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

rock physics modeling for the elastic properties of organic shale at different maturity stages abstractmodeling the elastic properties of organic shale has been of long standing interest for source rocks and unconventional reservoir characterization organic shales exhibit significant variabilities in rock texture and reservoir properties at different maturity stages subsequently affecting their elastic responses we have developed a new rock physics modeling scheme honoring the maturity levels immature mature and overmature which are constrained by the evolution of the physical properties of organic shale upon kerogen maturation in particular at different maturity stages the manners in which the compliant organic materials interact with the inorganic mineral matrix are characterized by different effective medium theories on the basis of the developed rock physics templates organic shales have different elastic behaviors at different maturity stages ignoring the impact of kerogen maturation is insufficient to adequately characterize the elasticity of the whole organic shale system mode

a model for seismic velocity and attenuation in petroleum source rocks petroleum source rock is modeled as a viscoelastic transversely isotropic medium composed of illite smectite and organic matter the wave velocities and attenuation of petroleum source rocks are obtained as a function of excess pore pressure initial kerogen content and water saturation the model generalizes a previous approach based on a pure elastic formulation of backus averaging and introduces the pressure effect and the presence of fluids oil and water the model allows the simulation of different maturation levels induced by pore pressure changes caused by the conversion of kerogen to oil the higher the oil saturation the higher the maturation level assuming that the source rock has a very low permeability the excess pore pressure can be calculated as a function of the conversion factor then the bulk modulus and density of the kerogen oil mixture are obtained with the kuster and toks oz model assuming that oil is the inclusion in a kerogen matrix finally backus averaging of this mixture with the illite smectite layers gives the complex stiffnesses of the transversely isotropic and anelastic medium computed p and s velocities and quality factors parallel to bedding are higher than those normal to bedding with attenuation anisotropy higher than stiffness anisotropy in particular for the north sea kimmeridge shale and at maximum anisotropy p and s parallel velocities are approximately 0 7 km s higher than the corresponding p and s normal velocities the maximum attenuation and stiffness anisotropies are obtained for 18 and 30 volumetric kerogen content respectively both velocities and quality factors decrease with increasing kerogen content at a given pore pressure the decrease in wave velocity is 2 km s for p waves and 1 km s for s waves when kerogen increases from zero to 100 moreover anisotropy increases and velocities decrease with increasing pore pressure i e with higher kerogento oil conversion finally the presence of water affects the normal bedding velocity i e higher water saturation implies lower velocities

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

characteristics of mixed layer smectite illite density separates during burial diagenesis we report a method to physically separate smectite from illite in natural shale samples this method is based upon the large contrast in the density of mixed layer clay minerals reported in the literature our objective was to investigate the behavior of separate density fractions of mixed layer smectite and illite during burial diagenesis samples were obtained from shale cuttings hand picked from a well drilled offshore louisiana each sample was separated into 5 fractions pure end member smectite ems smectite rich mixed layer clays sml illite rich mixed layer clays iml pure end member illite emi and quartz fgq the mineralogy of each clay mineral separate as determined by xrd was reasonably consistent at all depths although the abundance of the mixed layer separates varied the illite rich mixed layer fraction increased in abundance with depth at the expense of the smectite rich mixed layer fraction the fine grained quartz fraction showed an increase in abundance a decrease in average grain size a loss of k feldspar and a heavier isotopic signature with depth we did not however find a correlation with depth in the amount of the end member clay fractions the isotopic signature of the end member smectite shows evidence of equilibration with depth but the end member illite does not we conclude that the discrete illite fraction is detrital in origin and was not involved in the clay mineral transformation at the depths sampled in our well it reflects the sediment provenance the results of this study illustrate the efficacy of the newly developed density separation technique for physically isolating clay mineral species from one another

organic rich shale caprock properties of potential co2 storage sites in the northern north sea offshore norway abstract assessment of the geomechanical properties of organic rich shale caprocks is critical for a successful co2 storage into a saline aquifer in this study we investigated the geochemical properties of the organic rich shale caprocks of the draupne and heather formations overlying the potential sandstone reservoirs of sognefjord fensfjord and krossfjord formations in the northern north sea offshore norway the caprock s depositional variations within the sub basins are established by analyzing the gamma ray shape and stacking patterns the effect due to differences in depositional environments on the caprock compaction behavior is investigated by integrating petrographical analysis of core and cutting samples from 3 wells and by rock physical analysis of wireline log data from 27 exploration wells three rock physics templates are used where the wireline log data are interpreted using the published background trends the effect of kerogen type maturation level and deposition environment on caprock properties within the study area are also evaluated moreover the caprock property such as brittleness is estimated by using four mineralogy and elastic property based empirical relations which is a quantitative measure of caprock property with respect to changes in stress state finally the seismic inversion method is assessed for the possibility of extracting caprock properties from surface seismic data regardless of compaction processes the results indicate that the heather formation is mechanically stronger than the draupne formation however both formations appear to be ductile in nature the depositional environments control the mineralogical composition and fabric of the draupne and heather formations which influence the caprock properties significantly results also show that the effect of toc on caprock properties is insignificant in the study area the brittleness of the organic rich shale caprocks in the study area follows a different trend compared to the published trends we also observed an excellent correlation between the log derived elastic properties and geomechanical parameters still it is difficult to assess the caprock elastic properties from seismic due to the overlap of data clusters the evaluation of caprock geomechanical behaviors is challenging as these properties are site specific and also influenced by other factors such as exhumation in situ stress conditions the existence of natural fractures and their orientations

