joint two dimensional dc resistivity and seismic travel time inversion with cross gradients constraints it is now common practice to perform collocated dc resistivity and seismic refraction surveys that complement each other in the search for more accurate characterization of the subsurface although conventional separate dc resistivity and seismic models can be diagnostic we posit that better results can be derived from jointly estimated models we make the assumption that both methods must be sensing the same underlying geology and have developed an innovative resistivity velocity cross gradients relationship to evaluate the structural features common to both methods the cross gradients function is incorporated as a constraint in a nonlinear least squares problem formulation which is solved using the lagrange multiplier method the resultant iterative two dimensional 2 d joint inversion scheme is successfully applied to synthetic data serving as validation tests here and to field data from collocated dc resistivity and seismic refraction profiling experiments and also compared to conventional separate inversion results the joint inversion results are shown to be superior to those from separate 2 d inversions of the respective data sets since our algorithm leads to resistivity and velocity models with remarkable structural agreement

joint inversion of crosshole radar and seismic traveltimes acquired at the south oyster bacterial transport site the structural approach to joint inversion entailing common boundaries or gradients offers a flexible and effective way to invert diverse types of surface based and or crosshole geophysical data the cross gradients function has been introduced as a means to construct models in which spatial changes in two distinct physical property models are parallel or antiparallel inversion methods that use such structural constraints also provide estimates of nonlinear and nonunique field scale relationships between model parameters here we jointly invert crosshole radar and seismic traveltimes for structurally similar models using an iterative nonlinear traveltime tomography algorithm application of the inversion scheme to synthetic data demonstrates that it better resolves lithologic boundaries than the individual inversions alone tests of the scheme on gpr and seismic data acquired within a shallow aquifer illustrate that the resultant models have improved correlations with flowmeter data in comparison with models based on individual inversions the highest correlation with the flowmeter data is obtained when the joint inversion is combined with a stochastic regularization operator and the vertical integral scale is estimated from the flowmeter data point spread functions show that the most significant resolution improvements offered by the joint inversion are in the horizontal direction

influence of temperature on seismic velocities and complex conductivity of heavy oil bearing sands abstractthe joint inversion of seismic and electromagnetic data can be of great use to monitor the steam assisted production of heavy oils in field conditions seismic velocity and complex conductivity laboratory measurements were performed on three heavy oil bearing sands at confining and pore pressures similar to field conditions one of the samples 8h was initially oil wet and the two other samples 5p 3a and p 1a were initially water wet low frequency stress strain measurements and complex conductivity measurements were performed during two heating cycles at constant temperature 10 c steps in the range 20 c 70 c the temperature was first increased from 20 c 70 c simulating initial stage in a thermal recovery process during this temperature increase sample 8h changed to water wet with a clear irreversible signature on the seismic and electrical data then the temperature was decreased and cycled a second time in the temperature range 20 c 70 c the seismic and complex conductivity responses w

complex conductivity tomography using low frequency crosswell electromagnetic data abstractthe complex conductivity of partially saturated siliciclastic sediments can now be reasonably predicted through recently developed petrophysical models like the polaris model however classical crosswell induced polarization tomography using a galvanometric approach is characterized by a poor sensitivity map far from the wells and thus other methods should be analyzed for potential improvements the presence of low frequency 1 khz polarization effects in earth porous materials noticeably increases the amplitude and decreases the phase of measured electromagnetic em fields as such the quadrature conductivity directly associated with the low frequency polarization effect yields a significant contribution to the em fields we demonstrate that these contributions can be observed in crosswell em data in terms of signal to noise ratio with a realistic amount of noise we can recover the distribution of the in phase and quadrature conductivities for crosswell em tomography we use an integ

