bluuebunny/crossref_metadata_2025_split huggingface dataset:
An estimation of the intrinsic permeability of argillaceous rocks and the effects on long-term fluid migration
Authors: Tokunaga T. , Hosoya S. , Tosaka H. , Kojima K. , Hosoya S. 
Published: April 2008

Abstract

The effect of intrinsic permeability of argillaceous rocks on long-term petroleum migration is discussed from results of both laboratory experiments and numerical sensitivity studies. Results of our experimental studies on one-dimensional mechanical compaction of both muddy slurries and mudstones show that porosity(
φ
)-permeability(
K
) relationships are linear on double logarithmic scales, i.e.
φ
and
K
satisfy the relationship:
K
=
K
0
(
φ/φ
0
)

a

, where
K
0
is initial permeability,
φ
0
is initial porosity, and ‘
a
’ is a parameter depending on the samples used. Comparison with published
φ
-
K
relationships of mudstones indicates that the above mentioned relationship could be extrapolated to natural condition when
φ
>0.3. On the other hand, the relationship becomes deviated from measured data in the low porosity range.

Considering the importance of
φ
-
K
relationships in
φ
<0.3 on the timing of expulsion of petroleum from source rocks, this paper discusses the way to find out an appropriate
φ
-
K
relationship through trial and error matching of results of basin simulation using different
φ
-
K
relationships with observed pore pressure and porosity data. We also present one case study using an imaginary siliciclastic sedimentary basin and discuss the potential of a numerical study to establish one of the appropriate relationships, showing how calculated results become varied by choosing different relationships.
A comparison between 1-D, 2-D and 3-D basin simulations of compaction, water flow and temperature evolution
Authors: Throndsen T. , Wangen M. 
Published: April 2008

Abstract
Is 3-D basin modelling really necessary? The answer depends on the type of problem under consideration. The Institute for Energy Technology (IFE) 3-D Basin Simulator offers the possibility to investigate certain aspects of this issue. It is a prototype 1-D, 2-D or 3-D basin simulator for reconstruction of the time-dependent pressure and temperature evolution of compacting sedimentary basins. Comparison of results, from 1-D, 2-D and 3-D simulations confirms that there may be significant differences due to water flow and pressure behaviour. The advantage of 2-D simulations as compared to 1-D is seen in overpressured configurations where 2-D allows more realistic calculations, while 1-D is less predictable. When going from 2-D to 3-D advantages are evident in configurations with pronounced 3-D basin geometries in combination with rapid processes and overpressure. The differences in water flow velocities and consequently the pressure calculations, may be quite significant. The rates in 3-D may be several orders of magnitude higher than in 2-D due to lateral focusing effects, while the overpressure still remains high. One consequence is, for example, reduced compaction in 3-D as compared to 2-D, with notable effects on basin geometry and temperature evolution of individual layers. Temperature anomalies due to increased convection in 3-D seem to be of less importance, unless processes of lateral focusing of water flow reach extreme levels.
Comparative studies of pre- and post-drilling modelled thermal conductivity and maturity data with post-drilling results: implications for basin modelling and hydrocarbon exploration
Authors: Ho T. T. Y. , Jensen R. P. , Sahai S. K. , Leadholm R. H. , Senneseth O. 
Published: April 2008

Abstract
The primary objective of this paper is to demonstrate the successful application of maturation modelling using velocity-based thermal conductivity in the whole cycle of hydrocarbon exploration (frontier, developing and mature) on the Halten Terrace, Offshore Norway. This seismic geochemical method, used as a critical technique for selecting a favourable block in the early stages of exploration in the early 80s, enabled Conoco and its partners to make the first oil discovery and the subsequent discovery of the giant Heidrun Field in the area north of the 62nd parallel.
Additional data (modelled and measured) on the thermal conductivity and Ro values are now available, and provide an excellent opportunity to compare the original (pre-drilling) basin models and related modelled results of the early 80s with 1990s (post-drilling) state-of-the-art data and models. The results of the comparative study indicate that the velocity-based conductivity compares very well with measured data, particularly in an overpressured area where conventional porosity (modelled) based thermal conductivities were inadequate. The pre-drilling predicted values of heat flow, geothermal gradient and vitrinite reflectance (based on Arrhenius equation) and oil window limits also compared favourably with post-drilling measured results. Thus, the method of calculating thermal conductivity from seismic data provides a useful tool to integrate geochemistry and geophysical (seismic) data, to calibrate maturation models, and to enhance the value of geochemistry and basin modelling in hydrocarbon exploration.
Dating of crustal fluid flow by the Rb-Sr isotopic analysis of sphalerite: a review
Authors: Walshaw R. D. , Menuge J. F. 
Published: April 2008