investigations of fennoscandian glacial isostatic adjustment using modern sea level records we present a new method for determining the rates from a network of regional tide gauge data the method involves using a model for the sea level observations annual averages of relative sea level that explicitly includes a term for the interannual sealevel variations which are assumed to be constant for all sites in the network the resulting simultaneous analysis of all the sea level observations yields sea level rates which are biased by the unknown temporal slope of the interannual variations by differencing sea level rate estimates with respect to one site site referenced sea level rates are calculated which are free from this bias the differencing procedure also removes any signal due to a common sea level rate such as might be associated with eustatic sea level rise the resulting site referenced sea level rates therefore in principle reflect only the relative vertical crustal motions of the tide gauge sites with respect to the geoid these site referenced sea level rates represent a potentially more accurate data set than have previously been used for sea level studies we have used these rates to investigate glacial isostatic adjustment gia in fennoscandia specifically we have used the site referenced sea level rates within the baltic sea to estimate adjustments to the ice history and earth model which are used to calculate vertical rates of adjustment due to gia a method never before used for fennoscandia the parameters selected were lithospheric thickness the viscosities of assumed isoviscous upper and lower mantles and a fennoscandian ice thickness scaling parameter we present the results of this estimation procedure for a specific test ice model we also find evidence that the sea level record for the site nearest the center of uplift furuogrund may be contaminated by systematic errors of unknown origin data from this site have previously been used to determine a rate for the maximum uplift that we find is perhaps 1 mm yr 1 or 10 too large

mathematical modeling of microcrack growth in source rock during kerogen thermal maturation the success of hydraulic fracturing and increasing use of basin modeling packages drive the need to understand the effects of hydrocarbon hc generation on the mechanical properties of source rocks a better understanding of relationships among geological geochemical and geomechanical parameters can potentially reduce the uncertainties associated with conventional and unconventional prospect evaluation we present a simulation of microcrack growth based on a three dimensional source rock system upon thermal maturation the kerogen transforms into lighter products most of which are hcs the generated products exert excessive pore pressure to the system resulting from the effect of volume expansion this pressure is released through the expansion of pore space and formation of microcracks using linear elasticity and linear elastic fracture mechanics our model calculates microcrack sizes surface areas lengths apertures and volumes and the amount of overpressure throughout the maturation process we validated this model with experimental data from kobchenko et al 2011 and performed sensitivity analysis for both laboratory and geological settings much larger microcracks are generated in laboratory settings compared to the subsurface because of the lack of overburden resulting in secondary porosity over 100 times larger than the original organic porosity and crack lengths obtaining millimeter scale in contrast microcracks are much smaller in geological settings because of the presence of significant overburden and stiffer rock frames the crack apertures are in the submicron regime with a crack length ranging from 100 to 300 m the formation of microcracks connects isolated microscale hc pockets providing pathways for primary migration

quartz silt in mudrocks as a key to sequence stratigraphy kimmeridge clay formation late jurassic wessex basin uk sequence stratigraphic interpretation of mudrocks is often carried out using proxy indicators for grain size or by consideration of other aspects of lithology thought to relate to sea level change such as organic matter content an alternative stratigraphic analysis based on direct estimation of quartz silt content was carried out on a major late jurassic mudrock and oil source rock the kimmeridge clay formation of the wessex basin dorset uk the new data generated by backscatter sem x ray and image analysis show decametrescale stratigraphic patterns that are incompatible with many previous sequence stratigraphic interpretations based on gamma ray logs or visual lithofacies and biofacies description correlation with a basin margin section in the boulonnais northern france indicates that silt rich intervals in basinal facies are coeval within the limits of biostratigraphic resolution with shallow water sand rich packages on the margin variation in silt content in the kimmeridge clay therefore appears to be a record of relative sea level change of at least regional extent it is suggested that analysis of silt content offers the most reliable basis for generation of a regional sequence stratigraphy in basinal mudrocks a revised relative sea level curve for the wessex basin kimmeridgian and early tithonian is presented based on this premise