self potential monitoring of a salt plume nonintrusively monitoring the spread of contaminants in real time with a geophysical method is an important task in hydrogeophysics we have developed a sandbox experiment showing that the self potential method can locate both the source of leakage and the front of a contaminant plume we monitored the leakage of a plume of salty water from a hole at the bottom of a small tank located at the top of a main sandbox initially the sand was saturated by tap water at a given time a hole was opened at the bottom of the tank allowing the salty water to migrate by diffusion and buoyancy driven flow in the main sandbox the bottom of the sandbox contained a network of 32 nonpolarizing silver silver chloride electrodes with amplifiers connected to a multichannel voltmeter the self potential response associated withthe migration of the salt plume in the sandbox was recorded over time a self potential anomaly was observed with amplitude varying from a few millivolts at the start of the leak to a few tens of mi

application of time lapse ert imaging to watershed characterization time lapse electrical resistivity tomography ert has many practical applications to the study of subsurface properties and processes when inverting time lapse ert data it is useful to proceed beyond straightforward inversion of data differences andtakeadvantageofthetime lapsenatureofthedata weassess various approaches for inverting and interpreting time lapse ertdataanddeterminethattwoapproachesworkwell thefirst approachismodelsubtractionafterseparateinversionofthedata from two time periods and the second approach is to use the inverted model from a base data set as the reference model or prior information for subsequent time periods we prefer this second approach data inversion methodology should be considered when designing data acquisition i e to utilize the second approach it is important to collect one or more data sets for which the bulk of the subsurface is in a background or relatively unperturbed state athird and commonly used approach to time lapse inversion invertingthedifferencebetweentwodatasets localizes the regions of the model in which change has occurred however varying noise levels between the two data sets can be problematic to further assess the various time lapse inversion approaches weacquiredfielddatafromacatchmentwithinthedry creek experimental watershed near boise idaho u s a we combined the complimentary information from individual static ertinversions time lapseertimages andavailablehydrologicdatainarobustinterpretationschemetoaidinquantifyingseasonalvariationsinsubsurfacemoisturecontent

crustal structure of the arabian plate new constraints from the analysis of teleseismic receiver functions an edited version of this paper was published by elsevier science copyright 2005 elsevier science see also http dx doi org 10 1016 j epsl 2004 12 020 http atlas geo cornell edu saudiarabia publications al damegh 202005 htm

crosswell seismic imaging of reservoir changes caused by co 2 injection monitoring of enhanced oil recovery processes with crosswell data has been one of the earliest applications of time lapse geophysics because data with frequencies up to a few kilohertz can often be collected with the crosswell geometry the method can potentially offer imaging resolution of the order of a few feet such resolution is often necessary for time lapse investigation to be useful in building reservoir models and for accurately describing fluid flow in heterogeneous reservoirs

crustal and upper mantle structure in the eastern mediterranean from the analysis of surface wave dispersion curves summary the dispersive properties of surface waves are used to infer earth structure in the eastern mediterranean region using group velocity maps for rayleigh and love waves from 7 to 100 s we invert for the best 1 d crust and upper mantle structure at a regular series of points assembling the results produces a 3 d lithospheric model along with corresponding maps of sediment and crustal thickness a comparison of our results to other studies finds the uncertainties of the moho estimates to be about 5 km we find thick sediments beneath most of the eastern mediterranean basin in the hellenic subduction zone and the cyprus arc the ionian sea is more characteristic of oceanic crust than the rest of the eastern mediterranean region as demonstrated in particular by the crustal thickness we also find significant crustal thinning in the aegean sea portion of the backarc particularly towards the south notably slower s wave velocities are found in the upper mantle especially in the northern red sea and dead sea rift central turkey and along the subduction zone the low velocities in the upper mantle that span from north africa to crete in the libyan sea might be an indication of serpentinized mantle from the subducting african lithosphere we also find evidence of a strong reverse correlation between sediment and crustal thickness which while previously demonstrated for extensional regions also seems applicable for this convergence zone

time lapse tomography in time lapse analysis we have to distinguish the seismic response changes due to oil and gas production at a reservoir over the years from several other causes such as the recording signature and random noise in this paper we focus our attention on the velocity macromodel provided by seismic tomography which is a basic tool for the data regularization its depth or time migration and a possible final subtraction among different vintages we show first that we cannot use just a single velocity model for all data sets because of seasonal variations of the overburden velocity which is mainly due to seawater temperature in marine cases and to the water table depth in land cases however we can exploit the basic assumption of time lapse analysis for constraining reflection refraction tomography i e by imposing the constraint that the layer structure and the local velocities do not change outside the reservoir and in the shallowest part over time we thus get coupled models that are physically consistent with a better spatial coverage and higher information redundancy the new method is illustrated by a marine case history from the north sea

