interpreting basal sediments and plant fossils in kettle lakes insights from silver lake michigan usa we report on pollen plant macrofossils and associated lithostratigraphy of a sediment core extracted from the base of silver lake a kettle lake in northern lower michigan usa which reveal a co

physics and seismic modeling for monitoring co2 storage we present a new petro elastical and numerical simulation methodology to compute synthetic seismograms for reservoirs subject to co2 sequestration the petro elastical equations model the seismic properties of reservoir rocks saturated with co2 methane oil and brine the gas properties are obtained from the van der waals equation and we take into account the absorption of gas by oil and brine as a function of the in situ pore pressure and temperature the dry rock bulk and shear moduli can be obtained either by calibration from real data or by using rock physics models based on the hertz mindlin and hashin shtrikman theories mesoscopic attenuation due to fluids effects is quantified by using white s model of patchy saturation and the wet rock velocities are calculated with gassmann equations by using an effective fluid modulus to describe the velocities predicted by white s model the simulations are performed with a poro viscoelastic modeling code based on biot s theory where viscoelasticity is described by generalizing the solid fluid coupling modulus to a relaxation function using the pseudo spectral method which allows general material variability a complete and accurate characterization of the reservoir can be obtained a simulation that considers the utsira sand of the north sea illustrates the methodology

seismic attenuation and velocity dispersion in heterogeneous partially saturated porous rocks summary using a numerical approach we explore wave induced fluid flow effects in partially saturated porous rocks in which the gas water saturation patterns are governed by mesoscopic heterogeneities associated with the dry frame properties the link between the dry frame properties and the gas saturation is defined by the assumption of capillary pressure equilibrium which in the presence of heterogeneity implies that neighbouring regions can exhibit different levels of saturation to determine the equivalent attenuation and phase velocity of the synthetic rock samples considered in this study we apply a numerical upscaling procedure which permits to take into account mesoscopic heterogeneities associated with the dry frame properties as well as spatially continuous variations of the pore fluid properties the multiscale nature of the fluid saturation is taken into account by locally computing the physical properties of an effective fluid which are then used for the larger scale simulations we consider two sets of numerical experiments to analyse such effects in heterogeneous partially saturated porous media where the saturation field is determined by variations in porosity and clay content respectively in both cases we also evaluate the seismic responses of corresponding binary patchy type saturation patterns our results indicate that significant attenuation and modest velocity dispersion effects take place in this kind of media for both binary patchy type and spatially continuous gas saturation patterns and in particular in the presence of relatively small amounts of gas the numerical experiments also show that the nature of the gas distribution patterns is a critical parameter controlling the seismic responses of these environments since attenuation and velocity dispersion effects are much more significant and occur over a broader saturation range for binary patchy type gas water distributions this analysis therefore suggests that the physical mechanisms governing partial saturation should be accounted for when analysing seismic data in a poroelastic framework in this context heterogeneities associated with the dry frame properties which do not play important roles in wave induced fluid flow processes per se should be taken into account since they may determine the kind of gas distribution pattern taking place in the porous rock

tracking textural mineralogical and geochemical signatures in soils developed from basalt derived materials covered with loess sediments sw poland abstract this study investigates the scale of inheritance of signatures typical of loess and basalt derived substrates in soils having both components present as parent material due to past periglacial processes based on field description particle size distribution mineralogy heavy minerals and clay minerals as well as geochemistry we track the signal of both materials local basalt derived and loess derived estimate the maximum thickness of loess mantles and mixed zones having both loess and basaltic components and note the presence or absence of basal layers without allochtonous additions the results show that geochemistry and heavy minerals are the most reliable proxies for a verification of aeolian silt contributions and to define individual layers in complex soil parent materials soil formation in the studied landscape depends on the type of slope sediments typical fine grained weathering of basalt without input from aeolian silt would promote rather vertic development however in thick loess deposits as well as in thin silt textured materials superimposed on clay loam beds clay illuviation dominates development of argic horizons however results in decreasing permeability promoting water stagnation and enhanced degradation processes in clay rich subsoil instead of luvisols stagnosols and retisols developed in the study regions basaltic block covers mixed with loess host cambic horizons based on our findings it seems that at the edge of thin loess deposits no soils exist that developed exclusively from basaltic parent materials

saturation path dependency of p wave velocity and attenuation in sandstone saturated with co2 and brine revealed by simultaneous measurements of waveforms and x ray computed tomography images abstractwe performed a laboratory experiment to measure compressional p wave velocity and its attenuation in low permeability striped sandstone at ultrasonic frequency during drainage co2 injection and imbibition brine injection x ray computed tomography ct images of the rock sample were simultaneously recorded during the injections on the basis of the ct images we calculated the co2 saturation inside a prolate spheroid shaped volume the first fresnel zone that enclosed the wave propagation path the relationship of p wave velocity and that of attenuation to the co2 fraction were then obtained both relationships showed nonuniqueness with remarkable hysteresis in a drainage imbibition cycle to explain the nonunique relationship of p wave velocity to the co2 fraction we investigated the continuous random patchy saturation model by using exponent type autocorrelation the nonunique relationship of velocity to the co2 fraction was explained by the model with a correlation length from an order

equivalent viscoelastic solids for heterogeneous fluid saturated porous rocks differenttheoreticalandlaboratorystudiesonthepropagation ofelasticwavesinrealrockshaveshownthatthepresenceofheterogeneities larger than the pore size but smaller than the predominant wavelengths mesoscopic scale heterogeneities may producesignificantattenuationandvelocitydispersioneffectson seismic waves such phenomena are known as mesoscopic effects and are caused by equilibration of wave induced fluid pressure gradients we propose a numerical upscaling procedure to obtain equivalent viscoelastic solids for heterogeneous fluidsaturated rocks it consists in simulating oscillatory compressibility and shear tests in the space frequency domain which enable us to obtain the equivalent complex undrained plane wave and shear moduli of the rock sample we assume that the behavior of the porous media obeys biot s equations and use a finiteelementproceduretoapproximatethesolutionsoftheassociated boundary value problems also because at mesoscopic scales rock parameter distributions are generally uncertain and of stochastic nature we propose applying the compressibility and sheartestsinamontecarlofashion thisfacilitatesthedefinition of average equivalent viscoelastic media by computing the moments of the equivalent phase velocities and inverse quality factors over a set of realizations of stochastic rock parameters described by a given spectral density distribution we analyzed the sensitivity of the mesoscopic effects to different kinds of heterogeneities in the rock and fluid properties using numerical examples also theapplicationofthemontecarloprocedureallowed us to determine the statistical properties of phase velocities and inverse quality factors for the particular case of quasi fractal heterogeneities

comparison of p wave attenuation models of wave induced flow abstract wave induced oscillatory fluid flow in the vicinity of inclusions embedded in porous rocks is one of the main causes for p wave dispersion and attenuation at seismic frequencies hence the p wave velocity depends on wave frequency porosity saturation and other rock parameters several analytical models quantify this wave induced flow attenuation and result in characteristic velocity saturation relations here we compare some of these models by analyzing their low and high frequency asymptotic behaviours and by applying them to measured velocity saturation relations specifically the biot rayleigh model considering spherical inclusions embedded in an isotropic rock matrix is compared with white s and johnson s models of patchy saturation the modeling of laboratory data for tight sandstone and limestone indicates that by selecting appropriate inclusion size the biot rayleigh predictions are close to the measured values particularly for intermediate and high water saturations

scale effects on modelling the seismic signature of gas results from an outcrop analogue numerous examples of reservoir fields from continental and marine environments involve thin bedded geology yet the inter relationship between thin bedded geology fluid flow and seismic wave propagation is poorly understood in this paper we explore the 4d seismic signature due to saturation changes of gas within thin layers and address the challenge of identifying the relevant scales and properties which correctly define the geology fluid flow and seismic wave propagation in the field based on the study of an outcrop analogue for a thin bedded turbidite we model the time lapse seismic response to fluid saturation changes for different levels of model scale and explore discrepancies in quantitative seismic attributes caused by upscaling our model reflects the geological complexity associated with thin bedded turbidites and its coupling to fluid flow which in turn affects the gas saturation distribution in space and its time lapse seismic imprint rock matrix and fluid properties are modelled after selected fields to reproduce representative field models with realistic impedance contrasts in addition seismic modelling includes multiples in order to assess their contribution in seismic propagation through thin gas layers our results show that multiples could contribute significantly to the measured amplitudes in the case of thin bedded geology this suggests that forward inverse modelling involving the flow simulation and seismic domains used in time lapse seismic interpretation should account for thin layers when these are present in the geological setting

