bluuebunny/crossref_metadata_2025_split huggingface dataset:
Reservoir characterization: how can anisotropy help?
Authors: Owen Roderick J. , Li Xiang-Yang , Macbeth Colin D. , Booth David C. 
Published: April 2008

Abstract

We present a brief review on the use of seismic anisotropy for reservoir characterization. Seismic anisotropy utilizes the concept of scattering interference from subwavelength heterogeneities and may provide a powerful tool for characterizing these heterogeneities. An ordered system of reservoir heterogeneity may display seismic anisotropy diagnosed by shear-wave splitting, and the polarization of the fast split shear-wave (
qS1
), the time delay between the two split shear-waves (
qS1, qS2
), and the differential reflectivity at normal incidence may be used to quantify the heterogeneities. An example of field data obtained from a multicomponent seismic survey is presented to demonstrate how hydrocarbon production can be correlated with seismic anisotropy, and its potential application to reservoir characterization.
Numerical simulation of fluid flow in complex faulted regions
Authors: Foley L. , Daltaban T. S. , Wang J. T. 
Published: April 2008

Abstract
Faults exist in most hydrocarbon reservoirs. In general, they interfere with the transport of the fluids within the porous medium, and in other cases they may compartmentalize the reservoir and alter its connectivity. When performing any simulation procedure on a faulted reservoir it is important to take account of the sealing characteristics of the faults, especially (1) the effects of the pressure distribution across a fault and (2) the relationship between the porosity and permeability of the fault zone material and that of the bulk reservoir rock.
Current numerical fluid flow modelling techniques of faults are generally limited to the use of special connections, which involve modifying the transmissibilities between cells of the finite difference simulation grid. In many cases, the simulated flow is allowed to occur only between cells which are physically in contact. This may not be appropriate in the event of flow occurring along the fault plane and thus between a number of blocks which are not adjacent to each other. Modelling of fluid flow in complex faulted regions may be enhanced by implementing a boundary-fitted co-ordinate technique. This allows the geometry of the fault to be represented more accurately by constructing the simulation grid around the fault zone such that the inner boundary of the grid is coincident with the boundary of the fault. The permeability of the reservoir in the vicinity of the fault needs to be described using available information on fault zone characteristics (e.g. cataclastic slip band densities, clay smear potential, cementation etc.) to enable the construction of permeability distributions in the faulted region.
Curvature analysis of gridded geological surfaces
Authors: Stewart S. A. , Podolski R. 
Published: April 2008

Abstract
Surface curvature is related to strain and hence fracture density in most lithologies relevant to hydrocarbon exploration, and can be calculated at negligible expense as a surface attribute of horizons mapped on three-dimensional (3D) seismic data. Surfaces mapped using 3D seismic exist as data grids. Direct application of strict mathematical approaches to curvature measurement of gridded data is hindered by several problems inherent to discretized data. The grid node spacing in a horizontal plane is initially equal to the 3D seismic bin spacing and is some arbitrary value greater than the infinitely small mathematical limit, so the measured curvature is also arbitrary. Poor resolution of reflectors gives noise which can be removed by smoothing, but this subjective step impacts subsequent curvature extraction.

Fracture distributions also reflect the effect of large- and small-scale fold structures so there is merit in measuring curvature at a range of scales in addition to that defined by the grid node spacing. As curvature varies with direction of measurement, observations in the grid
x
and
y
directions alone are unlikely to coincide with the key maximum and minimum curvature values. Resampling a data grid using a large sliding window permits curvature measurement at a range of different wavelengths, and several orientations can be searched in addition to those parallel to the grid axes. Problems which are present regardless of the sample interval include inherent curvature of geological structures, signal aliasing and regional surface tilt relative to the horizontal grid reference plane.

