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

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

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

petroleum charge history in the lunnan low uplift tarim basin china evidence from oil bearing fluid inclusions abstract the petroleum charge history in the lunnan low uplift tarim basin china was investigated by comparing the geochemical characteristics of fluid inclusion fi oils from ordovician and triassic reservoirs with crude oils from stratigraphically different reservoirs quantitative grain fluorescence qgf and total scanning fluorescence tsf were used to screen the reservoir samples so as to identify suitable samples for molecular composition of inclusion mci analysis all of the samples contain c 30 n propylcholestanes diagnostic of marine source rocks the ordovician hosted fi oils differ from the triassic hosted fi oils having higher relative abundances of c 19 tricyclic terpane c 24 tetracyclic terpane and rearranged hopanes ts and c 29 ts and higher pr ph ratios while the triassic hosted fi oils have lower pr ph ratios and higher relative abundances of c 23 tricyclic terpane arylisoprenoids 25 norhopanes and c 35 homohopane several of the crude oils are similar to the triassic hosted fi oils based on the geochemical characteristics of the fi and crude oils combined with information on the burial history of the area at least two petroleum charge episodes can be distinguished in the lunnan low uplift an early charge represented by the ordovician hosted fi oils was biodegraded as evidenced by the presence of 25 norhopanes in the triassic hosted fi oils and crude oils but not in the ordovician hosted fi oils ordovician hosted fi oils provide the only evidence for oil generated from cambrian lower ordovician source rocks triassic hosted fi oils and crude oils in the ordovician carboniferous and triassic reservoirs are mixtures of biodegraded oil from an early charge episode and more mature oil from later charge

catalytic hydropyrolysis of asphaltenes in marine oil from the tarim basin nw china implications to complicated oil charging histories in an old composite basin abstract oil asphaltenes have been used to characterize the source s and timing of expulsion of early charged oils however the application on asphaltene in a complex petroleum basin have been limited marine oils from the tarim basin nw china were selected to release asphaltene bound molecules by the catalytic hydropyrolysis technique hypy the analyzed samples were 10 heavy oils from two major oil production regions the tabei and tazhong uplifts in the basin the asphaltenes may be mixed products from multiple hydrocarbon charging stages if we consider the main oil filling events and the regional geothermal histories of corresponding reservoirs however the similar molecular and isotopic characteristics of the hydropyrolyzates indicate contributions from one major source rock possibly lower cambrian mudstone during relatively early periods based on the presently known source characteristics the preservation of asphaltenes probably reflects a low reservoir temperature after charging the asphaltenes were derived from marine algae deposited in a strongly reducing environment given the biomarker data e g relatively abundant aryl isoprenoids and low pr ph and carbon isotopic data 35 5 to 34 4 asphaltenes were expelled around the oil generation peak moreover molecular ratios indicative of maturity e g tricyclic terpanes hopanes derived by hypy of asphaltenes suggest that the asphaltenes of the tazhong uplift are generally more mature than those of the tabei uplift moreover this is mainly related to different maturities when the oil was expelled the free hydrocarbons in the tazhong uplift show greater molecular and isotopic variations than those in the tabei uplift this might be attributed to more complex accumulation processes in the former late oils with a range of maturities mixing proportions with early biodegraded oils and degrees of alteration by thermochemical sulfate reduction could all have played a role in generating this variability the results indicate that the hydrocarbons released from oil asphaltenes by hypy can provide insights into multiple charging processes in an old composite petroleum basin

tropical cloud top height distributions revealed by the ice cloud and land elevation satellite icesat geoscience laser altimeter system glas 1 we analyze cloud top height data obtained at tropical latitudes between 29 september and 17 november 2003 from the geoscience laser altimeter system glas carried onboard the ice cloud and land elevation satellite icesat about 66 of the tropical observations show one or more cloud layers of those observations that do show a cloud about half show two or more cloud layers maxima in the cloud top height distribution occur in the upper troposphere between 12 and 17 km and in the lower troposphere below about 4 km a less prominent maximum occurs in the midtroposphere between 6 and 8 km the occurrence of cloud layers tends to be consistent with the well known diurnal cycles of continental and oceanic convection and we find that cloud layers tend to occur more frequently over land than ocean except in the lower troposphere where the opposite is true a particular emphasis of this paper is the convection that penetrates into the so called tropical tropopause layer ttl we find more frequent occurrence of thick clouds in the ttl and above the tropopause than other studies with 3 0 and 19 of the thick and thin cloud observations respectively showing a cloud top in the ttl and 0 34 and 3 1 showing a cloud top above the average level of the tropopause these values are higher than those found in other data sets and suggest that an upward revision of ttl cloud frequency might be necessary ttl clouds are observed more frequently in the evening than in the morning and more frequently over land than over ocean

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

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

timing and chemistry of igneous events associated with the southern oklahoma aulacogen abstract igneous activity in the southern oklahoma aulacogen of north america was concentrated in the early rifting stages of aulacogen development the time span over which liquids rose may not have exceeded 50 m y and certainly terminated before the upper cambrian igneous activity began with three basaltic liquids stratigraphically identifiable but perhaps not all distinct genetically this was followed by one large rhyolitic granitic episode of a type character one final basaltic event ended the activity all the basaltic types seem to be tholeiitic showing more kinship with either the older proterozoic north american midcontinental rift or the northern part of the cenozoic rio grande rift than the cenozoic east african rift two major uplifts occurred one between the earlier basalts and the rhyolite and one much later after all igneous activity was over in the pennsylvanian

