the influence of fluid sensitive dispersion and attenuation on avo analysis summary analysis of seismic data suggests that hydrocarbon deposits are often associated with higher than usual values of attenuation but this is generally ignored during amplitude versus offset avo analysis the effect can be modelled with equivalent medium theory based on the squirt flow concept but the excess attenuation is associated with strong velocity dispersion consequently when we study reflections from the interface between such an equivalent medium and an elastic overburden we find that the reflection coefficient varies with frequency the impact of this variation depends on the avo behaviour at the interface class i reflections tend to be shifted to higher frequency while class iii reflections have their lower frequencies amplified we calculate synthetic seismograms for typical models using the reflectivity method for materials with frequency dependent velocities and attenuations and find that these effects are predicted to be detectable on stacked data two field data sets show frequency anomalies similar to those predicted by the analysis and we suggest that our modelling provides a plausible explanation of the observations

shear wave splitting and subcontinental mantle deformation splitting observations are interpreted in terms of the strain induced lattice preferred orientation of mantle minerals especially olivine we consider three hypotheses concerning the origin of the continental anlsotropy 1 strain associated with absolute plate motion as in the oceanic upper mantle 2 crustal stress and 3 the past and present internal deformation of the subcontinental upper mantle by tectonic episodes it is found that the last hypothesis is the most successful namely that the most recent significant episode of internal deformation appears to be the best predictor of q for stable continental regions this is interpreted as fossil anisotropy whereas for presently active regions such as alaska the anisotropy reflects present day tectonic activity in the stable portion of north america there is a good correlation between delay time and lithospheric thickness this is consistent with the anisotropy being localized in the subcontinental lithosphere and suggests that intrinsic anisotropy is approximately constant the acceptance of this hypothesis has several implications for subcontinental mantle deformation first it argues for coherent deformation of the continental lithosphere crust and mantle during orogenies this implies that the anisotropic portion of the lithosphere was present since the deformational episode and rules out the addition of undeformed material to this layer by subsequent underplating or conductive growth of the thermal boundary layer one of the most important issues in the study of orogenies is the need to reconcile the formation of thickened lithosphere with the paradoxically high mantle temperatures often associated with orogenic episodes most efforts to date have focussed on modes of deformation whereby the cold lithospheric mantle is removed by convective instability or delamination and replaced by warm asthenosphere these models however are incompatible with the evidence for preserved coherent lithospheric deformation rather the deformed mantle appears to have been heated in place we suggest that the elevated mantle temperatures may be due to the strain heating accompanying the deformation

hydrocarbon generation and expulsion characteristics of eocene source rocks in the huilu area northern pearl river mouth basin south china sea implications for tight oil potential abstract in recent years new oil reservoirs have been discovered in the eocene tight sandstone of the huilu area northern part of the pearl river mouth basin south china sea indicating good prospects for tight oil exploration in the area exploration has shown that the huilu area contains two main sets of source rocks the eocene wenchang e2w and enping e2e formations to satisfy the requirements for further exploration in the huilu area particularly for tight oil in eocene sand reservoirs it is necessary to re examine and analyze the hydrocarbon generation and expulsion characteristics based on mass balance this study investigated the hydrocarbon generation and expulsion characteristics as well as the tight oil resource potential using geological and geochemical data and a modified conceptual model for generation and expulsion the results show that the threshold and peak expulsion of the e2w source rocks are at 0 6 vitrinite reflectance and 0 9 vitrinite reflectance respectively there were five hydrocarbon expulsion centers located in the western eastern and northern huizhou sag and the southern and northern lufeng sag the hydrocarbon yields attributed to e2w source rocks are 2 4 1011 tons and 1 6 1011 tons respectively with an expulsion efficiency of 65 the e2e source rock threshold and peak expulsion are at 0 65 vitrinite reflectance and 0 93 vitrinite reflectance respectively with hydrocarbon expulsion centers located in the centers of the huizhou and lufeng sags the yields attributed to e2e source rocks are 1 1 1011 tons and 0 2 1011 tons respectively with an expulsion efficiency of 20 using an accumulation coefficient of 7 13 the eocene tight reservoirs could contain approximately 1 3 1010 tons to 2 3 1010 tons with an average of 1 8 1010 tons of in place tight oil resources highest recoverable coefficient can reach 17 18 indicating that there is significant tight oil potential in the eocene strata of the huilu area