insar measurements of compaction and subsidence in the ganges brahmaputra delta bangladesh many of the world s largest river deltas are sinking due to sediment loading compaction and tectonics but also recently because of groundwater extraction hydrocarbon extraction and reduced aggradation little is known however about the full spatial variability of subsidence rates in complex delta systems this study reconstructs subsidence rates in the eastern portion of the ganges brahmaputra delta gbd bangladesh covering more than 10 000 km2 at a high spatial resolution of 100 m the map was produced using interferometric synthetic aperture radar insar covering the period 2007 to 2011 eighteen advanced land observing satellite phased array l band sar scenes were used to generate 30 interferograms calibrated with gps interferograms were stacked to yield average subsidence rates over the study period small baseline subset insar was then applied to validate the results against an additional gps record from dhaka bangladesh land subsidence of 0 to 10 mm yr is seen in dhaka with variability likely related to local variations in shallow subsurface sediment properties outside of the city rates vary from 0 to 18 mm yr with the lowest rates appearing primarily in pleistocene madhupur clay and the highest rates in holocene organic rich muds results demonstrate that subsidence in this delta is primarily controlled by local stratigraphy with rates varying by more than an order of magnitude depending on lithology the ability of l band insar to differentiate between stratigraphic units in this humid vegetated subtropical river delta demonstrates the power of interferometry as a tool for studying the subsurface in deltaic environments

avo effects of a hydrocarbon source rock layer the organic content of petroleum source rock layers can be determined from seismic data with a suitable avo technique since the source rock has a layered structure the best forward model is a transversely isotropic layer between two isotropic half spaces parameterized by the layer thickness and the amount of organic material this limited number of parameters is essential to obtain a robust inversion method here i compute the pp and ps reflection coefficients of the source bed as a function of layer thickness and organic content including attenuation mechanisms related to different stages of maturation the source rock is modeled as a viscoelastic medium composed of illite smectite solid organic matter kerogen and fluids oil and water the properties of the kerogen oil water mixture are obtained with the kuster and toksoz model assuming that oil and water are the inclusion in a kerogen matrix then backus averaging gives the complex stiffnesses of the layer to derive the reflection coeffic

effective elastic properties of solid clays clay minerals are perhaps the most abundant materials in the earth s upper crust as such their elastic properties are extremely important in seismic exploration seismic reservoir characterization and sonic log interpretation because little exists in the literature on elastic properties of clays we have designed a method of measuring effective elastic properties of solid clays clays without pores in this method clay minerals are mixed with a material with known elastic properties to make composite samples elastic properties of these clay minerals are then inverted from the measured elastic properties of the composite samples using the weighted hashin shtrikman average using this method we have measured 66 samples of 16 types of clays in this paper we present a comprehensive data set of elastic properties of solid clays that commonly occur in or are related to petroleum reservoirs although uncertainties up to 10 exist the data set reported here is by far the most comprehensive set of e

amplitude variations with offset of pressure seal reflections knowledge of pressure compartments is essential for identifying potential risks in advance of drilling and in understanding the mechanism of hydrocarbon trapping and migration these compartments are bounded by pressure seals which under certain conditions can be detected and characterized with seismic reflection data use of prestack seismic data requires the analysis of reflections generated at the pressure seals such as the top of a reservoir rather than the properties of the rock volume in this sense amplitude variations with offset avo techniques can be a good tool to obtain information from such pressure seals or pressure transition zones in this work i investigate the avo response of compartment seals by analyzing the plane wave reflection coefficients as a function of pore pressure above and below the seal incidence angle and seal thickness for the case investigated in this work berea sandstone with high gas saturation the avo effects are important at low effective pressures tha

principles of avo crossplotting hydrocarbon related avo anomalies may show increasing or decreasing amplitude variation with offset conversely brine saturated background rocks may show increasing or decreasing avo

rock physics templates for clay rich source rocks shale source rocks are composed of various minerals mainly smectite and illite depending on the burial depth and they can be described as transversely isotropic media the pore space may contain kerogen water oil and gas determined by the in situ conditions a petroelastic description is based on the following smectite illite transformation as a function of depth is described by a fifth order kinetic reaction backus averaging to mix isotropic smectite and anisotropic illite is then used to obtain the elasticity constants of the mineral composing the frame porosity is obtained from density and water is part of the mineral whose elasticity constants are obtained from gassmann equations oil and gas generated from kerogen are assumed to saturate the kerogen phase the bulk modulus of the oil gas mixture is calculated by a mesoscopic loss model and the stiffnesses of the kerogen fluid mixture are obtained with the kuster and toksoz model assuming that the fluid is included in a kerogen matrix two models are considered to obtain the seismic velocities of the shale namely backus averaging and the gassmann equation generalized to the anisotropic case with a solid pore infill we built rock physics templates rpts containing only kerogen immature and kerogen plus hydrocarbons mature pore pressure effects were modeled and used as templates we considered the kimmeridge shale at different depths to model kerogen oil and oil gas conversions we assumed a basin evolution model with a constant sedimentation rate geothermal gradient and a first order kinetic arrhenius reaction the detection of the hydrocarbons was investigated from rpts built with wave velocities impedances lame constants density poisson ratio young modulus and anisotropy parameters for varying kerogen content fluid saturations and pore pressure moreover the amplitude variation with offset intercept and gradients were computed corresponding to the seismic response of a source rock layer for varying kerogen content and fluid saturation

