predicting the elastic response of organic rich shale using nanoscale measurements and homogenisation methods determination of the mechanical response of shales through experimental procedures is a practical challenge due to their heterogeneity and the practical difficulties of retrieving good quality core samples here we investigate the possibility of using multiscale homogenisation techniques to predict the macroscopic mechanical response of shales based on quantitative mineralogical descriptions we use the novel peakforce quantitative nanomechanical mapping technique to generate high resolution mechanical images of shales allowing the response of porous clay organic matter and mineral inclusions to be measured at the nanoscale these observations support some of the assumptions previously made in the use of homogenisation methods to estimate the elastic properties of shale and also earlier estimates of the mechanical properties of organic matter we evaluate the applicability of homogenisation techniques against measured elastic responses of organic rich shales partly from published data and also from new indentation tests carried out in this work comparison of experimental values of the elastic constants of shale samples with those predicted by homogenisation methods showed that almost all predictions were within the standard deviation of experimental data this suggests that the homogenisation approach is a useful way of estimating the elastic and mechanical properties of shales in situations where conventional rock mechanics test data cannot be measured

volcaniclastic rocks and volcaniclastic facies in the middle precambrian aphebian belcher group northwest territories canada the middle precambrian flaherty formation consists of a thick sequence of volcanic rocks of both effusive and explosive origin derived from a source area west of the belcher islands the effusive

proterozoic continental volcanism in the belcher islands implications for the evolution of the circum ungava fold belt the belcher islands of eastern hudson bay expose a continuous sequence of early proterozoic volcanics and continental and shallow marine sedimentary rocks the volcanic rocks comprise two sequences of continental basalts the older eskimo formation and the younger flaherty formation the flows of both formations are composed of tholeiitic basalts mgo 9 wt which in each formation are divided into two groups based on the concentrations of high field strength elements both groups of eskimo flows have fractionated rare earth element ree patterns with negative nb anomalies relative to eskimo flows the flaherty flows have flatter ree profiles and higher nb contents the chemical variations observed in the eskimo flows are consistent with an assimilation fractional crystallization process involving a lower continental crust contaminant the major and most trace element trends of the flaherty flows are attributed to gabbroic crystal fractionation of two parental liquids which are interpreted to

intrinsic elasticity of a textured transversely isotropic muscovite aggregate comparisons to the seismic anisotropy of schists and shales 1 the anisotropic properties of phyllosilicate rocks are investigated through the modeling of the pore free intrinsic elasticity of a textured muscovite aggregate the elastic constants were calculated for textures as defined using orientation distribution functions odfs ranging from perfectly aligned to completely random the odfs were described using a gaussian distribution the width of which is controlled by the standard deviation of the orientations of the crystal c axis with respect to the sample foliation plane under the assumption that the sample has hexagonal transversely isotropic symmetry the values were obtained using the widely used voigt reuss hill averaging techniques as well as the geometric mean average gma the gma is more physically meaningful in that it requires that the elastic constants determined in either the stiffness or the compliance domains be invertible comparisons between these different averages indicate that strictly the voigt and reuss values do not necessarily provide the limiting bounds as is expected for the isotropic case despite this some characteristics of the elastic wave p wave anisotropy are only weakly dependent on the averaging procedure employed the calculated elastic constants are converted to the anisotropic and parameters in order to allow for comparison to existing measurements in the literature however these intrinsic results are not intended to provide a measure of the properties of phyllites per se but to provide a reference against which more sophisticated models that incorporate porosity layering and composition may be constructed

ultrasonic velocity and anisotropy of hydrocarbon source rocks an experimental study of the physical properties of black kerogen rich shales also including maturation analysis scanning electron microscope sem observations and physical modeling revealed fairly peculiar petrophysical parameters specifically these rocks have very low porosity and density but most importantly both p and s ultrasonic velocities normal to bedding are extremely low whereas they are much higher parallel to bedding giving rise to a strong anisotropy even at high confining pressures we found that these parameters primarily reflect kerogen content microstructure and maturation level of these rocks we found also that microcracks inferred from ultrasonic velocity measurements occur only in mature shales these microcracks are parallel to the bedding plane and further enhance strong intrinsic anisotropy notably at low effective pressure our results show that on a small scale kerogen rich shales are transversely isotropic rocks and can be effectively modeled using the thin laye

understanding of elastic anisotropy of shale under triaxial loading porosity deformation approach abstracttheoretical models for the description of stress dependencies for anisotropic rocks are important for building velocity models and the interpretation of seismic data with respect to stress lithology and pore content especially important is the accurate description of the change of anisotropy due to applied anisotropic stress by means of a quantitative model to aid the interpretation the porosity deformation approach pda originally introduced as the piezosensitivity theory describes stress induced changes of elastic properties without any knowledge about the geometry and orientation of the microcracks we have developed a formulation of the theory for a transverse isotropic rock which was loaded parallel to the bedding plane and we found that it can be described theoretically as an orthorhombic rock we also found out how properties that described the velocity change due to hydrostatic loading can be used to predict elastic anisotropy under additional axial loading the number of free para

stress concentrations and failure modes in horizontal wells accounting for elastic anisotropy of shale formations abstract this study presents a systematic analysis of stress changes near the horizontal well sections drilled in shale and clay formations using a new approach most of the prior analyses of stress concentrations and wellbore stability in anisotropic shale formations use the traditional lekhnitskii amadei solutions we present a faster set of analytical stress functions based on largely overlooked solutions by green and taylor first the full theoretical range of possible compliances for transverse isotropic materials is evaluated using data for 5 shale clay samples and 12 additional test materials contour plots show the principal stress trajectory patterns and variation in the spatial stress concentration due to deviation from isotropic elasticity next we show how uni axial far field stress solutions can be mutually superposed and combined with stress function solutions for local stress concentration due to internal pressure on the wellbore the reappraised set of green and taylor equations is then applied to horizontal wells in three andersonian stress states for compressional strike slip and extensional basins the stress concentrations in the horizontal wellbore are evaluated for well depths between 0 and 10 000 ft using the elastic stiffnesses from five shale and clay samples to show the stress deviations from the isotropic reference case finally a full wellbore stability evaluation model combines the stress concentrations around the wellbore with failure criteria to determine the safe drilling window at each well depth for each andersonian stress state practical graphs and supporting equations are provided to assess wellbore stability in transverse isotropic shale

controlled laboratory experiments to assess the geomechanical influence of subsurface injection and depletion processes on 4d seismic responses laboratory experiments are performed with soft synthetic reservoir sandstone cemented under stress and with synthetic overburden caprock material consisting of compacted clay kaolinite in brine the rock like materials are loaded mechanically under stress paths representative of stress changes occurring in the subsurface as a result of injection increasing pore pressure or depletion followed by injection into a storage reservoir static stress strain behaviour and multidirectional p and s wave velocities are monitored during the tests the tests with sandstone are performed on dry material and simple poroelastic modelling is performed to relate these data to the behaviour of fluid water co2 saturated samples under the same stress paths the focus is on identifying 4d seismic attributes that may be used in the field to interpret monitoring measurements this could help diagnose stress changes in the overburden signalling the risk of co2 leakage from a reservoir if the compressive or tensile strength limit of the overburden is reached and of course to help quantify amounts of co2 stored

stress dependent anisotropy in transversely isotropic rocks comparison between theory and laboratory experiment on shale understanding the effect of stress and pore pressure on seismic velocities is important for overpressure prediction and for 4d reflection seismic interpretation a porosity deformation approach originally called the piezosensitivity theory and its anisotropic extension describe elastic moduli of rocks as nonlinear functions of the effective stress this theory assumes a presence of stiff and compliant parts of the pore space the stress dependent geometry of the compliant pore space predominantly controls stress induced changes in elastic moduli we show how to apply this theory to a shale that is transversely isotropic ti under unloaded conditions the porosity deformation approach shows that components of the compliance tensor depend on exponential functions of the principal components of the effective stress tensor in the case of a hydrostatic loading of a ti rock only the diagonal elements of this tensor expressed in contracted notation are significantly stress dependent two equal shear compo

velocity anisotropy of upper jurassic organic rich shales norwegian continental shelf abstractthis study investigates the seismic velocity anisotropy of two organic rich shales from the norwegian continental shelf the tested organic rich shale samples were from the upper jurassic draupne and hekkingen formations collected from two wells 16 8 3s and 7125 1 1 drilled in the central north sea and western barents sea respectively the two tested shales are different in organic matter richness and thermal maturation and they have experienced different burial histories the shale core plugs were tested in a triaxial cell under controlled pore pressure seismic velocities vp and vs were measured along different orientations with respect to layering to identify the complete tensor of the rock elastic moduli and to investigate the velocity anisotropy as a function of increasing effective stress the measured velocity values exhibit strong anisotropy for the two tested organic rich shales the anisotropy for both shales is strongest for vs seismic velocities follow an increasing trend as th

