bluuebunny/crossref_metadata_2025 huggingface dataset:
Considerations on wave-induced fluid mud streaming at open coasts
Authors: Rodriguez Hugo N. , Mehta Ashish J.
Published: April 2008

Wave-induced streaming of fluid mud at open coasts under damped, non-breaking waves is examined as a likely mechanism to explain nearshore bottom evolution in such an environment. For a two-layered, water-fluid mud domain in which mud is considered to be a viscous continuum, an expression for the streaming velocity is obtained. Preliminary data on alongshore streaming of fluid mud in a wave basin show an order of magnitude agreement with theory. Previous observations on the rates of mud movement along the coasts of Surinam, Guyana and Louisiana are shown to yield alongshore velocities that are commensurate with those obtained by considering streaming to be the prevalent cause of mud transport. These velocities are considerably lower than those which would occur due to breaking waves. Off the southwestern coast of India, shoreward streaming of mud under monsoonal waves results in the formation of shore-fast mudbanks. It is argued that among transport mechanisms which govern the dynamics of microtidal muddy coasts, streaming may be an important means by which fluid mud influences the formation, migration and dissipation mudbanks in areas where wave breaking is significantly attenuated by viscous damping.
Comparison of flocculated and dispersed suspended sediment in the Dollard estuary
Authors: Mikkelsen Ole , Pejrup Morten
Published: April 2008

The purpose of this paper is to give a Lagrangian description of the changes in field settling diameter over a tidal period, while carrying out a tidal excursion with a research vessel. Settling tube analyses were carried out in the Dollard estuary, North-East Netherlands, by use of the Braystoke SK110 settling tube. From each tube settling velocity and grain size grading curves for the suspended material were computed. Subsequently, the sediment was dispersed from the filters and analysed in a laser diffraction analyser, a Malvern Mastersizer/E. The resulting grain size distribution of the primary particles was plotted together with the
in situ
distribution as bar diagrams. In this way it was possible to graphically determine the smallest equivalent floc size occurring in each sample as the intersect between the two distributions. Plotting this size against SSC, a linear relationship appeared: the greater the SSC, the smaller the smallest floc. It is suggested that this relates to high current velocities, at the same time causing both high values of SSC and high internal shear rates causing floc breakage. Plotting the settling velocities of the smallest floc against SSC yields an exponential relationship. Examples of the use of these relationships are presented. Flocs in the Dollard were larger than flocs sampled in the Danish Wadden Sea in earlier experiments. For comparative purposes, settling tube analyses were also carried out over the tidal flat.
Observations of the morphodynamic behaviour of an intertidal mudflat at different timescales
Authors: Whitehouse Richard J. S. , Mitchener Helen J.
Published: April 2008

This paper concerns the morphological (bed level) behaviour of the intertidal mudflat at Portishead on the Severn Estuary and discusses how the prevailing hydraulic and cohesive sediment processes contribute to observed changes in the bed level. The characteristics of the mudflat behaviour during a fortnightly cycle is presented, based upon a continuous high resolution time series of the bed level measured at one location during 31 tidal immersions. During spring tides the sediment supply to the mudflat is increased and the tidal-mean bed elevation is at least 10 mm higher following the peak of spring tides than on the previous or following neaps. On a tide by tide basis the bed level varies by 10–20 mm and the preservation of fresh mud deposits on the intertidal area is controlled by the hydraulic conditions prevailing during the shallow water phase of the tide (less than 0.5 m depth) and the processes operating during the dry part of the tide. Hence, the bed level is controlled by the phasing of the tidal range (ambient sediment supply) with local water depth and wave activity. In comparison, on the annual timescale the bed level variation on the middle and upper mudflat is of the order of 100 mm and seasonal changes in storminess, subaerial environment and biostabilization appear to play a significant role.
The erosion threshold of biotic sediments: a comparison of methods
Authors: Sutherland T. F. , Amos C. L. , Grant J.
Published: April 2008

Laboratory and field studies were carried out to determine the effect of biofilms on sediment erodibility. In the laboratory setting, a diatom culture of
Nitzschia curvilineata
was incubated on sediment and eroded in a recirculating flume at successive stages of growth. Several methods for determining erosion thresholds were employed: (1) the visual determination of particle and bed threshold, (2) an extrapolation method and (3) a digitiza tion method. A comparison of the derived erosion thresholds by these three methods is discussed. In the field setting, an
in situ
flume (Sea Carousel) was deployed at stations along a transect in a microtidal temperate estuary (Upper South Cove, Nova Scotia, Canada). The extrapolation method was used to determine the erosion thresholds of seabed constituents, such as chlorophyll, phaeopigment and sediment. The differences observed between the erosion threshold of chlorophyll, phaeopigment, and sediment lead to ambiguities in the definition of the erosion threshold of a seabed.
Spatial heterogeneity in an intertidal sedimentary environment and its macrobenthic community
Authors: Meadows Azra , Meadows Peter S. , McLaughlin Pat
Published: April 2008

