three dimensional seismic transmission prospecting of the mont dore volcano france summary the three dimensional seismic structure of the mont dore volcano is studied by inversion of the arrival times of seismic waves with this aim two new methods are developed first the arrival times are those of moho reflected waves at a critical distance from artificial sources in different azimuths secondly the inversion uses a technique which does not require the traditional a priori partition of the space into blocks the resulting picture reveals such features as 1 a circular caldera within the basement the rim of which is marked by magnetic anomalies associated with post caldera activity 2 a clear lower limit of the volcano sedimentary sequence under part of the caldera opposed to low velocity anomalies extending deeper beneath another part and which may have been the site of volcanic material transport and 3 eeper heterogeneities possibly related to foundered basement blocks

tomographic determination of velocity and depth in laterally varying media estimation of reflector depth and seismic velocity from seismic reflection data can be formulated as a general inverse problem the method used to solve this problem is similar to tomographic techniques in medical diagnosis and we refer to it as seismic reflection tomography seismic tomography is formulated as an iterative gauss newton algorithm that produces a velocity depth model which minimizes the difference between traveltimes generated by tracing rays through the model and traveltimes measured from the data the input to the process consists of traveltimes measured from selected events on unstacked seismic data and a first guess velocity depth model usually this first guess model has velocities which are laterally constant and is usually based on nearby well information and or an analysis of the stacked section the final model generated by the tomographic method yields traveltimes from ray tracing which differ from the measured values in recorded data by approximately 5 ms root mean square the i

integrated hyperspectral remote sensing geochemical and isotopic studies for understanding hydrocarbon induced rock alterations abstract the main objective of this work was to determine if there are characteristic mineral assemblages and chemical changes in areas affected by hydrocarbon microseepages for this purpose remote sensing was utilized for mapping surficial rock alterations and geochemical tools were used to understand the alteration processes the key area chosen for this type of work were altered and unaltered wingate sandstone outcrops in lisbon valley utah the spectral angle mapper method was applied on hymap hyperspectral data to classify the extent of altered and unaltered outcrops as well as to map the changes in mineral content within the outcrops the spectral feature fitting method was used to identify lithological changes in the area reflectance spectroscopy thin section studies major minor and trace element analyses and stable carbon and oxygen studies on both bleached altered and unbleached unaltered samples were successfully used to delineate areas of similar rock composition and relate changes due to hydrocarbons leaking from underlying petroleum reservoirs unbleached wingate sandstone samples had higher hematite and feldspar content than bleached wingate samples which were characterized by larger amounts of clay calcite and pyrite some bleached samples also had higher concentrations of elements u mo characteristic of hydrocarbon related reducing environments and were depleted in 13c when compared to the unbleached samples based on these results the following model of chemical reactions is suggested for diagnostic changes within wingate sandstone hydrocarbon induced reducing environment caused the transformation of sulfate ion obtained from groundwater or from oxidation of h2s to sulfide ion resulting in the reduction of hematite to pyrite the released hydrogen ion from this reaction reacted with available feldspars in the rock leading to precipitation of kaolinite these conditions favor the reaction between bicarbonate ion and ca2 ions that can be obtained from the groundwater leading to precipitation of calcite in pore spaces left open after the reduction and removal of hematite

chemical diagenesis in near surface zone above oil fields in geochemical exploration abstract hydrocarbon microseepages result in chemical and mineralogical changes in the near surface zone above oil reservoirs the results of geochemical research within the three oil fields of the west siberian basin demonstrate that chemical diagenetic processes lead to an increased inhomogeneity in chemical element distribution in soils subsoil atmosphere and snow pulse cathodoluminescence pcl study of soils and transmission electron microscopy tem study of micro and nanoparticles collected from the subsoil atmosphere showed that geochemical conditions over oil reservoirs were favorable for the enrichment of silicate and aluminosilicate minerals by chemical impurities chemical composition of micro and nanoparticles of metal compounds collected from within the vertical projection of the oil field outline suggested that these compounds were formed under intense reductive conditions that are not characteristic for the hypergene zone

remote sensing and petroleum seepage a review and case study when reservoirs leak varying quantities of oil and gas migrate to the surface as macroseeps which are visible and microseeps which are invisible this review article describes the mechanisms of seepage and the resulting surface manifestations in relation to optical high resolution remote sensing data oil pools and tar deposits macroseeps often can be detected directly by remote sensing microseeps are more difficult to study using remote sensing but they give rise to vegetation stress and cause geochemical alterations in soil and rocks which can be studied indirectly using hyperspectral sensors an integrated methodology is presented to combine various geoscience and remote sensing datasets for seepage detection a combination of red edge modelling algorithms and spectral matching tools is identified that provides a validated technique for onshore microseepage detection these remote sensing tools are not only important for petroleum exploration but also have environmental implications because seeps emit greenhouse gases a statistical data integration approach was developed based on bayesian assumptions which can be used to integrate hyperspectral remote sensing data other satellite remote sensing data and ancillary field geological and geochemical datasets for modelling microseepage in a case study from the ventura basin santa barbara in southern california probe 1 data from the 1998 geosat group shoot are integrated with field and subsurface geological and geochemical data to predict possible sites of hydrocarbon microseepage

