reservoir fluid substitution effects on seismic profile interpretation a physical modeling experiment p wave seismic surveys are performed on realistic physical models of a reservoir formed of interbedded sand and shale layers and filled with gas water and oil they show characteristic behaviour which can be used to distinguish between fluids with significant implications for the interpretation of time lapse experiments discontinuous reflections originate in gas filled reservoirs with widely varying amplitude compared to oil or water filled reservoirs anomalous changes in seismic amplitude difference attributes for reflections within the reservoir are seen for gas oil substitution oil water substitution results in only weak variations of reservoir elastic properties thus amplitude difference attributes may be unsuitable for monitoring changes in oil water saturation however direct differences between the time traces are strong on time lapse sections strong amplitude difference anomalies do not necessarily correspond to the region where the fluid variations occur this is significant for monitoring oil field development by water injection

estimation of effective porosity using geostatistics and multiattribute transforms a case study the middle eocene kalol formation in the north cambay basin of india is producing hydrocarbons in commercial quantity from a series of thin clastic reservoirs these reservoirs are sandwiched between coal and shale layers and are discrete in nature the kalol formation has been divided into eleven units k i to k xi from top to bottom multipay sands of the k ix unit 2 8 m thick are the main hydrocarbon producers in the study area apart from their discrete nature these sands exhibit lithological variation which affects the porosity distribution low porosity zones are found devoid of hydrocarbons in the available 3d seismic data these sands are not resolved and generate a composite detectable seismic response making reservoir characterization through seismic attributes impossible after proper well to seismic tie the major stratigraphic markers were tracked in the 3d seismic data volume for structural mapping and carrying out attribute analysis the 3d seismic volume was inverted to obtain an aco

finite difference calculation of traveltimes in three dimensions the traveltimes of first arriving seismic rays through most velocity structures can be computed rapidly on a three dimensional numerical grid by finite difference extrapolation head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 11 percent are found between the results of this technique and ray tracing for a complex but smooth model this scheme has proven useful for earthquake location and shows promise as an inexpensive well behaved substitute for ray tracing in forward modeling and kirchhoff inversion applications

seismic architecture of a lower cretaceous platform to slope system santa agueda and poza rica fields mexico two three dimensional seismic data sets over the albian western golden lane margin and time equivalent basinal deposits of poza rica field allowed us to investigate the linked architecture of a steep sided carbonate platform el abra formation and a thick accumulation of redeposited carbonate sediment at the toe of the slope and in the basinal area tamabra formation regional seismic cross sections show that the most aggrading albian platform has an eroded platform top a scalloped margin and a channelized slope that are equivalent to a 20 km 12 4 mi wide westward thinning thick toe of slope apron made of chaotic contorted mounded moderate to high amplitude reflections detailed reflection geometries in the albian toe of slope and basinal deposits consist of chaotic to short discontinuous low amplitude reflection at the toe of the slope of the golden lane platform laterally changing to a discontinuous mounded shingling reflection which ultimately turns into high amplitude parallel reflections we interpret this lateral change to reflect the seismic signature of the change from the block and debris flow dominated toe of slope area to debris flow and concentrated density flow deposits in the basin that ultimately grade laterally into pelagic deposits on a flattened seismic slice mounded reflections correspond to lobate to fan shaped seismic events several kilometers wide that are interpreted as a carbonate basin floor fan comparison between core and seismic data shows a dominance of debris flows in the lower two albian sequences albian 1 and albian 2 that grade vertically into more lobate concentrated density flows and turbidites in the upper two albian sequences albian 3 and albian 4 seismic data used in this study combined with core observations do not support the interpretation of the albian tamabra formation being of shallow water origin seismic features identified as basin floor fan channel and debris flow deposits have a shape and size that are similar to those of other redeposited basinal carbonate deposits elsewhere the seismic architecture shows that the poza rica field is a typical example of thick accumulation of grainy porous carbonate deposits in a basinal setting this example shows the potential of a large hydrocarbon accumulation in a tectonically modified stratigraphic trap around shallow water carbonate platforms

applications of 3d seismic attribute analysis in hydrocarbon prospect identification and evaluation verification and validation based on fluvial palaeochannel cross sectional geometry and sinuosity ness county kansas usa abstract due to their high resolution and established success rates the analysis of geometrical and stratigraphic 3d seismic reflection data attributes have become one of the most important tools in many hydrocarbon exploration and development programs in areas with high drilling risk as a result of the lack of spatial continuity and lithological variation of potential prospects analysis of relevant seismic attributes is essential to successful placement of wells this study of the york field ness county kansas presents a corroborative finding based on the analysis of a set of 3d seismic attributes revealing a meandering fluvial channel system incised on the mississippian stratigraphic unconformity north east of a previously interpreted weirman field palaeoshoreline and submarine channels the york field prospect identification and appraisal program targeted the cherokee sands where reservoir properties are favorable and where it was thought that thick cherokee sands correlate with structural mississippian highs we produce evidence that cherokee sand prone fluvial facies is mappable based on synergistic analysis of seismic arrival time amplitude spectral decomposition acoustic impedance and waveform attributes seismic amplitude highs and relative acoustic impedance lows showed moderate conformance with mississippian horizon time lows controls exerted by channel post confluence water and sediments supply provide corroborating hydraulic geometry aspects for the interpreted fluvial system time structural maps in addition to time and horizon slices of several 3d seismic attributes including amplitude spectral decomposition components and relative acoustic impedance all seem to indicate that five previously drilled dry wells within the study area were outside the boundary of a meandering cherokee fluvial system of potential reservoir quality additionally comparisons of the results of this research to previous studies conducted in the south west of ness county have provided an opportunity to support and contribute to interpreted paleodepositional setting established by raef et al 2015 where a palaeoshorline was interpreted the results of this study support a broadly ne sw trending meandering channel system with se flow direction

