determination of the series of even carbon numbered n alk 1 enes trapped inside geomacromolecules abstract even carbon numbered n alk 1 enes trapped inside organic geomacromolecules such as kerogen asphaltene and solid bitumen can survive geologic time because of the effective protection provided by the complex matrix structures of geomacromolecules these alkenes are presumed to be derived from esters which are commonly present in various organisms subjected to either normal maturation increase or the impact of drastic thermal events these trapped n alk 1 enes gradually decrease in concentration and eventually disappear

carbonate source rock with low total organic carbon content and high maturity as effective source rock in china a review abstract carbonate rocks with high maturity and low total organic carbon content are widely distributed in china whether they can be effective source rocks remains controversial but they have great significance for the evaluation of hydrocarbon generation potential and exploration prospects of carbonate rocks dataset reveals that as the depth or maturity increases total organic carbon toc content atomic h c ratio and hydrocarbon generation potential of carbonate source rocks with low total organic carbon csrltoc all decrease because of hydrocarbon expulsion moreover some pyrolysis experiments also indicate that the csrltoc are able to generate and expel a quantity of hydrocarbons the above studies indicate that csrltoc can be effective source rocks for oil gas pools the unique features of carbonate rocks and csrltoc demonstrate that they are easier to expel hydrocarbons and contribute to oil gas reservoirs than shale and thus the lower limit of toc lltoc of effective carbonate source rocks could be smaller than shale 0 5 the lltocs of effective carbonate source rocks with type i ii1 kerogen mainly sapropelic group at the levels of immaturity and low maturity maturity high maturity and over maturity are toc 0 5 0 5 0 3 0 3 0 2 and 0 2 0 1 respectively if the carbonate source rocks are at the high over mature stage we could take 0 2 as the lltoc the present organic poor source rocks with high maturity are possibly moderate or good source rocks at the low mature level in the geological periods especially carbonate source rocks if type i ii1 kerogen some typical oil and gas fields in china derive partly or mostly from the csrltoc proving that csrltoc could be effective source rock in china

double beam imaging mapping lower mantle heterogeneities using combinations of source and receiver arrays we present a new technique for imaging spatially distributed heterogeneities using information from combinations of source and receiver arrays the method is based on the single scattering assumption and is closely related to the double beam method of kruger et al 1993 1995 1996 in that it exploits amplitude delay time slowness and azimuth information in two arrays simultaneously a crucial step in the method is the application of static time corrections for a chosen reference phase here pcp one type of image is obtained as a spatial likelihood distribution for prescribed source and receiver array slowness and azimuth values and delay times with respect to a reference phase this allows the determination of the spatial origin of coherent phases in the p coda in a complementary approach we perform a double beam stack migration according to the theoretical slowness and azimuth values for candidate scatterers distributed over a three dimensional 3 d grid the scattering strength is expressed as the resulting beam power beam amplitude or semblance in a time window determined from the theoretical delay time with respect to the reference phase while likelihood mapping provides an image reflecting the probability of a region to explain observed kinematic phase properties by single scattering double beam migration provides information about the scattering strength the method is applied to nuclear explosion sources in eastern kazakhstan recorded at the yellowknife array in northern canada we identify several scattering volumes within the lower mantle below the arctic producing individual anomalous lower mantle phases in the p coda these anomalies range in depth from the core mantle boundary cmb up to 500 km into the lowermost mantle and are mainly located under the eurasian side of the arctic the joint interpretation of these results with the results of previous studies suggests a connection of these anomalies to the cenozoic and mesozoic subduction of the pacific plate and the kula plate the determination of the nature of such 3 d anomalies necessitates further array studies with better azimuthal coverage

