bluuebunny/crossref_metadata_2025 huggingface dataset:
Fire and water
Authors: Cashman Katharine V. , Deligne Natalia I. , Gannett Marshall W. , Grant Gordon E. , Jefferson Anne
Published: April 2010

This fi eld trip guide explores the interactions among the geologic evolution, hydrology, and fluvial geomorphology of the central Oregon Cascade Range. Key topics include the geologic control of hydrologic regimes on both the wet and dry sides of the Cascade Range crest, groundwater dynamics and interaction between surface and groundwater in young volcanic arcs, and interactions between rivers and lava flows. As we trace the Willamette and McKenzie Rivers back to source springs high in the young volcanic rocks of the Cascade Range, there is abundant evidence for the large permeability of young lava flows, as manifested in streams that dewater into lava flows, lava-dammed lakes in closed basins, and rivers that emerge from single springs. These dynamics contrast sharply with the older, lower permeability Western Cascades terrane and associated runoff-dominated fluvial systems. On the east side of the Cascades we encounter similar hydrologic characteristics resulting in complex interactions between surface water and groundwater as we follow the Deschutes River downstream to its confluence with the Crooked River. Here, deep canyons have cut through most of the permeable part of the geologic section, have been invaded by multiple large intracanyon lava flows, and are the locus of substantial regional groundwater discharge. The groundwater and surface-water interaction in the Deschutes Basin is further complicated by surface-water diversions and an extensive network of leaking irrigation canals. Our west-to-east transect offers an unparalleled opportunity to examine the co-evolution of the geology and hydrology of an active volcanic arc.
Geothermal geology and utilization in Oregon
Authors: Lund John W. , Boyd Toni L. , Cornachione Harriet , Clark Anne Hiller , Marcus Sara A.
Published: April 2010

This field guide is for a three-day trip from Portland to Klamath Falls, Oregon, and back, traversing many of the physiographic provinces in Oregon, including the Columbia River, the Willamette Valley, the Western and High Cascade Mountains, the High Lava Plains, and the Basin and Range. Geologic field stops on Day 1 will be made along the drive to Klamath Falls at Salt Creek Falls and Crater Lake, and will include short discussions of Oregon's geological history and a brief introduction to geothermal resources in the state. Day 2 includes an extensive introduction to geothermal resources in Oregon and how these relate to Oregon geology, with tours to examine how the Oregon Institute of Technology, the City of Klamath Falls, and several local businesses in the Klamath Falls area use a local geothermal resource. Day 3 is devoted to the return trip to Portland, and will include geological stops at Newberry Crater, Crooked River Bridge, and Mount Hood, with more discussions of geology, geothermal resources, and geothermal exploration in Oregon.
An introduction to the stratigraphy, structural geology, and hydrogeology of the Columbia River Flood-Basalt Province
Authors: Tolan Terry L. , Martin Barton S. , Reidel Stephen P. , Anderson James L. , Lindsey Kevin A. , Burt Walter
Published: April 2010

The Miocene Columbia River Basalt Group (CRBG) covers a large part of Oregon, Washington, and Idaho and is one of the youngest and perhaps the best studied flood-basalt province on Earth. Decades of study have established a regional strati-graphic framework for the CRBG, have demonstrated the CBRG flows can be correlated with dikes and vents, have documented a wide variety of physical features within the CRBG flows, and have demonstrated that many characteristics of the CRBG are recognizable throughout its extent. Detailed studies of individual flows and their feeder dikes have allowed the development of models for the emplacement of voluminous basaltic lava flows. The interplay between the regional structure, contemporaneous deformation, preexisting topography, and paleodrainage systems helped to control the emplacement of individual CRBG flows. These features have also affected the nature of late Neogene sedimentation in the region covered by basalt flows. Finally, the distribution of sediments within the CRBG and the character of the intraflow and interflow structures have played a significant role in the development of aquifers within the CRBG. In this paper we present an overview of the regional aspects of the stratigraphy, structural geology, tectonics, and hydrogeology of the CRBG.
Factors associated with incorrect bicycle helmet use
Authors: Hagel B E , Lee R S , Karkhaneh M , Voaklander D , Rowe B H
Published: April 2010

Background

Incorrect bicycle helmet use increases head injury risk.

Objective

To evaluate the patterns of incorrect helmet use based on unobtrusive field observations.

Methods

Two observational surveys conducted in Alberta in 2000 and 2006 captured information on cyclist characteristics, including correct helmet use. Prevalence of correct helmet use was compared across multiple factors: age, gender, riding companionship, and environmental factors such as riding location, neighbourhood median family income, and region. Poisson regression analysis was used to relate predictor variables to the prevalence of incorrect helmet use, adjusting for clustering by site of observation.

Results

Among helmeted cyclists (n=5862), 15.3% were wearing their helmet incorrectly or were using a non-bicycle helmet. Children (53%) and adults (51%) tended to wear their helmet too far back, while adolescents tended not have their straps fastened (48%). Incorrect helmet use declined approximately 50% over the study period for children and adolescents, but 76% (95% CI 68% to 82%) in adults. Children were 1.8 times more likely to use their helmets incorrectly in 2000 compared with adults, but this effect increased to 3.9 (95% CI 2.9 to 5.4) in 2006. Adolescents were more likely to use their helmets incorrectly in 2006 compared with adults (prevalence ratio 2.76; 95% CI 1.9 to 4.02). Children and adolescents cycling alone, compared with adults cycling alone, cycling at non-school sites and cycling in Edmonton, was associated with incorrect helmet use.