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

statistics of cold cumulonimbus anvils based on enhanced infrared photographs infrared photographs from the atlantic geosynchronous satellite enhanced to resolve cold anvil temperatures of tropical clouds are analyzed statistically to determine their spatial temporal variability during the nasa u2 flight experiment of 1980 diurnal dependence varies regionally indicating topographic control via low level convergence and release of convective instability anvil growth rates area covered and duration are discussed for individual and merging anvil systems gradients of anvil temperatures implied by infrared photographs are shown to be caused in part by radial decrease in anvil depth i e to emissivities less than 1 an error in cloud top temperature of 10c is caused by 10 reduction in emissivity errors are near zero in dense actively growing portions of the anvil

detecting tropical thin cirrus using multiangle imaging spectroradiometer s oblique cameras and modeled outgoing longwave radiation 1 we report the improved detection of thin cirrus clouds over the tropics using oblique camera stereo retrieval of cloud top heights from the multiangle imaging spectroradiometer misr instrument on the terra satellite the misr oblique stereo captures 10 of thin cirrus with mean height of 13 km over all scenes that the standard stereo misses completely especially when they are over lower level clouds that provide more contrast to determine thin cirrus properties missed by misr differences between modeled and measured outgoing longwave radiation olr were used to compute its fractional cover and optical depth the oblique misr measurements were used as inputs to the model and a merged data set from ceres modis and misr instruments on the terra satellite provided the measured fluxes and the cloud properties for the cases investigated including all clear and cloudy scenes in the tropics the difference between modeled and measured olr cirrus forcing averaged 19 w m 2 this can be accounted for by the addition of thin cirrus of coverage 77 however oblique analysis only detects 10 of thin cirrus 0 1 0 3 and misses 67 of cirrus with 0 3 the missed cirrus coverage includes 32 of homogeneous cirrus 0 1 0 3 and 35 of subvisual cirrus 0 1 to improve the detection of homogeneous cirrus with misr the current contrast threshold should be decreased this will increase the number of pixels to be matched stereoscopically that were screened as noise initially

major stages of rifting evolution in the earth s history abstract linear extensional rift and rift like structures have been generated many times during various periods of the earth s history since early times these structures have varied with time however in scale morphology formations paragenesis of tectonic features regularity of distribution and evolution i distinguish and consider five major stages of rifting they are katarchean archean early proterozoic late proterozoic paleozoic and mesozoic cenozoic linear structures of the oldest stage combine features of development and structure similar to those typical of the rift and geosynclinal zones in the later periods of the earth s history at the second stage proto rift and proto geosynclinal structures can be distinguished for the first time though differences are not distinct paleo rift zones of the third and fourth stages differ from geosynclinal belts and zones their structural and genetic evolution however is related to the development of the latter in contrast the distribution and evolution of the rift zones and belts during the fifth stage are connected mainly with the destruction of the continents and formation of the secondary oceanic basins they are complementary to the mesozoic cenozoic geosynclinal orogenic belts periods of the greatest development of rift and rift like structures in the archean riphean and mesozoic cenozoic probably correspond to the major phases of the earth s expansion which can be distinguished in its general pulsating evolution

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

application of the monoterpane ratio mtr to distinguish marine oils from terrigenous oils and infer depositional environment in northern tarim basin china abstract six monoterpenoid hydrocarbons including two acyclic two monocyclic and two aromatic components were identified and quantified in 49 oil and condensate samples using comprehensive two dimensional gas chromatography coupled to time of flight mass spectrometry gc gc tofms among them 2 6 dimethyloctane 2 6 dmo and 2 methyl 3 ethylheptane 2 m 3 eh are the most abundant compounds and geochemically significant used in conjunction with other geochemical parameters such as pristane phytane pr ph and dibenzothiophene phenanthrene dbt p ratios the 2 m 3 eh 2 6 dmo ratio monoterpane ratio mtr provides a useful tool for distinguishing marine oils and condensates from those of terrigenous origin oils and condensates derived from marine source rocks have high mtr 0 4 low pr ph and high dbt p values whereas those generated from terrigenous source rocks have lower mtr

late proterozoic to early palaeozoic supracrustal succession of sierra leone an aulacogen at the western margin of the west african craton three parallel zones of upper proterozoic to lower palaeozoic sedimentary volcanic cover rocks have been recognized in western sierra leone the kasila group m the sw ist metamorphosed to the granulite facies and grades into the marampa schist group and this in turn grades into the unmetamorphosed rokel river group in the ne prior to this investigation these rocks were thought to belong to different ages the most highly metamorphosed was thought to be the oldest and the unmetamorphosed the youngest this view is unrealistic since field mapping has failed to reveal any sharp contacts between them and all available age data indicate their involvement in the pan african ca 550 ma orogeny a model is proposed involving an intracontinental graben aulacogen extending from western sierra leone into the adjacent territories developed about 1000 ma ago during the pan african orogeny a portion of the aulacogen fill overlying the remobilized basement was subjected to a regional metamorphism and deformation the grade of metamorphism and the degree of deformation decreased steadily from the centre of the pan african domain to the contact with the west african craton the unmetamorphosed and mildly deformed to undeformed equivalent rests on the craton

an assessment of cirrus heights from misr oblique stereo using ground based radar and lidar at the tropical western pacific arm sites 1 we compare cirrus presence and heights cths using oblique stereo by the multiangle imaging spectroradiometer misr with measurements from ground based cloud radar and lidar sensors at the tropical western pacific twp sites operated by the u s department of energy atmospheric radiation measurement program precise point wise comparisons limited to only 195 coincident cases showed that the total number of cirrus retrieved using oblique stereo analysis improved to 70 from 39 using the standard stereo technique the stereo technique detects cloud with the highest contrast which is often at lower altitude the oblique stereo technique s efficiency depends on the thickness and number of underlying cloud layers a histogram approach allowed similar regions to be compared statistically with many more samples and showed three distinct peaks at 13 km 15 km and 19 km related to deep convective clouds tropical tropopause layer ttl cirrus and overshooting convective clouds respectively most differences between the satellite and ground based measurements resulted from a number of cases of invalid cloud comparisons 14 blunders from edges and broken clouds 7 low contrast stereo mismatches 4 and under estimation of cths 3 overall the oblique stereo analysis detected a cirrus top layer in 65 of all the valid coincident cases mostly 1 km in thickness the oblique stereo derived cirrus cths differed from the heights of cirrus top layers from ground based cloud radar and lidar by 0 5 1 0 km validating the misr retrievals this suggests global thin cirrus retrievals are possible with the oblique stereo technique after the screening of occasional blunders