The intertidal sedimentary environment is an extremely varied one in which marked differences in habitats and animal communities occur over very short distances. This study reports small scale heterogeneity of an intertidal macrobenthic community and its sedimentary environment in large sand waves in a bay in the Clyde Estuary, Scotland. Three 50 m transects ran across sand waves along a peak (P), along a trough (T) and across a peak and trough (P/T). Five sediment parameters [redox potential (Eh), organic carbon, particle size, shear strength and water table] and abundance of 14 macrobenthic species were measured in contiguous 1 m
2
quadrats along each transect. There were more positive and negative significant correlations along the P/T transect than the P and T transects. Thirteen correlations were common between pairs of transects. Multivariate cluster and principal component analyses were conducted on the data. The results of the two techniques were broadly in agreement. Distinct clusters of macrobenthic species and sediment parameters were identified. Some species clustered with sediment parameters. Others clustered only with species. These analyses may imply important causal relationships some of which are physically controlled and some of which are biologically controlled. Some clusters contained solely species that were deposit feeders. Clusters of quadrats along the P/T transect grouped quadrats on the peaks, in the troughs and on the slopes of the sand waves. These show that the peaks, troughs and slopes are significantly different sedimentary microenvironments. Clusters of quadrats along the P and along the T transect grouped quadrats that were spatially adjacent. These clusters indicate significant small scale spatial variability along the peaks and along the troughs of the sand waves.
The role of vegetation in determining patterns of the accretion of salt marsh sediment
Authors: Boorman L. A. , Garbutt A. , Barratt D.
Published: April 2008

Vegetation contributes to the stability of the salt marsh surface both through the soil reinforcement provided by the root mass and by the ability of the aerial component of plant growth to increase the rates of sediment deposition. Salt marsh vegetation is variable in height, thickness and also in stiffness. These characteristics can all modify the role of the vegetation in trapping sediment. As the height of the vegetation increases so also does Manning’s ‘
n
’, coefficient of roughness, but the taller vegetation is more easily flattened by moving water. It is not necessarily, therefore, more effective in slowing water flow and increasing sediment deposition. Shorter vegetation (mean height = 50 mm) has been shown to be quite effective, particularly if it is stiff enough to resist being flattened by the water at the rates of flow experienced.

The interplay of rates of sediment deposition is discussed with reference to data relating vegetation structure and pattern to local variations in accretion rates in salt marshes at Stiffkey, Norfolk, and Tollesbury, Essex, over a period of three years. At Tollesbury the mean annual rate of accretion was estimated to be 4.27 mm a
−1
but there was no correlation between the vegetation height (mean height = 148 mm) and changes in surface level. At Stiffkey however the annual rate of accretion was estimated to be 3.08 mm a
−1
, but there was a significant positive correlation between vegetation height (mean height = 75 mm) and accretion.

There is evidence that the relationship between effective vegetation height and the process of sediment accumulation is complex. Factors that can affect the relationship include the nature of the sediment, the height and composition of the vegetation and the microtopography and elevation of the marsh itself.
Basin modelling: how well have we done?
Authors: Waples D. W.
Published: April 2008

Model developers have been highly successful in building usable, useful, and reliable one-dimensional models, and in convincing explorationists to use them. Development of convenient, universal software played an instrumental role in the acceptance of 1-D modelling. The remaining weaknesses in technology and training, while serious, can be resolved through a few years of intensive work in certain specific areas. 2-D and 3-D fluid-flow modelling, in contrast, finds itself today largely in the position occupied by 1-D modelling more than a decade ago. The concept of fluid-flow modelling has not yet been adequately sold to explorationists, mainly because existing software is often inadequate to meet the real needs of exploration personnel. Development of appropriate software will probably have to precede widespread popularization of fluid-flow modelling. To improve existing software, two major areas must be addressed: (1) making models more comprehensive by including all relevant geologic phenomena, and (2) making software easier to use.
Geochemical modelling in an organic-rich source rock: the Bazhenov Formation
Authors: Hegre J. A. , Pittion J. L. , Herbin J. P. , Lopatin N. V.
Published: April 2008

Three wells located in the West Siberian basin have a high density of geochemical information (closely spaced samples) from the Upper Jurassic Bazhenov Formation. The nature of the organic matter is homogeneous and is classified as a marine type II (Hydrogen Indices up to 700 mg of HC g
−1
of TOC). The organic content is very high with TOC values up to 20 %. The source rock potential is also very good (S2 up to 100 kg HC tonne
−1
of rock). The maturity level in the wells varies from immature (T
max
around 435 °C) to near the end of the oil window (T
max
around 455 °C). This situation is somewhat puzzling since the source rock is at the same depth in the three wells (between 2800–2900 m). The IFP 1-D software GENEX, which is a maturity model that integrates subsidence, thermal reconstruction, hydrocarbon generation and expulsion, was used in order to:

(a)

test a geological hypothesis, which could reasonably explain this situation;