Conclusions

Important factors not previously identified were associated with incorrect bicycle helmet use. This information can be used to target interventions to increase correct use.
Accuracy of self-report of on-road crashes and traffic offences in a cohort of young drivers: the DRIVE study
Authors: Boufous Soufiane , Ivers Rebecca , Senserrick Teresa , Stevenson Mark , Norton Robyn , Williamson Ann
Published: April 2010

In order to determine the accuracy of self-report of on-road crashes and traffic offences among participants in the DRIVE study, 2991 young drivers in New South Wales, Australia who completed the follow-up questionnaire were asked whether they had been involved in an on-road crash or were convicted for a traffic offence while driving during the year prior to the survey. This information was linked to police crash data to determine the level of accuracy of self-report of on-road crashes. There was a high level of accuracy in young drivers' self-report of police recorded crashes (85.1%; 95% CI 78.2% to 92.1%) and of police recorded traffic offences (83.0%; 95% CI 79.4% to 86.6%).

Results suggest that surveys may be useful tools for estimating the incidence of on-road crashes and traffic offences in young drivers. The findings are particularly relevant to jurisdictions where access to administrative data is limited.
A FULLY QUANTUM METHOD OF DETERMINATION OF PENETRABILITY AND REFLECTION COEFFICIENTS IN QUANTUM FRW MODEL WITH RADIATION
Authors: MAYDANYUK SERGEI P.
Published: April 2010

In the paper the closed Friedmann–Robertson–Walker model with quantization in the presence of the positive cosmological constant and radiation is studied. For analysis of tunneling probability for birth of an asymptotically de Sitter, inflationary universe as a function of the radiation energy, a new definition of a "free" wave propagating inside strong fields is proposed. On such a basis, tunneling boundary condition is corrected, penetrability and reflection relative to the barrier are calculated in fully quantum stationary approach. For the first time nonzero interference between the incident and reflected waves has been taken into account which turns out to play important role inside cosmological potentials and could be explained by non-locality of barriers in quantum mechanics. Inside the whole region of radiation energy the tunneling probability for the birth of the inflationary universe is found to be close to its value obtained in the semiclassical approach. The reflection from the barrier is determined for the first time (which differs essentially on 1 at the energy of radiation close to the barrier height). The proposed method could be easily generalized on the cosmological models with barriers of arbitrary shape, as demonstrated for the FRW model with included Chaplygin gas. The result is stable for variations of the studied barriers, accuracy is found to be 11–18 digits for all coefficients and energies below the barrier height.
Historical overview of exploration of Tertiary plays in the UK North Sea
Authors: BAIN J. S.
Published: April 2010

This paper primarily discusses those Tertiary (Paleocene and Eocene) plays and trapping mechanisms that have proved successful over the 22 years to 1990 since oil was first discovered in the UK North Sea in 1969. These successful traps (both structural and stratigraphic) are illustrated by seismic sections, uninterpreted pre-drilling and interpreted post-drilling. As well as discussing these discoveries, some of the risks associated with the more subtle stratigraphic traps are addressed.

A field size distribution of hydrocarbons in place for these discoveries in the area is presented, illustrating the rewards found to date. A brief reference is made to what the future potential may be for Tertiary prospectivity in the UK North Sea.
Log-motif analysis of Paleogene oppositional systems tracts, Central and Northern North Sea: defined by sequence stratigraphic analysis
Authors: ARMENTROUT J. M. , MALECEK S. J. , FEARN L. B. , SHEPPARD C. E. , NAYLOR P. H. , MILES A. W. , DESMARAIS R. J. , DUNAY R. E.
Published: April 2010

Sequence stratigraphic analysis of North Sea Eocene and Paleocene seismic-reflection profiles and well data provides examples of lowstand, transgressive and highstand systems tracts, including the ‘basin-floor thick’, ‘slope thick’ and prograding-wedge facies of the lowstand systems tract. This study was initiated to evaluate the interpretation methodology, refine the biostratigraphic control and test the Vail–Exxon depositional model prior to undertaking a more regional study. The primary data consisted of 4200 km of multifold seismic reflection profiles distributed in a 20 km grid, calibrated using log suites from 45 wells including 37 with biostratigraphic data. Thirty-two micropalaeontologic bioevents from top Cretaceous to top Eocene were evaluated. Twenty-three bioevents were identified as useful chronostratigraphic markers and were used to constrain both well-log and seismic reflection profile correlations. In general, the mapped systems tracts are more spatially separated than suggested by the diagrammatic Vail–Exxon model and require biostratigraphic correlation to confirm temporal relationships. Many of the lowstand systems tracts appear to be line-sourced by several sediment-supply systems. Ten Paleocene and Eocene sequences were recognized in this study, compared to 22 on the Cenozoic cycle chart. The remaining 12 Cenozoic sequences are either absent or are coalescent and below the resolution of this study.
Stratigraphic evolution of sand provenance during Paleocene deposition in the Northern North Sea area
Authors: MORTON A. C. , HALLSWORTH C. R. , WILKINSON G. C.
Published: April 2010

