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

effects of contact line movement on the dissipation of waves in partially saturated rocks a model is presented to describe the attenuation of seismic waves in a partially saturated rock in particular we include the dissipation due to contact line movement in some cases this can dominate the dissipation mechanisms the model includes both dissipation due to viscosity and contact line movement this additional dissipation can increase the specific dissipation function by an order of magnitude this could account for some of the observed difference between theory and experiment an exact calculation of the dissipation due to contact line movement in an in viscid fluid is also presented

visual observation of gas hydrate formation and dissociation in synthetic porous media by means of glass micromodels visual observation of gas hydrates at the microscopic scale in synthetic porous media provides unequivocal visual evidence that clathrates can form in systems without the presence of a free gas phase hydrates were formed from a soluble liquid hydrate former tetrahydrofuran c 4 h 8 o from free gas ch 4 and from dissolved gas co 2 clathrates were found to form within the center of pore spaces rather than on grain surfaces cementation of grains only occurred in regions of a small grain size or where a large proportion of pore space was filled with hydrate however even at high clathrate saturations a thin film of free water persisted on grain surfaces the results have important implications for the potential cementing effect of hydrates on sediments and thus for sediment permeability slope stability and seismic interpretation of hydrate bearing sediments

zonal jet structure and the leading mode of variability an observational analysis of the northern hemisphere circulation during winter reveals that the leading mode of variability depends on longitude in particular the first eof of the zonal mean circulation differs over the atlantic and pacific sectors these results provide motivation for a series of model runs where a simple gcm is used to investigate the effects of the zonal jet structure on the leading mode of variability in the northern hemisphere model results indicate that the leading mode of variability depends on the distance between the eddy driven and subtropical jets when the jets are well separated the leading mode of variability describes latitudinal shifting of the eddy driven jet however when the two jets are nearly collocated pulsing of the combined jet dominates the variability this change coincides with a weakening of the positive feedback between the eddies and zonal flow anomalies these results provide a possible explanation for the reduced amplitude of the northern annular mode in the pacific sector relative to that in the atlantic sector during northern hemisphere winter

north atlantic eddy driven jet in interglacial and glacial winter climates the atmospheric westerly flow in the north atlantic na sector is dominated by atmospheric waves or eddies generating via momentum flux convergence the so called eddy driven jet the position of this jet is variable and shows for the present day winter climate three preferred latitudinal states a northern central andsouthernpositioninthena here theauthorsanalyzethebehavioroftheeddy drivenjetunderdifferent glacial and interglacial boundary conditions using atmosphere land only simulations with the ccsm4 climate model as state of the art climate models tend to underestimate the trimodality of the jet latitude the authors apply a bias correction and successfully extract the trimodal behavior of the jet within ccsm4 the analysis shows that during interglacial times i e the early holocene and the eemian the preferred jet positions are rather stable and the observed multimodality is the typical interglacial character of the jet during glacial times the jet is strongly enhanced its position is shifted southward and the trimodal behavior vanishes this is mainly due to the presence of the laurentide ice sheet lis the lis enhances stationary waves downstream thereby accelerating and displacing the na eddy driven jet by anomalous stationary momentum flux convergence additionally changes in the transient eddy activity caused by topography changes as well as other glacial boundary conditions lead to an acceleration of the westerly winds over the southernnaattheexpenseofmorenorthernareas consequently bothstationaryandtransienteddiesfoster the southward shift of the na eddy driven jet during glacial winter times

seismic anisotropy in sedimentary rocks part 2 laboratory data part one of this paper presents a method for measuring seismic velocities and transverse isotropy in rocks using a single core plug this method saves at least two thirds of the time for preparing core samples and measuring velocities in transversely isotropic ti rocks using this method we have measured velocity and anisotropy of many shale and reservoir rocks from oil and gas fields around the world we present some of the data in this paper which include seismic velocity and anisotropy in 17 brine saturated shale samples 1 gas and brine saturated coal sample 8 brine saturated sands 12 gas saturated sands 32 gas saturated carbonate samples and 25 brine saturated carbonate samples the results show that clays and fine layering in sedimentary rocks are the main causes of seismic anisotropy very little intrinsic anisotropy exists in unfractured reservoir rocks such as sands sandstones and carbonates under reservoir conditions in contrast all shales were found seismically anisotropic anisotr

