sediment dewatering in the makran accretionary prism abstract sediments within the makran accretionary prism are considerably more compacted than the material entering the subduction zone due to the additional tectonic stresses resulting from plate convergence and accretionary processes tectonic compaction of the offscraped sediments has been documented by deriving in situ porosities in the upper 4 km from their seismic velocities wide angle seismic reflection refraction profiles were analysed from a transect crossing both the makran accretionary prism and the undeformed abyssal plain sediments to the south the 6 7 km thick abyssal plain sediments exhibit normal compaction with depth the sediments incorporated into the accretionary prism have higher seismic velocities at all depths corresponding to reductions in porosity of 30 40 mapping the porosity depth gradient across the prism shows that there is a marked change in porosity at the seaward toe of the prism the frontal fold there is then little further change until further folding begins to occur 70 km landward of the toe the dewatering and consolidation of the sediments is an important control on deformation occurring within the sedimentary prism

spectral analysis of ground penetrating radar response to thin sedimentary layers 1 ground penetrating radar gpr systems utilized in studies of sedimentary deposits generate wavelengths tens of centimeters that are commonly much longer than the thickness of bedding often millimeters to centimeters within the target strata where this is the case radar profiles represent interference patterns simple models of radar response to sequences of thin beds such as those found in coastal deposits show potentially detectable spectral shifts toward higher frequencies in radar returns spectral analysis of radar data over barrier beach deposits at waites island south carolina shows that returns from packages with heavy mineral laminations are shifted toward higher frequencies relative to returns from more isolated contacts such spectral shifts may be useful as an indicator of fine scale layering on radar profiles

three dimensional seismic tomography from p wave and s wave microearthquake travel times and rock physics characterization of the campi flegrei caldera 1 the campi flegrei cf caldera experiences dramatic ground deformations unsurpassed anywhere in the world the source responsible for this phenomenon is still debated with the aim of exploring the structure of the caldera as well as the role of hydrothermal fluids on velocity changes a multidisciplinary approach dealing with three dimensional delay time tomography and rock physics characterization has been followed selected seismic data were modeled by using a tomographic method based on an accurate finite difference travel time computation which simultaneously inverts p wave and s wave first arrival times for both velocity model parameters and hypocenter locations the retrieved p wave and s wave velocity images as well as the deduced v p v s images were interpreted by using experimental measurements of rock physical properties on cf samples to take into account steam water phase transition mechanisms affecting p wave and s wave velocities also modeling of petrophysical properties for site relevant rocks constrains the role of overpressured fluids on velocity a flat and low v p v s anomaly lies at 4 km depth under the city of pozzuoli earthquakes are located at the top of this anomaly this anomaly implies the presence of fractured overpressured gas bearing formations and excludes the presence of melted rocks at shallow depth a high v p v s anomaly located at 1 km suggests the presence of rocks containing fluids in the liquid phase finally maps of the v p v s product show a high v p v s horseshoe shaped anomaly located at 2 km depth it is consistent with gravity data and well data and might constitute the on land remainder of the caldera rim detected below sea level by tomography using active source seismic data

velocity determination for pore pressure prediction overpressured formations exhibit several of the following properties when compared with a normally pressured section at the same depth dutta 2002 1 higher porosities 2 lower bulk densities 3 lower effective stresses 4 higher temperatures 5 lower interval velocities and 6 higher poisson s ratios

inverse modelling and seismic data constraints on overpressure generation by disequilibrium compaction and aquathermal pressuring application to the eastern black sea basin summary pore pressure above the hydrostatic overpressure is common in deep basins it plays an important role in pore fluid migration represent a significant drilling hazard and is one of the factors controlling slope stability and deformation in seismically active areas here we present an inverse model to calculate overpressure due to disequilibrium compaction and aquathermal pressuring we minimize a function that contains the misfits between estimates from our forward model and observed values using a non linear least squares approach the inverse model allows the introduction of observed seismic and geological constraints such as p wave velocity vp and density data and depth of the layer boundaries for a better pore pressure prediction the model output also provides estimates of 1 surface porosity 2 compaction factor 3 intrinsic permeability at surface conditions 4 a parameter controlling the evolution of the intrinsic permeability with porosity 5 the ratio between horizontal and vertical permeability and 6 uncompacted thickness so sedimentation rate assuming known time intervals for each sedimentary layer we apply our inverse approach to the centre of the eastern black sea basin ebsb where the vp structure has been inferred from wide angle seismic data first we present results from a 1 d inverse model and an uncertainty analysis based on the monte carlo error propagation technique to represent the observed rapid change from low vp to normal vp below the maikop formation we impose a zero overpressure bottom boundary and subdivide the layer below the maikop formation into two sublayers an upper layer where the rapid change is located and a lower layer where the vp is normal secondly we present the results from a 2 d inverse model for the same layers using two alternative bottom boundary conditions zero overpressure and zero flow we are able to simulatetheobserved vp suggestingthatthelowvelocityzone lvz at 3500 6500mdepth below the seabed mbsf can be explained by overpressure generated due to disequilibrium compaction 90 per cent and to aquathermal pressuring 10 per cent our results suggest thattheuppersublayer belowthemaikopformation behavesasasealduetoitslowpermeability 0 3 2 10 14 ms 1 this seal layer does not allow the fluids to escape downwards and hence overpressure develops in the maikop formation and not in the layers below this overpressure was mainly generated by the relatively high sedimentation rate of 0 29 m ka 1 of the maikop formation at 33 9 20 5ma and an even higher sedimentation rate of 0 93 m ka 1 at 13 11 ma we estimate a maximum ratio of overpressure to vertical effective stress in hydrostatic conditions o f 0 62 at 5200 mbsf associated with an overpressure

effects of diagenesis and clays on compressional velocities in rocks experimental results at ultrasonic frequencies in brine or water saturated samples cut perpendicular to bedding demonstrate that compressional velocities vary linearly with porosity and volume fraction clay in detrital silicate rocks characterized by pores with low aspect ratios p wave velocity is more sensitive to porosity than clay content obeying the empirically derived expression vp 2 4c 8 6 5 8 at 800 bars confining pressure and 400 bars pore pressure where the units of vp are kilometers per second is the volume fraction pores and c is the volume fraction clay deviations from this equation are less than 2 with the exception of the high pore aspect ratio st peter sandstone which has a compressional velocity that is 17 higher than the predicted value the equation is insensitive to the chemical compostion of the dominant clay mineral and apparently insensitive to the location of the clay grains with respect to the mineral framework e g in free pore space or in contact zones between mineral grains of lower compressibilities

origin and accumulation of crude oils in triassic reservoirs of wuerhe fengnan area wfa in junggar basin nw china constraints from molecular and isotopic geochemistry and fluid inclusion analysis abstract the wuerhe fengnan area wfa in the junggar basin nw china has recently obtained exploration success these accumulations are characterized by oil from multiple source rocks with multiple stage accumulation however the origin of oils and their charging history have been controversial making it difficult to understand the general pattern of hydrocarbon accumulation here we reconstruct this process mainly based on molecular and isotopic geochemistry of hydrocarbons and comprehensive fluid inclusion analysis four conclusions were reached firstly oils in various regions came from different source rocks the oil in the fault zone was derived from the lower permian fengcheng formation p1f argillaceous dolomite source rocks in situ in wfa and or from mahu depression the oil in the slope area originated from the middle permian lower wuerhe formation p2w mudstone source rocks in the mahu depression secondly oil reservoirs in various regions were charged at different times three episodes of p1f sourced oil charging took place in triassic reservoirs in the fault zone which occurred at 230 ma 198 ma and 125 ma years ago respectively there are only two episodes of p2w sourced oil charging in the slope area namely 196 ma and 136 ma before present thirdly oil reservoirs in various regions have different hydrocarbon migration directions and mechanisms oils in the fault zone display obvious vertical migration characteristics hydrocarbons mainly migrated from lower structural positions to higher structural positions laterally in other words the hydrocarbons in the fault zone mainly migrated from southwest to northeast while the hydrocarbons in the slope area mainly migrated from southeast to northwest the oil migration in the fault zone is driven both by excessive formation pressure and buoyancy while that in the slope area is likely driven by buoyancy finally a comprehensive three stage oil migration and accumulation model of triassic reservoirs in wfa was established the first stage oil accumulation p1f sourced oils occurred during the middle triassic 230 ma which was concentrated only in the fault zone the second stage and third stage oil accumulation occurred during the early jurassic 200 ma and early cretaceous 140 120 ma respectively with the p1f sourced oils concentrated in the fault zone and the p2w sourced oils concentrated in the slope area in summary oil reservoirs in various regions fault zone and slope area were derived from different source rocks with different charging time and accumulation models

the elastic anisotrophy of shales shales constitute about 75 of the clastic fill sedimentary basins and have a decisive effect on fluid flow and seismic wave propagation because of their low permeability and anisotropic microstructure the elastic stiffnesses of a shale with partially oriented clay particles is expressed in terms of the coefficients w sub lmn in an expansion of the clay particle orientation distribution function in generalized legendre functions application is made to the determination of the anellipticity of shales for transverse isotrophy the anellipticity quantifies the deviation of the p wave slowness curve from an ellipse and is shown to depend on a single coefficient w sub 400 in the expansion of the clay particle orientation distribution function if w sub 400 is small the anellipticity may be neglected as is apparently the case for a near surface late tertiary shale studied by winterstein and paulson strongly aligned clay particles result in a positive value of w sub 400 and a positive anellipticity in agreement with the majority of the field measurements however less well ordered shales could have a significantly positive second moment w sub 200 but only a small positive or even negative value of w sub 400 for such shales the anellipticity would be small or negative despite amore preferred alignment of clay particles in the bedding plane numerical examples of clay particle orientation distribution functions leading to zero or negative anellipticity are given less

