controls on reservoir quality of an upper jurassic reef mound in the palmers wood field area weald basin southern england an upper jurassic oxfordian reef mound in the palmers wood field area of the weald basin southern england clearly shows the relationship of facies diagenesis and porosity development to relative sea level changes the coral microbial reef mound was initiated over a drowned oolite shoal during a third order marine transgression and exhibits changes in coral morphology from base to top as the reef mound caught up with sea level during the subsequent highstand during the highstand extensive encrustation of the reef mound took place by microbial stromatolitic cements with subsequent porosity loss during the following lowstand of relative sea level extensive leaching of the aragonitic corals took place and a lowstand wedge accumulated down ramp porosity was lost during burial related cementation and compaction coral microbial reef mounds of this type have moderate potential for porosity formation unlike tighter deeper ramp reefs in the jurassic which are less prone to subaerial leaching and have less potential for secondary porosity development because they are less rich in aragonitic components although the upper jurassic reef mound is only a minor contributor to reservoirs in the palmers wood field it may provide a model for other upper jurassic reef plays

interferometric daylight seismic imaging summary claerbout s daylight imaging concept is generalized to a theory of interferometric seismic imaging ii interferometric seismic imaging is defined to be any algorithm that inverts correlated seismic data for the reflectivity or source distribution as examples we show that ii can image reflectivity distributions by migrating ghost reflections in passive seismic data and generalizes the receiver function imaging method used by seismologists interferometric seismic imaging can also migrate free surface multiples in common depth point cdp data and image source distributions from passive seismic data both synthetic and field data examples are used to illustrate the different possibilities of ii the key advantage of ii is that it can image source locations or reflectivity distributions from passive seismic data where the source position or wavelet is unknown in some cases it can mitigate defocusing errors as a result of statics or an incorrect migration velocity the main drawback with ii is that severe migration artefacts can be created by partial focusing of virtual multiples

tutorial on seismic interferometry part 1 basic principles and applications seismic interferometry involves the crosscorrelation of responses at different receivers to obtain the green s function between these receivers for the simple situation of an impulsive plane wave propagating along the x axis the crosscorrelation of the responses at two receivers along the x axis gives the green s function of the direct wave between these receivers when the source function of the plane wave is a transientas in exploration seismology or a noise signalas in passive seismology then the crosscorrelation gives the green s function convolved with the autocorrelation of the source function direct wave interferometry also holds for 2d and 3d situations assuming the receivers are surrounded by a uniform distribution of sources in this case the main contributions to the retrieved direct wave between the receivers come from sources in fresnel zones around stationary points the main application of direct wave interferometry is the retrieval of seismic surface wave responses from ambient noise and the subsequent tomographic determination of the surfacewave velocity distribution of the subsurface seismic interferometry is not restricted to retrieving direct waves between receivers in a classic paper claerbout shows that the autocorrelation of the transmission response of a layered medium gives the plane wave reflection response of that medium this is essentially 1d reflected wave interferometry similarly the crosscorrelation of the transmission responses observed at two receivers of an arbitrary inhomogeneous medium gives the 3d reflection response of that medium one of the main applications of reflected wave interferometry is retrieving the seismic reflection response from ambient noise and imaging of the reflectors in the subsurface a common aspect of direct and reflected wave interferometry is that virtual sources are created at positions where there are only receivers without requiring knowledge of the subsurface medium parameters or of the positions of the actual sources

point spread functions for interferometric imaging interferometric redatuming is a data driven method to transform seismic responses with sources at one level and receivers at a deeper level into virtual reflection data with both sources and receivers at the deeper level although this method has traditionally been applied by cross correlation accurate redatuming through a heterogeneous overburden requires solving a multidimensional deconvolution problem input data can be obtained either by direct observation for instance in a horizontal borehole by modelling or by a novel iterative scheme that is currently being developed the output of interferometric redatuming can be used for imaging below the redatuming level resulting in a so called interferometric image internal multiples from above the redatuming level are eliminated during this process in the past we introduced point spread functions for interferometric redatuming by cross correlation these point spread functions quantify distortions in the redatumed data caused by internal multiple reflections in the overburden in this paper we define point spread functions for interferometric imaging to quantify these distortions in the image domain these point spread functions are similar to conventional resolution functions for seismic migration but they contain additional information on the internal multiples in the overburden and they are partly data driven we show how these point spread functions can be visualized to diagnose image defocusing and artefacts finally we illustrate how point spread functions can also be defined for interferometric imaging with passive noise sources in the subsurface or with simultaneous source acquisition at the surface

