bluuebunny/crossref_metadata_2025_split huggingface dataset:
Simulation of oil expulsion by 1-D and 2-D basin modelling — saturation threshold and relative permeabilities of source rocks
Authors: Okui A. , Siebert R. M. , Matsubayashi H. 
Published: April 2008

Abstract
In order for oil to accumulate in economic quantities, it first has to be generated and expelled from source rocks in sufficient quantities. In spite of long term efforts, the mechanism of oil expulsion from the source rocks is not completely understood. For modelling expulsion, the adoption of pressure-driven multiple-phase fluid flow governed by Darcy’s law is widely accepted. However, relative permeabilities for fine-grained source rocks, which is an essential parameter for this model, are very difficult to specify. The conventional reservoir-rock curve is obliged to be used for the modelling. Simplification of the relative permeability model is generally used for one-dimensional basin modelling. The 1-D model also requires substantial optimization of the key parameter, saturation threshold.
Laboratory measurement of relative permeabilities for fine-grained rocks is very difficult, therefore, we carefully interpreted the analysed laboratory data on various sandstones to establish a relationship between relative permeability curves and pore geometry parameters, with a view to extrapolate the relationships developed in sandstones to fine-grained source rocks. It was found that the relative permeability curves, or irreducible water saturation are controlled by two factors ; grain size and clay content. Since the total surface area of the pore system becomes greater as the grain size decreases, we consider surface water adsorbed on the grain surface as a part of irreducible water. Since clay contains micro-porosity which cannot be displaced by oil due to high capillary pressure, we regard this to also play a role. Prediction of relative permeability curves for fine-grained rocks by both processes results in the curve with high irreducible water saturation.
The new relative permeability curves were tested by both one-dimensional and two-dimensional basin modelling. Test results indicate that the new curves can reproduce expulsion efficiency, locations of accumulations and leaking through cap rock, which is consistent with actual observations.
Some thoughts on porosity reduction — rock mechanics, overpressure and fluid flow
Authors: Waples D. W. , Couples G. D. 
Published: April 2008

Abstract
A currently popular paradigm, that porosity reduction occurs as a direct consequence of the effective stress acting on the rock framework grains, is mechanistically incorrect. The commonly observed covariance between porosity and effective stress does not reflect a cause-and-effect relationship. Instead, it arises because both low effective stress and slow porosity reduction are consequences of the inability of compacting rocks to expel their pore fluids quickly enough to maintain normal fluid pressures. The process of porosity loss is here divided into sequential steps, and we argue that the expulsion of pore fluids is the rate-determining step leading to overpressuring. Thus, Darcy’s law assumes equal importance with the relationships describing the mechanical compaction of sediments. In this paper we describe how compaction can be treated as a Coulomb-plastic response that is functionally dependent on effective mean stress, deviatoric stress, and the state of compaction. In the next generation of basin models, a mechanistically correct approach is needed, combining both rock mechanics and hydrogeology.
Central North Sea overpressures: insights into fluid flow from one- and two-dimensional basin modelling
Authors: Darby D. , Haszeldine R. S. , Couples G. D. 
Published: April 2008

Abstract
Jurassic and Triassic reservoirs in the Central North Sea are highly overpressured (>40 MPa above hydrostatic pressure). Simulation of the interplay between rapid Tertiary subsidence, seal permeability and fluid flow allows insight into the geological controls on the distribution and magnitude of the overpressure. One-dimensional models demonstrate that, unlike other basins, the overpressure developed in the Graben is not determined by the thickness and permeability of the shale pressure seal. A two-dimensional model simulating lateral flow beneath the pressure seal provides an accurate simulation of the overpressure distribution. Disequilibrium compaction of shale-dominated off-structure regions forms the principal overpressuring mechanism. Lateral flow in the permeable Fulmar sandstones leads to high overpressure and focused vertical escape on an axial high, where the seal is thinner above a subcropping Fulmar Fm. A layered hydrogeological regime is suggested, with shallow Tertiary pressure cells separated from deep Cretaceous-Triassic pressure cells by normally pressured, permeable Palaeocene sandstones. The pre-Cretaceous rift-associated configuration of the Graben, in combination with 3 km of Tertiary subsidence, controls the distribution of overpressure.
A review of techniques used to determine geological and thermal history in the Southern North Sea
Authors: Archard G. , Stafford J. , Bardwell K. , Bagge M. , Stafford J. , Bardwell K. 
Published: April 2008

