bluuebunny/crossref_metadata_2025_split huggingface dataset:
An integrated basin modelling study applying asphaltene kinetics from reservoired petroleum in the Snorre Area, northern North Sea
Authors: Skeie Jon Erik , Primio Rolando Di , Karlsen Dag A. , Bjørlykke Knut 
Published: April 2008

Abstract
The evolution of the petroleum systems in the Tampen Spur area, with main focus on the filling directions of the northern part of Snorre field, was addressed through 2D basin modelling (Petromod V. 4.5 and 7.0). The geochemical classification of the petroleum populations in the area represented the framework for considering the different kitchen areas and migration systems. Results from the basin modelling support, in general terms, the previous geochemical classification and petroleum families in the region. However, a separate well-defined main kitchen area for the Snorre Field was deduced opposed to the multiple kitchen areas having contributed to the filling as proposed in the literature. Our conclusions are based on the quantitative evaluation of the different proposed kitchen areas and the timing and extent of petroleum generation.
Modelling of petroleum generation was performed using asphaltene kinetics determined on petroleum asphaltenes from Snorre oils. This approach was chosen in order to avoid problems associated with the kinetic variability encountered in the Draupne formation. The petroleum asphaltene kinetics was used to delineate the extent of the kitchen area, which reached the time/temperature conditions necessary for the generation of the analysed oil phase. The results thus differ from conventional oil window approximations as we utilize kinetic source rock parameters in the migrated oil for tracing out the generative basin.
Three 2D lines crossing the main kitchen areas were modelled in this study. The models were calibrated to data from eight wells, consisting of measured vitrinite reflectance, corrected well temperatures and pore pressure.
Three main kitchen areas were considered; one to the west and northwest of Snorre field, one directly to the north (Møre basin) and one to the east of the field (34/5 kitchen). Modelling suggests that the kitchen area to the west and northwest of Snorre is largely immature and that the volume of potentially generated petroleum is too small to fill the Snorre structure. In the northern kitchen area, the seismic indicated very thin upper Jurassic deposits, which reaches oil window maturities only at a relatively large distance from the structure. The modelling also demonstrated problems related to the filling of the Snorre structure from the Møre Basin. The combined effect of a thin source rock, which implies a regionally large drainage area to fill the structure, and the large distance to the mature kitchen, lead to the conclusion that the Møre Basin did not contribute significant volumes of petroleum to the Snorre field. In contrast, the kitchen area east of Snorre Field (the 34/5 kitchen) proved in the modelling to be mature and volumetrically large enough to account for the entire filling of the Snorre Field.
Problems in interpreting AMS parameters in diamagnetic rocks
Authors: Hrouda František 
Published: April 2008

Abstract

The AMS parameters widely used to characterize the magnetic fabric of rocks (
L, F, P, T
) are not directly applicable to diamagnetic rocks. Namely, there are two principal methods of their definition: (1) from the signed principal susceptibilities or (2) from the absolute values of the principal susceptibilities. The first method results in
L, F
and
P
values less than one in contrast to materials whose susceptibility arises from paramagnetism and/or ferromagnetism
sensu lato
, where they are greater than one by definition. The ratio parameters decrease with increasing intensity of alignment of the magnetic minerals; the calculated shape parameters are, however, correct. The second method gives
L, F
and
P
values greater than one; they increase with increasing preferred orientation, however the ellipsoid shape parameters are inverse. The development of AMS parameters with increasing preferred orientation is modelled mathematically for quartzite/evaporite (para- and/or ferromagnetic AMS superimposed on the isotropic diamagnetic matrix) and for marble/limestone (preferred orientation of calcite in a rock). A rational set of AMS parameters is then recommended.
Anisotropy of magnetic susceptibility of lava flows and dykes: A historical account
Authors: Cañón-Tapia Edgardo 
Published: April 2008

AbstractThe basic assumptions made in the interpretation of the anisotropy of magnetic susceptibility (AMS) of lava flows, dykes and other tabular intrusive rocks have changed with time. This paper presents a historical account of those changes. Because several aspects of the AMS of these types of rocks are still open to debate, the historical perspective helps us to appreciate better the limitations that had to be faced at different times, therefore providing some clues that can be used to solve such controversies. Also, by benefiting from hindsight it is possible to devise alternative approaches that can be employed to interpret the AMS of these types of rocks. Although some adjustments to current models will be made as new results become available, it seems that at present the main commponents of the basic model of AMS in lava flows and tabular intrusive rocks have been finally reached, leaving behind most of the apparent contradictions found in earlier works. This progress is undoubtedly an important advance in our understanding of the nature of AMS in general.
Magmatic flow paths and palaeomagnetism of the Miocene Stoddard Mountain laccolith, Iron Axis region, Southwestern Utah, USA
Authors: Petronis M. S. , Hacker D. B. , Holm D. K. , Geissman J. W. , Harlan S. S. 
Published: April 2008