geological storage of carbon dioxide carbon dioxide co2 is the main compound identified as affecting the stability of the earth s climate a significant reduction in the volume of greenhouse gas emissions to the atmosphere is a key mechanism for mitigating climate change geological storage of co2 or the injection and long term stabilization of large volumes of co2 in the subsurface in saline aquifers in existing hydrocarbon reservoirs or in unmineable coal seams is one of the more technologically advanced options available a number of studies have been carried out and are reported here they are aimed at understanding the safety physical and chemical behaviour and long term fate of co2 when stored in geological formations until efficient alternative energy options can be developed geological storage of co2 the subject of this volume provides a mechanism to reduce carbon emissions significantly whilst continuing to meet the global demand for energy

role of fluid mixing and fault related sulfide in the origin of the ray point uranium district south texas the lamprecht and felder deposits are two of many roll type uranium deposits hosted by the miocene oakville sandstone in the ray point south texas uranium district the deposits in this district are aligned parallel to or are intersected by the oakville fault which suggests control by the faults on their origin and or preservation the lamprecht and felder deposits show fundamentally similar patterns of geochemical zonation and of distribution of authigenic iron disulfide fes sub 2 minerals distribution of u mo and se are typical of roll type deposits that result from invasion of geochemically reduced rock by oxygenated uranium bearing solutions sulfur content of these deposits is high as much as 9 with almost all sulfur occurring as fes sub 2 minerals organic carbon is virtually absent four distinct stages of fes sub 2 mineral formation are recognized 1 a generation of isotopically light delta sup 34 s 0 o and 4 a yet later generation of marcasite with isotopically light sulfur close to the values of stages 1 and 2 the alteredmore tongue in these deposits is anomalous in that it contains fes sub 2 minerals in contrast to other texas and wyoming roll type deposits which typically have an oxidized ferric iron bearing altered tongue the dominant fes sub 2 mineral in the altered tongue is isotopically heavy pyrite stage 3 with subordinate amounts of late marcasite stage 4 less

crustal structure of the colorado plateau arizona application of new long offset seismic data analysis techniques the colorado plateau is a large crustal block in the southwestern united states that has been raised intact nearly 2 km above sea level since cretaceous marine sediments were deposited on its surface controversy exists concerning the thickness of the plateau crust and the source of its buoyancy interpretations of seismic data collected on the plateau vary as to whether the crust is closer to 40 or 50 km thick a thick crust could support the observed topography of the colorado plateau isostatically while a thinner crust would indicate the presence of an underlying low density mantle this paper reports results on long offset seismic data collected during the 1989 segment of the u s geological survey pacific to arizona crustal experiment that extended from the transition zone into the colorado plateau in northwest arizona we apply two new methods to analyze long offset data that employ finite difference travel time calculations 1 a first arrival time inverter to find upper crustal velocity structure and 2 a forward modeling technique that allows the direct use of the inverted upper crustal solution in modeling secondary reflected arrivals we find that the crustal thickness increases from 30 km beneath the metamorphic core complexes in the southern basin and range province to about 42 km beneath the northern transition zone and southern colorado plateau margin we observe some crustal thinning to 37 km thick and slightly higher lower crustal velocities farther inboard beneath the kaibab uplift on the north rim of the grand canyon the crust thickens to a maximum of 48 km we observe a nonuniform crustal thickness beneath the colorado plateau that varies by 15 and corresponds approximately to variations in topography with the thickest crust underlying the highest elevations crustal compositions as inferred from seismic velocities appear to be the same beneath the colorado plateau as those in the basin and range province to the southwest implying that the plateau crust represents an unextended version of the basin and range some of the variability in crustal structure appears to correspond to preserved lithospheric discontinuities that date back to the proterozoic era

integrated ground based hyperspectral imaging and geochemical study of the eagle ford group in west texas abstract this study used ground based hyperspectral imaging to map an outcrop of the eagle ford group in west texas the eagle ford group consists of alternating layers of mudstone wackestone grainstone packstone facies and volcanic ash deposits with high total organic content deposited during the cenomanian turonian time period it is one of the few unconventional source rock and reservoirs that have surface representations ground based hyperspectral imaging scanned an outcrop and hand samples at close ranges with very fine spatial resolution centimeter to sub millimeter spectral absorption modeling of clay minerals and calcite with the modified gaussian model mgm allowed quantification of variations of mineral abundances petrographic analysis confirmed mineral identifications and shed light on sedimentary textures and major element geochemistry supported the mineral quantification mineral quantification resulted in mapping of mudstone wackestone grainstone packstone facies and bentonites volcanic ash beds the lack of spatial associations between the grainstones and bentonites on the outcrop calls into question the hypothesis that the primary productivity is controlled by iron availability from volcanic ash beds enrichment of molybdenum mo and uranium u indicated unrestricted marine paleo hydrogeology and anoxic to euxinic paleo redox bottom water conditions hyperspectral remote sensing data also helped in creating a virtual outcrop model with detailed mineralogical compositions and provided reservoir analog to extract compositional and geo mechanical characteristics and variations the utilization of these new techniques in geo statistical analysis provides a workflow for employing remote sensing in resource exploration and exploitation