Abstract
The Southern North Sea has been a prolific source of gas to the UK economy over the last 30 years. As many of the producing fields are now becoming depleted, attention has switched to exploration in more marginal areas of the basin. In order to evaluate suitable structures in these areas, an understanding of the complex structural and thermal history of the Southern North Sea Basin is required. Particular emphasis must be placed upon the prediction of source rock maturity, the timing of generation and migration of hydrocarbons, and the thermal controls exerted on potential reservoir sand units.
Over large parts of the basin the Carboniferous source rocks are not at their maximum depth of burial at present day. A variety of techniques utilizing sonic velocity, vitrinite reflectance and apatite fission track analysis have been used to quantify the magnitude of uplift that the Carboniferous section has undergone through geological time. With the exception of apatite fission track analysis, these techniques provide only an estimate of ‘net uplift’, i.e. the amount of uplift relative to maximum depth of burial or maximum temperature. They record neither the timing and effects of individual uplift events nor the timing of maximum burial prior to net uplift. In order to accurately reconstruct the burial and thermal history of the basin these techniques must be integrated with a detailed knowledge of the geological history of the Southern North Sea.
The use of these techniques in isolation, together with a lack of appreciation of the limitations of the data has in the past resulted in spurious results, leading to criticism and mistrust of the techniques. This paper attempts to show that when correctly applied and in appropriate geological circumstances, each analytical technique can provide useful data for burial and thermal history reconstruction. Examples are shown to highlight the effects of incomplete data interpretation and the impact of inaccurate determination of present day temperatures. Particular attention is paid to determining the burial and thermal history of the economically important Carboniferous source and Permian reservoir units, and the interpretation of uplift data is restricted to the post-Zechstein section.
Aspects of applied basin modelling: sensitivity analysis and scientific risk
Authors: Thomsen R. O. 
Published: April 2008

Abstract
Basin modelling is a powerful quantitative tool and in order to be able to use modelling for the correct purpose and to expand the variety of problems where basin modelling with advantage can be applied, it is necessary to view basin modelling in the context of the general exploration process. Results from basin modelling are often directly used for ranking and risking of exploration targets. Due to the integrated nature of basin modelling it is applied more or less routinely throughout the exploration process for quantitative assessments. Awareness of some fundamental limitations of the models used is therefore vital in order to assess the overall uncertainty associated with the results. It will be shown how, through sensitivity analysis and risking of the modelling results, uncertainty ranges and confidence levels can be attached to the results. Examples of how sensitivity analysis helps in the process of understanding the system behaviour, reveals the critical factors, and provides the resolution limits on specified parameters will be given. Finally, a probabilistic procedure for assessing the uncertainty ranges and the level of confidence associated with modelling results will be given. A case history shows how the procedure can be used for providing risked entry parameters for the general risk assessment.
The Argentine Precordillera: its odyssey from the Laurentian Ouachita margin towards the Sierras Pampeanas of Gondwana
Authors: Dickerson Patricia wood , Keller Martin 
Published: April 2008