A garnet geochemical study of Paleocene sandstones in the Northern North Sea has enabled the definition of six mineralogical units. The boundaries between these units are consistent with biostratigraphic events, indicating that they can be correlated on a regional basis. The units reflect marked changes in sediment provenance resulting from variations in the interplay between three source areas, all of which lay on the East Shetland Platform: the northern part of the platform provided first-cycle metamorphic detritus, whereas the central and southern parts provided two different suites derived from Paleozoic or Mesozoic sandstones. Both local tectonism and relative changes in sea-level controlled the changes in provenance and generated the markedly different regional geometries shown by the six units.
The role of Paleocene magmatism in the Tertiary evolution of basins on the NW seaboard
Authors: ENGLAND R. W. , BUTLER R. W. H. , HUTTON D. H. W.
Published: April 2010

The presence of magma within a sedimentary basin can have positive effects on its maturation history, and adverse effects which make imaging the basin structure difficult. Gravity data were modelled to image parts of the Sea of the Hebrides Basin not visible on seismic due to reflective near-surface igneous rocks. Magmatism in the Sea of the Hebrides Basin was short-lived (<5 Ma), but resulted in localized extension of up to 20% by dyke emplacement. The high strain rates are the result of two factors: softening of crustal rocks as a result of increased heat flow; and the development of a linked system of dykes, sills and faults which dissipated variations in strain with depth within the lithosphere. The absence of a relationship between igneous structure and existing basin structure suggests that magmatism may play a similar role in the development of the Faeroe–Shetland Trough and North Shetland Trough, which have similar igneous structures to the Hebrides Basin. Central volcanic complexes in the Hebrides Basin are surrounded by zones of enhanced source rock maturity. Minor intrusions appear to have had little effect on thermal histories due to the incremental nature of their emplacement and the presence of pore waters in the sediments. The large number of variables involved makes it difficult to predict the thermal effects of magmatism in different basins.
Sandstone architecture of the Balder Formation depositional system, UK Quadrant 9 and adjacent areas
Authors: TIMBRELL G.
Published: April 2010

Within UK Quadrant 9 and adjacent areas, several recent hydrocarbon discoveries have been made in the Upper Paleocene Balder Formation. These sandstones were deposited mainly from high-density turbidity currents and have a complex geometry making them a difficult exploration target. However, the Balder Sands are considered to hold significant remaining oil and gas potential in what is now considered a ‘mature’ area. Detailed geoseismic studies have enabled a regional sub-surface model to be generated. The overall geometry of the system can be compared to that of a prograding slope produced by the aggradation of depositional channel systems. Moreover, similarities are observed with the Valencia margin off southeast Spain where large-scale erosive and depositional channel systems are recognized. The regional architecture is further compared to the Lowstand Wedge systems tract of Posamentier and Vail.
Origin of complex mound geometry of Paleocene submarine-fan sandstone reservoirs, Balder Field, Norway
Authors: JENSSEN A. I. , BERGSLIEN D. , RYE-LARSEN M. , LINDHOLM R. M.
Published: April 2010

The Balder Field is located on the northwestern margin of the Utsira High in Norwegian Blocks 25/10 and 25/11. The oil is trapped in thick massive submarine-fan sandstones of the Paleocene Heimdal and Hermod Formations and the Early Eocene Balder Formation. These sandstones which were deposited from high-density turbidity currents originating from the East Shetland Platform, are located close to the Paleocene sandstone pinch-out and form thick mounded reservoirs in the field. High-relief mounded geometries are believed to have been caused by a complex interaction between deposition and syn- and post-depositional soft-sediment deformation processes. Slumping, sliding and sand remobilization were the dominant deformational processes. Associated sand injections into overlying shales occurred during the soft-sediment deformation processes which dominantly occurred during Early Eocene. The sandstones which have excellent reservoir properties, appear to be in pressure communication and have a common oil-water contact which is probably related to the soft-sediment deformation processes with associated sand injections.
The Alba Field: evolution of the depositional model
Authors: NEWTON S. K. , FLANAGAN K. P.
Published: April 2010

The Alba Field; discovered in 1984 by Well 16/26-5, is situated in UK Block 16/26, approximately 225 km northeast of Aberdeen. The field overlies the Mesozoic Witch Ground Graben, south of the Fladen Ground Spur, and north of the Renee Ridge. The main field is 9 km in length, elongate along a northwest-southeast axis. Field delineation was based upon 2D seismic data, the latest of which were acquired in 1988. Sixteen wells, inclusive of sidetracks, have been drilled to appraise the 16/26-5 discovery. Annex B approval was granted in 1991, and first oil production is expected in 1993.

The Middle Eocene sands which comprise the reservoir at Alba display remarkable petrographic uniformity, and are thought to have been deposited by high-density turbidity currents. The presence of water-escape structures and sand injection features suggests rapid deposition and burial.