prediction of coal seam details and mining safety using multicomponent seismic data a case history from china abstractwith the increasing mining depth of coal mines geologic hazards have become the main source of accidents for this reason coal seam prediction requires more assessment parameters such as the degree of anisotropy vp vs value and elastic modulus these parameters are difficult to determine using only the pp wave we have inverted and interpreted multicomponent seismic data acquired from a 2 56 km2 area in the guqiao mine located on the southern margin of the north china plate under the constraints of drill log and rock physics test data the production coal seam 11 2 of the mine located in the permian formation was our focus of this study and our objective was to determine the structure fracture development thickness surrounding rock lithology roof stability and mining safety of the seam to achieve this we first performed an analysis of s wave splitting and joint pp and ps wave inversions the inversion results were then combined to derive additional parameters such as the vp vs

identification of fractured carbonate vuggy reservoirs in the s48 well area using 3d 3c seismic technique a case history from the tarim basin

shear wave splitting in the upper mantle wedge above the tonga subduction zone summary intermediate period seismograms of shear waves from deep earthquakes are examined for shear wave splitting diagnostic of seismic velocity anisotropy in the upper mantle wedge between the subducting tonga slab and stations in the fiji islands earthquakes with near vertical incidence angles are selected to minimize complications of converted phases and the free surface horizontal component seismograms for 25 deep earthquakes recorded at station lak on the lau ridge show splitting of up to 0 9 s with an average of 0 45 0 25 s between fast and slow s wave components anisotropy in the upper mantle is the most likely cause of the splitting the ese orientation of the fast velocity direction at station lak corresponds to an axis of symmetry of the anisotropic mantle and is approximately perpendicular to magnetic lineations in the lau basin and the northeastern portion of the south iiji basin the observations are consistent with a model of flow alignment of olivine 100 and orthopyroxene 001 axes parallel to the direction of basin extension seismograms for eight deep earthquakes at station sva on viti levu show up to 1 0 s splitting with an average of 0 65 0 29 s and a weak nne preferred orientation of fast velocity polarizations of shear wave particle motions corrected for anisotropy are within 36 5 26 of polarixations predicted for nine moment tensor solutions the magnitude of shearwave splitting and estimates of the thickness of the lithosphere in the fiji region imply that the anisotropy cannot be contained in the lithosphere alone either the anisotropy is distributed in both the lithosphere and asthenosphere or the asthenosphere alone is anisotropic

linear unit response functions as indicators of recharge areas for large karst springs abstract the delineation of groundwater recharge areas for karst springs is important for estimating groundwater supplies and for identifying sources and directions of contaminant movement this paper suggests the potential utility of spring discharge kernel functions analogous to instantaneous unit hydrographs for surface runoff in the identification of the recharge areas of large springs examples from southeastern missouri u s a show that when consistent methods are used for baseflow separation and excess precipitation determinations derived linear kernels are most physically realistic and have the least fitting error when the assumed spring recharge area is consistent with tracer study results

frequency dependent seismic anisotropy and its implication for estimating fracture size in low porosity reservoirs the use of seismic anisotropy for characterizing subsurface fracture orientations and intensity has become increasingly popular however the reluctance of reservoir engineers to accept seismic anisotropy as a routine technique for fracture characterization is partly because of its inability to provide information about sizes and volume of fractures although both grain scale micro cracks and formation scale macro fractures are considered causes of seismic anisotropy reservoir engineers are more interested in the latter as permeability in many hydrocarbon reservoirs is believed to be dominated by formation scale fluid units on the order of meters we intend to fill this gap by developing new practical applications of seismic anisotropy including new theoretical models and new analysis methods

fracture detection in manderson field a 3 d avaz case history oil from wyoming s manderson field is produced from a complex fracture system with possible significant lateral connectivity it is therefore important to obtain as much information as possible about the nature of the fractures within the reservoir especially between the wells