detection of overpressure zones and a statistical model for pore pressure estimation from well logs in the krishna godavari basin india abnormally high pressures measured by repeat formation tester rft and detected by well log data from 10 wells in the krishna godavari k g basin occur in the vadaparru shale of miocene and raghavapuram shale of early cretaceous age overpressures generated by disequilibrium compaction and pore pressures have been estimated using the conventional eaton sonic equation with an exponent of 3 0 the observed abnormal pore pressure gradient ranges from 11 85 to 13 10 mpa km whereas fracture pressure gradient varies from 17 40 to 19 78 mpa km the magnitude of vertical stress sv has a gradient from 21 00 to 23 10 mpa km the minimum horizontal principal stress sh magnitude is found to vary from 64 to 77 of the sv in normally pressured to overpressured sediments a multiple linear regression model with a squared multiple correlation coefficient r2 of 0 94 is proposed for pore pressure prediction from gamma ray density and sonic logs to focus on efficient drilling operations and to prevent borehole instability the statistical model has been calibrated with the rft data from five wells covering about 3400 sq km area of the onshore k g basin the model predicted pore pressure values are in close agreement with the actual rft data for another four wells including a well in the offshore k g basin hence the proposed regression model may be useful for predicting pore pressure from other well logs in the k g basin

significance of geopressure in predicting lithology maybe this is too late in the exploration program to emphasize this position we will argue that if you don t post geopressure on your seismic section then you are only interested in a structural interpretation not lithology to persuade you the interrelationship of geopressure to sand percentage rock type depth and depositional environment will be shown to correlate strongly to the velocity and density assigned to a particular lithology surprisingly this holds not only for seismic but also for potential fields

detecting high overpressure normal pressure is pore fluid pressure that equals the hydrostatic pressure of a column of formation water extending to the surface overpressure is pore fluid pressure greater than normal pressure however no standard definition exists for what constitutes high overpressure what can be said is that high overpressure often means trouble for an explorationist it could mean blown reservoir seals for a driller it could mean excessive time spent fighting formation fluid influxes and or drilling fluid losses

mechanical behaviour of fine grained sediments experimental compaction and three dimensional constitutive model abstract the usual undimensional description of deformations of sediments based on a phenomenological relationship between porosity and the vertical effective stress does not give information about the horizontal stress and moreover is irrelevant for sedimentary structures in which deformation process is not only vertical modelling three dimensional deformation processes in sedimentary basins requires a three dimensional mechanical constitutive model for sediments a special dometric cell was conceived in g 3s this cell allows the measurement of the lateral stress during dometric compaction and so enables us to elaborate a three dimensional model of mechanical behaviour four varieties of fine grained sediments were studied by this cell in a large scale of strain and stresses the modified cam clay model was used for fitting the experimental data and it was shown that this model can reproduce the mechanical compaction of sediments up to 50 mpa of vertical effective stress about 3 km burial depth if its parameters are deduced from dometric zero lateral strain data

estimation of biot s effective stress coefficient from well logs effective stress governs the mechanical response of rock formations to variations in stress and pore pressure which affect wellbore stability and reservoir integrity during drilling and production biot s coefficient is employed to calculate effective stresses from total stress and pore pressure therefore the measurement of biot s coefficient becomes crucial however the laboratory measurement of biot s coefficient is expensive and laborious this paper presents three methods for computing biot s coefficient using logging data the first method calculates biot s coefficient using the existing empirical correlations between porosity and biot s coefficient the second and third methods calculate biot s coefficient using dynamic rock and solid bulk modulus computed using rock and solid wave velocities respectively however the second and third methods calculate the necessary solid wave velocities in different ways the second method calculates solid shear and compressive velocities vs and vp using a newly developed correlation between the differential pressure porosity and wave velocity of sandstone the third method calculates solid wave velocities based on the significant finding that the vp vs ratio with respect to the s wave velocity is constant for sediments including highly compacted sand case studies were undertaken using logging data from the gulf coast gas wells it was found that biot s coefficient calculated using the first method was highly dependent on the chosen relation while the coefficients calculated using the second and third methods were related to well logs results from the third method show that biot s coefficient deflects to higher values in situations where gamma ray surveys read low api values this is in agreement with the phenomenon that rocks with a smaller api should have lower a clay content and bigger value of biot s coefficient therefore the third method is more reliable and also requires fewer input parameters

geological and geochemical characterization of the lower cretaceous pearsall formation maverick basin south texas a future shale gas resource as part of an assessment of undiscovered hydrocarbon resources in the northern gulf of mexico onshore mesozoic section the u s geological survey usgs evaluated the lower cretaceous pearsall formation of the maverick basin south texas as a potential shale gas resource wireline logs were used to determine the stratigraphic distribution of the pearsall formation and to select available core and cuttings samples for analytical investigation samples used for this study spanned updip to downdip environments in the maverick basin including several from the current shale gas producing area of the pearsall formation the term shale does not adequately describe any of the pearsall samples evaluated for this study which included argillaceous lime wackestones from more proximal marine depositional environments in maverick county and argillaceous lime mudstones from the distal lower cretaceous shelf edge in western bee county most facies in the pearsall formation were deposited in oxygenated environments as evidenced by the presence of biota preserved as shell fragments and the near absence of sediment laminae which is probably caused by bioturbation organic material is poorly preserved and primarily consists of type iii kerogen terrestrial and type iv kerogen inert solid bitumen with a minor contribution from type ii kerogen marine based on petrographic analysis and pyrolysis carbonate dominates the mineralogy followed by clays and quartz the low abundance and broad size distribution of pyrite are consistent with the presence of oxic conditions during sediment deposition the pearsall formation is in the dry gas window of hydrocarbon generation mean random vitrinite reflectance values ro 1 2 2 2 and contains moderate levels of total organic carbon average 0 86 wt which primarily resides in the inert solid bitumen solid bitumen is interpreted to result from in situ thermal cracking of liquid hydrocarbon generated from original type ii kerogen that was prevented from expulsion and migration by low permeability the temperature of maximum pyrolysis output tmax is a poor predictor of thermal maturity because the pyrolysis s2 peaks from rock eval analysis are ill defined vitrinite reflectance values are consistent with the dry gas window and are the preferred thermal maturity parameter a maverick basin pearsall shale gas assessment unit was defined using political and geologic boundaries to denote its spatial extent and was evaluated following established usgs hydrocarbon assessment methodology the assessment estimated a mean undiscovered technically recoverable natural gas resource of 8 8 tcf of gas and 3 4 and 17 8 tcf of gas at the f95 and f5 fractile confidence levels respectively significant engineering challenges will likely need to be met in determining the correct stimulation and completion combination for the successful future development of undiscovered natural gas resources in the pearsall formation

sediment compaction and fluid migration in the makran accretionary prism the makran continental margin in the gulf of oman forms the seaward extremity of an accretionary sediment prism which extends several hundred kilometers inland a recently acquired multichannel seismic reflection profile shot across the margin imaged the structure of the prism in greater detail than was previously possible and allowed us to investigate the relationship between deformation and pore fluid motion in the region velocity analyses of the common midpoint gathers reveal a marked change in velocity structure at the toe of the accretionary wedge as seen in previous sonobuoy wide angle data accreted sediments show significantly higher vertical velocity gradients than those of sediments entering the prism this change is interpreted as due to porosity reduction as pore fluids are squeezed out of the compacting sediment a prominent bottom simulating reflector appears 500 800 m beneath the sea bed several lines of evidence suggest that this reflector represents the base of a gas hydrate zone underlain by widespread free gas which may be exsolved from pore water migrating from deep within the sediment pile up permeable fault planes imaged in the profile the hydrate reflector appears to shallow in the region of some faults suggesting a temperature anomaly due to the presence of warm pore fluids a heat flow profile derived from the depth of the hydrate reflector does not show the expected landward decrease as the sediment pile thickens simple thermal modeling suggests that advective heat flow within the prism may explain this anomaly the inferred presence of overpressured pore fluids in the makran suggests that accreted sediments have a low permeability the seismic evidence suggests a two stage compaction process with rapid initial dewatering through intergranular permeability as sediment enters the prism followed by a buildup of pore pressure as the permeability decreases and fluid migration is restricted to fault zones

frequency dependent attenuation analysis of ground penetrating radar data in the early 1990s it was established empirically that in many materials ground penetrating radar gpr attenuation is approximately linear with frequency over the bandwidth of a typical pulse further a frequency independent q parameter characterizes the slope of the band limited attenuation versus frequency curve here i derive the band limited q function from a first order taylor expansion of the attenuation coefficient this approach provides a basis for computing q from any arbitrary dielectric permittivity model for cole cole relaxation i find good correlation between the first order q approximation and q computed from linear fits to the attenuation coefficient curve over two octave bands the correlation holds over the primary relaxation frequency for some materials this relaxation occurs between 10 and 200 mhz a typical frequency range for many gpr applications frequency dependent losses caused by scattering and by the commonly overlooked problem of frequency dependent reflection

evolution of the se asian continent from u pb and hf isotopes in single grains of zircon and baddeleyite from large rivers to better understand the evolution of the se asian continent 235 single zircon and baddeleyite grains from large rivers were dated by the u pb chronometer and 148 of these grains were simultaneously analyzed for hf isotopes this combination of methods is applied to sand samples from the mekong irrawaddy salween and red rivers which sample the continent on the plate scale u pb dates and hf isotopic signatures of these grains resolve the age spectra of crust and they elucidate source characteristics of magmas involved in continental growth and recycling for sufficient statistical coverage more than 80 of zircons and baddeleyites from each river sample were analyzed representing an erosion area of about 1 6 106 km2 our analyses reveal five different proterozoic crustal growth events occurring at about 2 5 ga 2 3 ga 1 9 ga 1 1 ga and 0 8 ga however none of these basement terrains is exposed in se asia being entirely covered by phanerozoic sediments the data also substantiate granitoid magmatism during the caledonian indosinian and himalayan orogenies initial hf isotope signatures ehfi obtained for grains lying less than 15 discordant in the concordia diagram range between 13 3 and 16 7 plotting in both the domains of strongly lile depleted and enriched reservoirs relative to a chondritic evolution of the mantle approximately half of the grains crystallized in magmas derived from significantly depleted mantle sources and about 18 formed in magmas showing nearly chondritic signatures ehfi 1 37 to 1 59 27 grains the remaining grains yield strongly negative ehfi documenting the incorporation of important amounts of melts generated from crust formed during the paleoproterozoic events at 2 3 and 1 9 ga which seem to have produced the dominant mass of the se asian continent all younger orogenic cycles are characterized by substantial melting of continental material which probably dominate over juvenile crust addition an exception are the irrawaddy terrains where substantial mantle input characterizes post collisional magmatism since 50 ma