Abstract

The Stoddard Mountain laccolith is part of a complex of Early Miocene laccoliths intruded along the western edge of the Colorado Plateau in the Iron Axis region of Southwestern Utah. Most Colorado Plateau laccoliths (e.g. Henry and La Sal Mountains) are considered to be fed by a central axial feeder system. However, detailed mapping in the Iron Axis region suggests that the Stoddard Mountain laccolith was fed laterally from the west. Structural and field data suggest the quartz monzonitic magma initially migrated laterally eastward at ∼1 km depth as a sill before spreading laterally north-south where it inflated to ∼1–1.5 km thickness. To test the model of a lateral feeder system, data were collected from 32 palaeomagnetic sites and 76 AMS stations (763 accepted specimens) sampled over the ∼54 km
2
exposed part of the N-S oval-shaped laccolith. The
in situ
AMS fabrics, inferred to correlate with magmatic fabrics, typically show NE trending lineations in the north and S-SE trending lineations in the south part of the intrusion. The palaeomagnetic data are interpreted to indicate a very minimal amount of post-emplacement deformation of the intrusion. The overall lack of westerly-directed and steep magnetic lineations argues against emplacement via a central axial feeder system.
Magma flow inferred from preferred orientations of plagioclase of the Rio Ceará-Mirim dyke swarm (NE Brazil) and its AMS significance
Authors: Archanjo Carlos J. , Launeau Patrick 
Published: April 2008

Abstract
Low-field magnetic and plagioclase fabrics were compared in Mesozoic mafic dykes of the Rio Ceará-Mirim swarm. Coarse titanomagnetites with pervasive ilmenite lamellae constitute the main carrier of the magnetic anisotropy. The hysteresis parameters of the mafic dykes fall in the pseudo-single domain field. The resulting AMS ellipsoid is usually oblate and has a very low anisotropy (<3%). Textures indicate that the oxi-exolution processes and size reduction of the ferrimagnetic domains occurred at subsolidus temperatures on cooling of the dykes. The magmatic fabric was determined by the shape preferred orientation of plagioclase laths. It rarely matches the magnetic fabric. Besides their contrasting shape ellipsoids, prolate and oblate respectively, their corresponding principal directions diverge from each other or exchange their positions depending on the symmetry of the ellipsoids. These discrepancies are attributed principally to small differences in the net shape of Ti-poor magnetite after exsolution of ilmenite and in the inherently oblique fabric of grains with different shapes. These results draw attention to the need to use independent methods to confirm the conclusions about flow fabrics of weakly anisotropic mafic dykes based only in AMS.
Application of magnetic fabrics to the emplacement and tectonic history of Devonian granitoids in central Argentina
Authors: López de Luchi M. G. , Rapalini A. E. , Siegesmund S. , Steenken A. 
Published: April 2008

Abstract
Regional considerations on the tectonic regime during the emplacement of the Early Devonian magmatic units in the Sierra de San Luis are inferred from combined field, petrographic and AMS observations. Devonian granitoids of the Sierra de San Luis, in central Argentina, constitute elliptical composite batholiths and make up the most voluminous magmatism that appears in the Sierra. Detailed fabric studies have been carried out on the La Totora batholith (33°09′S, 65°42′W), which complement previous studies on two of the largest plutons in the Sierra de San Luis: The Renca and Las Chacras-Potrerillos batholiths. The studies comprised systematic field surveys, petrographic observations and anisotropy of magnetic susceptibility (AMS) measurements. Microstructural studies indicate that the batholith rocks are mainly characterized by magmatic microstructures with limited sub-magmatic to high-temperature solid-state deformation. All three batholiths possess concentric foliation patterns. The average magnetic foliation patterns in the studied plutons agree well with the macroscopic fabrics measured in the field indicating that the AMS-data can be used to study the orientation of fabric elements. Bulk susceptibility indicates a predominance of ferromagnetic contributions, although some paramagnetic sub-units are also present. Most foliations and lineations reflect magmatic flow and their attitude is linked to the interference between regional deformation and batholith inflation, i.e. fabrics may be due to regional strain in combination with the internal dynamics of the magma bodies. Rock fabrics are mainly described by oblate magmetic fabric ellipsoids. Magnetic lineations generally show a NNE-SSW trend that is interpreted to be controlled by the opening transtensional pull-apart structures during batholith inflation. It turns out that the Devonian batholiths intruded the basement syn-kinematically with respect to the Achalian deformational cycle.
Oblique magnetic fabric in siderite-bearing pelitic rocks of the Upper Carboniferous Culm Basin, SW England: an indicator for palaeo-fluid migration?
Authors: De Wall Helga , Warr Laurence N. 
Published: April 2008