Previous workers have favoured deposition of the reservoir sands within an aggradational channel/levee complex. This model was reviewed by the current authors to assess possible variations of sand quality and shale distribution, and their impact on reservoir performance. A revised model, based on interpretation of a 3D seismic survey acquired in 1989, re-examination of core, and a comprehensive review of recent literature on deep-water depositional processes, proposes that high-density turbidity currents rapidly deposited large volumes of petrographically uniform sand into a previously eroded channel-like feature. The erosional and depositional processes are interpreted to have been largely independent of one another.
Jurassic exploration history: a look at the past and the future
Authors: CORDEY W. G.
Published: April 2010

The Groningen gas discovery in 1959 was the starting point for exploration of the North Sea basin. A decade later, the Ekofisk oil discovery set into motion the exploration of the Northern North Sea.

The critical discovery on the United Kingdom Continental Shelf (UKCS) of oil in the Paleocene of the Forties Field was in 1969. This was quickly followed in 1971 by the Brent discovery of oil in Middle Jurassic sandstones. Following on from the UKCS Fourth Round acreage awards, Jurassic exploration, in what was later to become known as the Brent Province, rapidly accelerated so that in the space of some 5 years, a succession of world ranking discoveries were made. As a consequence, of the 40 billion barrels of hydrocarbon discovered in the UKCS, almost half occurs in the Jurassic.

A number of these discoveries are regarded as ‘milestones’ in Jurassic exploration: Brent, as the first Jurassic discovery, was followed by Magnus, the first discovery in deep water Upper Jurassic sediments; Brae opened up the Upper Jurassic submarine fan play; Piper, together with Claymore, were the major discoveries that presaged a string of successes in the Witch Ground Graben area in Upper Jurassic sands ranging from shallow marine to turbiditic in origin; finally, the Fulmar discovery in Upper Jurassic shallow marine sands saw the prolific Jurassic play extended into the Central Graben.

The remaining exploration potential is likely to be concentrated in the Outer Moray Firth, but more especially within the Central Graben with the Fulmar-type sands continuing to provide a main objective.

The rapidly extending 3D seismic coverage will necessitate a reappraisal of much old well data. There will be an increasing need to devise means to exploit the many Jurassic discoveries which remain undeveloped.
Sequence stratigraphic control on Middle and Upper Jurassic reservoir distribution within the UK Central North Sea
Authors: DONOVAN A. D. , DJAKIC A. W. , IOANNIDES N. S. , GARFIELD T. R. , JONES C. R.
Published: April 2010

An integrated sequence stratigraphic analysis, utilizing seismic data, well-log cross-sections, biostratigraphic information, and core descriptions, provides a chronostratigraphic framework to analyse and predict the distribution of reservoir sandstones within the Middle to Upper Jurassic section of the UK Central North Sea.

The Callovian (Middle Jurassic) through Ryazanian (lowermost Cretaceous) section in the UK Central North Sea forms a depositional wedge that thins towards the western graben margin. This wedge is bounded by surfaces traditionally interpreted as the Middle Cimmerian and Late Cimmerian unconformities. Marginal marine (Fulmar) sandstones are present within this wedge, and can be subdivided into informal lower and upper Fulmar members. Each member has a unique spatial and temporal distribution within the basin that can be related to primary depositional palaeogeography, post-depositional erosion, and basin tectonics.

The lower member of the Fulmar Formation is Callovian to Early Oxfordian in age, and is restricted to the Central Graben. This member overlies Middle Jurassic strata of the Pentland Formation, and is conformably overlain by Oxfordian-age strata of the Kimmeridge Clay. The upper member of the Fulmar Formation is Early Kimmeridgian in age, and is distributed along the western graben margin. The upper member is conformably overlain by Kimmeridgian-age strata of Kimmeridge Clay, and typically overlies Triassic deposits of the Skagerrak Formation.

Post-depositional erosion, association with relative falls in sea-level and accentuated by basement and salt tectonism, is the major factor that modifies primary depositional patterns within the Fulmar Formation. Truncation associated with unconformities interpreted as the 142 Ma, 138 Ma, and 136 Ma sequence boundaries affect the distribution, fades patterns, and thickness of the upper member of the Fulmar. These unconformities, as well as the 155.5 Ma, 150.5 Ma and 144 Ma sequence boundaries, may also affect the lower member of the Fulmar.
Application of sequence stratigraphy and trace fossil analysis to reservoir description: examples from the Jurassic of the North Sea
Authors: TAYLOR A. M. , GAWTHORPE R. L.
Published: April 2010

Recent sequence stratigraphic schemes proposed for the North Sea Jurassic have been developed primarily as exploration tools to predict reservoir distribution away from well control. As a result, most of these schemes are at the megasequence and depositional sequence scale. In field-scale studies where significant core is available, integration of trace fossil studies with other available correlation data (sedimentological, biostratigraphic, seismic, well log) can increase the precision and resolution of the sequence stratigraphic framework so that it is applicable to development and production problems.

Trace fossils effectively provide an in situ record of environment and environmental change. They can be used to identify depositional facies and facies shifts, as indicators of salinity change, as direct indicators of stratal surfaces and condensed sections, and in evaluating the significance of palaeosols. This often allows stratal surfaces to be identified where other data fail (e.g. tracing marine flooding surfaces into the coastal plain and offshore shelf) and provides a way of tackling highly bioturbated shallow marine reservoirs.