seismic attenuation due to wave induced flow analytical expressions for three p wave attenuation mechanisms in sedimentary rocks are given a unified theoretical framework two of the models concern wave induced flow due to heterogeneity in the elastic moduli at mesoscopic scales scales greater than grain sizes but smaller than wavelengths in the first model the heterogeneity is due to lithological variations e g mixtures of sands and clays with a single fluid saturating all the pores in the second model a single uniform lithology is saturated in mesoscopic patches by two immiscible fluids e g air and water in the third model the heterogeneity is at microscopic grain scales broken grain contacts and or micro cracks in the grains and the associated fluid response corresponds to squirt flow the model of squirt flow derived here reduces to proper limits as any of the fluid bulk modulus crack porosity and or frequency is reduced to zero it is shown that squirt flow is incapable of explaining the measured level of loss 10 sup 2 q sup 1 10 sup 1 within the seismic band of frequencies 1 to 10 sup 4 hz however either of the two mesoscopic scale models easily produce enough attenuation to explain the field data

northern hemisphere storm tracks during the last glacial maximum in the pmip2 ocean atmosphere coupled models energetic study seasonal cycle precipitation mid latitude eddies are an important component of the climatic system due to their role in transporting heat moisture and momentum from the tropics to the poles and also for the precipitation associated with their fronts especially in winter we study northern hemisphere storm tracks at the last glacial maximum lgm and their influence on precipitation using ocean atmosphere general circulation model oagcm simulations from the second phase of the paleoclimate modelling intercomparison project pmip2 the difference with pmip1 results in terms of sea surface temperature forcing fundamental for storm track dynamics is large especially in the eastern north atlantic where sea ice extends less to the south in oagcms compared to atmospheric only gcms our analyses of the physics of the eddies are based on the equations of eddy energetics all models simulate a consistent southeastward shift of the north pacific storm track in winter related to a similar displacement of the jet stream partly forced by the eddies themselves precipitation anomalies are consistent with storm track changes with a southeastward displacement of the north pacific precipitation pattern the common features of north atlantic changes in the lgm simulations consist of a thinning of the storm track in its western part and an amplification of synoptic activity to the southeast in the region between the azores islands and the iberian peninsula which reflects on precipitation this southeastward extension is related to a similar displacement of the jet partly forced by the eddies in the western north atlantic the synoptic activity anomalies are at first order related to baroclinic generation term anomalies but the mean flow baroclinicity increase due to the presence of the laurentide ice sheet is partly balanced by a loss of eddy efficiency to convert energy from the mean flow moisture availability in this region is greatly reduced due to more advection of dry polar air by stationary waves leading to less synoptic scale latent heat release and hence less precipitation also in terms of seasonality the stormy season is shifted later in the year by a few days to a month depending on the season and the model considered this shift does not directly reflect on the first order seasonal cycle of precipitation which also depends on other mechanisms especially in summer

a robust experimental determination of thomsen s δ parameter abstracta novel inversion method for the laboratory determination of thomsen s anisotropy parameter on cylindrical rock specimens from ultrasonic data has been recently reported in the literature we further assessed this method through a direct comparison of the results of the traditional method involving a single off axis p wave velocity measurement at 45 and the new method involving 65 p wave velocity measurements at several angles to the symmetry axis we prepared and characterized two vertical shale specimens from the same preserved vertical core to assess their similarity in terms of structure mineralogy porosity and density the shale was assumed to be transversely isotropic in view of the observed horizontal bedding we subjected both specimens to the same brine saturation and effective stress state using the two methods we obtained similar results for thomsen s vertical p wave and e p wave anisotropy parameters however a significant discrepancy was observed for thomsen s p

patterns of wintertime jet stream variability and their relation to the storm tracks abstract a new approach is put forward for defining extratropical teleconnection patterns the zonal wind field at 250 hpa is analyzed separately in the north atlantic and north pacific ocean sectors during the winter season december march teleconnectivity of this field is found to be particularly strong eof analysis of the zonal wind field yields patterns that i are robust with respect to the range of frequencies included in the data ii relate clearly to the position of the climatological mean jets and iii are broadly consistent with their traditionally defined counterparts in terms of climatic impacts the patterns are characterized by a north south shifting or an extension retraction of the eddy driven jet in its exit region and similar changes at the entrance region of the subtropical jet the patterns also reflect the degree of separation between the subtropical and eddy driven jets atlantic eofs 1 and 2 are counterparts of the north atlantic oscillation nao and eastern atlantic patter