Abstract

A zone of siderite dominated magnetic fabrics is recognized within clastic argillaceous rocks of the southern part of the Upper Carboniferous Culm foreland basin of SW England. This zone was identified by measuring the anisotropy of magnetic susceptibility (AMS) before and after heat treatment of samples. A detailed investigation of a recumbent fold structure within this zone (at the well-known Crackington Haven locality) reveals the pre-folding nature of siderite formation. The restored
κ
max
axes of AMS-ellipsoids plot on a segment of a small circle, with a mean inclination of
c.
45° to the pole of the sedimentary bedding planes. This oblique magnetic fabric geometry is considered to reflect substrate-controlled siderite growth within a migrating fluid medium, which crystallized during diagenesis and the early stages of Variscan compression. The regional distribution of siderite growth, in combination with the directional information from the AMS, is discussed as an indicator for the palaeo-flow direction of diagenetic fluids within a foreland basin setting.
Three-dimensional geological models from outcrop data using digital data collection techniques: an example from the Tanqua Karoo depocentre, South Africa
Authors: Hodgetts D. , Drinkwater N. J. , Hodgson J. , Kavanagh J. , Flint S. S. , Keogh K. J. , Howell J. A. 
Published: April 2008

Abstract
Recent technological advances have made the collection of digital geological data from outcrops a realistic and efficient proposition. The world-class exposures of Permian basin-floor turbidite fans of the Tanqua depocentre, Karoo Basin, South Africa have been the focus of one such study. These outcrops are faulted at a subseismic scale (displacements of up to 40 m), with continuous exposures of up to 40 km in depositional dip and 20 km strike directions. Digital data collection has been undertaken using a variety of methods: differential global-positioning systems (DGPS) mapping, surveying using laser total station and laser rangefinders, ground- and helicopter-based digital photography and photogrammetry, and digital sedimentary outcrop logging as well as geophysical data from boreholes. These data have then been integrated into several 3-D geological models of the study area, built using a subsurface reservoir-modelling system. The integrated dataset provides insights into the stratigraphic evolution of a deep-water fan complex by allowing true 3-D analysis and interpretation of data collected in the field. The improved understanding of these deep-water fan systems will improve existing models of offshore analogues by enhancing understanding of geometries and trends not resolvable from existing offshore data and by identifying potential problematic areas for fluid flow. Initial results from the application of this approach have been successfully applied to the conditioning of stochastic geological models of a subsurface deep-water reservoir from the North Sea.
Building confidence in geological models
Authors: Bowden R. Andrew 
Published: April 2008

Abstract
Geological models are required because we do not have complete knowledge, in time or space, of the system of interest. Models are constructed in an attempt to represent the system and its behaviour based on interpretation of observations and measurements (samples) of the system, combined with informed judgement (expert opinion) and, generally, constrained for convenience by the limitations of the modelling medium. Geological models are inherently uncertain; broadly those uncertainties can be classified as epistemic (knowledge based) or aleatory (reflecting the variability of the system). Traditional, quantitative methods of uncertainty analysis address the aleatory uncertainties but do not recognize incompleteness and ignorance. Evidence-based uncertainty analysis provides a framework within which both types of uncertainty can be represented explicitly and the dependability of models tested through rigorous examination, not just of data and data quality, but also of the modelling process and the quality of that process. The inclusion of human judgement in the interpretation and modelling process means that there will be frequent differences of opinion and the possibility of alternative, inconsistent and/or conflicting interpretations. The analysis presented here uses evidence-based uncertainty analysis to formulate a complete expression of the geological model, including presentation of the supporting and the conflicting or refuting evidences, representation of the remaining uncertainties and an audit trail to the observations and measurements that underpin the currently preferred and the possible alternative hypotheses.
Beyond kriging: dealing with discontinuous spatial data fields using adaptive prior information and Bayesian partition modelling
Authors: Stephenson John , Gallagher K. , Holmes C. C. 
Published: April 2008

Abstract
The technique of kriging is widely known to be limited by its assumption of stationarity, and performs poorly when the data involve localized effects such as discontinuities or nonlinear trends. A Bayesian partition model (BPM) is compared with results from ordinary kriging for various synthetic discontinuous 1-D functions, as well as for 1986 precipitation data from Switzerland. This latter dataset has been analysed during a comparison of spatial interpolation techniques, and has been interpreted as a stationary distribution and one thus suited to kriging. The results demonstrate that the BPM outperformed kriging in all of the datasets compared (when tested for prediction accuracy at a number of validation points), with improvements by a factor of up to 6 for the synthetic functions.
Using prior subsidence data to infer basin evolution
Authors: White Nicky 
Published: April 2008

