compositional fractionation of petroleum from reservoir to wellhead in the niobrara shale oil play abstract hydraulic fracturing is routinely used to stimulate unconventional reservoirs in the niobrara shale oil play there are several fracking targets but the actual stimulated rock volume is not well constrained this means that allocating produced oil to specific reservoirs in essence oil reservoir correlation is not straightforward the data presented here support that the chalk units are the principal production zones in the niobrara shale oil play several lines of evidence such as the presence of heavy end n alkanes n c31 consistence in composition of gross fractions the distribution of c27 28 29 diasteranes as well as the pristane to phytane ratio all suggest that oils were produced from the a b chalks particularly from the a chalk during production a selective partitioning of lighter hydrocarbons into the migrating fluids could nevertheless occur in particular as regards the n alkanes domain and their carbon isotopic compositions regarding the latter a depletion of 13c in the produced oil s n alkanes by more than three per mil relative to all of those core extracts was observed this finding suggests that compound specific isotope analysis in both oil reservoir and oil source rock correlations cannot be taken at face value i e by simple matching of values besides that fractionation appears to result in the enrichment of rather aliphatic nitrogen containing compounds in crude oils

quantifying measurement uncertainty of thirty meter shear wave velocity thirty meter shear wave velocity v s 30 is commonly used to estimate near surface conditions for site classification seismic site response liquefaction analysis and other geotechnical earthquake engineering application quantifying the uncertainty in v s 30 measurements is important for determining the accuracy and precision of this geophysical test this study gathers existing available comparative and blind shear wave velocity tests to evaluate the apparent or observable intra and intermethod variability presented in this article are estimates of v s 30 uncertainty for the invasive methods of downhole suspension logging and seismic cone penetration testing the noninvasive method of spectral analysis of surface waves and the method of shear wave velocity correlated geologic units discussed is the issue of soil disturbance with respect to invasive methods and how this may result in measurement bias results of this study indicate that uncertainty of shear wave velocity measurements are on the order of 1 3 coefficient of variation standard deviation mean for downhole suspension logging and seismic cone penetration testing 5 6 coefficient of variation for spectral analysis of surface waves and 20 35 coefficient of variation for shear wave velocity correlated geologic units presented here are procedures for propagating the uncertainty and or bias in forward analyses

de convoluting crude oil mixtures from palaeozoic reservoirs in the tabei uplift tarim basin china abstract geochemical characteristics of 61 crude oil samples collected from palaeozoic reservoirs in the tarim basin 60 from the tabei uplift and one from the tazhong uplift were analyzed the samples proved to be mixed oils of different maturity from diverse source rocks concentrations of 40 biomarkers and carbon isotopic compositions for the whole oils were analyzed by alternating least squares als regression to de convolute the mixtures three endmember em oils were identified em1 is the minimum contributor to the mixed oils accounting for less than 10 of most oils em1 originated from cambrian lower ordovician source rocks in the early to peak oil window stage and experienced two phases of mixing and biodegradation em2 is the secondary contributor with proportions ranging from 10 to 40 in most oil samples em2 originated from middle upper ordovician source rocks at the early oil generation stage and underwent two phases of mixing and one stage biodegradation in the reservoirs em3 is the major contributor to most samples with proportions ranging from 13 to 95 em3 was generated from middle upper ordovician source rocks at the late oil generation stage and mixed with earlier emplaced mixtures in the reservoirs the final mixtures that were not biodegraded are currently exploited from palaeozoic reservoirs in the tabei uplift biomarkers in the crude oils reveal mixed characteristics including evidence for two phases of oil charge and severe biodegradation

source rock heterogeneity and migrated hydrocarbons in the triassic shublik formation and their implication for unconventional resource evaluation in arctic alaska abstract this organic geochemical study of the triassic shublik formation aims to investigate source rock heterogeneity facies variation and source and maturity of migrated hydrocarbons in the tenneco phoenix 1 well ocs y 0338 drilled in offshore arctic alaska in 1986 recovered continuous core is nearly 90 m thick continuous section throughout the entire shublik formation guided by previously published analyses of the phoenix 1 core by robison et al 1996 this study provides the most detailed core based analysis of the shublik formation to date analysis of biomarkers and diamondoids combined with rock eval pyrolysis results indicates evidence of mature migrated hydrocarbons that may have affected previous interpretations of organic matter type and maturity of this core despite the variable lithology four identified source rock intervals contain oil prone type i kerogens with maturity ranging from immature to marginally mature biomarker analysis indicates the presence of two organic facies deposited under anoxic clay poor and suboxic clay rich environments that likely generated genetically distinct oils

regression analysis of vs30 using topographic attributes from a 50 m dem abstract the average shear wave velocity for the top 30 m v s30 is one of the simple predictors of earthquake ground motion amplification we performed a multiple linear regression analysis of the logarithm of observed v s30 at 1646 locations in japan with three topographic attributes slope gradient surface texture and the logarithm of elevation calculated from a 50 m dem a v s30 map was created using the partial regression coefficients the determination coefficient was 0 318 the development of the estimation method of v s30 from a dem will be useful for earthquake vulnerability assessment

waveform inversion for one dimensional near surface structure in the new madrid seismic zone waveform inversion is applied to p and s waveforms selected from microearthquakes of duration magnitude m d between 1 8 and 2 4 recorded at station parm in stahl farm missouri operated by the cooperative new madrid seismic network in the upper mississippi embayment to resolve the one dimensional 1d velocity structure of uppermost near surface soils constrained by vertical seismic profiling vsp and standard cone penetration test scpt data at nearby sites we begin by defining a gradient velocity structure in the soils a reference velocity model is constructed by grid search in which the observed p and p s wave shapes graphic 1 travel time and p p s amplitude ratio are the controlling factors in the systematic selection from among 136 000 models a waveform inverse scheme is then implemented to obtain the least spectral misfit and best waveform correlation between synthetic and observed data four simultaneous inversions of joint waveforms from p and s wave types are performed resolved four 1d final models with associated uncertainties are listed in this article the uppermost 7 m of near surface soil exhibit very low velocities through which v p and v s are in the ranges of 140 m s to 470 m s and 95 m s to 215 m s respectively this noninvasive technique demonstrates that the observed high frequency reverberations 1 17 hz of p s and p s waveforms from local microearthquakes can be utilized to provide a view of the near surface soil structure although there are trade offs between layer thickness and slowness this method explains much of the high frequency site response due to microearthquake wave propagation through the very low velocity near surface soils 1 embed inline graphic 1 gif

source apportionment of the hydrocarbon background in sediment cores from hecate strait a pristine sea on the west coast of british columbia canada abstract significant reserves of oil and gas have been predicted for hecate strait a pristine semi enclosed sea on the continental shelf adjacent to british columbia on the west coast of canada to establish a baseline for the natural background of hydrocarbons in sediment prior to any further offshore oil and gas development or increase in oil tanker traffic in the hecate strait region three sediment box cores were collected along a west to east transect across southern hecate strait in september 2003 210 pb measurements established that the bottom sections date to 1920 pre 1800 and 1870 respectively which predate any significant industrial development on the coast alkane and polycyclic aromatic hydrocarbon pah concentrations are low in most sediment samples and both the concentrations and fluxes differ little between surface and bottom core sections pah profiles exhibit a dominance of alkyl pahs for each alkyl pah homologous series with varying amounts of parent unsubstituted pahs while alkane chromatograms show no unresolved complex mixture ucm and there is little change in composition between present day and pre 1800 sediments for most parameters principal components analysis pca models and pah and biomarker ratios indicate that composition patterns are consistent with low and varying natural petrogenic and pyrogenic inputs with little or no anthropogenic input the most likely primary source of petrogenic pahs to the sediments is cenozoic lignites from the skonun formation which outcrops on haida gwai and underlies most of hecate strait two subsurface sections deposited in 1990 and 1930 in the core from milbanke sound on the east side of the transect have elevated concentrations for the alkyl phenanthrene anthracenes and dibenzothiophenes with no ucm and most likely also have a source in immature coal this study suggests that the hecate strait environment has low hydrocarbon concentrations with an apparent minor role for oil seeps and a likelihood that most of the petrogenic pah sources are shales or immature coals with limited pah bioavailability if these characteristics are representative of hecate strait sediments overlying the queen charlotte basin it may mean that biota are likely unadapted to the presence of oil and thus would be more sensitive to exposure to oil from an oil spill than those in a more impacted environment

mantle flow as a trigger for subduction initiation a missing element of the wilson cycle concept the classical wilson cycle concept describing repeated opening and closing of ocean basins hypothesizes spontaneous conversion of passive continental margins into subduction zones this process however is impeded by the high strength of passive margins and it has never occurred in cenozoic times here using thermomechanical models we show that additional forcing provided by mantle flow which is induced by neighboring subduction zones and midmantle slab remnants can convert a passive margin into a subduction zone models suggest that this is a long term process thus explaining the lack of cenozoic examples we speculate that new subduction zones may form in the next few tens of millions of years along the argentine passive margin and the u s east coast mantle suction force can similarly trigger subduction initiation along large oceanic fracture zones we propose that new subduction zones will preferentially originate where subduction zones were active in the past thus explaining the remarkable colocation of subduction zones during at least the last 400 myr

