bluuebunny/crossref_metadata_2025_split huggingface dataset:
Role of the Chalk in development of deep overpressure in the Central North Sea
Authors: Swarbrick R. E. , Lahann R. W. , O'Connor S. A. , Mallon A. J. 
Published: May 2011

Abstract

A high magnitude of overpressure is a characteristic of the deep, sub-Chalk reservoirs of the Central North Sea. The Upper Cretaceous chalk there comprises both reservoir and non-reservoir intervals, the former volumetrically minor but most commonly identified near the top of the Tor Formation. The majority of non-reservoir chalk has been extensively cemented with average fractional gross porosity of 0.08, and permeability in the nano- to microDarcy range (10
−18
–10
−21
m
2
), and sealing properties comparable to shale. Hence deeply buried chalk is comparable to shale in preventing dewatering and allowing overpressure to develop. Direct pressure measurements in the Chalk are restricted to the reservoir intervals, plus in rare fractured chalk, but reveal that Chalk pressures lie on a pressure gradient which links to the Lower Cenozoic reservoir above the Chalk and the Jurassic/Triassic reservoir pressures below. Hence a pore pressure profile of constantly increasing overpressure with increasing depth is indicated. Mud weight profiles through the Chalk, by contrast, show many borehole pressures lower than those indicated by these direct measurements, implying wells are routinely drilled underbalanced. The Chalk is therefore considered the main pressure transition zone to high pressures in sub-Chalk reservoirs. In addition to its role as a regional seal for overpressure, the Base Chalk can be shown to be highly significant to trap integrity. Analysis of dry holes and hydrocarbon discoveries relative to their aquifer seal capacity (the difference between water pressure and minimum stress) shows that the best empirical relationship exists at Base Chalk, rather than Base Seal/Top Reservoir, where the relationship is traditionally examined. Using a database of 65 wells from the HP/HT area of the Central North Sea, and extending the known aquifer gradients from the Fulmar reservoirs via Base Cretaceous to Base Chalk, leads to a risking threshold at 5.2 MPa (750 psi) aquifer seal capacity. Discoveries constitute 88% of the wells above the threshold and 36% below, with 100% dry holes where the aquifer seal capacity is zero (i.e. predicted breached trap). This relationship at Base Chalk can be used to identify leak points which control vertical hydrocarbon migration as well as assessing the risk associated with drilling high-pressure prospects in the Central North Sea.
Applying time-lapse seismic methods to reservoir management and field development planning at South Arne, Danish North Sea
Authors: Herwanger J. V. , Schiøtt C. R. , Frederiksen R. , If F. , Vejbæk O. V. , Wold R. , Hansen H. J. , Palmer E. , Koutsabeloulis N. 
Published: May 2011

Abstract

At South Arne a highly repeatable time-lapse seismic survey (normalized root-mean-square error or NRMS of less than 0.1) allowed us to reliably monitor reservoir production processes during five years of reservoir depletion. Time-lapse AVO (amplitude v. offset) inversion and rock-physics analysis enables accurate monitoring of fluid pathways. On the crest of the field, water injection results in a heterogeneous sweep of the reservoir, whereby the majority of the injected water intrudes into a highly porous body. This is in contrast to a pre-existing reservoir simulation model predicting a homogeneous sweep. On the SW flank, time-lapse AVO inversion to changes in water saturation Δ
S
w
reveals that the drainage pattern is fault controlled. Time-lapse seismic data furthermore explain the lack of production from the far end of a horizontal producer (as observed by production logging), by showing that the injected water does not result in the expected pressure support. On the highly porous crest of the reservoir compaction occurs. Time-lapse time shifts in the overburden are used as a measure for compaction and are compared with predictions of reservoir compaction from reservoir geomechanical modelling. In areas where compaction observations and predictions disagree, time-lapse seismic data give the necessary insight to validate, calibrate and update the reservoir geomechanical model. The information contained in time-lapse seismic data can only be fully extracted and used when the reservoir simulation model, the reservoir geomechanical model and the time-lapse seismic inversion models are co-visualized and available in the same software application with one set of coordinates. This allows for easy and reliable investigation of reservoir depletion and gives deeper insight than using reservoir simulation or time-lapse seismic individually.
Synchronous exhumation events around the Arctic including examples from Barents Sea and Alaska North Slope
Authors: Green P. F. , Duddy I. R. 
Published: May 2011