Abstract
The Argentine Precordillera (Cuyania terrane) and the Marathon/Solitario basin (west Texas), both underpinned by Grenvillian Laurentian basement, evolved together during Early Cambrian to Mid-Ordovician times. Ages, Pb-isotope and geochemical data for Precordilleran and for west-central Texas basement (including the Llano uplift) are strikingly similar. Carbonate platform sequences developed on both sides (e.g., El Paso and Chica de Zonda) of the Marathon/Solitario outer-shelf to slope basin and hosted homologous reef organisms which were unique to the Laurentian Ouachita margin. The Marathon/Solitario basin received sediments from both north and south; much detritus came from the northern shelf, including olistoliths bearing shelf fauna. Erosional vacuities on the platforms correlate with coarse detrital basin deposits. Cuyania constituted the long-sought southern source. Stratigraphy and structures of the Precordillera/Marathon/Solitario basin are consonant with plate reconstructions that place southern Laurentia near western Gondwana from Late Cambrian into mid-Ordovician time. During Caradoc time, Cuyania moved beyond range of faunal exchange with Laurentia, and tholeiitic basalts were intruded into off-shelf turbidites in the western Precordillera. The attenuated, thermally weakened, Laurentian slab broke apart with continued extension and right-oblique separation of Laurentia and Gondwana. Severance of Cuyania from Laurentia was complete before the onset of Taconic or Ocloyic orogenesis.
The Famatinian magmatic arc in the central Sierras Pampeanas: an Early to Mid-Ordovician continental arc on the Gondwana margin
Authors: Pankhurst R. J. , Rapela C. W. , Saavedra J. , Baldo E. , Dahlquist J. , Pascua I. , Fanning C. M. 
Published: April 2008

Abstract

A new multi-disciplinary study of the central Sierras Pampeanas encompasses fieldwork, petrography, metamorphic and micro-structural analysis, geochemistry and geochronology. Remnants of a low-to-medium grade metasedimentary sequence, which also occurs in the Sierras de Córdoba to the east, are considered regionally equivalent to the Puncoviscana Formation; a ?mid-Cambrian Rb-Sr whole-rock isochron of 513 ± 31 Ma probably dates their main metamorphism. The predominant granitoids of the Los Llanos-Ulapes batholith constitute a calc-alkaline suite representative of the Famatinian subduction-related magmatic arc. The main granodiorite phase of the batholith is associated with an S2 fabric and shear zone formation, and was emplaced late during the deformational history of the metasediments. Conventional and SHRIMP U-Pb zircon dating yielded a combined age of 490 ± 5 Ma. Younger monzogranites gave Rb-Sr whole-rock ages of 470–450 Ma, typical of granites in the Sierra de Famatina, but geochemical continuity with the main granodiorite suite raises the possibility that these are partially reset ages. A minor cordierite granite phase is ascribed to local anatexis caused by heat from the granodiorites. All the calc-alkaline rocks of the Los Llanos-Ulapes batholith have high initial
87
Sr/
86
Sr (0.7075–0.7105) and low ɛNd
t
(−4.6 to −6.3), inherited from lower crust. Sm-Nd model ages of 1600–1700 Ma indicate that the underlying crust is identical to that beneath the foreland to the east. This part of the Famatinian arc was thus a continental magmatic arc and was established significantly before the arrival of the allochthonous Precordillera terrane in mid-Ordovician times.
Palaeomagnetic dating of ancient fluid-flow events in the Arbuckle Mountains, southern Oklahoma
Authors: Elmore R. Douglas , Campbell T. , Banerjee S. , Bixler W. G. 
Published: April 2008

Abstract

Palaeomagnetic and geochemical data, and petrographic observations from Palaeozoic rocks in the Arbuckle Mountains provide data on the timing and pathways of fluid flow events. The lower part of the Upper Cambrian Reagan Sandstone, the basal palaeoaquifer in the Palaeozoic section, and the upper part of underlying 525 Ma Colbert Rhyolite are geochemically altered and contain two late Palaeozoic secondary magnetizations. The rhyolite as well as the overlying strata contain apparent primary Cambrian magnetizations. One of the secondary magnetizations (
D
= 150°,
I
= 5°, α95 = 5°, 45% tilt corrected) resides in hematite and is interpreted to be a chemical remanent magnetization (CRM) that formed due to hematite authigenesis as a result of fluid migration. The other secondary magnetization (
D
= 146°,
I
= 17°, α95 = 4°, 80% tilt corrected) resides in magnetite and is older than the CRM in hematite on the basis of the pole positions. The origin of this magnetization is more ambiguous and could have been caused by hot fluids resetting previously formed magnetite. Evidence for alteration by fluids includes secondary mineralization of calcite, hematite and quartz in veins, depletion/enrichment of elements in the rhyolite, and authigenic hematite cement in the lower Reagan Sandstone. Fluids also migrated along fractures during multiple episodes in the late Palaeozoic, locally remagnetizing and altering younger Palaeozoic strata in the Arbuckle Mountains.
The origin of helium in deep sedimentary aquifers and the problem of dating very old groundwaters
Authors: Pinti Daniele L. , Marty Bernard 
Published: April 2008