paleo heat flow evolution of the tabei uplift in tarim basin northwest china abstract the paleo heat flow evolution of the tabei uplift in the tarim basin is investigated based on burial and thermal history reconstruction of 14 wells and using basin modeling numerous geological parameters such as temperature data and missing sediment thickness by erosion were used in the modeling the basin model was calibrated using 460 measured vitrinite reflectance vr o and vitrinite like maceral reflectance vlmr o values to constrain the validity of the maturity model the heat flow history of the tabei uplift tarim basin shows the following characteristics 1 the highest paleo heat flow was predicted to have occurred in the early ordovician as 65 5 mw m 2 and gradually decreased to 55 5 mw m 2 during the late carboniferous 2 a thermal kick was modeled to have occurred in the permian as suggested by an abrupt rise in the heat flow 3 the heat flow gradually decreased since the triassic 4 the present day heat flow was predicted to be as low as 38 mw m 2 this heat flow history honors the geologic and tectonic evolution history of the tabei uplift and is suggested as the best case heat flow model

geochemistry and possible origin of petroleum in palaeozoic reservoirs from halahatang depression abstract the halahatang depression in the tabei uplift of the tarim basin is an active exploration area because it has substantial reservoir potential and contains or is near to many commercial oil fields geochemical analysis indicates that halahatang oils were derived from marine carbonate source rocks deposited under anoxic reducing conditions the maturities for halahatang oils are corresponding to the peak of the oil window and slightly higher than the neighboring tahe oils the halahatang oils feature low pr ph c 21 c 23 tricyclic terpane and c 28 c 29 sterane ratios high c 29 c 30 hopane and c 35 c 34 hopane ratios a v shape in the distribution of c 27 c 28 c 29 steranes and light carbon isotope ratios similar to the tahe oils and correlate well with the middle upper ordovician source rock however some source related biomarker parameters imply a more reducing source organofacies with more zooplanktonic contribution than that for the tahe oils

the origin migration and accumulation of the ordovician gas in the tazhong iii region tarim basin nw china abstract the ordovician large scale gas reservoir in the tazhong iii region burial depth 6000 m is a typical deep strata gas reservoir in the tarim basin of nw china the origin migration and accumulation of the ordovician natural gas in the tazhong iii region were investigated by integrating geological geophysical and geochemical parameters the parameters that were successfully analyzed included the gas compositions and carbon isotope ratios production data burial and geothermal histories oil compositions and properties together with the diamantane index the results indicated that the ordovician natural gas in the tazhong iii region originated from cambrian ordovician paleo oil cracking accompanied by a large amount of h2s generated from thermochemical sulfate reduction tsr when the oil cracking gas migrated vertically into the ordovician reservoir through the tazhong i fault and strike slip faults it was preferentially charged in the pinnate fault zones of strike slip faults with high porosity and permeability leading to the enrichment of natural gas and an abnormal distribution of the compositions and properties of hydrocarbon then oil cracking gas intruded into and altered the previous oil reservoir from northeast to southwest through the strike slip faults unconformities and pore fracture reservoir belt leading to the differential accumulation of hydrocarbon in districts of the tazhong iii region the ordovician natural gas migration accumulation model in the tazhong iii region indicates a great exploration potential in the deep or super deep strata of the tarim basin further exploration activities in the ordovician reservoir of the tarim basin should be conducted in the regions where cambrian ordovician source rocks are well developed and the stress fracture zones related deep fault should be emphasized

co occurrence statistics of tropical tropopause layer cirrus with lower cloud layers as derived from cloudsat and calipso data 1 radar and lidar data collected by instruments aboard the cloudsat and calipso satellites are used to demonstrate statistics of the spatial variability of tropical tropopause layer ttl cirrus along with their tendency to occur with or without lower clouds during the period july 2006 through june 2007 this time period included a mild el nino event ttl cirrus occurrence patterns contain maxima over the tropical convective areas of south america of africa and of the west pacific it is demonstrated from co occurrence statistics that ttl cirrus events and general lower cloud events are nominally independent in a zonal average however tendencies toward co occurrence between ttl cirrus and lower clouds that appear in specific base height and geometrical thickness bins do exist nominally independent of clouds based below 3 km ttl cirrus become increasingly less likely to occur with lower cloud layers of increasing base height than they are to occur generally the independence of ttl cirrus from clouds based in the boundary layer is due to the ubiquitous unconnected co occurrence of ttl cirrus with thin trade cumulus clouds however we find that ttl cirrus are more likely to occur with low based clouds of moderate depth 3 10 km than they are generally and less likely to occur with deep thicker than 10 km low based clouds than they are generally results are used in commenting generally on the ttl cirrus maintenance and formation hypotheses of hartman et al 2001 and of garret et al 2006