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

the vertical component p wave receiver function the vertical component p wave receiver function is an important source of data in studies of the crust mantle transfer function for determining earth structure under isolated receivers or under receiver arrays this waveform illuminates a missing aspect of the wave propagation in receiver function studies that employ only the horizontal components of motion and yields complementary constraints on near receiver heterogeneity and p wave propagation the vertical component p wave receiver function is formed using an array estimate for the effective teleseismic source function that is then deconvolved from all the vertical and horizontal components of ground motion at each station in the array one dimensional three dimensional and stochastic wave propagation models are used to test the robustness of the technique breakdown of single station receiver function deconvolution occurs because of high levels of noncorrelated noise between the ground motion components receiver functions for stations of the southern california terrascope array are investigated using the array technique vertical receiver functions for stations in the los angeles basin and long valley caldera show high amplitude secondary arrivals that cannot be explained by simple 1d structures but probably reflect wave propagation in 3d basin structures three component receiver functions from the station at mammoth lakes california show pathological behavior where the horizontal components of ground motion exceed the amplitude of the vertical components suggesting extreme topographic and 3d velocity heterogeneity use of all three components of the receiver function in modern passive array experiments is encouraged to reduce the problems of nonuniqueness in determining earth models

buoyancy driven fracture ascent experiments in layered gelatine laboratory experiments on air filled fracture propagation in solidified homogeneous and layered gelatine have been carried out providing an analogue model for magma filled dikes ascending in the crust the effects of layering on fracture velocity and shape have been analyzed in detail the free surface is found to accelerate approaching fractures layering accelerates or decelerates fractures approaching discontinuities of the elastic parameters depending on the value of the rigidity contrast the shape of fractures are strongly influenced as they pass from one layer to another the observed cross sectional shape when crossing a layer interface and the acceleration with decreasing rigidity can be explained with theoretical models our experiments also reproduce the arrest of fractures in proximity of joints and the formation of sills in the layer below the interface these findings could help in the interpretation of accelerated seismicity and deformation rates observed in volcanic areas

petroleum source in the tazhong uplift tarim basin new insights from geochemical and fluid inclusion data abstract a total of 108 drill stem test dst crude oil samples and 10 reservoir fluid inclusion samples were investigated geochemically to identify the characteristics and origin of the crude oil in the tazhong uplift tarim basin nw china results show that the majority of oils share typical biomarker characteristics from the middle upper ordovician o2 3 source rock and related crude oil features these features include a distinct v shape in the relative abundance of c27 c28 and c29 regular steranes and low abundances of dinosterane 24 norcholestanes triaromatic dinosteroids and gammacerane only a few oils display typical biomarker features indicating a cambrian lower ordovician o1 genetic affinity such as linear or anti l shape c27 c28 and c29 regular sterane distributions and relatively high concentrations of dinosterane 24 norcholestanes triaromatic dinosteroids and gammacerane it appears that most of the oils studied were derived from the o2 3 intervals as suggested by previous studies however the 13c values of individual n alkanes indicate that most of the crude oils in the tazhong uplift represent a mixture of two end member oils an o1 derived oil such as from well td2 or tz62 s and an o2 3 derived oil such as from well ym2 the data suggest that most of the oils in the uplift have a mixed origin and do not originated from the middle upper ordovician strata alone this conclusion is supported by data on the molecular composition of petroleum inclusions this new oil mixing model is critical for reconstructing the hydrocarbon formation and accumulation history for the region and may have important implications for further petroleum exploration in the tarim basin