estimation of formation fluid pressure using high resolution velocity from inversion of seismic data and a rock physics model based on compaction and burial diagenesis of shales accurate assessment and prediction of formation fluid pressure and fracture gradient form an essential part of the planning process during various phases of hydrocarbon exploration and exploitation these include regional basin analysis and basin high grading prospect identification analysis and drilling campaign to lift hydrocarbons while the literature is full of activities in this field that are linked to the need for drilling safety by providing help with casing and mud weight program and quite justifiably so very little discussion addresses another and very important need seal integrity and trap configuration analysis

predicting pore pressure in active fold thrust systems an empirical model for the deepwater sabah foldbelt abstract measurements related to mudrock shale and siltstone porosity such as acoustic velocity density or electrical resistivity have traditionally been used to predict pore pressures in extensional stress settings the underlying assumption is that burial and vertical effective stress ves which is the overburden minus the pore pressure controls the compaction of these rocks through porosity loss the dataset presented here compares ves and acoustic velocity of similar composition mudrocks in both an extensional and a compressional stress setting in the extensional stress environment the mudrocks follow a typical compaction trend with a porosity loss and increase in acoustic velocity that can be related to ves in an active fold thrust belt the compressive stresses further reduce the porosity and increase the acoustic velocity of the mudrocks first a layer parallel shortening compacts sediments beyond what is observed for the ves this additional compaction is further enhanced near thrust faults and in anticlinal forelimbs presumably due to additional shear stress in these areas the mudrocks located in folds that are buried by additional sedimentation do not compact again until the tectonic compaction is overridden by enough new burial after that the mudrocks follow the observed extensional setting compaction trend in the fold thrust belt the observed reduction in porosity by stresses other than burial leads to an under prediction of pore pressure using traditional methods to account for this we present a correction that can be applied to the acoustic velocity or porosity using two parameters a proximity to thrust faults and anticlinal forelimbs and b the amount of burial after fold formation with these corrections the extensional velocity ves compaction trend can be used to accurately predict pore pressure within the active fold thrust belt the correction is calibrated with well data and is empirical none the less it is a first step toward understanding the magnitudes of the compressive lateral stresses involved in generating the observed porosity loss within the fold thrust belt

investigation of present day in situ stresses and pore pressure in the south cambay basin western india implications for drilling reservoir development and fault reactivation abstract this work presents the assessment of present day stresses and pore pressures in a prolific onshore hydrocarbon bearing field located in the southern cambay basin western india through the development of a comprehensive geomechanical model a c quality wellbore breakouts inferred from the available four arm caliper logs and anisotropy analyses of dipole shear sonic logs indicate a ne n40 e to n50 e azimuth for maximum horizontal stress shmax pore pressure characterisation reveals mild overpressure in the lower eocene shale caused by disequilibrium compaction resulting from high sedimentation rates vertical stress sv was derived from density logs and a poroelastic strain model was employed to quantify the minimum shmin and maximum horizontal stress components shmax being later validated with leak off tests based on the relative magnitudes of three principal in situ stress components post rift strata upper eocene and younger reveal a normal faulting regime sv shmax shmin whereas a normal fault to strike slip faulting shmax sv shmin transition is observed in the syn rift unit lower eocene and older the mohr coulomb rock failure criterion was utilised to depict the shear failure gradient to prevent wellbore instability and results were validated with caliper logs we have also analysed the fault reactivation potential at reservoir level using frictional fault theory and stress polygons the results indicate that a minimum of 31 increase in pore pressure by fluid injection and hydraulic fracturing treatment can cause shear slippage of critically oriented faults resulting in induced seismicity our study has helped to understand the interplay between stress states and pore fluid pressure and their impact on reservoir development drilling and completion design and fault stability analysis in any given oil and gas field

experimental compaction of na montmorillonite clay mixed with crude oil and seawater abstract the mechanism of primary migration of generated petroleum from source rocks to reservoirs is still poorly understood to investigate some of problems involved in primary migration of oil na montmorillonite clay mixed with seawater and crude oil was compacted for 25 days under a pressure of 1000 kg cm 2 and a temperature of 60 c the amount of expelled liquid from the clay was large at the early stage of compaction and decreased gradually as compaction progressed the proportion of oil in the expelled liquid gradually increased with increasing time of compaction porosity of the compacted sample decreased from 81 of original clay to 26 this may indicate that the primary migration of oil from source to reservoir rocks will occur chiefly during the late compaction stage 10 30 by the effect of capillary pressure of continuous oil flow

inverse q filter for seismic resolution enhancement a principal limitation on seismic resolution is the earth attenuation or q effect including the energy dissipation of high frequency wave components and the velocity dispersion that distorts seismic wavelets an inverse q filtering procedure attempts to remove the q effect to produce high resolution seismic data but some existing methods either reduce the s n ratio which limits spatial resolution or generate an illusory high resolution wavelet that contains no more subsurface information than the original low resolution data in this paper seismic inverse q filtering is implemented in a stabilized manner to produce high quality data in terms of resolution and s n ratio stabilization is applied to only the amplitude compensation operator of a full inverse q filter because its phase operator is unconditionally stable but the scheme neither amplifies nor suppresses high frequencies at late times where the data contain mostly ambient noise the latter property makes the process invertible differ

p wave traveltime tomography for a seismic characterization of black shales at shallow depth on bornholm denmark abstractblack shales are organic rich rocks with the potential to contain oil or gas on the danish island bornholm lower palaeozoic black shales at shallow depth 50 m have a high maturity and a high total organic carbon content we carried out seismic measurements in the southern part of bornholm in october 2010 along two profiles to study the seismic properties of the shallow lying black shales the profiles were located as near as possible to existing borehole locations for geologic control and were arranged perpendicular to each other to allow an estimate of the 3d structure of the subsurface we analyzed the data using p wave traveltime tomography and obtained 2d p wave velocity models with a good resolution up to a depth of 100 m based on borehole information and the geologic setting three formations can be identified in the tomography models a the komstad limestone formation with a thickness of about 4 m b the alum shale formation with a total thickness of 33 m and c the laesa forma

evolution of structural and physical parameters of clays during experimental compaction abstract to provide a better understanding of sedimentary basin geological history it is important to describe correctly the evolution of the various physical mechanical and hydraulic properties of clayey rocks as a function of burial depth as a contribution to this field a programme of experimental studies on reworked clay samples compacted under various load pressures in oedometric conditions has been set up the evolution of samples under compaction was followed with microscopic and macroscopic measurements in a specially designed oedometric cell samples are compacted under different total stresses from 0 1 to 50 mpa in this cell cylindrical cores are submitted to progressive loading from both ends under controlled pore pressure conditions the symmetrical loading allows more even deformation about the midplane of the sample this device allows the evolution of hydraulic pressure radial stress displacement and expelled pore fluid to be followed as a function of time in a first step kaolinite was chosen because it retains a high permeability compared with other clays such as illite or smectite which allows compaction tests to be performed within a few days a complete set of measurements was performed after the tests these measurements are 1 micro structures investigated by means of transmission electron microscopy tem mercury porosimetry water removal under low water vapour pressure granulometry and specific area measured by ethylene glycol adsorption and 2 various physical parameters measured including hydraulic conductivity and thermal conductivity tem gives an understanding of the arrangement of particles it was found that each particle is composed of several crystal units each unit formed by 25 individual kaolinite layers during compaction these particles remain undeformed but are rotated the angular distribution of grain orientation is a function of the applied effective stress this reorientation is in agreement with the observed decrease in porosity and pore size it also explains the occurrence of a strong anisotropy in the thermal conductivity and hydraulic permeability the combination of these experimental results allows a qualitative and quantitative understanding of the behaviour of kaolinite with respect to parameters such as permeability porosity mechanical and thermal properties the knowledge of which are necessary for basin modelling

origin of overpressure and pore pressure prediction in the baram province brunei accurate pore pressure prediction is critical in hydrocarbon exploration and is especially important in the rapidly deposited tertiary baram delta province where all economic fields exhibit overpressures commonly of high magnitude and with narrow transition zones a pore pressure database was compiled using wireline formation interval tests drillstem tests and mud weights from 157 wells in 61 fields throughout brunei overpressures are observed in 54 fields both in the inner shelf deltaic sequences and in the underlying prodelta shales porosity vs vertical effective stress plots from 31 fields reveal that overpressures are primarily generated by disequilibrium compaction in the prodelta shales but have been generated by fluid expansion in the inner shelf deltaic sequences however the geology of brunei precludes overpressures in the inner shelf deltaics being generated by any conventional fluid expansion mechanism e g kerogen to gas maturation and we propose that these overpressures have been vertically transferred into reservoir units via faults from the prodelta shales sediments overpressured by disequilibrium compaction exhibit different physical properties to those overpressured by vertical transfer and hence different pore pressure prediction strategies need to be applied in the prodelta shales and inner shelf deltaic sequences sonic and density log data detect overpressures generated by disequilibrium compaction and pore pressures are accurately predicted using an eaton exponent of 3 0 sonic log data detect vertically transferred overpressures even in the absence of a porosity anomaly and pore pressures are reasonably predicted using an eaton exponent of 6 5

the role of shear and tensile failure in dynamically triggered landslides summary dynamic stresses generated by earthquakes can trigger landslides current methods of landslide analysis such as pseudo static analysis and newmark s method focus on the effects of earthquake accelerations on the landslide mass to characterize dynamic landslide behaviour one limitation of these methods is their use mohr coulomb failure criteria which only accounts for shear failure but the role of tensile failure is not accounted for we develop a limit equilibrium model to investigate the dynamic stresses generated by a given ground motion due to a plane wave and use this model to assess the role of shear and tensile failure in the initiation of slope instability we do so by incorporating a modified griffith failure envelope which combines shear and tensile failure into a single criterion tests of dynamic stresses in both homogeneous and layered slopes demonstrate that two modes of failure exist tensile failure in the uppermost meters of a slope and shear failure at greater depth further we derive equations that express the dynamic stress in the near surface in the acceleration measured at the surface these equations are used to approximately define the depth range for each mechanism of failure the depths at which these failure mechanisms occur suggest that shear and tensile failure might collaborate in generating slope failure

