bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sub-basalt imaging using converted waves: numerical modelling
Authors: Martini F. , Lafond C. , Kaculini S. , Bean C. J. 
Published: September 2007

Abstract

Both ray-tracing and frequency-wavenumber integration modelling have been used to investigate the behaviour of P waves and P to S converted waves in simple geological models, which involve a basaltic layer above a lower-velocity layer of sediments. Model parameters were adjusted to study the behaviour of these waves, under conditions of changing water depth, basalt layer thickness and a number of permutations with respect to basalt-sediment stratification. Synthetic shot gathers were generated and then analysed and processed as real data. The general approach was to document changes in reflection curves with offset, changes in the stacking velocity, variations in the imaging of deeper reflectors under different model scenarios and to understand which offsets are useful for converted wave processing. Although this work is preliminary, some general principles have been identified, which may be of use in an operational context. For example, the modelling indicates that S waves have larger amplitudes than P waves at long offsets and that P to S converted waves arrive before the sea bottom arrival at the far offset. Consequently, the recording and identification of converted waves is favoured by long offset (
c.
10 km) acquisition arrays. However, the modelling also indicates that the presence of sediment-basalt interlayering makes the identification of converted waves more difficult.
The Mesozoic evolution of the southern North Atlantic region and its relationship to basin development in the south Porcupine Basin, offshore Ireland
Authors: Johnston Sarah , Doré Anthony G. , Spencer Anthony M. 
Published: September 2007

Abstract
The Mesozoic history of a number of Atlantic borderland sedimentary basins can be related to the early opening history of the southern North Atlantic Ocean. Regional tectonic controls such as plate motion vectors and the pre-existing tectonic grain had an important role in basin development and are expressed as local tectonostratigraphic events. The evolving palaeogeographies for the region are demonstrated in a series of maps based on computer-generated plate reconstructions. The Porcupine Basin, centrally located in the study area, lay close to the intersection of three plate boundaries that separated Eurasia from North America and controlled opening of the Bay of Biscay. The south Porcupine Basin, where there is relatively poor data control, is considered in the context of broader platetectonic controls, which were also responsible for the development of contiguous and better understood basins during Mesozoic time. This approach provides new insight into the structural evolution and likely facies development in the south Porcupine Basin, allowing broad inferences for petroleum prospectivity to be made. Initial Permo-Triassic fault-controlled extension led to continental deposition, which, if associated with aeolian and/or fluvial reservoir rocks, will mostly be too deep to be prospective. Thermal subsidence during Early Jurassic time was associated with flooding and fine-grained clastic deposition with anticipated moderate source rock potential. Regional uplift of the northern Porcupine area during Mid-Jurassic time forced shorelines and shelves southwards and the south Porcupine Basin could contain good reservoir quality sandstones and possible waxy deltaic-type source rocks of this age. In Late Jurassic time, major crustal extension took place with potential for reservoir and source rocks in locally expanded footwall successions. Further extensional faulting occurred in earliest Cretaceous (Neocomian) time with further synrift plays possible at this level. Growth of the Porcupine Median Volcanic Ridge is attributed to Barremian-Aptian time and related to continuing extension associated with a northwesterly arm of a triple junction positioned to the south of the Porcupine area. Strong subsidence of the basin centre during this time will have a significant impact on source rock maturation and flank trap geometries in the south Porcupine Basin.
Aspects of the structure of the Porcupine and Porcupine Seabight basins as revealed from gravity modelling of regional seismic transects
Authors: Johnson H. , Ritchie J. D. , Gatliff R. W. , Williamson J. P. , Cavill J. , Bulat J. 
Published: September 2007

Abstract
The Porcupine Basin is characterized by a large central free air gravity anomaly high (+ 55 mGal) flanked by local lows. In contrast, the Procupine Seabight Basin has low-amplitude anomalies in its centre, flanked by edge anomalies. Two transects, one in each of these basins, have been modelled using satellite gravity data; the upper parts of the transects are constrained by interpretation of recent commercial seismic reflection data and two wells. Results from the modelling suggest that the Porcupine Basin is not in isostatic equilibrium. In contrast, the essentially zero free air anomaly over the centre of the Porcupine Seabight Basin suggests that this basin is isostatically compensated. The difference in isostatic compensation between the two basins may reflect a fundamental contrast between the strength of the crust; the crust underlying the Porcupine Basin possesses the greater strength. The Clare Lineament may represent a fundamental boundary within the ‘Avalonian Terrane’ that juxtaposes basement blocks of differing rheologies.
Reservoir characteristics of the Upper Jurassic sequence in the 35/8-2 discovery, Porcupine Basin
Authors: Robinson A. J. , Canham A. C. 
Published: September 2007