changes in shear wave polarization azimuth with depth in cymric and railroad gap oil fields shear wave s wave polarization azimuths although consistent over large depth intervals changed abruptly and by large amount of various depths in nine component vertical seismic profiling vsp data from the cymric and railroad gap oil fields of the southwest san joaquin basin a simple layer stripping technique made it possible to follow the polarization changes and determine the s wave birefringence over successive depth intervals because the birefringence and polarization azimuth are related to in situ stresses and fracture information from such analysis could be important for reservoir development near offset vsp data from cymrix indicated that the subsurface could be appproximated roughly as two anisotropic layers the upper layer from the surface to 800 ft 240 m had vertical s wave birefringence as large was about 6 percent down to 1300 ft 400 m in the upper layer the polarization azimuth of the fast s wave was n 60 e while in the lower layer it was about n 10 e refinement of the laye

the relationship between acoustic properties and the petrographic character of carbonate rocks laboratory studies of the detailed relationships between acoustic properties and the petrographic character of brine and air saturated carbonate rocks with a wide range of facies porosities lithologies and rock fabrics indicate that porosity is the major factor influencing both p and s wave impedance and velocity primary lithology and secondary mineralogy have only a small influence on impedance and velocity combined use of p and s wave velocity data discriminates porosity changes from lithologic changes all other variables including pore fluid type and petrographic fabric have no significant influence on velocities laboratory measurements of p wave velocity under simulated in situ conditions reproduce well log velocity values reliably laboratory porosity velocity trends agree with the time average equation when the correct matrix velocities are used rock property results were used to interpret porosity lithology variations for an inverted seismic section from the williston basin where well

sks splitting measurements with horizontal component misalignment summary the measurement of sks splitting parameters is widely used for the study of deformation in the upper mantle but the misalignment of the station horizontal components for example misorientation of the sensors may result in false measurements in this paper we suggest that the splitting analysis should be repeated with different assumed angles of misalignment two criteria can be applied to correct the measurement of the sks splitting parameters 1 the horizontal rotating angle should produce the global minimum transverse energy as determined using the least transverse energy method 2 there should be consistent results between the least transverse energy method and the minimum eigenvalue method model tests show that the method is suitable for complex anisotropy models such as two layer anisotropy

3 d seismic attributes applied to carbonates coherency mapping has become a widely used tool within amoco and is being applied in both frontier exploration and exploitation areas coherency and other 3 d seismic attributes have been successfully used to identify and delineate features in clastic depositional environments including reworked deltaic sand bodies deltaic channels with associated point bars slump features debris flow outrunner blocks and various geologic drilling hazards including faults salt diapirs buried channels and shallow gas pockets

using avo for fracture detection analytic basis and practical solutions tight low porosity reservoirs can produce significant amounts of hydrocarbons if fracture networks provide the necessary permeability characterization of naturally fractured reservoirs using surface seismic data is an important exploration problem that has attracted much attention in the literature tle for example had an entire issue august 1996 on this subject while the data and modeling in existing publications demonstrate that fracturing causes significant azimuthal variation in recorded seismic signatures the problem is how to infer fracture parameters from these data

early paleozoic tropical paleokarst geomorphology predating terrestrial plant growth in the tahe oilfield northwest china abstract a deeply buried tropical paleokarst landscape that predates terrestrial plant growth was discovered in west district 10 of the tahe oilfield located on the northern margin of the tarim basin in the xinjiang uygur autonomous region of northwestern china the paleokarst unconformity surface at depths deeper than 6000 m had been subjected to subaerial karstification under humid tropical climatic conditions during the first hiatus period in the early paleozoic a high quality full azimuthal 3d seismic survey was conducted in this study area area of 10 10 km2 in order to visualize the buried paleokarst landscape with high resolution seismic data with this data and previous geological geochemical and paleomagnetic data we reconstructed the large scale paleokarst landform assemblage compared it to a modern humid tropical subtropical karst and investigated the different controlling factors for the formation of the paleokarst and the modern karst results show that 1 the original landform assemblages of the tropical paleokarst landscape are distinct from those of the modern humid tropical subtropical karst geomorphology 2 the paleokarst denudation surface that formed in the early paleozoic was relatively smooth with shallow depressions and the relative relief was less than that of the modern tropical subtropical cockpit karst area 3 during the time of epigenetic paleo karstification lithological hydrogeological and climate conditions were optimal for the formation of cockpit karst the tropical paleokarst landscape demonstrates that extensive terrestrial plant growth plays an important role in creating large scale karst landform assemblages of peak clusters and depressions cockpit karst