target oriented joint least squares migration inversion of time lapse seismic data sets two related formulations are proposed for target oriented joint least squares migration inversion of time lapse seismic data sets time lapse seismic images can be degraded when reservoir overburden is complex or when acquisition geometries significantly differ because the migration operator does not compensate for the resulting amplitude and phase distortions under these circumstances time lapse amplitudes are poor indicators of production related changes in reservoir properties to correct for such image degradation time lapse imaging is posed as joint inverse problems that utilize concatenations of target oriented approximations to the linear least squares imaging hessian in both formulations spatial and temporal constraints ensure inversion stability and geologically consistent time lapse images using two numerical time lapse data sets we confirmed that these formulations can attenuate illumination artifacts caused by complex overburden or geometry differences and that they yield better quality images than obtainable with migration

geophysical modeling via simultaneous joint inversion of seismic gravity and electromagnetic data application to prestack depth imaging geophysical modeling of multiple geophysical parameters can take place reliably through the simultaneous joint inversion of the different geophysical domains the desired objective is the derivation of a model expressing different geophysical properties of the earth but at the same time showing consistency among the parameters this concept generally referred to as data integration is widespread in geophysics but the way of achieving it is not obvious several authors have proposed different approaches where data interpretation and experience all contributed to the task the result is that no general workflows could be defined that left ample margins for uncertainties and personal judgment

stochastic bayesian inversion of borehole self potential measurements summary we propose a mechanistic model to compute and to invert self potential log data in sedimentary basins and for near surface geophysical applications the framework of our analysis is founded in a unified electrical conductivity and self potential petrophysical model this model is based on an explicit dependence of these properties on porosity water saturation temperature brine salinity cementation and saturation archie exponents and the volumetric charge density per unit pore volume associated with the clay fraction this model is consistent with empirical laws widely used to interpret self potential logs according to the two limiting cases corresponding to a clean sand and a pure shale we present a finite element calculation of the self potential signal produced by sand reservoirs interstratified with shale layers for layered strata normal to the well we demonstrate that the 3 d poisson equation governing the occurrence of self potentials in a borehole can be simplified to a 2 d axisymmetric partial differential equation solved at each depth providing a common self potential reference can be defined between these different depths this simplification is very accurate as long as the vertical salinity gradients are not too strong over distances corresponding to the borehole diameter the inversion of borehole data self potential resistivity and density well logs incorporating information derived from neutron porosity and gamma ray log data is performed with the adaptive metropolis algorithm ama we start by formulating an approximate analytical solution for the six model parameters water saturation porosity the two archie s exponents the pore water conductivity and the volumetric charge density of the diffuse layer this solution is used for the ama algorithm to converge in less than 60 iterations at each depth for the real case study the posterior probability distributions are computed using 50 60 additional realizations our approach is applied to a case study concerning a small sedimentary sequence in the piceance basin colorado in a series of tight gas reservoirs

joint inversion of marine magnetotelluric and gravity data incorporating seismic constraints preliminary results of sub basalt imaging off the faroe shelf breakup of the north atlantic during the early tertiary was accompanied by widespread and massive magmatism resulting in the coverage of large areas of the north atlantic with flood basalts these flood basalts hamper seismic investigations of underlying sequences and thus the understanding of the rifting subsidence and evolution of the margin which in turn increases the risk for hydrocarbon exploration in this paper we present a methodology for the simultaneous joint inversion of diverse geophysical datasets i e free air gravity and magnetotelluric soundings mt using seismic a priori constraints the attraction of the joint inversion approach is that different geophysical measurements are sensitive to different properties of the sub surface so through joint inversion we significantly reduce the null space and produce a single model that fits all datasets within a predefined tolerance using sensitivity analysis of synthetic data we show how each data set contains complementary important information of the supra and sub basalt structure while separate inversions of individual datasets fail to image through the basalt layer our joint inversion approach leads to a much improved sub basalt structure application of the joint inversion algorithm to satellite gravity data and mt data acquired on the flare10 seismic line south west of faroe islands supports the existence of a 1 km to 2 km thick low velocity region that might be indicative of the existence of a sedimentary basin underneath the basalt layer though in this paper we demonstrate the use of joint inversion on a sub basalt target we believe it has wider applicability to other areas where conventional seismic imaging fails