analysis of co2 leakage through low permeability faults from natural reservoirs in the colorado plateau east central utah the numerous co 2 reservoirs in the colorado plateau region of the united states are natural analogues for potential geologic co 2 sequestration repositories to better understand the risk of leakage from reservoirs used for long term underground co 2 storage we examine evidence for co 2 migration along two normal faults from a reservoir in east central utah co 2 charged springs geysers and a hydrocarbon seep are localised along these faults these include natural springs that have been active for long periods of time and springs that were induced by recent drilling the co 2 charged spring waters have deposited travertine mounds and carbonate veins the faults cut siltstones shales and sandstones and the fault rocks are fine grained clay rich gouge generally thought to be barriers to fluid flow the geologic and geochemical data are consistent with these faults being conduits for co 2 to the surface consequently the injection of co 2 into faulted geologic reservoirs including faults with clay gouge must be carefully designed and monitored to avoid slow seepage or fast rupture to the biosphere

three dimensional determination of structure and velocity by seismic tomography a computerized seismic tomographic method was developed to obtain body wave velocities and three dimensional 3 d structure of interfaces from reflection data simultaneously the medium consists of layers with continuous arbitrary 3 d curved interfaces separating homogeneous material with different acoustic properties the interface is defined by a polynomial surface the elastic waves are assumed to be transmitted or reflected at curved interfaces in which the raypaths satisfy snell s law the ray tracing for each source receiver pair is determined by solving a system of nonlinear equations this method of 3 d ray tracing is effective in computing many seismic rays including converted phases and multiples a damped least squares inversion scheme is formulated to reconstruct the interval velocity and 3 d structure of the interface by minimizing the difference between observed traveltimes and computed traveltimes the results from a synthetic model indicate that the solutions converge quickly to the true

a cause of rupture segmentation and synchronization in the nankai trough revealed by seismic imaging and numerical simulation 1 a giant earthquake occasionally occurs in a subduction zone owing to a simultaneous rupture in adjacent segments which have been previously ruptured by large earthquakes however it is still unknown if a giant earthquake coincidentally occurs or if there is a causal factor to control its generation in this study we show a cause and a growth process of a giant earthquake which may occur along southwestern japan on the basis of seismic images obtained from wide angle seismic data and a numerical simulation incorporating the structural images the wide angle seismic data were acquired along three trough parallel profiles crossing the rupture segmentation boundary between the 1944 tonankai moment magnitude mw 8 1 and the 1946 nankai mw 8 4 earthquakes the seismic imaging detected a high seismic velocity body forming a strongly coupled patch at the segmentation boundary the numerical simulation explained the historic rupture patterns and shows the occurrence of a giant earthquake along the entire nankai trough a distance of over 600 km long mw 8 7 the growth process revealed from the simulated slip history in and around the strongly coupled patch is 1 prior to the giant earthquake a small slow event or earthquake occurs near the segmentation boundary 2 this accelerates a very slow slip slower than the plate convergent rate at the strong patch which reduces a degree of coupling and 3 then a rupture easily propagates through the strong patch when the next earthquake is nucleated near the segmentation boundary consequently growing into a giant earthquake

inversion of seismic reflection traveltimes using a nonlinear optimization scheme we present the use of a nonlinear optimization scheme called generalized simulated annealing to invert seismic reflection times for velocities reflector depths and lengths a finite difference solution of the eikonal equation computes reflection traveltimes through the velocity model and avoids ray tracing we test the optimization scheme on synthetic models and compare it with results from a linearized inversion the synthetic tests illustrate that unlike linear inversion schemes the results obtained by the optimization scheme are independent of the initial model the annealing method has the ability to produce a suite of models that satisfy the data equally well we make use of this property to determine the uncertainties associated with the model parameters obtained synthetic examples demonstrate that allowing the reflector length to vary along with its position helps the optimization process obtain a better solution we put this to use in imaging the garlock fault whose geometry at depth is po