chemometric identification of crude oil families and deconvolution of mixtures in the surrounding niuzhuang sag bohai bay basin china a total of 46 crude oil samples recovered from the surrounding niuzhuang sag were investigated to gain insight into the petroleum systems in the dongying depression chemometrics identified four genetically distinct oil families family 1 fails to match any of the source rocks that have been discovered thus far the candidate source rock must contain algal organic matter that could produce more negative carbon isotopic composition large quantities of wax c29 steranes and tricyclic terpenoids compared to the eocene shahejie es formation intervals es3 and es4 and deposited in a reducing stratified saline water environment family 2 is featured by high ratios of sterane hopane gammacerane hopane and c35 c34 homohopane and low pristane phytane ratios the source rock is the upper es4 interval family 3 is characterized by distinctive or even opposite features to family 2 the source rock is the lower es3 interval family 4 is a mixed oil derived from the lower es3 and upper es4 source rocks at different thermal maturation three end member oil samples em1 em2 and em3 were identified by alternating least squares as a minor contributor em1 has an average value of 10 as the main contributors em2 and em3 average 53 and 37 respectively oil samples from em1 and em2 are derived from the upper es4 source rock but em1 was generated at a lower thermal maturity than em2 oil from em3 was derived from the lower es3 source rock at peak hydrocarbon generation

variations in the sterane carbon number distributions of marine source rock derived crude oils through geological time abstract the analysis of the sterane data of a large set of crude oils 414 derivedfrom marine carbonate 27 and siliciclastic source rocks 14 where influences of terrestrial or lacustrine derived organic matter can reasonably be excluded shows that there are increases in the relative content of c28 steranes and decreases in the relative content of c29 steranes through geological time there are no consistent variations in the relative content of c27 steranes through time with one major exception a proterozoic oil from oman palaeozolic and older crude oils are thus generally characterised by strong predominances of c29 steranes and low relative concentrations of c28 steranes significantly higher proportions of c28 steranes and lower proportions of c29 steranes occur in oils derived from jurassic and upper cretaceous source rocks these changes through time do not appear to reflect the chemical evolution of the sterols of one particular variety of marine organism the increase in c28 steranes may be related to the increased diversification of phytoplantonic assemblages in the jurassic and cretaceous possible sources of the c28 sterols necessary for the observed changes in crude oil steranes includes diatoms coccolithophores and dinoflagellates although the technique does not give an accurate means of determining the age of the source rock of a crude oil it is possible to distinguish younger crudes derived from the upper cretaceous and tertiary from palaeozoic and older crudes

north slope alaska source rock distribution richness thermal maturity and petroleum charge four key marine petroleum source rock units were identified characterized and mapped in the subsurface to better understand the origin and distribution of petroleum on the north slope of alaska these marine source rocks from oldest to youngest include four intervals 1 middle upper triassic shublik formation 2 basal condensed section in the jurassic lower cretaceous kingak shale 3 cretaceous pebble shale unit and 4 cretaceous hue shale well logs for more than 60 wells and total organic carbon toc and rock eval pyrolysis analyses for 1183 samples in 125 well penetrations of the source rocks were used to map the present day thickness of each source rock and the quantity toc quality hydrogen index and thermal maturity tmax of the organic matter based on assumptions related to carbon mass balance and regional distributions of toc the present day source rock quantity and quality maps were used to determine the extent of fractional conversion of the kerogen to petroleum and to map the original toc toco and the original hydrogen index hio prior to thermal maturation the quantity and quality of oil prone organic matter in shublik formation source rock generally exceeded that of the other units prior to thermal maturation commonly toco 4 wt and hio 600 mg hydrocarbon g toc although all are likely sources for at least some petroleum on the north slope we used rock eval and hydrous pyrolysis methods to calculate expulsion factors and petroleum charge for each of the four source rocks in the study area without attempting to identify the correct methods we conclude that calculations based on rock eval pyrolysis overestimate expulsion factors and petroleum charge because low pressure and rapid removal of thermally cracked products by the carrier gas retards cross linking and pyrobitumen formation that is otherwise favored by natural burial maturation expulsion factors and petroleum charge based on hydrous pyrolysis may also be high compared to nature for a similar reason

origin charging and mixing of crude oils in the tahe oilfield tarim basin china abstract forty eight crude oil samples collected from different reservoirs in the tahe oilfield of the tarim basin were investigated based on geochemical characteristics it is concluded that the oil samples originated from multiple marine source rocks deposited in various sedimentary environments and subsequently altered by different levels of thermal maturation these mixtures were de convoluted to three endmember oils em1 em2 and em3 by alternating least squares regression using 38 concentration parameters em1 is the minimum contributor with an average of 13 while em2 and em3 are the main contributors to the mixtures with averages of 52 and 35 respectively em1 oil originated from cambrian lower ordovician source rocks in the early to peak oil window and subsequently experienced two phases of mixing and biodegradation em2 and em3 oils originated from middle upper ordovician source rocks but em2 was generated at lower thermal maturity than em3 the em2 oil underwent two phases of mixing and one stage biodegradation while the em3 oil mixed with previous existing mixtures in the reservoirs the final mixtures that might be affected by secondary processes such as evaporative fractionation are currently produced from the tahe oilfield the general orientation of oil filling was from south to north and east to west based on variations in the relative contributions of ems and the total concentrations of dibenzothiophenes and dibenzofurans in the oils considering the histories of sedimentary tectonic evolution hydrocarbon generation and expulsion and the de convolution results a model of three stages of oil charge and two phases of mixing and biodegradation was established for the tahe oilfield oils

cracking mixing and geochemical correlation of crude oils north slope alaska forty one crude oil samples from the north slope of alaska have variable diamondoid and biomarker concentrations indicating different extents of oil cracking some of the samples are mixtures of high and low maturity components containing high concentrations of both diamondoids and biomarkers compound specific isotope analysis of diamondoids csiad shows that the shublik formation accounts for the higher maturity component in several mixed oil samples whereas biomarkers especially those providing information on the age of the source rock show either a cretaceous hue gamma ray zone grz or triassic shublik source for the lower maturity component oil samples in this study mainly correlate to six source rocks based on their biomarker characteristics and csiad chemometrics of selected source related biomarker and isotope ratios helps to classify the oil samples into different genetic families the source rocks include carbonate and shale organofacies of the triassic shublik formation jurassic kingak shale lower cretaceous pebble shale lower cretaceous hue grz and cenozoic canning formation oil presumed to originate from a seventh source rock interval the carboniferous permian lisburne group was not clearly differentiated from well established shublik oil by any geochemical age related parameter or csiad which suggests that the lisburne is not an effective source rock for any of the studied oil samples four oil samples collected from wells located north of the barrow arch show unique biomarker characteristics but age related biomarker parameters indicate likely triassic source rock organofacies that is not represented by any of the samples from south of the arch the source rock for these four oil samples appears to be a clay rich equivalent of the calcareous shublik formation that occurs to the north of the barrow arch

origin and mixing of crude oils in triassic reservoirs of mahu slope area in junggar basin nw china implication for control on oil distribution in basin having multiple source rocks abstract the origin of crude oils and their varied geochemical features along the western and northern slope of the mahu depression in the junggar basin has been controversial based on the molecular and isotopic geochemistry of hydrocarbons from 46 drill stem test crude oil samples and 36 core samples three oil groups i ii iii and five subgroups i 1 i 2 ii iii 1 and iii 2 have been recognized and oil source correlations have been established the subgroup i 1 oils originated mainly from lower permian fengcheng p 1 f carbonate source rocks subgroup i 2 from p 1 f mudstone source rock and group ii oils from middle permian wuerhe p 2 w mudstone source rock whose potential was underestimated in the past group iii consists of mixed oils i e subgroup iii 1 received contributions from p 1 f carbonates and p 2 w mudstones and subgroup iii 2 is a mixture of oils from p 1 f mudstones and p 2 w generated oils in order to determine the main source rocks the laboratory oil mixing experiments were carried out tricyclic terpane biomarker parameters tts were used to quantify the source contributions whole oil carbon isotope ratios were also used to verify the proportions of different oils in each mixture the results show that subgroup iii 1 oils have diverse mixing ratios in different reservoir subgroup iii 2 oils are mainly from p 1 f mudstones and p 2 w source rock contributes little finally the accumulation process of oil fields along the northern slope of the mahu depression was analyzed and the contributions from different sources were revealed this study provides an effective quantitative method to identify contributions from different lacustrine source rocks to mixed oils in the mahu depression which could be helpful in predicting location and composition of undiscovered oils