upper jurassic reef play east texas basin an updated overview part 2 inboard trend this paper is the second part of a two part paper summarizing new data on the upper jurassic reef play in the east texas basin information presented in this paper focuses on carbonate buildups of the inboard trend inboard buildups represent significant backstepping of reefal facies from the ramp margin outboard trend to more updip sites along a developing shelf margin inboard features resemble pinnacles that can be identified with two dimensional seismic data but that require three dimensional data to properly image such pinnacles represent stacked features that resulted from three to five cycles of reef growth the general upward progression of facies within each cycle exhibits a shallowing trend with the overall proportion of shallow water facies also increasing upward among these cycles most inboard buildups possess a low porosity micritic cap immediately overlying vuggy coral bearing facies with good to excellent porosity evidence of both primary and secondary porosity exists with some correlation between porosity and permeability development log and rock sample data from the frost buildup freestone county confirm the existence of diverse microfacies in these buildups with complex lateral variation in porosity permeability distribution two models of buildup occurrence in the basin are presented

least squares horizons with local slopes and multigrid correlations most seismic horizon extraction methods are based on seismic local reflection slopes that locally follow seismic structural features however these methods often fail to correctly track horizons across discontinuities such faults and noise because the local slopes can only correctly follow laterally continuous reflections in addition seismic amplitude or phase information is not used in these methods to compute horizons that follow consistent phase e g peaks or troughs to solve these problems we propose a novel method to compute horizons that globally fit both local slopes and multi grid correlations of seismic traces in this method we first estimate local reflection slopes by using structure tensors and compute laterally multi grid slopes by using dynamic time warping to correlate seismic traces within multiple laterally coarse grids these coarse grid slopes can correctly correlate reflections that may be significantly dislocated by faults or other discontinuous structures we then compute a

comparison of pelagic and nepheloid layer marine snow implications for carbon cycling abstract marine snow from upper and mid water i e pelagic depths on the california margin is texturally and compositionally different from that traveling in the nepheloid layer transmission electron microscopy shows that pelagic marine snow consists primarily of bioclasts e g diatom frustules foram tests organic matter and microbes these components are entrained as discrete particles or small aggregates 10 m in diameter in a loose network of exocellular muco polysaccharide material clays are infrequent but when present are constituents of comparatively compact organic rich microaggregates microbes are abundant and appear to decrease in number with increasing water depth in contrast marine snow aggregates collected from just above the sea floor in the nepheloid layer are assemblages of clay particles clay flocs and relatively dense clay organic rich microaggregates in an exocellular organic matrix bioclasts and microorganisms occur only rarely the prevalence of clay organic rich aggregates in the nepheloid layer suggests that prior to final deposition and burial marine snow from the pelagic zone is subject to disaggregation and recombination with terrigenous detrital material near or at the sea floor results have significant implications for the accumulation and burial rates of organic carbon on continental margins and the aging and bioavailability of sedimentary organic matter samples examined were collected offshore of northern and central california

near wellbore vsp imaging without overburden in seismic exploration a complex overburden can cause defocused and distorted seismic images of deeper target areas while in surface seismic imaging it is difficult to overcome this problem vertical seismic profile vsp borehole seismic imaging with its well oriented recording geometry has proven able to circumvent the overburden s detrimental impact recently vspnear wellboresaltflankimagingwithout knowledge of the overburden has shown encouraging results in this paper we introduce another method for a more common imaging purpose imaging near wellbore horizons without knowledge of the overburden a key component of ourmethodisareverseray tracingtechniquethatusesactual vspdirect wave traveltime picks and extrapolates through a local velocity model to obtain the direct wave traveltimes in the vicinity of the well the extrapolated traveltimes then serve as references for migration of the vsp reflected data from near wellbore horizons the merits of this method are that all source side effects such as shot position and triggeringtimestaticsareavoided anditcanefficientlyandrobustly imagethenear wellborehorizonsbecauseitdoesnotneedan estimated overburden velocity model prone to errors however the image is limited to a diamond shaped area around the well whose size is proportional to the vsp array a synthetic vsp experiment on the seg eage 2d overthrust modelshowsthatthismethod withalocalevenanestimated 1d velocity model effectively images structural features suchasdipdirectionanddiscontinuitiesofthenear wellbore horizons

subsurface fractures and their relationship to stress history in east texas basin sandstone abstract subsurface fractures were sampled with more than 400 m of core from the lower cretaceous travis peak formation a tabular sandstone and shale unit approximately 600 m thick that was deposited in the gradually subsiding gulf coast basin depth to the top of the formation in east texas now ranges between 1800 and 2900 m fractures in sandstone exhibit features that are due to intermittent fracturing and sealing crack seal which suggest that the fractures are the result of episodes of fluid pressure in excess of hydrostatic correlation of the vein mineral precipitation sequence with the diagenetic history and the results of previous 18 o studies of quartz cement indicates that fractures propagated at depths of between 900 and 1500 m during the migration of quartz precipitating fluids fracture permeability provides a mechanism for the passage of large fluid volumes recorded by the precipitation of extensive quartz cement in the formation fractures stopped propagating before maximum burial depth was achieved during approximately 1500 m of subsequent burial fractures either remained partly open or were sealed by postkinematic ankerite and clay minerals