(b)

investigate the accuracy of the model’s ability to calibrate with geochemical data;

(c)

test the applicability of calibrating the expulsion saturation threshold from S1 and PI data. The very high S1 values with respect to the immaturity are also discussed. Model results indicate that different expulsion saturation thresholds are required in order to calibrate S1 and PI data. This is probably related to an inadequate definition of the formation’s porosity.
The proto-Andean margin of Gondwana: an introduction
Authors: Pankhurst R. J. , Rapela C. W.
Published: April 2008

A basic background is presented for the discussion of the Early Palaeozoic geology of western Argentina covered by this book. This includes the definition and terminology of orogenic cycles on this part of the Gondwana margin, represented by the Eastern Sierras Pampeanas. The Pampean orogeny (Early Cambrian) relates to an intense but short-lived period of terrane collision predating the rifting of the Precordillera terrane from Laurentia. The Famatinian cycle is predominantly represented by intense subductionrelated magmatism of Early-Middle Ordovician age, developed on the continental margin of Gondwana during the rifting and drifting of the Precordillera terrane. The Grenvillian basement of the latter is further exemplified by a new Rb-Sr whole-rock isochron age of 1021 ± 12 Ma for orthogneisses from the Western Sierras Pampeanas. A mid-Ordovician granite in this area (dated at 481 ± 6 Ma by U-Pb ion microprobe data) may be related to rifting while the Precordillera terrane was still attached to Laurentia. A divergence of opinion is pointed out between some authors in this book who favour mid-Ordovician collision of the Precordillera with Gondwana, and others who place it much latter, in Silurian or Devonian times.
Stratigraphical evidence supporting the rifting, drifting and collision of the Laurentian Precordillera terrane of western Argentina
Authors: Astini Ricardo A.
Published: April 2008

Major stratigraphical evidence points toward initial rifting of the Precordillera terrane of western Argentina during the Early Cambrian from the Ouachita embayment in southeastern Laurentia. A first fully developed rifting episode is suggested from subsidence analysis and the sedimentary record. Restricted graben-fill red-beds and evaporites in the eastern tectofacies, together with coarse arkose and quartz conglomerate preserved as blocks in the western tectofacies, are interpreted as deposits of the initial rift-related brittle extension. Stratigraphical similarities with localities surrounding the Ouachita embayment leads to a model in which the Precordillera was the southern part of the pre-Appalachian Laurentia margin and the conjugate margin of the Texas promontory, separated along the Alabama-Oklahoma transform and the Ouachita rift, respectively. Overstepping of syn-rift facies by a thick succession of Lower Cambrian to Lower Ordovician carbonates indicates completion of rift-to-drift transition and initiation of thermo-tectonic subsidence characteristic of continental terrace passive-margin development. Slope facies, marginal faunal belts and recently dated mafic rocks indicate the development of an ocean basin separating the Precordillera from Laurentia by the Mid-Cambrian. A 20–30 Ma period of drifting and isolation is indicated from faunal and sedimentological evidence. Subsidence-induced incipient drowning and abundant K-bentonites suggest the influence of subduction and the progressive approach of the terrane to western Gondwana. Continuous Mid- and Late Ordovician post-collisional extension brackets the collision, although no clear evidence of shortening has been detected in the preserved former sedimentary bank. Post-collisional extension is separated by >70 Ma from the initial rifting.
The stratigraphical record of the Argentine Precordillera and its plate-tectonic background
Authors: Keller Martin , Buggisch Werner , Lehnert Oliver
Published: April 2008

The stratigraphical record of the Argentine Precordillera from Early Cambrian to Late Devonian times reveals its plate-tectonic history from incipient rifting and the evolution of a marginal platform to the separation from Laurentia, its drift in higher latitudes and amalgamation with Gondwana. This pre-Carboniferous succession can be subdivided into four supersequences bounded by major unconformities and their main features are discussed with respect to plate-tectonic implications. The basal two supersequences which include the carbonate platform deposits are subdivided into 13 third-order sequences, each with a duration of 2–10 Ma. Supersequence A reflects intracratonic rifting, creating a graben system and forming a marginal plateau. In its in higher part a progradational carbonate complex covered the entire platform. Supersequence B shows the development of an aggradiational carbonate succession and the evolution of reef ecosystems comparable to those that developed around the margins of the Ouachita embayment. It also shows the demise of the carbonate platform by drowning. Deposits of Supersequence C reflect crustal extension and rifting, which led to the final separation of the Precordillera from mainland Laurentia. Supersequence D reveals the approach, and probably the accretion, of the Argentine Precordillera to Gondwana.
The geochemistry and provenance of Ordovician turbidites in the Argentine Puna
Authors: Bahlburg Heinrich
Published: April 2008