Abstract
The sphalerite Rb-Sr isochron technique is a relatively new and powerful geochronological tool allowing the direct dating of zinc sulphide mineralization. Recently, insights have been gained into the Rb-Sr isotope systematics of sphalerite, in particular the crystallographic residence sites of Rb and Sr and the mechanisms by which the Rb/Sr ratio of sphalerite is fractionated over that of its parent hydrothermal fluid. This, along with independent testing against three other dating techniques, has resulted in the vindication of the sphalerite Rb-Sr isochron technique. The resultant isochron ages have allowed very precise chronological constraints to be placed on the genesis of American and Australian Mississippi Valley-type deposits, greatly reducing the controversy which has surrounded this class of base metal deposit.
Reconstructing fluid history: an integrated approach to timing fluid expulsion and migration on the Carboniferous Derbyshire Platform, England
Authors: Hollis Cathy 
Published: April 2008

Abstract
Galena-sphalerite-baryte-fluorite mineralization and non-economic reserves of liquid hydrocarbon and bitumen are hosted on the Derbyshire Platform within Lower Carboniferous limestone which was deposited during Variscan back-arc extension. The limestone also hosts a sequence of burial calcite cements, precipitated dominantly in crosscutting and refractured extensional vein systems, which typically follow Caledonian-Variscan trends. The calcite cements are often intergrown with galena, sphalerite, baryte and fluorite as well as bitumen, whilst epifluorescence reveals hydrocarbon inclusions. Paragenetic relationships, in conjunction with geochemical results, permit definition of a precise timing for mineralization and hydrocarbon emplacement, and modelling of the source, composition and migration pathways of the mineralizing fluids.
Geochemical constraints on the origin and timing of palaeofluid flow in the Presqu’ile barrier reef, Western Canada Sedimentary Basin
Authors: Qing Hairuo 
Published: April 2008

Abstract
The Mississippi Valley-type ore deposits at Pine Point are spatially and genetically associated with saddle dolomite cements. The origin and timing of fluid flow that produced these ore deposits are, therefore, constrained by paragenesis and geochemistry of the saddle dolomite cements. Because saddle dolomites occur continuously across the sub-Watt Mountain unconformity, dolomitization and associated mineralization must have occurred after the sub-Watt Mountain exposure during burial. The lateral continuity of saddle dolomite along the barrier for 400 km suggests that dolomitization and mineralization were probably associated with the lateral fluid migration along the barrier reef.

From northeastern British Columbia to Pine Point, over a lateral distance of 400 km, saddle dolomites display remarkable trends of decreasing
87
Sr/
86
Sr ratios (0.7106 to 0.7081) and homogenization temperatures of fluid inclusions (178°C to 92°C) with a corresponding increase in δ
18
O values (−16‰ to −7‰ PDB). These regional trends suggest that hot, radiogenic basinal fluids moved eastward up-dip along the Presqu’ile barrier reef. The movements of basinal fluids were probably related to tectonic compression and sedimentary loading on the western margin of the Western Canada Sedimentary Basin during either the late Devonian-early Carboniferous (Antler Orogeny) or the Jurassic-early Tertiary (Columbia-Laramide Orogenies).