seismic velocity anisotropy of phyllosilicate rich rocks characteristics inferred from experimental and crack model studies of biotite rich schist summary seismic velocity anisotropy of biotite schist 30 per cent mode biotite was measured under confining pressures up to 150 mpa the rock shows weak orthotropy which was altered from transverse isotropy ti generated by biotite preferred orientation the orthotropy was caused by microfolding in the rock the velocity increase under confining pressure indicates that most crack planes are aligned parallel to the cleavage planes silicate sheet of the oriented biotite minerals the anisotropy of the rock is basically ti due to both the aligned biotite minerals and cracks which have a common symmetry axis we found that other sheet silicate rich rocks have a similar anisotropy with the biotite schist in which the ti type anisotropy is characterized by the slow p and s wave velocities along the symmetry axis this is caused by the preferred orientation of sheet silicate minerals and the extremely slow p and s wave velocities along the axis perpendicular to the silicate sheet compared to the directions along the silicate sheet when rock contains a large percentage of highly oriented sheet silicates the fast and slow shear waves exchange their polarities at some off symmetry axis directions indicating that the qswave quasi s wave velocity exceeds the sh wave velocity the phase velocity distribution of qs wave shows an asymmetry with respect to the angle from the symmetry axis which is characterized by a bulge in this distribution located near the symmetric axis this is inherent to most sheet silicate minerals when crack density of aligned cracks increases the p wave velocity along the symmetry axis decreases considerably the qs wave phase velocity in the off axis directions also decreases in accordance with the decrease of the p velocity along the symmetry axis the asymmetry of the qs wave phase velocity distribution increases as the p wave velocity decreases along the symmetry axis this relationship can be well understood by means of berryman s extended thomsen approach

attenuation anisotropy in shale at elevated confining pressures shale has been estimated to comprise approximately two thirds of all sedimentary rocks 1 nevertheless studies of the physical properties of shale are relatively uncommon compared to other sedimentary lithologies especially rare are studies of shale attenuation anisotropy at elevated confining pressure an understanding of attenuation and attenuation mechanisms is particularly important for seismic exploration vsp and cross well experiments have used attenuation information to help determine the lithology of subsurface formations 2 4 attenuation is also believed to have a significant affect on avo responses 5 and may affect lithological interpretations based on avo analyses measurements of attenuation have been correlated with fluid content e g 6 and porosity e g 7 and may be used to determine in situ hydraulic properties seismic attenuation has also been linked to rock strength 8 9 and may be useful in relation to blasting and the location of landslide material accurate values of attenuation are also necessary to estimate ground motion associated with earthquakes 10 11 shale has been shown to have significant velocity anisotropy e g 12 that persists at elevated confining pressure it is unclear however whether attenuation displays the same anisotropic relationships with pressure previous studies of attenuation in shale have involved either measurements in a single direction measurements at atmospheric pressure or measurements on unsaturated samples only e g 13 15 this study provides the first measurements of shale attenuation in multiple directions at elevated confining pressure under both saturated and unsaturated conditions laboratory measurements have been made on four samples up to 250 mpa velocity and attenuation have been measured parallel and perpendicular to

velocity anisotropy of shales and depth estimation in the north sea basin it is known that in the north sea basin the depths to major reflectors as determined from surface seismic data are often larger than the well log depths from a study of data sets which tie 21 wells i found a strong correlation between the occurrence of the depth error and the presence of shales in the subsurface assuming that the error is caused by elliptical velocity anisotropy in shales i measured the anisotropy from a comparison of the well log sonic data and the interval velocity profile obtained from the surface seismic data and also from a comparison of the seismic depth and the well log depth it was found that the two methods of measurements agree with each other and also agree qualitatively with the previous laboratory measurements of anisotropy in shale samples the results strongly suggest that the depth anomaly in the north sea basin is caused by the velocity anisotropy of shales a simple method to correct the seismic depth is given

experimental mechanical compaction of reconstituted shale and mudstone aggregates investigation of petrophysical and acoustic properties of sw barents sea cap rock sequences abstract this study investigates petrophysical and acoustic properties of experimentally compacted reconstituted samples of seal sequences from the southwestern barents sea the aggregates were collected from drill cuttings of mudstone and shale formations of two exploration wells 7220 10 1 salina discovery and 7122 7 3 goliat field the washed and freeze dried samples were characterized for grain size distributions geochemical analyses and mineralogical compositions a total of 25 compaction tests 12 dry and 13 brine saturated were performed with a maximum effective vertical stress of 50 mpa the laboratory measurements demonstrated that petrophysical and acoustic properties of argillaceous sediments can change within a sedimentary basin and even within a given formation the results show that the collected aggregates from goliat field are compacted more compared to salina discovery the maximum and minimum compaction are measured in samples collected from snadd and fuglen formations respectively the final porosity of brine saturated specimens varies between 5 and 22 the ultrasonic velocity measurements depict that samples with the same porosity values can have a broad range of velocity values the resulting compaction trends in this study were compared to published compaction curves for synthetic mixtures of quartz and clay all compaction trends show higher porosity reduction than the silt fraction with 100 quartz comparison of experimental compaction result of each mudstone and shale aggregate with its corresponding acquired well log data helps to delineate the burial history and exhumation in the study area a net exhumation of 950 m and 800 m is estimated at salina and goliat wells respectively the outcomes of this study can provide insights for hydrocarbon prospect discovery in a pre mature sedimentary basin in terms of exploration and production and also for geological co2 storage sites the experimental results may provide information for well log and seismic interpretation basin modeling and seal integrity of investigated horizons

metallogenesis of an early proterozoic foreland sequence eastern hudson bay canada on the e side of hudson bay the nw margin of the archaean superior structural province is overlain by an unmetamorphosed little deformed early proterozoic supracrustal sequence the sequence is divisible into three parts possible tectosomes each characterized by a distinct style of mineralization the arkosic alluvial richmond gulf group was shed eastward from a thermal uplift and has been preserved only in a later aulacogen the richmond gulf graben it contains an apatite cemented redbed secondly a widespread post aulacogen carbonate rich w facing miogeocline blanketed the region a pyritic zone developed at its basal contact is particularly thick and hosts disseminated copper mineralization where formed on the arkose in the graben a pyritic brecciated stromatolite rich horizon within the carbonate contains galena and sphalerite thirdly widespread iron formation and a local 60 cm thick manganese carbonate bed overlying w derived basalt flows flysch and arkosic molasse all of uncertain tectonic affinity terminate the sequence

elastic anisotropy of core samples from the taiwan chelungpu fault drilling project tcdp direct 3 d measurements and weak anisotropy approximations summary the study of seismic anisotropy has become a powerful tool to decipher rock physics attributes in reservoirs or in complex tectonic settings we compare direct 3 d measurements of p wave velocity in 132 different directions on spherical rock samples to the prediction of the approximate model proposed by louis et al based on a tensorial approach the data set includes measurements on dry spheres under confining pressure ranging from 5 to 200 mpa for three sandstones retrieved at a depth of 850 1365 and 1394 metres in tcdp hole a taiwan chelungpu fault drilling project as long as the p wave velocity anisotropy is weak we show that the predictions of the approximate model are in good agreement with the measurements as the tensorial method is designed to work with cylindrical samples cored in three orthogonal directions a significant gain both in the number of measurements involved and in sample preparation is achieved compared to measurements on spheres we analysed the pressure dependence of the velocity field and show that as the confining pressure is raised the velocity increases the anisotropy decreases but remains significant even at high pressure and the shape of the ellipsoid representing the velocity or elastic fabric evolves from elongated to planar these observations can be accounted for by considering the existence of both isotropic and anisotropic crack distributions and their evolution with applied pressure

geochemistry and tectonic setting of lewisian clastic metasediments from the early proterozoic loch maree group of gairloch nw scotland abstract the early proterozoic 2 0 ga loch maree group lmg of the lewisian complex consists of a supracrustal sequence of metasedimentary schists and associated tholeiitic metavolcanic amphibolites within the archaean basement the metasediments comprise three main mapped units the flowerdale schists kerrysdale schists and charlestown schists together with numerous narrower bands the dominant clastic metasediments within the schist units semipelites and psammites are chemically distinguished as a series of greywackes and lithic sandstones with variable lil and transition element abundances fractionated ree patterns and overall compositions similar to paas three chemical groups are recognized whose range of composition largely reflects the mixing between two main source components lewisian gneissose basement with an intermediate acid continental crust composition and local rift related amphibolites with a primitive tholeiitic composition which also incorporates components not preserved within the lmg the geochemistry of the clastic metasediments confirms a previous tectonic model for the lmg as an intracontinental extensional rift receiving clastic detritus from the adjacent uplifted basement as well as from internal volcanogenic sources