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

internally generated decadal cold events in the northern north atlantic and their possible implications for the demise of the norse settlements in greenland we attribute and describe the governing mechanisms of decadal cold excursions in the subpolar north atlantic of similar amplitude and duration to cold events reconstructed from climate proxies during the last millennium detected in an ensemble of three transient and one unperturbed climate simulation the cold events are attributed to internal regional climate variability with varying external forcing increasing their magnitude and frequency the underlying general mechanism consists of a feedback loop initiated by a weakening of the north atlantic subpolar gyre which induces persistent colder and fresher surface conditions in the labrador sea and eventually a deep convection shutdown we thus exclude a hemispheric climate reorganization or a weak ocean overturning circulation as necessary trigger for such events an associated northeastward atmospheric cold advection over the labrador sea deteriorates local living conditions on south greenland essential for the sustainability of the norse settlements

estimating petrophysical parameters and average mud filtrate invasion rates using joint inversion of induction logging and pressure transient data we introduce an inversion approach for determining the water based mud filtrate invasion profile as well as the formation porosity and horizontal permeability from the induction logging data the inversion is constrained by a multiphase fluid flow simulator that simulates the mud filtrate invasion process to obtain the spatial distributions of the water saturation and the salt concentration which are in turn transformed into the formation resistivity using a resistivity saturation formula by ignoring the diffusion effect we assume that the mud filtrate invasion process is mainly convective so that it can be equivalently simulated by providing an average invasion rate and the duration of invasion the average invasion rate can be directly inverted from the fluid flow constrained inversion of induction logging data we also obtain the mud filtrate invasion profile which is consistent with the fluid flow physics the reconstructed mud filtrate invasion profile benefits the interpretation of the formation test when the pressure transient data are available this approach can be also used to jointly invert both induction logging data and pressure transient data to obtain the mud filtrate invasion profile as well as a parametric distribution of the ti anisotropic formation permeability and porosity assuming a vertical well penetrating horizontal formations the fluid flow problem is solved using an implicit black oil finite difference simulator with brine tracking option based on a cylindrical axially symmetric grid whereas the response of the induction logging tool is simulated using a frequency domain finite difference solver based on a cartesian grid a gauss newton inversion scheme using the multiplicative regularization technique is used for either the fluid flow constrained inversion or the joint inversion the reliability of the inversion results depends on the accuracy of a priori knowledge of the reservoir which needs to be confirmed via sensitivity analysis

thermoelectric self potential and resistivity data localize the burning front of underground coal fires abstractself potential signals and resistivity data can be jointly inverted or analyzed to track the position of the burning front of an underground coal seam fire we first investigate the magnitude of the thermoelectric coupling associated with the presence of a thermal anomaly thermoelectric current associated with a thermal gradient a sandbox experiment is developed and modeled to show that in presence of a heat source a negative self potential anomaly is expected at the ground surface the expected sensitivity coefficient is typically on the order of 0 5 mv c 1 in a silica sand saturated by demineralized water geophysical field measurements gathered at marshall near boulder co show clearly the position of the burning front in the electrical resistivity tomogram and in the self potential data gathered at the ground surface with a negative self potential anomaly of about 50 mv to localize more accurately the position of the burning front we developed a strategy based on two steps 1 we