a double bottom simulating reflector in the western ross sea antarctica 1 we present seismic evidence of the presence of gas hydrates and free gas in victoria land basin western ross sea antarctica the occurrence of gas hydrates is inferred from a bottom simulating reflector bsr the first identified in the ross sea area the gas presence was analyzed through targeted reprocessing of the multichannel seismic reflection data 3000 m streamer 120 channels 60 fold acquired in 1990 by the italian r v ogs explora the seismic data were reprocessed in order to increase the signal to noise ratio by adopting a true amplitude approach allowing a subsequent amplitude variations with offset avo analysis to extract information on both p and s wave reflectivity along a profile from the deeper basin to an intrabasin structural high the bsr evolves into crosscutting reflectors ccrs and enhanced amplitude reflectors ears locally another seismic event is interpreted to be a second bsr bsr0 identified about 150 m below the first bsr and is possibly related to the presence of a mixture of gases comprising methane and hydrocarbons with heavier molecular weight and therefore associated with a deeper hydrate stability zone the presence of faults controls the upward gas migration connecting the free gas zone below the bsr and the mud volcanoes and pockmarks on the seafloor the modeling of the hydrate equilibrium zone shows that the observed bsr bsr0 could be stable at the present pressure temperature conditions

permeability effects on the seismic response of gas reservoirs summary in this work we analyse the role of permeability on the seismic response of sandstone reservoirs characterized by patchy gas water saturation we do this in the framework of johnson s model which is a generalization of white s seminal model allowing for patches of arbitrary geometry we first assess the seismic attenuation and velocity dispersion characteristics in response to wave induced fluid flow to this end we perform an exhaustive analysis of the sensitivity of attenuation and velocity dispersion of compressional body waves to permeability and explore the roles played by the johnson parameters t and s v which characterize the shape and size of the gas water patches our results indicate that within the typical frequency range of exploration seismic data this sensitivity may indeed be particularly strong for a variety of realistic and relevant scenarios next we extend our analysis to the corresponding effects on surface based reflection seismic data for two pertinent models of typical sandstone reservoirs in the case of softer and more porous formations and in the presence of relatively low levels of gas saturation we observe that the effects of permeability on seismic reflection data are indeed significant these prominent permeability effects prevail for normal incidence and non normal incidence seismic data and for a very wide range of sizes and shapes of the gas water patches for harder and less porous reservoirs the normal incidence seismic responses exhibit little or no sensitivity to permeability but the corresponding non normal incidence responses show a clear dependence on this parameter again especially so for low gas saturations the results of this study therefore suggest that for a range of fairly common and realistic conditions surface based seismic reflection data are indeed remarkably sensitive to the permeability of gas reservoirs and thus have the potential of providing corresponding first order constraints

finite difference simulations of seismic scattering implications for the propagation of short period seismic waves in the crust and models of crustal heterogeneity synthetic seismograms produced by the finite difference method are used to study the scattering of elastic and acoustic waves in two dimensional media with random spatial variations in seismic velocity the results of this study provide important insights about the propagation of short period 5 the self similar medium is characterized by a scattering q that is constant with frequency whereas theory predicts that the apparent q in an exponential medium is proportional to frequency these alternative models of crustal heterogeneity can thus be tested by improved measurements of the frequency dependence of crustal q at frequencies greater than about 1 hz assuming that scattering is responsible for most of the attenuation at these frequencies measurements of the time decay of the synthetic coda waves clearly show that the single scattering model of coda decay is not appropriate in the presence of moderate amounts of scattering attenuation scattering q 200 in these cases q values derived from the coda decay rate using the single scattering theory do not correspond to the transmission q of the medium the cross correlation of synthetic waveforms observed for an array of receivers along the free surface is observed to be dependent on the correlation distance of the medium the self similar random medium proposed here for the crust produces waveform variations at high frequencies 15 30 hz similar to those reported for actual small scale seismic arrays with apertures of hundreds of meters

a laboratory study of the dependence of elastic wave velocities on pore scale fluid distribution laboratory data have been collected during a continuous imbibition drainage experiment that show a clear dependence of elastic wave velocities on the details of the pore scale distribution of water and air in a sandstone compressional wave velocity vp was measured at a frequency of 1 mhz shear wave velocity vs was measured at a frequency of 600 khz during the experiment vp showed little variation with the level of water saturation sw during increasing sw through imbibition until sw 0 80 at which point vp increased dramatically when sw was decreased pronounced saturation induced hysteresis was observed in the region 03 0 4 as a simple model we consider the imbibition process as producing a partially saturated state in all pores i e all pores contain both air and water the drainage process in contrast favors the existence of either air filled or water filled pores as elastic wave velocities are very sensitive to the saturation state in the smaller crack like pores these variations in fluid distribution cause related variations in velocities

the distribution of silty soils in the grayling fingers region of michigan evidence for loess deposition onto frozen ground this paper presents textural geochemical mineralogical soils and geomorphic data on the sediments of the grayling fingers region of northern lower michigan the fingers are mainly comprised of glaciofluvial sediment capped by sandy till the focus of this research is a thin silty cap that overlies the till and outwash data presented here suggest that it is local source loess derived from the port huron outwash plain and its down river extension the mainstee river valley the silt is geochemically and texturally unlike the glacial sediments that underlie it and is located only on the flattest parts of the finger uplands and in the bottoms of upland dry kettles on sloping sites the silty cap is absent the silt was probably deposited on the fingers during the port huron meltwater event a loess deposit roughly 90 km down the manistee river valley has a comparable origin data suggest that the loess was only able to persist on upland surfaces that were either closed depressions currently dry kettles or flat because of erosion during and after loess deposition deep low order tributary gullies almost ubiquitous on finger sideslopes could only have formed by runoff and soil data from them confirm that the end of gully formation and hence the end of runoff was contemporaneous with the stabilization of the outwash surfaces in the lowlands therefore runoff from the finger uplands during the loess depositional event is the likely reason for the absence of loess at sites in the fingers because of the sandy nature and high permeability of the fingers sediments runoff on this scale could only have occurred under frozen ground conditions frozen ground and windy conditions in the fingers at the time of the port huron advance is likely because the area would have been surrounded by ice on roughly three sides this research 1 shows that outwash plains and meltwater streams of only medium size can be significant loess sources and 2 is the first to present evidence for frozen ground conditions in this part of the upper midwest

geochemical variations in peoria loess of western iowa indicate paleowinds of midcontinental north america during last glaciation peoria loess deposited in western iowa during the last glacial maximum lgm shows distinct geochemical and particle size variations as a function of both depth and distance east of the missouri river geochemical and particle size data indicate that peoria loess in western iowa probably had two sources the missouri river valley and a source that lay to the west of the missouri river both sources indicate that lgm paleowinds in western iowa had a strong westerly component similar to interpretations of previous workers a compilation of loess studies in iowa and elsewhere indicates that westerly winds were dominant during loess transport over much of the midcontinent south of the laurentide ice sheet which is not in agreement with paleowinds simulated by atmospheric general circulation models agcms agcms consistently generate a glacial anticyclone with easterly or northeasterly winds over the laurentide ice sheet and the area to the south of it loess deposition in the midcontinent during the lgm may be a function of infrequent northwesterly winds that were unrelated to the presence of the glacial anticyclone