Total, or Gaussian, curvature which is the product of the maximum and minimum curvatures may not be the best format for presenting curvature data, as strata characterized by zero total curvature may be significantly strained within cylindrical fold structures. Instead, the sum of the absolute values of the principal curvatures gives a representation of spatial variance in strain due to maximum and double curvature.
Strain partitioning during flexural-slip folding
Authors: Couples Gary D. , Lewis Helen , Geoff Tanner P. W. 
Published: April 2008

Abstract
In upper-crustal structures, folding by flexural slip leads to the partitioning and ordering of strains, which are commonly expressed by means of faults, fractures and joints. Flexural slip occurs along only some of the numerous layer-to-layer contacts within a sedimentary rock sequence, and these active bedding-plane slip surfaces partition the succession into mechanical units, each of which, although composed of many rock layers, deforms as though it were a single beam. Thus, in upper-crustal flexural-slip folds, the strain domains associated with bending are sharply deliminted by the active slip horizons and also are related to structural position within the beam. Progressive folding leads to the development of additional active slip surfaces and, therefore, to an increased number of mechanical units which each develop bending strains. As a result of this sequence of events, there is a hierarchical overprinting of strains, which leads to considerable complexity in fracture fabrics; nevertheless, order in the fracture patterns is retained. Most petroleum reservoirs appear to be affected by fracture networks created during flexure, and their fluid flow characteristics are probably related to a fracture-dominated, flexural deformation state which is disposed relative to the layering, is inhomogeneous, and is not distributed stochastically throughout the whole rock volume.
Structural geology of the Gullfaks Field, northern North Sea
Authors: Fossen Haakon , Hesthammer Jonny 
Published: April 2008

Abstract
The large amount of structural data available from the Gullfaks Field have been used to unravel the structural characteristics of the area. Two structurally distinct subareas have been revealed (a major domino system and an eastern horst complex) that show significant differences with respect to fault geometry, rotation and internal block deformation. The main faults have very low dips in the domino system (25–30°) as compared to the horst complex (65°), whereas most minor faults are steep in all parts of the field. Forward modelling indicates that the horst complex balances with rigid block operations. However, the domino area underwent significant internal deformation, reflected by the low acute angle between bedding and faults, and by non-planar bedding geometries. The internal deformation is modelled as a shear synthetic to, but steeper than, the main domino faults. This deformation explains a large-scale (kilometre sized) drag zone that has a triangular geometry in cross-section. Much of this shear deformation occurred by strain-dependent grain reorganization in the poorly consolidated Jurassic sediments, which led to a decrease in porosity. A strain map is presented for the domino area, indicating where the porosity is likely to have been decreased due to internal shear. Hangingwalls are generally more deformed (sheared) than footwalls. This is seen on both the kilometre scale (large-scale drag) and the metre scale (local drag).
Recent UK legal developments relating to pollution of water resources
Authors: Mylrea Kathy 
Published: April 2008

Abstract
The new UK statutory contaminated land provisions are expected to come into effect in 1997. Land will be contaminated for the purposes of the legislation if the presence of substances in, on or under it mean that significant harm is being caused or there is a possibility of such harm being caused or pollution of controlled waters is being caused or is likely to be caused. In a separate legal development, powers contained in the Water Resources Act 1991 for dealing with water pollution are also being strengthened. There is some concern that there is potential for overlap or conflict between these two regimes.
Developments at EU level include a communication of European Community water policy. It is expected to lead to a framework directive on water resources. The European Commission is shortly expected to take some action on the issue of liability for Environmental Damage.
Methyl tertiary butyl ether (MTBE): a groundwater contaminant of growing concern
Authors: Burgess W. G. , Dottridge J. , Symington R. M. 
Published: April 2008