pn velocities beneath continental collision zones the turkish iranian plateau summary tomographic imaging of the uppermost mantle velocity in the middle east shows normal pn velocities 8 0 8 2 kms beneath the black sea and the southern caspian sea in contrast low pn velocities 7 9 km s i are found beneath the aegean sea and much of the turkish iranian plateau a region of exceptionally low pn velocities c7 6 km s beneath the lesser caucasus mountains and along the turkish iranian border coincides with a region of high sn attenuation and extensive neogene volcanism all these features suggest that near solidus conditions exist within the uppermost mantle beneath the turkish iranian plateau such conditions may result either from the decompression melting associated with upwelling convection cells or by the infiltration of water released from subducted lithosphere into the mantle above the presence of a partially melted uppermost mantle weakens the lithosphere beneath the turkish iranian plateau thus allowing it to become the locus of deformation in the arabian eurasian collision zone

using multi attribute neural networks classification for seismic carbonate fades mapping a workflow example from mid cretaceous persian gulf deposits abstract seismic facies mapping in large seismic surveys can be time consuming even if only a basic overview of the facies distribution is needed therefore this study outlines an approach for the use of volume based seismic attributes from 2d surveys for automated seismic facies mapping within carbonate settings the study area is located in the central persian gulf offshore iran the interval of interest is the mid cretaceous sarvak formation which is part of the extensive cretaceous shallow water carbonate platform of the eastern arabian plate a set of nine volume based seismic attributes calculated from time amplitude and frequency information of post stacked 2d seismic data was chosen to characterize geological information within the interval of interest the volume based attributes were supplemented by two grid based attributes to highlight structural elements the geological significance of each attribute was evaluated by comparing it with results of seismic sedimentological geomorphological studies furthermore statistical methods were applied to highlight direct relationships amongst the attributes the results of these tests were then used to choose a limited set of attributes for neural network based multi attribute classifications the results show that seismic attributes derived from 2d surveys can be used to map basic seismic facies types in carbonate settings and that the outlined general approach might be applied in other studies

sinking of the dharwar basin south india implications for archaean tectonics abstract archaean tectonic regimes can be constrained by structural analysis of greenstone belts and adjacent granite gneiss masses the late archaean bababudan greenstone belt dharwar craton south india contains a low grade volcanosedimentary basin sequence the dharwar supergroup which unconformably overlies a previously eroded basement made up mainly of granite and gneiss fabric trajectories kinematic indicators and superimposed deformation patterns show that greenstones have undergone a radial converging downward flow with respect to underlying basement rocks as well as strike slip shearing this is attributed to the progressive sagduction gravity sinking of the greenstone belt into its basement along a decollement horizon and to late transcurrent shearing we propose a deformation model for the bababudan belt that may explain common features of many greenstone belts such as decollements and superimposed upright fold patterns which are attributed to the progressive sinking of the supracrustals into their basement the results of our study and other field investigations in the crust of the dharwar craton as well as structural evidence from other cratons zimbabwe and pilbara raise the possibility that a unique continental tectonic regime existed during the archaean controlled by the emplacement of dense volcanic traps mantle underplating and thermal blanketing of the continental crust this tectonic regime differs from that observed within the modern lithosphere as it is characterized by the pervasive development of gravity i e rayleigh taylor instabilities between the volcanic traps and the rest of the continental crust it allowed heat and material transfer through the crust and has to be seen as an efficient recycling mechanism for the young continental crust during periods of mantle underplating the diapiric phenomenon is independent of the boundary forces acting at the limits of the protocontinents and is associated in time and space with large scale accretion events of the continental crust perhaps in hot spot environments

finite difference calculation of travel times the travel times of the first arriving seismic waves through any velocity structure can be rapidly computed on a two or three dimensional numerical grid by finite difference extrapolation from point to point wavefronts rather than the traditional rays are tracked head waves are properly treated and shadow zones are filled by the appropriate diffractions differences of less than 0 03 per cent are found between the results of this technique and raytracing for a complex two dimensional model this scheme is useful for the windowing of finite difference calculations to increase computing speed and promises to aid in earthquake location tomographic inversion and kirchhoff migration in structures that have strong lateral velocity gradients