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

thermally driven and eddy driven jet variability in reanalysis two important dynamical processes influence the extratropical zonal wind field angular momentum transport by the thermally direct hadley circulation thermal driving t and momentum flux convergence by atmospheric waves eddies that develop in regions of enhanced baroclinicity eddy driving e the relationship between extratropical zonal wind variability and these driving processes is investigated using 40 yr european centre for medium range weather forecasts re analysis era 40 data indices representing the processes it and ie are defined based on vertically integrated diabatic heating and meridional convergence of the meridionalflux of zonal momentum by eddies respectively zonal wind signatures associated with these indices are identified via composite analysis in the atlantic sector zonal wind variability is mainly associated with momentum flux convergence by baroclinic eddies supporting the established view that the atlanticjetis primarilyeddydriven inthe pacificsector zonal windvariability isassociatedwith bothdriving processes evidence that the pacific jet is both thermally driven and eddy driven the thermally driven pacific signature reflects changes in jet strength intensity and longitudinal extent with some resemblance to the zonal wind anomalies of the pacific north america pna pattern the eddy driven signature reflects a latitudinal shift of the jet exit region in both sectors that resembles the zonal wind anomalies of the north atlantic oscillation nao or west pacific wp patterns

an assessment of the impact of transient eddies on the zonal flow during a blocking episode using localized eliassen palm flux diagnostics abstract the eliassen palm e p flux applied to zonal men flows is an indicator of both the flux of eddy activity and the eddy forcing of the zonal mean flow for time mean flows a localized e p flux is derived and used diagnostically to assess the impact of transient eddies on a major blocking episode that occurred over the south pacific during the southern hemisphere winter of 1979 in contrast to previous studies that have focused on the mean quasi geostrophic potential vorticity equation the focus here is on the mean momentum equations eddy transports and the associated induced meridional circulation and other internal adjustments necessary to maintain the thermal wind balance are gathered together allowing the residual circulation and the effects of the eddies to be determined the time mean equations of motion are thus transformed to consist of mean terms the residual circulation and the divergence of a localized e p flux vector the latter is a measure of the eddy forcing of the mean flow

simulated winter circulation types in the north atlantic and european region for preindustrial and glacial conditions 1 winter circulation types under preindustrial and glacial conditions are investigated and used to quantify their impact on precipitation the analysis is based on daily mean sea level pressure fields of a highly resolved atmospheric general circulation model and focuses on the north atlantic and european region we find that glacial circulation types are dominated by patterns with an east west pressure gradient which clearly differs from the predominantly zonal patterns for the recent past this is also evident in the frequency of occurrence of circulation types when projecting preindustrial circulation types onto the glacial simulations the elevation of the laurentide ice sheet is identified as a major cause for these differences in areas of strong precipitation signals in glacial times the changes in the frequencies of occurrence of the circulation types explain up to 60 of the total difference between preindustrial and glacial simulations

impact of the north american ice sheet orography on the last glacial maximum eddies and snowfall the present work evaluates the influence of the north american ice sheet orography on the last glacial maximum lgm 21 000 years ago atmospheric circulation and snowfall in the northern mid latitudes focusing on the north atlantic sector three atmospheric general circulation model experiments are analysed a control and an lgm climate simulation and an lgm run with flat ice sheets over northern north america this ice sheet orography affects lee cyclogenesis over north america and forces differences in stationary waves and therefore in the baroclinicity of the mean flow as a result the atlantic storm track is reinforced in the flat ice sheet experiment compared to the lgm one this in turn has a profound impact on snowfall over northern europe implying a coupling between the two ice sheets

