static and dynamic effective stress coefficient of chalk deformation of a hydrocarbon reservoir can ideally be used to estimate the effective stress acting on it the effective stress in the subsurface is the difference between the stress due to the weight of the sediment and a fraction effective stress coefficient of the pore pressure the effective stress coefficient is thus relevant for studying reservoir deformation and for evaluating 4d seismic for the correct pore pressure prediction the static effective stress coefficient n is estimated from mechanical tests and is highly relevant for effective stress prediction because it is directly related to mechanical strain in the elastic stress regime the corresponding dynamic effective stress coefficient is easy to estimate from density and velocity of acoustic elastic waves we studied n and of chalk from the reservoir zone of the valhall field north sea and found that n and vary with differential stress overburden stress pore pressure for valhall reservoir chalk with 40 porosity ranges between 0 98 and 0 85 and decreases by 10 if the differential stress is increased by 25 mpa in contrast for chalk with 15 porosity from the same reservoir ranges between 0 85 and 0 70 and decreases by 5 due to a similar increase in differential stress our data indicate that measured from sonic velocity data falls in the same range as for n and that n is always below unity stress dependent behavior of n is similar decrease with increasing differential stress to that of during elastic deformation caused by pore pressure buildup for example during waterflooding by contrast during the increase in differential stress as in the case of pore pressure depletion due to production n increases with stress while decreases

reservoir monitoring and characterization using satellite geodetic data interferometric synthetic aperture radar observations from the krechba field algeria deformation in the material overlying an active reservoir is used to monitor pressure change at depth a sequence of 11 field estimates allows us to construct a measure of diffusive traveltime throughout a reservoir the dense distribution of traveltime values means that we can construct an exactly linear inverse problem for reservoir flow properties application to interferometric synthetic aperture radar insar data gathered over a carbon dioxide c o2 injection site in algeria reveals pressure propagation along two northwest trending corridors an inversion of the traveltimes indicates the existence of two northwest trending high permeability zones the high permeability features trend in the same direction as the regional fault and fracture zones model parameter resolution estimates indicate the features are well resolved

seismic noise based time lapse monitoring of the valhall overburden we used two vintages of ambient seismic noise recorded at the valhall life of the field seismic network in 2004 and 2005 to perform a passive time lapse imaging of the subsurface first the cross correlations between each pair of stations were computed for both vintages to extract scholte waves second the relative velocity variations between the 2004 and 2005 cross correlations were measured on the ballistic waves using the moving window cross spectral technique finally the best quality relative velocity variation measurements were regionalized using a modified eikonal tomography technique the results albeit noisy because of the short duration of the available records show a large patch of increased seismic velocity in the southern part of the network and a weaker anomaly in the northern part the southern increase of velocity can be attributed to the exploitation of the southern flank of the valhall reservoir with new wells and is in good agreement with a previous time lapse study using scholte waves

initiation of the neomagmatism in east anatolia abstract in eastern anatolia the neotectonic episode commenced with the complete elemination of the neo tethyan ocean floor as a result of collision between arabia and eurasia during early miocene time after the collision continuing convergence initiated a new tectonic regime and coeval magmatic activity the post collisional convergence caused crustal shortening and thickening as evidenced by regionwide development of e w trending folds and thrusts and conjugate strike slip faults the related volcanic activity has progressed in three cycles in the initial cycle weakly alkaline volcanic rocks were produced that are known as the solhan volcanics they outcrop at the western end of an e w striking neotectonic depression called the mus basin which constitutes the western prolongation of the lake van basin the basin is a thrust bounded depression that developed out of an original syncline by the disruption of its limbs the lavas of the first cycle reached the surface along n s aligned extensional structures in the second volcanic cycle a widespread k type ca volcanism occurred through crustal contribution during the late miocene early pliocene time when the continuing north south convergence caused substantial shortening and thickening of the continental crust the last volcanic cycle produced a thick volcanic cover consisting of rocks of alkaline affinity during the pleistocene and the quaternary when the thickened crust began to accommodate the ongoing north south shortening by east west extension after the formation of the east and north anatolian transform faults