kinematic interpretation of the 3d shapes of metamorphic core complexes 1 metamorphic core complexes form dome shaped structures in which the ductile crust is exhumed beneath a detachment fault the 3d dome geometry inferred by mapping the schistosity in the exhumed crust can be either elongated normal to the stretching direction or along it in the first case the domes are interpreted as having formed during extension however in the second case they are interpreted either as strike slip transpressive or constrictive extensional structures depending on the geodynamic context numerical models of metamorphic core complexes published to date are all two dimensional and therefore theoretically only apply to domes which are elongated normal to the stretching direction here we explore by means of 3d thermomechanical modeling the impact of 3d kinematic extensional boundary conditions on the shape of metamorphic core complexes we examine the impact of a transtensional step over and of horsetail splay fault kinematics on the dynamics of exhumation finite strain and p t paths and compare them to cylindrical 3d models we show for the first time that domes formed in transtensional step over or at the tip of propagating strike slip faults display a finite strain field which can be interpreted as characteristic of a transpressive domes although no shortening was applied in the far field applying our models to the cyclades we propose that the coeval formation of domes elongated normal and parallel to the stretching during the miocene can be the result of horsetail splay fault kinematics which could correspond to the formation of a tear in the aegean slab

analysis and interpretation of seismic data from thin reservoirs northwest java basin indonesia a detailed analysis and interpretation is performed of a 2 d seismic line over a sequence of thin reservoirs in the upper cibulakan formation in the northwest java basin most well sites in this area are selected to be structures near fault zones as faults are assumed to be the main hydrocarbon migration paths amplitude variation with offset analysis is little used because of contamination by thin layer tuning effects attribute analysis impedance inversion and full wavefield modeling suggest that gas reservoirs are detectable even when they are less than their tuning thickness as they correspond to acoustic impedance anomalies and low instantaneous frequency the presence of hydrocarbons can also be detected by anomalous behavior in crossplots of acoustic impedance versus density and p wave velocity sandstone reservoirs show low velocity and low impedance two dimensional p velocity and density distributions resulting from impedance inversion produce synthetic elastic common source gathers that disp

assessment of crustal velocity models using seismic refraction and reflection tomography two tomographic methods for assessing velocity models obtained from wide angle seismic traveltime data are presented through four case studies the modelling inversion of wide angle traveltimes usually involves some aspects that are quite subjective for example 1 identifying and including later phases that are often difficult to pick within the seismic coda 2 assigning specific layers to arrivals 3 incorporating pre conceived structure not specifically required by the data and 4 selecting a model parametrization these steps are applied to maximize model constraint and minimize model non uniqueness however these steps may cause the overall approach to appear ad hoc and thereby diminish the credibility of the final model the effect of these subjective choices can largely be addressed by estimating the minimum model structure required by the least subjective portion of the wide angle data set the first arrival times for data sets with moho reflections the tomographic velocity model can be used to invert the pmp times for a minimum structure moho in this way crustal velocity and moho models can be obtained that require the least amount of subjective input and the model structure that is required by the wide angle data with a high degree of certainty can be differentiated from structure that is merely consistent with the data the tomographic models are not intended to supersede the preferred models since the latter model is typically better resolved and more interpretable this form of tomographic assessment is intended to lend credibility to model features common to the tomographic and preferred models four case studies are presented in which a preferred model was derived using one or more of the subjective steps described above this was followed by conventional first arrival and reflection traveltime tomography using a finely gridded model parametrization to derive smooth minimum structure models the case studies are from the se canadian cordillera across the rocky mountain trench central india across the narmada son lineament the iberia margin across the galicia bank and the central chilean margin across the valparaiso basin and a subducting seamount these case studies span the range of modern wide angle experiments and data sets in terms of shot receiver spacing marine and land acquisition lateral heterogeneity of the study area and availability of wide angle reflections and coincident near vertical reflection data the results are surprising given the amount of structure in the smooth tomographically derived models that is consistent with the more subjectively derived models the results show that exploiting the complementary nature of the subjective and tomographic approaches is an effective strategy for the analysis of wide angle traveltime data

seismic attribute technology for reservoir forecasting and monitoring during the 1970s and 1980s the seismic attributes most used in petroleum exploration were amplitude based instantaneous attributes however in the 1990s seismic attribute technology has dramatically advanced in several directions techniques now range from single trace instantaneous event attribute computations to more complex multitrace windowed seismic event attribute extractions to the generation of seismic attribute volumes applications run from simple amplitude anomaly detection to monitoring fluid front movement over time