Abstract

Methyl tertiary butyl ether (MTBE) is a fuel oxygenate rapidly becoming the preferred alternative to leaded and other, unleaded, additives in petrol. MTBE was introduced in the US as a fuel oxygenate in 1979, and has been used in the UK since the mid 1980s. Environmental legislation is expected to lead to increased use of MTBE in the future. Current UK legislation allows MTBE to constitute up to 10% by volume of unleaded petrol. MTBE has a low toxicity, yet its low odour and taste threshold makes it a problem at concentration levels above 2–3 μgl
−1
in water. It is more than ten times more soluble than the BTEX components of fuel, is apparently not retarded by sorption, and is reported to be non-biodegradable. Suggestions that MTBE exhibits co-solubility with BTEX components, thereby increasing their mobility, add to concerns about its behaviour in aquifers. This paper reviews the properties of MTBE and the limited published work on its behaviour as a groundwater contaminant.
Minewater remediation at a French zinc mine: sources of acid mine drainage and contaminant flushing characteristics
Authors: Sadler Piers J. K. 
Published: April 2008

Abstract
Recent closure of a zinc mine in southwestern France has resulted in flooding of workings and discharge of contaminated minewater from the workings, polluting a small stream. The minewater discharge is of near neutral pH and is contaminated with high levels of zinc, cadmium, manganese, iron and sulphate. With the exception of iron, concentrations of these contaminants have fallen dramatically since the discharge arose.
The main source of recharge to the mine is likely to be overlying aquifers associated with near-surface weathering. A classification is proposed to explain the hydrogeochemical sources of contaminants and the changes in discharge water quality with time. Primary sources related to active sulphide oxidation dominate the minewater chemistry in the unflooded workings, whilst secondary sources related to remobilization of secondary minerals dominate in the flooded workings. Prediction of contaminant flushing rates has been carried out on the basis of this classification. Zinc and cadmium levels are expected to reach stable medium-term levels within 2–5 years of the discharge first occurring.
Potential remediation strategies include plugging of the discharging mine portal and flooding of upper workings, coupled with conventional chemical and wetland treatment.
Investigation and clean-up of jet-fuel contaminated groundwater at Heathrow International Airport, UK
Authors: Clark L. , Sims P. A. 
Published: April 2008

Abstract
British Airways in 1987 discovered a leak of jet fuel (kerosene) at Heathrow Airport, west of London. The leak had led to free-phase kerosene floating on top of the shallow water-table beneath the site, with thicknesses of product of almost 1 m in places. WRc alert was employed to undertake a programme of investigations to delimit the free product. Work was then initiated to remove the free product from the water-table and restore the aquifer. This has been successful, with a total of 39 4001 of kerosene being recovered from the site. The recovery of kerosene took about four years of continuous work, illustrating the difficulty of aquifer remediation and the long time involved in remediation programmes.
Remediation of a petroleum spill to groundwater at a fuel distribution terminal (Long Island, USA) using pump-and-treat and complementary technologies
Authors: Holden John M. W. , Tunstall-Pedoe Nadine 
Published: April 2008

Abstract

A petroleum leakage to groundwater of up to 4000 m
3
was discovered in November 1987 at a fuel terminal site on Long Island, USA. A pure petroleum product pool of up to 1 m in thickness was floating on the water-table, and associated dissolved hydrocarbon and halogenated hydrocarbon plumes appeared to extend in three directions from source areas within the site. Risk assessments indicated that some local private wells were threatened by the migration of a dissolved petroleum plume. The petroleum spill is being treated using pump-and-treat technology with associated free product recovery, soil vapour extraction, air sparging wells and intrinsic bioremediation techniques. The treatment is proving to be successful, with half the petroleum free product being recovered and protection of the local residents and groundwater achieved.
Contaminant migration from disposal of acid tar wastes in fractured Coal Measures strata, southern Derbyshire
Authors: Banks D. , Nesbit N. L. , Firth T. , Power S. 
Published: April 2008