sonic qp qs ratio as diagnostic tool for shale gas saturation abstractsonic qp qs ratio obtained from full waveform acoustic logs in conventional sandstone reservoirs is known to be sensitive to the presence of gas and it is regarded as a potential diagnostic tool for saturation discrimination however it is not known if such a saturation diagnostic tool will be applicable in unconventional reservoirs such as in gas saturated shales we have analyzed the monopole and dipole waveform logs acquired from a shale gas exploration well in the cooper basin south australia the depth interval of interest is 300 m thick and it intersects three shale units in which the two underlying formations contain gas saturation of more than 30 and are identified as the primary exploration targets we use the statistical average method to extract the p and the s wave attenuation profiles and obtain an average p wave quality factor of qp 33 and s wave quality factor of qs 46 the gas saturation of the lithological layers having qp qs 1 is appreciably larger than the gas saturation

water level changes subsidence and sea level rise in the ganges brahmaputra meghna delta being one of the most vulnerable regions in the world the ganges brahmaputra meghna delta presents a major challenge for climate change adaptation of nearly 200 million inhabitants it is often considered as a delta mostly exposed to sea level rise and exacerbated by land subsidence even if the local vertical land movement rates remain uncertain here we reconstruct the water level wl changes over 1968 to 2012 using an unprecedented set of 101 water level gauges across the delta over the last 45 y wl in the delta increased slightly faster 3 mm y than global mean sea level 2 mm y however from 2005 onward we observe an acceleration in the wl rise in the west of the delta the interannual wl fluctuations are strongly modulated by el nino southern oscillation enso and indian ocean dipole iod variability with wl lower than average by 30 to 60 cm during co occurrent el nino and positive iod events and higher than average wl by 16 to 35 cm during la nina years using satellite altimetry and wl reconstructions we estimate that the maximum expected rates of delta subsidence during 1993 to 2012 range from 1 to 7 mm y by 2100 even under a greenhouse gas emission mitigation scenario representative concentration pathway rcp 4 5 the subsidence could double the projected sea level rise making it reach 85 to 140 cm across the delta this study provides a robust regional estimate of contemporary relative wl changes in the delta induced by continental freshwater dynamics vertical land motion and sea level rise giving a basis for developing climate mitigation strategies

caprock characterization of upper jurassic organic rich shales using acoustic properties norwegian continental shelf abstract our analysis of a comprehensive well log database and complementary mineralogical and geochemical information indicates that the risk for upper jurassic shales on the norwegian continental shelf ncs to permit severe leakage of hydrocarbons from the reservoir is generally low even in the case of substantial uplift the content of brittle minerals organic content and compaction are dominant factors that explain the observed discrepancies in acoustic properties of organic rich caprock shales in particular variations in silt clay content in clay dominated shales are found to primarily influence sonic velocity and to correlate closely with gamma ray where the uranium contribution is limited grey shales changes in organic content exhibit a stronger density component and are seen to counteract or mask the compaction effect on velocity and density in kimmeridgian black shales the hekkingen draupne and tau formations are distinctly different from the underlying grey shale formations in acoustic properties despite that the latter group also contains significant amounts of organic matter based on the low permeability and high capillary sealing capacity of clay dominated shales we conclude that even for a silty seal migration through the caprock matrix is highly unlikely furthermore tectonic fracturing is an ineffective leakage mechanism when the seal is poorly consolidated cemented prior to uplift brittleness related to both mineralogical composition and consolidation is consequently a crucial parameter for predicting seal integrity in exhumed basins our rock physics framework and interpretations relate this rather qualitative parameter to acoustic properties and thus to seismic data

elastic anisotropy of source rocks implications for hydrocarbon generation and primary migration we combined acoustic velocities and anisotropy measurements with x ray diffraction mineralogy rock eval organic geochemical analyses vitrinite reflectance and scanning electron microscope observations on 69 cores of hydrocarbon source rocks collected from eight sedimentary basins the velocity data indicate the lamellar distribution of solid organic matter kerogen in compacted black shales and show a strong correlation between their elastic anisotropy and organic richness the experimental results are consistent with the two component anisotropic model of black shales with a continuous kerogen network in both bedding parallel and bedding normal directions beginning from relatively low toc values the strong elastic anisotropy of tight thermally mature source rocks i further enhanced by overpressure induced bedding subparallel microcrack development during the main stage of hydrocarbon hc generation and primary migration at r0 greater than 0 75 in agreement with published petrographic observations these microcracks significantly aid primary hc migration particularly horizontally elastic anisotropy of medium to high porosity illite smectite shales is weaker than in lower porosity predominantly illite shales however the overall positive trend of elastic anisotropy with kerogen content remains unchanged

lithology and fluid differentiation using a rock physics template the elastic properties such as velocity density impedance and vp vs ratio take an important role in reservoir characterization because they are related to the reservoir properties to analyze these elastic properties rock physics knowledge is a bridge that links the elastic properties to the reservoir properties such as water saturation porosity and shale volume in this study we build up a rock physics template and plot it along with the inverted elastic properties to aid the efficient interpretation using this method we can estimate the lithology and fluid content of undrilled areas if the undrilled area has the same geological deposition environment as a drilled area the final results show that the lithology and fluid content can be efficiently interpreted for our target reservoirs using the inverted elastic properties plotted with a rock physics template rather than only using the inverted elastic properties