microfracturing and microporosity in shales shales are ubiquitous rocks in sedimentary basins where their low permeability makes them efficient seals for conventional oil and gas reservoirs and underground waste storage repositories waste waters co2 nuclear fuels moreover when they contain organic matter they form source rocks for hydrocarbons that may escape towards a more porous reservoir during burial a process referred to as primary migration and when the hydrocarbons cannot escape these rocks can be exploited as oil or shale gas reservoirs while the presence of fractures at the outcrop scale has been described the existence of fractures at smaller scales their link with microporosity the mechanisms that created them their persistence over geological times and their effect on the petrophysical properties of shales represent scientific challenges for which drillings in various sedimentary basins over the past decades may hold timely key data here we review and synthetize the current knowledge on how microfractures and micropores in shales can be imaged and characterized and how they control their anisotropic mechanical properties and permeability one question is whether such microfractures when observed in outcrops or in drilled core samples extracted from boreholes are related to decompaction and do not exist at depth another question is whether veins observed in shales represent microfractures that were open long enough to have acted as flow paths across the formation the mechanisms of microfracture development are described some have an internal origin fracturing by maturation of organic matter dehydration of clays while others are caused by external factors tectonic loading importantly the amount of microfracturing in shales is shown to depend strongly on the content in 1 organic matter and 2 strong minerals the nucleation of microfractures depends on the existence of mechanical heterogeneities down to the nanometer scale their propagation and linkage to create a percolating network will depend on the presence of heterogeneities at the meso to macro scales such percolating microfracture networks could control both the long term sealing capabilities of cap rocks and the further propagation of hydraulic fracturing cracks finally possible areas of research for describing the mechanism of microfracture formation in greater detail and how this impacts the transport and mechanical properties of shales are also discussed

ultrasonic velocity and mechanical anisotropy of synthetic shale with different types of clay minerals clay minerals are the most abundant materials in shale their presence significantly influences the elastic behavior of reservoir rocks as a function of mineral type volume and distribution and their orientation controls the shale s intrinsic anisotropic behaviors thus knowing the elastic properties of shale with different types of clay minerals is imperative for fully understanding the seismic properties of the reservoir however it is extremely difficult to measure the elastic properties of natural shale by means of a single variable in this case the type of clay due to the influences of multiple factors including water toc content complex minerals composition and so on thus we use quartz clay kaolinite illite and smectite carbonate and kerogen extract as the primary materials to construct synthetic shale with different types of clay ultrasonic experiments were conducted to study the anisotropy of velocity and mechanical properties young s modulus and poisson s ratio in dry synth

basinal and shelf sedimentation in relation to the archaean proterozoic boundary abstract in most countries the archaean proterozoic boundary has been designated as an unconformity between the oldest shelf type quartz arenites and a basement consisting of greenstone belts intruded by granitic rocks or high grade gneisses the quartz arenites have been characterized as shallow water shelf deposits and sediments in the greenstone belts as resedimented basinal wackes of volcanogenic origin radiometric ages for rocks of the canadian shield led to initial designation of the archaean proterozoic boundary as thus defined at about 2 5 ga subsequent age determinations have clearly established that a number of quartz arenites originally assigned to the proterozoic are 2 7 2 94 ga old e g witwatersrand and pongola supergroups of south africa to accommodate these old quartz arenites some have suggested that the arch aean proterozoic boundary should be regarded as diachronous embracing a span of time about equivalent to that of the phanerozoic however quartz arenites also are abundant in 3 2 3 5 ga old greenstone belts and high grade metamorphic terranes of south africa western australia and the u s a likewise large regions of basinal volcanogenic sediments occur in post 2 5 ga terranes this greatly expands the diachroneity of geological units that were initially regarded as either uniquely archaean or proterozoic we therefore recommend that chronometric and chronostratigraphic sense be retained for the archaean proterozoic boundary divested of the requirement for all quartz arenites to be proterozoic according to this analysis of the precambrian record shelf sediments have increased in abundance relative to basinal sediments through time but at different rates in different areas this change is attributable to progressive cratonization of shield areas a process that was strongly diachronous on a worldwide scale

impact of fabric microcracks and stress field on shale anisotropy summary few data are available on shales in terms of seismic to ultrasonic properties and anisotropy although all are important with regards to imaging problems often encountered in such lithologies additionally mechanisms causing changes in these properties are not well documented due to the fine grain size of such materials and time required for testing under controlled pore pressure conditions the results presented here are derived from a set of experiments run on muderong shale with pore pressure control in order to evaluate the effect of stress magnitude and stress anisotropy on ultrasonic response this shale was noted to have a linear velocitymean effective stress response and extremely high anisotropy both likely the result of the presence of fluid filled cracks in a low permeability porous medium changes in velocity and vp vs ratios are dependent on both stress and smectite content s wave velocity is significantly affected by the presence of smectite in this and other shales and at low stress 20 mpa is less sensitive to stress change than p wave velocity vp vs ratios are noted to increase in this shale up to 20 mpa effective stress then decrease slightly due to stress induced loss of interlayer water in smectite intrinsic anisotropy comes from composition a strong compaction fabric and the presence of microfractures changes to ultrasonic anisotropy are the result of the magnitude of the stresses their orientation with respect to the fractures and the degree of stress anisotropy

the sediment delivery problem abstract the linking of on site rates of erosion and soil loss within a drainage basin to the sediment yield at the basin outlet and improved knowledge and representation of the associated processes of sediment delivery represent a major research need within the field of erosion and sedimentation and also an important scale problem in drainage basin studies this paper reviews the limitations of the sediment delivery ratio concept by considering the problems of temporal and spatial lumping and its blackbox nature some recent advances in our understanding of the sediment delivery system and its modelling are described and the lack of detailed empirical investigations is highlighted the significance of recent concern for the role of sediments in the transport of nutrients and contaminants to sediment delivery studies is introduced and the need for further work in this field is emphasised

estimation of stress dependent anisotropy from p wave measurements on a spherical sample our aim is to understand the stress dependent seismic anisotropy of the overburden shale in an oil field in the north west shelf of western australia we analyze data from measurements of ultrasonic p wave velocities in 132 directions for confining pressures of 0 1 400 mpa on a spherical shale sample first we find the orientation of the symmetry axis assuming that the sample is transversely isotropic and then transform the ray velocities to the symmetry axis coordinates we use two parameterizations of the phase velocity one in terms of the thomsen anisotropy parameters a b e d as the main approach and the other in terms of a b g d we invert the ray velocities to estimate the anisotropy parameters a e d and g using a very fast simulated reannealing algorithm both approaches result in the same estimation for the anisotropy parameters but with different uncertainties the main approach is robust but produces higher uncertainties in particular for g whereas the alternative approach is unstable but gives lower uncertainties these approaches are used to find the anisotropy parameters for the different confining pressures the dependency of p wave velocity a on pressure has exponential and linear components which can be contributed to the compliant and stiff porosities the exponential dependence at lower pressures up to 100 mpa corresponds to the closure of compliant pores and microcracks whereas the linear dependence at higher pressures corresponds to contraction of the stiff pores the anisotropy parameters e and d are quite large at lower pressures but decrease exponentially with pressure for lower pressures up to 10 mpa d always is larger than e this trend is reversed for higher pressures despite the hydrostatic pressure the symmetry axis orientation changes noticeably in particular at lower pressures

effects of diagenesis and clays on compressional velocities in rocks experimental results at ultrasonic frequencies in brine or water saturated samples cut perpendicular to bedding demonstrate that compressional velocities vary linearly with porosity and volume fraction clay in detrital silicate rocks characterized by pores with low aspect ratios p wave velocity is more sensitive to porosity than clay content obeying the empirically derived expression vp 2 4c 8 6 5 8 at 800 bars confining pressure and 400 bars pore pressure where the units of vp are kilometers per second is the volume fraction pores and c is the volume fraction clay deviations from this equation are less than 2 with the exception of the high pore aspect ratio st peter sandstone which has a compressional velocity that is 17 higher than the predicted value the equation is insensitive to the chemical compostion of the dominant clay mineral and apparently insensitive to the location of the clay grains with respect to the mineral framework e g in free pore space or in contact zones between mineral grains of lower compressibilities