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

dynamic permeability of porous rocks and its seismic signatures in inhomogeneous porous media the mechanism of wave induced fluid flow causes significant attenuation and dispersion of seismic waves in connection with this phenomenon we study the impact of spatial permeability fluctuations on the dynamic behavior of porous materials this heterogeneous permeability distribution further complicates the ongoing efforts to extract flow permeability from seismic data based on the method of statistical smoothing applied to biot s equations of poroelasticity we derive models for the dynamic equivalent permeability in 1d and 3d randomly inhomogeneous media the low frequency limit of this permeability corresponds to the flow permeability governing fluid flow in porous media we incorporate the dynamic equivalent permeability model into the expressions for attenuation and dispersion of p waves also obtained by the method of smoothing the resulting attenuation and dispersion model is confirmed by numerical computations in randomly layered poroelastic structures the results suggest that the effect of wave induced fluid flow can be observed in a broader frequency range than previously thought the peak attenuation shifts along the frequency axis depending on the strength of the permeability fluctuations we conclude that estimation of flow permeability from seismic attenuation is only possible if permeability fluctuations are properly accounted for

experimental case study of seismically induced loess liquefaction and landslide abstract the 1920 haiyuan ms 8 5 earthquake induced a large number of fluidized loess landslides in china characterized by low slope angles long run out distances and fluidized movement the mechanism of these landslides has aroused considerable interest although additional research is needed to understand more fully the behavior of the loess and the failure mechanism field investigation was conducted on the shibeiyuan landslide and loess samples collected for later laboratory analysis by conventional geotechnical tests triaxial compression tests and ring shear tests the field survey revealed that the shibeiyuan landslide occurred on a concave slope

rates of weathering and chemical depletion in soils across a chronosequence of lake michigan sand dunes abstract accumulation of soil organic matter and depletion of base cations and trace metals were measured in surface soils i e o horizon and upper 15 cm of mineral soil across a 4150 year soil chronosequence of dune capped beach ridges bordering northern lake michigan within 400 years of beach ridge formation coniferous forest develops soil c and n accumulate to steady state levels of 40 and 1 3 mg ha 1 respectively and the ph of the upper mineral soil decreases from 8 5 to 4 3 as carbonate minerals dissolve after substantial proportions of ca and mg have been removed an incipient spodic horizon can be observed the upper surface of which progressively deepens with increasing soil age analysis of soil strain of the upper mineral soil showed gradual dilation reaching 121 after several centuries of soil development after accounting for soil dilation quantities of ca mg p zn mn fe and v in the upper 15 cm of mineral soil decreased exponentially to low asymptotic levels representing quantities contained in weathering resistant minerals mass balance modeling indicated weathering and elemental losses in the order of decreasing decay constant as ca mg mn zn p v fe al k na ti this sequence is consistent with weathering of carbonates then ferromagnesian minerals then feldspars p levels are tightly coupled with ca losses in soils older than 200 years suggesting that ca rather than fe or al stabilizes p high concentrations of heavy metals in the organic horizon relative to the upper mineral soil indicate atmospheric inputs of industrial pollutants

on the reactivation of a large landslide induced by rainfall in highly fissured clays abstract the paper discusses the field investigations geotechnical characterization and time evolution of horizontal displacements in a wide landslide the latter triggered by an earthquake occurring in september 2002 is located in sicily and involves a thick body of stiff and highly fissured clays belonging to a varicoloured clay formation in order to characterise the reactivation of landslide mechanisms induced by rainfall a three year monitoring programme 2008 2011 was implemented to measure rain pore water pressures and deep and superficial displacements the monitoring data made it possible to recognize three distinct landslides which evolve at variable rates in different directions within the overall landslide area the landslides were reactivated by the increase in pore water pressures in the period autumn 2009 spring 2010 the data clearly show the mechanical role of pore water pressures in the stability of the slope and point out the dependence of the time evolution of the horizontal displacement on the pore water pressure variation induced by rainfall back analysis carried out on the single landslides confirmed that they are reactivated ones since the residual shear strength is mobilised on the pre existing sliding surfaces the pore water pressure variation and the landslide body displacement rates can be effectively related to 5 month cumulative rainfall by simple models characterised by three parameters these models calibrated on the period october 2009 september 2010 made it possible to predict the horizontal displacement rates in the ensuing time period the displacements forecasted by the model in the period september 2010 may 2011 agree very well with the measured ones

a porosity based biot model for acoustic waves in snow phase velocities and attenuation in snow cannot be explained by the widely used elastic or viscoelastic models for acoustic wave propagation instead biot s model of wave propagation in porous materials should be used however the application of biot s model is complicated by the large property space of the underlying porous material here constant properties for ice and air and empirical relationships are used to estimate unknown porous properties from snow porosity using this set of equations phase velocities and plane wave attenuation of shear and compressional waves are predicted as functions of porosity or density for light snow the peculiarity was found that the velocity of the first compressional wave is lower than that of the second compressional wave that is commonly referred to as the slow wave the reversal of the velocities comes with an increase of attenuation for the first compressional wave this is in line with the common observation that sound is strongly absorbed in light snow the results have important implications for the use of acoustic waves to evaluate snow properties and to numerically simulate wave propagation in snow

impact of fluid saturation on the reflection coefficient of a poroelastic layer the impact of changes in saturation on the frequencydependent reflection coefficient of a partially saturated layer was studied seismic attenuation and velocity dispersion in partially saturated i e patchy saturated poroelastic media were accounted for by using the analytical solution of the 1d white s model for wave induced fluid flow white s solution was applied in combination with an analytical solution for the normal incidence reflection coefficient of an attenuating layer embedded in an elastic or attenuating background medium to investigate the effects of attenuation velocity dispersion and tuning on the reflection coefficient approximations for the frequency dependent quality factor its minimum value and the frequency at which the minimum value of the quality factor occurs were derived the approximations are valid for any two alternating sets of petrophysical parameters an approximation for the normal incidence reflection coefficient of an attenuating thin compared to the wavelength layer was also derived this approximation gives insight into the influence of contrasts in acoustic impedance and or attenuation on the reflectivity of a thin layer laboratory data for reflections from a water saturated sand layer and from a dry sand layer were further fit with petrophysical parameters for unconsolidated sand partially saturated with water and air the results showed that wave induced fluid flow can explain low frequency reflection anomalies which are related to fluid saturation and can be observed in seismic field data the results further indicate that reflection coefficients of partially saturated layers e g hydrocarbon reservoirs can vary significantly with frequency especially at low seismic frequencies where partial saturation may often cause high attenuation

dynamic equivalent medium approach for thinly layered saturated sediments the phase velocity and the attenuation coefficient of compressional seismic waves propagating in poroelastic fluid saturated laminated sediments are computed analytically from first principles the wavefield is found to be strongly affected by the medium heterogeneity impedance fluctuations lead to poroelastic scattering variations of the layer compressibilities cause inter layer flow a 1 d macroscopic local flow these effects result in significant attenuation and dispersion of the seismic wavefield even in the surface seismic frequency range 10 100 hz the various attenuation mechanisms are found to be approximately additive dominated by inter layer flow at very low frequencies elastic scattering is important over a broad frequency range from seismic to sonic frequencies biot s global flow the relative displacement of solid frame and fluid contributes mainly in the range of ultrasonic frequencies from the seismic frequency range up to ultrasonic frequencies attenuation due to heterogeneity is strongly enhanced compared to homogeneous biot models simple analytical expressions for the p wave phase velocity and attenuation coefficient are presented as functions of frequency and of statistical medium parameters correlation lengths variances these results automatically include different asymptotic approximations such as poroelastic backus averaging in the quasi static and the no flow limits geometrical optics and intermediate frequency ranges

sensitivity analysis from single well ert simulations to image co2 migrations along wellbores co2 plume imaging is a required step in co2 geological storage for both performance assessment and risk management purposes this work has been performed in the frame of the co2care project and its aim is to develop tools and methodologies to monitor co2 migration and verify the long term well integrity after site abandonment the timely detection of an anomaly is essential to perform a suitable remediation for this purpose downhole tools are permanently installed but it is important to check the resolution and efficiency of the adopted techniques in particular this study investigates the possibility of using electrical resistivity tomography ert to image co2 migrations around observation boreholes through a sensitivity study

seismic signatures of permeability in heterogeneous porous media in homogeneous poroelastic systems the permeability tensor practically does not influence propagating seismic waves in the low frequency range 0 1000 hz see e g schmitt 1989 gelinsky and shapiro 1996 in this paper we show that this situation changes in heterogeneous systems such as layered or fractured sediments due to the heterogeneities of poroelastic structures the attenuation of p waves is influenced by the permeability in an enhanced way we show however that such a seismic permeability can differ very strongly from the hydraulic permeability