a terrain based site conditions map of california with implications for the contiguous united states abstract we present an approach based on geomorphometry to predict material properties and characterize site conditions using the v s 30 parameter time averaged shear wave velocity to a depth of 30 m our framework consists of an automated terrain classification scheme based on taxonomic criteria slope gradient local convexity and surface texture that systematically identifies 16 terrain types from 1 km spatial resolution 30 arcsec shuttle radar topography mission digital elevation models srtmdems using 853 v s 30 values from california we apply a simulation based statistical method to determine the mean v s 30 for each terrain type in california we then compare the v s 30 values with models based on individual proxies such as mapped surface geology and topographic slope and show that our systematic terrain based approach consistently performs better than semiempirical estimates based on individual proxies to further evaluate our model we apply our california based estimates to terrains of the contiguous united states comparisons of our estimates with 325 v s 30 measurements outside of california as well as estimates based on the topographic slope model indicate our method to be statistically robust and more accurate our approach thus provides an objective and robust method for extending estimates of v s 30 for regions where in situ measurements are sparse or not readily available

topographic slope as a proxy for seismic site conditions and amplification we describe a technique to derive first order site condition maps directly from topographic data for calibration we use global 30 arc sec topographic data and v s 30 measurements here v s 30 refers to the average shear velocity down to 30 m aggregated from several studies in the u s as well as in taiwan italy and australia v s 30 values are correlated against topographic slope to develop two sets of parameters for deriving v s 30 one for active tectonic regions where topographic relief is high and one for stable shields where topography is more subdued by taking the gradient of the topography and choosing ranges of slope that maximize the correlation with shallow shear velocity observations we can recover to first order many of the spatially varying features of sitecondition maps developed for california our site condition map for the low relief mississippi embayment also predicts the bulk of the v s 30 observations in that region despite rather low slope ranges we find that maps derived from the slope of the topography is often well correlated with other independently derived regional scale site condition maps but the latter maps vary in quality and continuity and subsequently also in their ability to match observed v s 30 measurements contained therein alternatively the slope based method provides a simple approach to uniform site condition mapping

source apportionment of elevated pah concentrations in sediments near deep marine outfalls in esquimalt and victoria bc canada is coal from an 1891 shipwreck the source abstract previous studies have suggested that coal from the 1891 shipwreck of a collier off victoria bc canada is responsible for elevated parent unsubstituted pah concentrations in sediments near deep marine outfalls from esquimalt and victoria in the strait of juan de fuca to resolve this question we analysed a comprehensive suite of resolved and unresolved complex mixture ucm alkanes tricyclic terpane hopane and sterane biomarkers and parent and alkyl polycyclic aromatic hydrocarbons pahs in samples of coal wastewater and sediments composition patterns principal components analysis pca models and pah and biomarker ratios all indicate that coal from the collier does not make a dominant contribution to any sediment sample mass balance calculations based on the n c 24 content and 24 4 tetracyclic terpane to 26 3r tricyclic terpane ratio in coal provide a particularly good match between predicted and observed alkyl pah concentrations for sediments with high alkyl naphthalenes and phenanthrene anthracenes and low ucm but the predicted coal contribution substantially underestimates the measured parent pahs for all sediment samples methylbenz a anthracene chrysene profiles for sediments with a dominance of parent pahs are very close to coal tar with a marked predominance of methylbenz a anthracenes and the possible 10 methylbenz a anthracene as a major constituent while the methylchrysenes predominate in coal hence coal from the collier could account for most alkyl pahs in the sediments but dredged sediment containing pyrolised coal waste from a former coal gas plant in victoria harbour is a more likely source for the samples with elevated parent pahs pah ratios indicate that these sources are superimposed on combustion pahs introduced by a combination of atmospheric deposition and delivery via stormwater and the outfalls parent pah distributions also suggest that pahs in wastewater that originate from oils and soot in liquid fossil fuel combustion are dispersed and degraded while the larger wood char particles containing pahs more protected from degradation settle closer to the outfalls overall results suggest that pahs have predominant sources in wood combustion coal and possibly coke with a likelihood of much lower bioavailability than would be expected from wastewater dominated by oils and soot from vehicle combustion

turbulent dissipation over the continental slope off vancouver island abstract thirteen profiles of the rate of viscous dissipation of turbulent kinetic energy epsi were made over the continental slope off vancouver island between 12 and 14 may 1980 in conjunction with ctd and moored current meter observations systematic variability was observed in the vertical but not in the horizontal direction above 200 m depth numerous salt stabilized temperature inversions were seen and dissipation rates were significantly larger than below 200 m dissipation rates below 200 m are the lowest ever reported and coincide with a low level of energetics revealed by the current meter moorings comparison with the garrett munk internal wave spectrum indicates an e folding decay time of internal wave energy of 50 days at depths below 200 m

fine scale temperature variability the influence of near inertial waves measurements made with a towed thermistor chain and acoustic doppler current profiler in the seasonal thermocline of the sargasso sea are examined for relationships among small scale temperature activity shear and internal wave variability patches of intense activity measuring 5 10 m high and several kilometers in length are found to persist within a near inertial wave packet the packet was tagged with a drogue and followed for about 16 hours as it was advected along an edge of a cold core ring the patches occur along surfaces of high vertical shear where the richardson number 7 m vertical resolution falls to values less than one within the patches are groups of small scale internal waves and fluid overturns the overturns are 1 3 m high and are associated with wave breaking events away from the wave packet activity levels are less and the active fraction of the water column appears to be linked to variability in the internal wave field it is conjectured that the near inertial wave patches are the same species as persistent mixing patches observed by gregg et al 1986 which were also associated with a near inertial wave

local earthquake wave propagation through mississippi embayment sediments part ii influence of local site velocity structure on qp qs determinations elastic near surface structure and receiver depth effects are seen to control body wave amplitude spectra in the band from 2 to 50 hz for local earthquake observations in the new madrid seismic zone p and s wave spectral peaks are created by resonance in shallow low velocity zones and spectral nulls are created by interference of direct and free surface reflections due to receiver depth these wave propagation effects dominate sp s spectral ratios and mimic anelastic attenuation effects by making it appear that s waves are deficient in higher frequencies relative to sp waves there is no evidence from sp s spectral ratios that unconsolidated sediments of the mississippi embayment are highly attenuating dominance of p and s wave resonance suggests that the unconsolidated sediments amplify rather than attenuate seismic waves at high frequency this has important implications for estimating hazards from strong ground motions in the area in the absence of any identifiable anelastic attenuation effect in the spectral ratio the only allowable q p q s relationship for embayment sediments is that q s 3 q p based on consideration of wave travel times manuscript received 11 march 2003

recognizing and compensating for interference from the sediment s background organic matter and biodegradation during interpretation of biomarker data from seafloor hydrocarbon seeps an example from the marco polo area seeps gulf of mexico usa abstract a suite of seep samples from the vicinity of the marco polo field in the green canyon area of the gulf of mexico provides an exceptional opportunity to study the impact of interference from sediment background organic matter and alteration by biodegradation on thermogenic hydrocarbons from seafloor seeps these seep samples contain a range in both the concentration of seeped hydrocarbons present and level of biodegradation experienced in addition the subsurface oil that sources the seepage was available for comparison the results of the study show that it is essential to have the biomarker data from the sediment s background organic matter when dealing with low concentration seepage these data provide a means to characterize the contribution of background organic matter to the biomarker distributions this in turn allows the identification of thermogenic hydrocarbons when the concentration of seeped oil in seafloor sediments is low in high concentration seepage the hopanes and regular steranes were found to be more susceptible to near surface microbial alteration while tricylic tetracyclic terpanes diasteranes monoaromatic steroids and triaromatic steroids were more resistant if biodegradation is severe enough all biomarker compounds are vulnerable to alteration and very little information is preserved in an effort to reconstruct the altered distributions low temperature pyrolysis of the seeped oils asphaltenes was done to liberate occluded biomarkers compounds although biomarkers were recovered they did not resemble the parent oil characteristics of some of the recovered biomarker distributions suggest alteration by biodegradation this implies the three dimensional structure of the asphaltenes may not offer complete protection from microbial attack these results demonstrate why interpretation of biomarker data from seafloor seeps can be a difficult task care must be taken to recognize contributions from the sediment s background organic matter as well as identify alteration by biodegradation failure to understand these processes can lead to erroneous interpretations being made about the seep s parent oil and source rock