Abstract
In many areas of the Arctic, sedimentary sequences have been exhumed from significantly greater depths during the Cenozoic, with 2 km of section or more removed in some areas. Implications for exploration include enhanced maturity levels, possible loss of reservoired hydrocarbons as a result of seal breach, and phase changes due to pressure reduction. While the importance of Cenozoic exhumation to hydrocarbon prospectivity in individual basins is widely recognized, less well recognized is the regional synchroneity in the main phases of Cenozoic exhumation over wide areas of the Arctic and North Atlantic. Thermal history reconstruction studies in the Barents Sea and the Alaskan North Slope, based on application of apatite fission track analysis and vitrinite reflectance, reveal three main episodes of exhumation, in Paleocene, Eocene–Oligocene and Miocene times, and correlative exhumation episodes have been identified in a number of published studies in these and other areas. Previous attempts to explain these episodes of exhumation have been focussed on local mechanisms. However, our results reveal a pattern of regionally synchronous exhumation over a wide region, not only of the Arctic but also in many areas around the European North Atlantic margin, suggesting that events in each area are a regional response to events at plate boundaries, perhaps coupled to imbalances of crustal forces at continental boundaries. To date, no convincing mechanism has been put forward for producing such regional exhumation episodes, despite the fact that in many areas they exert critical control on regional hydrocarbon prospectivity. We suggest that serious attention should be directed to investigating the underlying mechanisms.
The hydrocarbon prospectivity of the Egyptian North Red Sea basin
Authors: Gordon G. , Hansen B. , Scott J. , Hirst C. , Graham R. , Grow T. , Spedding A. , Fairhead S. , Fullarton L. , Griffin D. 
Published: May 2011

Abstract
Recent work by a multi-disciplinary team has led to a significantly better understanding of the prospectivity of the North Red Sea. New regional biostratigraphic and environmental analysis from north to south through the Gulf of Suez and into the Red Sea have placed the Nubian sequences into a regional chronostratigraphic framework. The Nubian Upper Cretaceous pre-rift sandstones are observed in the field on both the Egyptian and Saudi Arabian side of the North Red Sea. This regionally extensive sequence was deposited in a continental to shallow marine setting fringing the Mesozoic Tethys Ocean, which lay further north. Extensive onshore fieldwork and mapping of sediment input points, fault orientations and fault linkages have helped to develop an understanding of the expected controls on syn-rift sandstone and carbonate deposition offshore. Thick halite with interbedded evaporite and clastics in the Late Miocene sequences of the Red Sea pose seismic imaging challenges. Recent reprocessing and newly acquired seismic data have produced a step change improvement in imaging of the prospective pre-rift section. Petroleum systems modelling incorporating new information on rift timing and crustal thinning as well as onshore core analysis for source rock properties and temperature variation through time indicates that oil expulsion occurs in the inboard section of North Red Sea – Block 1. This is supported by hydrocarbon shows in the drilled offshore wells which can be typed to pre-rift source rocks from stable isotope and biomarker data. All the key elements of the Gulf of Suez petroleum system exist in the North Red Sea. An integrated exploration approach has enabled prospective areas in the North Red Sea – Block 1 to be high-graded for drilling in early 2011.
Properties and distribution of lower crustal bodies on the mid-Norwegian margin
Authors: Reynisson R. F. , Ebbing J. , Lundin E. , Osmundsen P. T. 
Published: May 2011