the effect of anisotropy on the young s moduli and poisson s ratios of shales young s modulus and poisson s ratio are required for geomechanics applications such as hydraulic fracture design analysis of wellbore stability and rock failure determination of in situ stress and assessment of the response of reservoirs and surrounding rocks to changes in pore pressure and stress shales are usually anisotropic and models that neglect shale anisotropy may fail to describe geomechanical behaviour correctly anisotropy in shales results from a partial alignment of anisotropic clay particles kerogen inclusions microcracks low aspect ratio pores and layering for shales the young s modulus measured parallel to bedding e1 is usually greater than the young s modulus measured perpendicular to bedding e3 however the poisson s ratio 31 corresponding to stress applied perpendicular to bedding and strain measured parallel to bedding can be greater than equal to or less than the poisson s ratio 12 for stress applied parallel to bedding and strain measured parallel to bedding for transverse isotropy the elastic anisotropy resulting from a partial alignment of clay particles can be written in terms of the coefficients w200 and w400 which describe the impact of clay particle orientation on the anisotropy of shales disorder in the orientation of clay particles acts to reduce w400 faster than w200 since w400 is a higher order moment of the clay particle orientation distribution function than w200 this is confirmed by analysis of measured anisotropy parameters for shales a partial alignment of clay particles is consistent with the measured young s moduli for shales and with values of poisson s ratio 31 12 but not with values 31 12 these values can be explained if there exist kerogen inclusions microcracks or low aspect ratio pores aligned parallel to the bedding plane

present day trends of vertical ground motion along the coast lines vertical ground motion vgm rates stand as crucial information either for predicting the impact of the actual sea level rise along low lying coasts or refining geodynamic problems because present day vgm rates have a magnitude smaller than 10 mm yr they remain challenging to quantify and often elusive we focus on the quantification of global scale vgm rates in order to identify global or regional trends we computed vgm rates by combining tide gauges records and local satellite altimetry which yield a new dataset of 634 vgm rates we further compare this database to previous studies that use geodetic techniques and tide gauges records in order to evaluate the consistency of both our results and previous ones the magnitudes differ by less than 5 mm yr and similar subsidence and uplift general tendencies appear even if the asset of our database stands in the greater number of sites the combination of all studies each with different pros and cons yields a hybrid dataset that makes our attempt to extract vgm trends more robust than any other independent study fennoscandia the west coast of north america and the eastern coast of australia are uplifting while the eastern coast of north america the british isles and western europe the eastern mediterranean sea japan and the western coast of australia are subsiding glacial isostatic adjustment gia is expected to provide a major contribution to the present day signal aside from fennoscandia observed vgm often depart from the gia model predictions of peltier 2004 this either results from an underestimate of the model predictions or from the influence of other processes indeed the influence of the geodynamic setting appears in particular along the coasts of western north america or japan where the alternation of transform faults and subduction zones makes it possible to assign contrasted behaviours to the local geodynamic context local mechanisms like anthropogenic processes or sediment compaction also contribute to vgm this remains true for the critical cases of venice the gulf of mexico the ganges delta and the maldives which are particularly exposed to the current sea level rise

recent hiatus caused by decadal shift in indo pacific heating recent modeling studies have proposed different scenarios to explain the slowdown in surface temperature warming in the most recent decade some of these studies seem to support the idea of internal variability and or rearrangement of heat between the surface and the ocean interior others suggest that radiative forcing might also play a role our examination of observational data over the past two decades shows some significant differences when compared to model results from reanalyses and provides the most definitive explanation of how the heat was redistributed we find that cooling in the top 100 meter layer of the pacific ocean was mainly compensated for by warming in the 100 to 300 meter layer of the indian and pacific oceans in the past decade since 2003

rock physics analysis of clay rich source rocks on the norwegian shelf abstract rock physics trends and properties of clay rich source rocks are investigated in selected wells in the north sea and norwegian sea properties can vary significantly because of burial compaction composition diagenesis organic richness and maturation the many competing effects can be difficult to disentangle in traditional rock physics crossplots however nearly all the source rock data in the study are bounded nicely by linear trends that are based on rock physics models in acoustic impedance ai versus shear impedance si crossplots these reference models serve as a nice screening tool for organic richness and or maturation level i e hydrocarbon generation and expulsion regardless of burial depth the use of rock physics templates for the early mature to mature stage of clay rich source rocks is demonstrated by combining a simple basin modeling approach with a rock physics model using backus average in which the organic rich shale is represented by a transverse isotropic mixture o

source rock seismic velocity models gassmann versus backus source rocks are described by a porous transversely isotropic medium composed of illite and organic matter kerogen oil and gas the bulk modulus of the oil gas mixture is calculated by using a model of patchy saturation then the moduli of the kerogen fluid mixture are obtained with the kuster and toksoz model assuming that oil is the inclusion in a kerogen matrix to obtain the seismic velocities of the shale we used backus averaging and gassmann equations generalized to the anisotropic case with a solid pore infill in the latter case the dry rock elastic constants are calculated with a generalization of krief equations to the anisotropic case we considered 11 samples of the bakken shale data set with a kerogen pore infill the backus model provides lower and upper bounds of the velocities whereas the krief gassmann model provides a good match to the data alternatively we obtain the dry rock elastic moduli by using the inverse gassmann equation instead of using krief equations four cases