evaluation of methods for estimating linear site response amplifications in the los angeles region we have evaluated two methods of estimating linear site response amplifications and the standard index for classifying sites by comparing the results of each technique to observed ground motions at 33 sites in the los angeles region using velocity and density profiles from 33 boreholes we evaluated the use of the average 30 m shear wave velocity and associated site classifications the quarter wavelength method and the haskell propagator matrix method we correlated the average 30 m shear wave velocity and nehrp site classification at the borehole sites colocated within 290 m of a site with observed ground motion the observed data follow the expected trend of higher ground motion amplifications for lower average shear wave velocities but there is a significant degree of variability also there is a great deal of scatter in the observed amplifications within each national earthquake hazards reduction program nehrp class we used the velocity and density information in the database to calculate the average frequency dependent site response in the frequency ranges 1 3 hz 3 5 hz and 5 7 hz for a one dimensional flat layered structure using the haskell propagator matrix method and the quarter wavelength method there is a general correlation with the ground motion data however once again there is a great degree of scatter although slightly less for the quarter wavelength method we note that both the observed and predicted amplifications can change dramatically over a distance as small as 1 km or less even though all techniques considered give results that follow the expected trend of higher amplifications for softer sediments the predicted site response at any particular site with the current level of information may not be representative of the shaking that will actually occur during an earthquake the disparity between observed and predicted amplifications appears to be a result of oversimplification inherent in the amplificationestimation methods such as the use of average or assumed values for the site conditions in the absence of measured values the smoothing effect of using an average velocity limiting the properties considered to the uppermost 30 m of material and complexities in the wave propagation that are not addressed by these methods

local earthquake wave propagation through mississippi embayment sediments part i body wave phases and local site responses p and s body waves from microearthquakes in the new madrid seismic zone nmsz are investigated at selected sites in an effort to understand wave propagation from future large earthquakes earthquake body waveforms display distinctive features that constrain the nature of p and s wave local site responses and wave propagation within the unconsolidated mississippi embayment sediments modeling of the waveforms demonstrates that a near surface low velocity zone is characteristic of structure within the upper 60 m of the sedimentary column and produces large p and s wave resonance effects that can be used to infer near site conditions site resonance effects change because of velocity heterogeneity between individual receivers but imply that embayment sediments will substantially amplify ground motions at high frequencies site resonance affects p and s wave amplitude spectra and can bias estimates of source and anelastic attenuation parameters travel times of observed body wave phases such as p ppphp the first p wave reverberation within the entire sedimentary column ps sp s and ssphp can be used to estimate the average wave slownesses and poisson s ratio within the embayment sediments an average poisson s ratio of 0 44 is obtained for the central nmsz under station pebm detailed s wave velocities are derived for a nafe drake sediment model using acoustic well logs and the travel time constraints of observed seismic phases v p v s ratios vary from 5 5 near the surface to approximately 2 4 at the base of the sediments use of the well log data in wave calculations also explains much of the nature of p and s wave coda within the waveforms and shows that 1d heterogeneity is a first order influence on seismic wave propagation within the mississippi embayment manuscript received 11 march 2003

unraveling petroleum mixtures from the south viking graben north sea a study based on δ13c of individual hydrocarbons and molecular data abstract mixtures of compositionally different petroleum occur in the norwegian north sea one of the world s major oil producing regions the objective of the present contribution was to appraise the source maturity in reservoir mixing and alteration processes in a set of condensate and oil samples covering the main producing areas in the south viking graben svg furthermore this study focused on unraveling complex mixtures of petroleum and quantifying mixing ratios of hydrocarbons generated from jurassic source rocks the present research was based on a multiparameter approach that comprised the molecular composition of light hydrocarbons and heterocyclic and polycyclic aromatic compounds as well as the 13c of individual hydrocarbons in oils condensates and upper and middle jurassic source rock extracts from the svg according to the relative contribution of oils from type iii kerogen rich source rocks seven populations a g of mixed petroleum were identified by combining source related ratios of heterocyclic and non heterocyclic aromatic hydrocarbons and 13c values of n alkanes pristane pr and phytane ph the heterocyclic and polycyclic aromatic hydrocarbons provided a useful means to discriminate mixed hydrocarbons from source rocks of distinct organic matter type depositional environment and lithology in the svg the 13c enrichments of c10 c14 n alkanes and pr and ph were good indicators of the scale of the terrigenous source contribution and allowed quantitative determination of the proportions of jurassic source contributions enriched in type ii and type iii kerogens in complex petroleum mixtures from the southern part of the svg

statistics of mixing patches observed in the sargasso sea temperature measurements made with a towed thermistor chain in the seasonal thermocline of the sargasso sea have been converted to sections of fine structure activity by normalizing values of meter scale horizontal fluctuations by the local vertical gradient individual patches of high activity are then separated from background and examined for length l height h aspect ratio l h and signal intensity over the range 0 5m h 20m and 30 m l 2 km the aspect ratio tends to be about 100 similar to reports of turbulent patches measured with velocity microstructure profilers numbers of patches decrease with increasing patch height and length and large patches tend to have higher activity levels

chemometrics reveals oil sources in the fangzheng fault depression ne china one hundred and twenty five rock and oil samples collected from the fangzheng fault depression were analyzed by gc ms principal component analysis pca and multidimensional scaling mds based on nine biomarker ratios were used for oil source rock correlation in this region the oils are characterized by a predominance of low to middle molecular weight normal alkanes n c12 n c20 or n c12 n c25 moderate to high pr ph ratios 1 44 5 3 relatively low c27 c29 regular steranes c35 c34 hopanes and gammacerane c31r ratios all of which suggest relatively oxic conditions under fresh water depositional conditions with significant terrigenous organic matter input pca and mds results show that the investigated oils were derived mainly from the xinancun wuyun formation and also illustrate the maturation and depositional conditions of the rocks and oils through an mds plot we show that mds is a reliable multi parameter oil source rock correlation method

temperature fine structure patches near an upper ocean density front measurements with a towed thermistor chain have been used to map temperature fine structure variability along vertical sections through a frontal shear zone in the seasonal thermocline of the sargasso sea fine structure levels with 1 3 m horizontal wavelengths were normalized with local values of the vertical fine scale stratification to give values of normalized fine structure variance patches of increased levels of normalized variance were found to occur throughout the thermocline but were most extensive in the frontal zone where richardson numbers 7 m by 450 m averages were lowest 1 the largest patches were 5 10 m in vertical extent and horizontally coherent over distances of several kilometers away from the frontal zone patches tended to be smaller and were fewer in number simultaneous microstructure measurements along two depths were spatially correlated with the fine structure patches implying that many patches were areas of increased mixing intensity no consistent relationship was found between the patches and features in the vertical stratification such as inversion zones or sheets and layers internal wave overturns on the scale of a few meters high by 10 m in the horizontal were found within the larger patches suggesting that wave breaking perhaps enhanced by the background shear may be an ingredient in the formation or maintenance of some patches

turbulent dissipation and shear in thermohaline intrusions laterally coherent patches of turbulence were discovered on the upper and lower boundaries of thermohaline intrusions the ratio jb is used to compare the relative importance of turbulence produced by reynolds stress and that produced by the buoyancy flux of double diffusion velocity profiles show near inertial motions through the intrusions

using biomarkers to improve heavy oil reservoir management an example from the cymric field kern county california for biodegraded oil accumulations field development can be optimized by using geochemical indicators of variations in the extent of bacterial alteration biodegradation typically reduces oil producibility by increasing oil viscosity in the cymric field kern county california sidewall core extracts reveal that the extent of oil biodegradation changes substantially over extremely short vertical distances in a shallow low permeability reservoir zones of more degraded oil can extend laterally for more than a mile the relationships between oil viscosity and biomarker biodegradation parameters in this field were calibrated from analyses of produced oils and these relationships were used to convert sidewall core biomarker analyses into quantitative predictions of lateral and vertical changes in oil viscosity and gravity compositional variations were also used to allocate production to discrete zones viscosity prediction and production allocation can be used to optimize 1 the placement of new wells 2 the placement of completion intervals 3 the thickness of steam injection intervals and 4 the spacing between injection intervals in the same well

resolving shallow shear wave velocity structure beneath station cbn by waveform modeling of the mw 5 8 mineral virginia earthquake sequence abstract the 23 august 2011 m w 5 8 mineral virginia earthquake was the largest earthquake in the central and eastern united states in the past 100 years and it was well recorded by strong motion and broadband seismometers thus providing abundant ground motion data for earthquake ground motion studies the largest recorded ground motion among advanced national seismic system stations was at station cbn but the site effects at station cbn need to be understood because the strong motions recorded there do not represent bedrock site conditions on the radial component of these recordings the initial p wave is very weak and is followed by a strong signal 0 3 s later which is interpreted to be the s wave converted from the p wave ps at the interface between the sediments and bedrock we first estimate the subsurface shear wave velocity by modeling the ratio of the radial to vertical components of the initial p waves and then resolve the velocity structure and thickness of the unconsolidated sediments by modeling the ps wave the subsurface shear wave velocity is found to be approximately 300 m s consistent with field survey results the shear wave velocity at the bottom of the sediments is constrained to be in the range of 320 780 m s from which the thickness of the layer is estimated to be 100 230 m the estimates of shear wave velocity structure and thickness of the sediments are further improved by modeling the oscillatory waveforms between the p and s waves this study suggests that site characterization for the estimation of ground motion amplification at a site can be achieved inexpensively and noninvasively by modeling local p waveforms recorded at the site