Abstract
The 35/8-2 well, drilled by Phillips Petroleum in 1981, tested oil and gas from a Late Jurassic reservoir within a plunging, tilted fault block. The reservoir is overpressured by 5000 psi and, despite having good porosity and high net to gross ratio, exhibits very low permeability. Three hydrocarbon-bearing sandstone intervals were encountered in the well, and more than 120 m of core was taken from these reservoir sections. The sedimentological structures identified in core are clearly indicative of a deep-water (below storm wave base) submarine fan system, comprising a wide spectrum of turbidite and debris-flow, channel and lobe deposits. Detailed petrographic analysis of the reservoir was undertaken to identify the key factors affecting reservoir quality. The sandstones are chemically immature lithic arenites, containing abundant quartz, feldspar and rock fragments. Reservoir quality is generally poor, largely as a result of the chemical instability of the sandstones. Diagenetic overprinting is the main agent of downgrading the sandstones, with kaolinites and carbonate cements blocking pore throats and reducing permeability. Facies type, sand to mud ratio and ultimately the clastic provenance of the sandstones are also critical factors affecting the reservoir quality in these sandstones. Hydrocarbon flow was predominantly from a single sandstone facies (B1) and was confined to the ‘A’ sand interval in well 35/8-2, but it is inferred that this facies may occur away from the wellbore in all three sand intervals. Uncertainties in the results of the drillstem test and pressure data demonstrate that it is not possible to confirm whether the hydrocarbons present in the reservoir are gas condensate or volatile oil. Uncertainty in the extent of the productive reservoir facies, hydrocarbon columns and hydrocarbon type are challenges that must be overcome before the reserves contained within the 35/8-2 structure can be developed.
Comparative Tertiary stratigraphic evolution of the Porcupine and Rockall basins
Authors: McDonnell A. , Shannon P. M. 
Published: September 2007

Abstract
The Tertiary development of the Porcupine and Rockall basins is compared in terms of stratigraphy and sedimentation. Four main unconformities are correlated between the basins and these are interpreted as being of Paleocene (C40), latest Eocene-Early Oligocene (C30), latest Early Miocene (C20) and Early Pliocene (C10) age. Seismic stratigraphic analysis of both basins suggests a greater similarity in post-Eocene deposition than in the Paleocene to Eocene stratigraphy. During Early Tertiary time a regressive succession, punctuated by minor transgressions, marks a major interruption in the general post-rift thermal subsidence pattern of the region. This regression, possibly triggered by lithospheric thermal effects and/or ridge-push stresses, resulted in deltaic and submarine fan deposition in the Porcupine Basin, with submarine channel trends indicating that sediment was sourced mainly from the Porcupine High to the north and west. Sand deposition in the Porcupine Basin occurred principally during Mid- to Late Eocene times. In contrast, Early Eocene sand input is postulated in the Rockall Basin, whereas deposition during the Mid- to Late Eocene times was more mud-prone. In Oligocene and Mio-Pliocene times, sediment build-ups, interpreted as contourites, developed towards the margins of both basins, with sedimentation principally influenced by oceanographic circulation patterns at this time. During Neogene to Recent times limited marginal sediment influx occurred in the Porcupine Basin whereas sediment input continued locally, during Neogene time, in the Hebrides region of the Rockall Basin.
Evidence of shallow gas above the Connemara oil accumulation, Block 26/28, Porcupine Basin
Authors: Games K. P. 
Published: September 2007

Abstract
The results of a site survey investigation, carried out in Block 26/28 of the Porcupine Basin, suggest the presence of shallow gas above the Connemara oil accumulation. The evidence for shallow gas at or close to the sea bed consists of a series of features interpreted as gas or fluid escape structures. The presence of gas at depth is suggested by two different features: an anomalously high-amplitude seismic reflector, interpreted as a gas-charged sand layer, and some isolated, seismically disturbed zones, which are identified as gas chimneys on both high-resolution 2D seismic and conventional 3D seismic data.
Thermally driven porosity reduction: impact on basin subsidence
Authors: Bjørkum P. A. , Walderhaug O. , Nadeau P. H. 
Published: September 2007

Abstract

At temperatures higher than
c.
80°C, thermally driven, isochemical diagenetic porosity loss in siliciclastic sediments leads to a thinning of the sediment column. This process, termed thermochemical compaction, results in surface subsidence and generation of sediment accommodation space. The diagenetic reactions driving thermochemical compaction will operate regardless of the initial mechanism of basin formation and in addition to any externally controlled processes causing continued subsidence. Thermochemical subsidence rates are an inverse function of geothermal gradients. The total rates of subsidence at the surface, including isostatic and mechanical compaction effects, may reach several tens of metres per million years, and may have been important in driving Tertiary subsidence in basins west of Ireland. Unlike the exponentially decaying subsidence caused by tectonic thinning and rifting of the crust, thermochemical basin subsidence is a self-regulated intrabasinal process, which proceeds at a relatively high constant rate over geological time. If not arrested by extrabasinal or tectonic events, the overall effect can ultimately result in sediment metamorphism and granitization.
Slope instability and sediment redistribution in the Rockall Trough: constraints from GLORIA
Authors: Unnithan V. , Shannon P. M. , McGrane K. , Readman P. W. , Jacob A. W. B. , Keary R. , Kenyon N. H. 
Published: September 2007