cloud classes and radiative heating profiles at the manus and nauru atmospheric radiation measurement arm sites 1 the tropical western pacific is a convective regime however the frequency and depth of convection is dependent on dynamical forcing which exhibits variability on a range of temporal scales and also on location within the region manus island papua new guinea lies in the heart of the western pacific warm pool region and exhibits frequent deep convection much of the time while nauru which lies approximately 20 degrees to the east of manus is in a transition zone where the frequency of convection is dependent on the phase of the el nino southern oscillation because of this difference in dynamical regime the distribution of clouds and the associated radiative heating is quite different at the two sites individual cloud types boundary layer cumulus thin cirrus stratiform convective outflow do occur at both sites but with different frequencies in this study we compare cloud profiles and heating profiles for specific cloud types at these two sites using data from the atmospheric radiation measurement arm climate research facility results of this comparison indicate that while the frequency of specific cloud types differ between the two sites as one would expect the characteristics of individual cloud classes are remarkably similar this information could prove to be very useful for applying tropical arm data to the broader region

association of tropical cirrus in the 10 15 km layer with deep convective sources an observational study combining millimeter radar data and satellite derived trajectories abstract in this paper millimeter cloud radar mmcr and geosynchronous meteorological satellite gms data are combined to study the properties of tropical cirrus that are common in the 10 15 km layer of the tropical troposphere in the western pacific millimeter cloud radar observations collected by the atmospheric radiation measurement program on the islands of manus and nauru in the western and central equatorial pacific during a 12 month period spanning 1999 and 2000 show differences in cirrus properties over manus where clouds above 7 km are observed 48 of the time the cirrus are thicker and warmer on average and the radar reflectivity and doppler velocity are larger over nauru clouds above 7 km are observed 23 of time to explain the differences in cloud properties the relationship between tropical cirrus and deep convection is examined by combining the radar observations with gms satellite derived back trajectories using a data record of 1 yr it is found that 47 of the cirrus observed o

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

thermochemical sulphate reduction in cambro ordovician carbonates in central tarim h2s and co2 are found in elevated concentrations in palaeozoic reservoirs in the tarim basin in china we have carried out analyses on gas petroleum mineral cement and bulk rock compositions and isotope ratios together with petrography and fluid inclusion to assess the origin of the h2s a deep crustal e g volcanic origin of the h2s and co2 is unlikely since the inert gases n2 and he have isotope ratios totally uncharacteristic of this source organic sources are also unlikely since the source rock has low a sulphur content and the sulphur isotope ratio of the petroleum correlates positively with the sulphur content the opposite of what would be anticipated from petroleum derived h2s bacterial sulphate reduction is unlikely because temperatures are too high for bacteria to have survived thermochemical sulphate reduction of petroleum fluids by anhydrite in lower ordovician and cambrian carbonate reservoirs is the most likely source of both the h2s and the co2 causing isotopically characteristic pyrite co2 gas and calcite cement h2s and possibly co2 migrated into silurian sandstone reservoirs by cross formational flow the h2s with the same sulphur isotope ratio as ordovician anhydrite was partially lost from the fluid phase by extensive growth of late diagenetic pyrite similarly the co2 was partially lost from the fluid phase by precipitation of late diagenetic calcite the h2s that resulted from tsr underwent reaction with the remaining petroleum resulting in locally elevated organic sulphur concentrations in the petroleum and the progressive adoption of the ordovician anhydrite sulphur isotope ratio

chemometric differentiation of crude oil families in the san joaquin basin california chemometric analyses of geochemical data for 165 crude oil samples from the san joaquin basin identify genetically distinct oil families and their inferred source rocks and provide insight into migration pathways reservoir compartments and filling histories in the first part of the study 17 source related biomarker and stable carbon isotope ratios were evaluated using a chemometric decision tree cdt to identify families in the second part ascendant hierarchical clustering was applied to terpane mass chromatograms for the samples to compare with the cdt results the results from the two methods are remarkably similar despite differing data input and assumptions recognized source rocks for the oil families include the 1 eocene kreyenhagen formation 2 eocene tumey formation 3 4 upper and lower parts of the miocene monterey formation buttonwillow depocenter and 5 6 upper and lower parts of the miocene monterey formation tejon depocenter ascendant hierarchical clustering identifies 22 oil families in the basin as corroborated by independent data such as carbon isotope ratios sample location reservoir unit and thermal maturity maps from a three dimensional basin and petroleum system model five families originated from the eocene kreyenhagen formation source rock and three families came from the overlying eocene tumey formation fourteen families migrated from the upper and lower parts of the miocene monterey formation source rocks within the buttonwillow and tejon depocenters north and south of the bakersfield arch the eocene and miocene families show little cross stratigraphic migration because of seals within and between the source rocks the data do not exclude the possibility that some families described as originating from the monterey formation actually came from source rock in the temblor formation

geologic and geochemical evidence for the nature and development of the middle proterozoic keweenawan midcontinent rift of north america abstract general models of active continental rifting must take into account the large plateau basalt provinces many of which have been precursors of or associated with continental breakup the keweenawan middle proterozoic midcontinent rift mcr of north america 2300 km long is one such major continental rift but it aborted before significant crustal separation was achieved these plateau basalt rifts including the mcr differ from the east african type in being dominated by broad subsidence rather than rift valleys tholeiitic flood basalts rather than alkalic central volcanoes and large positive gravity anomalies geologic and geophysical evidence is reviewed which contradicts some recent models which have been proposed for the development of the mcr the basic causes of the pre rift subsidence the u shaped nature of the structure and the abrupt termination of its activity are obscure a triple junction in the usual sense does not appear to have been formed

the rokelides of west africa pan african aulacogen or back arc basin abstract a reassessment of the stratigraphy structure and metamorphism of the pan african rokelides tectono thermal belt in senegal guinea bissau guinea sierra leone and liberia indicates that the belt developed not as a plate margin collision orogen but as either an aulacogen or a back arc basin oblique to the main trend of the west african fold belt the main southern part of the late proterozoic to mid phanerozoic west african fold belt trends southwestwards via the koulountou belt of senegal and guinea bissau into south america where relics of pan african age occur within the andean cordilleras