molecular correlation of crude oils and oil components from reservoir rocks in the tazhong and tabei uplifts of the tarim basin china molecular data from a large set of source rock crude oil and oil containing reservoir rock samples from the tarim basin demonstrate multiple sources for the marine oils in the studied areas of this basin based on gammacerane c31 hopane and c28 c27 c 28 c 29 sterane ratios three of the fifteen crude oils from the tazhong uplift correlate with cambrian lower ordovician source rocks while the other crude oils from the tazhong uplift and all 39 crude oils from the tahe oilfield in the tabei uplift correlate with middle upper ordovician source rocks these two ratios further demonstrate that most of the free oils and nearly all of the adsorbed and inclusion oils in oil containing reservoir rocks from the tazhong uplift correlate with cambrian lower ordovician source rocks while the free and inclusion oils in oil containing carbonates from the tahe oilfield correlate mainly with middle upper ordovician source rocks this result suggests that crude oils in the tazhong uplift are partly derived from the cambrian lower ordovician source rocks while those in the ordovician carbonate reservoirs of tahe oilfield are overwhelmingly derived from the middle upper ordovician source rocks the scatter of c23 tricyclic terpane c23 tricyclic terpane c30 17a 21b h hopane and c21 c21 rc29 sterane ratios for the free and inclusion oils from oil containing carbonates in the tahe oilfield possibly reflects the subtle organofacies variations in the source rocks implying that the ordovician reservoirs in this oilfield are near the major source kitchen in contrast the close and positive relationship between these two ratios for oil components in the oil containing reservoir rocks from the tazhong uplift implies that they are far from the major source kitchen

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

near surface scholte wave velocities at ekofisk from short noise recordings by seismic noise gradiometry we propose a new approach for imaging the subsurface using a stochastic wavefield of interface waves present in the ambient seismic field unlike seismic interferometry our technique does not rely on cross correlations to obtain the green s function between two seismic receivers rather it relies on the local measurements of phase velocity obtained directly from the ratio between second order temporal and spatial derivatives of the wavefield we process 10 min of ambient seismic noise recording made using a large and dense array installed over ekofisk we image a subsidence induced geomechanical imprint on the scholte wave phase velocities in the near surface this resulting phase velocity pattern is verified by comparison to results from a seismic noise cross correlation tomography

multiple sourced features of marine oils in the tarim basin nw china geochemical evidence from occluded hydrocarbons inside asphaltenes abstract the tarim basin nw china is a large composite basin with multiple sets of petroleum source rocks the basin has undergone numerous episodes of hydrocarbon generation migration and accumulation making it difficult to assess the source rocks and oil source correlation for the widespread marine oils in this area protected by the molecular structure of asphaltenes occluded hydrocarbons can provide information about the early source rocks in this work the occluded hydrocarbons released from the asphaltenes by a mild chemical degradation method were compared with the crude oil maltenes and the adsorbed compounds from asphaltenes analysis of biomarker distribution and the carbon isotope composition of individual n alkanes suggests that the widespread marine oils in the tazhong uplift tabei lunnan uplift and halahatang depression were contributed by cambrian lower ordovician source rocks at an early stage and later mixed with hydrocarbons derived from middle upper ordovician source rocks the marine oils in the tarim basin demonstrate extensive characteristics of having been derived from multiple source rocks

imaging widespread seismicity at midlower crustal depths beneath long beach ca with a dense seismic array evidence for a depth dependent earthquake size distribution we use a dense seismic array composed of 5200 vertical geophones to monitor microseismicity in long beach california poor signal to noise ratio due to anthropogenic activity is mitigated via downward continuation of the recorded wavefield the downward continued data are continuously back projected to search for coherent arrivals from sources beneath the array which reveals numerous previously undetected events the spatial distribution of seismicity is uncorrelated with the mapped fault traces or with activity in the nearby oil fields many events are located at depths larger than 20 km well below the commonly accepted seismogenic depth for that area the seismicity exhibits temporal clustering consistent with omori s law and its size distribution obeys the gutenberg richter relation above 20 km but falls off exponentially at larger depths the dense array allows detection of earthquakes two magnitude units smaller than the permanent seismic network in the area because the event size distribution above 20 km depth obeys a power law whose exponent is near one this improvement yields a hundred fold decrease in the time needed for effective characterization of seismicity in long beach