crustal thickness variations in the aegean region and implications for the extension of continental crust 1 we installed 5 broadband and 45 short period temporary seismic stations distributed partly as a dense 100 km long n s linear array and partly as a regional network throughout the menderes massif of western turkey in order to study crust upper mantle structure and seismicity in this study we have combined teleseismic waveform data from these stations with data from several permanent seismic stations to determine crustal thickness variations in the aegean region receiver function studies at seven broadband stations using the h stacking method have yielded crustal thicknesses and vp vs ratios over a broad region of the aegean a more detailed crustal image was obtained in the central menderes massif where we applied common conversion point stacking to receiver functions obtained from the n s linear array the results show a general trend of westward crustal thinning from 36 km in central anatolia to 28 30 km in the central menderes massif to 25 km beneath the aegean sea the results also indicate that crustal thinning in the aegean is not uniform in the n s extensional direction the crust is thinner in the central menderes massif 28 30 km of crustal thicknesses and the cycladic massif 25 26 km than in surrounding regions where crustal thicknesses are 32 34 km the long lived elevated moho under the metamorphic core complexes suggests that the lower crust in the aegean region is at least 3 times more viscous than that in the basin and range province where the moho is much flatter

time lapse joint inversion of crosswell dc resistivity and seismic data a numerical investigation abstracttime lapse joint inversion of geophysical data is required to image the evolution of oil reservoirs during production and enhanced oil recovery co2 sequestration geothermal fields during production and to monitor the evolution of contaminant plumes joint inversion schemes reduce space related artifacts in filtering out noise that is spatially uncorrelated and time lapse inversion algorithms reduce time related artifacts in filtering out noise that is uncorrelated over time there are several approaches that are possible to perform the joint inverse problem in this work we investigate the structural crossgradient scg joint inversion approach and the crosspetrophysical cp approach which are appropriate for time lapse problems in the first case the inversion scheme looks for models with structural similarities in the second case we use a direct relationship between the geophysical parameters time lapse inversion is performed with an actively time constrained atc approach in this a

2d joint inversion of geophysical data using petrophysical clustering and facies deformation geologic expertise and petrophysical relationships can be brought together to provide prior information while inverting multiple geophysical data sets the merging of such information can result in more realistic solution in the distribution of the model parameters we have evaluated the geophysical inverse problem in terms of gaussian random fields with mean functions controlled by petrophysical relationships and covariance functions controlled by a prior geologic cross section including the definition of spatial boundaries for the geologic facies the petrophysical relationship problem is formulated as a regression problem upon each facies the inversion of the geophysical data is performed in a bayesian framework we have developed the usefulness of this strategy using a first synthetic case for which we have performed a joint inversion of gravity and galvanometric resistivity data with the stations located at the ground surface the joint inversion was used to recover the density and resistivity distributions of the subsurface in a second step we considered the possibility that the facies boundaries were deformable and their shapes were inverted as well we used the level set approach to perform such deformation preserving a priori topological properties of the facies throughout the inversion with the help of a priori facies petrophysical relationships and the topological characteristics of each facies we made a posteriori inference about multiple geophysical tomograms based on their corresponding geophysical data misfits we have applied this method to a second synthetic case showing that we can recover the heterogeneities inside the facies the mean values for the petrophysical properties and to some extent the facies boundaries using the 2d joint inversion of gravity and galvanometric resistivity data

local earthquake le tomography with joint inversion for p and s wave velocities using structural constraints local earthquake le tomography with joint inversion for p and s wave velocities using structural constraints

characterization of heterogeneous near surface materials by joint 2d inversion of dc resistivity and seismic data 1 we have developed a robust 2d joint inversion scheme incorporating the new concept of cross gradients of electrical resistivity and seismic velocity as constraints so as to investigate more precisely the resistivity velocity relationships in complex near surface environments the results of joint inversion of dc resistivity and seismic traveltime data from collocated experiments suggest that one can distinguish between different types or facies of unconsolidated and consolidated materials refining a previously proposed resistivity velocity interrelationship derived from separate inversions of the respective data sets a consistent interpretive structural model can be obtained from the joint inversion models