new insights into nitrate dynamics in a karst groundwater system gained from in situ high frequency optical sensor measurements abstract understanding nitrate dynamics in groundwater systems as a function of climatic conditions especially during contrasting patterns of drought and wet cycles is limited by a lack of temporal and spatial data nitrate sensors have the capability for making accurate high frequency measurements of nitrate in situ but have not yet been evaluated for long term use in groundwater wells we measured in situ nitrate continuously in two groundwater monitoring wells one rural and one urban located in the recharge zone of a productive karst aquifer in central texas in order to resolve changes that occur over both short term hourly to daily and long term monthly to yearly periods nitrate concentrations measured as nitrate nitrogen in milligrams per liter mg l during drought conditions showed little or no temporal change as groundwater levels declined during aquifer recharge extremely rapid changes in concentration occurred at both wells as documented by hourly data at both sites nitrate concentrations were affected by recharging surface water as evidenced by nitrate concentrations in groundwater recharge 0 8 1 3 mg l that were similar to previously reported values for regional recharging streams groundwater nitrate concentrations responded differently at urban and rural sites during groundwater recharge concentrations at the rural well approximately 1 0 mg l increased as a result of higher nitrate concentrations in groundwater recharge relative to ambient nitrate concentrations in groundwater whereas concentrations at the urban well approximately 2 7 mg l decreased as a result of the dilution of higher ambient nitrate concentrations relative to those in groundwater recharge notably nitrate concentrations decreased to as low as 0 8 mg l at the urban site during recharge but postrecharge concentrations exceeded 3 0 mg l a return to higher nitrate concentrations postrecharge indicates mobilization of a localized source of elevated nitrate within the urbanized area of the aquifer changes in specific conductance were observed at both sites during groundwater recharge and a significant correlation between specific conductance and nitrate correlation coefficient r 0 455 was evident at the urban site where large 3 fold changes in nitrate occurred nitrate concentrations and specific conductance measured during a depth profile indicated that the water column was generally homogeneous as expected for this karst environment but changes were observed in the most productive zone of the aquifer that might indicate some heterogeneity within the complex network of flow paths resolving the timing and magnitude of changes and characterizing fine scale vertical differences would not be possible using conventional sampling techniques the patterns observed in situ provided new insight into the dynamic nature of nitrate in a karst groundwater system

integrate instead of ignoring base rate neglect as a common fallacy of petroleum explorers when petroleum explorers estimate geological probability of success pos and success case volumes for their prospects they commonly suffer from various biases and fallacies that result in poor assessments using a data set of 25 exploration wells drilled by lundin petroleum on the norwegian continental shelf ncs during the 5 yr period from 2011 to 2015 i demonstrate the base rate neglect fallacy in petroleum exploration lundin explorers consistently and significantly underestimated the geological pos and overestimated the success case volumes relative to the available base rate information on historical exploration success rates and sizes of previously discovered fields in the ncs area these findings are consistent with previous studies of exploration track records of the industry and individual companies explorers erroneously tend to ignore the base rates likely because they do not see them as relevant to the evaluation of their specific prospects as a result exploration portfolios generally fail to deliver on promise however base rate neglect fallacy can be mitigated and eliminated explorers should make an effort to learn the base rates relevant to their prospects and integrate them with prospect evaluations and managers should ensure that modeled portfolio outcomes are consistent with relevant base rates

shear wave polarizations and subsurface stress directions at lost hills field 2 2 s wave data matrix accomplished by computationally rotating sources and receivers although polarization directions obtained by assuming a homogeneous subsurface were moderately consistent with depth considerable improvement in consistency resulted from analytically stripping off a thin near surface layer whose fast s wave polarization direction was about n 6 e s wave birefringence for vertical travel averaged 3 percent in two zones 200 700 ft and 1200 2100 ft 60 210 m and 370 640 m which had closely similar s wave polarizations between those zones the polarization direction changed and the birefringence magnitude was not well defined s wave polarizations from two concentric rings of offset vsps were consistent in azimuth with one another and with polarizations of the near offset vsp this consistency argues strongly for the robustness of the s wave polarization technique as applied in this area the s wave polarization pattern in offset data fits a model of vertical cracks striking n 55 e