Petrographical and major, trace and rare earth element data are combined in a provenance study of Early and Mid-Ordovician volcaniclastic turbidites in the Puna of NW Argentina. The tectonic setting of the depositional basin béhind a west-facing volcanic arc is well established from the literature, so that the new data may be used to test published geochemical discrimination schemes of tectonic setting of sedimentary rocks. However, there is a controversy whether volcanism took place in an island arc or a mature continentalmargin arc. The data show that the arc had a sediment source of average upper crustal composition dominated by silicic and intermediate magmatic rocks. Major elements document that subaerial weathering significantly influenced the detritus composition, whereas the HFS elements in particular retained the original source signal. The HFS and REE characteristics, as well as other parameters, compare favourably with those of Recent deep sea sands derived from continental arcs.
Laurentia-Gondwana collision: the origin of the Famatinian-Appalachian Orogenic Belt (a review)
Authors: Dalla Salda Luis H. , López de Luchi Mónica G. , Cingolani Carlos A. , Varela Ricardo
Published: April 2008

Evidence from Cambrian to Devonian palaeogeography, the Laurentian provenance of Precordillera, and comparison of Lower Palaeozoic tectonic, metamorphic, and magmatic events, suggests a common collisional origin for the Taconian Appalachians and the Famatinian (Puna, Sierras Pampeanas, North Patagonian Massif) orogenic belt. Detached from Eastern Laurentia following collision, the Occidentalia terrane (west of the Famatinian orogenic belt) is partly covered by the Precordillera carbonate bank, which contains syn-collisional 460 Ma K-bentonites, related to the Puna and Famatinian arcs. In both the Appalachian and the Famatinian belts, a mostly Cambrian pre-collisional subduction regime developed at the western margin of Gondwana, following the opening of Iapetus. Laurentia-Gondwana collision produced deep thrusting and crustal melting. As in the Blue Ridge of the Appalachian Mountains, oceanic and mantle rocks, and slices of Grenvillian basement were emplaced along the western side of the Famatinian belt. This hypothesis gives continuity to a paired Taconian-Famatinian tectonic setting: a western Lower Palaeozoic platform overlying Grenvillian basement, and an eastern complex of a Lower-Middle Palaeozoic igneous-metamorphic belt with Proterozoic inliers.
Structural evolution of the Sierra de San Luis (Eastern Sierras Pampeanas, Argentina): implications for the Proto-Andean Margin of Gondwana
Authors: Von Gosen W. , Prozzi C.
Published: April 2008

The Western Basement Complex of the Sierra de San Luis underwent a complex deformational and metamorphic history of presumed Proterozoic age. The Phyllite Group and equivalents consist of a thick clastic sequence, whose time of deposition is compared with that of the Late Precambrian-Early Cambrian Puncoviscana Formation. This is intruded by early Famatinian magmatic arc tonalites to granodiorites, whereas an eastern basement unit was affected by early Famatinian mafic/ultramafic intrusions, metamorphism, and deformation. This Early Ordovician plutonism is related to east-directed subduction beneath the western margin of the Pampean terrane. Subsequent compression, plutonism, and variable-grade metamorphism are considered to be Mid- to Late Ordovician in age. Post-Famatinian
c.
WNW-ESE contraction under greenschist facies conditions led to folding of the cover sediments and uplift of different metamorphic units along mylonite zones which record an oblique sinistral component in the western part of the sierra. Based on a few radiometric data, this stage is interpreted as Devonian in age. It is possible that the compressive event was the result of the collision with the Precordillera (Cuyania) terrane in the west: oblique kinematic displacements, together with some evidence from outside the Sierra de San Luis, can be interpreted as the effect of the indenting terrane.
Age and duration of the Mississippi Valley-type mineralizing fluid flow event in the Viburnum Trend, southeast Missouri, USA, determined from palaeomagnetism
Authors: Symons D. T. A. , Lewchuk M. T. , Leach D. L.
Published: April 2008

The Viburnum Trend is a world-class Mississippi Valley-type (MVT) lead-zinc ore deposit in platform carbonates of the Upper Cambrian Bonneterre Dolomite in the midcontinent of the USA. Palaeomagnetic methods have been used to analyse 233 specimens from early octahedral (nine sites) and late-stage cubic (13 sites) galena ore from four mines along the
c.
70 km north-south length of the Trend. The characteristic remanence is carried by single to pseudo-single domain pyrrhotite and magnetite. This is the first MVT deposit in which pyrrhotite is shown to be a remanence carrier and present in galena crystals. The remanence directions define an Early Permian mean age of 273 ± 10 Ma for the ore-stage mineralization, a maximum duration for the mineralization event of 12 Ma, and a time difference of 5 Ma between the early octahedral and late cubic galena ore stages. The Early Permian age for the ore is consistent with models of ore genesis that invoke fluid flow from the Ouachita orogen during Ouachitan orogenesis.
Dating and duration of hot fluid flow events determined using AFTA® and vitrinite reflectance-based thermal history reconstruction
Authors: Duddy Ian R. , Green Paul F. , Hegarty Kerry A. , Bray Richard J. , O’Brien Geoffrey W.
Published: April 2008