simultaneous velocity and interface tomography of normal incidence and wide aperture seismic traveltime data summary a tomographic inversion technique that inverts traveltimes to obtain a model of the subsurface in terms of velocities and interfaces is presented it uses a combination of refraction wide angle reflection and normal incidence data it simultaneously inverts for velocities and interface depths and it is able to quantify the errors and trade offs in the final model the technique uses an iterative linearized approach to the non linear traveltime inversion problem the subsurface is represented as a set of layers separated by interfaces across which the velocity may be discontinuous within each layer the velocity varies in two dimensions and has a continuous first derivative rays are traced in this medium using a technique based on ray perturbation theory and two point ray tracing is avoided by interpolating the traveltimes to the receivers from a roughly equidistant fan of rays the calculated traveltimes are inverted by simultaneously minimizing the misfit between the data and calculated traveltimes and the roughness of the model this smoothing regularization stabilizes the solution of the inverse problem in practice the first iterations are performed with a high level of smoothing as the inversion proceeds the level of smoothing is gradually reduced until the traveltime residual is at the estimated level of noise in the data at this point a minimum feature solution is obtained which should contain only those features discernible over the noise the technique is tested on a synthetic data set demonstrating its accuracy and stability and also illustrating the desirability of including a large number of different ray types in an inversion

coincident seismic reflection refraction studies of the continental lithosphere a global review nearly 50 coincident seismic reflection refraction studies to depths of at least the moho provide an improved understanding of the continental lithosphere some conclusions include the following 1 a transparent upper crust a common observation on vertical reflection profiles cannot generally be correlated with velocity gradients or low velocity zones rather a commonly transparent upper crust may be explained by short wavelength steeply dipping features in the brittle upper crust and to a lesser degree by signal contamination from source generated noise 2 the reflective lower crust in extensional terranes appears to be characterized by a high average seismic velocity 6 6 7 3 km s and to consist of laminated high and low velocity layers with typical thicknesses of 100 200 m 3 landward dipping reflectors observed in the middle to lower crusts of convergent zones have been identified as paired high and low velocity slabs which represent oceanic crust and mantle accreted via underplating to the continental margin 4 the crust mantle boundary may differ sufficiently when imaged with vertical incidence and wide angle data to justify the retention for the present of the concept of separate reflection and refraction mohos while there is good evidence that these features are coincident within measurement uncertainties in most regions recently recorded data from the basin and range admit the possibility for noncoincidence in that area 5 upper mantle reflections which cannot be migrated into the lower crust remain rare despite isolated unequivocal examples thus the upper mantle appears to be relatively homogeneous at seismic reflection wavelengths and to lack the laminations inferred for the lower crust the wide angle method will likely provide the most reliable information on the velocity structure and physical state of this portion of the lithosphere for some years to come 6 there appear to be clear and consistent basic differences between convergent and extensional terranes which have been identified from coincident experiments these differences may be sufficiently universal to infer the tectonic history of poorly exposed terranes 7 no truly three dimensional coincident experiment i e including three dimensional migration has been conducted but some three dimensional data have been collected using both methods measurements of attenuation poisson s ratio and anisotropy within the crust using coincident data sets remain frontiers

seismic attributes a historical perspective a seismic attribute is a quantitative measure of a seismic characteristic of interest analysis of attributes has been integral to reflection seismic interpretation since the 1930s when geophysicists started to pick traveltimes to coherent reflections on seismic field records there are now more than 50 distinct seismic attributes calculated from seismic data and applied to the interpretation of geologic structure stratigraphy and rock pore fluid properties the evolution of seismic attributes is closely linked to advances in computer technology as examples the advent of digital recording in the 1960s produced improved measurements of seismic amplitude and pointed out the correlation between hydrocarbon pore fluids and strong amplitudes bright spots the introduction of color printers in the early 1970s allowed color displays of reflection strength frequency phase and interval velocity to be overlain routinely on black and white seismic records interpretation workstations in the 1980s provided

ignimbrite depositional facies the anatomy of a pyroclastic flow a model is presented for the depositional regimes in a pyroclastic flow to explain the origin of facies in the taupo ignimbrite and to compare these with other published examples in this model a pyroclastic flow consists of a head a body and a tail the head which is where fluidization caused by air ingestion occurs generates layer 1 deposits on lithological grounds these are divided into layers 1 p which is fines depleted and rich in pumice and 1 h which is fines depleted and rich in lithics and crystals layer 1 p represents material thrown forwards from the flow head and is termed the jetted deposits layer 1 h represents material sedimented from within the flow head and is termed the ground layer the body represents the bulk of the flow and the tail is its trailing part which is slowed by ground friction these parts generate the layer 2 deposits which include the valley pond ignimbrite and its associated ignimbrite veneer deposit localized depositional modes within the body and tail generate distinctive coarse pumice concentration zones and pumiceous lee side lenses behind obstacles at its outer limits all of the flow on interfluves is affected by air ingestion fluidization producing the distant facies which combines features of both layer 1 and 2 deposits one important conclusion of this work is that the thicknesses and compositions of the various facies are not related in any simple way to the thickness and composition of the parent flow