influence of oil wettability upon spectral induced polarization of oil bearing sands the presence of oil in an unconsolidated granular porous material like a sand changes both the resistivity of the material and the value of the phase lag between the current and the voltage we performed laboratory experiments to investigate the influence of oil wettability and water saturation upon the complex resistivity of oil bearing sands in the frequency range 1 mhz 1 khz for a sand saturated by a nonwetting oil both the resistivity and the magnitude of the phase increase with the oil saturation as expected from theoretical considerations in the case of a sand partially saturated by a wetting oil we found that both the magnitude of the phase and the resistivity decrease with the oil saturation the quadrature conductivity decreases with the oil with the same trend in presence of wetting and nonwetting oils for relative water saturation above 0 5 in the case of a nonwetting oil the results are quantitatively predicted by available theories in the case of a wet oil our results could be inte

improved hydrogeophysical characterization using joint inversion of cross hole electrical resistance and ground penetrating radar traveltime data appropriate regularizations of geophysical inverse problems and joint inversion of different data types improve geophysical models and increase their usefulness in hydrogeological studies we have developed an efficient method to calculate stochastic regularization operators for given geostatistical models the method which combines circulant embedding and the diagonalization theorem of circulant matrices is applicable for stationary geostatistical models when the grid discretization in each spatial direction is uniform in the volume of interest we also used a structural approach to jointly invert cross hole electrical resistance and ground penetrating radar traveltime data in three dimensions the two models are coupled by assuming at all points that the cross product of the gradients of the two models is zero no petrophysical relationship between electrical conductivity and relative permittivity is assumed but is instead obtained as a by product of the inversion the approach has been applied to data collected in a u k sandstone aquifer in order to improve characterization of the vadose zone hydrostratigraphy by analyzing scatterplots of electrical conductivity versus relative permittivity together with petrophysical models a zonation could be obtained with corresponding estimates of the electrical formation factor the water content and the effective grain radius of the sediments the approach provides greater insight into the hydrogeological characteristics of the subsurface than by using conventional geophysical inversion methods

crustal structure of the levant basin eastern mediterranean abstract a seismic refraction wide angle reflection experiment was undertaken in the levant basin eastern mediterranean two roughly east west profiles extend from the continental shelf of israel toward the levant basin the northern profile crosses the eratosthenes seamount and the southern profile crosses several distinct magnetic anomalies the marine operation used 16 ocean bottom seismometers deployed along the profiles with an air gun array and explosive charges as energy sources the results of this study strongly suggest the existence of oceanic crust under portions of the levant basin and continental crust under the eratosthenes seamount the seismic refraction data also indicate a large sedimentary sequence 10 14 km thick in the levant basin and below the levant continental margin assuming the crust is of cretaceous age this gives a fairly high sedimentation rate the sequence can be divided into several units a prominent unit is the 4 2 km s layer which is probably composed of the messinian evaporites overlying the evaporitic layer are layers composed of plio pleistocene sediments whose velocity is 2 0 km s the refraction profiles and gravity and magnetic models indicate that a transition from a two layer continental to a single layer oceanic crust takes place along the levant margin the transition in the structure along the southern profile is located beyond the continental margin and it is quite gradual the northern profile north of the carmel structure presents a different structure the continental crust is much thinner there and the transition in the crustal structure is more rapid the crustal thinning begins under western galilee and terminates at the continental slope the results of the present study indicate that the levant basin is composed of distinct crustal units and that the levant continental margin is divided into at least two provinces of different crustal structure

structural joint inversion of time lapse crosshole ert and gpr traveltime data 1 time lapse geophysical monitoring and inversion are valuable tools in hydrogeology for monitoring changes in the subsurface due to natural and forced tracer dynamics however the resulting models may suffer from insufficient resolution which leads to underestimated variability and poor mass recovery structural joint inversion using cross gradient constraints can provide higher resolution models compared with individual inversions and we present the first application to time lapse data the results from a synthetic and field vadose zone water tracer injection experiment show that joint 3 d time lapse inversion of crosshole electrical resistance tomography ert and ground penetrating radar gpr traveltime data significantly improve the imaged characteristics of the point injected plume such as lateral spreading and center of mass as well as the overall consistency between models the joint inversion method appears to work well for cases when one hydrological state variable in this case moisture content controls the time lapse response of both geophysical methods