high temperature elasticity of iron bearing olivines the first high temperature data on the nine adiabatic elastic moduli for iron bearing olivine are reported these measurements are on two single crystal specimens of natural olivine at ambient pressure and from room temperature to a maximum of 1500 k the two specimens contain 8 and 9 modal percent fayalite which required the oxygen fugacity be controlled at high temperature to preserve their chemical stability the rectangular parallelepiped resonance apparatus was adapted to buffer the specimens from the atmosphere with a mixture of co and co2 gas a small increase 1 2 gpa in the adiabatic bulk modulus of each specimen over that of end member forsterite was found the data are high quality to extreme temperatures with good agreement found when comparing the temperature derivatives of the elastic moduli of the two specimens neither specimen exhibits measurable nonlinear temperature dependence in the computed isotropic bulk and shear moduli which is in contrast to published forsterite data the temperature derivatives of the isotropic bulk modulus ks are 1 69 1 80 10 2 gpa k 1 for the two olivine specimens and the shear modulus g derivatives are 1 38 1 36 10 2 gpa k 1 these derivatives are only slightly larger in magnitude than ks t p 1 56 10 2 and g t p 1 30 10 2 gpa k 1 found previously for iron bearing olivine over a very small temperature range there are also no significant differences between the temperature derivatives found here and the average derivatives of end member forsterite from data retrieved over a slightly larger temperature range several dimensionless parameters have been calculated from these results and are discussed in view of systematics which bear on high pressure phases in earth s transition zone one result from these systematics related to the seismic velocities in the earth and especially the shear wave velocities is that an olivine content of less than 50 is implied at the 400 km discontinuity if earth s upper mantle is isochemical furthermore the substitution of almost 10 iron for magnesium at the forsterite end of the olivine solid solution series has little effect on the dimensionless parameters or on the temperature derivatives of the elastic moduli at high temperature

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

estimation of pore pressure change in a compacting reservoir from time lapse seismic data abstract an approach is developed to estimate pore pressure changes in a compacting chalk reservoir directly from time lapse seismic attributes it is applied to data from the south east flank of the valhall field the time lapse seismic signal of the reservoir in this area is complex despite the fact that saturation changes do not have an influence this complexity reflects a combination of pressure depletion compaction and stress re distribution throughout the reservoir and into the surrounding rocks a simple relation is found to link the time lapse amplitude and time shift attributes to variations in the key controlling parameter of initial porosity this relation is sufficient for an accurate estimation of pore pressure change in the inter well space although the time lapse seismic estimates mostly agree with reservoir simulation unexplained mismatches are apparent at a small number of locations with lower porosities less than 38 the areas of difference between the observations and predictions suggest possibilities for simulation model updating or a better understanding of the physics of the reservoir

linking reservoir geomechanics and time lapse seismics predicting anisotropic velocity changes and seismic attributes seismic technology has been used successfully to detect geomechanically induced signals in repeated seismic experiments from more than a dozen fields to explain geomechanically induced time lapse 4d seismic signals we use results from coupled reservoir and geomechanical modeling the coupled simulation yields the 3d distribution over time of subsurface deformation and triaxial stress state in the reservoir and the surrounding rock predicted changes in triaxial stress state are then used to compute changes in anisotropic p and s wave velocities employing a stress sensitive rock physics transform we predict increasing vertical p wave velocities inside the reservoir accompanied by a negative change in p wave anisotropy e 0 a stress sensitive rock physics transform that predicts a

time lapse inverse theory with applications abstractcompaction in the reservoir overburden can impact production facilities and lead to a significant risk of well bore failures prevalent practices of time lapse seismic processing of 4d data above compacting reservoirs rely on picking time displacements and converting them into estimated velocity changes and subsurface deformation this approach relies on prior data equalization and requires a significant amount of manual interpretation and quality control we have developed methods for automatic detection of production induced subsurface velocity changes from seismic data we have evaluated a time lapse inversion technique based on a simultaneous regularized full waveform inversion fwi of multiple surveys in our approach baseline and monitor surveys are inverted simultaneously with a model difference regularization penalizing nonphysical differences in the inverted models that are due to survey or computational repeatability issues the primary focus of our work was the inversion of long wavel

shear wave splitting in a young continent continent collision an example from eastern turkey an edited version of this paper was published by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl017390 shtml http atlas geo cornell edu turkey publications sandvol et al 2003b htm

stress arching and its impact on 4d seismic amplitudes and traveltimes abstract pressure depletion during production from a reservoir can cause geomechanical changes in both the reservoir and overburden dropping the pore pressure in the reservoir increases the load on the rock matrix resulting in compaction in most cases the magnitude of this compaction is negligible however when depletion pressures are large or when the reservoir rock is highly compressible the compaction may be significant as the reservoir pulls away from the surface of the earth a stress arch forms in the overburden with the vertical stress decreasing directly above the reservoir and increasing in the pillars of the stress arch these stress changes can perturb the seismic velocities which combined with the changes in path length to the reservoir can cause traveltime changes in the overburden the unloading of the overburden directly above the reservoir shields the reservoir from seeing the full change in pore fluid pressures and thus can have a significant impact on the amplitude changes in