porosity prediction from seismic attributes of the ordovician trenton black river groups rochester field southern ontario this article integrates three dimensional 3 d seismic attributes and log data to determine porosity distribution of the ordovician trenton black river groups within the rochester field southern ontario the rocks are composed of tight limestone parts of which were dolomitized to form porous reservoir rock previous studies of the trenton black river dolomite reservoirs have indicated a close relationship between faulting and reservoir development but few published studies have attempted to examine these relationships using 3 d seismic data this study explores the stratigraphy and structure of the rochester fault related dolomite reservoir using 3 d seismic data and neural networks to predict porosity by predicting porosity using seismic attributes vertical and lateral distributions of porosity that can be used to guide development and exploration drilling for optimal hydrocarbon recovery were obtained the sites of highest porosity were found to be along and within the fault zones faults extending from the basement into overlying paleozoic rocks are composed of several short plane vertical and subvertical fault segments however some of these faults appear to have originated and died within the paleozoic rocks they cannot be traced to the basement because of little or no offset where they penetrate the basement although the five identified attributes are considered important in exploration for fault related dolomite reservoirs the single most important attribute to employ is the amplitude envelope because the other attributes are mathematically related to it furthermore the sags that are seen in the rochester field are due to the combined effects of low velocity pushdown and faulting methods and results presented in this study can be used to explore and develop fault related dolomite reservoirs elsewhere in similar geologic settings

mid crustal partitioning and attachment during oblique convergence in an arc system palaeoproterozoic ketilidian orogen southern greenland abstract the ketilidian orogen in se greenland contains a continental magmatic arc julianehab batholith and forearc which formed in the overriding plate of a palaeoproterozoic oblique subduction boundary between c 1854 and 1795 ma during uplift and deformation of the forearc between c 1795 and 1780 ma its sedimentary sequences were invaded by arc type magmas and metamorphosed at ht lp upper amphibolite facies conditions which led to widespread anatexis and generation of abundant s type granites transpression during early deformation d 1 was partitioned into arc parallel sinistral strike slip in the magmatic arc rocks of the batholith and arc normal contraction in the sedimentary and volcaniclastic sequences of the proximal forearc psammite zone subsequently d 1 fabrics in the psammite zone were overprinted and transposed in an intense flat lying d 2 ductile shear zone with arc parallel stretching lineations and top ne kinematic indicators the kinematic significance of the d 2 shear zone is that it accommodated vertical differences in strain and displacement and permitted deformation to be partitioned differently at different levels in the crust as such it is an attachment or coupling zone that provided kinematic linkage between deformation at different crustal levels during ne transport of a forearc sliver overprinting of the upper crustal domain of d 1 strike slip partitioned transpression in the forearc during d 2 is attributed to migration of the attachment zone to a higher crustal level this migration was a consequence of an enhanced geothermal gradient in the proximal part of the forearc due to the emplacement of batholith related plutonic suites during d 2

three dimensional seismic refraction tomography a comparison of two methods applied to data from the faeroe basin this paper presents a comparison of two tomographic methods for determining three dimensional 3 d velocity structure from first arrival travel time data the first method is backprojection in which travel time residuals are distributed along their ray paths independently of all other rays the second method is regularized inversion in which a combination of data misfit and model roughness is minimized to provide the smoothest model appropriate for the data errors both methods are nonlinear in that a starting model is required and new ray paths are calculated at each iteration travel times are calculated using an efficient implementation of an existing method for solving the eikonal equation by finite differencing both inverse methods are applied to 3 d ocean bottom seismometer obs data collected in 1993 over the faeroe basin consisting of 53 479 travel times recorded at 29 obss this is one of the most densely spaced large scale 3 d seismic refraction experiments to date different starting models and values for the free parameters of each tomographic method are tested a new form of backprojection that converges more rapidly than similar methods compares favorably with regularized inversion but the latter method provides a simpler model for little additional computational expense when applied to the faeroe basin data bounds on two model features are assessed using regularized inversion with combined smoothness and flatness constraints an inversion of synthetic data corresponding to 100 data recovery from the real experiment shows a marked improvement in lateral resolution at deeper depths and demonstrates the potential of currently feasible 3 d refraction experiments to provide well resolved long wavelength velocity models the similarity of the final models derived from the two tomographic methods suggests that the results from the new form of backprojection can be relied on when limited computational resources rule out regularized inversion

crustal velocity structure of the neoarchean convergence zone between the eastern and western blocks of dharwar craton india from seismic wide angle studies abstract the dharwar craton in the southern part of the indian shield comprises two distinct blocks viz the meso neoarchean western and the predominantly neoarchean eastern blocks which are popularly referred to as western dharwar craton wdc and eastern dharwar craton edc the boundary between the wdc and edc is marked by a prominent shear zone the chitradurga eastern margin shear zone csz several studies suggested neoarchean convergence between the edc and wdc although there is diversity of opinion on the tectonic process we present here the results of a new seismic refraction wide angle reflection experiment along a 200 km long profile across the wdc and edc encompassing the csz to elucidate the crustal velocity structure of the convergence zone travel time inversion and amplitude modeling of the seismic data delineate a five layered crustal velocity model for the dharwar craton with a 42 km minimum thick crust in the wdc grading to a distinctly thinner crust up to 38 km in the edc the transect is also characterized by a high velocity 7 0 7 1 km s 1 mafic lower crustal layer but with distinctly variable thickness 10 km in wdc and 8 km in edc the transition from thick to thinner crust coincides with the csz the thick crust with a high velocity basal layer is atypical of archean cratons but more akin to proterozoic terrains the crustal velocity structure across the edc wdc boundary zone is consistent with the neoarchean plate convergence model that invoke tectonic scenarios such as accretion of a hot orogen the edc and or westward subduction of the latter beneath the wdc spatial variation in the high velocity lower crustal layer across the craton is ascribed to post accretional mafic magmatism and underplating mainly during the paleoproterozoic and phanerozoic