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

effective stress coefficient in shales and its applicability to eaton s equation pore pressure within formations determines the mud weight required to build a balancing fluid pressure downhole an improper understanding of the subsurface geology and the formation pressures may result in fracturing the formation if the mud weight is too high in contrast if mud weight is too low then formation fluids can flow into the well potentially leading to well blowouts if not controlled complex geological settings make pore pressure prediction difficult and often inaccurate due to uncertainty in pressure generating mechanisms estimation of proper pore pressures is necessary for designing stable holes and an optimized casing program in exploration knowledge of pore pressures can assist in assessing seal effectiveness and in high grading reservoir sweet spots it also provides useful calibration information for basin modeling hence it becomes very important to accurately predict pore pressures

relationship between p and s wave velocities and geological properties of near surface sediments of the continental slope of the barents sea seismic velocities v p and v s of compressional p and shear s waves are important parameters for the characterization of marine sediments with respect to their sedimentological and geotechnical properties p and s wave velocity data of near surface marine sediments upper 9 m of the continental slope of the barents sea are analysed and correlated to sedimentological and geotechnical properties the results show that the s wave velocity is much more sensitive to changes in lithology and mechanical properties than the p wave velocity which is characterized by a narrow range of values the correlation coefficients between s wave velocity and silt and clay content wet bulk density porosity water content and shear strength are higher than 0 5 while the correlation coefficients of p wave velocity and the same parameters are always lower than 0 4 although the relationship between v s and clay content has been widely described the data show that v s is better correlated with silt content than with clay content for the sediments of the area investigated however they show different trends while v s increases with increasing clay content it decreases with increasing silt content

understanding geophysical responses of shale gas plays unconventional resources such as shale gas are becoming increasingly important exploration and production targets to understand the geophysical responses of shale gas plays we use a rock physics relationship which is constrained with geology and formation evaluation analysis to calculate effective properties such as impedance and vp vs numerical studies suggest that in situ rock para meters such as mineral composition e g clay quartz and calcite and toc as well as the interaction among them can significantly influence the geophysical responses of the organic rich rocks thus providing the basis for the geophysical characterization of shale gas plays

scale dependence of textural alignment in shales quantified using electron microscopy abstract textural alignment is the primary cause of anisotropy associated with the permeability and mechanical and acoustic properties of rocks although particle alignment in shales is known to be influenced by burial depth mineralogical composition and diagenetic history understanding how these influence image based measures of compaction at the micrometer to nanometer scale is not well understood here we use a novel method which combines scanning electron microscopy and image analysis algorithms to quantify clay alignment in sedimentary rocks for a given field of view the alignment intensity in shales from the podhale basin in poland is positively correlated with clay content based on image analysis however our analysis also shows that the intensity is strongly dependent on the spatial scale of imaging as magnification increases and the field of view in the sem images decreases the alignment intensity drops therefore in images with small fields of view clay alignment is determined by the presence of localized equant silicate mineral grains which effectively hinder the alignment process at the micrometer scale by contrast in images with larger fields of view alignment intensity is determined by the overall compaction state we also show that when the field of view is constant alignment intensity decreases with pixel density and we suggest a range of operating parameters required for obtaining optimum values for alignment intensity from sem images of shales

the validity of generic trends on multiple scales in rock physical and rock mechanical properties of the whitby mudstone united kingdom abstract finding generic trends in mechanical and physical rock properties will help to make predictions of the rock mechanical behaviour of shales understanding the rock mechanical behaviour of shales is important for the successful development of unconventional hydrocarbon reservoirs this paper presents the effect of heterogeneities in mineralogy and petrophysical properties on the validity of generic trends on multiple scales in rock mechanical and rock physical properties of the whitby mudstone rock mechanical laboratory experiments have been performed on whitby mudstone samples from multiple outcrops within five kilometres laterally in order to investigate the heterogeneity and possible trends on an outcrop scale unconfined compression tests and acoustic measurements have been conducted to obtain the rock mechanical properties including rock strength young s modulus poisson s ratio and velocity anisotropy the rock physical properties including mineralogy porosity and matrix density were measured using x ray fluorescence and helium pycnometry various methodologies have been applied to the resultant data in order to derive different brittleness indices significant heterogeneity in rock mechanical and rock physical properties is present on an outcrop scale there is no obvious correlation between mineral content and rock mechanical properties on an outcrop scale in the whitby mudstone comparison with shales from different basins show however correlations between composition and elastic properties the presence of significant heterogeneities on an outcrop scale and between shales from different basins make it difficult to find generic trends in rock physical and rock mechanical properties

estimating snow water equivalent over long mountain transects using snowmobile mounted ground penetrating radar abstractthe water balance in alpine watersheds is dominated by snowmelt which provides infiltration recharges aquifers controls peak runoff and is responsible for most of the annual water flow downstream accurate estimation of snow water equivalent swe is necessary for runoff and flood estimation but acquiring enough measurements is challenging due to the variability of snow accumulation ablation and redistribution at a range of scales in mountainous terrain we have developed a method for imaging snow stratigraphy and estimating swe over large distances from a ground penetrating radar gpr system mounted on a snowmobile we mounted commercial gpr systems 500 and 800 mhz to the front of the snowmobile to provide maximum mobility and ensure that measurements were taken on pristine snow images showed detailed snow stratigraphy down to the ground surface over snow depths up to at least 8 m enabling the elucidation of snow accumulation and redistribution processes we estimated snow density an

multi channel 2d seismic constraints on pore pressure and vertical stress related gas hydrate in the deep offshore of the mahanadi basin india abstract estimation of pore pressure and in situ vertical stress magnitude is essential for understanding the geomechanical behavior of the gas hydrate sediments in deep offshore of the mahanadi basin the basin located at northern side of eastern continental margin of india ecmi contains gas hydrate in clay silt sediments the pore pressure and vertical stress are mapped on two 2d multi channel seismic data of lines mh 38a and mh 38b with aid of information of three wells namely nghp 01 19 nghp 01 09 and nghp 01 08 initially the coefficients of best fit curve have been computed from velocity effective stress plot for the individual wells and applied on the seismic velocity to transform into the effective stress the vertical stress has been computed from both the seismic and log data therefore the pore pressure is predicted by subtracting the effective stress from the vertical stress the pore pressure have been mapped in gas hydrate stability zone ghsz and sediments below bottom simulating reflector bsr the pore pressure and vertical stress gradient are 10 11 mpa km and 10 67 mpa km respectively the pore pressure and vertical stress from seismic data are closely matched at well location with excellent goodness of fit r2 varying from 0 82 to 0 95 normal pressure is observed in the gas hydrate bearing sediments but slightly high pressures are noticed below the bsr indicating presence of free gas the pore pressure from seismic data will guide drillers for choosing the mud weight during well drilling and casing optimizing in other part of deep offshore in the mahanadi basin

shear wave velocity anisotropy in sedimentary rocks a laboratory study a systematic laboratory study of shear wave velocity anisotropy in sedimentary rocks has been carried out as a function of both hydrostatic and uniaxial stress the presence of shear wave velocity anisotropy in sedimentary rocks was confirmed by transmitting a polarized shear wave in a rock sample and receiving a signal on an orthogonally polarized receiver the magnitude of the observed velocity anisotropy is dependent upon the magnitude and nature of the applied stress and the lithology of the rock sample shales exhibit significant velocity anisotropy independent of both uniaxial and hydrostatic stress which suggests the presence of preferentially aligned minerals sandstones also exhibit significant velocity anisotropy but the anisotropy is strongly dependent upon the stress hydrostatic stress was found to diminish the velocity anisotropy and uniaxial stress was found to enhance it this implies the presence of preferentially oriented cracks limestones exhibit weak velocity anisotropy these laboratory observations may be helpful in in situ identification of lithology

assessment of β the compression coefficient of mudstones and its relationship with detailed lithology abstract the mechanical compaction of soils and fine grained sediments is commonly described in soil mechanics by a relationship between void ratio and effective stress the relationship is defined by two parameters derived from the slope of the line relating void ratio and log effective stress and e the void ratio at a chosen effective stress e g 100 kpa and e are strongly correlated and are related to the atterburg liquid limit which is itself related in a general way to the grain size and mineralogy of the sediment in general finer grained sediments have higher initial void ratios and compact faster than coarser sediments porosity depth trends for mudstones in sedimentary basins are therefore strongly influenced by lithology steps or changes in the slope of porosity depth trends can be caused by lithological change rather than changes in the pressure regime a method is presented to evaluate for mechanically compacted mudstones using porosities determined from the density log fdc and based on the relationship between effective stress and void ratio developed in soil mechanics the method allows one to obtain rapidly approximate values for materials for which it is essentially impossible to obtain compaction parameters experimentally calculated values for mudstones in wells 8 3 2 and 30 2 1 on the norwegian margin vary between 0 2 and 0 65 the values correlate positively with the clay particle content of the mudstones which we have determined for 50 mudstone samples from the same wells the strong link between mudstone lithology and suggests that a downhole log may be a useful way to visualize downhole variations in mudstone lithology the log also shows how lithology affects the rate of porosity loss with depth or effective stress for example porosity in mudstones within both wells 8 3 2 and 30 2 1 is essentially constant over 700 m sections of normally pressured mudstones the log and grain size data indicate that this reflects changes in the lithological character and of the muds and not as commonly inferred a change in the pressure regime