kame deltas provide evidence for a new glacial lake and suggest early glacial retreat from central lower michigan usa abstract in association with an undergraduate honors seminar at michigan state university we studied two small kame deltas in north central lower michigan these recently identified deltas provide clear evidence for a previously unknown proglacial lake glacial lake roscommon in this large basin located in an interlobate upland our first goal was to document and characterize the geomorphology of these deltas because both deltas are tied to ice contact ridges that mark the former position of the retreating ice margin within the lake our second goal was to establish the age of one of the deltas thereby constraining the timing of ice retreat in this part of michigan for which little information currently exists both deltas are composed of well sorted fine and medium sands with little gravel and have broad nearly flat surfaces and comparatively steep fronts samples taken from the upper 1 5 m of the deltas show little spatial variation in texture aside from a general fining toward their outer margins gullies on the outer margins of both deltas probably postdate the formation of the deltas proper we suggest that they formed by runoff during a permafrost period subsequent to lake drawdown we named the ice lobe that once covered this area the mackinac lobe because it had likely advanced into the region across the mackinac straits area five of six optically stimulated luminescence osl ages from one of the deltas had minimal scatter and were within 1000 years of one another with a mean age of 23 1 0 4 ka these ages suggest that the mackinac lobe had started to retreat from the region considerably earlier than previously thought even while ice was near its maximum extent in illinois and indiana and the remainder of michigan was ice covered this early retreat which appears to coincide with a short lived warm period indicated from the greenland ice core formed an opening that was at least occasionally flooded thick and deep fine textured deposits which underlie much of the region probably date to this time our work provides the first evidence of this extremely early ice retreat from central lower michigan occurring almost 4000 years before the southern margin of the ice saginaw lobe had started its retreat from the state

thin bed prestack spectral inversion prestack seismic data has been used in a new method to fully determine thin bed properties including the estimation of its thickness p and s wave velocities and density the approach requires neither phase information nor normal moveout nmo corrections and assumes that the prestack seismic response of the thin layer can be isolated using an offset dependent time window we obtained the amplitude versus angle ava response of the thin bed considering converted p waves s waves and all the associated multiples we carried out the estimation of the thin bed parameters in the frequency amplitude spectrum domain using simulated annealing in contrast to using zero offset data the use of ava data contributes to increase the robustness of this inverse problem under noisy conditions as well as to significantly reduce its inherent nonuniqueness to further reduce the nonuniqueness and as a means to incorporate a priori geologic or geophysical information e g well log data we imposed appropriate bounding constraints to the parameters of the media lying above and below the thin bed which need not be known accurately we tested the method by inverting noisy synthetic gathers corresponding to simple wedge models in addition we stochastically estimated the uncertainty of the solutions by inverting different data sets that share the same model parameters but are contaminated with different noise realizations the results suggest that thin beds can be characterized fully with a moderate to high degree of confidence below tuning even when using an approximate wavelet spectrum

quantitative analysis of time lapse seismic monitoring data at the sleipner co2 storage operation the co2 storage operation at sleipner in the norwegian north sea provides an excellent demonstration of the application of time lapse surface seismic methods to co2 plume monitoring under favorable conditions injection commenced at sleipner in 1996 with co2 separated from natural gas being injected into the utsira sand a major saline aquifer of late cenozoic age co2 injection is via a near horizontal well at a depth of about 1012 m below sea level bsl some 200 m below the reservoir top at a rate approaching 1 million tonnes mt per year with more than 11 mt currently stored

paleobotanical and environmental implications of a buried forest bed in northern lower michigan usa sediments and stratigraphy at the tower buried forest site provide a glimpse into the immediate post glacial environment of northern lower michigan usa at this site sandy glacial outwash is overlain by 1 37 cm of peat associated with a wetland above which are 2 flat lying spruce and larch logs and branches that date between 10 910 and 10 340 cal years bp above the woody materials are 55 75 cm of sand interbedded with organic muck laminae which we interpret as local alluvium this stratigraphic sequence is overlain by muck soil materials associated with the modern wetland pollen and plant macrofossil analysis of the lower peat indicate that a tundra boreal parkland had been established here shortly after final deglaciation later picea glauca white spruce picea mariana black spruce larix laricina larch and abies balsamea balsam fir became abundant in an open boreal forest spaghnum peatland subsequent increases in pinus pine and typha cattail indicate drying and possibly warming conditions at ca 10 340 cal years bp or a few centuries prior nearly two millennia after final deglaciation water flowed across the site possibly knocking over the trees interbedded sand and muck deposits above the flat lying logs are interpreted as alluvial deposits from this event after which the wetland became quiescent again

seismic attenuation in finely layered porous rocks effects of fluid flow and scattering scattering caused by fine layering is known to play an important role in seismic attenuation if the rock is also porous and permeable additional attenuation can be caused by a flow of the pore fluid induced by the passing wave see e g white 1983 at frequencies higher than 100 khz standard biot s attenuation biot 1962 bourbie et al 1987 may also contribute to the overall attenuation in a layered poroelastic rock while standard biot s attenuation has been well known for decades the effects of scattering by fine layering and interlayer flow have been studied extensively both theoretically and numerically in recent years however in all theoretical approaches proposed thus far these effects have been treated separately scattering was studied for purely elastic rocks burridge and chang 1989 shapiro et al 1994 while attenuation caused by interlayer flow was considered either for periodically stratified media that causes no scattering norris 1993 or for frequencies at which scatterin

p wave seismic attenuation by slow wave diffusion effects of inhomogeneous rock properties recent research has established that the dominant p wave attenuation mechanism in reservoir rocks at seismic frequencies is because of wave induced fluid flow mesoscopic loss the p wave induces a fluid pressure difference at mesoscopic scale inhomogeneities larger than the pore size but smaller than the wavelength typically tens of centimeters and generates fluid flow and slow diffusion biot waves continuity of pore pressure is achieved by energy conversion to slow p waves which diffuse away from the interfaces in this context we consider a periodically stratified medium and investigate the amount of attenuation and velocity dispersion caused by different types of heterogeneities in the rock properties namely porosity grain and frame moduli permeability and fluid properties the most effective loss mechanisms result from porosity variations and partial saturation where one of the fluids is very stiff and the other is very compliant such as a highly permeable sandstone at shallow depths saturated with small amounts of gas around 10 saturation and water grain and frame moduli variations are the next cause of attenuation the relaxation peak moves towards low frequencies as the background permeability decreases and the viscosity and thickness of the layers increase the analysis indicates in which cases the seismic band is in the relaxed regime and therefore when the gassmann equation can yield a good approximation to the wave velocity

seismic rheological model and reflection coefficients of the brittle ductile transition it is well established that the upper cooler part of the crust is brittle while deeper zones present ductile behaviour in some cases this brittle ductile transition is a single seismic reflector with an associated reflection coefficient we first develop a stress strain relation including the effects of crust anisotropy seismic attenuation and ductility in which deformation takes place by shear plastic flow viscoelastic anisotropy is based on the eigenstrain model and the zener and burgers mechanical models are used to model the effects of seismic attenuation velocity dispersion and steady state creep flow respectively the stiffness components of the brittle and ductile media depend on stress and temperature through the shear viscosity which is obtained by the arrhenius equation and the octahedral stress criterion the p and s wave velocities decrease as depth and temperature increase due to the geothermal gradient an effect which is more pronounced for shear waves we then obtain the reflection and transmission coefficients of a single brittle ductile interface and of a ductile thin layer the pp scattering coefficient has a brewster angle a sign change in both cases and there is substantial ps conversion at intermediate angles the pp coefficient is sensitive to the layer thickness unlike the ss coefficient thick layers have a well defined brewster angle and show higher reflection amplitudes finally we compute synthetic seismograms in a homogeneous medium as a function of temperature

shaking table tests on reinforced soil retaining walls subjected to the combined effects of rainfall and earthquakes abstract earthquakes and rainfall often occur together and their combined effects on reinforced soil retaining walls rsrw are not investigated in detail in this paper shaking table tests were carried out in model scale to investigate seismic performance of rsrw subjected to the combined forces of rainfall and earthquakes five cases with different degrees of saturation for the model ground were considered for comparison and each wall was shaken by a horizontal motion with a peak acceleration of 0 5 g various mechanical quantities such as wall deformation horizontal and vertical effective earth pressures pore water pressure horizontal acceleration and reinforcement strain were monitored carefully it was found that wall displacement and reinforcement strain at naturally dry and saturated states are larger than those at unsaturated state meaning that suction does have an enhancement effect on the seismic performance of rsrw furthermore a special film force sensor that can measure effective pressure in saturated ground accurately was used to measure the effective earth pressure along the facing panel of rsrw based on which the seismic performance was discussed in a systematical way