the role of texture cracks and fractures in highly anisotropic shales organic shales generally have low permeability unless fractures are present however how gas oil and water flows into these fractures remains enigmatic the alignment of clay minerals and the alignment of fractures and cracks are effective means to produce seismic anisotropy thus the detection and characterization of this anisotropy can be used to infer details about lithology rock fabric and fracture and crack properties within the subsurface we present a study characterizing anisotropy using s wave splitting from microseismic sources in a highly anisotropic shale we observe very strong anisotropy up to 30 with predominantly vti vertical transverse isotropy symmetry but with evidence of an hti horizontal transverse isotropy overprint due to a ne striking vertical fracture set parallel to the maximum horizontal compressive stress we observe clear evidence of a shear wave triplication due to anisotropy which to our knowledge is one of only a very few observations of such triplications in field scale data we use modal proportions of minerals derived from x ray fluorescence data combined with realistic textures to estimate the contribution of intrinsic anisotropy as well as possible contributions of horizontally aligned cracks we find that aligned clays can explain much of the observed anisotropy and that any cracks contributing to the vertical transverse isotropy vti must have a low ratio of normal to tangential compliance zn zt typical of isolated cracks with low hydraulic connectivity subhorizontal cracks have also been observed in the reservoir and we propose that their reactivation during hydraulic fracturing may be an important mechanism to facilitate gas flow

hydrocarbon generation induced microcracking of source rocks laboratory measurements of ultrasonic velocity and anisotropy in kerogen rich black shales of varying maturity suggest that extensive bedding parallel microcracks exist in situ in most mature source rocks undergoing the major stage of hydrocarbon generation and migration given the normal faulting regime with the vertical stress being the maximum principal stress typical of most sedimentary basins this microcrack alignment cannot be accounted for using simplified fracture mechanics concepts this subhorizontal microcrack alignment is consistent with 1 a model of local principal stress rotation and deviatoric stress reduction within an overpressured formation undergoing hydrocarbon generation and with 2 a strong mechanical strength anisotropy of kerogen rich shales caused by bedding parallel alignment of kerogen microlayers microcracks originate within kerogen or at kerogen illite interfaces when pore pressure exceeds the bedding normal total stress by only a few mpa due to the extremely low fractu

primary migration by oil generation microfracturing in low permeability source rocks application to the austin chalk texas fracturing of low permeability source rocks is induced by pore pressure changes caused by the conversion of organic matter to less dense fluids oil and gas these fractures increase the permeability and provide pathways for hydrocarbon migration an equation for the pressure change is derived using four major assumptions 1 the permeability of the source rock is negligibly small 0 01 d 10 20 m2 so that the pore pressure buildup by the conversion is much faster than its dissipation by pore fluid flow 2 the stress state is isotropic so that horizontal and vertical stresses are equal the source rock fails when the pore pressure equals the overburden pressure 3 the properties of the rock organic matter and fluids remain constant during oil generation this assumption is valid when the change in depth i e pressure and temperature is small 4 only two reaction rates are required for the conversions a low temperature reaction rate for the kerogen oil conversion e approx 24 kcal mol a approx 1014 m y and a high temperature reaction rate for oil gas conversion e approx 52 kcal mol a approx 5 5 1026 m y the equations for generation rate and pressure change are applied to the austin source rock by adjusting the several variables to fit geochemical data core saturations and observed levels of oil and gas production this application demonstrates that the equations are easily applied in calculating depths of primary migration for low permeability source rocks

comparison of the krief and critical porosity models for prediction of porosity and vp vs vp vs relations are key to the determination of lithology from seismic or sonic log data as well as for direct seismic identification of pore fluids using for example amplitude variation with offset avo analysis while there are a variety of published vp vs relations and vs prediction techniques most reduce to two simple elements 1 for each lithology establish empirical relations among vp vs and porosity for one reference fluid usually water and 2 use gassmann s 1951 relations to map these to other pore fluid states in this short note we point out similarities between the critical porosity models of nur 1992 and krief et al 1990 for predicting vp vs both are useful primarily because they incorporate the above two robust elements although derived from different directions they are nearly identical

tide gauge and gps measurements of crustal motion and sea level rise along the eastern margin of adria 1 we use observations from tide gauges and colocated continuous gps cgps stations to investigate crustal deformation and sea level changes along the eastern margin of the adriatic sea we develop a new method to separate common mode relative sea level from spatially variable signals precise vertical crustal motions determined by cgps allow us to further separate relative sea level into absolute sea level changes and crustal motions with respect to a local central mediterranean fixed gps defined reference frame from the tide gauge data we find fairly uniform relative sea level rise along the coast with mean rate of 0 84 0 04 mm yr and weighted rms variation about this mean of 0 2 mm yr this rate is a factor of 2 4 lower than estimates for global average sea level rise in contrast vertical motion of coastal rocks determined by cgps vary appreciably from an average of 1 7 0 4 mm yr in southern adria to 0 0 0 4 mm yr in northern adria this difference in crustal motion between the northern and southern regions is independent of our ability to separate sea level from crustal motion and may be explained by crustal strain associated with an active thrust fault accommodating southern adria microplate convergence with eurasia enigmatically the combination of tide gauge and cgps measurements shows that absolute sea level relative to the gps determined reference frame varies by as much as 1 8 mm yr along the croatian coast in such a way that the relative sea level remains roughly constant there are several potential explanations for this result deriving from ocean atmosphere and solid earth dynamics