a simplified model of effective elasticity for anisotropic shales a simple method to deal with cracklike pores in anisotropic matrix rock such as shales enhances analytical models and their applications actually clayrocks shales in particular are the dominant clastic component in sedimentary basins representing about two thirds of all sedimentary rocks shales are usually assumed to be transversely isotropic ti media they are known to be highly anisotropic because of 1 intrinsic elastic anisotropy of the solid phase matrix forming the rock more or less ordered clay layers and 2 anisotropy induced by the presence of cracklike pores we focus on this second component of anisotropy current analytical models deal with it but they are complex and are restricted in the case of matrix ti symmetry to cracks lying in the symmetry plane we simplify such models within a reasonably good approximation and develop an analysis scheme in which cracklike pore effects are calculated in an equivalent isotropic matrix this simplifies the theoretical approach and potentially broadens its application to any crack and or pore orientation e g damaged shale with horizontal and vertical perpendicular to the bedding plane cracks a high pressure confinement test provides experimental data for checking the proposed tool against a reference model in the case of cracklike pores lying in the bedding plane the results in terms of thomsen parameters are consistent with results from large scale field data

stress induced seismic azimuthal anisotropy in the upper crust across the north west shelf australia seismic azimuthal anisotropy saa is observed in many areas of the earth and fast polarized directions have been mapped using earthquake surface waves and teleseismic s wave splitting over large regional and tectonic scales higher resolution petroleum exploration data including 3 d seismic surveys and dipole shear logs often exhibit azimuthal anisotropy however we are unaware of any published studies mapping saa from exploration scale data to study large scale regional and tectonic saa trends the physical mechanisms causing saa in earthquake data are a subject of great interest comparing regional trends to the higher resolution exploration trends may help understand these mechanisms we present a saa analysis using seismic exploration data across the north west shelf nws of australia we map the fast polarization directions from 34 dipole shear logs and two 3 d seismic surveys and compare them to in situ maximum horizontal stress orientations h our results show that the and h trends correlate across a geographical area spanning almost 2000 km and are similar to published results in the region from earthquake seismology these results suggest that differential horizontal stress is the likely mechanism causing saa at a wide range of spatial scales on the nws of australia we also show that saa is not observed at exploration scales in some areas of the nws and propose a lithology dependent stress sensitivity model in which saa is strongest in clean unconsolidated quartz dominated sandstones and weaker or nonexistent in well consolidated cemented rocks and shale dominated sediments

estimation of the anisotropy parameters of transversely isotropic shales with a tilted symmetry axis summary this paper reports a new approach for the estimation of thomsen anisotropy parameters and symmetry axis orientation from ultrasonic p wave traveltime measurements on transversely isotropic shale samples of arbitrary geometry this approach can be used for core samples cut in any direction with respect to the bedding plane because no a priori assumption regarding the symmetry axis orientation is made this orientation is rather part of the solution of the inverse problem together with the anisotropy parameters themselves very fast simulated reannealing is used to search for the best possible estimate of the model parameters the methodology is applied to spherical and cylindrical anisotropic shale samples

subaqueous deposition of accretionary lapilli significance for palaeoenvironmental interpretations in archaean greenstone belts abstract accretionary lapilli from phreatomagmatic eruptions are abundant in the late archaean fortescue group of the pilbara region western australia where the sequence is uncleaved and gently folded well preserved depositional structures include densely packed accretionary lapilli in trough cross beds and sparse accretionary lapilli in trough and wedge to tabular cross beds accretionary lapilli also occur in conglomerate layers and localised pebbly channel fills associated with granite and pegmatite clasts up to 10 cm in diameter these lapilli are clearly robust being capable of withstanding fairly energetic aqueous transport in contrast to the opinion of many authors who consider that all accretionary lapilli would disintegrate if settled through extensive water columns or incorporated in turbidite deposits accretionary lapilli indicate subaerial or very shallow water eruption but their presence cannot be used alone to support very shallow water or subaerial deposition accretionary lapilli are found throughout many volcanic piles and are probably widespread in archaean greenstone successions but their environmental significance has to be assessed carefully using a variety of associated features

the umsoli chert turbidite testament for a major phreatoplinian event at the onverwacht fig tree transition swaziland supergroup archaean south africa abstract the volcanogenic origin of accretionary grains in the oolitic umsoli chert is proved by the unequivocal identification of constituent vesicular and pumiceous ash particles by the discovery of authigenic alkali feldspars and by the k meta bentonite parentage of associated illites celadonites ash particle morphology and ash grain size distribution suggest a phreato magmatic process of eruption sedimentary structures indicate that the felsic ash precursor of this ancient chert was deposited by turbidity currents the sedimentologic model invokes the transition of parts of pyroclastic falls and base surges into turbidites accretionary lapilli forming a major constituent of this silicified tuff oolite may be indicators of subaerial eruption but they can probably not be used as evidence for subaerial deposition

measured anisotropy in pierre shale the five elastic coefficients which characterize a transversely isotropic medium have been measured for the pierre shale the first arrival times deduced from two closely spaced vertical seismic profiles provide values of magnitude and direction of the phase velocity at a given depth for different locations of the sources from these velocities we can estimate the five elastic coefficients by assuming that the p and sv wave velocities have only a small dependence on the angle of propagation on the other hand it is shown that the accuracy in the difference between the directions of propagation and particle motion is not sufficient to determine the anisotropy this work was industrially sponsored through the integrated geophysics project

anisotropic effective medium modeling of the elastic properties of shales shales are complex porous materials normally consisting of percolating and interpenetrating fluid and solid phases the solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure the shape orientation and connection of the two phases control the anisotropic elastic properties of the composite solid we develop a theoretical framework that allows us to predict the effective elastic properties of shales its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments the theory is based on a combination of anisotropic formulations of the self consistent sca and differential effective medium dem approximations this combination guarantees that both the fluid and solid phases percolate at all porosities our modeling of the elastic properties of shales proceeds in four steps first we consider the case of an aligned biconnected clay fluid composite composed of ellipsoidal inclusion

stress anisotropy and velocity anisotropy in low porosity shale abstract shales are known for often marked intrinsic anisotropy of many of their properties including strength permeability and velocity for example in addition it is well known that anisotropic stress fields can also have a significant impact on anisotropy of velocity even in an isotropic medium this paper sets out to investigate the ultrasonic velocity response of well characterised low porosity shales from the officer basin in western australia to both isotropic and anisotropic stress fields and to evaluate the velocity response to the changing stress field during consolidated undrained multi stage triaxial tests on core plugs cut normal to bedding vpv increases monotonically with increasing effective stress and vs1 behaves similarly although with some scatter vph and vsh remain constant initially but then decrease within each stage of the multi stage test although velocity from stage to stage at any given differential stress increases this has the impact of decreasing both p wave e and s wave anisotropy through application of differential stress within each loading stage however increasing the magnitude of an isotropic stress field has little effect on the velocity anisotropies the intrinsic anisotropy of the shale remains reasonably high at the highest confining pressures the results indicate the magnitude and orientation of the stress anisotropy with respect to the shale microfabric has a significant impact on the velocity response to changing stress fields

elastic properties of anisotropic synthetic calcite muscovite aggregates 1 a set of synthetic aggregates containing mixtures of calcite and muscovite were compacted with varying uniaxial loads ranging from 20 mpa up to 400 mpa their elastic properties have been measured using compressional and shear waves in confining hydrostatic pressures up to 475 mpa measured seismic velocities are shown to depend on 1 the ratio of calcite to muscovite 2 the uniaxial load used during sample manufacturing and 3 the porosity amount prior to velocity measurements the matrix framework may also affect the seismic velocities but this effect is not easily quantifiable in general measured seismic velocities decrease with increasing muscovite content and porosity elastic properties have been calculated based on texture measurements which were obtained by neutron diffraction the calculated velocities are based on the calcite and muscovite single crystal elastic tensors their orientation distribution functions and their modal fractions a large discrepancy is apparent between calculated and measured velocities where the former always overestimate the actual velocities shear waves display less of a difference between calculated and measured values than do compressional waves indicating that waves propagating by shearing are less affected by sample porosity and matrix framework a better agreement between measured and calculated seismic velocities arises when the initial porosity is taken into account using a differential effective medium model seismic anisotropy is evident from both measured and calculated velocities and is low for samples containing pure calcite but becomes prominent as the muscovite concentration increases the intensity of anisotropy further depends on the uniaxial load used during sample compaction and the initial porosity