seismic wave attenuation and dispersion resulting from wave induced flow in porous rocks a review one major cause of elastic wave attenuation in heterogeneous porous media is wave induced flow of the pore fluid between heterogeneities of various scales it is believed that for frequencies below 1 khz the most important cause is the wave induced flow between mesoscopic inhomogeneities which are large compared with the typical individual pore size but small compared to the wavelength various laboratory experiments in some natural porous materials provide evidence for the presence of centimeter scale mesoscopic heterogeneities laboratory and field measurements of seismic attenuation in fluid saturated rocks provide indications of the role of the wave induced flow signatures of wave induced flow include the frequency and saturation dependence of p wave attenuation and its associated velocity dispersion frequency dependent shear wave splitting and attenuation anisotropy during the last four decades numerous models for attenuation and velocity dispersion from wave induced flow have been developed with varying degrees of rigor and complexity these models can be categorized roughly into three groups according to their underlying theoretical framework the first group of models is based on biot s theory of poroelasticity the second group is based on elastodynamic theory where local fluid flow is incorporated through an additional hydrodynamic equation another group of models is derived using the theory of viscoelasticity though all models predict attenuation and velocity dispersion typical for a relaxation process there exist differences that can be related to the type of disorder periodic random space dimension and to the way the local flow is incorporated the differences manifest themselves in different asymptotic scaling laws for attenuation and in different expressions for characteristic frequencies in recent years some theoretical models of wave induced fluid flow have been validated numerically using finite difference finite element and reflectivity algorithms applied to biot s equations of poroelasticity application of theoretical models to real seismic data requires further studies using broadband laboratory and field measurements of attenuation and dispersion for different rocks as well as development of more robust methods for estimating dissipation attributes from field data

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

the impact of saturation on seismic dispersion in shales laboratory measurements previous studies found a significant increase of acoustic velocities between seismic and ultrasonic frequencies seismic dispersion for shales which would have to be taken into account when comparing seismic or sonic field data with ultrasonic measurements in the laboratory we report on a series of experiments performed with partially saturated mancos shale and pierre shale i in which the influence of water saturation on acoustic velocities and seismic dispersion was investigated the experiments were carried out in a triaxial set up allowing for combined measurements of quasi static rock deformation ultrasonic velocities and dynamic elastic stiffness at seismic frequencies under deviatoric stresses prior to testing the rock samples were preconditioned in desiccators at different relative humidities for both shale types we present and discuss experimental results that demonstrate strong saturation and frequency dependence of dynamic young s moduli poisson s ratios and thomsen s anisotropy parame

multi model analysis of northern hemisphere winter blocking model biases and the role of resolution blocking of the tropospheric jet stream during northern hemisphere winter december january february is examined in a multi model ensemble of coupled atmosphere ocean general circulation models gcms obtained from the coupled model intercomparison project phase 5 cmip5 the cmip5 models exhibit large biases in blocking frequency and related biases in tropospheric jet latitude similar to earlier generations of gcms underestimated blocking at high latitudes especially over europe is common in general model biases decrease as model resolution increases increased blocking frequency at high latitudes in both the atlantic and pacific basins as well as more realistic variability of atlantic jet latitude are associated with increased vertical resolution in the mid troposphere to lowermost stratosphere finer horizontal resolution is associated with higher blocking frequency at all latitudes in the atlantic basin but appears to have no systematic impact on blocking near greenland or in the pacific basin results from the cmip5 analysis are corroborated by additional controlled experiments using selected gcms key pointscmip5 models have large blocking biases and associated jet biasesincreased spatial resolution is associated with reduced blocking and jet biasesvertical and horizontal resolution give blocking changes in different regions 2013 american geophysical union all rights reserved

theoretical derivation of a brie like fluid mixing law prediction of the velocity of acoustic waves in partially saturated rocks is very important in geophysical applications the need to accurately predict acoustic velocities has resulted in a widespread popularity of brie s effective fluid mixing law this empirical model together with gassmann s formula are used routinely in fluid substitution problems in petroleum geophysics and seismic monitoring of carbon capture and storage most attempts to justify brie s model have been focused on interpretation in terms of patchy saturation models and attaching meaning to the brie parameter in terms of the patch size in this paper using a microstructural description of the rock and a parameter relating to capillary pressure we calculate an effective fluid modulus that is very similar to brie s law the fluid mixing law we propose is independent of frequency and has a solid theoretical foundation this proposed law produces analytically harmonic and arithmetic averaging at the endpoints our results indicate that brie like behaviour may not necessarily be related to frequency and patch size dependent phenomena