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

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

application of sulfur and carbon isotopes to oil source rock correlation a case study from the tazhong area tarim basin china abstract up until now it has been assumed that oil in the palaeozoic reservoirs of the tazhong uplift was derived from upper ordovician source rocks oils recently produced from the middle and lower cambrian in wells zs1 and zs5 provide clues concerning the source rocks of the oils in the tazhong uplift tarim basin china for this study molecular composition bulk and individual n alkane 13 c and individual alkyl dibenzothiophene 34 s values were determined for the potential source rocks and for oils from cambrian and ordovician reservoirs to determine the sources of the oils and to address whether 13 c and 34 s values can be used effectively for oil source rock correlation purposes the zs1 and zs5 cambrian oils and six other oils from ordovician reservoirs were not significantly altered by tsr the zs1 oils and most of the other oils have a v shape in the distribution of c 27 c 29 steranes bulk and individual n alkane 13 c values predominantly between 31 to 35 vpdb and bulk and individual alkyldibenzothiophene 34 s values between 15 to 23 vcdt these characteristics are similar to those for some cambrian source rocks with kerogen 13 c values between 34 1 and 35 3 and 34 s values between 10 4 and 21 6 the oil produced from the lower ordovician in well ym2 has similar features to the zs1 cambrian oils these new lines of evidence indicate that most of the oils in the tazhong uplift contrary to previous interpretations were probably derived from the cambrian source rocks and not from the upper ordovician conversely the 13 c and 34 s values of zs1c cambrian oils have been shown to shift to more positive values due to thermochemical sulfate reduction tsr thus 13 c and 34 s values can be used as effective tools to demonstrate oil source rock correlation but only because there has been little or no tsr in this part of the section

origins of palaeozoic oils in the tarim basin evidence from sulfur isotopes and biomarkers abstract crude oil h 2 s and pyrite samples from palaeozoic formations in the tarim basin have been analyzed for 34 s values together with oil samples for biomarkers and fluid inclusions for chemical composition to elucidate the origin of sulfur in the oil and to address potential applications in oil source rock correlation the results show that crude oil samples have sulfur contents from 0 02 to 2 47 and 34 s values from 11 9 to 28 2 non degraded oils without associated h 2 s gas have 34 s values from 11 9 to 20 5 and are relatively rich in c 28 20r sterane aryl isoprenoids and or gammacerane the features are well correlated with the cambrian and lower ordovician source rocks with 34 s values from 10 4 to 19 4 non degraded oils with associated h 2 s gas have 34 s values from 15 1 to 19 1 close to the h 2 s from 15 0 to 18 5 suggesting that the h 2 s was incorporated into the oils leading to the generation of 2 thiaadamantanes and likely alkyl thiolanes in the oil with a 34 s value of 18 5 heavily biodegraded oils have the highest sulfur contents and show 34 s values from 20 0 to 28 2 significantly heavier than those of any of the potential source rocks 15 3 to 19 4 thus it is likely that isotopically heavy sulfides have been incorporated into the biodegraded oils resulting in 34 s values of the oils becoming closer to cambrian and ordovician age seawater sulfates the sulfides may have originated from thermochemical sulfate reduction tsr as evidenced by the occurrence of h 2 s rich fluid inclusions and late stage and fracture filling pyrite with 34 s values mainly from 25 to 34 in the palaeozoic reservoirs

spatial gradient analysis for linear seismic arrays i incorporate the spatial gradient of the wave field recorded from one dimensional arrays into a processing method that yields the horizontal wave slowness and the change of geometrical spreading with distance in general the model for seismic wave propagation is enough to be appropriate for body and surface waves propagating from nearby seismic sources but can be simplified into a plane wave model although computation of the spatial gradient requires that array elements be closer than 10 of the horizontal wavelength seismic array apertures in the usual sense may extend over many horizontal wavelengths and illuminate changes within the wave field array images of horizontal slowness and the relative geometrical spreading changes of seismic waves are derived using filter theory and used to interpret observed array wave fields errors in computing finite difference spatial gradients from array nodes are explicitly considered to avoid spatial aliasing in the estimates i apply the method to interpret waves in strong ground motion and small scale refraction data sets use of the wave spatial gradient accentuates spatial differences in the wave field that can be theoretically exploited in fine scale tomographic studies of structure and is complementary to frequency wavenumber or beam forming array processing techniques