ultrasonic velocities in cretaceous shales from the williston basin compressional and shear wave velocities were measured in the laboratory from 1 bar to 4 kbar confining pressure for wet undrained samples of cretaceous shales from depths of 3200 and 5000 ft in the williston basin north dakota these shales behave as transversely isotropic elastic media the plane of circular symmetry coinciding with the bedding plane for compressional waves the velocity is higher for propagation in the bedding plane than at right angles to it and the anisotropy is greater for the 5000 ft shale for shear waves the sh wave perpendicular to bedding and the sv wave parallel to bedding propagate with the same speed which is about 25 percent lower than that for the sh wave parallel to bedding in general compressional and shear velocities are higher for the indurated 5000 ft shale than for the friable 3200 ft shale all velocities increase with in increasing confining pressure to 4 kbar the 3200 ft shale exhibits velocity hysteresis as a function of pressure whereas this effect is a

sonic logging in deviated boreholes penetrating an anisotropic formation laboratory study development of deepwater fields requires drilling deviated or horizontal wells many formations are highly anisotropic that is the p and s wave velocities vary with propagation direction sonic logs acquired in these wells need to be corrected for anisotropy effects before the logs can be used in formation evaluation and seismic applications in this study we use a laboratory model made of an orthorhombic phenolite block to study acoustic logging in deviated wells we first measure the qp qsv and sh wave group velocities by using body waves at angles of 0 15 30 45 60 75 and 90 relative to the slowest p wave principal axis of the phenolite block we then drill holes at the same angles in the block we record monopole and dipole sonic waveforms in these holes and extract the qp qsv sh and stoneley wave velocities by using the slowness time semblance method the velocities measured through the use of monopole logging and dipole logging vary with borehole deviations we find that an equivalent transversely isotropic ti model can fit the measured qp qsv and stoneley wave velocities very well the s wave velocities at low to medium borehole deviations can be used to differentiate an orthorhombic material from a ti one

iron formations a global record of neoarchaean to palaeoproterozoic environmental history abstract iron formations if represent an iron rich rock type that typifies many archaean and proterozoic supracrustal successions and are chemical archives of precambrian seawater chemistry and post depositional iron cycling given that if accumulated on the seafloor for over two billion years of earth s early history changes in their chemical mineralogical and isotopic compositions offer a unique glimpse into environmental changes that took place on the evolving earth perhaps one of the most significant events was the transition from an anoxic planet to one where oxygen was persistently present within the marine water column and atmosphere linked to this progressive global oxygenation was the evolution of aerobic microbial metabolisms that fundamentally influenced continental weathering processes the supply of nutrients to the oceans and ultimately diversification of the biosphere and complex life forms many of the key recent innovations in understanding if genesis are linked to geobiology since biologically assisted fe ii oxidation either directly through photoferrotrophy or indirectly through oxygenic photosynthesis provides a process for if deposition from mineral precursors the abundance and isotope composition of fe ii bearing minerals in if additionally suggests microbial fe iii reduction a metabolism that is deeply rooted in the archaea and bacteria linkages among geobiology hydrothermal systems and deposition of if have been traditionally overlooked but now form a coherent model for this unique rock type this paper reviews the defining features of if and their distribution through the neoarchaean and palaeoproterozoic this paper is an update of previous reviews by bekker et al 2010 2014 that will improve the quantitative framework we use to interpret if deposition in this work we also discuss how recent discoveries have provided new insights into the processes underpinning the global rise in atmospheric oxygen and the geochemical evolution of the oceans

geomechanical appraisal and prospectivity analysis of the goldwyer shale accounting for stress variation and formation anisotropy abstract profitable exploitation of unconventional shale gas reservoirs relies on the success of hydraulic fracturing stimulation this is more likely in brittle rock formations because natural and hydraulic fractures remain open after stimulation allowing for more hydrocarbon production identification of the most favourable depth intervals relies on the robust analysis of available well logs and on laboratory derived mechanical and elastic data obtained under controlled stresses replicating the actual conditions at depth beyond their use for predictive geomechanical modelling such laboratory data can act as calibration points for existing well logs well logs can also be used to guide the selection of the rock samples to be characterised and tested in the laboratory ensuring that they are representative of the rock formation here we apply the above principles and demonstrate how this improves the geomechanical appraisal of the goldwyer formation and assesses its prospectivity this workflow integrates rock eval geochemical analyses elastic properties anisotropy in situ stress state and pore pressure mechanical brittleness and fracturing indices derived from petrophysical and sonic logs in the theia 1 and pictor east 1 wells we estimated an average total organic carbon of 2 w t maximum 5 w t a moderate to high dynamic young s modulus 14 52 gpa a low poisson s ratio 0 24 0 27 and an average elasticity based brittleness index b1 of 41 in the deeper g iii unit this unit also exhibits a low differential horizontal stress ratio and a high fracture index such attributes suggest a good prospectivity of the g iii unit not only in terms of potential resources but as importantly in terms of fracability

cenozoic exhumation on the southwestern barents shelf estimates and uncertainties constrained from compaction and thermal maturity analyses abstract the barents sea is believed to have been influenced in most parts by cenozoic uplift and erosion episodes the rocks in the area are not currently at their maximum burial depth the exhumation of the sedimentary rocks has had large effects on rock physical properties and hydrocarbon maturation and migration the current study seeks to estimate exhumation from shale compaction and thermal maturity techniques and discuss its implications for hydrocarbon exploration in the uplifted barents sea area this study uses well logs and thermal maturity data together with widely distributed shot gather data along long offset seismic reflection lines the use of shale compaction techniques to estimate exhumation was focused particularly on the regionally preserved aptian albian kolmule formation and paleogene torsk formation shales normal compaction reference curves were established for these units in areas currently at their maximum burial depth e g sorvestsnaget basin and vestbakken volcanic province the results suggest widespread cenozoic exhumation throughout the southwestern barents sea the exhumation magnitudes increase towards east and northeast the average exhumation estimates from the three data sources range from 800 to 1400 m within the hammerfest basin 1150 1950 m on the loppa high 1200 1400 m on the finmark platform and 1250 2400 m on the bjarmeland platform the marked differences in glacial erosion from mass balance and average erosion estimates from the current study suggest a significant pre glacial uplift and erosion in the southwestern barents sea area the observed stratigraphy and presence of significant volumes of late oligocene middle miocene sediments in basins at the outer margin and increased erosion rates at the same time in source areas suggest that maximum burial in the southwestern barents sea may have occurred sometime during the oligocene or even earlier in the eocene the results from this study are useful input for modelling of source rock maturation generation migration and trapping of hydrocarbons in the area these results are also an important input for the prediction of more precise reservoir and seal rock properties in frontier areas away from the exploration wells and provide valuable knowledge for the use of interval velocities in the uplifted areas

noncontacting benchtop measurements of the elastic properties of shales we evaluated a laser based noncontacting method to measure the elastic anisotropy of horizontal shale cores whereas conventional transducer data contained an ambiguity between phase and group velocity measurements small laser source and receiver footprints on typical core samples ensured group velocity information in our laboratory measurements with a single dense acquisition of group velocity versus group angle on a horizontal core we estimated the elastic constants c11 c33 and c55 directly from ultrasonic waveforms and c13 from a least squares fit of modeled to measured group velocities the observed significant p wave velocity and attenuation anisotropy in these dry shales were almost surely exaggerated by delamination of clay platelets and microfracturing but provided an illustration of the new laboratory measurement technique although challenges lay ahead to measure preserved shales at in situ conditions in the lab we evaluated the fundamental advantages of the proposed method over conventional transducer measurements

anisotropy effects in p wave and sh wave stacking velocities contain information on lithology depths calculated from s wave stacking velocities and event times almost always exceed actual depths sometimes by as much as 25 percent in contrast depths from corresponding p wave information are often within 10 percent of actual depths discrepancies in depths calculated from p and s wave data are attributed to velocity anisotropy a property of sedimentary rocks that noticeably affects s wave moveout curves but leaves the p wave relatively unaffected two careful studies show that discrepancies in depths and hence in constituent layer thicknesses correlate with lithology discrepancies ranged from an average of 13 percent midland basin to greater than 40 percent paloma field in shales but were within expected errors in massive sandstones or carbonates hence anisotropy effects are indicators of lithology analysis of seismic data involved determining interval velocities from stacking velocities calculating layer thicknesses and then comparing layer thicknesses from s wave data with thickne