marine oil source of the yingmaili oilfield in the tarim basin abstract although a large amount of petroleum has been discovered in the tarim basin the origin of the oils is still disputed yingmaili oilfield was selected as a case study to further examine hydrocarbon generation and accumulation in the basin detailed geochemical studies were conducted to unravel the formation mechanisms the oils in the field correlate well with middle upper ordovician o 2 3 rocks or similar rocks oil oil and oil source rock correlation by maturity parameters of saturate and aromatic hydrocarbons suggest that the yingmaili and adjacent oils are primarily comparable to source rocks deeper than 6000 m the results also showed that carbonates might be important potential source rocks as indicated by a relatively high abundance of aromatic sulfur compounds and relatively high c 29 c 30 hopane and c 35 c 34 hopane ratios of the oils which are typical features of carbonate source rocks we suggest the oil from wells yg2 and yg2 1c are more suitable to be end members from the o 2 3 source rocks or similar rocks than the oil from well ym2 as previously suggested we also suggest that the previous model of hydrocarbon migration along the ordovician unconformity should be revised

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

correlation of crude oils and oil components from reservoirs and source rocks using carbon isotopic compositions of individual n alkanes in the tazhong and tabei uplift of the tarim basin china abstract carbon isotopic compositions were determined by gc irms for individual n alkanes in crude oils and the free adsorbed and inclusion oils recovered by sequential extraction from reservoir rocks in the tazhong uplift and tahe oilfield in the tabei uplift of tarim basin as well as extracts of the cambrian ordovician source rocks in the basin the variations of the 13 c values of individual n alkanes among the 15 oils from the tazhong uplift and among the 15 oils from the triassic and carboniferous sandstone reservoirs and the 21 oils from the ordovician carbonate reservoirs in the tahe oilfield demonstrate that these marine oils are derived from two end member source rocks the major proportion of these marine oils is derived from the type a source rocks with low 13 c values while a minor proportion is derived from the type b source rocks with high 13 c values type a source rocks are within either the cambrian lower ordovician or the middle upper ordovician strata not drilled so far while type b source rocks are within the cambrian lower ordovician strata as found in boreholes td2 and fang 1 in addition the three oils from the cretaceous sandstone reservoirs in the tahe oilfield with exceptionally high pr ph ratio and 13 c values of individual n alkanes are derived or mainly derived from the triassic jurassic terrigenous source rocks located in quka depression the difference of the 13 c values of individual n alkanes among the free adsorbed and inclusion oils in the reservoir rocks and corresponding crude oils reflects source variation during the reservoir filling process in general the initial oil charge is derived from the type b source rocks with high 13 c values while the later oil charge is derived from the type a source rocks with low 13 c values the 13 c values of individual n alkanes do not simply correlate with the biomarker parameters for the marine oils in the tazhong uplift and tahe oilfield suggesting that molecular parameters alone are not adequate for reliable oil source correlation for high maturity oils with complex mixing

multiscale geological geophysical characterization of the epigenic origin and deeply buried paleokarst system in tahe oilfield tarim basin abstract the irregular structures of paleokarst systems are among the major factors resulting in carbonate reservoir heterogeneity which restricts the further exploration of paleokarst reservoirs using multiscale geological geophysical g g data including thin section core sample and well log data the caves cave fillings and fractures in individual wells in the northern tahe oilfield were characterized guided by seismic datasets the interwell paleokarst structures were interpreted in profile and plane view the paleokarst system in the study area was divided into four vertical zones and the relative genetic structures were classified in the upper three zones the epikarst zone includes paleo canyons karst towers dolines paleo soils and fractures and the water flows horizontally the vadose zone includes vadose caves and fractures and the water flows vertically the epiphreatic zone includes chambers main channels branch channels and fractures and the water flows primarily horizontally along the water table for each genetic type the total hydrocarbon production and monthly production were analyzed furthermore a genetic classification model was built for the paleokarst reservoirs of the study area which increased our understanding of the structure of the paleokarst system the results of the structure classification and production analysis can effectively guide hydrocarbon exploration and this approach can be applied to similar paleokarst reservoirs

identification of aryl isoprenoids in source rocks and crude oils biological markers for the green sulphur bacteria abstract a series of c13 to c31 aryl isoprenoids 1 alkyl 2 3 6 trimethylbenzenes have been identified in reef hosted oils and their source rocks from the middle and upper silurian of the michigan basin and middle devonian of the alberta basin canada their structure has been confirmed by unambiguous synthesis of the c14 member of the series their structure and isotopic composition indicate that they are derived from isorenieratene from the chlorobiaceae family of sulphur bacteria these results are consistent with geological and geochemical studies that show that the source rocks were deposited under metahaline to hypersaline sulphate and sulphide rich water columns the distribution of other biomarkers in these oils and source rocks indicates that a diverse biota contributed organic matter to the source environment in conjunction with the aryl isoprenoids they show that there is a remarkable similarity in composition between the two sets of oils and source rocks despite their great temporal and geographic separation this reflects the similarity of their environments and emphasizes the importance of sedimentary facies in controlling the composition of organic matter in source rocks and their derived oils