using image warping for time lapse image domain wavefield tomography abstracttime lapse seismic data are widely used for monitoring subsurface changes a quantitative assessment of how reservoir properties have changed allows for better interpretation of fluid substitution and fluid migration during processes such as oil and gas production and carbon sequestration full waveform inversion fwi has been proposed as a way to retrieve quantitative estimates of subsurface properties through seismic waveform fitting however for some monitoring systems the offset range versus depth of interest is not large enough to provide information about the low wavenumber component of the velocity model we evaluated an image domain wavefield tomography idwt method using the local warping between baseline and monitor images as the cost function this cost function is sensitive to volumetric velocity anomalies and it is capable of handling large velocity changes with very limited acquisition apertures where traditional fwi fails we described the theory and workflow of our method la

a new approach to separate seismic time lapse time shifts in the reservoir and overburden abstractfor a robust way of estimating time shifts near horizontal boreholes we have developed a method for separating the reflection responses above and below a horizontal borehole together with the surface reflection data the method uses the direct arrivals from borehole data in the marchenko method the first step is to retrieve the focusing functions and the up down wavefields at the borehole level using an iterative marchenko scheme the second step is to solve two linear equations using a least squares minimizing method for the two desired reflection responses then the time shifts that are directly linked to the changes on either side of the borehole are calculated using a standard crosscorrelation technique the method is applied with good results to synthetic 2d pressure data from the north sea one example uses purely artificial velocity changes negative above the borehole and positive below and the other example uses more realistic changes based on well logs in the 2d case with an adequ

the crustal structure of the east anatolian plateau turkey from receiver functions an edited version of this paper was published by the american geophysical union agu copyright 2003 agu see also http www agu org pubs crossref 2003 2003gl018192 shtml http atlas geo cornell edu turkey publications zor et al 2003 htm

volcanostratigraphy and petrogenesis of the nemrut stratovolcano east anatolian high plateau the most recent post collisional volcanism in turkey abstract the nemrut stratovolcano with its well defined summit caldera is the most recent volcanic eruption center 1441 a d in the east anatolian high plateau one of the best examples of an active colllision zone widespread volcanism has been active in this region for the last 10 ma producing large volumes of lavas and pyroclastics covering a broad belt across the bitlis suture zone from the anatolian plate in the north to the arabian plate in the south three major evolutionary stages have been identified in the evolution of the nemrut stratovolcano pre caldera post caldera and late stages the pre caldera stage is further differentiated into effusive extrusive and explosive phases the latter being responsible for the caldera formation the products of this stage cover a broad compositional range from basalts to rhyolites and consist of lava flows domes large volumes of ignimbrites and associated pyroclastics the post caldera stage consists of three phases comprising phreatomagmatic eruptions vitrophyric rhyolitic lava flows and dykes the late stage consists of the explosive and the following effusive phases with vitrophyric rhyolitic and basaltic lava flows respectively the post caldera and late stages show a compositional gap between the younger mafic and the older felsic members the products of all three stages are silica saturated and display a gradual transition in nature from sodic in the mafic to potassic in the felsic members the overlaps in the compositional spectra and the geochemical trends on bivariate plots suggest the derivation of the products of all three stages from a single parental magma or similar parental magmas yet the stratigraphic position of the mafic and felsic members points to a periodically replenished magma chamber the major and trace element systematics along with petrographic evidences suggest clinopyroxene plagioclase olivine amphibole as the major fractionating phases governing the liquid evolutionary paths with a progressive increase in the proportions of plagioclase and amphibole joined by k feldspar biotite and apatite in the fractionating assemblages during the course of magmatic differentiation the volcanics of all three stages exhibit enrichment in light rare earth elements lree over heavy rare earth elements hree and large ion lithophile elements lile over high field strength elements hfse the multi element patterns and low th y and nb y ratios imply a within plate type mantle asthenospheric source for this volcanics trace element modelling suggests derivation of parental magma s from 10 to 30 partial melting of a spinel lherzolite source assimilation fractional crystallization afc modelling reveals significant but variable degrees of crustal contamination in the evolution of the volcanics with a range of r values assimilation rate crystallization rate from 0 2 to 0 8 these interpretations are in conformity with the recent findings from seismic studies showing that lithospheric mantle is absent in eastern anatolia the crust in the region is about 45 km thick and directly underlain by the asthenosphere possibly due to slab breakoff following the collision of the arabian and the anatolian plates along the bitlis suture zone