analysis of teleseismic p waves with a 5200 station array in long beach california evidence for an abrupt boundary to inner borderland rifting we analyze teleseismic p waves from four mw 6 5 earthquakes recorded by a petroleum industry survey in long beach california the survey used a 2 d array with up to 5200 seismometers 120 m mean spacing and 7 10 km aperture at frequencies near 1 hz p wave travel times and amplitudes exhibit coherent lateral variations over scales as short as 400 m including locally delayed travel times and increased amplitudes at the crest of the long beach anticline deeper heterogeneity is indicated by p wave phase velocities that deviate from reference model predictions for events from southwestern azimuths we postulate that a sharp northeastward increase in moho depth from the inner borderland ib to mainland southern california causes the anomalous phase velocities elastic forward modeling finds the travel times are fit well by a moho that dips 65 to the northeast and flattens 10 km southwest of the newport inglewood fault zone constraining the felsic thickness of mainland crust to 28 km requires an 8 km thick layer with a p velocity of 7 km s beneath it which could result from basal accretion of former farallon ocean crust or magmatic underplating during miocene volcanism forward models with a 65 moho dip predict a p to s conversion with a phase velocity of 5 km s deconvolution of the array s mean p wave signal isolates a similar later arriving phase the steep crust thickness transition supports a locally abrupt boundary to ib rifting our results highlight the utility of dense short period arrays for passive imaging at near surface to uppermost mantle depths

distinguishing cambrian from upper ordovician source rocks evidence from sulfur isotopes and biomarkers in the tarim basin abstract the reported source rocks for the abundant petroleum in the tarim basin china range from cambrian to lower ordovician and or upper ordovician in age however the difference between the two groups of source rocks is not well characterized in this study pyrite was removed from eleven mature to over mature kerogen samples from source rocks using the method of crcl 2 reduction and grinding the kerogen and coexisting pyrite samples were then analyzed for 34 s values results show that the kerogen samples from the cambrian have 34 s values between 10 4 and 19 4 the values are significantly higher than those from the lower ordovician kerogen 34 s of between 6 7 and 8 7 which in turn are generally higher than from the upper ordovician kerogen samples 34 s of between 15 3 and 6 8 the associated pyrite shows a similar trend but with much lower 34 s values this stratigraphically controlled sulfur isotope variation parallels the evolving contemporary marine sulfate and dated oil 34 s values from other basins suggesting that seawater sulfate and source rock age have an important influence on kerogen and pyrite 34 s values the relatively high 34 s values in the cambrian to lower ordovician source rocks are associated with abundant aryl isoprenoids gammacerane and c 35 homohopanes in the extractable organic matter indicating that these source rocks were deposited in a bottom water euxinic environment with water stratification compared with the upper ordovician the cambrian to lower ordovician source rocks show abundance in c 28 20r sterane c 23 tricyclic terpanes 4 23 24 trimethyl triaromatic dinosteroids and depletion in c 24 tetracyclic terpane c 29 hopane thus 34 s values and biomarkers of source rock organic matter can be used for distinguishing the cambrian and upper ordovician source rocks in the tarim basin

biomarker signatures of sinian bitumens in the moxi gaoshiti bulge of sichuan basin china geological significance for paleo oil reservoirs abstract chen et al precambrian research 296 1 19 2017 presented a biomarker study on solid bitumens and associated source rock extracts from the moxi gaoshiti bulge of the sichuan basin sw china biomarker characteristics revealed that the solid bitumens and related paleo oils belong to the same group and are well correlated to source rocks of the neoproterozoic dengying and lower cambrian qiongzhusi formations the thermal maturity of solid bitumens and their migration direction have been assessed it appears that these interpretations are internally inconsistent and are also inconsistent with much published geochemical data and the biomarker data are over interpreted and flawed