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 characterization of thin beds containing patchy carbon dioxide brine distributions a study based on numerical simulations we studied the seismic attenuation and velocity dispersion effects produced by wave induced fluid flow in weakly consolidated sandstones containing patchy carbon dioxide co2 brine distributions the analysis also focuses on the velocity pushdown because of the presence of this gas as well as on the role of the wave induced fluid flow mesoscopic effects on the amplitude variation with angle ava seismic response of thin layers containing co2 such as those found at the utsira sand sleipner field offshore norway we found that this loss mechanism may play a key role on conventional surface seismic data suggesting that further data analysis may provide useful information on the characteristics of the fluid distributions in these environments numerical experiments let us observe that although mesoscopic effects can be very significant in this kind of media the seismic response of a given isolated thin layer computed considering such effects is very similar to that of a homogeneous elastic thin layer with a compressional velocity equal to that of the original porous rock averaged in the effective data bandwidth this suggests that the thin bed prestack spectral inversion method published by the authors could be used to estimate representative compressional velocities and layer thicknesses in these environments in effect results using realistic synthetic prestack seismic data show that isolated co2bearing thin beds can be characterized in terms of their thicknesses and representative compressional velocities this information can be qualitatively related to co2 saturations and volumes thus the prestack spectral inversion method could find application in the monitoring of the evolution of co2 plumes at injection sites similar to that at the sleipner field

numerical simulation of the biot slow wave in water saturated nivelsteiner sandstone the development of rock acoustic models is important for interpreting seismic data these models should relate seismic properties such as wave velocity and attenuation to the production and lithological properties of reservoir rocks such as porosity permeability fluid type and fluid saturation

anisotropic poroelasticity and wave induced fluid flow harmonic finite element simulations summary a dominant p wave attenuation mechanism in reservoir rocks at seismic frequencies is due to wave induced fluid flow mesoscopic loss the p wave induces a fluid pressure difference at mesoscopic scale inhomogeneities larger than the pore size but smaller than the wavelength generating fluid flow and slow diffusion biot waves the theory has been developed in the 1970s for the symmetry axis of the equivalent transversely isotropic ti medium corresponding to a finely layered medium and has recently been generalized to all propagation angles the new theory states that the fluid flow direction is perpendicular to the layering plane and it is independent of the loading direction as a consequence the relaxation behaviour can be described by a single relaxation function since the medium consists of plane homogeneous layers besides p wave losses the coupling between the qp and qsv waves generates shear wave anisotropic velocity dispersion and attenuation in this work we introduce a set of quasi static numerical experiments to determine the equivalent viscoelastic ti medium to a finely layered poroelastic medium which is validated using a recently developed analytical solution the modelling technique is the finite element fe method where the equations of motion are solved in the space frequency domain numerical rock physics may in many circumstances offer an alternative to laboratory measurements numerical experiments are inexpensive and informative since the physical process of wave propagation can be inspected during the experiment moreover they are repeatable essentially free from experimental errors and may easily be run using alternative models of the rock and fluid properties we apply the methodology to the utsira aquifer of the north sea where carbon dioxide co2 has been injected during the last 15 years the tests consider alternating layers of the same rock saturated with gas and brine and a sequence of gas saturated sandstone and mudstone layers which represent possible models of the reservoir and cap rock of the aquifer system the numerical examples confirm the new theory and illustrate the implementation of the harmonic tests to determine the complex and frequency dependent effective stiffnesses and the associated wave velocities and quality factors

seismic reflection dispersion due to wave induced fluid flow in heterogeneous reservoir rocks we have investigated the impact of wave induced fluid flow including biot flow and mesoscopic flow on the signatures of seismic reflectivity in heterogeneous reservoir rocks we have incorporated the dynamic poroelastic responses of mesoscopic flow into the classical biot theory the resulting effective biot media could capture the characteristics of velocity dispersion and wave attenuation in heterogeneous poroelastic media on the basis of this effective biot media an approach was developed to compute the poroelastic reflection at arbitrary angles and frequencies from the boundary of two heterogeneous porous media the computed poroelastic reflections not only depended on the elastic properties contrast and incident angle but also relied on the fluid mobility and observational frequency for a typical sand shale reflector with the given rock and fluid properties we found that the effect of mesoscopic flow causes pwave reflection amplitude variations with the frequency being as high as 40 and a maximum phase shift as high as 16 at the seismic exploration frequency band in addition it was found that the amplitudevariation with offset intercept and the gradient at the poroelastic interface were impacted by the mesoscopic flow and had a decreasing trend with frequency therefore ignoring the impact of mesoscopic flow could possibly lead to uncertainty in seismic imaging as well as quantitative interpretation of reservoir properties in comparison the biot flowinduced seismic dispersion effect which occured at a very highfrequency range was almost negligible

the grayling fingers region of michigan soils sedimentology stratigraphy and geomorphic development abstract this paper provides data on the landforms soils and sediments within a unique northern michigan landscape known as the grayling fingers and evaluates these data to develop various scenarios for the geomorphic development of this region composed of several large flat topped ridges that trend n s the physiography of the fingers resembles a hand previously interpreted as remnant moraines the grayling fingers are actually a pleistocene constructional landscape that was later deeply incised by glacial meltwater the sediments that comprise the fingers form a generally planar assemblage with thick 100 m sandy glacial outwash forming the lowest unit above the outwash are several meters of till that is remarkably similar in texture to the outwash below thus the region is best described as an incised ground moraine finally a thin silty cap is preserved on the flattest most stable uplands this sediment package and the physiography of the fingers are suggestive of geomorphic processes not previously envisioned for michigan although precise dates are lacking we nonetheless present possible sequences of geomorphic sedimentologic processes for the fingers this area was probably a topographic high prior to the advance of marine isotope stage 2 woodfordian ice much of the glacial outwash in the fingers is probably associated with a stagnant early woodfordian ice margin implying that this interlobate area remained ice free and ice marginal for long periods during stage 2 woodfordian ice eventually covered the region and deposited 5 10 m of sandy basal till over the proglacial outwash plain small stream valleys on the outwash surface were palimpsested onto the till surface as the ice retreated as kettle chains and as dry upland valleys the larger of these valleys were so deeply incised by meltwater that they formed the large through flowing finger valleys the silt cap that occupies stable uplands was probably imported into the region while still glaciated the fingers region a col on the ice surface could have acted as a collection basin for silts brought in as loess or in superglacial meltwater this sediment was let down as the ice melted and preserved only on certain geomorphically stable and fluvially isolated locations this study demonstrates that the impact of woodfordian ice in this region was mostly erosional and suggests that mississippi valley loess may have indirectly impacted this region

geomorphology of the chippewa river delta of glacial lake saginaw central lower michigan usa abstract we introduce characterize and interpret the geomorphic history of a relict pleistocene aged delta of the chippewa river in central lower michigan the broad sandy chippewa delta developed into various stages of glacial lake saginaw between ca 17 and 15 ka bp calibrated ages although the delta was first identified in 1955 on a statewide glacial geology map neither its extent nor its pleistocene history had been previously determined the delta is typically forested owing to its wet sandy soils which stand out against the agricultural fields of the surrounding loamy lake plain sediments the delta heads near the city of mt pleasant and extends eastward onto the saginaw lowlands i e the plain of glacial lake saginaw data from 3285 water well logs 180 hand augered sites and 185 points randomly located in a gis on two storied sand over loam soils were used to determine the extent textural properties and thickness of the delta the delta is 18 km wide and 38 km long and is sandy throughout deltaic sediments from neighboring rivers that also drained into glacial lake saginaw merge with the lower chippewa delta obscuring its boundary there the delta is thickest near the delta s head and in the center but thins to 1 2 m or less on its eastern margins mean thicknesses are 2 3 2 9 m suggestive of a thin sediment body frequently impacted by the waves and fluctuating waters of the lakes although beach ridges are only weakly expressed across the delta because of the sandy sediment the coarsest parts of the delta are generally coincident with some of these inferred former shorezones and have a broad incised channel that formed while lake levels were low the thick upper delta generally lies above the relict shorelines of glacial lakes saginaw and arkona 17 1 to 16 ka bp whereas most of the thin distal delta is associated with glacial lake warren 15 ka bp together these data suggest that the chippewa delta formed and prograded as lake levels in the saginaw lowlands alternated and episodically fell the result is a delta that is comparatively thin expansive and sandy in some places these sands have subsequently been reworked into fields of small parabolic dunes