a laboratory study of stratified accelerating shear flow over a rough boundary experiments are made in which a stratified shear flow accelerating from rest and containing a level where the direction of flow reverses is generated over a rough floor the roughness elements consist of parallel square bars set at regular intervals normal to the direction of flow radiating internal gravity waves are generated in the early stages of flow whilst flow separation behind the bars produces turbulent mixing regions which eventually amalgamate and entirely cover the floor this turbulent layer spreads vertically less rapidly than the internal waves observed features of the waves are compared with those predicted by a model in which the floor is assumed to be sinusoidal and fair agreement is found for the amplitude phase and vertical wavenumber of the waves even when the latter becomes large the rate of spread of the turbulent layer depends on the separation of the bars some interaction between the turbulence and the internal waves occurs near the edge of the turbulent layer wave breaking is prevalent and the vertical scale of the waves is affected by turbulent eddies the radiating internal waves are suppressed by replacing the bars by an array of square cubes but there is continued evidence of features resembling internal waves near the boundary of the turbulent region structures are observed which bear some similarities to those found at the foot of the near surface mixing layer in a lake

reflection and transmission imaging of the upper crust using local earthquake seismograms we utilize the characteristic features of primary p and sh wave coda and sp waveforms from local microearthquake data and perform prestacking 1d migration in an attempt to image prominent reflectors in the upper crust of the new madrid seismic zone nmsz this methodology applies to data from broadband stations parm and penm of the cooperative new madrid seismic network cnmsn nearby exploration well log acoustic data of the wilson 2 14 and dow chemical wilson number 1 wells are used to constrain the upper 4 km of p wave velocity model despite polarity differences among p sh and sp waveforms this technique demonstrates that consistent reflectors in the deep sedimentary section can be imaged commonly among the three wave types there are excellent correlations associated with the base of the upper cretaceous holocene mississippi embayment supergroup and the base of knox group which were also reported in a study of nearby seismic reflection profiles by hamilton and zoback 1982 the bonne terre formation seems to be a prominent seismic stratigraphic marker associated with an interface displayed in the profiling we find that earthquake event s p times must be 3 sec or more to resolve reflectors at about 4 km depth possible basement at about 4 0 to 4 5 km appears on the reflected p wave image for parm and sh wave image for penm we conclude that the velocity structure of the upper 4 km crust beneath parm can be represented by a constant velocity of graphic 1 and graphic 2 for the unconsolidated sediments and graphic 3 and graphic 4 for the paleozoic sedimentary rocks a constant velocity of graphic 5 and graphic 6 for the unconsolidated sediments and graphic 7 and graphic 8 for the paleozoic sedimentary rocks can represent structure beneath penm 1 embed inline graphic 1 gif 2 embed inline graphic 2 gif 3 embed inline graphic 3 gif 4 embed inline graphic 4 gif 5 embed inline graphic 5 gif 6 embed inline graphic 6 gif 7 embed inline graphic 7 gif 8 embed inline graphic 8 gif

circum arctic petroleum systems identified using decision tree chemometrics source and age related biomarker and isotopic data were measured for more than 1000 crude oil samples from wells and seeps collected above approximately 55n latitude a unique multitiered chemometric multivariate statistical decision tree was created that allowed automated classification of 31 genetically distinct circum arctic oil families based on a training set of 622 oil samples the method which we call decision tree chemometrics uses principal components analysis and multiple tiers of k nearest neighbor and simca soft independent modeling of class analogy models to classify and assign confidence limits for newly acquired oil samples and source rock extracts geochemical data for each oil sample were also used to infer the age lithology organic matter input depositional environment and identity of its source rock these results demonstrate the value of large petroleum databases where all samples were analyzed using the same procedures and instrumentation

horizontal variability of microstructure in the vicinity of a sargasso sea front abstract temperature microstructure variability has been determined from measurements of electrical conductivity 1 5 cm wavelength resolution along two depths in the seasonal thermocline of the sargasso sea in july 1981 the microstructure sensors were attached to a thermistor chain which was towed in and away from a frontal shear zone in the region of the subtropical convergence zone averaged over the 170 km long tow the estimated dissipation rate of temperature variance was 10 8 c2 s 1 but values ranged from 10 11 noise level to 10 5 in the most energetic events cox numbers c were calculated by making use of a local temperature gradient calculated over a fixed 1 m vertical spacing on the chain mean values of c were 10 but values as high as 105 were observed the signals wear highly intermittent varying by as much as five orders of magnitude over scales of the order of 10 m probability distributions of and c appeared to resemble the lognormal form only in cases where the data

oil source correlation in the slope of the qikou depression in the bohai bay basin with discriminant analysis abstract the commonly used tools for oil source correlation such as mass chromatograms of biomarkers and bivariate cross plots of geochemical parameters cannot deal with multiple geochemical parameters and plenty of samples simultaneously leading to uncertainties in the results and even failures sometimes in this paper the discriminant analysis da is selected from supervised machine learning algorithms as it is superior to the commonly used tools as well as other multivariate statistical methods with the accumulation of geochemical data of source rocks and oils in the slope of the qikou depression the main source rocks in the third es3 and first members es1 of the paleogene shahejie formation were deposited in similar depositional environments the source rocks cannot be distinguished with the commonly used tools we firstly extended geochemical parameters and then used stepwise da to select informative parameters and to develop a discriminant model for oil source correlation the 22 selected parameters are supported by geochemical characteristics of the source rocks in the study area the da of these parameters for oil source correlation achieved a high correct rate of original validation 96 8 and leave one out cross validation 89 4 indicating a sufficient discriminatory power the oil source correlation results with high posterior probabilities showing strong similarity between the sources and oils coincide with geological conditions and illustrate that there is still much exploration potential in the study area especially for the es3 petroleum system all these illustrate that da is one of the most useful tools for oil source correlation with the accumulation of geochemical data of source rocks and oils

the role of calcareous and shaly source rocks in the composition of petroleum expelled from the triassic shublik formation alaska north slope abstract for nearly thirty years the triassic marine carbonate shublik formation has been suggested and confirmed as a key source rock for hydrocarbons in the north slope of alaska the formation accounts for roughly one third of the oil in the supergiant prudhoe bay field and for nearly all of the oil in the second largest kuparuk river field recent studies of oil types in the vicinity of the northstar field suggested presence of shaly organofacies of the shublik formation based on the likely triassic age and marine shale biomarker signatures of some analyzed oil samples the current work fills the gap between biomarker analysis of predicted calcareous and shaly oil types and source rock geochemistry biomarker based oil source rock correlation confirms the presence of two genetically distinct organofacies and related oil families both groups were deposited under a similar redox condition anoxic to suboxic with dominantly marine algal input but in either 1 a clay rich or 2 a clay poor depositional setting chemometric evaluation of multivariate biomarker data reveals mixtures with variable degrees of mixing between end members analysis of diamondoids confirms mixed oil types and establishes diamondoid signatures of source rock end members this allows for correlation of biomarker poor overmature shublik source rock samples to oils and extends these interpretations over large areas of the north slope

alteration and multi stage accumulation of oil and gas in the ordovician of the tabei uplift tarim basin nw china implications for genetic origin of the diverse hydrocarbons abstract the ordovician is the most important exploration target in the tabei uplift of the tarim basin which contains a range of petroleum types including solid bitumen heavy oil light oil condensate wet gas and dry gas the density of the black oils ranges from 0 81 g cm 3 to 1 01 g cm 3 20 c and gas oil ratio gor ranges from 4 m 3 m 3 to 9300 m 3 m 3 oil source correlations established that most of the oils were derived from the mid upper ordovician marine shale and carbonate and that the difference in oil properties is mainly attributed to hydrocarbon alteration and multi stage accumulation in the tabei uplift there were three main periods of hydrocarbon accumulation in the late caledonian stage ca 450 430 ma late hercynian stage ca 293 255 ma and the late himalayan stage ca 12 2 ma the oil charging events mainly occurred in the late caledonian and late hercynian stage while gas charging occurred in the late hercynian stage during the late caledonian stage petroleum charged the reservoirs lying east of the uplift however due to a crustal uplifting episode in the early hercynian ca 386 372 ma most of the hydrocarbons were transformed by processes such as biodegradation resulting in residual solid bitumen in the fractures of the reservoirs during the late hercynian stage a major episode of oil charging into ordovician reservoirs took place subsequent crustal uplift and severe alteration by biodegradation in the west central basin resulted in heavy oil formation since the late himalayan stage when rapid subsidence of the crust occurred the oil residing in reservoirs was exposed to high temperature cracking conditions resulting in the production of gas and charged from the southeast further altering the pre existing oils in the eastern reservoirs a suite of representative samples of various crude oils including condensates lights oils and heavy oils have been collected for detailed analysis to investigate the mechanism of formation based on the research it was concluded that the diversity of hydrocarbon physical and chemical properties in the tabei uplift was mainly attributable to the processes of biodegradation and gas washing the understanding of the processes is very helpful to predict the spatial distribution of hydrocarbon in the tabei uplift and provides a reference case study for other areas