On a field scale, parasequence correlation is usually at a higher resolution than biostratigraphy and provides a deterministic approach to the evaluation of sandbody architecture and permeability barrier geometry. Such a sequence stratigraphic framework is crucial to (i) identifying field-wide permeability barriers (e.g. marine shales and cemented zones associated with marine flooding surfaces); (ii) understanding the stacking pattern, connectivity and anisotropy of reservoir sandbodies; and (iii) identifying horizons of incision (sequence boundaries) which may erode through units that would otherwise form field-wide permeability barriers. High-resolution, field-scale sequence stratigraphy thus provides a framework for prediction of reserves, reservoir simulation and field development planning.

Case studies from (i) the Halten Terrace (Lower to Middle Jurassic); and (ii) the Central Graben area (Upper Jurassic), both from the Norwegian Continental Shelf, are presented to illustrate the use of high-resolution sequence stratigraphy in the stratigraphic description of hydrocarbon fields.
Miller Field: reservoir stratigraphy and its impact on development
Authors: GARLAND C. R.
Published: April 2010

The Miller Field lies in UKCS Blocks 16/7b and 16/8b adjacent to the South Brae Field, and its reservoir is a high net-to-gross system of fine- to medium-grained turbiditic sandstones, interbedded with thin mudstones, which was deposited as part of an extensive submarine fan complex of Late Jurassic age, along the margin of the South Viking Graben. Recent studies of sequence stratigraphy in the area have contributed to a better understanding of the elements of the submarine fans, and, coupled with detailed biostratigraphy, have enabled the reservoir units to be correlated across the field with a fair degree of confidence. Pressure data have been incorporated into these studies. While detailed geophysical interpretation continues, a geological reservoir description has been used to map rock properties and reservoir connectivity across the field, and to indicate areas of greatest uncertainty. These uncertainties will be reduced as further data become available during production.
Effective stratigraphical subdivision of the Humber Group and the Late Jurassic evolution of the UK Central Graben
Authors: PRICE J. , DYER R. , GOODALL I. , McKIE T. , WATSON P. , WILLIAMS G.
Published: April 2010

New biostratigraphical analysis of the Humber Group sediments from the UK North Sea Central Graben, using integrated palynological and micropalaeontological zonation schemes, allows substage resolution and basin-wide discrimination of subunits of the Heather Formation/Kimmeridge Clay Formation, and associated sandstones. The integrated use of both zonation schemes is particularly important because thermally mature Humber Group sediments buried below 12 000 ft in the Central Graben cannot be dated consistently to substage level using palynology alone. Poor data and the undiagnostic log character of the mudstones and shallow marine sandstones have resulted in a simple lithological scheme being widely applied, with all sandstones assigned to the Fulmar Formation and mudstones to the Heather Formation and the Kimmeridge Clay Formation. Previous generalized usage of the Fulmar Formation for all Upper Jurassic shallow marine sandstones is inappropriate. The Upper Oxfordian Puffin Formation is present in the northern and western Central Graben. The largely Kimmeridgian Fulmar Formation is restricted to the south and east, and the coeval Ula Formation flanks the Jæren High. These three units are all interpreted as syn-rift sandstones, locally sourced from uplifted and eroded fault block crests within and marginal to the Central Graben. Latest Kimmeridgian or younger shallow marine sandstones are largely confined to platform areas outside the graben, and can be related to regressive phases.
Late Jurassic plays along the western margin of the Central Graben
Authors: WAKEFIELD L. L. , DROSTE H. , GILES M. R. , JANSSEN R.
Published: April 2010

The distribution of the Lower Kimmeridgian Fulmar sands along the edge of the Western Platform of the Central Graben is intimately related to Triassic halokinetic activity. Withdrawal of Zechstein evaporites resulted in the development of thick packages of Triassic Smith Bank claystones, the so-called ‘Smith Bank Pods’. The crests of the Zechstein evaporite highs were later subjected to groundwater dissolution, resulting in topographic lows, which controlled the pattern of drainage during the deposition of the Triassic Skagerrak sands.

The Triassic salt movements associated with this phenomenon also exercised the underlying control on later drainage patterns in the Jurassic. The relative sea-level rise in the Early Kimmeridgian flooded the margin of the Western Platform which reworked the original valley fill and, together with erosion products from the hinterland, resulted in the deposition of the shallow marine sands of the Fulmar Formation.

3D seismic can reveal the extent of these palaeovalley systems draining into the Central Graben. The Fulmar sand packages are effectively encased in shales; a lateral seal is formed by the Smith Bank Formation and the top seal consists of Kimmeridgian shales. They represent an attractive possibility for stratigraphically trapped hydrocarbons.
Appraisal geology of the Saltire Field, Witch Ground Graben, North Sea
Authors: CASEY B. J. , ROMANI R. S. , SCHMITT R. H.
Published: April 2010

Saltire is a structurally and stratigraphically complex field that lies within the Witch Ground Graben. It is located 200 km northeast of Aberdeen, Scotland in UK North Sea Block 15/17. Three sandstone reservoirs contain an estimated 224 × 10
6
BBL of oil-in-place within a 2500 acre closure.