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

a new laboratory apparatus for the measurement of seismic dispersion under deviatoric stress conditions abstract a better understanding of seismic dispersion and attenuation of acoustic waves in rocks is important for quantitative interpretation of seismic data as well as for relating seismic data sonic log data and ultrasonic laboratory data in the present work a new laboratory setup is described allowing for combined measurements of quasistatic deformations of rocks under triaxial stress ultrasonic velocities and dynamic elastic stiffness young s modulus and poisson s ratio at seismic frequencies the setup has been used mainly for the study of shales for such rocks it is crucial that the saturation of the samples is preserved which requires fast sample mounting the design of our setup together with a technique that was developed for rapid mounting of strain gauges onto the sample and subsequent sealing of the sample allows for sample preservation which is of particular importance for shales the performance of the new experimental setup and sample mounting procedure is demonstrated with test materials aluminium and polyetheretherketone and two different shale types mancos shale and pierre shale furthermore experimental results are presented that demonstrate the capability of measuring the impact of saturation stress and stress path on seismic dispersion for the tests with mancos shale and pierre shale large dispersion up to 50 in young s modulus normal to bedding was observed increased water saturation of mancos shale results in strong softening of the rock at seismic frequencies whereas hardening is observed at ultrasonic frequencies due to an increase in dispersion counteracting the rock softening the poisson s ratio of mancos shale strongly increases with the level of saturation but appears to be nearly frequency independent we have found that the different types of shale exhibit different stress sensitivities during hydrostatic loading and that the stress sensitivity is different at seismic and ultrasonic frequencies

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

influence of subsurface injection on time lapse seismic laboratory studies at seismic and ultrasonic frequencies seismic monitoring of reservoir and overburden performance during subsurface co2 storage plays a key role in ensuring efficiency and safety proper interpretation of monitoring data requires knowledge about the rock physical phenomena occurring in the subsurface formations this work focuses on rock stiffness and elastic velocity changes of a shale overburden formation caused by both reservoir inflation induced stress changes and leakage of co2 into the overburden in laboratory experiments pierre shale i core plugs were loaded along the stress path representative for the in situ stress changes experienced by caprock during reservoir inflation tests were carried out in a triaxial compaction cell combining three measurement techniques and permitting for determination of i ultrasonic velocities ii quasi static rock deformations iii dynamic elastic stiffnesses at seismic frequencies within single test which allowed to quantify effects of seismic dispersion in addition fluid substitution effects connected with possible co2 leakage into the caprock formation were modelled by the modified anisotropic gassmann model results of this work indicate that i stress sensitivity of pierre shale i is frequency dependent ii reservoir inflation leads to the increase of the overburden young s modulus and poisson s ratio iii in situ stress changes mostly affects the p wave velocities iv small leakage of the co2 into the overburden may lead to the velocity changes which are comparable with one associated with geomechanical influence v non elastic effects increase stress sensitivity of an acoustic waves iv both geomechanical and fluid substitution effects would create significant time shifts which should be detectable by time lapse seismic this article is protected by copyright all rights reserved

the shape propagation and mean flow interaction of large scale weather systems abstract for a zonal average operator the eliassen palm flux provides a diagnostic of both eddy behavior and the feedback of the eddies onto the mean flow this paper addresses the diagnosis problem for other averaging operators and in particular for time averaging which has proved in recent years such a powerful means of viewing the three dimensional tropospheric flow the horizontal velocity correlation tensor gives a measure of the characteristic horizontal eddy shape at a point it also implies the direction of the group velocity relative to the mean flow in cases where such a concept is valid however the major emphasis here is on the mean flow feedback of eddies in this respect the eddy vorticity flux is determined by derivatives of the components of the anisotropic part of the tensor making a reasonable approximation allows the eddy vorticity flux convergence to be written in terms of e v 2 u 2 u v a simple interpretation of the mean flow feedback of eddies is then possible a sligh