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

hydrocarbon microseepage related geobotanical analysis in and around oil fields hydrocarbon microseepage can be detected by its altering effect on rocks soils and overlying vegetation this study examines the impact of hydrocarbon seepage on vegetation microseeping hydrocarbons alter soil chemistry often creating an environment that can impact the health of overlying vegetation these effects can be observed using remote sensing blackburn and eagle springs oil fields in nevada patrick draw and little buffalo basin oil fields in wyoming and cement oil field in oklahoma were selected for this study because previous investigations confirmed the presence of microseeping hydrocarbons in these locations in this study moderate resolution imaging spectroradiometer s modis monthly average normalized difference vegetation index ndvi data from january 2003 to december 2012 were used to observe vegetation health inside oil fields average ndvi was calculated for these locations the typical range of ndvi in desert environments such as those observed in semi arid desert environments

seismic propagation across the east pacific rise finite difference experiments and implications for seismic tomography we use a full waveform acousto elastic finite difference technique to investigate seismic propagation across the east pacific rise at 9 30 n for a two dimensional velocity model based on that proposed by vera and others 1990 the primary feature of the model is an upper crustal low velocity region corresponding to the axial magma chamber which includes a small magma body located 1 6 km beneath the seafloor at the rise axis the high velocity gradients in this region result in a complex pattern of propagation which includes considerable scattering of energy above and below the magma chamber a qualitative comparison of finite difference seismograms with data collected by receivers located 9 km and 20 km off axis during a tomography experiment at 9 30 n shows generally good agreement for paths that cross the rise axis the first arrival in the finite difference solutions diffracts above the magma chamber this phase has a very low amplitude and at larger offsets falls below the ambient noise levels observed during the tomography experiment in such cases the first arrival with significant energy is a diffraction from below the magma chamber a high amplitude moho turning pmp phase which results from the large velocity change across the moho beneath the rise axis is apparent in both the finite difference solutions and the observations ray theoretical calculations of the paths of the diffracted arrivals are very unstable and for the diffractions above the magma chamber no solution can be found with a single precision algorithm synthetic delay time inversions using an approximate ray tracing algorithm demonstrate the importance of ensuring that picked arrival times are assigned to paths that pass to the correct side of the magma body synthetic inversions of spectral estimates of t show that q 1 models are compromised not only if the ray paths are incorrect but also if t estimates include significant contributions from more than one phase deterministic scattering from the magma chamber may contribute noticeably to spectral estimates of t but the results of the finite difference experiments imply that high levels of attenuation observed for phases passing below the magma chamber are predominantly the result of intrinsic attenuation

high pore fluid pressure may cause silent slip in the nankai trough silent slip events have been detected at several subduction zones but the cause of these events is unknown using seismic imaging we detected a cause of the tokai silent slip which occurred at a presumed fault zone of a great earthquake the seismic image that we obtained shows a zone of high pore fluid pressure in the subducted oceanic crust located down dip of a subducted ridge we propose that these structures effectively extend a region of conditionally stable slips and consequently generate the silent slip

theoretical and numerical issues in the determination of reflector depths in seismic reflection tomography seismic reflection tomography obtains an estimate of the subsurface slowness field and the location of strong reflectors by minimizing the difference between measured travel times from seismic reflection events and the corresponding travel times computed from a model of the subsurface we present some theoretical results for the undiscretized problem regarding the possible ambiguity between slowness and depth these results indicate that the depths of the reflectors are determined in theory except for edge effects but a sufficiently large aperture at the reflector is necessary to resolve this ambiguity in practice the slowness field however does have some undetermined features these results have strong implications for how the tomography problem should be discretized and regularized to compute solutions which are accurate in the features of the model which are well determined from the travel time data in particular the slowness model should not be discretized much more coarsely than the reflectors as a way of regularizing the problem because that may force the computed reflector depths to try to match aspects of the travel time data which are caused by features in the slowness field

a review of least squares inversion and its application to geophysical problems geophysical inversion involves the estimation of the parameters of a postulated earth model from a set of observations since the associated model responses can be nonlinear functions of the model parameters nonlinear least squares techniques prove to be useful for performing the inversion a common type of inversion applies iterative damped linear least squares through use of the marquardt levenberg method traditionally this method has been implemented by solving the associated normal equations in conventional ways however singular value decomposition svd produces significant improvements in computational precision when applied to the same system of normal equations iterative least squares modeling finds application in a wide variety of geophysical problems two examples illustrate the approach 1 seismic wavelet deconvolution and 2 the location of a buried wedge from surface gravity data more generally nonlinear least squares inversion can be used to estimate earth models for any set of geophysical observations for which an appropriate mathematical description is available

inversion for crustal structure using reflections from the passcal ouachita experiment an interface inversion has been tested and applied to wide angle reflection data from the 1986 passcal ouachita experiment an interface corrugation with a relief of 10 km and a width of 30 km was successfully imaged in a test of the interface inversion velocity depth curves derived for shot points 14 19 using the tail sum method are similar to an average one dimensional velocity model from forward modeling using travel time correlations from southern profiles 14 19 the similarity of these velocity depth curves positioned over the southern half of the passcal experiment suggests that crustal structure in this region is approximately laterally homogeneous lower crustal velocities are not well resolved due to the recording on most profiles of only small segments of the travel time triplications a two dimensional velocity structure was derived by using the average one dimensional velocities for the deeper crustal layers and formally inverting for depth to interfaces the final inversion model is found to be consistent with previous refraction interpretations south of the ouachita orogenic trend and concurrent interpretations of the passcal data set inversion results for the central and southern portion of the passcal profile indicate a depth of 10 12 km for a midcrustal layer which thins southward from approximately 10 km to about 4 km a lower crustal layer with an average thickness of 12 km and a moho depth of approximately 29 5 km are also determined interface depths are in agreement with a normal moveout stack of the passcal data set in particular the shallowing of the moho to a depth of 30 km over the northern 50 km of the profile matches previous interpretations of the data set and has been interpreted here and in previous studies as the location of the paleozoic continental margin geophysical studies of the modern atlantic continental passive margin provide the simplest comparison to the crustal structure derived here the lower crustal layer found south of the shallowing of the moho to 30 km beneath the passcal profile is analogous in thickness and position to rift stage lower crust however other tectonic interpretations are possible given the uncertainties in velocity and lithology relationships