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

origin and quantitative source assessment of deep oils in the tazhong uplift tarim basin abstract a large amount of deep oil has been discovered in the tazhong uplift tarim basin whereas the oil source is still controversial an integrated geochemical approach was utilized to unravel the characteristics origin and alteration of the deep oils this study showed that the lower cambrian oil from well zs1c 1x was featured by small or trace amounts of biomarkers unusually high concentration of dibenzothiophenes dbts high 34 s of dbts and high 13 c value of n alkanes these suggest a close genetic relationship with the cambrian source rocks and tsr alteration on the contrary the middle cambrian oils from well zs1 2a were characterized by low 13 c of n alkanes and relatively high 34 s of individual sulfur compounds and a general v shape of steranes indicating a good genetic affinity with the middle upper ordovician source rocks the middle cambrian salt rock separating the oils was suggested to be one of the factors responsible for the differentiation it was suggested that most of the deep oils in the tazhong uplift were mixed source based on biomarkers and carbon isotope which contain tsr altered oil in varied degree the percentage of the oils contributed by the cambrian lower ordovician was in the range of 19 100 average 57 controlled by several geological and geochemical events significant variations in the 34 s values for individual compounds in the oils were observed suggesting a combination of different extent of tsr and thermal maturation alterations the unusually high dbts concentrations in the tazhong 4 oilfield suggested as a result of mixing with the zs1c oil 1x and lower ordovician oils based on 34 s values of dbt this study will enhance our understanding of both deep and shallow oil sources in the tazhong uplift and clarify the formation mechanisms of the unusually high dbts oils in the region

geochemistry of palaeozoic marine petroleum from the tarim basin nw china part 1 oil family classification abstract a series of palaeozoic marine oils ranging from condensates to very heavy oils from the cratonic region of the tarim basin nw china have been examined to delineate oil families crude oils from the mesozoic foreland kuqa depression were also analyzed for comparison the genetic family was assessed using bulk hydrocarbon isotopic composition alkylation pattern of polycyclic aromatic hydrocarbons pahs and biomarker distributions detailed oil oil correlation suggests two distinct families occur in the cratonic region despite the diversity of the reservoir rocks and some variability in oil physical properties the tabei and tazhong oils are classified in general into a single family with a possible indication for secondary subdivision these oils are characterized by low pristane phytane pr ph ratio high dibenzothiophene phenanthrene dbt p ratio light bulk isotopic composition high degree of pah alkylation high proportion of c23 and c24 tricyclic terpanes and low abundance of c24 tetracyclic terpane and triaromatic dinosteroids this family is inferred to have a middle upper ordovician source rock the tadong family distinctly different from the tabei and tazhong families is characterized by relatively high pr ph ratio low dbt p ratio slightly heavier bulk isotopic compositions and low degree of pah alkylation it also has a unique biomarker signature with a high proportion of triaromatic dinosteroids possibly indicating cambrian lower ordovician source rocks the oils from the kuqa depression are easily distinguished from the other two families due to their terrigenous origin the major characteristics of the kuqa oils are high pr ph ratio very low dbt p ratio heavy bulk isotopic composition low pah alkylation degree high proportion of c20 and c21 tricyclic terpanes and c24 tetracylic terpane and abundance of triaromatic dinosteranes and 4 methyl 24 ethyltriaromatic cholestanes these characteristics are consistent with terrestrial organic source rocks deposited under sub oxic conditions

identifying the top of the tropical tropopause layer from vertical mass flux analysis and calipso lidar cloud observations 1 we identify the top of the tropical tropopause layer ttl by analyzing the vertical mass flux profile based on radiative transfer calculations employing observed atmospheric profiles and cloud information we find that the top of the ttl is located at 18 7 km 70 mb we have analyzed the calipso lidar cloud observations from june 2006 to february 2007 which indicates that almost no clouds occur above 19 km consistent with the top of ttl based on vertical mass flux analyses the total cloud fractions between 20s and 20n are about 0 05 at 18 5 km 0 5 at 18 0 km and 5 at 17 0 km where the clouds with optical depth larger than 0 5 contribute up to one tenth of these total cloud fractions the clouds above 17 km mainly originate over the west pacific south america central africa and south asia citation fu q y hu and q yang 2007 identifying the top of the tropical tropopause layer from vertical mass flux analysis and calipso lidar cloud observations geophys res lett 34 l 14813

geochemistry of palaeozoic marine petroleum from the tarim basin nw china part 2 maturity assessment abstract the thermal maturity of forty three crude oil samples collected from the cratonic portion of the tarim basin nw china has been assessed using a variety of parameters while compound ratios of diamondoids alkylated naphthalenes methyl phenanthrenes and methyl dibenzothiophenes showed consistent trends with increasing maturity a large discrepancy was observed for the maturity levels of the oils determined from these parameters equivalent vitrinite reflectance values calculated from methylphenanthrene index 1 mpi1 methyldibenzothiophene ratio mdr and methyldiamontane index mdi were in the range of 0 66 0 97 1 11 1 64 and 0 89 1 74 ro respectively while we caution that some of the discrepancy may be related to calibration problems the difference observed from different compound classes could be real reflecting the multiple charge to petroleum accumulations as the diamondoid hydrocarbons were possibly generated at later maturation stages than most aromatic hydrocarbons as diamondoids with methyl substitution on the bridgehead positions are more stable than those with substitution on other positions several compound ratios based on ethyl admantanes dimethyl admantanes trimethyl admantanes and dimethyl diamantanes also correlated with the established maturity indicators such as mdr and mdi while condensates with high maturity levels represent the late charge hydrocarbons some of them with relatively low maturity levels may be affected by evaporative fractionation processes the normal gravity oils cover a wide maturity range consistent with multiple charges and in reservoir mixing while the waxy oils with high apparent maturity levels may be the products of wax precipitation due to a later gas injection into an oil column heavy oils with low apparent maturity levels could be the residue of oil that has lost its light end