dynamic poroelasticity a unified model with the squirt and the biot mechanisms the velocities and attenuation of seismic and acoustic waves in rocks with fluids are affected by the two most important modes of fluid solid interaction 1 the biot mechanism where the fluid is forced to participate in the solid s motion by viscous friction and inertial coupling and 2 the squirt flow mechanism where the fluid is squeezed out of thin pores deformed by a passing wave traditionally both modes have been modeled separately with the biot mechanism treated in a macroscopic framework and the squirt flow examined at the individual pore level we offer a model which treats both mechanisms as coupled processes and relates p velocity and attenuation to macroscopic parameters the biot poroelastic constants porosity permeability fluid com pressibility and viscosity and a newly introduced microscale parameter a characteristic squirt flow length the latter is referred to as a fundamental rock property that can be determined experimentally we show that the squirt flow mechanism dominates the biot mechanism and is responsible for measured large velocity dispersion and attenuation values the model directly relates p velocity and attenuation to measurable rock and fluid properties therefore it allows one to realistically interpret velocity dispersion and or attenuation in terms of fluid properties changes e g viscosity during thermal enhanced oil recovery eor or to link seismic measurements to reservoir properties as an example of the latter transformation we relate permeability to attenuation and achieve good qualitative correlation with experimental data

stationary waves of the ice age climate abstract a linearized steady state primitive equation model is used to simulate the climatological zonal asymmetries stationary eddies in the wind and temperature fields of the 18 000 ybp climate during winter we compare these results with the eddies simulated in the ice age experiments of broccoli and manabe who used climap boundary conditions and reduced atmospheric co2 in an atmospheric general circulation model gcm coupled with a static mixed layer ocean model the agreement between the models is good indicating that the linear model can be used to evaluate the relative influences of orography diabatic heating and transient eddy heat and momentum transports in generating stationary waves we find that orographic forcing dominates in the ice age climate the mechanical influence of the continental ice sheets on the atmosphere is responsible for most of the changes between the present day and ice age stationary eddies this concept of the ice age climate is complicated by the sensitivity of t

fluid mobility and frequency dependent seismic velocity direct measurements the influence of fluid mobility on seismic velocity dispersion is directly observed in laboratory measurements from seismic to ultrasonic frequencies a forceddeformation system is used in conjunction with pulse transmission to obtain elastic properties at seismic strain amplitude 10 7 from 5 hz to 800 khz varying fluid types and saturations document the influence of pore fluids the ratio of rock permeability to fluid viscosity defines mobility which largely controls pore fluid motion and pore pressure in a porous medium high fluid mobility permits pore pressure equilibrium either between pores or between heterogeneous regions resulting in a low frequency domain where gassmann s equations are valid in contrast low fluid mobility can produce strong dispersion even within the seismic band here the low frequency assumption fails since most rocks in the general sedimentary section have very low permeability and fluid mobility shales siltstones tight limestones etc most rocks are not in the lowfrequency domain even at seismic frequencies only those rocks with high permeability porous sands and carbonates will remain in the low frequency domain in the seismic or sonic band

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

how does water near clay mineral surfaces influence the rock physics of shales clays and clay bearing rocks like shale are extremely water sensitive this is partly due to the interaction between water and mineral surfaces strengthened by the presence of nanometer size pores and related large specific surface areas molecular scale numerical simulations using a discrete element model show that shear rigidity can be associated with structurally ordered bound or adsorbed water near charged surfaces building on these and other molecular dynamics simulations plus nanoscale experiments from the literature the water monolayer adjacent to hydrophilic solid surfaces appears to be characterised by shear stiffness and or enhanced viscosity in both cases elastic wave propagation will be affected by the bound or adsorbed water using a simple rock physics model bound water properties were adjusted to match laboratory measured p and s wave velocities on pure water saturated kaolinite and smectite to fit the measured stress sensitivity particularly for kaolinite the contribution from solid grain contact stiffness needs to be added the model predicts particularly for s waves that viscoelastic bound water could be a source of dispersion in clay and clay rich rocks the bound water based rock physics model is found to represent a lower bound to laboratory measured velocities obtained with shales of different mineralogy and porosity levels