kirchhoff migration using eikonal equation traveltimes the use of ray shooting followed by interpolation of traveltimes onto a regular grid is a popular and robust method for computing diffraction curves for kirchhoff migration an alternative to this method is to compute the traveltimes by directly solving the eikonal equation on a regular grid without computing raypaths solving the eikonal equation on such a grid simplifies the problem of interpolating times onto the migration grid but this method is not well defined at points where two different branches of the traveltime field meet also computational and data storage issues that are relatively unimportant for performance in two dimensions limit the applicability of both schemes in three dimensions a new implementation of a gridded eikonal equation solver has been designed to address these problems a 2 d version of this algorithm is tested by using it to generate traveltimes to migrate the marmousi synthetic data set using the exact velocity model the results are compared with three other images an f x migration a standard for comparison a kirchhoff migration using ray tracing and a kirchhoff migration using traveltimes generated by a commonly used eikonal equation solver the f x migrated image shows the imaging objective more clearly than any of themore kirchhoff migrations and the authors advance a heuristic reason to explain this fact of the kirchhoff migrations the one using ray tracing produces the best image and the other two are of comparable quality less

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

on a plane wave based crosscorrelation type seismic interferometry we explored a new approach to retrieve virtual seismic responses from crosscorrelating acquired seismic data in the plane wave domain using this method slant stacking is first performed over shot or receiver locations of observed seismic data to produce plane wave transformed gathers crosscorrelation is then performed by selecting traces with the same ray parameters from different shot or receiver locations of the plane wave gathers unlike traditional crosscorrelation type time space domain interferometry where full range of ray parameters is used for each survey location this method directly selects common ray parameters to cancel overlapping raypaths this approach can be used to retrieve reflections in the presence of dispersive waves and to select certain ranges of ray parameters with directional wave paths for retrieval it can avoid spurious arrivals in supervirtual interferometry when unwanted arrivals such as reflections break the requirement of conventional interferometry in addition computation time can be saved with this approach because plane wave transform usually results in a reduction of the original data volume we demonstrate this method with synthetic and ocean bottom seismometer data examples

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

3 d prestack kirchhoff beam migration for depth imaging a beam implementation is presented for efficient full volume 3 d prestack kirchhoff depth migration of seismic data unlike conventional kirchhoff migration in which the input seismic traces in time are migrated one trace at a time into the 3 d image volume for the earth s subsurface the beam migration processes a group of input traces a supergather together the requirement for a supergather is that the source and receiver coordinates of the traces fall into two small surface patches the patches are small enough that a single set of time maps pertaining to the centers of the patches can be used to migrate all the traces within the supergather by taylor expansion or interpolation the migration of a supergather consists of two major steps stacking the traces into a p beam volume and mapping the beams into the image volume since the beam volume is much smaller than the image volume the beam migration cost is roughly proportional to the number of input supergathers the computational speedup of be

vsp beyond time to depth vsp or vertical seismic profile was originally designed and is currently primarily used to give us time to depth for seismic well ties beyond time to depth a number of possibilities exist recently there has been considerable interest in vsp imaging ray et al 2003 paulsson et al 2004 hornby et al 2004 hornby et al 2005a with extensive surveys being acquired both on land and offshore modeling studies using full waveform finite difference method fdm payne et al 1994 van gestel et al 2003 show us what we can image for a particular acquisition geometry and geology with best image results seen with 3d vsp surveys incorporating a large vsp array in the well and a 2d source pattern acquired using a surface seismic shooting vessel traditionally vsp imaging has been implemented using surface seismic processing algorithms however the vsp geometry poses its own challenges and unique opportunities in this article we explore some imaging methods to attempt to take advantage of the vsp g

interferometric imaging of a salt flank using walkaway vsp data vsp has long been a tool for investigating the location of salt flanks traditionally a salt proximity survey has been used to estimate the location of salt boundaries relative to a wellbore however this technique depends on accurate knowledge of the shape of the salt and the local sediment velocities in addition this method does not work well with complicated 3d salt structure beyond the traditional salt proximity survey many researchers have developed various methods and strategies for improving the locating and or imaging of salt flanks o brien et al 2002 brandsberg dahl et al 2003 zhao et al 2006 with these methods the quality of the resultant image depends on a prior knowledge of the possibly anisotropic overburden velocity field for very long offsets and also is concerned with multi pathing through salt invalidating a 2d assumption in looking for a simpler approach to this problem a single well imaging concept may be attractive using downhole sources and receivers it is possi