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

stereo observations of polar stratospheric clouds 1 we present the first observations of polar stratospheric clouds pscs within near infrared nir satellite images by using the multi angle imaging spectroradiometer misr to stereoscopically identify clouds with altitudes above the tropopause rather than using the operational misr stereo product a tailored stereo height algorithm operating upon misr s most oblique viewing cameras is employed to identify psc cloud top heights retrieved by this algorithm for scenes observed during the 2003 antarctic spring exhibit bias relative to the satellite borne lidar glas of 0 60 1 71 km for low 1 5 km altitude tropospheric clouds 0 35 1 48 km for high 5 km altitude tropospheric clouds and 0 77 1 86 km for low 18 km altitude stratospheric clouds during this period misr captured a sep 30th intensification of psc spanning over 1 million sq km and occurring as the apparent result of synoptic scale isentropic uplift associated with a potential vorticity anomaly tied to planetary waves but likely also strengthened by a nearby tropospheric depression

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

geochemistry of alkylbenzenes in the paleozoic oils from the tarim basin nw china a b s t r a c t monoaromatic hydrocarbons alkylbenzenes in paleozoic oils condensates from the tarim basin were quantitatively analyzed using gas chromatography mass spectrometry their relative abundances and distributions show large variation which are most likely controlled by the temperature and duration of the catagenesis stage of petroleum maturation relatively high abundance of long chain linear substituted alkylbenzenes and alkyltoluenes in the studied samples implies that source rocks of these oils condensates contain high contents of algal material the dominance of dodecylbenzene in these n alkylbenzenes suggests the formation of alkylbenzenes from fatty acids via lactone formation dehydration the 1 2 3 4 tetramethylbenzene temb 1 methyl 3 phytanylbenzene 1 m 3 pyb and aryl isoprenoids are mainly derived from carotenoids produced by chlorobiaceae and their occurrence may indicate a highly reducing depositional environment however the concentration of these compounds diminishes significantly at high maturity with increasing thermal maturity the prominent trend of demethylation of alkylbenzenes is accompanied by shortening of alkyl side chains large variation in the c4 alkylbenzene isomer distribution is also controlled by thermal maturity the 1 2 3 5 temb and 1 2 4 5 temb isomers are more stable than other temb isomers and the overall thermodynamic stability of tembs is lower than that of dimethylethylbenzenes therefore several maturity parameters can be derived based on alkylbenzene stability absolute concentrations of alkylbenzenes generally increase with increasing thermal maturity but concentrations of 1 m 3 pyb and aryl isoprenoids decrease significantly at high maturity maturity parameters obtained from alkylbenzenes are especially useful for highly mature oils and condensates when most biomarkers are depleted caution is advised when interpreting the paleoenvironment and thermal maturity of an oil from the alkylbenzene signatures because they are affected by various other processes such as evaporative fractionation thermal cracking and biodegradation as well

source of 1 2 3 4 tetramethylbenzene in asphaltenes from the tarim basin 1 alkyl 2 3 6 trimethylbenzenes and a high relative amount of 1 2 3 4 tetramethylbenzene ttmb have been previously detected in the marine oils and asphaltenes in the oils from the tarim basin in the present study the stable carbon isotopic compositions of ttmb and n alkanes in the pyrolysates of asphaltenes in the marine oils from the northern tarim basin and silurian tar sands from the tarim basin were determined ttmb has stable carbon isotopic compositions in the range from 23 to 24 and are about 12 more enriched in 13c than concomitant n alkanes 35 to 37 in the pyrolysates the results indicate a contribution from green sulfur bacteria chlorobiaceae to ttmb thus the depositional environments of the source rocks for the marine oils and the bitumen in tar sands from the tarim basin are characterized by periods of euxinic conditions within the photic zone

biomarker geochemistry of crude oils and lower paleozoic source rocks in the tarim basin western china an oil source rock correlation study abstract in order to select biomarker parameters that have potential to quantitatively distinguish between the cambrian lower ordovician and upper ordovician source rocks in the tarim basin with a total organic carbon content 0 5 42 lower paleozoic shale samples were collected from a number of wells and outcrops in the tarim basin northwestern china the biomarkers in the extracts of the source rocks were analyzed by gas chromatography mass spectrometry the results show that c23 and c30 were dominant in the tricyclic terpanes and pentacyclic triterpanes respectively and c27 and c29 were both dominant in c27 29 steranes of the source rock samples the distribution of n alkanes isoprenoids and terpanes indicate that the source rock samples have been slightly to moderately biodegraded and they originated from a reducing depositional environment with considerable marine algal input in comparatively upper ordovician source rock samples presented lower values of c28 c29 regular steranes and higher values of c29 20s 20s 20r and c29 abnormally lower values of c29 20s 20s 20r and c29 were observed in the cambrian lower ordovician strata the set of data in this study show that homohopane index including c31homohopane c30hopane c31 35homohopanes c30hopane and the ratios related to the triaromatic steroids including c26 20s c28 20s tas c27 20r c28 20r c26 20r c27 20s c28 20s and c28 c26 c27 tas could serve as potential biomarker parameters to distinguish between the two groups of source rocks in the tarim basin the values of those parameters in above order in cambrian lower ordovician source rocks were 0 3 0 5 0 85 and 0 8 1 9 1 2 respectively the correlation between the source rock samples and 19 oils obtained from the tadong tabei and tazhong uplifts in the tarim basin show that most of the oils in tabei uplift are probably from upper ordovician source rocks the oils in tadong uplift are more likely from cambrian lower ordovician source rocks and the tazhong uplift is more like a mixed oil region with oils from both of the two groups of source rocks