imaging of offset vsp data acquired in complex areas with modified reverse time migration a modified reverse time migration algorithm for offset vertical seismic profiling data is proposed this algorithm performs depth imaging of target areas in the borehole vicinity without taking into account the overburden originally recorded seismograms are used reliable results can be obtained using only the velocity profile obtained along the well the downgoing wavefield emitted from a surface source is approximated in the target area using the transmitted p wave recorded by the receivers deployed in the well this is achieved through a reverse time extrapolation of the direct transmitted p wave into the target area after its separation in offset vertical seismic profiling seismograms generated using a finite difference scheme for the solution of the scalar wave equation the proposed approach produces kinematically reliable images from reflected pp and ps waves and furthermore can be applied as a salt proximity tool for salt body flank imaging based on the transmitted ps waves our experiments on synthetic data demonstrate that the modified reverse time migration provides reliable depth images based on offset vertical seismic profiling data even if only the velocity profile obtained along the borehole is used

evaluation of elastodynamic interferometric redatuming a synthetic study on salt dome flank imaging summary the recent introduction of novel redatuming techniques based on the principles of timereversed acoustics and source receiver reciprocity has allowed seismic measurements collected on one datum to be extrapolated to another datum under favourable conditions this process can approximately remove the complicated overburden structures without any velocity information we introduce an elastic redatuming scheme for walkaway vertical seismic profiles wvsps based on these principles using p and s wave potentials which are derived from the spatial derivatives of the measured wavefields additional field acquisition is utilized to directly measure these derivatives we test our elastic redatuming scheme on data simulated with an elastic finite difference algorithm the elastodynamic green s functions between multicomponent receivers in a borehole are then extracted from data recorded using multicomponent p and s wave sources at the surface the wavefields are redatumed as four parts two related to the p wave potential and another two related to the s wave potential these parts are migrated separately and form four independent images of the salt dome flank providing a more complete elastic description of the subsurface

crosswell monitoring using virtual sources and horizontal wells time lapse crosswell seismic provides an efficient way to monitor the migration of a c o2 plume or its leakage after c o2 injection into a geologic formation recently crosswell seismic has become a powerful tool for monitoring underground variations using the concept of a virtual source with virtual sources positioned at the receivers installed in the well and thus the positions of sources and receivers can be invariant during monitoring however time lapse crosswell seismic using vertical wells and virtual sources has difficulty in describing the front of a c o2 plume which usually is parallel to the vertical wells and in obtaining sufficient ray coverage for the first arrival tomography these problems arise because of the theoretical downward illumination directivity limitation of the virtual source we have developed an effective monitoring method that uses virtual sources and two horizontal wells one above and one below the c o2 sequestration reservoir in our method we redatum the traces th

a novel application of time reversed acoustics salt dome flank imaging using walkaway vsp surveys in this paper we present initial results of applying time reversed acoustics tra technology to saltdome flank seismic imaging we created a set of synthetic traces representing a multilevel walkaway vsp for a model composed of a simplified gulf of mexico vertical velocity gradient and an embedded salt dome we first applied the concepts of tra to the synthetic traces to create a set of redatummed traces without having to perform velocity analysis moveout corrections or complicated processing each redatummed trace approximates the output of a zero offset downhole source and receiver pair to produce the final salt dome flank image we then applied conventional poststack depth migration to the zero offset section our results show a very good image of the salt when compared to an image derived using data from a downhole zero offset source and receiver pairs the simplicity of our tra implementation provides a virtually automated method to estimate a zero offset seismic section as if it had been collected from the reference frame of the borehole containing the vsp survey

local vertical seismic profiling vsp elastic reverse time migration and migration resolution salt flank imaging with transmitted p to s waves to avoid the defocusing effects of propagating waves through salt and overburden with an inaccurate overburden velocity model we introduce a vertical seismic profiling vsp local elastic reverse time migration rtm method for salt flank imaging by transmitted p to s waves this method back projects the transmitted ps waves using a local velocity model around the well until they are in phase with the back projected pp waves at the salt boundaries the merits of this method are that it does not require the complex overburden and salt body velocities and it automatically accounts for source side statics in addition the method accounts for kinematic and dynamic effects including anisotropy absorption and all other unknown rock effects outside of this lo cal subsalt velocity model numerical tests on an elastic salt model and offset 2d vsp data in the gulf of mexico using a finite difference time domain staggered grid rtm scheme partly demonstrate the effectiveness of this method over interferometry