comparison between analytical and 3d finite element solutions for borehole stresses in anisotropic elastic rock we present a rigorous validation of the analytical amadei solution for the stress concentration around an arbitrarily orientated borehole in general anisotropic elastic media first we revisit the theoretical framework of the amadei solution and present analytical insights that show that the solution does indeed contain all special cases of symmetry contrary to previous understanding provided that the reduced strain coefficients b11 and b55 are not equal it is shown from theoretical considerations and published experimental data that the b11 and b55 are not equal for realistic rocks second we develop a 3d finite element elastic model within a hybrid analytical numerical workflow that circumvents the need to rebuild and remesh the model for every borehole and material orientation third we show that the borehole stresses computed from the numerical model and the analytical solution match almost perfectly for different borehole orientations vertical deviated and horizontal and for several cases involving isotropic transverse isotropic and orthorhombic symmetries it is concluded that the analytical amadei solution is valid with no restriction on the borehole orientation or the symmetry of the elastic anisotropy

elastic anisotropy modeling of kimmeridge shale 1 anisotropy of elastic properties in clay rich sedimentary rocks has been of long standing interest these rocks are cap rocks of oil and gas reservoirs as well as seals for carbon sequestration elasticity of shales has been approached by direct velocity measurements and by models based on microstructures here we are revisiting the classical kimmeridge shale studied by hornby 1998 by first quantifying microstructural features such as phase volume fractions grain shapes and grain orientations and pore distributions with advanced analytical methods and then using this information in different models to explain bulk elastic properties it is shown that by application of a self consistent algorithm based on eshelby s 1957 model of inclusions in a homogeneous medium it is possible to explain most experimental elastic constants though some discrepancies remain which may be due to the interpretation of experimental data using a differential effective medium approach an almost perfect agreement with experimental stiffness coefficients can be obtained though the physical basis of this method may be questionable the influence of single crystal elastic properties grain shapes preferred orientation and volume and shapes of pores on elastic properties of shale is explored

subaqueous intermediate to silicic composition explosive volcanism a review abstract mass flow deposits of pyroclastic debris commonly consist of two parts a lower coarse grained basal section and an upper finer grained bedded section subaqueous pyroclastic flow deposits particularly those derived from a vertically directed eruption appear better sorted than their subaerial counterparts because of the efficient sorting characteristics of water compared to air subaqueous deposits frequently are depleted in bubble wall pumice that floats off and vitric ash that remains in suspension hence the deposits show a relative enrichment of crystals especially at the bases from 1 flotation and suspension of the vitric material and 2 ingestion of water at the head of the flow a subaqueous volcaniclastic flow deposit may contain evidence indicative of both turbulent and non turbulent movement the flow may have had a turbulent head and non turbulent body or flow transformations may have occurred from 1 collapse of the eruption column 2 changes in slope and in the velocity of the flow and or 3 the amount of water mixed into the flow retention of heat in the subaqueous environment may be enhanced by lateral eruptions high eruption rates large eruptive volumes and little or no mixing of pyroclastic debris with water the lack of welded subaqueous deposits in the geologic record may be a result of 1 effusive rather than explosive eruptions in a deep water environment 2 explosive phreatic disintegration of pyroclastic flows in a shallow subaqueous environment and or 3 the inability of subaerial pumiceous pyroclastic flows to penetrate the land water interface characteristics of explosive intermediate to silicic composition subaqueous volcanic eruptions also have been summarized in terms of 1 environment of the eruption 2 orientation of the eruption and 3 composition of the juvenile debris these three aspects of explosive subaqueous volcanism are ideal end members and gradations no doubt occur

linking preferred orientations to elastic anisotropy in muderong shale australia the significance of shales for unconventional hydrocarbon reservoirs nuclear waste repositories and geologic carbon storage has opened new research frontiers in geophysics among many of its unique physical properties elastic anisotropy had long been investigated by experimental and computational approaches here we calculated elastic properties of cretaceous muderong shale from australia with a self consistent averaging method based on microstructural information the volume fraction and crystallographic preferred orientation distributions of constituent minerals were based on synchrotron x ray diffraction experiments aspect ratios of minerals and pores determined from scanning electron microscopy were introduced in the self consistent averaging our analysis suggested that phyllosilicates i e illite mica illite smectite kaolinite and chlorite were dominant with 70 vol the shape of clay platelets displayed an average aspect ratio of 0 05 these platelets were aligned parallel to the bedding plane with a high degree of preferred orientation the estimated porosity at ambient pressure was 17 vol and was divided into equiaxial pores and flat pores with an average aspect ratio of 0 01 our model gave results that compared satisfactorily with values derived from ultrasonic velocity measurements confirming the validity and reliability of our approximations and averaging approach

elastic anisotropy of shales accompanying the resource potential of gas shales is a new interest in understanding the physical and petrophysical properties of shales shale by geochemical or stratigraphic measures is arguably the most common lithology encountered in sedimentary basins despite this shales remain little studied while engineers and explorationists focused on conventional reservoirs geophysicists did this knowing full well that often a reflection coefficient from a reservoir was controlled by the shale properties of the cap rock we compensated for this ignorance by arguing that shales are deposited in deepwater environments in which lateral and vertical changes are slow and therefore inconsequential we further compounded this ignorance by assuming that the shales were isotropic an example of the consequences of this ignorance was clearly documented by margesson and sondergeld 1999 engineers share culpability for this ignorance too since most of the drilling problems occur in shales and most of the lithologies d

the nanogranular acoustic signature of shale a multiscale micromechanics model has been developed for the prediction of anisotropic acoustic properties of shale the model is based on the recently identified nanogranular mechanical response of shale through indentation experiments it recognizes the dominant role of the anisotropic elastic properties of compacted clay in the anisotropic elasticity of shale at different length scales compared to contributions of shape and orientation of particles following a thorough validation at multiple length scales using mineral elasticity data nanoindentation experiment results and ultrasonic pulse velocity tests the model predictions compare adequately with measurements on kerogen free and kerogen rich shales and shaley sandstones the acoustic signature of shale thus is found to be controlled by two volumetric parameters that synthesize the porosity and mineralogy information the clay packing density and the silt inclusion volume fraction through a series of dimensionless isoparametric plots the micromechanics model predicts trends of increasing elastic anisotropy with increasing clay packing density or decreasing porosity which correspond to the intrinsic mechanical response of unfractured shale and quantifies the stiffness reduction induced by the presence of kerogen

velocity anisotropy in shale determined from crosshole seismic and vertical seismic profile data crosshole and vertical seismic profile vst data made possible accurate characterization of the elastic properties including noticeable velocity anisotropy of a near surface late tertiary shale formation shear wave splitting was obvious in both crosshole and vsp data in crosshole data two orthologonally polarrized shear s waves arrived 19 ms in the uppermost 246 ft 75 m vertically traveling s waves of the vsp separated about 10 ms in the uppermost 300 ft 90 m but remained at nearly constant separation below that level a transversely isotropic model which incorporates a rapid increase in s wave velocities with depth but slow increase in p wave velocities closely fits the data over most of the measured interval elastic constants of the transvesely isotropic model show spherical p and s2 wave velocity surfaces but an ellipsoidal s1 wave surface with a ratio of major to minor axes of 1 15 the magnitude of this s wave anisotropy is consistent with and lends credence to s wave anisotropy magn

texture and anisotropy analysis of qusaiba shales scanning and transmission electron microscopy synchrotron x ray diffraction microtomography and ultrasonic velocity measurements were used to characterize microstructures and anisotropy of three deeply buried qusaiba shales from the rub alkhali basin saudi arabia kaolinite illite smectite illite mica and chlorite show strong preferred orientation with 001 pole figure maxima perpendicular to the bedding plane ranging from 2 4 6 8 multiples of a random distribution m r d quartz feldspars and pyrite crystals have a random orientation distribution elastic properties of the polyphase aggregate are calculated by averaging the single crystal elastic properties over the orientation distribution assuming a nonporous material the average calculated bulk p wave velocities are 6 2 km s maximum and 5 5 km s minimum resulting in a p wave anisotropy of 12 the calculated velocities are compared with those determined from ultrasonic velocity measurements on a similar sample in the ultrasonic experiment which measures the effects of the shale matrix as well as the effects of porosity velocities are smaller p wave maximum 5 3 km s and minimum 4 1 km s the difference between calculated and measured velocities is attributed to the effects of anisotropic pore structure and to microfractures present in the sample which have not been taken into account in the matrix averaging