Abstract

Noble gases, inert elements having isotopes produced by the decay of long half-life radionuclides, offer a powerful approach for tracing fluid circulation and dating groundwaters. The (U + Th)-
4
He water ages — calculated from the accumulation rate in water of radiogenic
4
He produced by decay of U and Th contained in the aquifer rocks — is frequently higher than the hydrological ages. This discrepancy is generally interpreted by two contrasting models: (i) heterogeneities of the aquifers, which allow water stagnation and accumulation of large amounts of radiogenic
4
He, or (ii) addition of
4
He produced in deeper regions of the continental crust. In this contribution, we propose that the apparent contrast between (U + Th)-
4
He ages and hydrological ages in the Paris Basin reflects the mixing of different types of water, having different residence times. We show, using the helium isotopic signatures of waters, that this mixing occurs between three aquifers, the Middle Jurassic, the Triassic and the Palaeozoic basement, which have contrasting helium contents and heterogeneous chemical compositions and permeabilities. The difference of radiogenic
4
He/
40
Ar* ratios between the aquifers of Triassic and Middle Jurassic strongly suggests that a significant fraction of helium is produced in the aquifer rocks. This implies residence times for groundwaters circulating in the Middle Jurassic carbonate aquifer much longer than those obtained from hydrological studies. Independent fluid age estimates, based on the ground palaeotemperatures recorded in the same groundwaters by the atmosphere-derived noble gases, seem to confirm the presence of very old groundwaters in the Paris Basin.
The relationship between faults and pressure solution seams in carbonate rocks and the implications for fluid flow
Authors: Peacock D. C. P. , Fisher Q. J. , Willemse E. J. M. , Aydin A. 
Published: April 2008

Abstract
Pressure solution plays a major role in fault initiation and development in carbonate rocks. Strike-slip faults in the Triassic and Jurassic limestones of Somerset, UK, initiated as en echelon extension fractures, which became linked by pressure solution seams. Shear occurred along the pressure solution seams as the bridges between the veins rotated. The linked vein-pressure solution seam systems developed into pull-aparts and eventually into through-going faults. Normal fault planes in the Cretaceous Chalk at Flamborough Head, Yorkshire, UK, commonly have the pitted appearance of slickolites. Phyllosilicates are often concentrated along faults in Chalk, the thickness of the phyllosilicate gouge being proportional to fault displacement. The enrichment of phyllosilicates along the faults is due to pressure solution rather than simply to phyllosilicate smear. Pressure solution can be concentrated at the contractional quadrants of faults, particularly where there is a contractional overstep onto an adjacent fault. Metre-scale oversteps between strike-slip faults in Somerset often have pressure solution seams, while contractional oversteps and bends at Flamborough Head are accommodated by compaction of beds, with pressure solution apparently being important. The concentration of phyllosilicates by pressure solution can hinder fluid flow along and across faults in carbonate rocks. A high density of pressure solution seams between overstepping faults can effectively link these faults, increasing both the effective length of the barrier to fluid flow and the fault seal potential.
A seismic inversion study of the axial magma chamber reflector beneath the East Pacific Rise near 10°N
Authors: Collier J. S. , Singh S. C. 
Published: April 2008

Abstract
We have applied a full waveform inversion method to seismic reflection data from two adjacent fourth-order morphological segments of the East Pacific Rise near 10°N. Our inversion results show the ridge to be underlain by a thin (30 m) low P-wave velocity layer which we interpret as magma with less than 20±10% crystals. At one of the locations, the base of the mostly molten layer is underlain by a velocity gradient. Here the ridge is at an intermediate stage in its volcanic cycle and we interpret the gradient zone to be a result of an increase in crystals with depth, reaching 40–90% crystallinity over a vertical distance of 50 m. In contrast, beneath the second segment, which is at the onset of a vigorous volcanic stage, the mostly molten layer is underlain by a mostly solid floor. We infer that the melt layer has been newly emplaced. Our results provide support for the idea that the crustal magma system beneath fast spreading ridge axes is segmented on a similar scale to the fourth-order bathymetric segmentation.
Rare earth element mobility in a mineralized alteration pipe within the Troodos ophiolite, Cyprus
Authors: Wells D. M. , Mills R. A. , Roberts S. 
Published: April 2008