p and sv velocity structure of the south portuguese zone fold and thrust belt sw iberia from traveltime tomography imaging the architecture of the shallow crust of the south portuguese zone fold and thrust belt is essential to extend surface mapped geological information to depth and to help in developing model

crustal structure of granite greenstone terranes in the eastern goldfields yilgarn craton as revealed by seismic reflection profiling abstract a deep crustal seismic reflection profile across granite greenstones of the eastern goldfields in the archaean yilgarn craton has revealed new constraints on upper crustal geometries the ida fault which forms the western boundary of the eastern goldfields is a 30 east dipping normal fault that can be traced to a depth of about 25 km a mid crustal boundary is displaced with a throw of some 5 km across this fault in a broad region below the ida fault the crust mantle boundary moho is gently warped from a depth of c 33 km in the west to a depth of c 38 km to the east greenstones of the eastern goldfields are underlain by a regional detachment outlined by prominent reflectors at depths between 4 and 7 km open anticlines of the greenstone succession are truncated against this basal detachment or against gently dipping reflectors that can be correlated with terrane and domain boundary faults identified during regional mapping these truncations are not associated with changes in thickness of the successions these geometries suggest several stages of large scale movement possibly including out of section north south movements unresolved by the east west seismic reflection line reflectors representing boundary faults mostly sole out into the basal detachment however the west dipping bardoc shear zone is continuous across the basal detachment and may have been reactivated as a conjugate fault to the late stage ida fault granite plutons are imaged as steep sided and flat bottomed opaque regions locally underlain by continuous reflectors indicating greenstone stratigraphy these geometries in combinations with the map observations suggest that the plutons were emplaced as elongate ovoid sheets presumably fed through fractures

application of multi seismic attributes analysis in the study of distributary channels abstract during the exploration of stratigraphic reservoirs the key to locating these reservoirs is to identify the sandstone distribution seismic data can be used to recognize large scale distributary channel sedimentary bodies however depiction of sedimentary bodies in small distributary channels using traditional interpretation data from seismic profiles is extremely difficult in the upper cretaceous first sandstone bed of the third member of the nenjiang formation called the nen 3 member for simplicity in the xb area of the southern songliao basin distributary channels are the main sedimentary facies the distributary channels migrate frequently therefore it is difficult to precisely depict the morphology of the channel and the distribution of sandstone in this study we investigated the deposition of distributary channels using equal scale formation plane seismic attributes such as post stack amplitude instantaneous amplitude and seismic waveform classification analyzed well logging data from target formations and mapped the distribution of distributary channels this study shows that seismic sedimentological study and stacking multiple attribute analysis can identify the distribution of distributary channels precisely and effectively the attributes of equal scale strata slices are evidently superior to those of time and horizon slices attribute extraction and selection of equal scale formation slices is an essential step the comprehensive selection of seismic attributes that show a good correlation to a single well can be used to clearly depict channel bodies the overlap of the 40 hz single frequency energy and the rms amplitude depicts the sedimentary characteristics and shapes of sandstone bodies in main channels as well as small scale distributary channels more clearly than a single attribute these attributes show that the first sandstone bed of the nen 3 member was from distributary channels with complex shapes the distributary channels cut across each other vertically and laterally it indicates that during the deposition of the nen 3 member in xb area the direction of the main channel is from north to south and the provenance could be from north and east the method of this paper may provide some helpful suggestions to the geologist using seismic attributes to undertake research on sedimentary environment at other places in the world

shallow velocity structure along the hirapur mandla profile using traveltime inversion of wide angle seismic data and its tectonic implications summary in order to investigate the velocity structure and hence shed light on the related tectonics across the narmada son lineament traveltimes of wide angle seismic data along the 240 km long hirapur mandla profile in central india have been inverted a blocky laterally heterogeneous three layer velocity model down to a depth of 10 km has been derived the first layer shows a maximum thickness of the upper vindhyans 4 5 km s1 of about 1 35 km and rests on top of normal crystalline basement represented by the 5 9 km s1 velocity layer the anomalous feature of the study is the absence of normal granitic basement in the great vindhyan graben where lower vindhyan sediments 5 3 km s1 were deposited during the precambrian on high velocity 6 3 km s1 metamorphic rock the block beneath the narmada son lineament represents a horst feature in which high velocity 6 5 km s1 lower crustal material has risen to a depth of less than 2 km south of the lineament the deccan traps were deposited on normal basement during the upper cretaceous period and attained a maximum thickness of about 800 m