Abstract
Anomalously high velocity and high density bodies have been detected in the lower crust on the mid-Norwegian margin. The lower crustal bodies (LCB) are pronounced on the Møre and Vøring margins segments and have mainly been interpreted as either magmatic or high-grade metamorphic in origin. Evolutionary models of the whole margin are heavily affected by the interpretation of the LCB and so are estimates of vertical movements and thermal structure in the area. A 3D gravity and magnetic model of the mid-Norwegian margin was constructed to map the main geological features of the margin and acquire the distribution of the LCB. The model utilizes the most recent potential field compilations on the margin and is constrained by extensive reflection seismic data and published refraction profiles. Further constraints on the model were attained from studying the isostatic state of the lithosphere. We present a map showing the distribution of the different LCB and discuss the implications for the structural and thermal evolution of the margin. The properties of the LCB vary across the margin and at least three different processes may be responsible for their existence. The LCB is commonly interpreted as igneous rock either intruded into the lower crust or underplated beneath it. The distribution of the LCB along the Vøring margin has an apparent correlation with the offshore prolongations of major onshore detachments stemming from Late Caledonian orogenic collapse. This may point towards some relation between the LCB and these old zones of weakness and that the LCB represents high-grade metamorphic rocks. Detailed modelling on the Møre margin shows a spatial link between parts of the LCB and extremely thin crustal thickness, suggesting a serpentinized exhumed mantle origin.
Source-to-sink systems on passive margins: theory and practice with an example from the Norwegian continental margin
Authors: Martinsen O. J. , Sømme T. O. , Thurmond J. B. , Helland-Hansen W. , Lunt I. 
Published: May 2011

Abstract
Source-to-sink system analysis involves a complete, earth systems model approach from the ultimate onshore drainage point to the toe of related active deepwater sedimentary systems. Several methods and techniques have evolved in recent years, from experimental and numerical modelling through analysis of modern and recent systems, to analysis of ancient systems. A novel method has been developed, bridging between the previous approaches and dividing and analysing source-to-sink systems based on linked geomorphic segments along the source-to-sink profile. This approach builds on uniformitarian principles. The method is driven by the need to understand ancient, subsurface systems and still has high uncertainty but is an original, first-order approach to source-to-sink system analysis. In modern systems, entire onshore-to-offshore systems can be analysed with a higher degree of confidence than in ancient systems and semi-quantitative relationships can be established. Application in ancient systems is much more challenging but, in some cases, antecedent morphologies have been preserved onshore that can be matched with offshore known occurrences of, for instance, sandy submarine fan systems. Along the Norwegian North Sea and Norwegian Sea margins the Paleocene deep-marine reservoir of the giant Ormen Lange gas field is such an example. There, antecedent onshore drainage patterns which formed the feeder system to the offshore, deepwater fan system can be interpreted and aligned with onshore palaeogeomorphological evidence. Understanding the palaeogeomorphic development of basement regions such as the Fennoscandian shield is of high importance for understanding the offshore presence of deepwater sandstones.
An integrated study of Permo-Triassic basins along the North Atlantic passive margin: implication for future exploration
Authors: Redfern J. , Shannon P. M. , Williams B. P. J. , Tyrrell S. , Leleu S. , Fabuel Perez I. , Baudon C. , Štolfová K. , Hodgetts D. , van Lanen X. , Speksnijder A. , Haughton P. D. W. , Daly J. S. 
Published: May 2011