extended 3β alkyl steranes and 3 alkyl triaromatic steroids in crude oils and rock extracts abstract in oils and precambrian to miocene age source rocks from varying depositional environments we have conclusively identified several novel 3 alkyl sterane and triaromatic steroid series including 1 3 n pentyl steranes 2 3 isopentyl steranes 3 3 n hexyl steranes 4 3 n heptyl steranes 5 3 4 dimethyl steranes 6 3 butyl 4 methyl steranes 7 triaromatic 3 n pentyl steroids and 8 triaromatic 3 isopentyl steroids we have also tentatively identified additional homologs with 3 alkyl substituents as large as c11 the relative abundances of these compounds vary substantially between samples as indicated by 1 the ratio of 3 n pentyl steranes to 3 isopentyl steranes and 2 the ratio of 3 n pentyl triaromatic steroids to 3 isopentyl triaromatic steroids these data suggest possible utility for these parameters as tools for oil source rock correlations and reconstruction of depositional environments although no 3 alkyl steroid natural products are currently known several lines of evidence suggest that 3 alkyl steroids result from bacterial side chain additions to diagenetic 2 sterenes

gaussian beam migration just as synthetic seismic data can be created by expressing the wave field radiating from a seismic source as a set of gaussian beams recorded data can be downward continued by expressing the recorded wave field as a set of gaussian beams emerging at the earth s surface in both cases the gaussian beam description of the seismic wave propagation can be advantageous when there are lateral variations in the seismic velocities gaussian beam downward continuation enables wave equation calculation of seismic propagation while it retains the interpretive raypath description of this propagation this paper describes a zero offset depth migration method that employs gaussian beam downward continuation of the recorded wave field the gaussian beam migration method has advantages for imaging complex structures like finite difference migration it is especially compatible with lateral variations in velocity but gaussian beam migration can image steeply dipping reflectors and will not produce unwanted reflectio

imaging salt with turning seismic waves turning seismic waves which first travel downward and then upward before and after reflection have been recorded in a 3 d seismic survey conducted over an overhanging salt dome careful processing of these turning waves enables the imaging of the underside of the salt dome and of intrusions of salt into vertical faults radiating from the dome when seismic wave velocity increases with depth waves that initially travel downward are reflected and may turn so as to travel upward before reflection a simple geometrical argument suggests that these turning waves are likely to exhibit abnormal moveout in com mon midpoint cmp gathers in that reflection time decreases with increasing source receiver offset this abnormal moveout and the attenuation of turning waves by most migration methods suggest that conventional seismic processing does not properly image turning waves the most important step in imaging turning waves assuming that they have been recorded is the migration process simple and inexpensive modifications to the conventional phase shift migration method enable turning waves to be imaged for little additional computational cost the examples provided in this paper suggest that these and other such modifications to conventional processing should be used routinely when imaging salt domes

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

elastic reverse time migration of marine walkaway vertical seismic profiling data walkaway vertical seismic profiling vsp acquisition with three component geophones allows for direct measurement of compressional as well as shear energy this makes full elastic reverse time migration an attractive alternative for imaging data we present results from elastic reverse time migration of a marine walkaway vsp acquired offshore norway the reverse time migration scheme is based on a high order finite difference solution to the two way elastic wave equation depth images of the subsurface are constructed by correlation of forward and back propagated elastic wavefields in the walkaway vsp configuration the number of shots is much larger than the number of geophone levels using processing methods operating in the shot receiver domain it is advantageous to use the reciprocal relationship between the walkaway vsp and the reverse vsp configurations we do this by imaging each component of each geophone level as a reverse vsp common shot gather the final images are constructed by stacking partial images from each level the depth images obtained from the vertical components reveal the major characteristics of the geological structure below geophone depth a graben in the base cretaceous unconformity and a faulted coal layer can be identified the horizontal components are more difficult to image compared to the vertical components the horizontal component images are more corrupted by migration artifacts this is because the horizontal component images are more sensitive to aperture effects and to the shear wave velocity macromodel when converted to two way time the migration results tie well with the surface seismic section comparison of fully elastic and acoustic reverse time migration shows that the vertical component is dominantly pp reflected events whereas the horizontal components get important contributions from ps converted energy the horizontal components also provide higher resolution because of the shorter wavelength of the shear waves