Heating due to lateral introduction of hot fluids is becoming an increasingly recognized feature of the thermal histories of sedimentary basins. In some basins, heating by fluids may have an important effect on hydrocarbon source rock maturation history, so that quantification of the magnitude and timing of heating become essential elements in hydrocarbon prospectivity. In other cases, determining the time of fluid heating in a reservoir may provide a key constraint on hydrocarbon migration history. Examples are presented using AFTA apatite fission track analysis and vitrinite reflectance (VR) data to identify and quantify fluid heating in well sequences from several regions. In the West of Shetland region, in the vicinity of the Rona Ridge, non-linear palaeotemperature profiles defined by AFTA and VR results provide evidence of local heating shallow in the section. AFTA timing constraints suggest introduction of heated fluids produced by nearby Tertiary intrusive activity, although the time constraints are broad because of the low maximum palaeotemperatures involved (
R
0
max < 0.6%). In a well from Asia, transient maximum palaeotemperatures > 120°C resulted in
R
0
max > 0.6% in an Eocene section, with AFTA constraining the fluid flow event responsible for the early to mid Miocene (25 to 10 Ma). On the North West Shelf of Australia transient fluid flow associated with hydrocarbon leakage, and possibly charge, has been previously identified by a combination of AFTA, VR and fluid inclusion homogenization temperature (
T
h
) results. In the East Swan-2 well, a fracture inclusion in quartz from shallow Eocene sandstones gives a minimum
T
h
value of 88°C,
c.
40°C higher than the present temperature. AFTA and VR data show no direct evidence of
sustained
heating at such a temperature, and can only be reconciled if the duration of heating was
c.
20 000 years. The results are consistent with this event being associated with passage of a hot brine and hydrocarbon fluid (O’Brien and Woods, 1995). These case studies demonstrate that a combination of thermal history tools can be used to identify and quantify the thermal effect of fluid flow, potentially allowing much tighter constraints on hydrocarbon generation and migration histories.
Geology and timing of palaeohydrogeological events in the MacKenzie Mountains, Northwest Territories, Canada
Authors: Morris George A. , Nesbitt Bruce E.
Published: April 2008

Six distinct fluid events, which span a time frame from syndeposition (Cambrian-Devonian) to the last stages of the Laramide Orogeny (early Tertiary), have been identified in the MacKenzie Mountain range of the northern Canadian Rocky Mountains. The earliest event was a sedimentary exhalative event associated with the expulsion of brines onto the seafloor along extensional faults associated with a Silurian sedimentary basin. This was followed by a widespread diagenetic dolomitization event that affected the majority of carbonates from the early Devonian and older. The third event produced the stratigraphically restricted but regionally extensive Manetoe Facies dolomites, host to Mississippi Valley-type mineralization and reserves of natural gas. The formation of the Manetoe Facies dolomites is interpreted to have resulted from late diagenetic fluid flow in the late Devonian to early Carboniferous, possibly driven by the Antler Orogeny. The fourth fluid event, the vug-fill event, is constrained by low δD values to being early Cretaceous, or later in age. Features produced by this event are in turn cut by veins associated with the Laramide Orogeny (early Cretaceous to early Tertiary). The final recorded fluid event in this region is the calcite-barite event, interpreted to have been deposited by inflowing meteoric water. This study represents one of the most complete records of the fluid history of an area that has seen many palaeohydrogeological events. The combination of field and geochemical observations allows us to estimate the age, as well as the origin, of each event described.
Secondary oil migration: oil-rock contact volumes, flow behaviour and rates
Authors: Carruthers Dan , Ringrose Philip
Published: April 2008

Determining oil-rock contact volumes associated with secondary migration is a major challenge due to the heterogeneous nature of the sedimentary structures and petrophysical properties of carrier systems at multiple length scales. In this paper, we argue that migration occurs at, or near, the percolation threshold of the carrier system and show that the oil-rock contact volumes are a function of the heterogeneity of the threshold pressure field of the medium, as well as the orientation of the sedimentary fabric relative to the orientation of the net migration vector. The flow properties are intimately tied to the flow mechanism, which for secondary oil migration is likely to occur via capillary creep. An understanding of the distribution of threshold pressures within a sample volume will enable us to estimate the oil-rock contact volume during secondary oil migration, whether the volume considered is a core plug in size or an entire carrier sequence.
Dating Quaternary groundwater flow events: a review of available methods and their application
Authors: Metcalfe R. , Hooker P. J. , Darling W. G. , Milodowski A. E.
Published: April 2008