integration of the life of field seismic data with the reservoir model at the valhall field the frequent time lapse observations from the life of field seismic system across the valhall field provide a wealth of information the responses from the production and injection wells can be observed through time shift and amplitude changes these observations can be compared to modelled synthetic seismic responses from a reservoir simulation model of the valhall field the observed differences between the observations and the modelling are used to update and improve the history match of the reservoir model the uncertainty of the resulting model is reduced and a more confident prediction of future reservoir performance is provided a workflow is presented to convert the reservoir model to a synthetic seismic response and compare the results to the observed time lapse responses for any time range and area of interest correlation based match quality factors are calculated to quantify the visual differences this match quality factor allows us to quantitatively compare alternative reservoir models to help identify the parameters that best match the seismic observations three different case studies are shown where this workflow has helped to reduce the uncertainty range associated with specific reservoir parameters by updating various reservoir model parameters we have been able to improve the match to the observations and thereby improve the overall reservoir model predictability the examples show positive results in a range of different reservoir modelling issues which indicates the flexibility of this workflow and the ability to have an impact in most reservoir modelling challenges

relating 4d seismics to reservoir geomechanical changes using a discrete element approach a modified discrete element method is briefly introduced and used for modelling reservoir geomechanical response during fluid injection and depletion the modified approach works as a continuum method until some local failure is initiated after which it behaves like a discrete element method on a polygonal lattice the method is advantageous for modelling fracture developments in rocks it is applied here to synthetic models of two reservoirs taken from the north sea gullfaks and elginfranklin for gullfaks two cases of water injection were modelled one with low horizontal effective stress and the other with low vertical effective stress vertical fractures are developed in the first case whereas horizontal fractures are developed in the second case this would not have been seen using traditional methods based on 4d seismics data for the gullfaks field one may envision that horizontal fractures could have been formed the elgin franklin synthetic model is used to study various scenarios of changing stress field around the depleting reservoir based on 4d seismics data from this field one may see changes that could be interpreted in terms of possible fault reactivation

pressure dependent seismic velocities based on effective compliance theory and an asperity deformation model abstractseismic velocities of rocks depend strongly on confining pressure which is often explained by the fracture compliances changes within the rocks it is important to have an accurate model describing the relations between confining pressure and seismic velocities for applications such as time lapse reservoir characterization we propose a new model to address this problem by combining the existing effective compliance theory with new solutions for the pressure dependence of fracture compliances specifically we assume the fracture contact surface can be represented by a set of elastic hemispheres with radii following power law distribution and the pressure dependence of seismic velocities can be expressed through pressure dependent normal and tangential fracture compliances that are derived from hertzian contact theory joint data fittings of p and s wave velocity laboratory data show that our model is accurate we also implement fluid substitution using our model to explain the similar stress i

seismic time lapse effects and stress changes examples from a compacting reservoir compaction of unconsolidated reservoir rock represents a major drive mechanism in many oil and gas reservoirs significant volumes of produced hydrocarbons may be credited to this effect however compaction might also result in surface subsidence a dynamic overburden and local permeability losses in the reservoir

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

genesis of collision volcanism in eastern anatolia turkey late cenozoic volcanism in eastern anatolia extends in a broad sw ne trending belt across the arabia eurasia collision zone from the arabian foreland basin in the southwest and to the kars plateau and lesser caucasus in the northeast foreland volcanism is dominated by basaltic shield and fissure eruptions of transitional tholeiitic alkaline composition volcanism on the thickened crust north of the bitlis thrust zone varies from the mildly alkaline volcano nemrut and older mus volcanics in the south through the transitional calc alkaline alkaline volcanoes bingol and suphan and the alkaline volcano tendurek to the calc alkaline volcano ararat and older kars plateau volcanics in the north isotope sr nd and trace element systematics indicate that the lavas from the foreland were derived from the mantle lithosphere of the arabian continent which had been enriched by small volumes of asthenospheric melts over a period of time and that lavas from the alkaline volcanic area around mus and the volcanoes nemrut and tendurek north of the bitlis thrust zone were derived from a lithospheric source of similar composition either from the same underthrust arabian continent or from the bitlis massif microcontinent by contrast the transitional lavas from bingol and suphan and the calc alkaline lavas from ararat and kars were derived from lithosphere carrying a distinct subduction signature inherited from pre collision subduction events positive correlations between 87sr 86sr and sio2 and rb nb and sio2 in the alkaline and transitional lavas suggest that combined assimilation and fractional crystallization was an important process within at least part of the thickened crust of the collision zone trace element covariation diagrams such as y rb indicate the importance of hornblende crystallization at depth and orthopyroxene at shallow levels within the calc alkaline provinces in contrast to the consistently anhydrous crystallization sequences of the alkaline lavas trace element diagrams based on the covariation of compatible and incompatible elements point to moderate low degrees of partial melting with residual clinopyroxene throughout and residual garnet in the foreland province consideration of mineral stabilities mantle solidi and geothermal gradients before and after collision suggest that lithospheric thickening should both increase the thickness of metasomatized lithosphere and depress the metasomatized zone to greater depths probably beneath the amphibole and dolomite breakdown curves perturbation of the thickened lithosphere by delamination of the thermal boundary layer perhaps coupled with local stretching associated with pull apart basins on strike slip fault systems is then sufficient to generate melt the composition of that melt being largely dependent on the enrichment history of the lithosphere in question in eastern anatolia volcanism appears to have started between about 8 and 6 ma ago some 5 ma after the start of rapid uplift of the east anatolian plateau