predrill prediction of subsalt pore pressure from seismic impedance abstract a target oriented predrill pore pressure prediction method using seismically estimated acoustic impedance is applied to recently acquired and processed dual coil data in the green canyon and walker ridge areas of the gulf of mexico three deepwater subsalt wells are used in the study one was used as a calibration well and the other two were used as blind wells for comparing prediction results with the measured pore pressure and mud weight data all three wells are in the green canyon area penetrating thick salt bodies a new seismic inversion method is used for inversion of seismic impedance the pore pressure method uses a direct transform of the inverse of acoustic impedance with two adjustable parameters the optimization of the parameters is done through an iterative process to match the pore pressure gradient obtained from the well acoustic impedance with those of pore pressure measurements and mud weights within a tolerable range of those data for the calibration well the optimized p

estimation of the lateral correlation structure of subsurface water content from surface based ground penetrating radar reflection images 1 over the past decade significant interest has been expressed in relating the spatial statistics of surface based reflection ground penetrating radar gpr data to those of the imaged subsurface volume a primary motivation for this work is that changes in the radar wave velocity which largely control the character of the observed data are expected to be related to corresponding changes in subsurface water content although previous work has indeed indicated that the spatial statistics of gpr images are linked to those of the water content distribution of the probed region a viable method for quantitatively analyzing the gpr data and solving the corresponding inverse problem has not yet been presented here we address this issue by first deriving a relationship between the 2 d autocorrelation of a water content distribution and that of the corresponding gpr reflection image we then show how a bayesian inversion strategy based on markov chain monte carlo sampling can be used to estimate the posterior distribution of subsurface correlation model parameters that are consistent with the gpr data our results indicate that if the underlying assumptions are valid and we possess adequate prior knowledge regarding the water content distribution in particular its vertical variability this methodology allows not only for the reliable recovery of lateral correlation model parameters but also for estimates of parameter uncertainties in the case where prior knowledge regarding the vertical variability of water content is not available the results show that the methodology still reliably recovers the aspect ratio of the heterogeneity

spectral element modelling of fault plane reflections arising from fluid pressure distributions the presence of fault plane reflections in seismic images besides indicating the locations of faults offers a possible source of information on the properties of these poorly understood zones to better understand the physical mechanism giving rise to fault plane reflections in compacting sedimentary basins we numerically model the full elastic wavefield via the spectral element method sem for several different fault models using well log data from the south eugene island field offshore louisiana we derive empirical relationships between the elastic parameters e g p wave velocity and density and the effective stress along both normal compaction and unloading paths these empirical relationships guide the numerical modelling and allow the investigation of how differences in fluid pressure modify the elastic wavefield we choose to simulate the elastic wave equation via sem since irregular model geometries can be accommodated and slip boundary conditions at an interface such as a fault or fracture are implemented naturally the method we employ for including a slip interface retains the desirable qualities of sem in that it is explicit in time and therefore does not require the inversion of a large matrix we perform a complete numerical study by forward modelling seismic shot gathers over a faulted earth model using sem followed by seismic processing of the simulated data with this procedure we construct post stack time migrated images of the kind that are routinely interpreted in the seismic exploration industry we dip filter the seismic images to highlight the fault plane reflections prior to making amplitude maps along the fault plane with these amplitude maps we compare the reflectivity from the different fault models to diagnose which physical mechanism contributes most to observed fault reflectivity to lend physical meaning to the properties of a locally weak fault zone characterized as a slip interface we propose an equivalent layer model under the assumption of weak scattering this allows us to use the empirical relationships between density velocity and effective stress from the south eugene island field to relate a slip interface to an amount of excess pore pressure in a fault zone

experimental mechanical compaction of clay mineral aggregates changes in physical properties of mudstones during burial dry and brine saturated clay aggregates ranging from pure smectite to pure kaolinite were compacted in the laboratory experiments were conducted by increasing vertical effective stress up to 50 mpa to study the changes in physical properties of mudstones during burial the results suggest that the physical properties porosity density acoustic velocity etc of mudstones vary greatly with increasing effective stress clay mineralogy and fluid content kaolinite aggregates are much more compressible than those composed of smectite brine saturated clay mixtures are much more compressible than dry clay mixtures brine may soften and lubricate the clay matrix compared to dry clays resulting in higher compressibility in the brine saturated state the lesser degree of compaction of dry smectite compared to dry kaolinite aggregates can be explained by the differences in grain size as kaolinitic clays have much larger grains than smectitic clays the extremely fine grained nature of smectite implies that the imposed vertical stress is distributed over a very large number of grain contacts so that the force per contact area is very low in smectite compared to that in coarse grained kaolinite at 20 mpa effective stress corresponding to about 2 km burial depth with hydrostatic pore pressure brine saturated pure kaolinite compacted to 20 porosity while pure smectite retained 41 porosity brinesaturated clay mixtures show higher vp and lower vs than dry clay mixtures a pronounced difference in vs was observed among the brinesaturated clay mixtures the lowest vs as a function of vertical effective stress was found for pure smectite for a given porosity value smectitic clays have higher velocities and elastic moduli than the kaolinitic clays the vp vs ratio is significantly higher in smectite than in kaolinite aggregates treating mudstones as a uniform class of rocks introduces significant errors in estimates of physical properties which are strongly affected by the clay mineralogy grain size the amount of other minerals present and fluid content our results have implications for well log interpretation and mudstone and shale property determinations from seismic data at shallow burial depth o 2k m 801c above depths where significant chemical compaction takes place r 2007 elsevier ltd all rights reserved

subsurface radar propagation deconvolution the frequency dependence of attenuation is typically far greater for subsurface radar waves than for seismic waves since this frequency dependence causes the subsurface radar pulse shape to change as it propagates through the earth conventional wavelet deconvolution techniques are often inadequate to reconstruct the earth s reflectivity series the application of a time variant filter that undoes the effect of frequency dependent attenuation can substantially improve the resolution of subsurface radar data this filter is minimum phase with amplitude characteristics equal to the inverse of the attenuation function of the medium investigated preliminary tests on data from surveys over a water tank an underground mine stope and fractured granite suggest that good results can also be achieved by assuming attenuation is linearly proportional to frequency similar to a constant q model

book reviewseismic migration imaging of acoustic energy by wavefield extrapolation a theoretical aspects a j berkhout developments in solid earth geophysics 14a elsevier amsterdam 1982 2nd revised

experimental laboratory determination of the dynamic elastic properties of wet drained shales the ultrasonic anisotropic elastic properties of drained saturated shales were measured as a function of confining pressure two shales were characterized in this study a jurassic outcrop shale retrieved under the sea in a saturated state and a kimmeridge clay shale cut from a north sea borehole both shales were highly anisotropic both texturally as revealed by scanning electron microscopy analysis and elastically as measured ultrasonically in the laboratory the strongest anisotropy was seen in the kimmeridge clay shale where up to 38 compressional wave anisotropy thomsen s parameter e and up to 58 shear wave anisotropy thomsen s parameter were observed in addition for both shales e and were found to decrease as a function of increasing confining pressure with the pore pressure drained to atmosphere while the anellipticity deviation of the slowness surfaces from ellipses was found to be positive and decreased as a function of increasing confining pressure accompanying these changes in elastic properties was a decrease in porosity with increasing confining pressure from 10 5 to 8 5 for the jurassic shale the decrease in overall anisotropy of the shales with increasing confining pressure was found to be consistent with theoretical modeling of shale properties where the shale anisotropy and anellipticity were predicted to decrease as a function of decreasing fluid filled porosity

investigation into the use of 2d elastic waveform inversion from look ahead walk away vsp surveys pore pressure in sediments beneath salt in the gulf of mexico varies widely creating a potentially dangerous and difficult drilling challenge estimating elastic parameters of sediments beneath salt is key to the prediction of pore pressure and reducing the drilling risk in exiting the base of the salt in this paper we investigate the ability of 2d waveform inversion to recover the elastic parameters in the sedimentary layer beneath the salt from a walk away vsp vertical seismic profile carried out with the receivers in the salt with the objective of estimating pore pressure at the base of the salt to be estimated using traditional methods we propose an effective method for performing the inversion and apply this method to a blind test of a large and realistic synthetic dataset to facilitate the design of a vsp survey suitable to this type of inversion we also present an analysis into the effects of the receiver array receiver spacing it is shown that the resulting velocity estimates are sufficiently accurate to predict the pore pressure within the limits required for drilling