The field was discovered in 1988. Subsequent appraisal drilling incorporated 3D seismic and detailed stratigraphic studies to produce the coherent geological reservoir models needed for development planning. Field production will begin in 1993.

The Upper Jurassic section contains the Piper and Galley sandstone reservoirs which occur within a broad, E-W-orientated fault terrace. Northerly closure results from a down-to-the-south normal fault. Southern and westerly closures result from Piper sandstone erosional truncation and Galley sandstone pinch-out. Both reservoirs have easterly dip closure.

The Piper Formation is a fluvial to wave-influenced deltaic marine sequence of latest Oxfordian to mid-Kimmeridgian age. It is up to 280 ft thick. The reservoir is fault separated into Main and Western areas with API oil gravities of 42.5° and 38°, respectively.

The Galley sandstone reservoir contains 42.5° API gravity oil and occurs within the northeast area. It is a deep marine turbidite sequence of late Kimmeridgian age and has a maximum reservoir thickness of 205 ft.

An Early Cretaceous sandstone reservoir occurs within the upper Valhall Formation. It comprises two marine turbidite sandstones of late Barremian to early Aptian age, with up to 95 ft of composite thickness. The reservoir has three-way dip closure, pinches out by onlap to the north and contains 33° API gravity oil.
Salt control on Triassic reservoir distribution, UKCS Central North Sea
Authors: SMITH R. I. , HODGSON N. , FULTON M.
Published: April 2010

During Triassic deposition in the Central North Sea, synforms developed on the surface of the extending Zechstein salt. In the ensuing continental environment, coarse-grained clastic sediments were deposited in such depressions. These were later preserved as sediment ‘pods’. A progressive increase in coarse clastic input to the Central North Sea Basin during the Triassic was concurrent with continued salt movement and pod subsidence. During Late Triassic times the best initial reservoir quality sands were developed in the axes of TR30 sediment pods (e.g. Marnock facies). Early Fe-rich chloritization of these high-quality reservoir facies, combined with overpressure development, has resulted in the subsequent, relatively local, preservation of high-quality Triassic reservoirs, often at substantial depths.

Understanding the basin-scale halokinetic controls on Triassic sequence and facies development, as well as the subsequent diagenetic effects, is crucial to establishing a framework for Triassic reservoir prediction.

We have combined the re-interpretation of newly acquired and reprocessed seismic data with sedimentological and diagenetic studies of available core material. This has enabled the generation of a model for evaluating the distribution of Triassic reservoir and hence exploration potential in the Central North Sea.
Low-angle faulting in the Triassic of the South Viking Graben: implications for future correlations
Authors: MORGAN R. K. , CUTTS P. L.
Published: April 2010

A detailed study of bedding geometry in the Triassic strata of the Crawford Field, South Viking Graben, has revealed steep-bedding dips, in excess of 40° towards the west, sandwiched between Permian and Middle Jurassic to Cretaceous strata dipping gently eastwards. Reconstructions show an area of Triassic strata to be cut out at a high angle against the underlying Permian. This bedding geometry has been interpreted to indicate the presence of a detachment horizon towards the top of the Permian section onto which faulting within the Triassic has flattened. This faulting is pre-Middle Jurassic in age and affects the entire Triassic section in the region of the Crawford Field. The extent of bedding rotation is such that a considerable thickness of Triassic section has been cut out against the fault and detachment surface.

The formation of planar shear fractures is associated with faulting in the Triassic strata. Most of these fractures parallel the fault trend and are interpreted to have formed during the early stages of fault movement, as they presently dip at a low angle towards the east. Cataclastic processes have dramatically reduced porosity along the fractures which may now represent permeability baffles.

Recognition of this intra-Triassic structure means fault and roll-over geometries must be carefully modelled before any attempt at stratigraphic correlation within the Triassic can be made. Equally, if this style of faulting is more widespread, then areas of Triassic strata previously considered internally ‘uncorrectable’ may well benefit from a closer examination of bedding attitude and structure.
Clay mineral stratigraphy of Mesozoic and Paleozoic red beds, Northern North Sea
Authors: GLASMANN J. R. , WILKINSON G. C.
Published: April 2010

Differences in the clay mineralogy and stable isotope geochemistry of Triassic, Permian and Devonian red beds in UK Quadrant 9 aid in distinguishing samples of different age and provide a basis for delineating stratigraphic position during drilling of these unfossiliferous units. Triassic red beds are characterized by the presence of expandable clays (smectite and illite/smectite), kaolinite, illite and chlorite. Smectitic and kaolinitic samples are isotopically heavy (δ
18
O = 18.7–20.7‰) and probably represent clays formed near the earth’s surface from circulating meteoric water. The illite, mixed-layer illite/smectite (I/S), chlorite clay assemblage is isotopically lighter (δ
18
O = 16.7‰) and probably formed during burial diagenesis at elevated temperatures. The clay mineral assemblage of Permian Rotliegendes red beds is characterized by the presence of illite, ordered interstratified illite/smectite, kaolinite (shallow samples) and chlorite. Devonian red beds in Quadrant 9 are characterized by an isotopically light (δ
18
O = 14.5‰) illite-chlorite clay mineral assemblage, in conjunction with accessory albite and calcite. Clay geothermometry suggests that the mineralogy of Devonian red beds developed by metamorphic alteration and was either inherited from metamorphic provenance, or developed diagenetically during the Caledonian orogenesis. Clay crystal morphology provides additional criteria for distinguishing different-aged red beds: Triassic clays contain extremely small plates and laths of smectite or small plates of illite and chlorite; Permian red beds contain abundant lath-shaped and platy illite; Devonian red beds are dominated by coarse recrystallized mica and chlorite and lack lath-shaped or small dispersed crystallites.
Late Paleozoic plays in East Greenland
Authors: CHRISTIANSEN F. G. , LARSEN H. C. , MARCUSSEN C. , PIASECKI S. , STEMMERIK L.
Published: April 2010