modeling and analysis of compaction induced traveltime shifts for multicomponent seismic data abstractmodeling of time shifts associated with time lapse 4d seismic surveys is helpful in evaluating reservoir depressurization and inverting for subsurface stress using coupled geomechanical and full waveform seismic modeling we study the influence of compaction induced stress and strain around a simplified reservoir on compressional p shear s and mode converted ps waves we estimate compaction induced time shifts and analyze their dependence on reflector depth and pressure drop inside the reservoir time shifts between synthetic baseline and monitor surveys are obtained by processing techniques that are potentially applicable to field data although p wave time shift lags for reflectors in the overburden are indicative of induced anisotropy they are two to three times smaller than s wave time shift leads for reflectors beneath the reservoir we also investigate the contributions of the deviatoric and volumetric stains to the time shifts for all three modes time shifts for s and ps waves

4d gravity response of compacting reservoirs analytical approach abstracttime lapse gravity is a technique sensitive to subsurface change in mass and in mass distribution we attempted to devise a method to predict gravity effects caused by redistribution of subsurface mass induced by reservoir compaction first displacements and strains due to compaction were modeled using a geomechanical model then 4d gravity effects were derived from the displacements and the volumetric strains computed in and around the reservoir a sensitivity study was carried out for geomechanical parameters such as poisson s ratio as well as for geometrical parameters such as reservoir radius and depth finally changes in gravity due to compaction were compared to changes induced by reservoir fluid substitution given a rigid basement close below a strongly compacting reservoir our modeling case showed that the deformation itself could give gravity changes comparable to changes caused by reservoir fluid density changes which are the changes traditionally targeted by gravity monitoring

time lapse full waveform inversion with ocean bottom cable data application on valhall field abstractknowledge of changes in reservoir properties resulting from extracting hydrocarbons or injecting fluid is critical to future production planning full waveform inversion fwi of time lapse seismic data provides a quantitative approach to characterize the changes by taking the difference of the inverted baseline and monitor models the baseline and monitor data sets can be inverted either independently or jointly time lapse seismic data collected by ocean bottom cables obcs in the valhall field in the north sea are suitable for such time lapse fwi practice because the acquisitions are of a long offset and the surveys are well repeated we have applied independent and joint fwi schemes to two time lapse valhall obc data sets which were acquired 28 months apart the joint fwi scheme is double difference waveform inversion ddwi which inverts differenced data the monitor survey subtracted by the baseline survey for model changes we have found that ddwi gave a cleaner and more easily interpr

monitoring overburden layer changes and fault movements from time lapse seismic data on the valhall field summary a method developed by roste et al which discriminates between layer thickness and velocity changes is tested on pre stack time lapse seismic ocean bottom cable obc data from the valhall field a key parameter in this discrimination process is the dilation factor which is the relative velocity change divided by the relative thickness change within a given layer the high quality and good repeatability of the obc data enables us to estimate with a reasonable accuracy for values between 0 and 5 for values below 5 complementary information like for instance geomechanics is required for the top reservoir horizon we estimate a maximum subsidence of 0 50 m 0 29 m and a corresponding velocity decrease for the sequence from the seabed to the top reservoir of 2 0 m s 1 0 40 m s 1 time lapse distortion patterns with characteristic time shift versus offset signatures are observed the positions and vertical extents of the distortion zones are determined from ray path considerations and modelling the distortion zones correlate with buried faults indicating that a time lapse distortion zone might be produced by a localized slip in a fault zone we present an extended method which allows for vertical in addition to lateral variations in the relative thickness and velocity changes this method can be viewed as a simplified version of time lapse tomography but involving fewer unknown parameters giving more stability to the estimated changes in thickness and velocity using this technique we are able to estimate for positions with localized time lapse distortions

1 d 2 d and 3 d monte carlo ambient noise tomography using a dense passive seismic array installed on the north sea seabed