Abstract
Quantitative models, which predict the structural and thermal evolution of sedimentary basins and margins, can be used to extracted information from subsidence data derived from discrete and noisy stratigraphic records. Although many basin-modelling algorithms exist, most of them solve the forward problem and many assume that rifting is instantaneous. A 2-D optimization strategy, which calculates spatial and temporal variation of strain rate, is outlined. This general approach should help to elucidate the dynamical evolution of sedimentary basins but it also addresses three issues of interest to the hydrocarbon industry. First, the residual misfit between observed and predicted basin geometries allows competing structural and stratigraphic interpretations to be objectively tested. Second, the animated evolution of sedimentary basin and passive continental margins can be produced using the retrieved strain-rate tensor. Thirdly, spatial and temporal variations of strain rate control basal heat flow, which in turn constrains the temperature and maturation histories of the sedimentary pile. Here, a small selection of 2-D results are presented and the basis of a 3-D formulation is described.
Types of permeable fractures in granite
Authors: Sausse J. , Genter A. 
Published: April 2008

Abstract
This study presents a multidisciplinary approach to understanding and describing types of fracture permeability in the Soultz-sous-Forêts granite, Upper Rhine Graben. At Soultz, during the 1993 stimulation tests in the GPK1 well, it was shown that only a limited number of natural fractures contributed to flow, whereas there are thousands of fractures embedded within the massive granite. In order to understand the flow hierarchy, a detailed comparison between static (fracture apertures based on ARI raw curves) and dynamic data (hydraulic tests) was carried out. We propose that two scales of fracture networks are present: a highly connected network consisting of fractures with small apertures that may represent the far-field reservoir, and another network that contains isolated and wide permeable fractures (that produce an anisotropic permeability in the rock) and allows a hydraulic connection between the injection and production wells.
Natural fracturing and petrophysical properties of the Palisades dolerite sill
Authors: Goldberg D. , Burgdorff K. 
Published: April 2008

Abstract

This investigation of naturally occurring fractures in the mafic rocks of the Palisades dolerite sill characterizes the porosity of this crystalline rock sequence, and yields a method of determining the
in situ
porosity when complete down-hole information is not available. Two holes, 229 m and 305 m deep, were drilled 450 m apart through the sill and into the underlying Triassic sediments of the Newark Basin. Both holes were logged with geophysical tools, including the acoustic borehole televiewer (BHTV), to identify intervals of high porosity, fracturing, and potential zones of active fluid flow. Using the BHTV data, 96 and 203 fractures were digitally mapped within the sill in Well 2 and Well 3, respectively. Most fractures dip steeply (76–78°). There is a shift in fracture orientation between Well 2 and Well 3, although the lithology of the sill is continuous. The dolerite penetrated in both holes is fresh and unaltered, and intersects a 7-m thick olivine-rich layer about 15 m above the bottom of the sill. Several fractures identified in the sill have large apparent aperture (>6 cm) that correspond to high-porosity zones (6–14%), measured from both resistivity and neutron logs in Well 2. We use a relationship between porosity and apparent fracture aperture in Well 2 to infer the porosity in Well 3. This correlative method for estimating porosity may be applicable between holes in other crystalline rock environments where down-hole log data are incomplete. Changes in the temperature gradient log also indicate active fluid flow, although flow appears to be most active in fractured and high-porosity zones in the sediments.
Brittle fracture in two crystalline rocks under true triaxial compressive stresses
Authors: Haimson B. , Chang C. 
Published: April 2008

Abstract

We employed our new polyaxial cell to carry out true triaxial compression tests on dry (jacketed) rectangular prisms of two crystalline rocks, in which different magnitudes of the least and intermediate principal stresses σ
3
and σ
2
were maintained constant, and the maximum stress σ
1
was increased to its peak level in strain control. Both Westerly granite (Rhode Island, USA) and KTB amphibolite (Bohemian Massif, Germany) revealed similar mechanical behaviour, much of which is missed in conventional triaxial tests in which σ
2
= σ
3
. Compressive failure in both took the form of a main shear fracture, or fault, steeply dipping in the σ
3
direction. Compressive strength rose significantly with the magnitude of σ
2
, suggesting that the commonly used Mohr-type strength criteria, which ignore the σ
2
effect, predict only the lower limit of rock strength. The true triaxial strength criterion for each of the crystalline rocks can be expressed as the octahedral shear stress at failure as a function of the mean normal stress acting on the fault plane. We found that the onset of dilatancy increases considerably for higher σ
2
. Thus, σ
2
extends the elastic range for a given σ
3
and, hence, retards the onset of the failure process. The main fracture dip angle was found to increase as σ
2
rises, providing additional confirmation of the strengthening effect of σ
2
. SEM inspection of the micromechanics leading to specimen failure showed a multitude of stress-induced microcracks localized on both sides of the through-going fault. Here too the effect of σ
2
is noted, in that microcracks gradually align themselves with the σ
1
-σ
2
plane as the magnitude of σ
2
is raised.