Abstract
Rare earth element (REE) mobility has been investigated in stockwork mineralized lavas and dykes that lie in a zone of former black smoker fluid upflow within Troodos oceanic lithosphere. Most lavas from the Pitharokhoma alteration pipe have REE compositions similar to Troodos volcanic glasses, indicating that on- and off-axis hydrothermal alteration processes have not induced significant net REE mobilization. A degree of REE mobility is inferred for some lavas which are depleted in the light REE ± Eu. Within the lavas, high- and low-temperature hydrothermal alteration phases analysed by laser ablation inductively coupled plasma-mass spectrometry (LA ICP-MS) display contrasting REE patterns (variably light REE enriched and depleted respectively). Thus during high- and low-temperature hydrothermal alteration of the lavas there may have been some relative loss or gain of light and heavy REEs, that did not necessarily cause any substantial net REE mobilization. Low-temperature hydrothermal phases have been identified as the major repository for the REEs in many of the altered lavas. These data suggest that much of the REE signature of the alteration pipe is not a relict of on-axis greenschist facies alteration, but a lower-temperature post-mineralisation overprint acquired in the waning stages of hydrothermal activity and during subsequent ageing of the oceanic basement.
The fossil record of hydrothermal vent communities
Authors: Little C. T. S. , Herrington R. J. , Maslennikov V. V. , Zaykov V. V. 
Published: April 2008

Abstract
There are 19 known fossiliferous volcanogenic massive sulphide (VMS) deposits which range in age from the Silurian to the Eocene. Most of these are in the Ural Mountains, Russia. The deposits contain assemblages of inarticulate and rhynchonellid brachiopods; gastropod, bivalve and monoplacophoran molluscs; and a small diversity of worm tube morphologies, some of which may be attributable to alvinellid polychaetes and vestimentiferans. The fossils are preserved mainly as external moulds of pyrite, which is consistent with biomineralization processes occurring at modern vent sites. Most of the fossil taxa are new to science, but the lack of original shells and organic tubes makes placement in existing phylogenetic schemes difficult. A comparison between modern vent communities and fossil vent assemblages shows that vestimentiferans, alvinellid polychaetes, bivalves, gastropods, monoplacophorans and perhaps brachiopods are shared at higher taxonomic levels, but that arthropods are found only in the modern communities. There are no direct ancestor-descendant relationships between the fossil and modern vent molluscs and brachiopods. This demonstrates that the modern vent environment is not a refuge for the known Palaeozoic and Mesozoic shelly vent taxa. Hence, taxonomic groups have moved in and out of the vent ecosystem through time. These findings are discussed in relation to alternative hypotheses for the origins of modern vent communities.
Global glacial isostatic adjustment and coastal tectonics
Authors: Peltier W. R. 
Published: April 2008

Abstract
A global and gravitationally self-consistent model of the process of glacial isostatic adjustment (GIA) has been developed that extremely well reconciles the vast majority of available records of Holocene relative sea-level history, not only from sites that were ice covered at last glacial maximum (LGM) but also from sites that are well removed from such locations. There do exist, however, data that have been construed to constitute a significant challenge to this theory, namely, the long records of relative sea-level history derived on the basis of U/Th-dated coral sequences from the Huon Peninsula of Papua New Guinea and from Tahiti in the central equatorial Pacific Ocean. Following a review of the theoretical model and a discussion of the extent to which it is able to successfully reconcile a very wide range of Holocene shoreline observations, the discussion focuses upon the interpretation of these very important and interesting records, which are subject to different levels and types of tectonic contamination. These analyses suggest that existing estimates of the levels of Holocene tectonic contamination at both locations may require revision. In this context, it is suggested that the global model of the GIA process is sufficiently accurate that the magnitude and form of local tectonic effects during the Holocene period might be sensibly estimated by simply subtracting the GIA prediction for a given site from the observed variation of relative sea level.