The δD values of aqueous fluid inclusions from Pine Point dolomite are very low (−80‰ SMOW to −100‰ SMOW) compared with that of Devonian seawater (−10‰ SMOW) suggesting an input of some Columbia-Laramide meteoric waters. If the low δD values are caused by a mixture of fluids from primary inclusions containing Devonian seawater with secondary inclusions that formed later during the Columbia-Laramide Orogenies, the fluid migration and associated dolomitization and mineralization could be interpreted as late-Devonian events. However, if the measured fluids were mostly from the primary inclusions, the low δD values indicate an entrapment of some Columbia-Laramide meteoric waters with Devonian formation waters at the time of dolomitization. This would suggest a Jurassic to early Tertiary age for dolomitization, which is supported by similar low δD values of present-day Devonian formation waters that consist of a mixture of Laramide meteoric waters and original connate brines. The light δD values of Pine Point dolomite inclusions could also occur as a result of reaction of fluids with organic matter associated with generation of oil and gas, which occurred at the maximum burial during the Laramide Orogeny.
On the vertical and lateral distribution of hydrocarbon migration velocities during secondary migration
Authors: Sylta Øyvind , Pedersen J. I. , Hamborg M. 
Published: April 2008

Abstract
Recent improvements in the techniques for modelling the flow of oil and gas through carrier systems allow us to compute the column heights of migrating oil and gas stringers. The calculations are performed throughout the history of the basin and suggest that secondary migration occurs at low saturation, and very often with velocities in excess of 100 km/Ma. The migrating hydrocarbon stringer columns are modelled to be very thin, i.e. in the centimetre range, over large areas. This paper discusses the lateral and vertical distribution of the above properties in order to elucidate and quantify the extreme focusing that hydrocarbons can experience during secondary migration. A result of these very efficient migration mechanisms is that we can successfully explore for hydrocarbons, even in traps that require lateral migration distances in excess of 1000 km from source to trap.
ESR isochron dating of the Nojima Fault gouge, southwest Japan, using ICP-MS: an approach to fluid flow events in the fault zone
Authors: Fukuchi Tatsuro , Imai Noboru 
Published: April 2008

AbstractThe absolute age of the earliest fault movement during the Quaternary period of the Nojima Fault, which moved in the 1995 Southern Hyogo Prefecture Earthquake (SHPE) in Japan, has been determined from clay grains in the fault gouge by election spin resonance (ESR) isochron dating using inductively coupled plasma mass spectrometry (ICP-MS). According to ICP-MS analysis, the concentrations of minor elements tend to increase with decreasing clay grain size, and they may adhere to the surface of clay grains, especially montmorillonite, in the fault gouge. The adherence of minor elements is possibly attributed to electrical charges caused on the surface of montmorillonite by substituting Al for some of the Si in the tetrahedral sites of the Si2O5sheets.238U,232Th and208Pb also increase with decreasing grain size, whereas the238U/232Th ratio is almost unchanged within the measurement error. This indicates that a closed system in the238U- and232Th- series had pertained in the fault gouge collected since the earliest fault movement. On the other hand, the208Pb/232Th ratio decreases with the grain size, and the208Pb/232Th ratio from a grain of <1 µm is about 14% of that from <500 µm.232Th decays to radioactively stable208Pb and produces220Rn in the decay process, but220Rn which is an inactive and non-ionized gas cannot be absorbed electrically on the surface of montmorillonite. Therefore, most of the220Rn gases produced on the surface of clay grains may be released from the fault fracture zone. A radon anomaly in ground water observed before the 1995 SHPE may be attributed to radon loss by huge clay mineralization in the Earth’s crust. The ESR isochron age of the fault clay gouge of the Nojima Fault is estimated as 0.84 ± 0.12 Ma to 1.23 ± 0.1 Ma from each clay grain by considering the calibration of radon loss, water content and defect creation efficiency by α-rays. This age is consistent with a date of about 0.53 −3 Ma that was estimated as the beginning of the Nojima Fault from recent drilling core data.
Experimental investigation of molecular transport and fluid flow in unfaulted and faulted pelitic rocks
Authors: Krooss B. M. , Schloemer S. , Ehrlich R. 
Published: April 2008