Abstract
Permo-Triassic rift basins offer important hydrocarbon targets along the Atlantic margins. Their fill is dominated by continental red beds, comprising braided fluvial, alluvial fan, aeolian, floodplain and lacustrine facies. These relatively lightly explored basins span both the Atlantic and Tethyan domains and developed above a complex basement with inherited structural fabrics. Sparse data in offshore regions constrain understanding of depositional geometries and sedimentary architecture, further impeded by their deep burial beneath younger strata, combined with the effects of later deformation during continental breakup. This paper provides results from a multidisciplinary analysis of basins along the Atlantic margin. Regional seismic and well data, combined with geochemical provenance analysis from the European North Atlantic margins, are integrated with detailed outcrop studies in Morocco and Nova Scotia. The research provides new insights into regional basin tectonostratigraphic evolution, sediment fill, and reservoir distribution, architecture and quality at a range of scales. Regional seismic profiles, supported by key well data, indicate the presence of post-orogenic collapse basins, focused narrow rifts and low-magnitude multiple extensional depocentres. Significantly, Permo-Triassic basin geometries are different and more varied than the overlying Jurassic and younger basins. Provenance analysis using Pb isotopic composition of detrital K-feldspar yields new and robust controls on the sediment dispersal patterns of Triassic sandstones in the NE Atlantic margin. The evolving sedimentary architecture is characterized by detailed sedimentological studies of key outcrops of age equivalent Permian–Triassic rifts in Morocco and Nova Scotia. The interplay of tectonics and climate is observed to influence sedimentation, which has significant implications for reservoir distribution in analogue basins. New digital outcrop techniques are providing improved reservoir models, and identification of key marker horizons and sequence boundaries offers a potential subsurface correlation tool. Future work will address source and seal distribution within the potentially petroliferous basins.
Timing, controls and consequences of compression in the Rockall-Faroe area of the NE Atlantic Margin
Authors: Tuitt A. , Underhill J. R. , Ritchie J. D. , Johnson H. , Hitchen K. 
Published: May 2011

Abstract
The simplest models of passive margins would suggest that they are characterized by tectonic quiescence as they experienced gentle thermal subsidence following the extensional events that originally formed them. Analysis of newly acquired and pre-existing 2D seismic data from the Rockall Plateau to the Faroe Shelf, however, has confirmed that the NE Atlantic Margin was the site of significant active deformation. Seismic data have revealed the presence of numerous compression-related Cenozoic folds, such as the Hatton Bank, Alpin, Ymir Ridge and Wyville–Thomson Ridge Anticlines. The distribution, timing of formation and nature of these structures have provided new insights into the controls and effects of contractional deformation in the region. Growth of these compressional features occurred in five main phases: Thanetian, late Ypresian, late Lutetian, Late Eocene (C30) and Early Oligocene. Compression has been linked to hotspot-influenced ridge push, far-field Alpine and Pyrenean compression, asthenospheric upwelling and associated depth-dependent stretching. Regional studies make it clear that compression can have a profound effect on seabed bathymetry and consequent bottom-water current activity. Bottom-water currents have directly formed the early Late Oligocene, late Early Miocene (C20), Late Miocene–Early Pliocene, and late Early Pliocene (C10) unconformities. The present-day Norwegian Sea Overflow (NSO) from the Faroe–Shetland Channel into the Rockall Trough is restricted by the Wyville–Ymir Ridge Complex, and takes place via the syncline (Auðhumla Basin) between the two ridges. The Auðhumla Basin Syncline is now thought to have controlled the path of the NSO into the Rockall Trough and the resulting unconformity formation and sedimentation therein, no later than the Mid Miocene.
Episodic uplift and exhumation along North Atlantic passive margins: implications for hydrocarbon prospectivity
Authors: Japsen P. , Green P. F. , Bonow J. M. , Rasmussen E. S. , Chalmers J. A. , Kjennerud T. 
Published: May 2011

Abstract

We present observations that demonstrate that the elevated passive margins around the North Atlantic were formed by episodic, post-rift uplift movements that are manifest in the high-lying peneplains that characterize the coastal mountains, in the unconformities in the adjacent sedimentary basins and in accelerated subsidence in the basin centres. Results from West Greenland show that subsidence of the rifted margin took place for
c
. 25 Myr after rifting and breakup in the Paleocene, as predicted by classical rift theory, but that this development was reversed by a series of uplift movements (starting at
c
. 35, 10 and 5 Ma) that remain unexplained. East Greenland and Scandinavia seem to have had a similar evolution of post-rift subsidence followed by uplift starting at
c
. 35 Ma. There was no notable fall in sea-level at this time, so the subsiding basins must have been inverted by tectonic forces. We speculate that the forces causing this phase were related to the plate boundary reorganization in the North Atlantic around Chron 13 time. One feature that these areas have in common is that uplift took place along the edges of cratons where the thickness of the crust and lithosphere changes substantially over a short distance. It may be that the lateral contrasts in the properties of the stretched and unstretched lithosphere make the margins of the cratons unstable long after rifting. These vertical movements have profound influence on hydrocarbon systems, not only in frontier areas such as West and East Greenland, where Mesozoic basins are deeply truncated and exposed onshore, but also for the understanding of near-shore hydrocarbon deposits in mature areas such as the North Sea Basin, where low-angular unconformities may represent episodes of deposition and removal of significant sedimentary sections.
Intra-basalt units and base of the volcanic succession east of the Faroe Islands exemplified by interpretation of offshore 3D seismic data
Authors: Ellefsen M. , Boldreel L. O. , Larsen M. 
Published: May 2011