Abstract

In excess of 60 000 m
3
of acidic tar wastes from a lubricating oil factory have been disposed in old clay pits at a site on Coal Measures strata near Belper, southern Derbyshire, UK. A site investigation was carried out to assess the nature and volume of the waste, the extent of contaminant migration and possible remediation options. The wastes have migrated as free phase, gravity-driven flows of semi-fluid tar. These tar flows have led to contamination of on-site ponds by hydrocarbon emulsions and dissolved phase contaminants. Limited groundwater contamination by dissolved phase contaminants has also occurred. At present, no impact on off-site surface water receptors has been detected and no risk to any water abstraction has been identified. The site investigation has confirmed the exceedingly complex nature of the Coal Measures sequence. The Coal Measures exhibit some aspects of a multilayer aquifer system, dominant fracture flow mechanisms, strong anisotropy governed by fracture orientation and a heterogeneous and discontinuous distribution of groundwater heads. Indications of strong vertical head gradients, possibly related to under-drainage by mine workings, were detected.
Great Bridge Marl Pit: a case study in the prevention of contaminant migration
Authors: Gore Barry C. , Campbell Ian M. 
Published: April 2008

Abstract
Great Bridge Marl Pit is a former brick pit located in the West Midlands. The pit is infilled by an assortment of materials including a wide range of toxic and aggressive substances (most significantly phenolic liquids). Phase 2 of the Black Country Spine Road (opened 1995) crosses the pit on a raised embankment.
Prior to the construction of the road, the site was derelict and contaminated groundwater within the pit was thought to present only a minor risk to the adjacent River Tame and virtually no risk to local groundwater abstractions. Mobile contaminants within the pit were contained by a combination of the geometry of the pit, the location of the bulk of the contaminative materials within the base of the excavation and the low permeability of the base of the excavation.
However, impact of road construction over the site, in particular the preconsolidation of the pit infill by surcharging, was considered to have the potential to mobilize significant volumes of contaminated groundwater from within the pit and therefore to present a considerable risk of pollution of the River Tame.
To minimize the potential for contaminant migration, groundwater flow within the Marl Pit and in its immediate vicinity was controlled during the surcharging period by the installation of a groundwater abstraction system. Contaminated water abstracted during the surcharging was disposed of to trunk sewer and treated at the local water treatment works. The efficiency of the groundwater abstraction system was assessed by monitoring groundwater pressures and concentrations of contaminants in a number of strategically located boreholes around the margins of the site.
During the surcharging period the groundwater control system successfully controlled excess groundwater pressures generated beneath the surcharge and there was no evidence of an increase in contaminant migration from the pit; in fact a considerable reduction in the volume of contaminated groundwater present within the pit is likely to have occurred.
Large submarine slides on the NE Faeroe continental margin
Authors: Van Weering Tjeerd C. E. , Nielsen Tøve , Kenyon Neil H. , Akentieva Katja , Kuijpers Antoon. H. 
Published: April 2008

Abstract
High-resolution seismic profiles of the NE Faeroe margin show large-scale slumping and sliding of the middle and lower continental slope, affecting sediments of presumed Miocene, Pliocene and Quaternary age. Mass-flow deposits on the upper slope are partially covered by more recent deposits, presumed to be contourites. A TOBI deep-tow side-scan sonar mosaic, in combination with deep-towed penetrating echosounder results, shows that the slump complex on the upper slope consists of a buried slide scar, bottleneck slides, debris-flow lobes and a number of shallow slides. Sliding at the middle and lower continental slope seems more recent and shows a steep, irregular main slump scar and very large, intact, angular blocks. The base of the slide at the lower continental slope shows numerous narrow and diverging tracks, 10–15 km length, that end at individual blocks. Several types of debris flows have been mapped, some with longitudinal flow fabrics.
Debris flows on the Sula Sgeir Fan, NW of Scotland
Authors: Baltzer A. , Holmes R. , Evans D. 
Published: April 2008