normalized measures of exploration performance in terms of basin sediment volumes the normalized measures of exploration performance defined in this paper are the exploratory drilling density in feet per cubic mile of sediments and the hydrocarbon discovery density in boe per cubic mile these density measures provide a convenient means for summarizing the status of exploration in the sedimentary provinces of the lower 48 states of the united states revealing that the smaller hydrocarbon rich provinces have been explored much more intensely than the larger ones the most important application of the drilling and hydrocarbon discovery densities is in defining normalized discovery functions that is the relationships between the normalized measures of cumulative exploratory drilling and discoveries normalized rather than absolute discovery functions are necessary for proper comparison of the results of exploration in regions or depth zones of differing sizes the normalized drilling and discovery measures are also useful for developing meaningful statistics of exploration performance

improved statistical method for assessment of undiscovered petroleum resources a statistically significant straight line correlation exists between logarithms of oil or gas field sizes and order of discovery in some of australia s petroleum provinces the correlation is predicted by the hypotheses 1 that the probability of discovery of each field is proportional to size raised to a constant power lambda lgr and 2 that fields are discovered without replacement from a population with a lognormal size distribution a computer program has been developed that uses extrapolations of the straight line to predict the number and size of future discoveries the program takes into account a dependent relationship among lambda and the average slope and intercept of the fitted lines and the average standard deviation of the residuals that is indicated by the hypotheses the new field wildcat drilling required is estimated using predicted success rates

contribution of correlation and spectral analyses to the regional study of a large karst aquifer charente france the purpose of the study is to demonstrate that correlation and spectral analyses can contribute to the regional study of a large karst aquifer an example is presented for the la rochefoucauld karst aquifer charente france different types of spatially distributed time series provide valuable spatio temporal information for the karst aquifer the available time series consist of the spring flow rates the flow rates at different locations in sinking streams the piezometric levels the electrical conductivity and temperature of the water the atmospheric pressure and the precipitation the analysis of the flow rates at the springs shows that the aquifer empties very slowly and has a large storage capacity hydrodynamic links were established between three of the four rivers flowing on the aquifer and the springs the results also demonstrate the important spatial heterogeneity of the aquifer and indicate that the most rapid flow occurs in the northern part of the aquifer hourly piezometric and electrical conductivity time series indicate that the transmissivity of the aquifer varies when some conductive channels become desaturated during the low water period the delays between the distributed recharge and the piezometric level between the localized river input and the flow rates at the springs and between the electrical conductivities in rivers and the main spring provide information on the travel times in the aquifer the observation of earth tides and barometric effects indicate that this apparently unconfined aquifer has a confined behaviour

determination of the principal directions of azimuthal anisotropy from p wave seismic data in an azimuthally anisotropic medium the principal directions of azimuthal anisotropy are the directions along which the quasi p and the quasi s waves propagate as pure p and s modes when azimuthal anisotropy is induced by oriented vertical fractures imposed on an azimuthally isotropic background two of these principal directions correspond to the directions parallel and perpendicular to the fractures s waves propagating through an azimuthally anisotropic medium are sensitive to the direction of their propagation with respect to the principal directions as a result primary or mode converted multicomponent s wave data are used to obtain the principal directions apart from high acquisition cost processing and interpretation of multicomponent data require a technology that the seismic industry has not fully developed anisotropy detection from conventional p wave data on the other hand has been limited to a few qualitative studies of the amplitude variation with offset avo for different azimutha

fracture detection in a carbonate reservoir using a variety of seismic methods we combine various methods to estimate fracture orientation in a carbonate reservoir located in southwest venezuela the methods we apply include the 2 d rotation analysis of 2 d p s data along three different azimuths amplitude variation with offset avo of 2 d p wave data along the same three azimuths normal moveout nmo analysis of the same 2 d data and both 3 d azimuthal avo and nmo analysis of 3 d p wave data recorded in the same field the results of all methods are compared against measures of fracture orientation obtained from formation microscanner logs recorded at four different locations in the field regional and local measures of maximum horizontal stress and the alignment of the major faults that cross the field p s data yield fracture orientations that follow the regional trend of the maximum horizontal stress and are consistent with fracture orientations measured in the wells around the carbonate reservoir azimuthal avo analysis yields a similar regional trend as that obtained from the p s data but the resolution is lower local variations in fracture orientation derived from 3 d avo show good correlation with local structural changes in contrast due to the influence of a variety of factors including azimuthal anisotropy and lateral heterogeneity in the overburden azimuthal nmo analysis over the 3 d p wave data yields different orientations compared to those obtained by other methods it is too early to say which particular method is more appropriate and reliable for fracture characterization the answer will depend on factors that range from local geological conditions to additional costs for acquiring new information