high resolution 3d shallow crustal structure in long beach california application of ambient noise tomography on a dense seismic array ambient noise tomography has proven to be effective in resolving shallow earth structure we applied ambient noise tomography on a dense seismic array in long beach california the array was composed of more than 5200 stations with an average spacing close to 100 m three weeks of passive ambient noise were crosscorrelated between each station pair which resulted in more than 13 5 million crosscorrelations within the area clear fundamental mode rayleigh waves were observed between 0 5 and 4 hz which were most sensitive to structure above 1 km depth for each station pair we applied frequency time analysis to determine the phase traveltime dispersion and for each frequency we applied eikonal tomography to determine the rayleigh wave phase velocity map the eikonal tomography accounted for ray bending by tracking the wavefront and allowed uncertainties to be estimated through statistical analysis the compilation of phase velocity maps was then used to invert for 3d shear velocity structure the inverted model showed clear correlation with the known geologic features such as the shallow south north velocity dichotomy and a deeper fast anomaly associated with the newport inglewood fault zone our results can potentially be used to complement traditional active source studies

palaeozoic oil source correlation in the tarim basin nw china a review abstract oil source correlation in the cratonic region of the tarim basin nw china has long been controversial current knowledge of the potential source rock distribution end member selection oil source correlation and impacts of secondary alteration processes have been reviewed two source rock systems from the cambrian lower ordovician o 1 and middle upper ordovician o 2 3 potentially contributed to oil accumulations in the cratonic region geochemical correlations suggest that oils are dominantly derived from the o 2 3 source rocks while geological evidence and sulfur isotopic compositions supports the o 1 source rocks as a main contributor such inconsistency is rooted in the selection of end members and their characterization changes in some biomarker parameters such as sterane distribution gammacerane index and ratio of tricyclic terpanes to pentacyclic terpanes are mainly controlled by thermal maturation and biodegradation rather than source input and depositional environment variation no clear boundary between the two source systems can be established using biomarkers except for a few diagnostic components some o 1 source signatures such as even odd predominance of n alkanes unusual tricyclic terpane distribution unusually enriched 13 c carbon isotopic compositions of oils and kerogens and the occurrence of combustion related polycyclic aromatic hydrocarbons largely result from an abnormal heating influence either from igneous intrusion or hydrothermal fluid activity local thermochemical sulfate reduction can also remove most source related signatures these so called markers in currently selected end members result from extensive secondary alteration processes and do not reflect source input differences while more research is needed for full reconstruction of oil source correlation in the cratonic region of the tarim basin the main source rocks most likely reside in the o 1 succession rather than o 2 3

paleozoic oil source rock correlations in the tarim basin nw china we studied a suite of 40 oils and extracts of purported source rocks from the tarim basin in nw china the main group of oils comes from tazhong and tabei wells which sample the largest known petroleum accumulations in the basin these oils can be statistically correlated with extracts of ordovician rocks based upon high relative concentrations of 24 isopropylcholestanes and low relative concentrations of dinosteranes triaromatic dinosteroids and 24 norcholestanes in contrast extracts from cambrian rocks have low relative concentrations of 24 isopropylcholestanes with high relative concentrations of dinosteranes triaromatic dinosteroids and 24 norcholestanes although some tarim basin cambrian rocks yield high total organic carbon contents we see little evidence in the analyzed oil samples to suggest that they came from cambrian source rocks

structural geology and tectonic evolution of los angeles basin oil in the los angeles basin has accumulated principally in anticlinal folds associated with strong neogene faulting and compression the still continuing pasadenan orogeny involved northwest trending right lateral wrench faults related to the san andreas system has been the dominant influence but that deformation has been overprinted on structures formed during two discrete earlier orogenic episodes 1 the major widespread block faulting of the middle miocene and 2 a less obvious phase of compressive deformation that occurred during latest miocene and earliest pliocene time involved left lateral faulting and related folding on more westerly trends and was especially significant along the northern margin of the basin the resulting present day structural pattern therefore is not a simple pattern of classical right lateral wrench fault deformation it is a pattern which reflects the radical neogene evolution of the regional stress field and the interplay of wrench faulting with the hinge lines and strong sedimentary wedge belts formed by earlier vertical movements