spectral and geochemical characterization of onshore hydrocarbon seep induced alteration in the dezful embayment southwest iran the presence of hydrocarbon seeps at the surface is indirect evidence of the presence of mature source rocks within a geological system at depth chemical changes in the environment of surface rocks caused by hydrocarbon seeps cause mineralogical alterations to determine the nature of the alterations and the influences of lithology and type of seep rock samples were collected from altered and unaltered evaporite and marly limestone formations in the dezful embayment southwest iran reflectance spectroscopy bulk rock wet chemical analyses and sulfur carbon and oxygen isotopic analyses were used to delineate surficial alterations and relate alterations to hydrocarbons seeping from underlying reservoirs in addition the boosted regression trees brt method was used to predict the presence of alterations from spectral indices comparisons of geochemical data and spectral data of altered evaporites and altered marly limestones showed that the minerals within alteration facies have distinctive spectral chemical and isotopic signatures gas induced alterations were characterized by the formation of gypsum and native sulfur and depletion in the released in natural gas reacted with gypsum in the evaporite sediments and calcite in the marly limestone formations which led to precipitation of secondary gypsum and native sulfur oil induced alterations were characterized by formation of secondary calcite and depletion in the oxidation of seeping oil and reactions between this oil and host rocks caused precipitation of secondary calcite within both formations the combination of fieldwork data and spectral geochemical data showed a connection exists between surficial alterations and underlying petroleum reservoirs which can be used in exploration campaigns

tomo3d 3 d joint refraction and reflection traveltime tomography parallel code for active source seismic data synthetic test we present a new 3 d traveltime tomography code tomo3d for the modelling of active source seismic data that uses the arrival times of both refracted and reflected seismic phases to derive the velocity distribution and the geometry of reflecting boundaries in the subsurface this code is based on its popular 2 d version tomo2d from which it inherited the methods to solve the forward and inverse problems the traveltime calculations are done using a hybrid ray tracing technique combining the graph and bending methods the lsqr algorithm is used to perform the iterative regularized inversion to improve the initial velocity and depth models in order to cope with an increased computational demand due to the incorporation of the third dimension the forward problem solver which takes most of the run time 90 per cent in the test presented here has been parallelized with a combination of multi processing and message passing interface standards this parallelization distributes the ray tracing and traveltime calculations among available computational resources the code s performance is illustrated with a realistic synthetic example including a checkerboard anomaly and two reflectors which simulates the geometry of a subduction zone the code is designed to invert for a single reflector at a time a data driven layer stripping strategy is proposed for cases involving multiple reflectors and it is tested for the successive inversion of the two reflectors layers are bound by consecutive reflectors and an initial velocity model for each inversion step incorporates the results from previous steps this strategy poses simpler inversion problems at each step allowing the recovery of strong velocity discontinuities that would otherwise be smoothened

nonlinear refraction and reflection travel time tomography we develop a rapid nonlinear travel time tomography method that simultaneously inverts refraction and reflection travel times on a regular velocity grid for travel time and ray path calculations we apply a wave front method employing graph theory the first arrival refraction travel times are calculated on the basis of cell velocities and the later refraction and reflection travel times are computed using both cell velocities and given interfaces we solve a regularized nonlinear inverse problem a laplacian operator is applied to regularize the model parameters cell slownesses and reflector geometry so that the inverse problem is valid for a continuum the travel times are also regularized such that we invert travel time curves rather than travel time points a conjugate gradient method is applied to minimize the nonlinear objective function after obtaining a solution we perform nonlinear monte carlo inversions for uncertainty analysis and compute the posterior model covariance in numerical experiments we demonstrate that combining the first arrival refraction travel times with later reflection travel times can better reconstruct the velocity field as well as the reflector geometry this combination is particularly important for modeling crustal structures where large velocity variations occur in the upper crust we apply this approach to model the crustal structure of the california borderland using ocean bottom seismometer and land data collected during the los angeles region seismic experiment along two marine survey lines details of our image include a high velocity zone under the catalina ridge but a smooth gradient zone between catalina ridge and san clemente ridge the moho depth is about 22 km with lateral variations