stratigraphic coordinates a coordinate system tailored to seismic interpretation in certain seismic data processing and interpretation tasks such as spiking deconvolution tuning analysis impedance inversion and spectral decomposition it is commonly assumed that the vertical direction is normal to reflectors this assumption is false in the case of dipping layers and may therefore lead to inaccurate results to overcome this limitation we propose a coordinate system in which geometry follows the shape of each reflector and the vertical direction corresponds to normal reflectivity we call this coordinate system stratigraphic coordinates we develop a constructive algorithm that transfers seismic images into the stratigraphic coordinate system the algorithm consists of two steps first local slopes of seismic events are estimated by plane wave destruction then structural information is spread along the estimated local slopes and horizons are picked everywhere in the seismic volume by the predictive painting algorithm these picked horizons represent level sets of the first axis of the stratigraphic coordinate system next an upwind finite difference scheme is used to find the two other axes which are perpendicular to the first axis by solving the appropriate gradient equations after seismic data are transformed into stratigraphic coordinates seismic horizons should appear flat and seismic traces should represent the direction normal to the reflectors immediate applications of the stratigraphic coordinate system are in seismic image flattening and spectral decomposition synthetic and real data examples demonstrate the effectiveness of stratigraphic coordinates

horizon volumes with interpreted constraints abstracthorizons are geologically significant surfaces that can be extracted from seismic images color coding of horizons based on amplitude or other attributes can help reveal ancient sedimentary environments and structural features extracted horizons are also used for building structure models and stratigraphic interpretations we propose two methods for constructing seismic horizons aligned with reflectors in a 3d seismic image the first method generates horizons one at a time the second method generates an entire volume of horizons at once by first computing a relative geologic time volume from seismic normal vectors rather than gradually building a horizon by extending one or more seed points to a surface along seismic reflectors both of our methods generate whole horizons at once by solving partial differential equations derived from seismic normal vectors the most significant new aspect of both methods is the ability to specify perhaps interactively during interpretation a small number of

haynesville and bossier mudrocks a facies and sequence stratigraphic investigation east texas and louisiana usa abstract upper jurassic haynesville and bossier shale gas plays of the northwestern gulf of mexico gom basin produce from organic rich marine transgressive to highstand mudrocks within mixed carbonate clastic depositional systems modern wireline log suites from 200 deep wells were used for detailed correlations and 10 cores throughout the upper kimmeridgian to lower tithonian basin were incorporated into detailed facies stratigraphic and lithologic analyses the haynesville shale lies within a 2nd order transgressive systems tract tst that encompasses back stepping ramp carbonates proximal and marine shales distal below a maximum flooding surface mfs this shale onlaps retrogradational carbonates and basement highs and is capped by the 2nd order mfs bossier shales and local sandstones prograde basinward above the haynesville shale and downlap the 2nd order mfs they grade upward and updip into the thick highstand systems tract hst fluvio deltaic sandstones of the cotton valley group distally organic rich facies developed in restricted bossier environments creating another productive gas shale opportunity several preexisting basement highs in the south and carbonate platforms in the northwest and west restrict and partition the basin thus influencing deposition of highly organic versus nonorganic and siliciclastic dominated versus carbonate dominated lithologies haynesville and bossier shales each compose three upward coarsening cycles that probably represent 3rd order sequences within the larger 2nd order tst and early hst respectively most of the three bossier 3rd order cycles are dominated by varying amounts of siliciclastics deposition of the haynesville mudrocks occurred below storm wave base under mostly dysoxic conditionsm allowing settlement of benthic bivalve communities and bioturbating organisms and oscillating periodically to more anoxic conditions on the seafloor however most of the sparse faunae found in these mudrocks are of planktonic origin bossier mudrocks exhibited more oxygenated and clastic rich lithologies related to progradation of the clastic shoreline and sea level highstand knowledge of lithologic stratigraphic geochemical and faunal variations across mudrock basins needs to be detailed so that shale gas basins might be successfully explored

fully automated carbonate petrography using deep convolutional neural networks abstract carbonate rocks are important archives of past ocean conditions as well as hosts of economic resources such as hydrocarbons water and minerals geologists typically perform compositional analysis of grain matrix cement and pore types in order to interpret depositional environments diagenetic modification and reservoir quality of carbonate strata such information can be obtained primarily from petrographic analysis a task that is costly labor intensive and requires in depth knowledge of carbonate petrology and micropaleontology recent studies have leveraged machine learning based image analysis including deep convolutional neural networks dcnn to automate description classification and interpretation of thin sections subsurface core images and seismic facies which would accelerate data acquisition and reproducibility for these tasks in carbonate rocks this approach has been applied primarily to recognize carbonate lithofacies and no attempt has been made to individually identify and quantify various types of carbonate grains matrix and cement in this study the applicability and performance of dcnn based object detection and image classification approaches are assessed with respect to carbonate compositional analysis the training data comprised of more than 13 000 individually labelled objects from nearly 4000 carbonate petrographic images the dataset is grouped into six and nine different classes for the image classification and object detection tasks respectively even with a small and relatively imbalanced training set the dcnn was able to achieve an f1 score of 92 for image classification and 84 mean precision for object detection by combining one cycle policy class weight and label mixup smoothing methods this study highlights the inefficiency of image classification as an approach to replicating human description and classification of carbonate petrography by contrast dcnn based object detection appears capable of approaching human speed and accuracy in the area of carbonate petrography because it is able to individually locate and identify different carbonate components with greater cost efficiency speed and reproducibility than conventional human petrographic analysis