seismic imaging of upper crustal structure using travel times from the passcal ouachita experiment a first arrival travel time inversion applied to the 1986 passcal ouachita experiment has been used to image upper crustal structure twenty one shot points every 10 km were recorded along two 100 km long segments with 400 seismographs on each segment a splined velocity model parameterization allowed for the inversion of laterally inhomogeneous models but not velocity discontinuities over 800 travel times were used in the inversion with a variable data covariance weighting the multiple source nature of the experiment design allowed the use of reciprocity relationships among 21 shot points to enhance data correlation a succession of models with velocities specified at 30 90 171 and 221 nodes were inverted for whose horizontal node spacing decreased from 100 to 12 5 km in the final 221 node model vertical node spacings of 3 0 and 1 5 km were used the results of the inversions indicate changes in depth of isovelocity lines which are interpreted as triassic fault structure based on nearby well data the final rms travel time residual is 0 045 s resolution using first arrivals deteriorates rapidly below 9 km depth three distinct velocity gradients can be correlated with geologic units surface exposed cretaceous and jurassic sediments with velocities from 3 0 tomore 3 5 km s extend to 1 5 km depth triassic rift fill sediments which do not outcrop have inverted velocities ranging from 3 5 to 4 75 km s between depths of 1 5 3 0 km paleozoic sediments are imaged by a decreased velocity gradient below a depth of 3 0 km lack of resolution at depths greater than 9 km necessitates detailed modeling of wide angle reflected phases to further constrain deeper crustal structure less

the dharwar craton southern india interpreted as the result of late archaean oblique convergence abstract the dharwar craton comprises two distinct parts separated by a steep n s sinistral shear zone in the western part a pre 2900 ma complex of orthogneisses granodiorites and narrow tracts of supracrustal rocks sargur group forms the basement to volcanic and sedimentary basins of the dharwar supergroup ca 2800 2550 ma late archaean deformation is characterised by ne sw crustal shortening and steep n s sinistral shear zones the eastern part is underlain by parallel steep n s or nw se linear belts of calc alkaline anatectic and juvenile granites and granodiorites dharwar batholith ca 2750 2510 ma with intervening volcanic and sedimentary schist belts ca 2800 2550 ma the plutonic belts are 15 25 km wide up to 150 km long and bounded by steep nw se high strain zones up to 2 km wide with sinistral shear sense except one which is dextral magmatic state fabrics and structures in the plutonic rocks are parallel to solid state sinistral shear fabrics in the high strain zones but diffuse magmatic banding is commonly oblique to these zones and coincides with the plane of instantaneous shortening in sinistral shear magmatic state structures swarms of vertical nw se dykes of granite and the vertical wedge shape of the linear belts are consistent with emplacement of the batholith during sinistral shear when magma pressure exceeded regional horizontal compressive stress upright folds and schistosity steep reverse faults and effects of regional ht lp metamorphism show that deformation was partitioned into ne sw shortening in the schist belts during emplacement of the plutonic belts in the sinistral shear regime the western part of the craton is interpreted as the foreland to an accretionary arc represented by the batholith and schist belts intra arc basins in the east ne sw shortening and sinistral transcurrent displacements in the foreland and arc are consistent with arc normal and arc parallel displacements during oblique convergence analogous to mesozoic cenozoic convergent settings

upper crust of the archean dharwar craton in southern india as revealed by seismic refraction tomography and its geotectonic implications s u m m a r y imaging shallow crustal structure is essential to extend the geological information from surface mapping to a depth and to develop tectonic models we applied seismic tomography modelling to refraction data acquired along a 200 km long line in the dharwar craton of the indian shield and we derived a crustal velocity model that was evaluated with checkerboard tests to demonstrate the reliability of the model we also tested the model for artefacts upper crustal velocities vary between 5 7 and 6 4 km s 1 and are determined to 10 km depth probably due to very low velocity gradients in the upper crust undulating high and low velocities in the top layers of the crust are terminated at a depth of 7 8 km consistent with a probable detachment we interpret the undulating upper crustal velocity layers to represent a fold thrust belt structure that developed during a collision in a transpressional tectonic regime consistent with themodel of chadwick et al which suggests oblique convergence and accretion of two crustal blocks in the region the velocity structure also correlates reasonably well with the distinct geological units we interpret relatively low velocities between the undulating layers as representative of faults that bound various tectonic domains