charging of elk hills reservoirs as determined by oil geochemistry crude oils from miocene and pliocene reservoirs from the elk hills field in california s san joaquin basin were analyzed for stable carbon isotopes and biomarkers cluster analysis of geochemical variables defines five principal oil families all derived from different organic rich facies of the miocene monterey formation carbon isotope analysis indicates no contribution from the basin s other major source rock the eocene kreyenhagen formation oil families show a strong correspondence to stratigraphic intervals oils from pre monterey reservoirs were probably generated from the lowermost organic rich facies of the monterey and are the most thermally mature upper miocene stevens zone turbidite reservoirs contain oils of various thermal maturity stages but mature light ends are abundant and are likely generated from the floors of the adjacent subbasins located north and south of elk hills the relatively minor presence of low thermal maturity biomarkers that are typically characteristic of monterey oils may indicate that stevens traps did not form until after the source intervals were at a higher level of thermal maturity all oils in stevens porcelanite reservoirs contain a higher concentration of low maturity biomarkers which may indicate derivation from more localized areas on the flanks of the elk hills anticlines the shallow pliocene oils have suffered biodegradation to different degrees and the lowest api gravities occur on the flanks of the anticline the carbon isotopic composition of these oils suggests yet another monterey source facies that charged the pliocene reservoirs and is not simply the result of vertical leakage from the older miocene reservoirs john e zumberge has been vice president and cofounder of geomark research in houston since 1991 he was manager of geochemical and geological research for cities service occidental general manager for ruska laboratories and director of geochemical services for core laboratories he has global experience in petroleum geochemistry focusing on crude oil biomarkers he obtained a b s degree in chemistry from the university of michigan and a ph d in organic geochemistry from the university of arizona judy a russell is a senior geological advisor for occidental and works on worldwide exploration and production with an emphasis on the integration of geochemistry she has extensive experience in many of occidental s projects in latin america far east the united states and the middle east she has a b s degree from phillips university and an m s degree from the new mexico institute of mining and technology stephen anthony reid is a senior geological advisor for occidental and works on international exploration with an emphasis on deep water projects he has extensive experience in california s san joaquin basin including the elk hills field where he conducted studies on stevens turbidite and monterey porcelanite reservoirs he has b s and m s degrees from california state university northridge

efficient calculation of differential seismograms for lithospheric receiver functions summary a new technique for computing differential seismograms for crustal and upper mantle response to a teleseismic wave receiver functions is developed using the matrix formalism of kennett the work was motivated by the difficulty of modelling teleseismic sv waves and has also proven useful for modelling teleseismic p waves this efficient method for calculating differential seismograms is based on three separate methods for computing synthetic seismograms two of the synthetic seismogram methods save intermediate results then the remaining synthetic seismogram algorithm uses the stored results in an efficient calculation of a new synthetic seismogram for a perturbed velocity model these developments have led to a faster for a 30 layer model a 90 per cent reduction in computation time and more accurate linearized inversion scheme for the determination of velocity models using teleseismic waves

source rock characterization and oil to source rock correlation of a cambrian ordovician fold and thrust belt petroleum system western newfoundland abstract in this study we use biomarker and isotope data to address the complexities of petroleum system analysis in fold thrust systems specifically related to hydrocarbon generation and migration such as variable thermal maturities of source rocks complex migration pathways and mixing source rocks extracts and oil samples are taken from paleozoic rocks along the appalachian structural front in western newfoundland oil seeps along this fold and thrust belt have motivated episodic exploration efforts over the last 150 years however economic development has been unsuccessful to date in part because of the complex nature of oil to source relationships pyrolysis analyses identify promising source intervals in lower ordovician floian formations with an excellent source potential containing type i ii organic matter toc up to 9 35 hi up to 840 a second good source interval identified within the late cambrian furongian continental slope and rise sediments contains type ii iii organic matter toc up to 2 34 hi 380 source rock samples from outcrops are marginally mature to mature with tmax values between 436 and 447 geochemical analyses of source rock extract imply a clastic shale dominated source rock with a minor contribution from carbonate source rocks chemometric analyses yield 3 extract groups groups 1 and 2 contain lower ordovician samples with organic matter derived from oxidized micro plankton with varying amounts of gleocapsomorpha prisca extract group 3 originates from cambrian samples and shows evidence of a bacterial derived organic matter similar genetic relationships among 10 oil samples from natural oil seeps and abandoned well sites are indicated by high resolution biomarker analyses seven oil samples originated from ordovician source rocks that produced high api oils with low bisnorhopane hopane tricyclic hopane ratios and high sterane concentrations supporting interpretation of a source containing algal derived organic matter three oils originated from cambrian shales these high api oils show high bisnorhopane hopane and tricyclic hopane ratios low sterane concentrations and low carbon isotope values all indicative of organic matter derived from bacteria generated over a wide range of maturities 0 98 1 26 ro thermal maturity sensitive biomarkers and naphthalene ratios show that source rocks generated oils with a wide range of maturities related to their dipping character in the imbricated thrust stack the cambrian source generated oils that locally experienced secondary cracking during acadian inversion whereas the ordovician source generated oil with low maturities after the acadian inversion oil operaters exploring fold and thrust belt petroleum systems may expect extreme changes of oil properties for example api gravity in spacially restricted areas

isopycnal dispersion in natre abstract finescale velocity and density fluctuations consist of both internal waves and vorticity containing perturbations vortical modes a recent decomposition of observations obtained as part of the north atlantic tracer release experiment natre permits one to investigate isopycnal stirring associated with vortical modes this stirring is treated here as a relative dispersion problem in the context of 2d turbulence isopycnal diffusivities attain values on the order of 1 m2 s 1 after an initial transient of 5 10 days after 2 weeks a patch of tracer with initial radius of 25 m is predicted to have evolved into a convoluted web having an rms radius of 2 4 km these estimates agree with observations of the evolution of an anthropogenic tracer in natre

observations of shear and vertical stability from a neutrally buoyant float measurements of 1 to 5 m shear and strain from a neutrally buoyant float are used to examine the statistics and causes of shear instability in a 9 day record unstable conditions defined as vz n 2 where vz vz are due to higher than average shear rather than lower than average buoyancy frequency and there are no instances of unstable buoyancy frequency or overturns on the 0 5 m spacing of the thermistors shear is dominated by upward propagating near inertial motions unstable events were more frequent when a near inertial wave packet occupied the water parcel tracked by the float groups of unstable events occur roughly every 5 7 hours at scales 2 5 m and much less often at larger scales events typically last 10 min one buoyancy period or longer these time scales appear to be controlled by vertical advection of 1 m fine structure past the float sensors so do not represent the intrinsic time scales of instability turbulent and mixing quantities are estimated from these fine scale measurements giving a dissipation rate of e 2 3 16 10 10 w kg and an eddy diffusivity of k 3 10 6 m2 s in agreement with direct microstructure estimates therefore the float adequately resolves those quantities needed to estimate turbulent dissipation and could be used to monitor turbulent mixing in the ocean

elevated mixing at a front 1 the mesoscale submesoscale and microscale structure of a front in the california current was observed using a towed vehicle outfitted with microconductivity sensors thirteen 60 km cross front sections from 0 to 350 m in depth were covered in 3 5 days objectively mapped data are fit via the omega equation to obtain vertical velocity a composite cross front section shows elevated mixing on the dense side within 10 20 km of the front water downwells and gradients are elevated there i e rossby number ro horizontal strain spice gradients and microscale thermal dissipation thermal eddy diffusivity kt reaches 10 3 m2 s 1 and increases 3 10 from the anticyclonic to the cyclonic side with a depth mean of 10 4 m2 s 1 the spatial structure of kt ro and are similar on the dense side suggesting an energy cascade from the mesoscale via the submesoscale to the microscale however it is unclear whether frontogenesis internal wave blocking by elevated vorticity or internal wave trapping by large produces the elevated mixing the mean turbulent heat flux opposes the mean restratifying mesoscale heat flux of 10 w m 2 and may allow the front to persist turbulent nitrate fluxes are 0 1 0 3 mmol m 2 s 1 chlorophyll fluorescence and beam transmission reveal a 6 km wide 100 km long alongfront streamer which is a deep biomass maximum time scales for mixing and nutrient fluxes are 0 3 3 days which are similar to phytoplankton growth rates and the time scale for frontal evolution