slope curvature influence on soil erosion and deposition processes sediment water quality problems are not necessarily the direct result of erosion from the most intense soil erosion areas a study of within basin variability of the sediment delivery processes is needed to identify areas where the most effective soil conservation strategies should focus in this paper the sediment delivery processes is examined along the hydraulic path from sediment source areas to the nearest stream reach the effects of shape convex concave and uniform of the hydraulic path are modeled using a power equation for slope profile and revised universal soil loss equation rusle with two different expressions of the topographic factors a criterion is proposed for the erosion active slope length i e the slope length in which no deposition processes occur then using the continuity equation for sediment transport a factor is deduced to correct the topographic factors of rusle and those proposed by moore and burch 1986 depending on slope curvature finally two relationships for correcting the topographic factors for an irregular slope are experimentally tested comparing the calculated sediment yields with net soil erosion values estimated by the proportional method of martz and de jong 1987 and cesium 137 data available from a sicilian basin

distribution of caesium 137 in soils across a hillslope hollow the distribution of soil 137cs in relation to selected soil and landform properties was studied across a 16 ha hillslope hollow in the hunter valley new south wales australia the hillslope was used as grazing for cattle caesium 137 was not significantly related to the amount of sand silt or clay the bulk density the organic matter content the slope angle or the relative distance downslope however 137cs was significantly related to the thickness of the soil a horizon spatial variations in 137cs were compared with topographic units and a six element hillslope model but there was little correspondence it was thought that the effects of microtopography could have masked potential interrelationships between 137cs and broader scale landform parameters

seismic anisotropy of shales the seismic properties and preferred clay mineral orientation of a suite of shales are investigated using laboratory velocity measurements as a function of confining pressure x ray diffraction techniques and electron microprobe backscatter bse imaging the velocity measurements indicate that these shales are transversely isotropic with the main symmetry axis perpendicular to bedding anisotropy at elevated pressures caused mainly by preferred orientation of clays illite parallel to bedding ranges from 20 vp and 19 vs for a sample of new albany shale to 30 vp and 35 vs for a sample of chattanooga shale the degree of clay mineral alignment in the shales is constrained by orientation indices produced using simple x ray diffraction techniques a strong positive correlation is found between the degree of preferred orientation as expressed in the orientation indices and seismic anisotropy bse images of the shale fabrics confirm in a qualitative manner the results of the x ray study to investigate wave propagation in the shales elastic constants of each sample are calculated and used to produce phase and group wave velocity surfaces which describe variation in velocity as a function of angle to the bedding normal the calculated velocity surfaces constrained by independent velocity measurements display a lack of shear wave splitting at near normal incidence in even the most anisotropic shales for the highly anisotropic chattanooga shales group velocity surfaces differ significantly from corresponding phase velocity surfaces

overland flow generation on hillslopes of complex topography analytical solutions the analytical solution of the overland flow equations developed by agnese et al 2001 hydrological processes15 3225 3238 for rectangular straight hillslopes was extended to convergent and divergent surfaces and to concave and convex profiles towards this aim the conical convergent and divergent surfaces are approximated by a trapezoidal shape and the overland flow is assumed to be always one dimensional a simple shape factor accounting for both planform geometry and profile shape was introduced for each planform geometry a brachistochrone profile was obtained by minimizing a functional containing a slope function of the profile minima shape factors are associated with brachistochrones interestingly brachistochrones associated with rectangular surfaces have a simple power law form for a fixed profile shape the rapidness of overland flow increases with the degree of divergence for a fixed planform geometry however the overland flow associated with convex profiles is more rapid than that associated with concave profiles an extended analytical solution is also proposed for the instantaneous response function copyright 2007 john wiley sons ltd

proterozoic transcurrent movements along the kapuskasing lineament superior province canada and their relationship to surrounding structures abstract analysis of large scale geological and geophysical lineaments provide evidence for a new model to explain the kapuskasing structural zone ksz and james bay james bay is interpreted to have formed due to rifting related to lateral strike slip along the ksz the sutton arc is interpreted to be an extension from hudson bay arc which has been displaced by rifting of james bay magnetic anomalies which terminate at the ksz on the west have correlated magnetic anomalies on the east which are displaced left laterally it is proposed that these displacements and the rifting of james bay and the strike slip along the ksz were caused as a result of 160 km of left lateral motion between east and west superior terranes with an accompanying 5 of anticlockwise rotation of the west superior terrane additional support for this model comes from structural evidence drawn from previous reports from the last twenty six years

mathematical modelling of anisotropy of illite rich shale summary the estimation of illite rich shale anisotropy to account for the alignment of clays and gas or brine filled cracks is presented via mathematical modelling such estimation requires analysis to interpret the dominance of one effect over another this knowledge can help to evaluate the permeability in the unconventional reservoir stress orientation and the seal capacity for the conventional reservoir effective media modelling is used to predict the elastic properties of the illite rich shale and to identify the dominant contributions to the shale anisotropy we consider two principal reasons of the shale anisotropy orientation of clay platelets and orientation of fluid filled cracks in reality both of these two factors affect the shale anisotropy the goal of this study is first to separately analyse the effect of these two factors to reveal the specific features in p and s wave velocity behaviour typical of each of the factors and then consider a combined effect of the factors when the cracks are horizontally or vertically aligned to do this we construct four models of shale the behaviour of p and s wave velocities is analysed when gas and water filled cracks embedded in a host matrix are randomly oriented or horizontally or vertically aligned the host matrix can be either isotropic or anisotropic of vti symmetry in such a modelling we use published data on mineralogy and clay platelet alignment along with other micromechanical measurements in the model where the host matrix is isotropic the presence of a singularity point when the difference changes its sign in shear wave velocities is an indicator of brine filled aligned cracks in the model with the vti host matrix and horizontally aligned cracks filled with gas an increase in their volume concentration leads to that the azimuth at which the singularity is observed moves toward the symmetry axis in this case if the clay content is small around 20 per cent the singularity point may even vanish the thomsen parameters are helpful in fluid type indication in shale an indicator of gas filled aligned cracks is if aligned cracks in illite rich shale are brine filled negative value of indicates brine filled cracks in illite rich shale a shale with brine filled cracks exhibits higher vp vs ratio in the vertical direction as compared to the gas filled shale a disorientation of clay platelets and brine filled cracks may lead to that the singularity point is absent for brine saturated shale as well in this case one can also observe and decreased values of vp vs in the vertical direction as in the case of gas filled cracks in the presence of vertically aligned cracks shales exhibit distinctly revealed features of orthorhombic symmetry the results have important applications where seismic measurements are applied to predict the maturity state of the shale

physical properties of shale at temperature and pressure deformational properties p wave and s wave velocities and electrical resistivity were measured for three north sea malm shales in the laboratory under pressures to 800 bars and temperatures to 100 c these data were used to evaluate how factors such as mineralogy microstructure compaction and pore fluid conductivity affect a shale s seismic and electrical responses deformation in the shales is dominated by inelastic processes which cause time dependent changes in velocity resistivity and pore pressure overall shales are less sensitive to pressure changes as compared to sandstones of similar porosity however changes in temperature result in large changes in physical properties as compared to sandstones or shaly sands p wave and s wave velocities may decrease by as much as 10 percent over the temperature range studied and calculated activation energies for surface conduction are nearly twice those observed in shaly sands these comparisons emphasize fundamental differences in fabric among the

anisotropy correction for deviated well sonic logs application to seismic well tie borehole sonic logs acquired in deviated wells penetrating the hrz and colville shales in the niakuk field in alaska s north slope are seen to be significantly faster than vertical well logs these differences are attributed to shale anisotropy an iterative inversion scheme was created to invert for shale anisotropy parameters using multiple wells penetrating shale sections at different angles the inversion involves fitting the sonic log data at a range of borehole angles to the compressional wave group velocity surface the result is an estimate of the anisotropy parameters e and and the vertical p wave velocity the results show that the shales are strongly anisotropic with compressional wave anisotropy thomsen s parameter e on the order of 40 and the anisotropy parameter relates vertical velocity to short offset nmo velocity around 10 this large anisotropy can affect seismic imaging avo and time depth calculations a procedure was created to estimate the anisotropy corrected vertical s

frequency dependent seismic attenuation in shales experimental results and theoretical analysis claudio delle piane 1 joel sarout 1 claudio madonna 2 erik h saenger 2 david n dewhurst1 and mark raven3 1csiro earth science and resource engineering australian resources research centre 26 dick perry avenue kensington wa 6151 australia e mail claudio dellepiane csiro au 2geological department eth sonneggstrasse 5 ch 8092 zurich switzerland 3csiro land and water waite rd urrbrae sa 5064 australia