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

formation pressure modeling in the baiyun sag northern south china sea implications for petroleum exploration in deep water areas abstract the baiyun sag lies in the deep water area of the pearl river mouth basin it is the largest and deepest sag in the northern south china sea with the highest hydrocarbon potential the pressure distribution and pressure evolution of the baiyun sag have been explained by combining analysis of measured pressure data prediction of overpressure using the seismic velocity volume and two dimensional basin modeling today shallow formations are mainly normally pressured but the deep enping and wenchang formations are over pressured rapid sedimentation and hydrocarbon generation are two mechanisms that lead to compaction disequilibrium and subsequent overpressure generation in the baiyun sag the former effect being considered more important than the latter the multiple identified episodes of overpressure release through the basin history allows the conclusion to be made that rapid mudstone sedimentation and hydrocarbon generation are considered to be the factors leading to overpressure generation and preservation while fault activity is considered to be a factor leading to overpressure release two major overpressure release episodes the baiyun event 23 ma and the dongsha event 10 ma are considered to have been important in allowing deep over pressured hydrocarbon fluids to migrate into shallow normally pressured formations and accumulate the primary pathways for migration are interpreted as being directions where pressure reduced fastest and this being linked to faulting related to tectonic events

pore pressure distribution of a mega splay fault system in the nankai trough subduction zone insight into up dip extent of the seismogenic zone we use the pore pressure distribution predicted from a waveform tomography wt velocity model to interpret the evolution of the mega splay fault system in the nankai trough off kumano japan to map pore pressure around the mega splay fault and plate boundary decollement we integrate the high resolution wt velocities with laboratory data and borehole well log data using rock physics theory the predicted pore pressure distribution shows that high pore pressures close to lithostatic pressure along the footwall of the mega splay fault extend seaward to the trough region and the normalized pore pressure ratio is nearly constant over that extent this continuity of the overpressured zone indicates that a coseismic rupture can potentially propagate nearly to the trough axis we interpret a high pressure belt within an accretionary wedge on the landward side of the present mega splay fault as evidence of the ancient mega splay fault because the ancient mega splay fault soles into the active mega splay fault the active mega splay fault may function as a basal detachment fault and is directly connected to the seaward plate boundary decollement

borehole guided avo analysis of p p and p s reflections quantifying uncertainty on density estimates seismic properties of isotropic elastic formations are characterized by the three parameters acoustic impedance poisson s ratio and density whilst the first two are usually well estimated by analysing the amplitude variation with angle ava of reflected p p waves density is known to be poorly resolved however density estimates would be useful in many situations encountered in oil and gas exploration in particular for minimizing risks in looking ahead while drilling we design a borehole seismic experiment to investigate the reliability of ava extracted density receivers are located downhole near the targeted reflectors and record reflected p p and converted p s waves a non linear wide angle based bayesian inversion is then used to access the a posteriori probability distributions associated with the estimation of the three isotropic elastic parameters the analysis of these distributions suggests that the angular variation of reflected p s amplitudes provides additional substantial information for estimating density thus reducing the estimate uncertainty variance by more than one order of magnitude compared to using only reflected p waves

elasticity of marine sediments rock physics modeling we offer an effective medium model for the elastic moduli of high porosity ocean bottom sediments the elastic constants of the dry sediment frame depend on porosity elastic moduli of the solid phase and effective pressure the model connects two end points in the elastic modulus porosity plane the hertz mindlin modulus of a dense elastic sphere pack at critical porosity and zero at 100 porosity the elastic moduli of saturated sediment are calculated from those of the dry frame using gassmann s equation unlike the suspension model our model assigns non zero elastic constants to the dry sediment frame and can predict the shear wave velocity unlike various modifications of the travel time average equation it is first principle based and contains only physical parameters we justify this model by matching sonic data in shallow marine sediments and in an odp well

velocity anisotropy of shales and depth estimation in the north sea basin it is known that in the north sea basin the depths to major reflectors as determined from surface seismic data are often larger than the well log depths from a study of data sets which tie 21 wells i found a strong correlation between the occurrence of the depth error and the presence of shales in the subsurface assuming that the error is caused by elliptical velocity anisotropy in shales i measured the anisotropy from a comparison of the well log sonic data and the interval velocity profile obtained from the surface seismic data and also from a comparison of the seismic depth and the well log depth it was found that the two methods of measurements agree with each other and also agree qualitatively with the previous laboratory measurements of anisotropy in shale samples the results strongly suggest that the depth anomaly in the north sea basin is caused by the velocity anisotropy of shales a simple method to correct the seismic depth is given

analysis of the charging process of the lacustrine tight oil reservoir in the triassic chang 6 member in the southwest ordos basin china with the success of bakken tight oil tight sandstone oil and shale oil and eagle ford tight oil in north america tight oil has become a research focus in petroleum geology in china tight oil reservoirs are predominantly distributed in lacustrine basins the triassic chang 6 member is the main production layer of tight oil in the ordos basin in which the episodes timing and drive of tight oil charging have been analyzed through the petrography fluorescence micro spectrometry micro thermometry and trapping pressure simulations of fluid inclusions in the reservoir beds several conclusions have been reached in this paper first aqueous inclusions with five peaks of homogenization temperatures and oil inclusions with three peaks of homogenization temperatures occurred in the chang 6 reservoir beds the oil inclusions are mostly distributed in fractures that cut across and occur within the quartz grains in the quartz overgrowth and calcite cements and the fractures that occur within the feldspar

high resolution water content estimation from surface based ground penetrating radar reflection data by impedance inversion 1 mapping hydrological parameter distributions in high resolution is essential to understand and simulate groundwater flow and contaminant transport of particular interest is surface based ground penetrating radar gpr reflection imaging in electrically resistive sediments because of the expected close link between the subsurface water content and the dielectric permittivity which controls gpr wave velocity and reflectivity conventional tools like common midpoint cmp velocity analysis provide physical parameter models of limited resolution only we present a novel reflection amplitude inversion workflow for surface based gpr data capable of resolving the subsurface dielectric permittivity and related water content distribution with markedly improved resolution our scheme is an adaptation of a seismic reflection impedance inversion scheme to surface based gpr data key is relative amplitude preserving data preconditioning including gpr deconvolution which results in traces with the source wavelet distortions and propagation effects largely removed the subsequent inversion for the underlying dielectric permittivity and water content structure is constrained by in situ dielectric permittivity data obtained by direct push logging after demonstrating the potential of our novel scheme on a realistic synthetic data set we apply it to two 2 d 100 mhz gpr profiles acquired over a shallow sedimentary aquifer resulting in water content images of the shallow 3 7 m depth saturated zone having decimeter resolution

influence of microheterogeneity on effective stress law for elastic properties of rocks understanding the effective stress coefficient for seismic velocity is important for geophysical applications such as overpressure prediction from seismic data as well as for hydrocarbon production and monitoring using time lapse seismic measurements this quantity is still not completely understood laboratory measurements show that the seismic velocities as a function of effective stress yield effective stress coefficients less than one and usually vary between 0 5 and 1 at the same time theoretical analysis shows that for an idealized monomineral rock the effective stress coefficient for elastic moduli and therefore also for seismic velocities will always equal one we explore whether this deviation of the effective stress coefficient from unity can be caused by the spatial microheterogeneity of the rock the results show that only a small amount less than 1 of a very soft component is sufficient to cause this effect such soft material may be present in grain contact areas of many rocks and may explain the variation observed experimentally

geochemical characteristics of the triassic chang 7 lacustrine source rocks ordos basin china implications for paleoenvironment petroleum potential and tight oil occurrence abstract the fact that high quality lacustrine source rocks generally shale and mudstone control the formation and distribution of conventional and unconventional oil and gas reservoirs in lacustrine basins has been well accepted in petroleum exploration and exploitation taking the chang 7 lacustrine source rocks in the ordos basin as an example several points having been reached are as follows 1 the chang 7 source rocks possess an excellent source rock potential and the shales hold a better potential than the mudstones 2 the paleoenvironments of the chang 7 source rocks were sub reducing to sub oxidizing conditions and fresh and brackish water depositional environments with a maximum water depth of 150 m the organic matter origins of the source rocks are mainly plankton algae bacteria and other aquatic microorganisms 3 the beginning time of the oil generation of the chang 7 source rocks is at 165 ma and the peak oil generation occurred during 115 95 ma the cumulative amounts of oil generation are up to 4711 103 t km2 and the ratios of peak generation amounts to cumulative generation amounts are 50 the beginning timing and peak generation timing of the shales are earlier than those of the mudstones respectively and the cumulative oil generation amount of the shales is higher than that of the mudstones indicating a better oil generation potential of the shales 4 due to the more remained oil possessed in the shales the hydrocarbon expulsion threshold of the chang 7 shales 2560 m is deeper than that of the chang 7 mudstones 2080 m 5 the occurrences of the chang 8 6 tight oils are predominantly controlled by the outer boundary of the chang 7 source rocks distribution while the transition areas between thickness toc and ro high value centers are the accumulation and enrichment zones the chang 7 shales controlled the occurrence of the chang 8 tight oil reservoirs and the chang 7 mudstones controlled the occurrence of the chang 7 and chang 6 tight oil reservoirs

the effective stress law for stress sensitive transversely isotropic rocks abstract this paper first presents a review of the development of the concept of effective stress followed by major experimental and theoretical studies carried out to estimate the biot s coefficient it then uses the constitutive equations for vertically transverse isotropic vti reservoirs like coal derived using the principles of thermodynamics for estimation of the biot s coefficients in the vertical and horizontal directions laboratory data for tests conducted on two coal types retrieved from different geologic settings and geographical locations was used to carry out the modeling and validation exercise evidence is presented that values of biot s coefficient can be greater than one proposed by biot to be the limiting value for sorptive rocks to address this the term biot s coefficient is replaced with effective stress coefficient finally this paper discusses the pressure and stress dependent behavior of the biot s coefficient the results clearly show that the estimated values of biot s coefficients in both vertical and horizontal directions are different varying with pressure for methane depletion but remaining constant for helium depletion at the same time the nature of biot s coefficient re termed as effective stress coefficient was found to be greater than unity for methane depletion as a last step a conceptual physical model is proposed to explain the pressure dependent variation of effective stress biot s coefficients in terms of the contact area between grains based on the findings that the effective stress coefficient decreases with pressure it is concluded that the effective vertical stress would increase significantly with depletion which in turn would result in shear failure and increased permeability

research note overpressure prediction from c wave seismic data abstract recently mode converted shear waves c waves have been shown to enable overpressure prediction in media where primary wave acquisition is inhibited by gas and fluid effects c wave moveout is analysed and a long standing relationship between differential stress and primary wave p wave velocity is modified and employed though pore pressure prediction based on c waves is supported by empirical evidence from laboratory and field experiments a theoretical justification has yet to be developed in this research note we provide a supporting algebra for the original relationship between pore pressure and c wave velocity