inversion for salt flank geometry using transmitted p and s wave travel times accurate delineation of the salt flank is important for oil and gas exploration in areas with salt intrusion we describe the application of deformable layer tomography dlt to invert for the geometry of salt flank using travel times of transmitted p and s waves from surface sources to downhole receivers the dlt allows us to take advantage of a common situation that the salt velocity is known and generally invariant but we need to determine the variable geometry of salt flank we demonstrate our new method using a physical model experiment mimicking the setup of a walkaway vertical seismic profiling vsp survey we first use picked p wave arrivals to invert for the salt flank geometry the sinusoid shape of the salt flank is estimated fairly by the dlt due to the uneven p wave raypath coverage as an improvement we further incorporate the s wave arrivals in the dlt the picking of s wave arrivals is assisted with modeled s wave arrivals based on the p wave dlt model the dlt solution using both p and s wave arrivals delineates the salt flank geometry more accurately than that using p wave arrivals alone the salt flank delineation using dlt can complement with the conventional salt proximity and migration methods it could also serve as constraints or the initial model for the full waveform inversion of salt geometry

interferometric hydrofracture microseism localization using neighboring fracture hydraulic fracturing is the process of injecting high pressure fluids into a reservoir to induce fractures and thus improve reservoir productivity microseismic event localization is used to locate created fractures traditionally events are localized individually available information about events already localized is not used to help estimate other source locations traditional localization methods yield an uncertainty that is inversely proportional to the square root of the number of receivers however in applications where multiple fractures are created multiple sources in a reference fracture may provide redundant information about unknown events in subsequent fractures that can boost the signal to noise ratio improving estimates of the event positions we used sources in fractures closer to the monitoring well to help localize events further away it is known through seismic interferometry that with a 2d array of receivers the traveltime between two sources may be recovered from a crosscorrelogram of two common source gathers this allowed an event in the second fracture to be localized relative to an event in the reference fracture a difficulty became evident when receivers are located in a single monitoring well when the receiver array is 1d classical interferometry cannot be directly employed because the problem becomes underdetermined in our approach interferometry was used to partially redatum microseismic events from the second fracture onto the reference fracture so that they can be used as virtual receivers providing additional information complementary to that provided by the physical receivers our error analysis showed that in addition to the gain obtained by having multiple physical receivers the location uncertainty is inversely proportional to the square root of the number of sources in the reference fracture because the number of microseism sources is usually high the proposed method will usually result in more accurate location estimates as compared with the traditional methods

fracture detection using crosswell and single well surveys we recorded high resolution 1 to 10 khz crosswell and single well seismic data in a shallow 15 to 35 m water saturated fractured limestone sequence at conoco s borehole test facility near newkirk oklahoma our objective was to develop seismic methodologies for imaging gas filled fractures in naturally fractured gas reservoirs the crosswell 1 4 m receiver spacing 50 to 100 m well separation surveys used a piezoelectric source and hydrophones before during and after an air injection that we designed to displace water from a fracture zone our intent was to increase the visibility of the fracture zone to seismic imaging and to confirm previous hydrologic data that indicated a preferred pathway for the single well seismic imaging a piezoelectric source and an eight element hydrophone array at 1 4 m spacing we also recorded data before and after the air injection the crosswell results indicate that the air did follow a preferred pathway that was predicted by hydrologic modeling in addition

virtual source applications to imaging and reservoir monitoring the virtual source method is a breakthrough that allows us to image and monitor the subsurface in cases where surface seismic or vsp fail to deliver in settings where the overburden is complex or changing traditional time lapse signals are weak or nonrepeatable leading to ineffective seismic input to reservoir modeling and little of value generated by repeated seismic surveys on the other hand the virtual source method allows us to image under complex overburden yields repeatable data for reservoir monitoring enables shear seismic and may help us look ahead as we drill