phased array compaction cell for measurement of the transversely isotropic elastic properties of compacting sediments sediments undergoing compaction typically exhibit transversely isotropic ti elastic properties we present a new experimental apparatus the phased array compaction cell for measuring the ti elastic properties of clay rich sediments during compaction this apparatus uses matched sets of p and s wave ultrasonic transducers located along the sides of the sample and an ultrasonic p wave phased array source together with a miniature p wave receiver on the top and bottom ends of the sample the phased array measurements are used to form plane p waves that provide estimates of the phase velocities over a range of angles from these measurements the five ti elastic constants can be recovered as the sediment is compacted without the need for sample unloading recoring or reorienting this paper provides descriptions of the apparatus the data processing and an application demonstrating recovery of the evolving ti properties of a compacting marine sediment sample

lattice preferred orientation and seismic anisotropy in sedimentary rocks summary although it is well known that sedimentary rocks can be seismically anisotropic there have been few detailed investigations of the underlying cause of such anisotropy here we investigate anisotropy due to the preferred orientation of minerals or lattice preferred orientation lpo in a suite of sedimentary rocks seismic properties are predicted by averaging single crystal elastic constants of minerals according to their crystal orientation and modal volume fraction in the rock aggregate both electron backscattered diffraction ebsd and x ray texture goniometry xtg are tested as quantitative techniques for measuring the lpo of sedimentary rocks although ebsd has promise for future lpo measurements in polymineralic sedimentary rocks problems currently remain in measuring low symmetry phases e g feldspars and very small clay or mica particles however the lpo of very fine grained phyllosilicates can be measured using xtg and the lpo of low symmetry minerals can be measured using manual ebsd pattern analysis here we use such a hybrid approach to estimate lpo in a suite of sedimentary samples the seismic properties calculated from lpo data show anisotropy values for p waves ranging from 1 5 per cent in sandstones to over 3 5 per cent in a siltstone to 12 per cent in a shale the effect of thin multilayering on long wavelength propagation in a siltstone is predicted by applying backus type averaging the layering does not enhance the anisotropy because of the small differences in density and in elasticity between the two layer types the lpo of phyllosilicates and to a lesser extent dolomite and siderite seem to contribute significantly to the seismic anisotropy of phyllosilicate rich rocks siltstones and shales the weak lpo of quartz in sandstones causes a few per cent anisotropy cumulatively our results suggest that field observations of seismic anisotropy have the potential to be used as an indicator of rock lithology

formation of 1 9 ga old trans hudson continental crust pb isotopic data pb isotopic data are reported for whole rock samples and feldspars from two parts of the 1 9 1 8 ga old trans hudson orogen in canada the reindeer zone in saskatchewan and the ottawa and belcher islands in hudson bay the first area contains a variety of volcanic granitoid and sedimentary rocks in several oceanic and magmatic arcs aligned parallel to the margin of the archean hearne craton the second is part of the circum superior belt a belt of oceanic basalts and sedimentary rocks that surrounds the superior craton in several regions pb pb isochrons gave ages generally consistent with available geochronological or geological data flin flon 1822 44 ma 2 peter lake complex 2710 220 ma ottawa islands 1790 80 ma belcher islands 1960 160 ma in other regions the pb pb age was too low reflecting disturbance of the pb system e g la ronge belt 1730 115 ma or too high perhaps because of contamination of certain samples with older crust e g wathaman batholith 2200 200 ma model values and th u ratios calculated from the pb data are interpreted in terms of variations in the compositions of mantle sources complicated by contamination with material from the upper or lower continental crust in the southern part of the reindeer zone and in volcanic rocks from the ottawa islands model values vary from 8 0 to 8 1 and correlate inversely with initial nd values this variation is thought to result from contamination of juvenile material 8 0 with material from archean upper crust which had low nd but relatively high in the northern part of the zone and in eskimo formation basalts from the belcher islands values remain constant or decrease as nd declines and this is attributed to contamination with u depleted lower crust calculated th u ratios vary from 1 34 to 6 67 the lowest values 1 4 1 8 come from mafic to felsic volcanic rocks of the flin flon and western la ronge belts these low th u values are like those in modern island arc volcanics and are attributed to enrichment of u in the source slightly higher values are calculated for oceanic basalts from the circum superior belt morb like basalts from the ottawa islands have a low th u of 2 5 reflecting depletion of th along with other incompatible elements higher values of 3 9 characterize the more enriched flaherty basalts the highest th u values which are found in samples with the lowest nd and low values wathaman batholith and eskimo basalts are thought to reflect the high th u of the u depleted lower crustal contaminant these results have several interesting implications the similarity between the isotopic and chemical characteristics inferred for these 1 9 ga old rocks and those of volcanics in modern convergent margin settings provides further indication that the tectonic and petrogenetic processes peculiar to modern subduction environments operated in the middle proterozoic the apparent presence of material from the lower and upper crust in the sources of the granitoids indicates that these rocks were not derived from subducting oceanic plate or the mantle wedge but probably formed and evolved within the crust itself

preferred orientation of phyllosilicates comparison of fault gouge shale and schist abstract samples of fault gouge from the san andreas fault drill hole safod a shale from the north sea sedimentary basin and schists from metamorphic rocks in the alps have been analyzed with high energy synchrotron x rays to determine preferred orientation of mica and clay minerals the method relies on obtaining 2d diffraction images which are then processed with the crystallographic rietveld method implemented in the software maud allowing for deconvolution of phases and extraction of their orientation distributions it is possible to distinguish between detrital illite muscovite and authigenic illite smectite kaolinite and chlorite and muscovite and biotite with strongly overlapping peaks in the diffraction pattern the results demonstrate that phyllosilicates show large texture variations in various environments where different mechanisms produce the rock microfabrics fault gouge fabrics are quite weak and asymmetric with maxima for 001 in the range of 1 5 2 5 multiples of random distribution m r d this is attributed to heterogeneous deformation with randomization as well as dissolution precipitation reactions shale fabrics have maxima ranging from 3 to 9 m r d and this is due to sedimentation and compaction the strongest fabrics were observed in metamorphic schists 10 14 m r d and developed by deformation as well as recrystallization in a stress field in the analyzed samples fabrics of co existing quartz are weak all phyllosilicate textures can be explained by orientation of 001 platelets with no additional constraints on a axes

experimental laboratory determination of the dynamic elastic properties of wet drained shales the ultrasonic anisotropic elastic properties of drained saturated shales were measured as a function of confining pressure two shales were characterized in this study a jurassic outcrop shale retrieved under the sea in a saturated state and a kimmeridge clay shale cut from a north sea borehole both shales were highly anisotropic both texturally as revealed by scanning electron microscopy analysis and elastically as measured ultrasonically in the laboratory the strongest anisotropy was seen in the kimmeridge clay shale where up to 38 compressional wave anisotropy thomsen s parameter e and up to 58 shear wave anisotropy thomsen s parameter were observed in addition for both shales e and were found to decrease as a function of increasing confining pressure with the pore pressure drained to atmosphere while the anellipticity deviation of the slowness surfaces from ellipses was found to be positive and decreased as a function of increasing confining pressure accompanying these changes in elastic properties was a decrease in porosity with increasing confining pressure from 10 5 to 8 5 for the jurassic shale the decrease in overall anisotropy of the shales with increasing confining pressure was found to be consistent with theoretical modeling of shale properties where the shale anisotropy and anellipticity were predicted to decrease as a function of decreasing fluid filled porosity

characterizing the primary material sources and dominant erosional processes for post fire debris flow initiation in a headwater basin using multi temporal terrestrial laser scanning data abstract wildfire dramatically alters the hydrologic response of a watershed such that even modest rainstorms can produce hazardous debris flows relative to shallow landslides the primary sources of material and dominant erosional processes that contribute to post fire debris flow initiation are poorly constrained improving our understanding of how and where material is eroded from a watershed during a post fire debris flow requires 1 precise measurements of topographic change to calculate volumetric measurements of erosion and deposition and 2 the identification of relevant morphometrically defined process domains to spatially constrain these measurements of erosion and deposition in this study we combine the morphometric analysis of a steep small 0 01 km 2 headwater drainage basin with measurements of topographic change using high resolution 2 5 cm multi temporal terrestrial laser scanning data made before and after a post fire debris flow the results of the morphometric analysis are used to define four process domains hillslope divergent hillslope convergent transitional and channelized incision we determine that hillslope divergent and hillslope convergent process domains represent the primary sources of material over the period of analysis in the study basin from these results we conclude that raindrop impact induced erosion ravel surface wash and rilling are the primary erosional processes contributing to post fire debris flow initiation in the small steep headwater basin further work is needed to determine 1 how these results vary with increasing drainage basin size 2 how these data might scale upward for use with coarser resolution measurements of topography and 3 how these results change with evolving sediment supply conditions and vegetation recovery