simultaneous inversion of reflection and refraction seismic data and application to field data from the northern rio grande rift summary an inversion scheme that determines a velocity model simultaneously from normalincidence reflection and refraction wide angle reflection seismic data has been developed tested and applied to real seismic data simultaneous inversion minimizes the non uniqueness of inversion results a common midpoint cmp stacked reflection section provides a detailed image of the structural configuration in time refraction or wide angle reflection data can be used to derive a velocity model if both refraction data and normal incidence reflection data are available along coincident profiles simultaneous inversion of the data sets can produce an improved model with the extra control of the interface depth provided by reflection data it is also possible to avoid ambiguity of phase identification the commonly used damped least squares dls inversion method often results in significant inversion artefacts we provide effective methods for reducing inversion artefacts using both damping and smoothing from tests using synthetic data we conclude that the simultaneous inversion scheme can improve resolution and can be applied to velocity models with a reasonably complex structure the simultaneous inversion scheme has been successfully applied to coincident seismic reflection and refraction data recorded by the sage program in 1990 1991 in the western boundary area of the rio grande rift near abiquiu new mexico in this example the simultaneous inversion derived a velocity model in which stratigraphic units and extensional fault blocks can be resolved

fracture characterization at valhall application of p wave amplitude variation with offset and azimuth avoa analysis to a 3d ocean bottom data set the delineation and characterization of fracturing is important in the successful exploitation of many hydrocarbon reservoirs such fracturing often occurs in preferentially aligned sets if the fractures are of subseismic scale this may result in seismic anisotropy thus measurements of anisotropy from seismic data may be used to delineate fracture patterns and investigate their properties here fracture induced anisotropy is investigated in the valhall field which lies in the norwegian sector of the north sea this field is a chalk reservoir with good porosity but variable permeability where fractures may significantly impact production e g during waterflooding to investigate the nature of fracturing in this reservoir p wave amplitude variation with offset and azimuth avoa is analyzed in a 3d ocean bottom cable obc data set in general 3d ocean bottom seismic obs acquisition leads to patchy coverage in offset and azimuth and this must be addressed when considering such data to overcome this challenge and others associated with 3d obs acquisition a new method for processing and analysis is presented for example a surface fitting approach which involves analyzing azimuthal variations in avo gradients is used to estimate the orientation and magnitude of the fracture induced anisotropy this approach is also more widely applicable to offset azimuth analysis of other attributes e g traveltimes and any data set where there has been true 3d data acquisition land or marine using this new methodology we derive high resolution maps of p wave anisotropy from the avoa analysis for the top chalk reflection at valhall these anisotropy maps show coherent but laterally varying trends synthetic avoa modeling using effective medium models indicates that if this anisotropy is from aligned fracturing the fractures are likely liquid filled with small aspect ratios and the fracture density must be high furthermore we show that the fracture normal direction is parallel to the direction of most positive avo gradient in other situations the reverse can be true i e the fracture normal direction can be parallel to the direction of the most negative avo gradient effective medium modeling or comparisons with anisotropy estimates from other approaches e g azimuthal variations in velocity must therefore be used to resolve this ambiguity the inferred fracture orientations and anisotropy magnitudes show a degree of correlation with the positions and alignments of larger scale faults which are estimated from 3d coherency analysis overall this work demonstrates that significant insight may be gained into the alignment and character of fracturing and the stress field variations throughout a field using this high resolution avoa method

remote sensing and geochemistry for detecting hydrocarbon microseepages this work tests the hypothesis that chemical and mineralogical alterations in rocks and soils are related to hydrocarbon microseepages above some of the major oil fields in this study we used hyperion hyperspectral imaging sensors to map alterations that appear to be associated with hydrocarbon microseepages in the patrick draw area of wyoming our mineralogical geochemical and carbon isotope data support the presence of hydrocarbon microseepages satellite imagery training classifications defined by areas of hydrocarbon microseepage have resulted in the successful identification of the areal extent of an anomalous area geochemical characteristics of samples that define this anomalous area were then compared to the remaining non anomalous samples using x ray diffraction xrd reflectance spectroscopy and carbon isotope techniques xrd analyses demonstrated the increased presence of feldspars in non anomalous samples compared to anomalous samples spectroscopy results demonstrated higher proportions of clays within the anomalous samples compared to non anomalous samples the 13 c values range from 2 88 to as low as 45 32 indicating hydrocarbon sources these methods may provide a foundation upon which further hydrocarbon exploration techniques can develop