generalised receiver functions and seismic interferometry abstract classical seismological receiver functions are correlational or deconvolutional combinations of vertical and horizontal component seismometer recordings of earthquake waves that focus information on near receiver subsurface earth structure and properties we show that seismic interferometry can be thought of as a generalisation of receiver functions analysis to cases where recordings at pairs of receivers are considered simultaneously and where either the same or different component recordings are combined further seismic interferometry uses any of deconvolution convolution and cross correlation and energy from either impulsive or random noise sources we show both how receiver functions can logically be extended to a new convolutional form and that the now little used correlational form of receiver functions contains more intuitive information than previously realised seismic interferometry has provided other extraordinary extensions to seismologists arsenal passive noise recordings can be converted into seismograms from virtual imagined earthquakes that in turn can be used to image the real earth active sources e g earthquakes or man made sources can be redatumed into new virtual sources elsewhere or can be converted into virtual sensors seismometers that record seismograms from other real earthquakes man made sources or noise sources that occur either in the future or in the past and the ability to construct virtual sources and sensors at desired times and locations rather than having to wait for earthquake sources that occur at uncontrollable locations promises more repeatable monitoring of changes in earth subsurface properties over time indeed so called coda wave interferometry offers unprecedented accuracy in detecting such changes finally existing theoretical extensions to other regimes such as electromagnetic electrokinetic and diffusive energy propagation may lead to future revolutions in other domains of science

gaussian beam migration of common shot records gaussian beam migration is a depth migration method whose accuracy rivals that of migration by wavefield extrapolation so called wave equation migration and whose efficiency rivals that of kirchhoff migration this migration method can image complicated geologic structures including very steep dips in areas where the seismic velocity varies rapidly however applications of prestack gaussian beam migration either have been limited to common offset common azimuth data volumes and thus are inflexible or suffer from multiarrival inaccuracies in a common shot implementation in order to optimize both the flexibility and accuracy of gaussian beam migration i present a common shot implementation that handles multipathing in a natural way this allows the migration of data sets that can include a variety of azimuths and it allows a simplified treatment of near surface issues application of this method to model data typical of canadian foothills structures and to model data that includes a complicate

imaging of near borehole structure using full waveform sonic data the full waveforms recorded by an array of receivers in a modern borehole sonic tool contain secondary arrivals that are reflected from near borehole structural features these arrivals are used to form an image of the near borehole structural features in a manner similar to seismic migration possible uses of this technique include horizontal well logging structural dip and contour determination fault salt dome pinnacle reef and fracture zone imaging and eor steam flood monitoring since both the source and the receivers pass through structures that cross the borehole the downdip structure and the updip structure can be imaged separately the technique involves a backprojection of the recorded data into a matrix of accumulation bins representing distances radially out from the borehole and along the borehole axis separate matrices are formed for the updip and for the downdip raypaths the basic technique is illustrated with synthetic data generated to approximate the case of a sonic tool logging

detrital zircon geochronology of the northeastern tibetan plateau u pb geochronologic analyses have been conducted on 413 detrital zircon grains collected from 16 samples in the altun shan nan shan and qilian shan the samples come primarily from quartz arenites and metaturbidites of middle to late proterozoic age and from feldspathic and volcanic clast rich sandstones of early paleozoic age zircon grains in proterozoic strata resting on tarim basement yielded mainly 2 0 1 9 ga ages whereas proterozoic strata of the qaidam and qilian terranes yielded mainly ca 930 820 ma and ca 1 9 1 1 ga ages the younger grains were apparently shed from local igneous rocks whereas the grains older than 1 1 ga were shed from an undetermined continental source grains in the lower paleozoic strata are mainly ca 500 430 ma and were shed from nearby plutonic and possibly volcanic rocks that formed in a magmatic arc setting our detrital zircon ages are consistent with a model first proposed by e r sobel and n arnaud in which early paleozoic magmatism occurred within a single northeast facing magmatic arc that was constructed across an assemblage of middle to late proterozoic accretionary complexes remnants of magmatic arcs and shallow marine strata this arc system was accreted to the tarim and sino korean cratons during silurian devonian time the resulting suture has been reactivated as tertiary thrust faults that currently define the structural and topographic margin of the tibetan plateau our data also provide two new estimates for the offset along the eastern altyn tagh fault a belt of middle proterozoic shallow marine strata is offset by 400 km whereas a belt of 490 480 ma magmatic arc rocks is offset by 370 km these values are generally similar to the 350 400 km offset reported in most previous studies

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