simple kinetic models of petroleum formation part i oil and gas generation from kerogen modern basin analysis uses kinetic models to predict the extent of petroleum generation within potential source rocks the global kinetic model presented here assigns kinetic parameters based on gross depositional environment and stratigraphic age this is useful in areas of low geochemical knowledge including exploration frontiers five kerogen kinetic organofacies each characterized by a specific organic matter input and early diagenetic overprint can broadly be related to sedimentary facies age associations even using seismic sequence stratigraphy alone a aquatic marine siliceous or carbonate evaporite any age b aquatic marine siliciclastic any age c aquatic non marine lacustrine phanerozoic d e terrigenous non marine ever wet coastal mesozoic and younger and f terrigenous non marine coastal late palaeozoic and younger routine pyrolysis data allow partitioning of organic carbon in the immature source rock into four initial components oil oil generative gas generative and inert separate kinetic parameters for the oil and gas generative fractions allow computation of the evolving concentration and composition of the products it was assumed that the activation energy distributions for each fraction were normally distributed non linear regression of large combined laboratory and field data sets varying by up to 12 orders of magnitude in heating rate established optimum values for the required ten 5 2 kinetic parameter sets a emean e differences in kinetic parameters can be reconciled with known chemical properties although our knowledge base is still inadequate to construct kinetic models from first principles mean activation energies governing oil generation increase systematically in the order a f causing a corresponding increase in generation temperature at a reference heating rate 2 c ma 1 the oil generation window 10 90 oil generative kerogen degraded increases from ca 95 135 c to 145 175 c organofacies c has the tightest energy distribution and narrowest oil generation window the gas generation window ranges from ca 105 155 c to 175 220 c thermal stress results from a combination of temperature and time an order of magnitude increase decrease in heating rate elevates depresses reaction temperatures by ca 15 c heating rates in subsiding sedimentary basins can vary by two orders of magnitude dramatic differences in generation temperature can result if the heating rate and organofacies effects compound thus global oil and gas generation temperature thresholds constitute blunt instruments with which to screen the petroleum potential of sedimentary basins because unexpelled oil provides a potential feedstock for oil to gas cracking in the source rock quantitative models of petroleum generation become really useful only when coupled with models of oil gas cracking and expulsion for example the frequently observed association between gas provinces and coals cannot be explained solely by their generation behaviour

rock physics of organic shales several publications over the last 20 years have established that black organic shales are generally characterized by strong velocity anisotropy low velocity in the bedding normal direction and relatively low density and porosity e g vernik and nur 1992 vernik and liu 1997 these rock properties are of interest in seismic attribute studies but even more so in geomechanical applications related to reservoir characterization and hydraulic fracture stimulation organic shales typically but not necessarily express strong vertical transverse isotropy vti with axis of symmetry perpendicular to the bedding parallel lamination and clay particle preferred orientation high resolution sem imaging figure 1 immediately reveals all these textural features in addition to silt grains and the lenticular distribution of the solid organic matter kerogen which in turn is characterized by significant intraparticle porosity in mature shales any ti medium is described by the five independent elastic consta

annually laminated lake sediments and the study of quaternary environmental changes a review abstract annually laminated lake sediments non glacial varves have in recent years been discovered in increasing abundance especially since the development of in situ freezer samplers so far the majority of examples have been found in three main areas eastern north america northern and central europe and east and central africa a much more widespread distribution seems highly probable however the formation of annual laminations in freshwater lakes is governed by a number of factors the most important of which appears to be morphometry seasonality of sediment supply which may be controlled by physical biological or even cultural processes in the lake or in its catchment is also clearly significant four main types of laminations here termed ferrogenic calcareous biogenic and clastic have so far been recorded although it is quite clear that others exist special field and laboratory techniques are needed in order that the particular properties of varved sediments may be fully exploited annually laminated sediments have so far been applied to the investigation of a number of aspects of the quaternary these include the study of a geochronology b climatic change c vegetation history especially the role of fire in forest ecosystems d the calculation of rates of sediment influx to lakes and of rates of erosion from their catchments and e the monitoring of processes in the modern environment such as heavy metal pollution eutrophication and acid rain annually laminated lake sediments combine an internal independent chronology with the preservation of discrete visible increments of seasonal and annual sedimentation given this unique property and the likelihood that many more examples will be discovered the prospects for further applications of studies of these sediments to the investigation of the quaternary seem very good indeed