A series of Late Paleozoic–Mesozoic basins, which formed as the result of rifting between Greenland and Norway following the Caledonian orogeny, are exposed in East Greenland between 70° and 76°N. The Paleozoic part of the sedimentary basin fill has a cumulative thickness of up to 13 km.

The region seems prospective but exploration is still at an early stage without exploration wells. Basic petroleum-related studies of outcrops have been carried out throughout the region, and 1800 km of high-quality multi-fold seismic data have been acquired in Jameson Land between 70° and 72°N.

A number of pre-, syn- and post-rift play types are suggested on the basis of inferred source and reservoir rock distribution as well as structural and thermal history. Some of the play concepts have been identified in outcrop, others have been recognized during the seismic interpretation.

The principal Upper Paleozoic source rocks include Upper Devonian shales (freshwater), Upper Carboniferous lacustrine shales (freshwater to slightly saline), and Upper Permian marine shales (some carbonate influence). The main reservoir facies are fluvial sandstones in the Upper Devonian to Lower Permian succession and Upper Permian platform and build-up carbonates.

Syn-rift Carboniferous plays (mainly structural) and post-rift Upper Permian carbonate plays (essentially stratigraphic) seem most promising. The syn-rift plays have lacustrine shales as source rocks, fluvial Carboniferous to Lower Permian sandstones as reservoirs, and overlying fluvial/lacustrine shales as seal. The post-rift Upper Permian plays have carbonate build-ups and platforms as reservoir targets and the juxtaposed marine shales as source rock and seal.
Carboniferous depositional systems of the Southern North Sea
Authors: COLLINSON J. D. , JONES C. M. , BLACKBOURN G. A. , BESLY B. M. , ARCHARD G. M. , McMAHON A. H.
Published: April 2010

A study of the Carboniferous sequences in some 93 wells from onshore England to onshore Netherlands has provided data on variations of depositional styles, sandbody dimensions and petrographic composition, both through time and, in the Upper Carboniferous, across the basin. Three separate sources of sediment input are recognized: a dominant, and petrographically fairly uniform, north to south-flowing sediment distribution system which shows a general southerly decrease in channel sandbody size and abundance; a less important source on the Anglo-Brabant Massif; and a probable third source in SE Holland.

Through time, there was a progressive increase in petrographic maturity, while channel sandbody percentages decrease to a minimum in the Westphalian B and then begin to increase again through the Westphalian C and D. Compared to the UK onshore, there is a close similarity between the Dinantian successions on the Mid North Sea High and in the Northumberland Basin and marked contrasts in sedimentation styles between the offshore Red Beds sequences in the centre of the basin and those seen onshore in the English Midlands. Regional mapping of channel sandbody statistics for different stratigraphic intervals could guide future exploration efforts towards areas with greater reservoir potential.
The evolution and hydrocarbon potential of the Northumberland–Solway Basin
Authors: CHADWICK R. A. , HOLLIDAY D. W. , HOLLOWAY S. , HULBERT A. G.
Published: April 2010

Seismic and well data establish the three-dimensional geometry and structural evolution of the Northumberland–Solway Basin. The basin-controlling southerly bounding normal faults, the E–W-trending Maryport–Stublick–Ninety Fathom fault system, formed in early Carboniferous times by extensional reactivation of a major basement thrust zone. The faults are sub-planar with a present-day throw (at the base of the Carboniferous) of <4 km. Other important Dinantian syn-sedimentary normal faults trend roughly NNE-SSW and suffered dominantly oblique-slip displacements. Extension and syn-sedimentary faulting accompanied deposition of the Lower and Middle Border groups. Thereafter, until late Westphalian times, sedimentation was mainly in response to regional thermal relaxation subsidence. The maximum thickness of Carboniferous rocks ranges from around 5000 m in the Northumberland Trough to about 7000 m in the Solway Basin. At the end of Carboniferous times, the basin was partially inverted by Variscan transpression, with preferential reversal of the NNE-trending faults and the development of major monoclinal and anticlinal folds. Locally, there is evidence of embryonic syn-depositional folding in late Namurian times. In the Solway area, a Permo-Triassic to Jurassic succession, locally over 1.5 km thick, rests with marked angular unconformity on the Carboniferous strata. The argillaceous rocks of the basin commonly have high TOC values but are dominantly gas prone. The reservoir potential of the interbedded limestones and sandstones is poor. Most strata at outcrop are in the oil window, but in some boreholes, or where the rocks have been metamorphosed by the Whin Sill, overmature values have been recorded. Peak hydrocarbon generation was in late Westphalian times, prior to inversion, although some post-Variscan generation is possible in the Solway area, where there are oil and gas shows.
Structural and sedimentological controls on diagenesis in the Ravenspurn North gas reservoir, UK Southern North Sea
Authors: TURNER P. , JONES M. , PROSSER D. J. , WILLIAMS G. D. , SEARL A.
Published: April 2010