During the Quaternary (the last 1.6 Ma), episodic groundwater flow occurred to depths of several hundred metres. In many regions, climatic fluctuations induced episodes of rapid and slow groundwater flow. The former, termed here ‘groundwater flow events’, were characterized by extensive fresh-water recharge, and flushing of pre-existing water. It is important to identify and characterize such events to: (i) calibrate predictive models for future flow, thereby underpinning Performance Assessments for underground waste repositories; (ii) establish what proportion of global fresh-water resources was recharged during early Holocene or Pleistocene flow; and (iii) help interpret the timing and nature of Pleistocene climatic changes. To date, hydrogeochemical, mineralogical and petrological data have been interpreted in terms of post-glacial Holocene groundwater flow, or pre-Quaternary palaeofluid flow. Typically, Pleistocene recharge before the last glacial maximum has been unresolved. The effect of any given Quaternary climate change on the flow of pre-existing groundwaters is rarely identified. This paper considers the methods available to date these flow events, and finds that mineralogical evidence has been under-used to interpret Quaternary groundwater flow. Used together with hydrogeochemical data, mineralogical observations offer the best prospect of improving our understanding of Quaternary groundwater flow events.
Faulting, fault sealing and fluid flow in hydrocarbon reservoirs: an introduction
Authors: Knipe R. J. , Jones G. , Fisher Q. J.
Published: April 2008

A predictive knowledge of fault zone structure and transmissibility can have an enormous impact on the economic viability of exploration targets and generate considerable benefits during reservoir management. Understanding the effects of faults and fractures on fluid flow behaviour and distribution within hydrocarbon provinces has therefore become a priority. To model fluid flow in hydrocarbon reservoirs, it is essential to gain a detailed insight into the evolution, structure and properties of faults and fractures. Generation of realistic flow models also requires calibration with data on the fluid distributions and flow rates from hydrocarbon fields. Most hydrocarbon geologists at one time or another have asked the question ‘What is the behaviour of this fault?’. This question, as emphasized by the contributions to this volume, should more fundamentally be phrased; ‘What is the geometry of this fault zone, what are the nature and petrophysical properties of any fault rocks developed and how are they distributed in the subsurface?’. An additional important question is ‘What impact could the fault zone have on fluid flow through time?’. The properties and evolution of fault zones can be evaluated using the combined results of structural core and down-hole logging, microstructural and physical property characterization, together with analysis of faults from seismic and outcrop studies and well test data. Successful fault analysis depends upon the amalgamation of these data and incorporation into robust numerical flow models.
The appearance of potential sealing faults on borehole images
Authors: Adams J. T. , Dart C.
Published: April 2008

Electrical and acoustic borehole images provide data on the structure, width, spacing and orientation of potential sealing faults in the subsurface. These data bridge the ‘scale of observation gap’ between the resolution limits of more conventional data such as seismic data and core, and provide continuous records often up to several thousand feet long. Potential fault seals can be measured from vertical, deviated or horizontal wells and from either clastic or carbonate rocks. Five categories of potential fault seals can be described from images:
juxtaposition fault seals
place reservoir against seal lithologies and appear as sharp image contrasts;
clay lined fault seals
commonly appear as shale rich bands on electrical images, which may be either resistive or conductive depending on the resistivity of the host lithology, and low amplitude bands on acoustic images;
grain size reduction fault seals
appear as resistive or high amplitude features;
cemented fault seals
appear as highly resistive or very high amplitude features, and
open/vuggy faults
appear as conductive or very low amplitude features. An integrated approach to image interpretation incorporates not only borehole image data but also core, conventional wireline logs, pressure data and production information.
Structure and content of the Moab Fault Zone, Utah, USA, and its implications for fault seal prediction
Authors: Foxford K. A. , Walsh J. J. , Watterson J. , Garden I. R. , Guscott S. C. , Burley S. D.
Published: April 2008

The structure and content of the Moab Fault zone are described for 37 transects across the fault zone where throws range from less than 100 m to
c.
960 m. The 45 km long fault trace intersects a sedimentary sequence containing a high proportion of sandstones with good reservoir properties, interspersed with numerous mudstone layers. Typically, the fault zone is bounded by two external slip zones with the fault zone components separated by up to nine internal slip zones. Fault zone components are tabular lenses of variably deformed sandstones and sandstone cataclasites and breccia, with a wide size range, usually enclosed in a matrix of shaley fault gouge containing mm to m scale entrained sandstone fragments. Neither fault zone structure nor content can be predicted by extrapolation over distances as little as 10 m. Although variable in thickness, shaley gouge is always present except where the mudstone is <
c.
20% of the faulted sequence. The distribution of shaley gouge conforms with existing algorithms for predicting the presence or absence of shaley gouge in subsurface fault zones. The fault zone heterogeneity is attributed to tip-line and asperity bifurcation processes.
The gas permeability of clay-bearing fault gouge at 20°C
Authors: Faulkner D. R. , Rutter E. H.
Published: April 2008