seismic interferometry using multidimensional deconvolution and crosscorrelation for crosswell seismic reflection data without borehole sources crosswell reflection method is a high resolution seismic imaging method that uses recordings between boreholes the need for downhole sources is a restrictive factor in its application for example to time lapse surveys an alternative is to use surface sources in combination with seismic interferometry seismic interferometry si could retrieve the reflection response at one of the boreholes as if from a source inside the other borehole we investigate the applicability of si for the retrieval of the reflection response between two boreholes using numerically modeled field data we compare two si approaches crosscorrelation cc and multidimensional deconvolution mdd si by mdd is less sensitive to underillumination from the source distribution but requires inversion of the recordings at one of the receiver arrays from all the available sources we find that the inversion problem is ill posed and propose to stabilize it using singular value decomposition the results show that the reflections from deep boundaries are retrieved very well using both the cc and mdd methods furthermore the mdd results exhibit more realistic amplitudes than those from the cc method for downgoing reflections from shallow boundaries we find that the results retrieved from the application of both methods to field data agree well with crosswell seismic reflection data using borehole sources and with the logged p wave velocity

reverse time migration migration of stacked or zero offset sections is based on deriving the wave amplitude in space from wave field observations at the surface conventionally this calculation has been carried out through a depth extrapolation we examine the alternative of carrying out the migration through a reverse time extrapolation this approach may offer improvements over existing migration methods especially in cases of steeply dipping structures with strong velocity contrasts this migration method is tested using appropriate synthetic data sets

geologic analysis of the upper jurassic haynesville shale in east texas and west louisiana the upper jurassic haynesville shale is currently regarded as one of the most prolific emerging shale gas plays in the continental united states it has estimated play resources of several hundred trillion cubic feet and per well reserves estimated as much as 7 5 bcf the reservoir spans more than 16 counties along the boundary of eastern texas and western louisiana although this basin has a long history of exploration and analysis of its mesozoic section a comprehensive subsurface study characterizing the haynesville shale has not been conducted this article is the first to address the structural setting stratigraphy depositional environment and facies fracturing and production challenges of the haynesville shale gas play basement structures and salt movement influenced carbonate and siliciclastic sedimentation associated with the opening of the gulf of mexico the haynesville shale is an organic and carbonate rich mudrock that was deposited in a deep partly euxinic and anoxic basin during the kimmeridgian to the early tithonian related to a second order transgression that deposited organic rich black shales worldwide the haynesville basin was surrounded by carbonate shelves of the smackover and haynesville lime louark sequence in the north and west several rivers supplied sand and mud from the northwest north and northeast into the basin haynesville mudrocks contain a spectrum of facies ranging from bioturbated calcareous mudstone laminated calcareous mudstone and silty peloidal siliceous mudstone to unlaminated siliceous organic rich mudstone framboidal to colloidal pyrite is variably present in the form of concretions laminae and individual framboids and replaces calcite cement and mollusk shells haynesville reservoirs are characterized by overpressuring porosity averaging 8 to 12 sw of 20 to 30 nanodarcy permeabilities reservoir thickness of 200 to 300 ft 70 to100 m and initial production of as much as 30 mmcf day reservoir depth ranges from 9000 to 14 000 ft 3000 to 4700 m and lateral drilling distances are 3000 to 5000 ft 1000 to 1700 m typical haynesville wells exhibit a steeper decline curve 80 in the first year than other shale gas plays which is attributed to a very high overpressure

lithospheric structure of the south central united states recent seismic data in the ouachita mountains area and the gulf of mexico make it possible to construct a lithospheric scale cross section transect from the midcontinent region to the gulf the authors constructed a transect in the form of a gravity model but it incorporates all available seismic drill hole and geologic data as constraints the thrust sheets of the ouachita orogenic belt appear as a thin veneer covering the southern part of the arkoma basin and the preserved paleozoic continental margin mesozoic rifting is evident in three areas 1 southern arkansas and northern louisiana where extension was minor 2 the vicinity of the texas louisiana coastline where modification of the lithosphere and subsidence were considerable and 3 the deep gulf of mexico where rifting was successful a significant variation in the average density of the mantle which could delineate the north american craton as a lithospheric feature was detected near the paleozoic continental margin

