeder
Cerastoderma edule
(
r
= +0.90;
P
< 0.05). The intertidal sites could be separated into three distinct groups on the basis of sediment stability/erodibility. Upper shore sites had the highest stability with critical erosion velocities (
u
crit
) of 30 cm s
−1
, whereas the pools and gullies were the most easily eroded with
u
crit
of 15 cm s
−1
. Site differences in sediment erodibility were not significantly correlated with measured physical properties of the sediment (bulk density, moisture content, % POM, % sand). However, there was a significant correlation between sediment erodibility and the density of
Cerastoderma
(
r
= +0.89;
P
< 0.01) and an index of the bioturbation activity of
Macoma balthica
(
r
= +0.96;
P
< 0.001).
Mapping intertidal sediment distributions using the RoxAnn System, Dornoch Firth, NE Scotland
Authors: Hull J. , Nunny R. 
Published: April 2008

Abstract
The RoxAnn system (manufactured by Marine Micro Systems Ltd) is a remote sensing technique available for mapping sediment distributions. The acoustic returns from a standard boat-mounted echo sounder are electronically processed and the output stream logged together with accurate position data from a Differential Global Positioning System (or similar high accuracy positioning systems). The RoxAnn output comprises depth and indices of bed roughness (E1) and bed hardness (E2). The combination of these indices require to be translated into traditionally used parameters (such as visual appearance and sediment particle size) to provide useful mapping data. The most reliable means of achieving this is through a ground-truthing exercise, where grab samples and video footage are collected at sites of known RoxAnn values. Two problems are encountered in this process: firstly RoxAnn acoustic signatures often do not uniquely represent a specific bed type as described in traditional terms, secondly positioning errors can lead to poor calibration of the RoxAnn signatures in the ground truthing process. The first problem is difficult to correct, and can only be mitigated against through good survey design and execution. The second problem can be addressed in the data processing, and procedures for this are discussed. The RoxAnn data collected from the Dornoch Firth, used in conjunction with qualitative analysis of colour aerial photographs of the upper intertidal areas, provided a detailed classification of substrate types, including a classification of sands which allowed detailed insight into active processes of transport.
Mussels and mussel beds (
Mytilus edulis
) as stabilizers of sedimentary environments in the intertidal zone
Authors: Meadows Peter S. , Meadows Azra , West Fraser J. C. , Shand Peter S. , Shaikh Masroor A. 
Published: April 2008

Abstract

Coastal zone protection of the intertidal zone is of great importance in view of the threats of sea level rise around the globe. Environmentally-friendly methods involving biological control may offer a solution. This paper studies mussels (
Mytilus edulis
) as stabilizers of the intertidal zone because they form beds that armour some intertidal sediments, hence reducing erosion. In field experiments we seeded high energy lower intertidal and low energy upper intertidal environments with isolated mussels and preformed clumps of mussels. More animals were lost from the higher energy site. Those that remained were transported landward for significant distances. Clumping protected animal loss at the low energy but not at the high energy site. Gravel placed under mussels improved their stability because mussels attached threads to them. Laboratory experiments show that mussels form clumps by attaching to other mussels, and when available to gravel which has to be at the sediment surface. Flume studies show single mussels decrease the critical erosion velocity of sediment near them. Similar effects are seen in the field at the edge of small mussel beds.
Compaction — the great unknown in basin modelling
Authors: Giles M. R. , Indrelid S. L. , James D. M. D. 
Published: April 2008

Abstract
Decompaction routines are used in basin modelling packages to calculate sediment thickness and material properties such as thermal conductivity. However, compaction in nature is dependent on initial porosity, composition, and effective stress, and a considerable range of porosity-depth trends exists. Simple thermal modelling demonstrates that significant uncertainties (up to VRE ± 0.5) arise in predicted maturities due to this variation. Furthermore, the validity of using porosity loss as a measure of compaction is questionable because changes in solid volume can occur. Chemical reaction may increase or decrease porosity without changing sediment thickness, although an apparently smooth transition occurs from dominantly mechanical processes of porosity loss (e.g. grain rearrangement) at shallow levels to dominantly chemical processes (e.g. grain dissolution/cementation) at depth. That compaction and porosity loss are processes dependent upon effective stress, time and temperature is illustrated by the observation of overpressuring in the subsurface, comparison of experimental and natural compaction rates and analysis of porosity-depth trends for sediments of different ages. Mechanistic models of the processes involved in compaction (e.g. pressure solution) also indicate time dependency. Time-dependent models of compaction can be constructed, but these are difficult to incorporate into basin models as they cannot be run in a simple backstripping mode.
Analysis of erosion events and palaeogeothermal gradients in the North Alpine Foreland Basin of Switzerland
Authors: Schegg R. , Leu W. 
Published: April 2008