AbstractA recent GLORIA (Geological LOng Range Inclined Asdic) sidescan survey covered 200 000 km2of the sea bed in the Irish Rockall Trough. It revealed a range of sedimentary features on the trough floor and its steep (>6°) margins. The western margin is characterized by large-scale (of the order of hundreds of kilometres in length) downslope mass movement. Smaller-scale slides and slumps (tens of kilometres across) occur on the eastern margin, but they are subordinate to canyon, channel and fan systems. The western and central parts of the trough floor contain the Feni Sediment Ridge, a 600 km long contourite sediment build-up covered by large sediment waves trending sub-parallel to the dominant modern current pattern. Strong, northward-flowing bottom currents are thought to have eroded the base of the slope in the east and redeposited the sediments on the western margin and the trough floor. Mass wasting and terrigenous sediment input through canyons is regarded as the primary source of sediment in the region. The increase in the degree and frequency of canyon incision along the NE margin of the trough reflects increased terrigenous input from the Irish mainland and a possible glacial influence on the basin margin. The GLORIA images reflect a broad interplay of alongslope and downslope sediment transport processes in the Rockall Trough with sediments sourced from the NE margin and redistributed by currents along the western margin. Although alongslope and downslope processes are the major controlling factors, basin subsidence, Quaternary glaciations and glacio-eustatic sea-level fluctuations have also influenced the pattern of sedimentation in the Rockall Trough.
Slope failure features on the margins of the Rockall Trough
Authors: Shannon P. M. , O’Reilly B. M. , Readman P. W. , Jacob A. W. B. , Kenyon N. 
Published: September 2007

Abstract
A TOBI sidescan sonar survey in the Irish sector of the Rockall Trough reveals the presence of a range of slope failure features of various sizes and extent along both the eastern and western margins. A number of different types are identified. These include incipient cuspate slides, slab failures and evolved slides, and debris flows. It is suggested that the incipient cuspate slides, slab failures and evolved slides represent slope failure of muddy sediments whereas the failures that gave rise to debris flows lie on steeper slopes and may be of less muddy composition. Many of the slope failure features are relatively recent (probably <15 ka), although some evidence points towards either a prolonged period of movement or a number of phases of slope movement locally along the margins. A comprehensive understanding of the nature, distribution, age and controls on the formation of the slope failure features will be necessary in planning the likely location of sea-bed structures in the event of petroleum development in the region.
Sustainable groundwater development
Authors: Hiscock K. M. , Rivett M. O. , Davison R. M. 
Published: September 2007

Abstract
Estimated annual water availability per person in 2025 is likely to result in at least 400f the world’s 7.2 billion people facing serious problems with obtaining freshwater for agriculture, industry or human health (Gleick 2001). To meet present and future needs with the currently available surface and groundwater resources, while at the same time preserving terrestrial and aquatic ecosystems, will require a sustainable approach to managing water. This paper discusses the importance of groundwater resources in industrialized and developing countries, and the associated problems of over-abstraction and groundwater pollution, with the objective of defining sustainable groundwater development. It is concluded that sustainable groundwater development at global and local scales is achieved through the maintenance and protection of groundwater resources balanced against economic, environmental and human (social) benefits. This interpretation of sustainable groundwater development is incorporated into the methodologies currently emerging in Europe (the EU Water Framework Directive) and England and Wales (Catchment Abstraction Management Strategies). However, success in achieving future sustainable groundwater development will require a common understanding at the level of the individual based on information and education within a legislatory framework that promotes co-operation and self-responsibility.
Geophysical investigations of the thermal springs of Bath, England
Authors: McCann C. , Mann A. C. , McCann D. M. , Kellaway G. A. 
Published: September 2007

Abstract
The origin of the thermal springs of Bath (England) remains unknown. As part of a programme of research into the structure of the thermal aquifer, the Carboniferous Limestone, an urban reflection seismic survey has been carried out to explore the deep geology of the Bath area. Existing gravity data have been used to provisionally identify the seismic reflectors and to map the depth of the (interpreted) Carboniferous Limestone in the area around the springs. The new seismic data show that at a distance of 2.1 km south-west of the springs, the depth of the (interpreted) Carboniferous Limestone surface increases from 0.4 km below Ordnance Datum (OD) to 1.35 km below OD within a distance of 1.8 km, an average apparent dip of nearly 30 degrees. In all other directions from the springs, the Carboniferous Limestone surface is at a depth of 300 m or less below OD. The work described in this paper is part of a continuing research programme.
Groundwater resource management in eastern England: a quest for environmentally sustainable development
Authors: Burgess D.B. 
Published: September 2007