seismic attenuation tomography using the frequency shift method we present a method for estimating seismic attenuation based on frequency shift data in most natural materials seismic attenuation increases with frequency the high frequency components of the seismic signal are attenuated more rapidly than the low frequency components as waves propagate as a result the centroid of the signal s spectrum experiences a downshift during propagation under the assumption of a frequency independent q model this downshift is proportional to a path integral through the attenuation distribution and can be used as observed data to reconstruct the attenuation distribution tomographically the frequency shift method is applicable in any seismic survey geometry where the signal bandwidth is broad enough and the attenuation is high enough to cause noticeable losses of high frequencies during propagation in comparison to some other methods of estimating attenuation our frequency shift method is relatively insensitive to geometric spreading reflection and transmission effects source and receiver coupling and radiation patterns and instrument responses tests of crosswell attenuation tomography on 1 d and 2 d geological structures are presented

a simple derivation of the effective stress coefficient for seismic velocities in porous rocks the effect of confining stress and pore pressure on seismic velocities is important for such geophysical applications as overpressure prediction from seismic data eaton 1975 dutta 2002 huffman 2002 sayers et al 2002 and more recently for hydrocarbon production monitoring using time lapse seismic measurements tura and lumley 1999 landr 2001 the dependence of seismic velocity on pressure has been confirmed for a variety of rocks by laboratory measurements of elastic wave velocities in samples with varying pressure in pore fluids see e g wyllie et al 1958 todd and simmons 1972 eberhart phillips et al 1989 prasad and manghnani 1997 in general for a rock subjected to a given confining stress c higher pore pressures p correspond to lower compressional and shear velocities confining stress has a similar effect but with opposite sign on seismic velocities

magnitude mechanisms and prediction of abnormal pore pressure using well data in the krishna godavari basin east coast of india abnormal pressures are encountered during exploration drilling in different parts of krishna godavari basin on the east coast of india the nature and stratigraphic occurrences of the overpressure zones vary across the basin three different clusters of wells covering a large part of the basin encompassing both onshore and offshore drilled wells are analyzed to capture this variation a wide range of pore pressure gradients from normal to as high as 18 mpa km was observed in the present data set the tops of overpressure zones demonstrate a large range from 2200 to 3000 m 6562 to 9842 ft these depths generally correspond to either a miocene deltaic sequence or cretaceous synrift and postrift sequences available well data reveal two main reasons for the development of overpressure considerably high pore pressure regimes in the cretaceous sequence in the eastern corner of the basin are found to be mainly caused by gas generation whereas disequilibrium compaction is proposed as the main cause for overpressure in the other parts of the basin the outcome of this analysis provides a fair idea of the nature magnitude and distribution of the overpressure and this will also help to strategize further exploration activities in the basin

mechanisms for overpressure generated by the undercompaction of paleogene strata in the baxian depression of bohai bay basin china abstract undercompaction is an important mechanism for developing fluid overpressure in the mudstone strata the main factors that affect undercompaction are the deposition rate dr and mudstone content mc however the manner in which the dr and the mc influence the development of undercompaction is still unclear to clarify the pressurization mechanism of undercompaction and the influence of dr and mc the acoustic and density logging as well as the sonic velocity effective stress schematic are used to identify the undercompaction overpressure furthermore the petromod software is used to simulate the development of overpressure and to analyze the influence of the dr and mc on the undercompaction of paleogene strata in the baxian depression of jizhong subbasin the baxian depression causes the development of overpressure in the dongying formation the first member of the shahejie formation the third member of the shahejie formation the fourth member of the shahejie formation and the kongdian formation whereas the undercompaction overpressure is observed to mainly develop in the dongying formation and in the first member of the shahejie formation a prerequisite for performing the simulation is that the total thickness and deposition time of the formation should remain constant further the effects of the varying dr and mc on the development of undercompaction are simulated the results exhibit that the dr and mc are prerequisites for developing undercompaction overpressure however the dr only affects the undercompaction development period and exhibits little effect on the final overpressure amplitude meanwhile the amount of mc not only increases the amplitude but also results in an early development of the undercompaction overpressure

u pb and lu hf isotope systematics of zircons from the mississippi river sand implications for reworking and growth of continental crust we carried out in situ u pb and lu hf isotope analyses of detrital zircons from the mississippi river in order to understand crustal reworking and continental growth rates the u pb analyses for 416 zircons reveal three major peaks of crust formation at 2 8 2 6 ga 1 8 0 9 ga and after 0 2 ga initial hf isotope ratios were obtained for 402 of the dated zircons and only 8 of the zircons have batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document hf mathit t dm end document values less negative than 2 5 these data correspond to a crustal residence time of 120 m y this finding indicates that crustal reworking was a very important process in continental crust formation the batchmode documentclass fleqn 10pt legalpaper article usepackage amssymb usepackage amsfonts usepackage amsmath pagestyle empty begin document hf mathit t dm end document population demonstrates that reworking was predominant at 2 5 2 0 ga and after 0 9 ga whereas juvenile crust formation dominated between 2 0 and 1 6 ga we calculated the mantle extraction model ages to estimate the continental growth rate approximately half of the grains have model ages between 2 0 and 1 3 ga indicating rapid crustal growth during this time the continental growth rate suggests that 15 and 78 crust in the source region of the zircons formed by 2 5 and 1 3 ga respectively

evolution of microstructures and of macroscopic properties of some clays during experimental compaction abstract in order to understand the evolution of clay sediments during their burial to three or four kilometers depth remoulded and non remoulded clay samples were oedometrically consolidated under loads ranging from 0 1 50 mpa and their microstructural mechanical and transport properties were studied for this study four clays were selected on mineralogical grounds a kaolinite st austell clay two illitic clays la bouzule clay and salins 14 clay and an illite smectite mixed clay marais poitevin clay among those materials two are almost pure clays st austell clay and salins 14 clay and were compacted in a remoulded state the other two have a clay fraction about 60 and were studied in non remoulded state for marais poitevin clay and both remoulded and non remoulded for la bouzule clay the oedometric tests have been performed in classical oedometers and in a new oedometric cell specially designed to measure lateral stresses and to perform hydraulic conductivity measurements under compaction load the two pure clays show an evolution of their void ratio differing from what is expected considering their liquid limits the behaviour seems to be governed by the size of the clay particles around 1 m for st austell clay and around 0 1 m for salins 14 clay marais poitevin clay very slightly compacted in its natural state and remoulded la bouzule clay have consolidation coefficients cc and void ratios consistent with their liquid limits a relationship reported in soil mechanics literature skempton 1944 burland 1990 nagaraj et al 1994 the natural la bouzule clay shows very low void ratios and cc due to overconsolidation the microstructure observed by tem showed that clay particles are platy and made of aggregates of individual crystals except for salins 14 clay where individual crystals do not aggregate the evolution of the microstructure with applied stress shows no change in the particles structure but a progressive reorientation of the particles perpendicular to the load axis these microstructural observations explain the transport properties measured and their evolution the thermal conductivity of kaolinite measured in the axial and radial direction reflects the evolution of anisotropy with compaction observed on particles orientation the different hydraulic conductivities observed on the various samples are compared to those obtained with the kozeny carman formula using two types of specific surface determination this comparison emphasizes the importance of inter and intraparticule pore size and of their intimate organisation

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

3d polarimetric gpr coherency attributes and full waveform inversion of transmission data for characterizing fractured rock ground penetrating radar gpr can detect and describe fractures to help us characterize fractured rock formations a fracture alters the incident waveform or wave shape of a gpr signal through constructive and destructive interference depending on the aperture fill and orientation of the fracture because the electromagnetic em waves of gpr are vectorial features exhibiting strong directionality can change the state of polarization of the incident field gpr methods that focus on changes in waveform or polarization can improve detection and discrimination of fractures within rock bodies an algorithm based on coherency a seismic attribute that delineates discontinuities in wavelet shape is developed for polarimetric gpr it uses the largest eigenvalue of the time domain scattering matrix when calculating coherence this algorithm is sensitive to wave shape and is unbiased by the polarization of gpr antennas polarimetric coherency works better than scalar coherency in removing the effects of polarization on field data collected from a fractured limestone plot used for hydrologic experimentation another method for time domain full waveform inversion of transmission data quantitatively determines fracture aperture and em properties of fill based on a thin layer model inversion results from field data show consistency with the location of fractures from reflection data these two methods offer better fracture detection capability and quantitative information on fracture aperture dielectric permittivity and electrical conductivity of the fill than traditional gpr imaging and scalar coherency attributes

the interdisciplinary use of overpressure abstract overpressure is a polysemic word that has a variety of meanings within and across different disciplines this is likely to be a particular problem in analysis of geothermal resources where reservoir engineers volcanologists and structural geologists may each confidently use overpressure but mean different things we suggest that to avoid confusion the term should be carefully and accurately defined whenever used and ideally only used to mean fluid pressure in excess of hydrostatic pressure

characteristics and controlling factors of lacustrine tight oil reservoirs of the triassic yanchang formation chang 7 in the ordos basin china abstract tight sandstone oil reservoirs have received increasing attention in petroleum exploration and exploitation previous research concerning tight oil reservoirs has predominantly focused on marine basins however in china tight oil reservoirs are mostly distributed in lacustrine basins taking the tight oil sandstones of the yanchang formation chang 7 oil reservoir interval the chang 7 for short in the ordos basin as an example five factors are identified that control their formation and occurrence firstly three episodes of oil charging took place during the early cretaceous which were 142 139 ma 128 122 ma and 114 106 ma respectively continuous generation and episodic expulsion led to multiple episodes of oil accumulation secondly widely distributed source rocks toc 1 0 provide hydrocarbons to the chang 7 the distribution of tight oil was controlled by the outer boundary of the source rock distribution while the transition areas between generation expulsion centers were the accumulation and enrichment zones in the chang 7 thirdly with the favorable conditions for retained hydrocarbons massive continuous tight reservoir beds average porosity 7 6 and average permeability 0 15 md developed in the chang 7 capable of forming large scale successive tight oil reservoirs fourthly different source reservoir assemblages have different expulsion patterns and amounts which led to different charging degrees and sizes of tight oil accumulations type iii source reservoir interbeds will be the most favorable target for exploration and exploitation in the chang 7 ordos basin finally under the driving mechanism of non buoyancy migration and accumulation pressure differences between source and reservoir rocks pdbsr serve as the primary expulsion and migration force for crude oil during the main accumulation periods in the chang 7