origin and mechanism of the formation of the low oil saturation moxizhuang field junggar basin china implication for petroleum exploration in basins having complex histories the moxizhuang field is a small oil field in the central junggar basin containing several low saturation low resistivity oil reservoirs which display a complex correlation between oil saturation and porosity and permeability that is atypical of both the filled and drained reservoirs biomarker associations of crude oil and grains containing oil inclusions gois of both the present day water bearing zones water zones and the oil and water bearing zones low oil saturation pay zones were analyzed to investigate the mechanisms for the formation of the low saturation low resistivity oil accumulations the biomarker assemblage and hierarchical cluster analysis indicate that oil in the moxizhuang field was mostly generated from permian source rock deposited in brackish to hypersaline anoxic environments the pay zones and several water zones display goi values as much as 38 greater than the generally accepted threshold goi value for an oil column 5 these goi values are similar to those for high saturation oil reservoirs in the bohai bay basin and oil zone samples from australian basins suggesting that both pay zones and water zones were high saturation oil reservoirs in the geologic past geologic history analysis shows that the moxizhuang field was located on the north wing of a paleoanticline during oil charge in the late cretaceous to paleogene this anticline has gradually evolved into a south dipping monocline since the neogene causing northward remigration of accumulated oil differential lateral leakage of accumulated oil in different sandstone layers during the remigration phase led to the formation of the water zones with high goi values completely drained reservoirs and the low saturation low resistivity pay zones partially preserved reservoirs and caused the complex correlation between oil saturation and porosity and permeability compared with other postaccumulation physicochemical alteration processes lateral leakage has rarely been recognized recognizing differential lateral leakage of accumulated petroleum with the existence of high quality unfaulted cap rocks has important implication for petroleum exploration in sedimentary basins having complex evolution histories

alkane and pah provenance and potential bioavailability in coastal marine sediments subject to a gradient of anthropogenic sources in british columbia canada abstract marine coastal areas of british columbia canada are subject to a gradient of increasing anthropogenic sources from pristine areas in the north to the more urbanised areas of the south along the gradient the relative contributions of polycyclic aromatic hydrocarbons pahs from multiple natural and anthropogenic sources are not well understood but concerns linger about bioavailability and consequent risks to marine biota composition patterns and principal components analysis pca models for surface sediment and core samples collected along this transect indicate that samples from the urbanised vancouver area have the highest proportions of tricyclic terpane hopane and sterane biomarkers ucm unresolved complex mixture the alkyl fluoranthene pyrene and benz a anthracene chrysene series and most parent pahs those from hecate and queen charlotte straits and other locations in the strait of georgia have on the other hand higher proportions of the resolved alkanes and petrogenic alkyl naphthalene fluorene dibenzothiophene and phenanthrene anthracene series pah ratios clearly indicate a predominance of combustion sources for the four ring and higher parent pahs for all the sediments most samples have values close to the biomass solid fuel and liquid fuel combustion borderline for ratios of the major pahs but liquid fuel combustion input dominates closer to urbanised locations ratios also suggest similar pyrogenic and petrogenic inputs between central hecate strait and reference sediments from hecate strait through to queen charlotte strait which indicates that biomass combustion and immature coal formations are the major putative respective sources for the reference areas alkyl pah ratios for the c3 and c4 naphthalenes c2 and c3 phenanthrenes and 3 and 2 methylchrysene reflecting terrigenous vascular plant sources and petroleum maturity exhibit marked differences between comox bituminous coal and alberta sweet mixed blend asmb oil and reveal that the petrogenic input in all of the sediments is non biodegraded ratios of these alkyl pahs with multiple substituents indicate that the sediment samples in the northern strait of georgia closest to the comox coal field receive relatively constant input of eroded coal while those in the southern strait of georgia and vancouver harbour show a composition closest to asmb oil pahs associated with liquid fossil fuel combustion and petroleum discharges adjacent to urbanised areas are expected to be fully bioavailable to marine food webs while the char from biomass combustion and coal from immature deposits in more remote areas would have limited bioavailability this implies that biota in remote areas of hecate strait queen charlotte sound are likely not adapted to the presence of oil and thus would be more sensitive to exposure to spilled oil than those in the more impacted environments in southern british columbia

sediment structure at grf from polarization analysis of p waves of nuclear explosions near vertical incidence angles and quasi elliptical particle motions characterize broadband p waves from nuclear explosions recorded at the three 3 component stations of the grafenberg array grf in southern germany which is situated on the jurassic sediments of the franconian jura comparison with data from the broadband stations khc ka perske hory czech republic and ksp ksiaz poland located on gneiss in the bohemian massif and precambrian sediments respectively show that the observed effect is caused by local receiver conditions polarization analysis shows that p to sv wave conversions at the basement sediment boundary and multiples in the sedimentary layers are mainly responsible for these observations at the grf array borehole and refraction data confirm low p wave velocities in the sediments under the grf stations by modeling the broadband particle motions of the p waves of nuclear explosions average models for the sedimentary layers below the grf stations are derived the main modifications to the model of aichele 1976 are one grf c1 and two low velocity layers grf b1 and grf a1 between the out cropping limestone and the basement the first low velocity layer has an s wave velocity of about 1 0 km sec and a thickness of about 200 m below the three 3 component stations and a p wave velocity about 2 8 km sec which is not well constrained the second low velocity layer underlying the first low velocity layer at the stations grf b1 and grf a1 has a lower p wave velocity of about 2 4 km sec but a higher s wave velocity of about 1 6 km sec together with the surficial limestone layer about 200 m thick the total thickness of the sediment column increases from about 400 m below grf c1 in the south to about 750 m below grf b1 and to about 1150 m below grf a1 in the north slow sediment layers near the surface are important for the polarization of teleseismic p waves in turn polarization analysis of broadband recordings can be used to analyze the structure of shallow sediment layers

sequence stratigraphy of the kingak shale jurassic lower cretaceous national petroleum reserve in alaska beaufortian strata jurassic lower cretaceous in the national petroleum reserve in alaska npra are a focus of exploration since the 1994 discovery of the nearby alpine oil field 400 mmbo these strata include the kingak shale a succession of depositional sequences influenced by rift opening of the arctic ocean basin interpretation of sequence stratigraphy and depositional facies from a regional two dimensional seismic grid and well data allows the definition of four sequence sets that each displays unique stratal geometries and thickness trends across npra a lower to middle jurassic sequence set includes numerous transgressive regressive sequences that collectively built a clastic shelf in north central npra along the south facing lobate shelf margin condensed shales in transgressive systems tracts downlap and coalesce into a basinal condensed section that is likely an important hydrocarbon source rock an oxfordian kimmeridgian sequence set deposited during pulses of uplift on the barrow arch includes multiple transgressive regressive sequences that locally contain well winnowed shoreface sandstones at the base of transgressive systems tracts these shoreface sandstones and overlying shales deposited during maximum flooding form stratigraphic traps that are the main objective of exploration in the alpine play in npra a valanginian sequence set includes at least two transgressive regressive sequences that display relatively distal characteristics suggesting high relative sea level an important exception is the presence of a basal transgressive systems tract that locally contains shoreface sandstones of reservoir quality a hauterivian sequence set includes two transgressive regressive sequences that constitute a shelf margin wedge developed as the result of tectonic uplift along the barrow arch during rift opening of the arctic ocean basin this sequence set displays stratal geometries suggesting incision and synsedimentary collapse of the shelf margin

kuparuk oil field alaska a mixture of kekiktuk gas condensate and shublik oil kuparuk river is a giant oil field located on the colville high west of prudhoe bay field on the north slope of alaska the kuparuk oils have values greater than 0 5 for the aromaticity b parameter toluene n c7 and less than 1 for the paraffinicity f parameter n c7 mch using two parameters in isolation one would interpret kuparuk as the residue from repeated episodes of phase segregation and gas cap leakage this process termed evaporative fractionation is experimentally proven to concentrate naphthenic and aromatic hydrocarbon with low fugacity in the parent oil phase while enriching the daughter gas condensate phase in alkanes reassessment of the geochemistry of the kuparuk field within the context of a regional evaluation of north slope petroleum systems suggests a very simple charge and filling model where the kuparuk accumulation remained a single phase throughout its history oil and solution gas derived mainly from the shublik formation together with gas and very light naphthenic aromatic condensate derived from kekiktuk conglomerate coals shared a common migration path into kuparuk field this study illustrates that the b f plot must be used with caution because factors other than evaporative fractionation such as source input can influence these ratios based on data from southeast asia alberta and north slope basins this study also suggests that the sohio 1 mukluk well did not successfully result from the presence of kuparuk thief sands thus petroleum migration continued to the kuparuk field