Abstract
This paper describes the various debris-flow processes which have occurred on the Sula Sgeir Fan, a well-documented feature situated on the Hebrides Slope, NW of Scotland. The Sula Sgeir Fan covers an area 65 km in length and 28 km in width, between the 400 m and 1200 m bathymetric contours. The fan appears as a build-up of stacked debrisflow packages with transparent acoustic facies. These are termed glacigenic debris flows, as they are derived from sediment deposited by ice at the shelfbreak. However, on the southwestern edge of the Sula Sgeir Fan, and on its northeastern flank, there are different acoustic features which are described here as ‘classic’ debris flows. They are larger than the glacigenic type, and a scarp or a sliding scour characterizes their heads; they are thought to have been triggered by seismic events. Associated with these ‘classic’ debris flows are features on the seismic profiles interpreted as gas- or liquid-escape structures.
The Var submarine sedimentary system: understanding Holocene sediment delivery processes and their importance to the geological record
Authors: Mulder Thierry , Savoye Bruno , Piper David J. W. , Syvitski James P. M. 
Published: April 2008

AbstractThe Var system extends off Nice in the Western Mediterranean. It comprises a river, a delta and a submarine valley leading to a deep-sea fan that together have been in operation since the Early Pliocene. The Var system is an area experiencing active sediment transport, where at least three major types of sediment transfer process are identified: hyperpycnal turbid plumes, surge-like turbidity currents generated by shallow failures induced by excess pore pressure during river flood periods, and by large earthquake-triggered slides. The last two processes might generate higher-density turbidity currents, but at different return intervals. Hydrological data, direct observations of the sea floor, geotechnical testing and numerical modelling confirm the very high frequency of these sediment transfer events. Some of the processes have catastrophic surge behaviour, others are continuous during periods of river flooding. In the latter case, all the sediment supplied to the vicinity of the river mouth is transferred seaward without or with only brief periods of deposition. The geological record of such continuous activity remains difficult to identify. The palaeo-events identified in sedimentary series are often widespread, high-magnitude events with return periods close to a millennium, i.e. usually beyond historical records. Normal ‘background’ processes provide only thin deposits that are not interpretable in the geological record.
Upper slope sand deposits: the example of Campos Basin, a latest Pleistocene-Holocene record of the interaction between alongslope and downslope currents
Authors: Viana A. R. , Faugères J.-C. 
Published: April 2008

AbstractUpper slope sand deposits constitute large accumulations of well-sorted very fine to coarse sand that are of great economic interest. A depositional model is here proposed based on hydrographic, physiographic and sedimentological characteristics of the modern Campos Basin margin, SE Brazil. Data comprise long-term bottom-current measurements, long and short cores, high-resolution seismic lines and side-scan sonar records. Results indicate that offshelf bed-load transfer of sand is driven by shelf bottom currents forced by combined oceanographic and meteorological factors, among them the ‘sea-floor polishing effect’, the rotatory sweeping of the sea bed by mesoscale eddies. The main conditions for development of upper slope sand accumulations are: (1) convex outer shelf-slope morphology; (2) sandy sediment available at the shelf edge; (3) net offshelf transport of shelf sands induced by shelf-edge bottom currents; (4) the presence of a relatively strong slope boundary current. Transfer to the slope occurs as successive, short-distance-flowing sand fluxes. The latter occur mainly through shelf-edge incisions and lead to elongated and narrow sand lobes on the upper slope. The convex morphology of the upper margin controls the Brazil Current (BC) flow and two main zones can be identified: a BC ‘funnelling zone’ where the current is accelerated, and a BC ‘expansion zone’ where the current has its speed decelerated. Reworking by the southward-flowing Brazil Current develops gravel lag deposits, erosional scours, and interchannel sand waves on the upper slope (between 200 and 350 m water depth). Downslope, the reduction of slope current intensity enhances the development of flat sand sheets, controlled by the northward flow of the Brazil Counter-Current. The upper Quaternary vertical facies succession is there characterized by a coarsening-to fining-up asymmetric sequence. Upper Pleistocene sand-mud intercalations are overlain gradually or with a sharp or erosive contact by lower Holocene coarse to finegrained clean sands that grade to upper Holocene fine-grained muddy sands toward the top.