new exploration concepts for the edwards and sligo margins cretaceous of onshore texas we examined the potential in onshore texas of the most prolific reservoirs found to date in the gulf of mexico basin cretaceous carbonates and in particular the edwards and sligo formations two dimensional 2 d and three dimensional 3 d seismic data with lithologic and biostratigraphic information led to a detailed sequence stratigraphic framework this framework resulted in a concentrated exploration effort in lavaca county a redefinition of the edwards shelf margin and confirmation of a major sequence boundary in the sligo the youngest edwards margin appears to have stepped seaward a distance of more than 3 mi 4 8 km from the position of the margin as indicated by the word field this seaward shift and repositioning of the margin is shown in 3 d seismic and well data recognized within the progradational package are distal slope wackestones reef and bank complexes and back reef lagoonal deposits that are offset seaward across sequence boundaries reef and grainstone deposits are located far seaward of the commonly recognized margin and numerous exposure surfaces occur in the shelf deposits proximity to faulting after burial ensures the development of a plumbing system that enhances secondary porosity and provides a migration pathway for hydrocarbons a sligo debris play is based on a sequence boundary within the upper part of the sligo in ferred from seismic geometry and surface exposures in mexico the seismic portrays a wedge geometry positioned downslope from the sligo margin base level change about the sequence boundary would have initiated coarse carbonate debris and grain flow deposition seaward of the sligo shelf margin rapid deposition may have helped preserve porosity within the thick debris wedge data from reservoir analogs confirm that downslope carbonates can retain reservoir quality porosity facies variation and slump faulting on the foreslope creates the potential for trapping and juxtaposition to deep water carbonates sets up the source and migration pathway this undrilled wedge extends for hundreds of miles along the sligo margin

changes in sources and storage in a karst aquifer during a transition from drought to wet conditions summary understanding the sources and processes that control groundwater compositions and the timing and magnitude of groundwater vulnerability to potential surface water contamination under varying meteorologic conditions is critical to informing groundwater protection policies and practices this is especially true in karst terrains where infiltrating surface water can rapidly affect groundwater quality we analyzed the evolution of groundwater compositions major ions and sr isotopes during the transition from extreme drought to wet conditions and used inverse geochemical modeling phreeqc to constrain controls on groundwater compositions during this evolution spring water and groundwater from two wells dominantly receiving diffuse and conduit flow termed diffuse site and conduit site respectively in the barton springs segment of the edwards aquifer central texas usa and surface water from losing streams that recharge the aquifer were sampled every 3 4 weeks during november 2008 march 2010 during this period water compositions at the spring and conduit sites changed rapidly but there was no change at the diffuse site illustrating the dual nature i e diffuse vs conduit of flow in this karst system geochemical modeling demonstrated that within a month of the onset of wet conditions the majority of spring water and groundwater at the conduit site was composed of surface water providing quantitative information on the timing and magnitude of the vulnerability of groundwater to potential surface water contamination the temporal pattern of increasing spring discharge and changing pattern of covariation between spring discharge and surface water steam recharge indicates that that there were two modes of aquifer response one with a small amount of storage and a second that accommodates more storage

shear wave polarization anisotropy in the upper mantle beneath honshu japan shear wave polarization anisotropy in the wedge portion of the upper mantle between a subducting plate and the earth s surface is investigated using three component seismograms of intermediate depth and deep earthquakes recorded at 14 local stations in honshu japan eighty nine high quality seismograms were selected from a period of 3 years the data used in this study are restricted such that incidence angles are smaller than the critical angle of 30 to the earth s surface in order to avoid phase shifts in the shear wave train to find directions of the maximum and minimum velocities in split shear waves where shear waves are resolved into two phases with the maximum time separation each set of the two horizontal component seismograms is rotated in the horizontal plane the split shear waves thus obtained are again recombined after the correction of anisotropy and the anisotropy corrected particle motion is compared with the focal mechanism for a cross check of the observed anisotropy directions of the maximum axes are plotted on azimuthincidence angle stereograms at each station the stereograms and the cross sections of seismic ray paths show that 1 the anisotropic material is distributed at intermediate location between earthquake sources and receiving stations and 2 the anisotropic region is separated into two parts one in the north of the present study area with the polarization of the maximum velocity shear wave trending 0 to 30 from the north north anisotropy and the other in the south with it trending 90 to 120 south anisotropy the maximum time delays between the two shear waves along a vertical seismic ray is about l s for both the anisotropic regions the horizontal extent of the anisotropic area in the north is 50 km at depths of 50 to 150 km perhaps prevalent in west honshu however the depth of anisotropic material is not well constrained because of insufficient coverage of seismic ray paths and angles if we assume the vertical extent of the anisotropic material to be 100 km the maximum velocity contrast would be 4 if we adopt a crack alignment model for the observed anisotropy cracks are inferred to be distributed vertically trending 0 to 30 in the north and 90 to 120 in the south if we assume an olivine alignment model olivine crystals are inferred to be aligned in the north with the a axis of the slip direction trending 0 to 30 and the slip plane normal to the b axis being vertical and in the south anisotropy with the axis trending 90 to 120 and the slip plane being horizontal