generating a relative geologic time volume by 3d graph cut phase unwrapping method with horizon and unconformity constraints abstractconstruction of a relative geologic time rgt volume is vital to seismic geomorphological and sedimentological interpretation seismic instantaneous phase unwrapping provides an excellent approach for generating an rgt volume although several 2d or 3d seismic phase unwrapping results have been published there is a clear need for discussions on concrete methods for seismic phase unwrapping we have developed the graph cut phase unwrapping method which performs well in the interferometric synthetic aperture radar image processing it has advantages of strong discontinuity preserving ability and high computing efficiency to make it suitable for 3d seismic phase unwrapping the method is improved by extending it from 2d to 3d and by introducing the seismic horizon and unconformity constraints the strong and continuous conformable seismic events which can be easily tracked by certain autopicking methods are introduced as horizon constraints for guiding the phase unwrapping to ensure a constant

diagenetic origin of quartz silt in mudstones and implications for silica cycling mudstone the most abundant sedimentary rock type1 composed primarily of clay or silt sized particles contains most of the quartz found in sedimentary rocks2 these quartz grains which are chemically and mechanically resistant and therefore preserve their characteristics well have long been considered to be derived from the continental crust1 here we analyse quartz silt from black shales in the eastern usa dating back to the late devonian period about 370 million years ago using backscattered electron and cathodoluminescence imaging and measure oxygen isotopes with an ion probe our results indicate that up to 100 of the quartz silt in our samples does not originate from the continental crust instead it appears to have precipitated early in diagenesis in algal cysts and other pore spaces3 with silica derived from the dissolution of opaline skeletons of planktonic organisms such as radiolaria and diatoms transformation of early diatoms into in situ quartz silt might explain the time gap between the earliest fossil occurrences of diatoms about 120 myr ago4 and molecular evidence for a much earlier appearance between 266 or even 500 myr ago5 6 moreover if many other mudstone successions show similarly high proportions of in situ precipitated rather than detrital quartz silt the sedimentary record in mudstones may have been misinterpreted in the past with consequences for our estimates of palaeoproductivity as well as our perceptions of the dynamics and magnitude of global biogeochemical cycling of silica

a genetic classification of carbonate platforms based on their basinal and tectonic settings in the cenozoic abstract this paper reassesses the usefulness of the morphological classification of carbonate platforms into rimmed shelves and ramps whilst the existing classifications have value in describing platform margin morphology at any one time the terms rimmed shelf and ramp are less successful at categorising the entire morphology and stratigraphy of carbonate platforms research on cenozoic carbonate platforms from a range of different tectono stratigraphic settings indicates that the basinal and tectonic setting of a platform can be used to erect a first order genetic classification of carbonate platforms the basinal and tectonic setting of carbonate platforms is shown to control their occurrence the overall 3 d platform morphology the large scale stratigraphic features and depositional sequences climate ocean chemistry and biological evolution control grain types facies and some elements of platform margins but not the larger scale features considered in this new classification from a review of well exposed outcropping and seismically imaged cenozoic platforms it is proposed that eight types of carbonate platform can currently be recognised and characterised based on their basinal and tectonic setting fault block salt diapir subsiding margin offshore bank volcanic pedestal thrust top delta top and foreland margin carbonate platforms these eight types are described using information from cenozoic platforms worldwide and the controls on their development are discussed many platform types e g subsiding margin offshore bank salt diapir thrust top and foreland margin are typical of particular classes of sedimentary basins others e g fault block volcanic pedestal and delta top are more widespread in their occurrence and occur in a range of basin types the value of this classification is that it is genetic rather than morphological the classification reflects the entire morphology and large scale stratigraphy of the platform and the controls on its development in addition the platform models can be used to understand the details of less well exposed or seismically imaged platforms so that they can be characterised and understood in terms of tectono sedimentary processes conversely the classification also provides valuable information on basin evolution as carbonate platforms house information on palaeoenvironments sea level change and are sensitive recorders of the tectonic environment

combination of surface and borehole seismic data for robust target oriented imaging a novel application of seismic interferometry si and marchenko imaging using both surface and borehole data is presented a series of redatuming schemes is proposed to combine both data sets for robust deep local imaging in the presence of velocity uncertainties the redatuming schemes create a virtual acquisition geometry where both sources and receivers lie at the horizontal borehole level thus only a local velocity model near the borehole is needed for imaging and erroneous velocities in the shallow area have no effect on imaging around the borehole level by joining the advantages of si and marchenko imaging a macrovelocity model is no longer required and the proposed schemes use only single component data furthermore the schemes result in a set of virtual data that have fewer spurious events and internal multiples than previous virtual source redatuming methods two numerical examples are shown to illustrate the workflow and to demonstrate the benefits of the method one is a synthetic model and the other is a realistic model of a field in the north sea in both tests improved local images near the boreholes are obtained using the redatumed data without accurate velocities because the redatumed data are close to the target