The Rotliegend Lower Leman Sandstone Formation has been studied near the northern limit of its development in Ravenspurn North to determine the influence of structure, sedimentology and diagenesis on reservoir quality. The Lower Leman Sandstone in this area is about 300 ft thick and comprises six depositional cycles which reflect alternating periods of relatively dry and wet climate. Aeolian sands form the best reservoir and formed as small westward-migrating transverse dune fields and draa, at most 60 ft thick. These dunes were frequently reworked by southerly derived, strong fluvial sheetfloods which drained into the Silverpit playa lake.

The Ravenspurn area is divided into main northwest-southeast-trending fault blocks which are markedly different in terms of their diagenetic evolution and reservoir performance. The northeasterly B structure contained gas earlier and was unaffected by mid- to late Jurassic illitization. The southwesterly A structure was uplifted later and received accumulated gas after reservoir quality was reduced by pervasive illitization.

A hierarchy of factors influenced the diagenesis. These were the primary lithological variation, burial history and the structural development of the Ravenspurn North area. Depositional processes also influenced diagenesis; the deposition of allogenic clay and the formation of early quartz, non-ferroan dolomite and anhydrite reduced the reservoir quality of fluvial sheetfloods. Burial diagenesis resulted initially in ferroan dolomite, kaolinite and later quartz precipitation in available primary and secondary porosity. Stable isotope and fluid inclusion studies indicate that ferroan dolomite and later quartz precipitated at about 100°C in Triassic-early Jurassic times from reduced fluids derived partly from the Carboniferous basement. Mixing of these fluids with more alkaline connate water was the main triggering mechanism for authigenic mineral formation.

Gas accumulation took place first in the northeasterly B structure which had early closure; the last authigenic phase to precipitate here was poikilotopic siderite at temperatures of about 120°C. Elsewhere diagenetic fluids evolved to a more alkaline state and widespread illitization took place which particularly affected more permeable aeolian facies. The illitization reduced the reservoir quality of the Lower Leman Sandstone and contributed to diagenetic sealing (to the northwest) of the field. K–Ar dating indicates that peak illitization took place between 150–170 Ma (mid–late Jurassic). Subsequent periods of uplift in the late Cimmerian and particularly during the early Tertiary–Miocene produced the final structure of Ravenspurn North and the spillage of gas into this structure. The combination of structural and diagenetic events explains the differences in reservoir quality and well performance of the two structural blocks in the field.
Geochemical modelling of the East Irish Sea Basin: its influence on predicting hydrocarbon type and quality
Authors: HARDMAN M. , BUCHANAN J. , HERRINGTON P. , CARR A.
Published: April 2010

A number of oil discoveries have been made in recent years in the East Irish Sea Basin (EISB). These have renewed industry interest in a basin which many thought to be essentially gas prone. British Gas, over a number of years, has developed and refined a basin model for the area based upon in excess of 23 000 km of seismic data and 40 wells. This model shows that the present-day distribution of oil and gas is controlled by complex interrelationships between the thermal and tectonostratigraphic history of the EISB. An integrated approach has been adopted in creating the model, which includes data generated from many sources including AFTA, detailed diagenetic and geochemical studies and more conventional geological, geophysical, and petrophysical analysis. The paper will address several aspects of the current basin model, including oil–source rock correlation, the origins of hydrogen sulphide within the EISB, and the problems and solutions in validating a basin model when so much of the rock record is missing.
The Fleetwood Dyke and the Tynwald fault zone, Block 113/27, East Irish Sea Basin
Authors: ARTER G. , FAGIN S. W.
Published: April 2010

A series of Tertiary dolerite intrusions, the Fleetwood Dyke Group, is intruded into Triassic sediments of the northern East Irish Sea Basin (EISB). Well 113/27-1 penetrated a total of 375 m of dolerite within the Mercia Mudstone Group (MMG). Samples of dolerite have been dated (K–Ar) at between 61 and 65 Ma. Apatite fission track analysis on samples from the same well indicates that approximately 2000 m of uplift occurred in the early Tertiary, at about the same time as dyke intrusion.

Using seismic and marine magnetic data, the Fleetwood Dyke Group has been mapped in the vicinity of Block 113/27 to reveal a complex set of dykes and sills. The presence of these intrusions within the MMG results in velocity pull-ups on the underlying Ormskirk Sandstone Formation (OSF), a potential exploration pitfall.

The geometry of the igneous intrusion has been influenced by the structure of the Tynwald fault zone. This feature is interpreted to have formed in the Triassic as a result of listric faulting detached on Permian evaporites. This interpretation is supported by balanced section reconstruction.