3d volumetric multispectral estimates of reflector curvature and rotation one of the most accepted geologic models is the relation between reflector curvature and the presence of open and closed fractures such fractures as well as other small discontinuities are relatively small and below the imaging rangeofconventionalseismicdata dependingonthetectonic regime structural geologists link open fractures to either gaussian curvature or to curvature in the dip or strike directions reflector curvature is fractal in nature with different tectonic and lithologic effects being illuminated at the 50 m and1000 m scales untilnow suchcurvatureestimateshave been limited to the analysis of picked horizons we have developed what we feel to be the first volumetric spectral estimates of reflector curvature we find that the most positive and negative curvatures are the most valuable in the conventional mapping of lineations including faults folds and flexures curvatureismathematicallyindependentof andinterpretatively complementary to the well established coherence geometric attribute we find the long spectral wavelengthcurvatureestimatestobeofparticularvalueinextracting subtle broad features in the seismic data such as folds flexures collapse features fault drags and under and overmigrated fault terminations we illustrate the value of these spectral curvature estimates and compare them to other attributes through application to two land data sets a salt domefromtheonshorelouisianagulfcoastandafractured karsteddatavolumefromfortworthbasinofnorthtexas

3 d seismic discontinuity for faults and stratigraphic features the coherence cube seismic data are usually acquired and processed for imaging reflections this paper describes a method of processing seismic data for imaging discontinuities e g faults and stratigraphic features one application of this nontraditional process is a 3 d volume or cube of coherence coefficients within which faults are revealed as numerically separated surfaces figure 1 compares a traditional 3 d reflection amplitude time slice with the results of the new method to our knowledge this is the first published method of revealing fault surfaces within a 3 d volume for which no fault reflections have been recorded

use of avoa data to estimate fluid indicator in a vertically fractured medium microstructural attributes of cracks and fractures such as crack density aspect ratio and fluid infill determine the elastic properties of a medium containing a set of parallel vertical fractures although the tangential weakness t of the fractures does not vary with the fluid content the normal weakness n exhibits significant dependence on fluid infill based on linear slip theory we used the ratio g n t termed the fluid indicator as a quantitative measure of the fluid content in the fractures with g representing the square of the ratio of s and p wave velocity in the unfractured medium we used a born formalism to derive the sensitivity to fracture weakness of pp and ps reflection coefficients for an interface separating an unfractured medium from a vertically fractured medium our formulae reveal that the pp reflection coefficient does not depend on the 2d microcorrugation surface roughness with ridges and valleys parallel to the fracture strike whereas the ps reflection coefficien

azimuthal anisotropy in the lithosphere from observations of long period s waves summary the paper gives a detailed description of the technique for measuring azimuthal anisotropy which was suggested earlier by vinnik kosarev makeyeva 1984 and used by kind et ai 1985 the technique is based on the observations of long period converted phases like sks additionally we describe a generalization of this approach which makes use of long period s waves of arbitrary polarization both modifications were applied to records of the grf array in southern germany the results of this analysis if combined with the data on p velocities bamford 1977 suggest that the direction of the fast velocity in the lithosphere of the region varies with depth