seismic and ultrasonic velocities in permafrost we calculate the compressional and shear wave velocities of permafrost as a function of unfrozen water content and temperature unlike previous theories based on simple slowness and or moduli averaging or two phase models we use a biot type three phase theory that considers the existence of two solids solid and ice matrices and a liquid unfrozen water the compressional velocity for unconsolidated sediments obtained with this theory is close to the velocity computed with wood s model since biot s theory involves a wood averaging of the moduli of the single constituents moreover the model gives lower velocities than the well known slowness averaging theory wyllie s equation for consolidated berea sandstone the theory underestimates the value of the compressional velocity below 0 c computing the average bulk moduli by slowness averaging the ice and solid phases and wood averaging the intermediate moduli with the liquid phase yields a fairly good fit of the experimental data the proportion of unfrozen water and temperature are closely related fitting the wave velocity at a given temperature allows the prediction of the velocity at the whole range of temperatures provided that the average pore radius and its standard deviation are known

conditions favourable for the formation of warm climate aeolian sand sheets aeolian sand sheets are areas of aeolian sand where dunes with slipfaces are generally absent sand sheets are ubiquitous to modern warm climate sand seas generally occurring marginal to dune fields although they may exist within the interior of a sand sea or independent of a dune field sand sheet deposits are recognized in ancient aeolian sequences where they may account for significant accumulations of low angle aeolian stratification we suggest that the occurrence of sand sheets instead of dunes indicates that conditions are outside the range within which dunes form or that one or more factors interfere with dune development while also favouring the accumulation of sand sheets a study of six modern sand sheets in north america located at great sand dunes gran desierto dumont algodones padre island and colorado river delta indicates that the factors favourable for sand sheet development are 1 a high water table 2 surface cementation or binding 3 periodic flooding 4 a significant coarse grained sediment population and 5 vegetation these factors are reflected in the nature of stratification and the accessory features of sand sheet accumulations within the areas of modern sand sheets as well as in their ancient counterparts in the triassic dolores and pennsylvanian permian rico formations

estimation of rock physics properties from seismic attributes part 1 strategy and sensitivity analysis abstractthe quantitative estimation of rock physics properties is of great importance in any reservoir characterization we have studied the sensitivity of such poroelastic rock physics properties to various seismic viscoelastic attributes velocities quality factors and density because we considered a generalized dynamic poroelastic model our analysis was applicable to most kinds of rocks over a wide range of frequencies the viscoelastic attributes computed by poroelastic forward modeling were used as input to a semiglobal optimization inversion code to estimate poroelastic properties porosity solid frame moduli fluid phase properties and saturation the sensitivity studies that we used showed that it was best to consider an inversion system with enough input data to obtain accurate estimates however simultaneous inversion for the whole set of poroelastic parameters was problematic due to the large number of parameters and their trade off consequently we restricted the sensitivity tests to

identification of gas hydrate dissociation from wireline log data in the shenhu area south china sea wireline logs were acquired in eight wells during china s first etas hydrate drilling expedition gmgs 1 in april june of 2007 well logs obtained from site sh3 indicated gas hydrate was present in the depth range of 195 206 in below seafloor with a maximum pore space gas hydrate saturation calculated from pore water freshening of about 26 assuming gas hydrate is uniformly distributed in the sediments resistivity calculations using archie s equation yielded hydrate saturation trends similar to those from chloride concentrations however the measured compressional p wave velocities decreased sharply at the depth between 194 and 199 mbsf dropping as low as 1 3 km s indicating the presence of free gas in the pore space possibly caused by the dissociation of gas hydrate during drilling because surface seismic data acquired prior to drilling were not influenced by the in situ gas hydrate dissociation surface seismic data could be used to identify the cause of the low p wave velocity observed in the well log to determine whether the low well log p wave velocity was caused by in situ free gas or by gas hydrate dissociation synthetic seismograms were generated using the measured well log p wave velocity along with velocities calculated assuming both gas hydrate and free gas in the pore space comparing the surface seismic data with various synthetic seismograms suggested that low p wave velocities were likely caused by the dissociation of in situ gas hydrate during drilling

velocity and attenuation in partially saturated rocks poroelastic numerical experiments we use a poroelastic modelling algorithm to compute numerical experiments on wave propagation in a rock sample with partial saturation using realistic fluid distribution patterns from tomography scans frequencies are in the range 10 to 500 khz the rock is a homogeneous isotropic sandstone partially filled with gas and water which are defined by their characteristic values of viscosity compressibility and density we assume no mixing and that the two different pore fills occupy different macroscopic regions the von karman self similar correlation function is used employing different fractal parameters to model uniform and patchy fluid distributions respectively where effective saturation is varied in steps from full gas to full water saturation without resorting to additional matrix fluid interaction mechanisms we are able to reproduce the main features of the variation in wave velocity and attenuation with effective saturation and frequency as those of published laboratory experiments furthermore the behaviour of the attenuation peaks versus water saturation and frequency is similar to that of white s model the conversion of primary p wave energy into dissipating slow waves at the heterogeneities is shown to be the main mechanism for attenuating the primary wavefield fluid gas patches are shown to affect attenuation more than equivalent patches in the permeability or solid grain properties

one dimensional random patchy saturation model for velocity and attenuation in porous rocks porous rocks encountered in hydrocarbon reservoirs are often saturated with a mixture of two or more fluids generation of synthetic seismograms as well as interpretation of in situ attenuation measurements require a theoretical understanding of the relation between the heterogeneous distribution of fluid patches and the acoustic properties of rocks thus the problem of calculating acoustic properties of rocks saturated with a mixture of two fluids has attracted considerable interest white 1975 murphy 1982 gist 1994 mavko and mukerji 1998 pride et al 2004 at the same time this problem is also interesting from the theoretical point of view because partially saturated rocks represent a particularly interesting situation when the effects of dynamic poroelasticity may be significant at seismic or sonic frequencies indeed it is a radical departure from the situation with a porous material fully saturated with a single fluid such a fully saturated material exhibits frequency dependent effects only at frequencies comparable with biot9s characteristic frequency bourbie et al 1987 c f where f is the fluid density is fluid viscosity is permeability and is porosity for frequencies much lower than c the dynamic effects can be ignored and gassmann theory applies

finite difference modeling of wave propagation and diffusion in poroelastic media numerical modeling of seismic waves in heterogeneous porous reservoir rocks is an important tool for interpreting seismic surveys in reservoir engineering various theoretical studies derive effective elastic moduli and seismic attributes from complex rock properties involving patchy saturation and fractured media to confirm and further develop rock physics theories for reservoir rocks accurate numerical modeling tools are required our 2d velocity stress finite difference scheme simulates waves within poroelastic media as described by biot s theory the scheme is second order in time contains high order spatial derivative operators and is parallelized using the domain decomposition technique a series of numerical experiments that are compared to exact analytical solutions allow us to assess the stability conditions and dispersion relations of the explicit poroelastic finite differ ence method the focus of the experiments is to model wave induced flow accurately in the vicinity of mesoscopic hete