Abstract
The management of groundwater resources in England and Wales was initially based only on measures of the renewable resource. This has been extended to include the need to preserve the springs, river flows and surface water levels dependent on groundwater discharges as a key objective of a sustainable management of groundwater resources. The impacts of all new groundwater abstraction proposals on the surface water environment are now evaluated using a number of techniques, some of which are under further development. The sustainable management of groundwater catchments also includes the control of pumping from existing groundwater sources to meet agreed environmental targets. This approach is illustrated by examples of groundwater catchments managed to augment surface flows, to prevent saline intrusion and to preserve the integrity of wetland conservation sites.
Who needs sustainability?
Authors: Price M. 
Published: September 2007

Abstract

Three inescapable factors face us at the turn of the century. First, the climate, and with it the supply of water, is becoming more variable. Regardless of whether this variability is the result of man-made global warming, it seems to be with us. Secondly, demand for water will increase; in many countries domestic water use is currently less than 25 1/personday and needs to increase if living conditions are to improve. In Great Britain,
per capita
use of water is low compared with many other western countries — including those that pay for water on a metered basis — and it is certain to rise as living standards improve. Thirdly, concern for the environment is likely to increase. We can counter the first problem only by ensuring that we have adequate water storage; most water storage in Great Britain and the rest of the world is in the ground. We need to counter the second by recognizing that the vast majority of public water use is non-consumptive, but that very little waste water is re-used efficiently. We need to counter the third by welcoming the concern but ensuring that the response is sensible. We must be prepared to question some of the accepted wisdom of the environmental movement, and remember that many of the developments in human history were non-sustainable. Do they represent environmental disasters, or human progress?
Sustainable groundwater development in arid, high Andean basins
Authors: Anderson Mark , Low Rob , Foot Stephen 
Published: September 2007

Abstract
Mining is an important part of the economy of Chile. A high proportion of mines are located in remote, high altitude, extremely arid environments in northern Chile. The demands of the mining industry for potable and ore-processing water, along with existing longer term demands, mean that water has a high commercial value in this region. Set against this is the desire to conserve the unique flora and fauna, highlighted by the existence of a number of conservation sites of international importance. A typical case study charting the investigation of an aquifer in this region [the Monturaqui-Negrillar-Tilopozo (MNT) aquifer] and the development of a plan for groundwater use observing the requirement for sustainability is presented. The important aspects of the geology and hydrogeology of the aquifer are presented, and a description is given of the techniques used to arrive at a sustainable groundwater development strategy. The unusual characteristics of the aquifer meant that the use of spatially distributed time-variant numerical models to identify a sustainable groundwater abstraction strategy was necessary. The abstraction strategy will enable sustainable abstraction of a significant volume of groundwater from the MNT basin, taking advantage of the high storage to recharge/discharge ratio of the aquifer.
Constraints on sustainable development of arsenic-bearing aquifers in southern Bangladesh. Part 1: A conceptual model of arsenic in the aquifer
Authors: Burgess W. G. , Burren M. , Perrin J. , Ahmed K. M. 
Published: September 2007

Abstract

Arsenic is widespread in groundwater of the Holocene alluvial aquifers in southern Bangladesh, yet its concentration is highly variable spatially and with depth. A conceptual model of arsenic in the aquifer is proposed, as a basis for addressing questions concerning sustainability of groundwater development. Patterns and profiles of arsenic distribution in the aquifer have been determined at Meherpur in western Bangladesh, over an area of 15 km
2
and a depth range of 15–225 m. The hydrochemical and hydraulic environments of arsenic occurrence have been established. The conceptual model incorporates the conditions of arsenic release to groundwater, the depth distribution of the arsenic source, likely sedimentological controls on the lateral discontinuity of the arsenic source, and the hydraulic regime imposed by pumping from the hydrogeologically leaky, multi-layered aquifer. Reducing conditions, conducive to arsenic release from sedimentary iron oxyhydroxides, are widespread. The arsenic source occurs at a distinct horizon at a depth of about 20m, but is laterally discontinuous. The catchments of shallow, hand-pumped tubewells (HTWs) are limited in extent by vertical leakage. Arsenic concentration in water pumped from tubewells depends on the depth separation between the HTW screen and the arsenic source, the overlap between the HTW catchment and the arsenic source layer, and the duration of pumping. Implications are drawn for treatment, tubewell location and design, monitoring, and predictive modelling.