qvoa analysis p wave attenuation anisotropy for fracture characterization this paper investigates q anisotropy for characterizing fractured reservoirs specifically the variation of the seismic quality factor q versus offset and azimuth qvoa w e derive an analytical expression for p wave attenuation in a transversely isotropic medium with horizontal symmetry axis hti and provide a method qvoa for estimating fracture direction from azimuthally varying q in pp wave reflection data the qvoa formula is similar to ruger s approximation for pp wave reflection coefficients the theoretical basis for amplitude variation with angle offset avoa analysis the technique for qvoa analysis is similar to azimuthal avo analysis we introduce two new seismic attributes q versus offset qvo gradient and intercept qvo gradient inversion not only indicates fracture orientation but also characterizes q anisotropy we relate the q anisotropy parameter q to fractured medium parameters and invert the qvo gradient to estimate q the attenuation parameter q and thomsen style anisotropy parameter v are found to be interdependent the attenuation anisotropy magnitude strongly depends on the host rock s vs vp parameter whereas the dependence on fracture parameters is weak this complicates the qvo gradient inversion for the fracture parameters this result is independent of the attenuation mechanism to illustrate the qvoa method in synthetic data we use hudson s first order effective medium model of a dissipative fractured reservoir with fluid flow between aligned cracks and random pores as a possible mechanism for p wave attenuation

processing modelling and predicting time lapse effects of overpressured fluid injection in a fractured reservoir summary time lapse seismology is important for monitoring subsurface pressure changes and fluid movements in producing hydrocarbon reservoirs we analyse two 4 d 3c onshore surveys from vacuum field new mexico usa where the reservoir of interest is a fractured dolomite in phase vi a time lapse survey was acquired before and after a pilot tertiary recovery programme of overpressured co2 injection which altered the fluid composition and the pore fluid pressure phase vii was a similar time lapse survey in the same location but with a different lowerpressure injection regime applying a processing sequence to the phase vi data preserving normal incidence shearwave anisotropy time delays and polarization and maximizing repeatability interval time analysis of the reservoir interval shows a significant 10 per cent change in shear wave velocity anisotropy and 3 per cent decrease in the p wave interval velocities a 1 d model incorporating both saturation and pressure changes is matched to the data the saturation changes have little effect on the seismic velocities there are two main causes of the time lapse changes any change in pore fluid pressures modifies crack aspect ratios additionally when there are overpressures as there are in phase vi there is a 90 change in maximum impedance directions and the leading faster split shear wave instead of being parallel to the crack face as it is for low pore fluid pressures becomes orthogonal to the crack face the anisotropic poro elasticity ape model of the evolution of microcracked rock calculates the evolution of cracked rock to changing conditions ape modelling shows that at high overburden pressures only nearly vertical cracks to which normal incidence p waves are less sensitive than s waves remain open as the pore fluid pressure increases ape modelling matches the observed time lapse effects almost exactly demonstrating that shear wave anisotropy is a highly sensitive diagnostic of pore fluid pressure changes in fractured reservoirs in this comparatively limited analysis ape modelling of fluid injection at known pressure correctly predicted the changes in seismic response particularly the shear wave splitting induced by the high pressure co2 injection in the phase vii survey ape modelling also successfully predicted the response to the lower pressure injection using the same phase vi model of the cracked reservoir the underlying reason for this remarkable predictability of fluid saturated reservoir rocks is the critical nature and high crack density of the fluid saturated cracks and microcracks in the reservoir rock which makes cracked reservoirs critical systems

3d visualization of carbonate reservoirs conventional 2d and 3d seismic mapping is not ideal for characterizing carbonate reservoirs mainly because of the complexity and heterogeneity of carbonate systems the unique depositional systems of carbonate environments means that a standard interpretation routine is often inadequate and more sophisticated techniques are needed

storm response of the karstic carbonate aquifer of southcentral kentucky abstract temperature and specific conductance were continuously measured in the downstream drainage of the turnhole spring subbasin in the southcentral kentucky karst precipitation was monitored with a rain gage network in the catchment area so that the storm response of specific conductance and temperature could be examined the aquifer feeding the turnhole spring is highly karstic with much of the discharge through integrated open conduits some of which carry water from surface sinking stream catchments both temperature and specific conductance fluctuate rapidly in response to storm events the conductivity curves and to a lesser extent the temperature curves show a sharp dip that lags some hours behind the storm pulse at the onset of the dip is a complicated sequence of fine structures that is interpreted to be the inputs from conduit tributaries to the master trunk drainage system the recovery curves have an exponential form that can be fitted to produce a characteristic response time for the conduit system