1d viscoelastic waveform inversion for q structures from the surface seismic and zero offset vsp data wave attenuation is an important physical property of hydrocarbon bearing sediments that is rarely taken into account in site characterization with seismic data we present a 1d viscoelastic waveform inversion scheme for determining the quality factor q from the normal incidence surface seismic and zero offset vertical seismic profile vsp data simultaneously the joint inversion problem is solved by the damped least squares method and the inversion result is successful using synthetic data the effects of initial model thickness q value and the existence of noise were studied through a synthetic example by extracting all of the information contained in the waveforms the waveform inversion of the seismic reflection and transmission data becomes a powerful tool for estimating q for a more comprehensive image of q the tomographic inversion of q is applied to the walkaway vsp and prestack surface seismic data using the waveform inversion result as the initial model results from applying the metho

pleistocene periglacial eolian deposits in southwestern alaska sedimentary facies and depositional processes abstract pleistocene periglacial eolian sediments are widespread in the nushagak holitna and upper kuskokwim lowlands of southwestern alaska these sediments comprise mainly sand sheet deposits and sand loess intergrades with subordinate sand dune deposits and loess sand sheet deposits range from 1 sharply defined parallel low angle laminae formed by migrating wind ripples to 2 irregular subhorizontal strata which reflect migration of poorly segregated wind ripples accumulation on a sparsely vegetated surface adhesion on a quasi planar bed and or niveo eolian deposition sand loess intergrades represent alternating bed load and suspension deposition related mainly to the stochastic and seasonal variability of former wind systems the dominance of sand sheet deposits over deposits of well formed dunes in the pleistocene eolian record of southwestern alaska reflects the limited availability of loose dry sand in this former periglacial environment immobilization of sand after deposition as low relief sheets resulted from a seasonally variable combination of ice cementation sparse vegetation high water tables and snow cover

holocene loess deposition and soil formation as competing processes matanuska valley southern alaska although loess paleosol sequences are among the most important records of quaternary climate change and past dust deposition cycles few modern examples of such sedimentation systems have been studied stratigraphic studies and 22 new accelerator mass spectrometry radiocarbon ages from the matanuska valley in southern alaska show that loess deposition there began sometime after f6500 14 c yr b p and has continued to the present the silts are produced through grinding by the matanuska and knik glaciers deposited as outwash entrained by strong winds and redeposited as loess over a downwind distance of f40 km loess thickness sand content and sand pluscoarse silt content decrease whereas fine silt content increases loess deposition was episodic as shown by the presence of paleosols at distances 10 km from the outwash plain loess source stratigraphic complexity is at a maximum i e the greatest number of loesses and paleosols at intermediate 10 25 km distances from the loess source surface soils increase in degree of development with distance downwind from the source where sedimentation rates are lower proximal soils are entisols or inceptisols whereas distal soils are spodosols ratios of mobile cao k2o and fe2o3 to immobile tio2 show decreases in surface horizons with distance from the source thus as in china where loess deposition also takes place today eolian sedimentation and soil formation are competing processes study of loess and paleosols in southern alaska shows that particle size can vary over short distances loess deposition can be episodic over limited time intervals and soils developed in stabilized loess can show considerable variability under the same vegetation d 2004 university of washington all rights reserved

numerical analysis of wave induced fluid flow effects on seismic data application to monitoring of co2 storage at the sleipner field 1 in this work we analyze how patchy distributions of co2 and brine within sand reservoirs may lead to significant attenuation and velocity dispersion effects which in turn may have a profound impact on surface seismic data the ultimate goal of this paper is to contribute to the understanding of these processes within the framework of the seismic monitoring of co2 sequestration a key strategy to mitigate global warming we first carry out a monte carlo analysis to study the statistical behavior of attenuation and velocity dispersion of compressional waves traveling through rocks with properties similar to those at the utsira sand sleipner field containing quasi fractal patchy distributions of co2 and brine these results show that the mean patch size and co2 saturation play key roles in the observed wave induced fluid flow effects the latter can be remarkably important when co2 concentrations are low and mean patch sizes are relatively large to analyze these effects on the corresponding surface seismic data we perform numerical simulations of wave propagation considering reservoir models and co2 accumulation patterns similar to the co2 injection site in the sleipner field these numerical experiments suggest that wave induced fluid flow effects may produce changes in the reservoir s seismic response modifying significantly the main seismic attributes usually employed in the characterization of these environments consequently the determination of the nature of the fluid distributions as well as the proper modeling of the seismic data constitute important aspects that should not be ignored in the seismic monitoring of co2 sequestration problems

the loess cover of northeastern wisconsin abstract we present the first study of the distribution genesis and paleoenvironmental significance of late pleistocene loess in northeastern wisconsin and adjacent parts of michigan s upper peninsula loess here is commonly 25 70 cm thick upland areas that were deglaciated early and remained geomorphically stable preferentially accumulated loess by providing sites that were efficient at trapping and retaining eolian sediment data from 419 such sites indicate that the loess was mainly derived from proglacial outwash plains and to a lesser extent hummocky end moraines within and near the region particularly those toward the east of the loess deposits most of the loess was transported on katabatic winds coming off the ice sheet which entrained and transported both silt and fine sands the loess fines markedly and is better sorted distal to these source regions only minimal amounts of loess were deposited in this area via westerly winds this research 1 reinforces the observation that outwash plains and end moraines can be significant loess sources 2 provides evidence for katabatic winds as significant eolian transport vectors and 3 demonstrates that the loess record may be variously preserved across landscapes depending on where and when geomorphically stable sites became available for loess accumulation

using pca to characterize and differentiate loess deposits in wisconsin and upper michigan usa abstract data on loess thickness as well as a variety of particle size fractions were determined for 875 samples taken from several loess sheets across wisconsin and upper michigan because the particle size characteristics of these samples varied widely within and between the loess sheets we used principal components analysis pca as a way of isolating the major textural components or signals that exist across the various loess sheets the purpose of this research was to examine and interpret these principal components or particle size signatures common to the different loesses in order to better understand the loess sheets character formation mechanisms and likely sources our initial assumption that many of these loesses varied markedly from the classical silty loess was supported by the particle size data and the pca although component 1 was interpreted as thick silty loess dominated by medium silts component 2 was mainly composed of very fine sand and coarse silt and is better viewed as coarse loess components 3 and 4 were less texturally homogeneous and may reflect mixing between the loess and the underlying sediment especially where the loess is

squirt flow in fully saturated rocks we estimate velocity frequency dispersion and attenuation in fully saturated rocks by employing the squirt flow mechanism of solid fluid interaction in this model pore fluid is squeezed from thin soft cracks into the surrounding large pores information about the compliance of these soft cracks at low confining pressures is extracted from high pressure velocity data the frequency dependence of squirt induced pressure in the soft cracks is linked with the porosity and permeability of the soft pore space and the characteristic squirt flow length these unknown parameters are combined into one expression that is assumed to be a fundamental rock property that does not depend on frequency the appropriate value of this expression for a given rock can be found by matching our theoretical predictions with the experimental measurements of attenuation or velocity the low frequency velocity limits as given by our model are identical to those predicted by gassmann s formula the high frequency limits may sign

mississippi valley regional source of loess on the southern green bay lobe land surface wisconsin loess has been recognized on the glacial land surface of the green bay lobe for over 100 yr but no systematic explanation of the source of the loess has been advanced intriguingly the loess on the green bay lobe land surface is thicker than predicted by regional thinning trends from the mississippi valley and is geographically separated from much loess of southwest wisconsin by a sandy region devoid of loess mapping based on soil survey interpretation indicates that the loess occurs above an escarpment marking the eastern end of the sandy loess free region particle size fining trends demonstrate that the loess was transported by northwesterly winds clay mineralogy of the green bay lobe loess is distinctly different than glaciogenic sediments and matches loess of the mississippi valley indicating a regional source and long distance transport of the loess we propose the loess was transported from the regional source along a surface of transport produced by migration of eolian sand through low relief landscapes including the glacial lake wisconsin basin eolian sand migration caused repeated entrainment of dust leading to east southeastward transport the loess accumulated above an escarpment that limited sand mobility and re entrainment of loess beyond this topographic barrier

influence of frequency and saturation on avo attributes for patchy saturated rocks abstractpartially saturated rocks are considered to be major sources of seismic wave velocity dispersion and attenuation in recorded real data from the physical description of partially saturated gas water and oil water reservoirs we use upscaling theories to compute an equivalent frequency dependent porous medium these homogenization methods are associated with mesoscale description of attenuation and dispersion coming from wave induced flow phenomena to compute wave propagation we use numerical codes in the frequency domain that allow us to take into account all the frequency dependent parameters without approximation or local time steps in this way the biot slow compressional wave is well modeled and its partially diffusive partially propagative behavior is completely considered the attenuation and dispersion of the waves in such media are coming partly from the wave mode conversion into diffusive slow waves not visible on seismograms but the amplitude of propagative p and s waves are mainl