Abstract

Laboratory experiments have been performed to investigate the fluid transport properties of fine-grained (pelitic) sedimentary rocks with respect to their hydrocarbon sealing efficiency. The experiments comprised the molecular transport (diffusion) of gases and the pressure-driven volume flow (Darcy flow). Diffusion coefficients of methane and nitrogen in water-saturated rock samples were measured at 90°C from an equimolar mixture of the two gases (10 MPa gas pressure). Methane had lower effective diffusion coefficients but higher steady-state molecular transport rates than nitrogen. Permeability coefficients measured with water on selected unfaulted natural samples, under controlled effective stress up to 47 MPa, ranged between 10
−22
and 10
−19
m
2
. The permeability reduction with increasing stress mostly followed an exponential relationship. Permeabilities of faulted mudstones from compressive fault zones ranged from 2 up to 20 × 10
−21
m
2
. No systematic relationship between permeability and microfault frequency within the samples or distance of samples from microfault planes could be identified. Permeability measurements were also performed on macroscopically homogeneous Carboniferous shales from a compressive tectonic stress field. These samples, which showed distinct sonic velocity anisotropies, had permeability coefficients in the nanodarcy (nDarcy; 10
−21
m
2
) range. Only in one case was a significant permeability anisotropy associated with the sonic velocity anisotropy.
Simulating polyphase faulting with a tensorial 3D model of fault growth
Authors: Maillot B. , Cowie P. , Lague D. 
Published: April 2008

Abstract
Fault growth in brittle media has previously been extensively studied via a numerical approach using scalar representation of the stress and strain fields. More realistic simulations and further investigations of fault array evolution demand a fully tensorial three dimensional (3D) representation of these fields. In this paper we present a tensorial model of the spontaneous birth and growth of faults in a 3D medium. The medium is elastic and attenuating up to a stress threshold, determined by the Mohr-Coulomb criterion, where brittle failure is modelled by a partial shear stress drop. Elastic radiations generated by the rupture are explicitly extrapolated in time by a finite-difference scheme of the equation of dynamics until the static state is reached. We do not consider the dynamic process explicitly; further ruptures can only be triggered by the resulting static stress field, or by the imposed straining of the medium. Preliminary simulations of 3D straining of a 2D plate show how a pre-existing fault set (appearing as a perturbed stress field)can influence the development of a second fault set. We believe that our model provides a valuable tool for the study of fault development and in particular for the assessment of the effects of anisotropic stresses around faults on strain accumulation and the spatial organization of crustal deformation.
The influence of fault compaction on fault zone evolution
Authors: Henderson J. R. 
Published: April 2008

Abstract
A numerical simulation of coupled fluid flow and failure in a fault zone is presented, that shows the impact of the dynamics of fault growth on the relationship between seismic and sub-seismic fault scaling. A tabular fault zone is modelled which undergoes non-uniform compaction, leading to development of pressure gradients in the fault zone. Increased pore fluid pressures result in a reduction of the fault-normal stresses, and hence frictional failure. The model suggests a possible physical mechanism for the development of non-power-law scaling of fault displacements, implying that observations of such behaviour are real, rather than the result of poor sampling. The fault displacement scaling law appears to result from the dynamics of the fault evolution, which depend upon the relative rates of compaction of fault material and fluid flow within the fault zone. When fault compaction is slow, event sizes show a power-law scaling relationship. When compaction is fast, pressure gradients are unable to dissipate and the distribution of these event sizes is non-power-law. It is suggested that the dynamics of fault evolution may be inferred from geological evidence, with the relics of repeated small events (e.g. aligned calcite fibres) implying a relatively high compaction rate, whereas cataclasites would suggest relatively low compaction rates.
Relating microscale rock-fluid interaction to macroscale fluid flow structure
Authors: Leary P. C. 
Published: April 2008