Permeability measurements of clay-bearing fault gouges have been made using the pulse-transient and pore pressure oscillation methods with argon as the pore fluid, and at effective pressures up to 160 MPa and at a constant pore pressure of 40 MPa. Samples were collected from the outcrop of a major transpressional fault in southeastern Spain, in three orthogonal directions relative to the planar fabrics developed within the fault zone. Measurements show the gouge to exhibit permeability anisotropies of up to 3 orders of magnitude. In addition, pressure cycling of the gouge reduced the permeability by 2 to 3 orders of magnitude after 5 pressure cycles, when minimum permeabilities slightly less than 10
−21
m
2
were measured.
Numerical simulation of departures from radial drawdown in a faulted sandstone reservoir with joints and deformation bands
Authors: Matthäi S. K. , Aydin A. , Pollard D. D. , Roberts S. G.
Published: April 2008

Field measurements constrain the fluid flow characteristics of an analogue hydrocarbon reservoir in the faulted Entrada sandstone, Arches National Park, Utah. These data comprise maps of the geometry, inhomogeneous permeability, and porosity of fault zones, joints, and deformation bands in a region where two discontinuous normal faults overlap. Two-dimensional computer simulations of drainage of this analogue reservoir identify normal faults with highly permeable slip planes as the most important reservoir inhomogeneities. These faults compartmentalize fluid pressure over timespans greater than years while fluid can be drained on the kilometre scale along their highly permeable slip planes. Joints induce the second most important distortions of radial drawdown, influencing the timespans over which fault signatures are observed in pressure decline curves. The joints often extend to the boundaries of the reservoir. This also reduces the time before the rate of pressure decline accelerates due to boundary interaction. Zones of deformation bands less than 25 cm wide with a spacing ≥30 m have little effect on radial drawdown in our single phase fluid flow simulations. When drawdown spreads with time over the deformation structures in the analogue reservoir, the different structures simultaneously influence the change of pressure at the wellbore (pressure derivative). This temporal overlap prohibits an analysis of the effects of individual structures. Drawdown does not ‘recover’ to radial flow after an inhomogeneity is encountered.
An integrated approach for characterizing fractured reservoirs
Authors: D’Onfro P. S. , Rizer W. D. , Queen J. H. , Majer E. L. , Peterson J. E. , Daley T. M. , Vasco D. W. , Datta-Gupta A. , Long J. C. S.
Published: April 2008

Experience has shown that fractures and faults within a given array are not all equally conductive or well-connected. To investigate new techniques for locating conductive fracture flow paths, a series of high resolution (1 to 10 kHz) crosswell and single well seismic surveys and interference tests were conducted in a shallow five spot well array penetrating a fractured limestone formation. Two inverse approaches for constructing fracture flow models were applied to the interference test data. Both approaches successfully reproduced the transient pressure behaviour at the pumping and observation wells and indicated a preferential fracture flow path between two wells aligned in an east-northeast direction, the dominant direction of fracturing mapped in the area. Crosswell and single well seismic experiments were performed before and after air injection designed to displace water from the fracture flow path and increase seismic visibility. The crosswell experiments showed that replacement of water with gas produces significant changes in the seismic signal. The single well reflection surveys were able to precisely locate the position of the fracture flow path. This location was confirmed by core from a slant well which intersected a single open fracture at the targeted depth.
An inverse problem to determine the piecewise homogeneous hydraulic conductivity within rocks
Authors: Lesnic D. , Elliott L. , Ingham D. B. , Knipe R. J. , Clennell B.
Published: April 2008

The experimental measurement of the piecewise homogeneous hydraulic conductivity of a rock sample in which the location of the discontinuities is unknown appears difficult, even in a one-dimensional situation. However, the values of these quantities can be obtained numerically using additional boundary and/or interior measurements of the pressure from transient hydraulic experiments. In the direct problem, the hydraulic conductivity is known, and only a solution for the pressure field is sought. However, in the inverse formulation of the problem, both the hydraulic conductivity and the pressure are unknown and have to be determined using additional pressure measurements. The numerical method employed for solving the diffusion equation is based on the boundary element method as a direct solution procedure, combined with an ordinary least-squares technique. The sensitivity coefficients are calculated for the unspecified boundary conditions and for interior pressures, and clearly show the need for interior measurement information to be imposed on the solution of the inverse ill-posed problem. The uniqueness of the solution of the inverse problem is thoroughly numerically investigated using additional pressure measurements at several prescribed times from various numbers of wells and different well locations. For a material presenting a single discontinuity in the hydraulic conductivity, and subject to certain experimental conditions, it was found that when the number of time measurements is limited then two interior well pressure measurements are necessary and sufficient in order to render a good estimate of the exact solution. Otherwise, it is necessary to increase the number of time measurements at a single interior well location to accomplish the same result.
Fault controlled communication in the Sleipner Vest Field, Norwegian Continental Shelf; detailed, quantitative input for reservoir simulation and well planning
Authors: Ottesen Ellevset S. , Knipe R. J. , Svava Olsen T. , Fisher Q. J. , Jones G.
Published: April 2008