localizing co2 at sleipner seismic images versus p wave velocities from waveform inversion abstractthe presence of injected co2 in the utsira sand at the sleipner site norway is associated with a high negative p wave velocity anomaly that is a low postinjection velocity and a strong seismic response time lapse seismic imaging of co2 injection at sleipner is thus a viable monitoring tool of the injected co2 the work flow usually involves conventional seismic processing including stacking and results in seismic images multiple reflections interference effects such as tuning and the velocity pushdown effect due to co2 injection render these seismic images ambiguous in terms of the localization and the quantification of the co2 in the utsira sand nonetheless seismic images often form the basis for analyses that aim to quantify the injected co2 we employed elastic 2d full waveform inversion to invert prestack seismic sleipner data from preinjection 1994 and postinjection 1999 and compared the resulting postinjection p wave velocity model with the corresponding seismic image we fou

ancient and modern cold climate aeolian sand deposition a review although partly active aeolian sand sheets and dunes cover large areas in the zones of dis continuous permafrost little precise information is available about the influence of cold climate conditions on modern aeolian processes this means that palaeoenvironmental reconstructions in the stabilised mainly late pleistocene dune fields and cover sand regions in the sand belts of the european lowlands and the northern great plains of the usa and canada are necessarily still based on ancient evidence cold climate wind deposits are typically derived from areas of abundant sediment supply like unvegetated flood plains glacial outwash plains till plains and lake shores the common parabolic and transverse dune forms resemble those observed in temperate regions although a variety of periglacial features has been identified in late pleistocene dune and cover sands none of them indicate that permafrost is crucial to aeolian activity specific structures in aeolian strata permit tentative interpretation of the moisture content of depositional sand surfaces the nature of annual sedimentation cycles and the processes by which strata were deposited and or contorted but surprisingly little is known about the role of vegetation in the process of sand accumulation dunes are most informative with respect to reconstructions of past wind regimes which offer important data for verification of palaeoclimatic simulations

numerical simulation of wave induced fluid flow seismic attenuation based on the cole cole model the acoustic behavior of porous media can be simulated more realistically using a stress strain relation based on the cole cole model in particular seismic velocity dispersion and attenuation in porous rocks is well described by mesoscopic loss models using the zener model to simulate wave propagation is a rough approximation while the cole cole model provides an optimal description of the physics here a time domain algorithm is proposed based on the grunwald letnikov numerical approximation of the fractional derivative involved in the time domain representation of the cole cole model while the spatial derivatives are computed with the fourier pseudospectral method the numerical solution is successfully tested against an analytical solution the methodology is applied to a model of saline aquifer where carbon dioxide co2 is injected to follow the migration of the gas and detect possible leakages seismic monitoring surveys should be carried out periodically to this aim the sensitivity of the seismic method must be carefully assessed for the specific case the simulated test considers a possible leakage in the overburden above the caprock where the sandstone is partially saturated with gas and brine the numerical examples illustrate the implementation of the theory

forest vegetation and origin of some spodic horizons michigan abstract three well drained soils that differ in bs horizon properties occur on sandy glacial deposits in northern michigan u s a each horizon was sampled and analyzed for chemical and physical properties in order to examine b horizon formation extractable c al and fe were found to increase from the lightest to the darkest colored b horizons differences in b horizon properties could not be explained by elemental composition of the c horizons particle size distribution topography or climate formation of the b horizons appears to be a function of forest vegetation we conclude that fire frequency played a role in the formation of the b horizons by influencing forest successional events

estimation of thickness and velocity changes of injected carbon dioxide layers from prestack time lapse seismic data in this study we bring together the two main categories of time lapse seismic analysis amplitude analysis and time shift analysis to estimate simultaneously the changes in thickness and velocity of a 4d seismic anomaly the methodology is applied to time lapse seismic monitoring of carbon dioxide c o2 storage at sleipner field norway that shows significant 4d effects the 4d anomalies resulting from c o2 injection appear as a multilayer reflection pattern within the relatively shallow utsira sand this multireflective appearance within the sand layer is interpreted as c o2 layers trapped below thin shale layers because most of the c o2 layers are believed to be thin 0 20 m the interference between top and base of these layers needs to be taken into account in 4d seismic analysis by studying the reflected event from a horizon below the utsira sand we estimate 4d traveltime shifts caused by the presence of the c o2 layer above thishorizon we then combine these traveltime shifts with measur

synthetic seismograms for marine sediments and determination of porosity and permeability we present numerical simulations of vertical seismic profiles vsps of marine sediments the theoretical seismograms which are computed for vertically incident waves in flat layered poroelastic media include the effects of dispersion and attenuation predicted by biot theory according to biot theory fast and slow compressional waves are excited and there is mode conversion at the interfaces we include this effect in the calculation of reflection and transmission coefficients as an energy loss mechanism through the slow compressional waves finally we examine the spectral ratio method for determining porosity and permeability from synthetic seismogram data analytical expressions for the velocity and specific attenuation are found based on the weak frame approximation once the frequency dependent velocity and specific attenuation are calculated the porosity and permeability of marine sediments can be determined by using the proposed weak frame approximations spectral ratio calculations on syntheti

aeolian silt contribution to soils on mountain slopes mt śleza southwest poland this paper evaluates the possible contribution of aeolian silt to soils of mt leza southwest poland silt loam textures are common across lower silesia and are often confused with silt clay loam especially at the outer boundaries with thin loess deposits eight study sites with different thicknesses of silt loam mantles that are covered and or mixed with underlying sediments were examined in the field to test our hypothesis we analyzed the particle size and geochemistry of representative horizons concentrations of major and trace elements as well as their cross ratios confirmed the aeolian origin of silt loam materials and clearly distinguished them from basal sediments there is a clear relationship between the presence and depth of aeolian mantles and mixing zones with the type of underlying material furthermore the incorporation of aeolian silt to regoliths soils was a main agent initiating and stimulating clay translocation leading to the formation of an argic horizon below the silt mantles mixing aeolian silt with acid granite regoliths and further illuviation resulted in the formation of alisols while silt contributions to serpentine sediments resulted in development of skeletic luvisols soils receiving very weak input of aeolian silts remain as leptosols cambisols

predicting subsurface co2 movement from laboratory to field scale abstractfinding an appropriate model for time lapse seismic monitoring of co2 sequestered carbonate reservoir poses a great challenge because carbonate rocks have varying textures and highly reactive rock fluid system we introduced a frequency dependent model based on eshelby s inclusion and differential effective medium dem theory that can account for heterogeneity in microstructure of rocks and squirt flow we showed that the estimated velocities from the modified dem theory match well with the laboratory measurements ultrasonic of velocities of carbonate rocks saturated with co2 rich water the theory predicts significant decrease in saturated p and s wave velocities in the seismic frequency band as a consequence of porosity and permeability enhancement by the process of chemical dissolution of carbonates with the saturating fluid the study also showed the combined effect of chemical reaction and free co2 saturation on the elastic properties of rock we observed that the velocity dispersion and

amplitude versus offset variations in gas sands seismic reflections from gas sands exhibit a wide range of amplitude versus offset avo characteristics the two factors that most strongly determine the avo behavior of a gas sand reflection are the normal incidence reflection coefficient r0 and the contrast in poisson s ratio at the reflector of these two factors r0 is the least constrained based on their avo characteristics gas sand reflectors can be grouped into three classes defined in terms of r0 at the top of the gas sand class 1 gas sands have higher impedance than the encasing shale with relatively large positive values for r0 class 2 gas sands have nearly the same impedance as the encasing shale and are characterized by values of r0 near zero class 3 sands have lower impedance than the encasing shale with negative large magnitude values for r0 each of these sand classes has a distinct avo characteristic an example of a gas sand from each of the three classes is presented in the paper the class 1 example involves a hartshorn channel s

acoustic properties of sediments saturated with gas hydrate free gas and water we obtain the wave velocities and quality factors of gas hydrate bearing sediments as a function of pore pressure temperature frequency and partial saturation the model is based on a biot type three phase theory that considers the existence of two solids grains and gas hydrate and a fluid mixture attenuation is described with the constant q model and viscodynamic functions to model the high frequency behaviour we apply a uniform gas water mixing law that satisfies wood s and voigt s averages at low and high frequencies respectively the acoustic model is calibrated to agree with the patchy saturation theory at high frequencies white s model pressure effects are accounted by using an effective stress law for the dry rock moduli and permeabilities the dry rock moduli of the sediment are calibrated with data from the cascadia margin moreover we calculate the depth of the bottom simulating reflector bsr below the sea floor as a function of sea floor depth geothermal gradient below the sea floor and temperature at the sea floor