Abstract

Borehole logs of rock-property spatial fluctuations in the metre to kilometre scale range have power-law Fourier power-spectra that scale inversely with spatial frequency to a power near unity,
S
(
k
) ∞ 1/
k
α
. The spectral scaling is ‘universal’ in the sense that a narrow range of scaling exponents, α
v
≈ 1.1 ± 0.1 for vertical wells and α
h
≈ 1.34 ± 0.1 for horizontal wells, describes rock density, elastic modulus, porosity and lithology fluctuation spectra of a sample of 50 well logs; for 35 vertical logs the bounds on α
v
hold for both sedimentary and crystalline rock types. The power-law nature of rock-property fluctuation spectra are modelled as long range spatial correlations arising from short range (grain scale) uncorrelated random fluctuations. Such long range random spatial correlations occur in thermodynamic order-disorder phase transitions. Applying to rock the statistical physics of thermodynamic order-disorder transitions, rock heterogeneity observed in borehole logs formally emerges from grain-scale elastic interactions and long range spatial organization of finite strain induced grain-scale defects associated with fluid percolation. If fluid flow paths in rock are significantly influenced by long range correlated random structures, reservoir management cannot be accurately conducted from flow models constrained by small-scale sampling of the reservoir rock; macro scale measurements of site-specific long range random correlation structures are needed.
Volcano-tectonic variability along segments of the Mid-Atlantic Ridge between Azores platform and Hayes fracture zone: evidence from submersible and high-resolution sidescan sonar data
Authors: Gràcia Eulàlia , Parson Lindsay M. , Bideau Daniel , Hekinian Roger 
Published: April 2008

Abstract

Three contrasting segments of the Mid-Atlantic Ridge (MAR) between the Azores platform and Hayes fracture zones have been studied to determine variations in the magmato-tectonic processes between segment centre and segment ends. Two of the segments (OH1 and OH3) were surveyed with the submersible
Nautile
and the third (Lucky Strike or PO1), with high resolution deep-tow side-scan sonar (TOBI). Segment OH1 is a long and robust segment with a wide and shallow axial valley floor. Submersible observations support the inference that this segment is characterized by intense volcanic activity concentrated principally at the segment centre. Segment OH3, with a narrow and deep rift valley, is dominated by tectonic features at the segment centre, whereas the most recent volcanic constructions are found to outcrop in its southern part. Lucky Strike contains a shallow centrally located volcanic platform but tectonic features predominate all along the segment. The only evidence of fresh volcanism are a lava lake and fresh sheet-flows located at the middle and northern part of the platform, respectively. Each of the three segments show ‘bull’s eye’ gravity lows suggesting a focused mantle diapiric source.
Fault-controlled magma transport through the mantle lithosphere at slow-spreading ridges
Authors: Allerton S. , Macleod C. J. 
Published: April 2008

Abstract
At the ends of spreading segments at slow-spreading ocean ridges the axial valleys are usually asymmetric and bounded by large valley-wall faults, in contrast to segment centres, which are usually symmetric, with relatively small faults. These morphological variations are believed to reflect differences in the thermal structure of the lithosphere, caused by focused upwelling of partially molten mantle beneath segment centres. This gives rise to a thinner crust but thicker, and consequently stronger, lithosphere at segment ends, which is likely to provide a barrier to melt migration in comparison with segment centres. High-resolution sidescan sonar images of parts of the Mid-Atlantic Ridge reveal that flattopped seamounts occur preferentially at segment ends. Many of these seamounts are situated asymmetrically within the axial valley, and show a spatial association with the large segment-end faults, raising the possibility that melt may be channelled through the lithospheric mantle by such faults. If this is the case, then one might expect to encounter gabbros within mantle shear zones. We here document one such case in the Lizard Ophiolite, Cornwall, Southwest England: the Carrick Luz shear zone, a 100m wide dykelike body of gabbro and gabbro mylonite occurring within mantle ultramafic rocks. The shear zone shows a progression from penetrative mylonite fabrics, discrete ultramylonitic shear planes, through to cataclasites and fault gouges. The penetrative mylonite fabrics themselves deform, and are in turn cut by, mafic dykes. Shear direction and sense is the same for all of the fault rock types, ductile and brittle, and after correction for the regional tilt of the ophiolite section, are consistent with normal faulting. Gabbro mylonitic shear zones such as this within the lithospheric mantle provide a mechanism for weakening the lithospheric mantle. They might be expected to have a high acoustic impedance contrast with the surrounding ultramafic rocks, and are strong candidates for dipping seismic reflectors observed in old oceanic crust.