Abstract

For basin modelling purposes, uplift and erosion analysis is as important as subsidence analysis. Within the North Alpine Foreland Basin of Switzerland (NAFB) three major interregional unconformities separate the sedimentary succession: the late Palaeozoic, the base Tertiary and the base Quaternary unconformity. The amount of missing section depends on the palaeogeographic basin position and on different inversion mechanisms (thermal uplift, intraplate stress, tectonic uplift or isostatic rebound movements). Several techniques exist to determine the magnitude and timing of maximum palaeotemperatures and palaeogradients, facilitating direct estimation of missing section. In our study coalification and fission track data are analysed and compared with recently published models concerning erosion in the NAFB. The results indicate that each inversion episode is accompanied by significant erosion (up to several km). The following range of removed section values were reconstructed:

(i)
late Palaeozoic unconformity: 1000–1200 m;

(ii)
base Tertiary unconformity: 800–1800 m;

(iii)
base Quaternary unconformity: 1500–3000 m in the SW, up to 700 m in the NE and 4100–4400 m in parts close to the Alpine front.

The reconstruction techniques provide only rough estimates as each approach is based on certain assumptions and calibration uncertainties. Also, the obtained values are higher than those expected from simple evaluation of the preserved stratigraphic record. Calculated palaeogeothermal gradients are very high (80–90 °C km
−1
) during the late Palaeozoic, slightly higher than normal during the late Cretaceous (30–50 °C km
−1
) and lower than normal (15–30 °C km
−1
) during the Cenozoic.
A multidisciplinary approach to modelling secondary migration: a Central North Sea example
Authors: Symington W. A. , Green K. E. , Huang J. , Pottorf R. J. , Summa L. L. 
Published: April 2008

Abstract
Numerical simulations assist in understanding secondary migration, and can help estimate which traps in a basin may have received a hydrocarbon charge. This is illustrated by a suite of numerical models used to track the secondary migration of hydrocarbons into an Upper Jurassic Fulmar discovery in the Central North Sea. The models include areal flow calculations using Exxon’s proprietary reservoir simulator, and cross-section calculations using TEMISPACK, a commercial basin modelling package. While the application of conventional reservoir simulation techniques to geologic time-scale problems is itself a novel approach, the most important development has been in the integration of fluid flow modelling with techniques for dating the timing of hydrocarbon charge. These techniques have been used to constrain and validate the model results. In addition, sensitivity studies permit evaluation of the required permeability for effective lateral migration.
The areal calculations provide information about migration timing and the fill history of several traps. These fields are charged from mature Kimmeridge source rocks, mapped within the local drainage area. Several model runs were used to evaluate the sensitivity of migration timing to carrier bed permeability and capillary pressure characteristics. Calculations indicated that for reservoir quality carrier beds (permeability ≥ 1 mD) secondary migration can be geologically instantaneous, and that even low permeability silts can serve as effective migration pathways.
A cross-sectional model was used to integrate cross-stratal and strata-parallel migration. The model included hydrocarbon expulsion from Kimmeridge source rocks into the Fulmar sandstone and lateral migration up the flank of the structure. Drilling results indicate that leakage into younger Tertiary strata has occurred. The calculation sugests a portion of the top seal breached by 10–20 Ma. Evidence of partial seal loss includes a seismic chimney interpreted above the predicted breached seal, and an appraisal well high on the Jurassic structure which encountered hydrocarbon-stained reservoir rocks with an apparent palaeohydrocarbon contact. Furthermore, hydrocarbons in the overlying Tertiary reservoirs can be geochemically tied to the remaining Jurassic accumulation. Finally, analysis of authigenic cements, particularly the K-Ar ages of fibrous illite, suggests that hydrocarbons occupied the trap until approximately 10 Ma. Analysis of Tertiary hydrocarbon fluid inclusions further indicates that hydrocarbons entered these Tertiary reservoirs approximately 10 Ma. These latter two techniques now enable the modeller to apply temporal constraints to hydrocarbon charge simulation. Such constraints allow ‘history matching’ analogous to field scale reservoir simulations.
Early Palaeozoic brachiopods and associated shelly faunas from western Gondwana: their bearing on the geodynamic history of the pre-Andean margin
Authors: Benedetto Juan L. 
Published: April 2008