the 1983 landsat soil gas geochemical survey of patrick draw area sweetwater county wyoming the geosat test site at patrick draw wyoming was resampled during the summer field season of 1983 to conduct a more detailed soil gas survey on and around the area s producing fields the results of this study agree with the 1980 geosat assessment that the faults and fractures visible as linear features on satellite and aircraft imagery provide paths for active microseepage of hydrocarbons from depth to the near surface this association is particularly true near the earlier described blighted sage zone where extensive resampling reveals a much wider area of anomalously high free soil gas values and fluorescence than was previously reported discriminant analysis suggests that the geochemical seepage signature found over the fields differs statistically from that present for adjacent areas of no known production this observation was found to be true for all three soil gas techniques used in this study anomaly patterns appear to be related to the type of soil gas sample studied data obtained from shallow free soil gas samples reveal that direct anomalies controlled by faults and fractures formed over production whereas data obtained from samples treated by acid extraction or thermal mechanical disaggregation techniques exhibit magnitude lows over the producing areas such patterns indicate halo features around the composite producing areas at present this conflicting behavior cannot be explained

the potential use of biogeochemistry in the detection of petroleum microseepage biogeochemistry was applied to the indirect detection of petroleum microseepage in the vicinity of eagle springs oil field railroad valley nevada and cave canyon field paradox basin utah trace elements were measured in native vegetation over and surrounding areas of production at the test sites the oxidation of microseepage in the upper part of the soil column is postulated to cause an increase in plant uptake of transition trace elements such as iron manganese and vanadium and a decrease in plant uptake of alkaline earth elements such as calcium strontium and barium compared to nonproductive areas an increase in uptake of transition trace elements and a decrease in alkaline earth elements was observed in fourwing saltbush over eagle springs field the postulated increase in uptake of transition trace elements and decrease in alkaline earth elements was not as apparent in big sagebrush nor in utah juniper over the cave canyon field the observation of the postulated effects on vegetation at eagle springs may be due to the relatively large rates of microseepage independently observed using other methods and the extensive faulting in railroad valley the weaker response observed at cave canyon may reflect the lack of faulting and the retention of light hydrocarbons in the reservoir another possible reason for weak response is that the available plant species at cave canyon do not exhibit the effect at the lower soil ph measured in the area at low ph and low eh the solubility of transition elements in soil pore waters and plant uptake is increased due to the high soil ph of the railroad valley area the uptake of alkaline earth elements should be decreased where microseepage is occurring because of crystallizat on of carbonate minerals

biogenic and nonbiogenic ore forming processes in the south texas uranium district evidence from the panna maria deposit geochemical and petrographic studies of core samples from the panna maria uranium deposit a roll type orebody in the eocene jackson group in karnes county texas yield important information on the origin of the deposit organic carbon content averages about 0 42 weight percent in reduced rock and correlates postively with sulfur content pyrite is the dominant iron disulfide fes 2 mineral in most of the ore zone and throughout a surrounding zone of reduced barren ground and it is commonly associated with organic debris marcasite is sparse except in ore adjacent to the altered tongue in one core and locally in mineralized lignite sulfur isotopic compositions delta 34 s of fes 2 minerals range broadly from 1 to 34 per mil the lightest delta 34 s values less than 20 per mil were measured in samples from mineralized lignite and from the nose of the ore roll petrographic and geochemical characteristics of the panna maria deposit contrast greatly with those of three other south texas roll type uranium deposits the benavides felder and lamprecht deposits which are devoid of organic carbon and which contain more sulfide than does the panna maria these three deposits are characterized by abundant isotopically light ore stage marcasite and by isotopically heavy preore in the benavides or postore in the felder and lamprecht pyrite we have concluded previously that sulfide bearing fault leaked solutions from underlying hydrocarbon accumulations were important in the formation of the benavides felder and lamprecht deposits although the panna maria deposit shows an apparent alignment along a fault zone and although underlying formations in the karnes county area contain sour gas delta 34 s asymp 14 per mil and produce oil the deposit lacks characteristics indicating that its formation or preservation involved extrinsically derived reductants such as fault leaked aqueous sulfide mineralization of the panna maria rather appears to have been controlled by intrinsically derived reductants related either directly or indirectly to the presence of organic matter

epigenetic zoning in surface and near surface rocks resulting from seepage induced redox gradients velma oil field oklahoma abstract abstract surface and near surface permian sandstone has been drastically altered over the productive part of the structurally complex velma oil field as a consequence of petroleum microseepage buried permian sandstone along the northwest southeast trending anticline is cemented with abundant pyrite ferroan calcite and ferroan dolomite at the surface along the anticlinal crest iron disulfide is scarce isotopically anomalous carbonate cemented sandstone is overlain by sandstone that is massively impregnated by hematite cement permian sandstone is normally reddish brown throughout southern oklahoma but along the anticlinal flank it has been bleached yellow and white owing to iron loss some units contain abundant solid bitumen the mineralogy in the vertical section over the anticline follows the calculated stability relations for iron sulfide iron carbonate and iron oxide along a gradient from strongly reducing conditions at depth to oxidizing conditions at the surface reducing conditions were provided by seeping hydrocarbons from subsurface reservoirs of this multizone giant field production depths range from 120 to 2 975 m the principal evidence that these alterations are seepage induced is provided by reports of oil seeps in the early literature by zones of solid bitumen cements and by c13 pdb values for carbonate cements that range from 7 8 to 36 7 ppt