elastic properties of rock salt laboratory measurements and gulf of mexico well log analysis abstractrock salt essentially halite is a special type of sedimentary rock that has played a large role throughout tectonic and economic history the unique physical properties of halite ductility low density flowability and impermeability can be critical factors in hydrocarbon traps and underground storage however seismic imaging and interpretation can be challenging when salt structures are present due to their complex geometry and large impedance contrasts relative to surrounding rocks to investigate the properties of rock salt in terms of elastic parameters we use ultrasonic laboratory measurements and well logs in the laboratory we have analyzed the effects of composition crystalline structure pressure and temperature on the elastic behavior of a variety of rock salt samples the samples include pure halite 95 wt from the gulf of mexico gom area argillaceous rock salt from the zipaquira mine colombia and crystalline salt from the goderich mine canada current measurements su

review of late jurassic depositional systems and potential hydrocarbon plays northern gulf of mexico basin abstract post salt upper jurassic siliciclastic and carbonate rocks in the east texas north louisiana mississippi region record the early post rift evolution of the interior zone rift basins of the northern gulf of mexico basin four major river systems were fixed in space but variable in supply rate they carried sand and mud in from the northwest ancestral red river the north ancestral ouachita river the northeast ancestral mississippi river and the east ancestral alabama river shoal water carbonate deposits formed when siliciclastic inputs were low and shallow water high energy conditions prevailed usually in association with basement highs salt swells and abandoned deltaic shelf margins smackover shoal water carbonates formed within an extensive carbonate ramp from south central arkansas to central texas and were influenced by initial salt movement subsequent haynesville age gilmer carbonate shoals in texas rimmed rift related high blocks as well as highs formed by early salt movement siliciclastic sedimentation progressively dominated east of shreveport and submarine fans developed in association with a lowstand episode during early cotton valley time a major southeastward advance of the ancestral red river delta formed the taylor and bossier sand series while to the east lower terryville shoreline sands began to prograde southward in front of an expanding lagoon during late cotton valley time continued clastic sedimentation formed wave dominated deltas in texas and upper terryville strike fed sandstones in north louisiana at the close of cotton valley deposition in the earliest cretaceous regional transgression allowed knowles carbonates to colonize the abandoned shelf edge and form a thick shelf edge reef complex on its seaward slope the significant calvin lowstand wedge of sandstones was deposited offshore of this edge in louisiana during a subsequent major sea level fall and was then covered by winn carbonates deposited during the subsequent sea level rise high potential exploration plays remain in upper jurassic strata smackover and buckner gilmer shoals have produced over 10 trillion cubic feet of gas tcfg and 750 million barrels of oil mmbo in east texas and north louisiana but large segments of the complex atolls along the sabine uplift have not been defined complex shoals may rim old rift related highs such as the sabine and wiggins highs the gilmer cotton valley lime pinnacle reefs of the robertson leon trend may develop in one form or another over a broad swath of east central texas into westernmost louisiana haynesville age submarine fans may extend eastward into mississippi updip cotton valley is an established 10 tcf tight gas sandstone play in texas and louisiana but its basinward extensions have high untapped potential significant high quality upper cotton valley production similar to the north louisiana blanket sands may still be found in central mississippi the earliest cretaceous knowles calvin winn margin is poorly tested calvin like sandstones of the lowstand wedge should occur in east central texas and in southwestern mississippi

upper jurassic reef play east texas basin an updated overview part 1 background and outboard trend this paper is the first part of a two part update on geologic and geophysical characterization of gas productive upper jurassic carbonate buildups in the cotton valley limestone of the east texas basin continued exploration in this play has yielded important new information on the nature timing and genesis of the relevant buildup features this information is crucial to an understanding of existing and future productive trends in the play recent drilling and discovery have resulted in the identification of two major fairways 1 an older outboard or downdip trend existing along the distally steepened portions of the ramp at present day depths of 16 000 17 000 ft 4880 5185 m and 2 a younger inboard or updip trend located along the salt deformed portion of the late jurassic ramp system and lying at depths of 14 100 15 300 ft 4300 4666 m this paper focuses on the outboard trend with discussion of the inboard trend reserved for part 2 both articles present core thin section and other sample data as well as seismic information that together offer the most comprehensive overview of these buildups yet available

predictive painting of 3d seismic volumes predictive painting is a numerical algorithm that spreads information in 3d volumes according to the local structure of seismic events the algorithm consists of two steps first local spatially variable inline and crossline slopes of seismic events are estimated by the plane wave destruction method next a seed trace is inserted in the volume and the information contained in that trace is spread inside the volume thus automatically painting the data space immediate applications of this technique include automatic horizon picking and flattening in applications to both prestack and poststack seismic data analysis synthetic and field data tests demonstrate the effectiveness of predictive painting

imaging internal multiples from subsalt vsp data examples of target oriented interferometry seismic interferometry has become a technology of growing interest for imaging borehole seismic data we demonstrate that interferometry of internal multiples can be used to image targets above a borehole receiver array by internal multiples we refer to all types of waves that scatter multiple times inside the model these include for instance interbed intrasalt and water bottom multiples as well as conversions among them we use an interferometry technique that is based on representation theorems for perturbed media and targets the reconstruction of specific primary reflections from multiply reflected waves in this interferometry approach we rely on shot domain wavenumber separation to select the directions of waves arriving at a given receiver using a numerical walkaway waw vsp experiment recorded by a subsalt borehole receiver array in the sigsbee salt model we use the interference of internal multiples to image the salt structure from below in this numerical example the interferometric i