Abstract
The strong provincialism exhibited by early Ordovician to Devonian brachiopod faunas provides an independent tool for testing palaeogeographical hypotheses. Patterns of biogeographical affinities of early Palaeozoic brachiopods from the Argentine Precordillera, the Sierra de Famatina and the Central Andean basin (NW Argentina, Bolivia, southern Peru) suggest that the pre-Andean margin was linked to northern Iapetus Ocean history. The low-grade Vendian-Early Cambrian Puncoviscana Formation and the broadly coeval rocks from the Carolina and Gander terranes may represent sedimentation in a narrow basin developed between Laurentia and Gondwana during rifting. Palaeontological evidence suggests that the Precordillera developed on the passive margin of Laurentia but moved away as an independent plate during the Ordovician; the hypothesis of the Precordillera as a Laurentian plateau does not explain faunal differences between their Late Arenig-Llanvirn brachiopods. Ordovician subduction beneath Gondwana resulted in formation of the Famatina-Puna-Avalonia volcanic-arc system. Affinities between Celtic brachiopods of this age in volcaniclastic rocks from South America (Famatina) and eastern North America (Maine, Gander, Central Newfoundland) suggest some geographical continuity between them, consistent with palaeomagnetic evidence. It is proposed that accretion of allochthonous terranes to eastern Laurentia was related to collision with the northwestern corner of South America in late Ordovician time, an idea supported by the affinities of Silurian and Devonian brachiopods from Venezuela and Colombia.
Ordovician K-bentonites in the Argentine Precordillera: relations to Gondwana margin evolution
Authors: Huff Warren D. , Bergström Stig M. , Kolata Dennis R. , Cingolani Carlos A. , Astini Ricardo A. 
Published: April 2008

AbstractOrdovician K-bentonites have now been recorded from >20 localities in the vicinity of the Argentine Precordillera. Most occur in the eastern thrust belts, in the San Juan Limestone and the overlying the Gualcamayo Formation, but a few ash beds are known also from the central thrust belts. The oldest occur in the middle ArenigI. victoriae lunatusgraptolite (Oe. evaeconodont) Zone, and the youngest in the middle LlanvirnP. elegans(P. suecicus) Zone. Mineralogical characteristics, typical of other Ordovician K-bentonites, include a matrix of illite/smectite mixed-layer clay and a typical felsic volcanic phenocryst assemblage: biotite, beta-form quartz, alkali and plagioclase feldspar, apatite, and zircon, with lesser amounts of hornblende, clinopyroxene, titanite and Fe-Ti oxides. The proportions of the mineral phases and variations in their crystal chemistry are commonly unique to individual (or small groups of) K-bentonite beds. Glass melt inclusions preserved in quartz are rhyolitic in composition. The sequence is unique in its abundance of K-bentonite beds, but a close association between the Precordillera and other Ordovician sedimentary basins cannot be established. The ash distribution is most consistent with palaeogeographical reconstructions in which early Ordovician drifting of the Precordillera occurred in proximity to one or more volcanic arcs, and with eventual collision along the Andean margin of Gondwana during the mid-Ordovician Ocloyic event of the Famatinian orogeny. The Puna-Famatina terrane northeast of the Precordillera might have served as the source of the K-bentonite ashes, possibly in concert with active arc magmatism on the Gondwana plate itself.
Time constraints on the Early Palaeozoic docking of the Precordillera, central Argentina
Authors: Ramos Victor A. , Dallmeyer R. D. , Vujovich Graciela 
Published: April 2008

Abstract

40
Ar/
39
Ar incremental-release ages have been determined for muscovite and hornblende concentrates prepared from basement rocks of the Sierra de Pie de Palo, in the western Sierras Pampeanas, east of the Early Palaeozoic Precordillera. The basement is mainly represented by variably metamorphosed units, including ophiolites, orthogneisses and schists. Previous U-Pb, Rb-Sr, K-Ar, and
40
Ar/
39
Ar dating of magmatic and metamorphic zircons from the basement has indicated a Middle Proterozoic age. The
40
Ar/
39
Ar plateau ages constrain a series of ductile deformational events that are correlated with development of structural discontinuities in adjacent foreland basins. The following deformational events are postulated: (1) initiation of collision and drowning of the Precordillera platform against Gondwana (470–460 Ma); (2) flexural extension associated with normal faulting due to tectonic loading of the Gondwana margin; and (3) development of a foreland basin (450–430 Ma). These Mid-Ordovician-Silurian events were related to collision of several exotic Early Palaeozoic terranes along the Gondwana margin. The Punta Negra foreland basin developed further west during Early to Mid-Devonian (410–380 Ma) times, and was linked to the beginning of the docking of the Chilenia terrane along the western margin of the Precordillera.