the influence of pore pressure and confining pressure on dynamic elastic properties of berea sandstone compressional and shear wave velocities of watersaturated berea sandstone have been measured as functions of confining and pore pressures to 2 kbar the velocities measured by the pulse transmission technique were obtained at selected pressures for the purpose of evaluating the relative importance of confining pressure and pore pressure on elastic wave velocities and derived dynamic elastic constants changes in berea sandstone velocities resulting from changes in confining pressure are not exactly canceled by equivalent changes in pore pressure for properties that involve significant bulk compression compressional wave velocities and bulk modulus an incremental change in pore pressure does not entirely cancel a similar change in confining pressure on the other hand it is shown that a pore pressure increment more than cancels an equivalent change in confining pressure for properties that depend significantly on rigidity shear wave velocity and poisson s ratio this behavior as well as observed

an efficient and self adaptive approach for q value optimization the time invariant gain limit constrained inverse q filter can control the numerical instability of the inverse q filter but it often suppresses the high frequencies at later times and reduces the seismic resolution to improve the seismic resolution and obtain high quality seismic data we propose a self adaptive approach to optimize the q value for the inverse q filter amplitude compensation the optimized q value is self adaptive to the cutoff frequency of the effective frequency band for the seismic data the gain limit of the inverse q filter amplitude compensation the inverse q filter amplitude compensation function and the medium quality factor in the processing of the inverse q filter amplitude compensation the optimized q value corresponding gain limit and amplitude compensation function are used simultaneously then the energy in the effective frequency band for the seismic data can be recovered and the seismic resolution can be enhanced at all times furthermore the small gain limit or time variant bandpass filter after the inverse q filter amplitude compensation is considered to control the signal to noise ratio and the time variant bandpass filter is based on the cutoff frequency of the effective frequency band for the seismic data synthetic and real data examples demonstrate that the self adaptive approach for q value optimization is efficient and the inverse q filter amplitude compensation with the optimized q value produces high resolution and low noise seismic data

removal of wavelet dispersion from ground penetrating radar data wavelet dispersion caused by frequency dependent attenuation is a common occurrence in ground penetrating radar gpr data and is displayed in the radar image as a characteristic blurriness that increases with depth correcting for wavelet dispersion is an important step that should be performed before gpr data are used for either qualitative interpretation or the quantitative determination of subsurface electrical properties over the bandwidth of a gpr wavelet the attenuation of electromagnetic waves in many geological materials is approximately linear with frequency as a result the change in shape of a radar pulse as it propagates through these materials can be well described using one parameter q related to the slope of the linear region assuming that all subsurface materials can be characterized by some q value the problem of estimating and correcting for wavelet dispersion becomes one of determining q in the subsurface and deconvolving its effects using an inverse q filter we present a

cyclostratigraphy and astronomical tuning during the oligocene in the jizhong depression bohai bay basin northeastern china abstract the dongying formation ed and the first member of the shahejie formation es1 in the central raoyang sag cover about 1705 m long sedimentary series of terrestrial lacustrine infill we employed the gamma ray gr log data as a paleoclimatic and paleoenvironmental proxy to conduct the high resolution cyclostratigraphy research in well w33 and w62 prominent sedimentary cycles in decameters and meters were revealed by multi taper mtm power spectra evolutionary fast flourier transformation fft and correlation coefficient analyses in the es1 and ed intervals the 405 kyr long eccentricity 125 kyr and 100 kyr short eccentricity 40 kyr obliquity and 23 kyr precession can be recognized with a wavelength ratio of approximately 20 5 2 1 respectively by tuning the 405 kyr filter output in well w33 to the orbital target curve of la2010d astronomical solution we established an astronomical time scale ats that provided absolute age controls during the oligocene and shed light on the event correlation among isolated depressions in the bohai bay basin sediment accumulation rates sars were derived from the extracted 405 kyr long eccentricity and were tested with an average of 17 cm kyr age boundaries of ng ed1 ed1 ed2 ed2 ed3 ed3 es1 and es1 es2 are 23 03 ma 24 34 ma 25 53 ma 29 05 ma and 33 10 ma respectively based on the ats and sars we discussed the depositional evolution within age boundaries cause of high sars and origin of formation overpressure after the largest lake transgression shallow water deltas and fluvial plains transitionally dominate the central raoyang sag with shallowing water depth thin interlayers of mudstones and sandstones originate from shallow water deltaic systems with low sand to mud ratios under high sars enhanced by mountain uplift and low sand to mud ratios formation overpressure results mainly from high porosities in under compacted mudstone intervals

wide angle seismic data reveal extensive overpressures in the eastern black sea basin summary we present new data that explores the link between pore pressure and seismic velocity to estimate the magnitude of the overpressure within the deep sediments of the eastern black sea basin new wide angle seismic data combined with coincident reflection data have been modelled simultaneously using the seismic tomography code jive3d to provide a wellconstrained seismic velocity model of the sediments our models reveal a widespread lowvelocity zone at the depth of 5 5 8 5 km which is characterized by a velocity decrease from 3 5 to 2 5 km s 1 using two separate methods that relate changes in seismic velocity to changes in effective stress we estimate pore pressures of at least 160 mpa within the lowvelocity zone these pore pressures give values of 0 8 0 9 within the centre of the basin and above the mid black sea high the low velocity zone occurs within the maikop formation an organic rich mud layer identified as the source of mud volcanism in the black sea and south caspian sea

predrill pore pressure prediction using seismic data 1a predrill estimate of pore pressure can be obtained from seismic velocities using a velocity to pore pressure transform but the seismic velocities need to be derived using methods having sufficient resolution for well planning purposes for a deepwater gulf of mexico example significant differences are found between the velocity field obtained using reflection tomography and that obtained using a conventional method based on the dix equation these lead to significant differences in the predicted pore pressure parameters in the velocity to pore pressure transform are estimated using seismic interval velocities and pressure data from nearby calibration wells the uncertainty in the pore pressure prediction is analyzed by examining the spread in the predicted pore pressure obtained using parameter combinations which sample the region of parameter space consistent with the available well data if calibration wells are not available the ideas proposed in this paper can be used with measurements made whi

anisotropic effective medium modeling of the elastic properties of shales shales are complex porous materials normally consisting of percolating and interpenetrating fluid and solid phases the solid phase is generally comprised of several mineral components and forms an intricate and anisotropic microstructure the shape orientation and connection of the two phases control the anisotropic elastic properties of the composite solid we develop a theoretical framework that allows us to predict the effective elastic properties of shales its usefulness is demonstrated with numerical modeling and by comparison with established ultrasonic laboratory experiments the theory is based on a combination of anisotropic formulations of the self consistent sca and differential effective medium dem approximations this combination guarantees that both the fluid and solid phases percolate at all porosities our modeling of the elastic properties of shales proceeds in four steps first we consider the case of an aligned biconnected clay fluid composite composed of ellipsoidal inclusion

simple quantitative evaluation of porosity of argillaceous sediments at various depths of burial abstract relationship of porosity to depth of burial d in m geologic age a in millions of years and lithology ratio of thickness of shales total thickness of terrigenous deposits r has been developed by the writers which gives satisfactory results 0 exp 0 014 13 3 log a 83 25 log r 2 79 10 3 d where 0 initial porosity of the argillaceous sediment a nomogram has been prepared for an easy solution of the above equation

dynamic effective pressure coefficient calibration abstractpore pressure prediction provides an important risk assessment in the oil and gas industry most predrill pore pressure prediction methods from seismic and or well log sonic velocities are based on the effective stress principle which relates velocity variation to the combined effect of overburden stress and pore pressure in the current practice of pore pressure prediction the effective stress coefficient n is often assumed as unity which is not always the case especially when sediments are deeply buried and consolidated to understand the variation of n with depth i analyzed density and velocity trends from more than 100 gulf of mexico wells near the louisiana continental shelf edge in the study area overpressure zones are present in most wells and compaction disequilibrium is the dominant overpressure mechanism normal compaction trends for velocity and density were built the overburden pressure model was refined by taking into account that the density gradient approaches zero at the on

the future of pore pressure prediction using geophysical methods predrill pressure prediction has historically been done using very simple models and overly simplistic estimates of the earth s velocity field the methods usually incorporate a locally calibrated set of curves for pressure the advent of the effective stress concept and pressure prediction methods that developed from that concept have led to a much needed inclusion of fundamental physics into the art of pressure prediction the use of effective stress methods has become the standard for pressure prediction this technique has many variants including the eaton method the bowers method and the sperry sun method

estimation of marine sediment bulk physical properties at depth from seafloor geophysical measurements a combination of geophysical techniques can yield estimates of several physical properties versus depth an example is presented for a thick sequence of sediments in middle valley near the present spreading axis of the juan de fuca ridge we have computed the porosity temperature and thermal conductivity versus depth by combining the results of seafloor electrical and heat flow surveys the electrical resistivity of the sediments is empirically related to the porosity of the medium and to the pore fluid electrical conductivity which is in turn sensitive to the temperature the temperature profile is determined from the heat flow and the thermal conductivity the latter is determined from calculated porosity and estimates of the constituent mineral and pore fluid thermal conductivities the measured surface heat flow is assumed to be and the resistivity has been determined to be approximately constant with depth the computation of the variation of temperature porosity and thermal conductivity with depth yields physically realistic and reasonable results other physical properties void ratio bulk density water content compressional wave velocity are estimated from the porosity the shear wave velocity is calculated empirically from the compressional wave velocity and poisson s ratio is then computed from the compressional and shear wave velocities the results are in good agreement with values derived for similar rapidly deposited sediment sequences elsewhere but the model calculations indicate that deep sea drilling project measurements may be biased toward higher porosity samples