application of seismic curvature attributes in the delineation of coal texture and deformation in zhengzhuang field southern qinshui basin coal texture refers to the in situ particle size morphological characteristics and structural components of coal beds and it determines the permeability and producibility of a coalbed methane cbm reservoir coal texture is commonly classified into undeformed coal with primary coal texture and deformed coal with increasing degree of deformation including cataclastic coal granulated coal and mylonitized coal geophysical logging has recently been proven effective for detecting coal texture in boreholes but it is inefficient for establishing a regional distribution where there have been only limited amounts of drilling in contrast seismic attributes have high lateral extent and an advantage in terms of characterizing fine structures even minor faults with throws of 2 3 m and other strata deformations by comparing seismic curvature data to the results of 221 core samples from the zhengzhuang field in the southern qinshui basin we provide a seismic curvature attribute based coal texture evaluation method evaluation of the results shows that the coal texture types of the no 3 coal seam include undeformed coal cataclastic coal and some granulated coal the undeformed coal is mainly located in the western and northwestern parts of the study area the cataclastic and granulated coals are mainly distributed in the southern and eastern parts of the study areas the permeability of no 3 coal seam is weakly correlated with undeformed coal and it has a high negative correlation with deformed coal permeability has a strong negative correlation with the maximum curvature attribute of the no 3 coal seam it is suggested that the in situ stress distribution combined with the curvature controlled the local development of the coal texture types and thus resulted in regional differences in permeability finally the distribution characteristics of coal textures of no 3 coal seam in the study area are divided into four types in which the undeformed cataclastic coal dominated area located in the midwestern part of the study area is the most favorable area for cbm production

monitoring viscosity changes from time lapse seismic attenuation case study from a heavy oil reservoir heating heavy oil reservoirs is a common method for reducing the high viscosity of heavy oil and thus increasing the recovery factor monitoring of these viscosity changes in the reservoir is essential for delineating the heated region and controlling production in this study we present an approach for estimating viscosity changes in a heavy oil reservoir the approach consists of three steps measuring seismic wave attenuation between reflections from above and below the reservoir constructing time lapse q and q 1 factor maps and interpreting these maps using kelvin voigt and maxwell viscoelastic models we use a 4d relative spectrum method to measure changes in attenuation the method is tested with synthetic seismic data that are noise free and data with additive gaussian noise to show the robustness and the accuracy of the estimates of the q factor the results of the application of the method to a field data set exhibit alignment of high attenuation zones along the steam injection wells and indicate that temperature dependent viscosity changes in the heavy oil reservoir can be explained by the kelvin voigt model

seismic attribute based characterization of coalbed methane reservoirs an example from the fruitland formation san juan basin new mexico the fruitland formation of the san juan basin is the largest producer of coalbed methane in the world production patterns vary from one well to another throughout the basin reflecting factors such as coal thickness and fracture and cleat density in this study we integrated conventional p wave three dimensional 3 d seismic and well data to investigate geological controls on production from a thick continuous coal seam in the lower part of the fruitland formation our objective was to show the potential of using 3 d seismic data to predict coal thickness as well as the distribution and orientation of subtle structures that may be associated with enhanced permeability zones to do this we first derived a seismic attribute based model that predicts coal thickness we then used curvature attributes derived from seismic horizons to detect subtle structural features that might be associated with zones of enhanced permeability production data show that the best producing wells are associated with seismically definable structural features and thick coal although other factors e g completion practices and coal type affect coalbed methane production our results suggest that conventional 3 d seismic data integrated with wire line logs and production data are useful for characterizing coalbed methane reservoirs

seismic measurements of the internal properties of fault zones the internal properties within and adjacent to fault zones are reviewed principally on the basis of laboratory borehole and seismic refraction and reflection data the deformation of rocks by faulting ranges from intragrain microcracking to severe alteration saturated microcracked and mildly fractured rocks do not exhibit a significant reduction in velocity but from borehole measurements densely fractured rocks do show significantly reduced velocities the amount of reduction generally proportional to the fracture density highly fractured rock and thick fault gouge along the creeping portion of the san andreas fault are evidenced by a pronounced seismic low velocity zone lvz which is either very thin or absent along locked portions of the fault thus there is a correlation between fault slip behavior and seismic velocity structure within the fault zone high pore pressure within the pronounced lvz may be conductive to fault creep deep seismic reflection data indicate that crustal faults sometimes extend through the entire crust models of these data and geologic evidence are consistent with a composition of deep faults consisting of highly foliated seismically anisotropic mylonites

lithofacies control on reservoir quality of the viola limestone in southwest kansas and unsupervised machine learning approach of seismic attributes facies classification the hydrocarbon development of the viola limestone in southern kansas usa has encountered challenges regarding the development of a robust data based model of the reservoir quality controls the legacy understanding that hydrocarbon entrapment and reservoir quality are controlled by structure has resulted in less than optimal drilling results in this study an integration of petrographic and geophysical well logs analyses established the main reservoir quality control as dolomitization induced porosity the dolomitization control is supported by comparing best fit trends on density porosity well log values with typical model trends of limestone and dolomite density porosity furthermore this study presents unsupervised artificial neural network ann classification based on five seismic attributes instantaneous frequency energy band width absorption quality factor seismic amplitude that comes in agreement with ca mg ratio and the observed sonic transit time dt log variation with dolomitization porosity increase the hydrocarbon reservoir facies identified by the attributes classification explains the drilling results with high accuracy match to facies class centers and can be used effectively in other settings the integration of multi scale multi data analysis and modeling has provided a solid understanding of the reservoir quality control and distribution this study can be considered as a reliable platform for placing future infill wells in the study area to lower the risk of drilling dry holes