Abstract
Recent exploration activities in the basalt covered part of the offshore Faroe Island region has stressed the need for a better understanding of the volcanic succession, especially the lowermost part and the transition to the underlying non-volcanic succession. Using the proposed interpretation methods, which include careful identification of inclined reflector segments and flattening to various reflectors representing pronounced continuous markers embedded horizontally and 3D visualization, six volcanic units have been identified. The upper three units consist of plane-parallel reflector packages and probably represent subaerially extruded lava flows. The three lower units are characterized by irregular hummocky and inclined reflectors and are interpreted as lava deltas composed mainly of hyaloclastites. Within the data coverage area, the direction of extrusion is inferred from the seismic interpretation and four units originate from the NW and two from the SE. It is believed that the base of the volcanic succession is situated at a deeper level than the base of the parallel bedded units. At the base of the basalt succession and in the lower part of the volcanic succession pronounced reflector segments are ascribed to saucer-shaped sills. Analysing the seismic data using principles of seismic stratigraphy and observing them in a 3D environment, it is possible to obtain a broader understanding of the volcanic succession in the area and thereby divide the volcanic succession into characteristic facies units and separate it from the non-volcanic lithology and sills. The study shows that applying the proposed interpretation technique allows an evolution model to be put forward and it is suggested that the approach used in the study can be of use for hydrocarbon exploration in other basalt-covered areas.
Shale gas in Europe: a regional overview and current research activities
Authors: Schulz H.-M. , Horsfield B. , Sachsenhofer R. F. 
Published: May 2011

Abstract

Shale gas is produced from fine-grained siliciclastic sediments that are typically rich in organic carbon. Nearly all shales contain thermal gas generated
in situ
at mature to overmature levels of thermal alteration, although gas of biogenic origin is also produced from some shales. While shale gas production in the USA began in 1821, it is only in the last few years that it has become widely significant (currently about 8% of the domestic gas). In contrast, European shale gas exploration is still in its infancy. In general, European sedimentary basins offer the best potential for shale gas occurrence because thick, organic matter-rich sediments occur in nearly all Phanerozoic strata. Even so, there is little knowledge about the factors controlling shale gas generation and, more importantly, shale gas production in European basins. These factors are not necessarily the same as those that control commercial shale gas production in the USA. Palaeozoic sediments of Cambrian to Ordovician age are currently being tested for their shale gas potential and productivity in Sweden, as are those of Silurian age in Poland. Moreover, Lower and Upper Carboniferous sedimentary successions from England in the west to Poland in the east probably contain shale gas, but their depth, thickness and thermal maturity may be limiting factors for exploration in continental regions. Lower Carboniferous black shales in the Dniepr–Donets Basin of the Ukraine may also hold a significant potential. Moreover, organic-rich sediments of Oligocene/Miocene age in the Paratethyan Basin may offer shale gas potential, for example in the Pannonian Basin. At present, Upper Jurassic black shales are currently being tested for their shale gas potential in the Vienna Basin. European analogues of known biogenic shale gas systems may occur locally in organic-rich Lower Cretaceous sediments in the North German Basin with gas generation being related to Pleistocene glaciation/deglaciation cycles.