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

miocene to recent tectonic evolution of the eastern mediterranean new pieces of the old mediterranean puzzle the mediterranean sea and its surrounding land mass fig 1 have long been recognized as an excellent bnatural laboratoryq for the study of fundamental plate tectonic processes including rifting passive margin development contraction and associated subduction ophiolite emplacement and orogenesis and as such it is one of the most extensively studied regions of the world e g hsu et al 1975 dixon and robertson 1984 kastens et al 1990 emeis et al 1996 comas et al 1996 robertson 1998 mcclusky et al 2000 the late cretaceous to holocene tectonic evolution of the eastern mediterranean region is extremely complex and controversial and several commonly conflicting hypotheses have been proposed the scope of this special issue does not permit a full discussion of these hypotheses we refer the reader to robertson 1998 for a review however there is general agreement that the eastern mediterranean evolved as a small ocean basin during the late triassic robertson and dixon 1984 robertson et al 1991 this embryonic ocean achieved its maximum

multiple cross gradient joint inversion for geospectral imaging 1 accurate characterization and monitoring of complex subsurface environments require the integration of all the available geophysical geochemical and geological information i developed a generalized cross gradient procedure that seeks multiple geometrically similar images that simplify the integration of cross property subsurface information i jointly invert near surface p wave s wave dc resistivity and magnetic data sets recorded at a field site and compound an integrated subsurface geospectral image based on the multiple property images found it is shown that by analogy to applications in satellite imagery the geospectral image assembles the multiple subsurface parameter values under a common structural framework that facilitates their visualization and analysis

joint inversion of geophysical and hydrological data for improved subsurface characterization understanding fluid distribution and movement in the subsurface is critical for a variety of subsurface applications such as remediation of environmental contaminants sequestration of nuclear waste and co2 intrusion of saline water into fresh water aquifers and the production of oil and gas it is well recognized that characterizing the properties that control fluids in the subsurface with the accuracy and spatial coverage needed to parameterize flow and transport models is challenging using conventional borehole data alone integration of conventional borehole data with more spatially extensive geophysical data obtained from the surface between boreholes and from surface to boreholes shows promise for providing quantitative information about subsurface properties and processes typically estimation of subsurface properties involves a two step procedure in which geophysical data are first inverted and then integrated with direct measurements and petrophysical relationship information to estimate hydrological parameters however errors inherent to geophysical data acquisition and inversion approaches and errors associated with petrophysical relationships can decrease the value of geophysical data in the estimation procedure in this paper we illustrate using two examples how joint inversion approaches or simultaneous inversion of geophysical and hydrological data offer great potential for overcoming some of these limitations

time lapse inversion of crosswell radar data the combination of differential radar tomography with conventional tracer and or hydraulic tests facilitates high resolution characterization of subsurface heterogeneity and enables the identification of preferential flow paths in dynamic imaging each tomogram is typically inverted independently under the assumption that data sets are collected quickly relative to changes in the imaged property e g attenuation or velocity however such snapshot tomograms may contain large errors if the imaged property changes significantly during data collection acquisition of less data over a shorter time interval could ameliorate the problem but the resulting decrease in ray density and angular coverage could degrade model resolution to address these problems we propose a new sequential approach for time lapse tomographic inversion the method uses space time parameterization and regularization to combine data collected at multiple times and to account for temporal variation the inverse algorithm minimizes the sum of weighted squared residuals and a measure of solution complexity based on an a priori space time covariance function and a spatiotemporally variable mean we demonstrate our approach using a synthetic 2 d time lapse x z t data set based loosely on a field experiment in which difference attenuation radar tomography was used to monitor the migration of a saline tracer in fractured rock we quantitatively show the benefits of space time inversion by comparing results for snapshot and time lapse inversion schemes inversion over both space and time results in superior estimation error model resolution and data reproduction compared to conventional snapshot inversion finally we suggest strategies to improve time lapse cross hole inversions using ray based inversion constraints and a modified survey design in which different sets of rays are collected in alternating time steps