The Sleipner Vest field, located in blocks 15/6 and 15/9 on the Norwegian Continental Shelf, contains hydrocarbons (mainly gas condensates) within the marginal marine units of the Middle Jurassic Hugin Formation. The field is segmented into fault-bounded compartments, which exhibit differences in gas-water contacts of between 10 and 100m. Microstructural analysis of core samples has identified three principal fault types; cataclasites, developed from clean sandstones, framework phyllosilicate fault rocks created from impure sandstones and clay smears developed from phyllosilicate-rich units. The distribution of these has been linked to the phyllosilicate content of the undeformed Hugin reservoir at the time of deformation. Petrophysical property analysis has been used to quantify the representative permeabilities and threshold capillary pressures of the fault rocks and their undeformed equivalents. Juxtaposition/seal diagrams and detailed fault plane maps were also constructed and provide a basis for mapping sand-sand juxtapositions and the distributions of the different fault rock types with assigned permeabilities and capillary threshold pressures. The results provide an explanation of the mapped variations in gas-water contacts. An important correlation exists between the type of fault rock predicted to dominate the fault plane near the hydrocarbon-water interface and the difference in hydrocarbon depths across the faults. Compartments separated by faults with windows of juxtaposed clean sandstone cataclasites have small hydrocarbon-water level differences (7–11 m), suggesting that the low capillary threshold pressure (more permeable) cataclastic fault rocks control communication. Compartments separated by faults predicted to have extensive phyllosilicate-rich fault rocks (developed from impure sandstones and clay rich units) with high capillary threshold pressures correlate to larger hydrocarbon-water differences (>39 m), reflecting the reduced communication.
The structure and controls on fluid-rock interactions in ocean ridge hydrothermal systems: constraints from the Troodos ophiolite
Authors: Bickle M. J. , Teagle D. A. H. , Beynon J. , Chapman H. J.
Published: April 2008

Rb-Sr isotopic compositions of rocks and minerals from the Troodos ophiolite have been analysed to constrain the rate limiting mechanisms that control fluid-solid exchange, the extent to which recharge fluids were channelled and the thermal evolution of oceanic hydrothermal systems. Systematic regional sampling has confirmed the Sr-isotopic alteration profile suggested by Bickle & Teagle (1992). This has been previously interpreted as a consequence of recharge fluids percolating down through the extrusive series with kinetically limited fluid-rock interaction but altering the underlying ≈1 km section of sheeted dykes with near equilibrium fluid-rock Sr-isotopic exchange. Detailed Sr-isotopic profiles reported here across structural heterogeneities such as pillows, dyke margins and faults have failed to show isotopic gradients related to channelling of fluid. Rather the fluid flow in the recharge was pervasive and the degree of alteration is largely controlled by the extent of mineral recrystallization, primarily by albitization of plagioclase, and to a lesser extent by recrystallization of pyroxene. Hydrothermal recharge should cool the sheeted dykes much faster than the progression of the Sr-isotope alteration through the crust and rocks at greenschist facies (∼250°C) or higher temperatures are predicted only to be found within a few hundred metres of the basal boundary layer of the system. The alteration pattern on Troodos with a zone a kilometre or more in thickness altered at greenschist facies temperatures and with significant Sr-isotope exchange is thus not easily explained.
Significance of modern and ancient oceanic Mn-rich hydrothermal sediments, exemplified by Jurassic Mn-cherts from Southern Greece
Authors: Robertson A. , Degnan P.
Published: April 2008

This paper considers the occurrence of Mn-oxide-rich hydrothermal deposits in the modern oceans and presents a case history of Jurassic Mn-cherts from a Tethyan area in Southern Greece. Manganese-oxide hydrothermal sediments are known from a wide variety of oceanic settings, including both on and off the axis of spreading ridges, in back-arc basins, arc-related areas, rifts and in small ocean basins. These Mn-rich sediments differ markedly from the chemical composition of better known metalliferous deposits associated with high-temperature black smokers (i.e. Fe-rich ochres and Fe-Mn-rich umbers). The ancient example discussed in detail here is that of Late Jurassic Mn-rich cherts spatially associated with basic-intermediate composition volcanics within sutured oceanic units in the Peloponnese, S Greece. The Mn enrichment there is interpreted as related to hydrothermal activity associated with Late Jurassic off-axis volcanism, rather than to a spreading ridge source. The Mn is strongly fractionated from Fe and is concentrated in thin beds and laminations, interpreted as of primary depositional origin. The silica is assumed to be mainly biogenic, as reflected in an association with red radiolarian cherts. The source hydrothermal activity is likely to have been of low-temperature type. Similar Mn-oxide deposits occur elsewhere in the Mesozoic Tethyan area, including N Greece, SW Turkey, Cyprus and Oman, and in other orogenic belts (e.g. in California). There are also metamorphosed counterparts of Mn-rich hydrothermal deposits that include metalliferous pelites and cherts; e.g. Cyclades, S Greece and Franciscan Complex, California. The record of deep-sea hydrothermal deposits exposed on land following tectonic emplacement is biased towards off-axis Mn-deposits within abyssal sediments, since axial spreading ridges (including massive sulphides, umbers and ochres) are rarely preserved, owing to subduction.