modeling earth deformation from monsoonal flooding in bangladesh using hydrographic gps and gravity recovery and climate experiment grace data 1 the ganges brahmaputra and meghna rivers converge in bangladesh with an annual discharge second to the amazon most of the flow occurs during the summer monsoon causing widespread flooding the impounded water represents a large surface load whose effects can be observed in gravity recovery and climate experiment grace and gps data bangladesh is at the center of the second largest seasonal anomaly in the grace gravity field reflecting water storage in southeast asia eighteen continuous gps stations in bangladesh record seasonal vertical motions up to 6 cm that inversely correlate to river level we use 304 river gages to compute water height surfaces with a digital elevation model to separate surface water from groundwater porosity of 20 was used to estimate groundwater mass and calculate the water load results show 100 gt of water are stored in bangladesh 7 5 of annual discharge but can reach 150 gt during extreme events the calculated water mass agrees with monthly grace water mass equivalents from bangladesh within statistical limits we compute the deformation due to this water load on an elastic half space and we vary young s modulus to fit gps data from our two most continuous records the water loading can account for 50 of the variance in the gps data the best fitting young s modulus is 117 124 gpa for dhak and 133 135 gpa for sust although the upper bound is not well constrained these estimates lie between sediment 30 75 gpa and mantle 190 gpa values indicating that response to loading is sensitive to structure throughout the lithosphere and is not absorbed by the weak sediments

elastic properties of clay minerals clay minerals are the most abundant materials in sedimentary basins the most common like kaolinite illite chlorite and smectite are found in various amounts in mudstones and are also often found in clastic and nonclastic reservoir rocks their presence alters the elastic behavior of reservoir rocks significantly as a function of mineral type volume and distribution thus two sandstones with the same clay amount might have different elastic properties due to differences within the clay population the elastic properties of clay minerals are therefore important in rock physics modeling to understand the seismic and sonic log responses of shaley sequences and clay bearing reservoir rocks

marine ice sheet collapse potentially under way for the thwaites glacier basin west antarctica resting atop a deep marine basin the west antarctic ice sheet has long been considered prone to instability using a numerical model we investigated the sensitivity of thwaites glacier to ocean melt and whether its unstable retreat is already under way our model reproduces observed losses when forced with ocean melt comparable to estimates simulated losses are moderate 1 mm per year of sea level rise collapse in the different simulations within the range of 200 to 900 years

subsidence of kolkata calcutta city india during the 1990s as observed from space by differential synthetic aperture radar interferometry d insar technique abstract in kolkata city india potential land subsidence due to over drafting of groundwater under confined condition has been reported by a number of previous workers and by the local media the presence of a thick surface clay layer with an average thickness of more than 40 m over the aquifer sand layer raises questions on the possibility and doubtfulness of land subsidence in kolkata city in this work d insar based study has been undertaken to detect and measure land subsidence phenomenon in kolkata city for detecting slow land subsidence phenomenon in kolkata city occurring primarily due to piezometric fall consequent to groundwater over drafting we have chosen the insar data pairs acquired during post monsoon t 1 pre monsoon t 2 periods when the lowering of piezometric head was the maximum and therefore land subsidence would be more prominent than that of pre monsoon t 1 pre monsoon t 2 and post monsoon t 1 post monsoon t 2 periods of similar time intervals for detecting slow land subsidence phenomenon essentially from long temporal baseline data pairs usually in years temporal decorrelation and atmospheric artefacts have been found to pose serious difficulties adaptive filtering of the noisy interferograms followed by summing of the independent interferograms was performed in complex domain in order to suppress noise from the fringes and highlight the deformation fringes over atmospheric artefacts respectively results indicate that an area in kolkata city surrounded by machhua bazar calcutta university and raja bazar science college had been undergoing subsidence during the observation period i e 1992 1998 with an estimated rate of 5 to 6 5 mm year

depositional impact on the elastic characteristics of the organic shale reservoir and its seismic application a case study of the longmaxi wufeng shale in the fuling gas field sichuan basindepositional elastic effects

methods for source rock identification on seismic data an example from the tanezzuft formation tunisia abstract source rocks occurrence extension and quality in the subsurface are usually characterized directly from well data seismic characterization is however becoming an emerging technique for extending source rock properties beyond well locations and an effective tool for mapping their lateral and vertical heterogeneities the tanezzuft formation in tunisia an extremely organic rich source rock was used as a test for applying and comparing different seismic methods aimed at organic rich sequences characterization the data used consist of a 2d seismic line shot in the northern flank of the ghadames basin tunisia pre stack gathers extracted from an inline of a 3d survey and four wells with a complete set of wireline and petrophysical logs impedance inversion avo and seismic attributes were computed on the seismic lines and compared to well data impedance inversion together with a rock physics model of the formation generated a quantitative estimate of total organic carbon toc content in the studied 2d seismic line avo analysis showed a class iv and a base class iv response for the upper and lower reflectors delimiting the organic rich interval respectively seismic attributes analyzed the formation by exploiting its high impedance contrast and intrinsic anelastic attenuation the three methods here discussed showed coherent results both when compared each other and when compared with the well data and the regional geological model in particular avo and seismic attribute analysis are methods that can be applied without the need of well information and are then feasible methods for the investigation of source rock properties in undrilled basins

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