temperature and pressure characteristics of ordovician gas condensate reservoirs in the tazhong area tarim basin northwestern china this paper investigates the temperature and pressure distribution characteristics and their evolution in the upper ordovician strata in the tazhong area tarim basin northwestern china based on hundreds of temperature data from boreholes the present day temperature ranges from 100 c to 130 c increasing from the southeast to the northwest and having a cool belt in the central fault horst pore pressures in the upper ordovician reservoirs range from 35 to 62 mpa 5076 to 8992 psi overpressures developed in the southwestern region and along the eastern segment of the central fault horst to the northern slope the lower ordovician reservoirs in the east reached 140 c during the late ordovician but those in the west heated continuously and reached the maximum temperature 130 c during present day paleopressures reconstructed from fluid inclusion data indicate that overpressures caused by hydrocarbon generation were formed in the areas away from fault belts but were absent in the area around the no 1 fault belt the temperature evolution indicates that the middle lower cambrian source rocks reached gas generation stage vitrinite reflectance ro 2 0 at the end of the ordovician whereas the middle upper ordovician source rocks are still in the high maturity stage ro 1 3 at the present day deep oil and gas migration is driven by overpressure and commercial reservoirs are predominantly distributed in the normally pressured zones along the no 1 fault belt the formation of gas condensate is controlled by specific temperature and pressure characteristics

comparative studies on compounds occluded inside asphaltenes hierarchically released by increasing amounts of h2o2 ch3cooh being the heaviest fraction of crude oils asphaltenes are liable to aggregate and other molecules in the oils can be steadily adsorbed onto and even occluded inside the macromolecular structures of the asphaltenes these occluded compounds inside the asphaltenes can survive over geological time in oil reservoirs owing to effective protection by the macromolecular structures of the asphaltenes the asphaltenes of a crude oil zg31 from the central tarim basin nw china were hierarchically degraded by increasing the amount of h2o2 ch3cooh to release the occluded compounds besides the common components series of even numbered n alk 1 enes and 3 ethylalkanes were detected among the occluded compounds comparison of the biomarker distributions and the compound specific c isotopic results between the compounds from the maltenes and those from the occluded fraction the zg31 reservoir was suggested to have been charged multiple times with different charges being derived from different strata of source rocks

molecular organic geochemistry of the tarim basin northwest china we conducted organic geochemical analyses on the largest suite of oils and source rock extracts from the tarim basin northwest china currently available statistical cluster analysis of the entire suite of tarim oils distinguishes at least seven genetic groups of oils the largest group of oils was collected from the tazhong and tabei uplifts and originated from marine middle upper ordovician anoxic marls that mark slope facies at the margins of structural uplifts two other genetic groups most likely originated from marine middle upper ordovician source rocks but of distinct facies with one an oxic shale rich source west of the bachu uplift and the other an anoxic shale source at tazhong

source facies of the paleozoic petroleum systems in the tabei uplift tarim basin nw china implications from aryl isoprenoids in crude oils abstract aryl isoprenoids have been detected for the first time in crude oils from paleozoic petroleum systems in the tabei uplift tarim basin northwestern china the principal compounds possess the 1 alkyl 2 3 6 trimethyl substitution pattern characteristic of diaromatic carotenoids found in the chlorobiaceae family of photosynthetic sulfur bacteria with a predominance of c13 c23 homologues in these samples flash pyrolysates of the asphaltene fractions isolated from crude oils show an unusual abundance of 1 2 3 4 tetramethylbenzene an indicator for a significant contribution of diaromatic carotenoids to the source kerogen of these oils the wide distribution of these compounds in crude oils reveals that penetration of the photic zone by sulfidic waters during deposition enabled prolific growth of photosynthetic green sulphur bacteria chlorobiaceae this suggests that the source rocks for the paleozoic petroleum systems in the tabei uplift were likely deposited under euxinic conditions with sulfate and sulfide rich water bodies which doesn t support previously published conclusions of a middle upper ordovician source that marks the slope facies at the margins of structural uplifts