stratigraphic surfaces in the depositional and chronostratigraphic wheeler transformed domain one of the controversial and still debated issues of sequence stratigraphy is the assessment of stratigraphic surfaces in a chronostratigraphic framework catuneanu 2006 to assess whether the bounding surfaces of systems tracts or sequences are isochronous or diachronous is of paramount importance for stratigraphic correlation new software developments enable us to study stratigraphic surfaces within such a chronostratigraphic framework and allow us to predict something about their time attributes

geometrical considerations in the acquisition of borehole interferometric data for imaging near vertical features design of field experiments abstractseismic interferometry applied to walkaway vertical seismic profile data has significant potential for imaging the steeply dipping structures often encountered in hard rock minerals exploration using the interferometry process surface shots can be redatumed to the borehole receivers resulting in virtual shot gathers the virtual shot gathers can then be processed using a standard common midpoint cmp processing flow carrying out this procedure for a subvertical borehole results in a geometry that is optimal for imaging structures that are near vertical field acquisition parameters play a critical role in recovering reliable virtual source images we evaluated the major factors that play a role in designing a field acquisition program with the objective of providing guidance to field practitioners the major issue to be considered is insuring that correlation gathers created in the interferometry process have a stationary phase component that when summed produces events with correct timing and

relative geologic time age volumes relating every seismic sample to a geologically reasonable horizon the age volume described in this paper can significantly increase the amount of useful geologic information extracted from a seismic data volume this paper has three goals the first is to introduce and describe the relative geologic time volume referred to herein as either an rgt volume or an age volume every seismic sample in an age volume contains an estimate of the relative geologic time for that sample which automatically relates every sample to a geologic horizon the second goal is to discuss some of the applications and advantages of using a rgt volume to store and access seismic interpretation for example it can be used to sculpt a seismic volume along a desired horizon or view depositional changes as a function of geologic time the third goal is to describe two methods for generating such a volume the first employing standard interpretation techniques and the second relying on unwrapping instantaneous phase unwrapping the instantaneous phase is a new holistic approach to interpreting seismic data that can produce a very detailed seismic interpretation the goal of building and using an rgt volume is to extract significantly more geologic information from the seismic data than is available from conventional methods the rgt volume is both a way of storing and retrieving seismic horizons to generate such a volume each seismic sample needs to be assigned an estimate of relative geologic time which in essence connects it to a geologically reasonable horizon in normal sections these relative geologic time values will increase with depth or traveltime high gradients in the rgt volume could be indicative of faults unconformities fluid contacts or interpretation errors while a constant value surface in a rgt volume is a seismic horizon figure 1 contains a portion of the seismic data used to illustrate the

cotton valley lime pinnacle reef play branton field a frontier play for gas charged jurassic carbonate buildups interpreted as pinnacle reefs is under way along the western shelf of the east texas basin scattered reef type features 200 800 ac in size have been identified thus far over an area approximately 6 mi 10 km wide by 50 mi 80 km long as of january 1996 four new fields had been discovered with individual well productivities of 9 30 mcf footnote gas day and per well reserves of 5 75 gcf footnote gas this paper presents new well log 3 d seismic and other information indicating the basic structural and depositional character of these features through a focus on branton field leon county these data strongly suggest the regional potential of the play and highlight the value gained by reevaluating k own provinces in the light of new interpretive schemes and technology

redatuming through a salt canopy and target oriented salt flank imaging we describe a new shortcut strategy for imaging the sediments and salt edge around a salt flank through an overburden salt canopy we tested its performance and capabilities on 2d synthetic acoustic seismic data from a gulf of mexico style model we first redatumed surface shots using seismic interferometry from a walkaway vertical seismic profile survey as if the source and receiver pairs had been located in the borehole at the positions of the receivers this process creates effective downhole shot gathers by completely moving surface shots through the salt canopy without any knowledge of overburden velocity structure after redatuming we can apply multiple passes of prestack migration from the reference datum of the bore hole in our example first pass migration using only a simple vertical velocity gradient model reveals the outline of the salt edge a second pass of reverse time prestack depth migration using full two way wave equation was performed with an updated velocity model that consisted of the velocity gradient and salt dome the second pass migration brings out dipping sediments abutting the salt flank because these reflectors were illuminated by energy that bounced off the salt flank forming prismatic reflections in this target oriented strategy the computationally fast redatuming process eliminates the need for the traditional complex process of velocity estimation model building and iterative depth migration to remove effects of the salt canopy and surrounding overburden this might allow this strategy to be used in the field in near real time