iron sulfide minerals at cement oil field oklahoma implications for magnetic detection of oil fields aeromagnetic anomalies at cement oil field anadarko basin oklahoma have been attributed to authigenic magnetite the following characteristics of the magnetite however indicate that it is contamination introduced by drilling 1 occurrence as sharp angular blades and as spheres commonly with metallographic textures typical of industrial alloys and with associated steel and wustite feo 2 presence only in well cuttings and absence from core and quarry samples and 3 lack of association with detrital framework grains or with authigenic carbonate and sulfide minerals ferrimagnetic pyrrhotite occurs in well cuttings cores and quarry samples at cement and is a possible natural source of the magnetic anomalies pyrrhotite which is intergrown with more abundant fes 2 minerals formed as a result of hydrocarbon seepage pyrrhotite is confined to beds above oil and gas reservoirs these beds which lack detrital organic matter contain higher mineral sulfide and lower mineral sulfate sulfur 1 7 and 0 1 wt respectively than do correlative beds off the field 0 2 and 1 1 wt respectively in the field isotopic values of sulfide s show a systematic decrease upward through the permian section from positive values maximum 12 per mil at 610 760 m depth to negative values 1 to 11 per mil between 32 and 230 m 26 to 30 per mil at the surface geochemical results together with time temperature data derived from burial curves limit the major sources of the sulfide in the fe s minerals to two possibilities isotopically heavy sulfide was generated either inorganically at temperatures 90 c in beds beneath permian beds or by bacterial sulfate reduction at temperatures

the uranium potential of diagenetically altered sandstones of the permian rush springs formation cement district southwest oklahoma reconnaissance and detailed geologic radiometric and geochemical investigations one previously unreported uranium occurrence was discovered during outcrop reconnaissance areas of uranium favorability in the subsurface were identified by the examination of gamma ray well logs and the interpretation of stratigraphic cross sections derived from electric log data an aureole of diagenetic alteration which affects the permian sedimentary sequence overlying the pre permian cement anticline exposed and subsurface diagenetically altered sandstones of the rush springs formation within this aureole constitute a favorable environment for the occurrence of shallow joint controlled sandstone type uranium deposits nonchannel controlled peneconcordant deposits and classic roll type deposits three subareas have been identified as especially favorable exploration targets within the overall favorable area modified journal abstract

study on identification of altered rock in hyperspectral imagery using spectrum of field object abstract in this article the spectrum of a field object was used to match the pixel spectrum in the hyperspectral imagery and determine whether there existed a dominant object in the pixel and to what extent the dominant object was present based on these recognition results altered rock in the hyperspectral imagery was identified the spectrum of a field object was obtained from field surveys in the study area and in the spectrum there was only one main object that could be effectively identified this main object was named as the dominant object in this paper in this study the overall shape of the spectrum was matched firstly and then the correlation coefficients between the pixel spectrum and the spectrum of field object in the corresponding wavelength ranges of the absorption bands were calculated to determine the matching effect of these spectra as well as the possibility that the dominant object existed in the pixel the recognition results were expressed by two images the first image was a figure that illustrated the dominant objects in the pixels the second image was a figure showing the correlation coefficients the study area was a primitive forest covered region located in the pulang porphyry copper mining area zhongdian county of yunan province china the figures illustrating the distribution of the altered rocks and the correlation coefficient were obtained from this study the on site verification showed that using the spectra of field objects it was possible to identify the dominant objects in the pixels which favored the identification of altered rocks in the image moreover compared to considering only the overall shape the recognition results obtained by considering the overall and partial shape of the spectra had higher reliability

turning ray tomography turning ray tomography is useful for estimating near surface velocity structure in areas where conventional refraction statics techniques fail because of poor data or lack of smooth refractor velocity structure this paper explores the accuracy and inherent smoothing of turning ray tomography in its capacity to estimate absolute near surface velocity and the statics times derived from these velocities and the fidelity with which wavefields collapse to point diffractors when migrated through these estimated velocities the method comprises nonlinear iterations of forward ray tracing through triangular cells linear in slowness squared coupled with the lsqr linear inversion algorithm it is applied to two synthetic finite difference data sets of types that usually foil conventional refraction statics techniques these models represent a complex hard rock overthrust structure with a low velocity zone and pinchouts and a contemporaneous near shore marine trench filled with low velocity unconsolidated deposits exhibiting no seismically apparent internal structure in both cases velocities are estimated accurately to a depth of one fifth the maximum offset as are the associated statics times of equal importance the velocities are sufficiently accurate to correctly focus synthetic wavefields back to their initial point sources so migration datuming applications can also use these velocities the method is applied to a real data example from the timbalier trench in the gulf of mexico which exhibits the same essential features as the marine trench synthetic model the timbalier velocity inversion is geologically reasonable and yields long and short wavelength statics that improve the cmp gathers and stack and that correctly align reflections to known well markers turning ray tomography estimates near surface velocities accurately enough for the three purposes of lithology interpretation statics calculations and wavefield focusing for shallow migration and datuming