identification of genetically distinct petroleum tribes in the middle magdalena valley colombia six distinct oil tribes were established using multivariate statistical analysis of source related biomarker and isotopic ratios for 73 crude oil samples from the middle magdalena valley mmv colombia these six tribes show a systematic distribution by both basin location and reservoir rock age and may originate from different source rocks or different organofacies of the same source rock biomarker and isotopic data further differentiate the tribes with respect to source rock depositional environment lithology organic matter type and thermal maturity the thermal maturity and reservoir interval for the northernmost tribe 5 suggest a middle cretaceous tablazo formation source rock in contrast tribes 1 through 4 are likely derived from the primary regional source rock the upper cretaceous la luna formation however we observe regional differences in bulk properties thermal maturity terrigenous input and oxicity between the four la luna derived oil tribes in addition tribe 3 appears to result from end member mixing between tribes 2 and 4 finally the southernmost tribe 6 is the only oil with terrigenous character diamondoid analysis shows the presence of significant secondary cracking in the tribe 6 oil with low levels of cracking present in oil samples from tribes 1 and 2 in the central mmv this suggests a more deeply buried nonmarine source along the western flank of the andean eastern cordillera the integration of chemometric biomarker and diamondoid analyses have improved our understanding of the mmv petroleum system and advocate for the presence of three or more source rock intervals within the basin

shear wave velocity of the sedimentary basin in the upper mississippi embayment using s to p converted waves from mid october 1989 to august 1992 40 three component panda portable array for numerical data acquisition stations were deployed in the central new madrid seismic zone three component digital seismograms recorded by the panda stations in the region are characterized by 1 the very weak direct s arrivals on the vertical component which can be identified unambiguously from the two horizontal components and 2 at least two prominent secondary arrivals between the direct p and s arrivals one sp dominant on the vertical component and another ps with smaller amplitude on the two horizontal components travel time differences between the sp and s and between the p and ps are the same for different earthquakes recorded at the same station but are different at different stations even for the same event polarization analyses of three component seismograms and travel time measurements confirm the interpretation that these two secondary arrivals are the p to s ps and s to p sp converted waves that occur at the bottom of the sedimentary basin beneath each station since abundant well log data are available in the upper mississippi embayment the thickness of the sediments beneath each seismic station can be estimated travel time differences between the direct and the converted waves can be used to calculate average shear wave velocity for the sediments beneath each station the estimated shear wave velocities of the sediments beneath panda stations vary from 0 45 to 0 67 km sec the higher shear wave velocity associated with thicker sediments can be interpreted as a consequence of increasing compaction of unconsolidated sediments due to increasing overburden

shear wave velocity structure of the shallow sediments in the bohai sea from an ocean bottom seismometer survey abstractto investigate the seismic velocity structure of the shallow sediments in the bohai sea of china we conducted a shear wave velocity inversion of the surface wave dispersion data from a survey of 12 ocean bottom seismometers obss and 377 shots of a 9000 in3 air gun with obs station spacing of approximately 5 km and air gun shot spacing of approximately 190 m high quality scholte wave data were recorded by the obss within 0 4 5 km offset we retrieved the scholte wave phase velocity dispersion for the fundamental mode and first overtone in the frequency band of 0 9 3 0 hz with the phase shift method and inverted for the shear wave velocity structure of the shallow sediments with a damped iterative least squares algorithm pseudo 2d shear wave velocity profiles with a depth of approximately 400 m revealed coherent features of relatively weak lateral velocity variation we also estimated the uncertainty in shear wave velocity structure based on the pseudo 2d profiles from six trial inversions wi

de convoluting mixed crude oil in prudhoe bay field north slope alaska abstract seventy four crude oil samples from the barrow arch on the north slope of alaska were studied to assess the relative volumetric contributions from different source rocks to the giant prudhoe bay field we applied alternating least squares to concentration data als c for 46 biomarkers in the range c19 c35 to de convolute mixtures of oil generated from carbonate rich triassic shublik formation and clay rich jurassic kingak shale and cretaceous hue shale gamma ray zone hue grz source rocks als c results for 23 oil samples from the prolific ivishak formation reservoir of the prudhoe bay field indicate approximately equal contributions from shublik formation and hue grz source rocks 37 each less from the kingak shale 26 and little or no contribution from other source rocks these results differ from published interpretations that most oil in the prudhoe bay field originated from the shublik formation source rock with few exceptions the relative contribution of oil from the shublik formation decreases while that from the hue grz increases in reservoirs along the barrow arch from point barrow in the northwest to point thomson in the southeast 250 miles or 400 km the shublik contribution also decreases to a lesser degree between fault blocks within the ivishak pool from west to east across the prudhoe bay field als c provides a robust means to calculate the relative amounts of two or more oil types in a mixture furthermore als c does not require that pure end member oils be identified prior to analysis or that laboratory mixtures of these oils be prepared to evaluate mixing als c of biomarkers reliably de convolutes mixtures because the concentrations of compounds in mixtures vary as linear functions of the amount of each oil type als of biomarker ratios als r cannot be used to de convolute mixtures because compound ratios vary as nonlinear functions of the amount of each oil type

shallow structure of the tangshan fault zone unveiled by dense seismic array and horizontal to vertical spectral ratio method abstract the tangshan fault zone has been considered to be a potential seismogenic fault from the devastating 1976 ms 7 8 tangshan earthquake based on the dense seismic array with interstation distance of 1 km and length of 40 km hvsr horizontal to vertical spectral ratio curves at 37 stations are obtained with the micro tremor seismic waveforms and the two dimensional quaternary sedimentary structures cross the tangshan fault zone are imaged by frequency to depth conversion results suggest that two significant seismic impedance interfaces at 100 m and 300 800 m depth are clearly revealed respectively the interface at 100 m depth can be attributed to the strong contrasts between the unconsolidated sand clay and semi consolidated silt which suggests very small variations and is well consistent with the seismic reflection interface from shallow seismic reflection exploration while the deeper interface at 300 800 m depth can be attributed to the quaternary sedimentary basement which increases from 300 to 800 m from the west to the east and is also consistent with the results in previous studies rapid variations 200 m of the quaternary sedimentary basement depth just beneath the fault zone well agrees with spatial characteristics of the fault revealed by deep seismic reflection profiling our work suggests that the tangshan fault zone has been significantly ruptured and modified by strong earthquake activities since quaternary this study also suggests that the hvsr method with dense seismic array is an efficient effective non invasive and low cost method for investigating active faults in shallow sediments it is useful for probing the active faults buried by thick sediments in the densely populated urban settings where seismic investigation with explosive sources are too hazardous to carry out

directional topographic site response at tarzana observed in aftershocks of the 1994 northridge california earthquake implications for mainshock motions abstract the northridge earthquake caused 1 78 g acceleration in the east west direction at a site in tarzana california located about 6 km south of the mainshock epicenter the accelerograph was located atop a hill about 15 m high 500 m long and 130 m wide striking about n78 e during the aftershock sequence a temporary array of 21 three component geophones was deployed in six radial lines centered on the accelerograph with an average sensor spacing of 35 m station c00 was located about 2 m from the accelerograph we inverted aftershock spectra to obtain average relative site response at each station as a function of direction of ground motion we identified a 3 2 hz resonance that is a transverse oscillation of the hill a directional topographic effect the top base amplification ratio at 3 2 hz is about 4 5 for horizontal ground motions oriented approximately perpendicular to the long axis of the hill and about 2 for motions parallel to the hill this resonance is seen most strongly within 50 m of c00 other resonant frequencies were also observed a strong lateral variation in attenuation probably associated with a fault caused substantially lower motion at frequencies above 6 hz at the east end of the hill there may be some additional scattered waves associated with the fault zone and seen at both the base and top of the hill causing particle motions not spectral ratios at the top of the hill to be rotated about 20 away from the direction transverse to the hill the resonant frequency but not the amplitude of our observed topographic resonance agrees well with theory even for such a low hill comparisons of our observations with theoretical results indicate that the 3d shape of the hill and its internal structure are important factors affecting its response the strong transverse resonance of the hill does not account for the large east west mainshock motions assuming linear soil response mainshock east west motions at the tarzana accelerograph were amplified by a factor of about 2 or less compared with sites at the base of the hill probable variations in surficial shear wave velocity do not account for the observed differences among mainshock acceleration observed at tarzana and at two different sites within 2 km of tarzana

sediment induced amplification and the collapse of the nimitz freeway the amplification of ground motion by low seismic velocity surface sediments is an important factor in determining the seismic hazard specific to a given site the ms 7 1 loma prieta earthquake of 17 october 1989 was the largest event in the contiguous united states in 37 years and yielded an unparalleled volume of seismic data from the main shock and aftershock sequence1 these data can be used to image the seismic source to study detailed earth structure and to study the propagation of seismic waves both through bedrock at depth and through sediment layers near the surface near the edge of san francisco bay site conditions vary considerably on scales of hundreds of metres the collapsed section of the two tiered nimitz freeway in oakland was built on san francisco bay mud whereas stiffen alluvial sediments underlie a southern section that was damaged but did not collapse here we analyse high quality digital aftershock recordings from several sites near the nimitz freeway and conclude that soil conditions and resulting ground motion amplification may have contributed significantly to the failure of the structure