oil filling history of the ordovician oil reservoir in the major part of the tahe oilfield tarim basin nw china abstract the ordovician oil reservoir in the tahe oilfield northern tarim basin is so far the largest marine oil reservoir in china ordovician oil was sampled from 73 exploration production wells in the oilfield according to oil oil correlation all the ordovician oil samples belong to the same oil population of mature to high mature phase based on the coexisting intact n alkane series evident ucm and 25 norhopanes in the oil as well as the bimodal distribution pattern of homogenization temperatures t h ranging from 80 to 100 c and from 115 to 135 c respectively in fluid inclusions within the reservoir rocks it is concluded that the oil reservoir has been twice charged during its oil filling history by means of 1d basin modeling the measured t h values can be related to relevant geological ages of 429 415 ma and of 8 2 ma respectively i e the middle to late silurian and the miocene to pliocene representing two phases of oil filling and entrapment using independent molecular parameters e g the 4 1 mdbt ratio and total concentrations of pyrrolic n compounds as indicators to reconstruct the oil filling process in the reservoir oil filling pathways can be traced and mapped the general orientation of oil filling is from south to north in the oil reservoir therefore it can be predicted that its source kitchen should be on the south side of the oilfield most probably at the shuntuoguole uplift between the awati and manjiaer depressions

isotopic compositions and biomarkers in crude oils from the tarim basin oil maturity and oil mixing abstract hydrogen and carbon isotopic compositions of n alkanes as well as biomarkers in various types of oil from the tarim basin were analyzed data were used to discuss the occurrence and formation of marine oils from this old composite basin of which we have limited understanding first hydrogen and carbon compositions of n alkanes clearly classify the collected oils into two distinct groups supporting the reported oil classifications based on biomarkers group i the majority of oil samples is characterized by relative enrichment in d and n alkane d values vary from 110 to 75 group ii includes two heavy oils and d values of n alkanes range from 145 to 142 second variations in the 13c value of n alkanes 2 3 show good correlations with the maturity indices indicating that kinetic isotopic fractionation is one control on the 13c value of n alkanes in the maturation process d values of n alkanes in most oils are also evidently influenced by the oil maturity finally by combining the isotopic compositions with biomarkers of oils two distinct oil mixing processes were recognized in the oils from the tabei and tazhong uplifts in this old composite basin the former process is the mixing of oils from the same source at different maturity stages while the latter involves the mixing of oils from distinct sources at different maturity stages biodegraded oils may contribute to the total oils but their proportions are minor

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

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

geochemistry and possible origin of crude oils from bashituo oil field tarim basin the entire range of hydrocarbons in bashituo oils from devonian and carboniferous reservoirs were investigated to determine their origin as well as their alteration mixing and maturity using gas chromatography gas chromatography mass spectrometry and stable carbon isotope analysis these geochemical studies indicate that the crude oils in the devonian and carboniferous reservoirs share similar c15 molecular marker compositions of marine organic matter origin whereas their light hydrocarbon compositions show distinct differences the carboniferous reservoired oils are characterized by a relatively greater abundance of cycloalkanes and methylcyclohexane which indicate a terrestrial organic matter om contribution based on biomarker and carbon isotope analysis cambrian ordovician j o marine rocks are assumed to be the main source for both the devonian and carboniferous reservoired oils whereas carboniferous rocks with terrestrial om input also contributed to the carboniferous reservoired oils the coexistence of 25 norhopanes evident humps from unresolved complex mixture and intact n alkanes in devonian reservoired oils indicate a mixture of early charged biodegraded oils with late fresh oils corresponding to at least two oil generation episodes by the j o rocks light hydrocarbon indicators suggest a relatively high maturity beyond peak oil generation for the j o sourced late fresh oil whereas c15 molecular marker parameters indicate a maturity equivalent to early peak oil generation for the j o sourced early charged biodegraded oil the maturity of the carboniferous sourced oil is equivalent to peak oil generation the application of the entire range of hydrocarbons is essential when assessing a mixed or altered oil system because light hydrocarbons and biomarkers may yield different source oil correlations and maturities

evaluation method and application of the relative contribution of marine hydrocarbon source rocks in the tarim basin a case study from the tazhong area abstract in total 2 37 million tons of marine crude oil originating from mixed source rocks has been discovered in the tarim basin geological and geochemical analyses have confirmed that these mixed hydrocarbons are mainly from two sets of source rocks including the cambrian lower ordovician and middle upper ordovician hydrocarbon source rocks in this study we determined the set of source rocks primarily responsible for the mixed hydrocarbons and the next location to be explored differences in n alkane carbon isotopes in end member oils from cambrian lower ordovician and middle upper ordovician source rocks were examined a material balance model and simulation methods were used to evaluate the relative amounts contributed by each source the results from known reserves in the tazhong area show that the mixing ratio or contribution is up to 65 from cambrian lower ordovician source rocks and is generally higher than that from middle upper ordovician source rocks the discovery of deep hydrocarbons has caused the total oil contribution from the cambrian lower ordovician to increase the mixing ratio of cambrian lower ordovician oil varies depending on the well formation and block it increases from west to east horizontally and from top to bottom vertically hydrocarbons from cambrian lower ordovician source rocks migrate upward along faults and the mixing ratio decreases as the distance from the oil source fault increases favorable areas for cambrian lower ordovician hydrocarbon exploration are deep layers and areas near the fault zone that are connected to deep layers the material balance model for carbon isotopes and evaluation methods for relative contributions considered differences in relative concentration and carbon isotope structure of n alkanes herein new methods for the identification and evaluation of hydrocarbons in the petroleum system of this superimposed basin are presented

comparison of the calipso satellite and ground based observations of cirrus clouds at the arm twp sites 1 statistics of ice cloud macrophysical and optical properties from the cloud aerosol lidar with orthogonal polarization caliop instrument on board the cloud aerosol lidar and infrared pathfinder satellite observations calipso satellite are compared with those from ground based lidar observations over a 31 month period ground based lidar observations are taken from the micropulse lidars mpl at the three department of energy atmospheric radiation measurement arm tropical western pacific twp sites manus nauru and darwin calipso observations show a larger cloud fraction at high altitudes while the ground based mpls show a larger cloud fraction at low altitudes the difference in mean ice cloud top and base heights at the manus and nauru sites are all within 0 51 km although differences are statistically significant mean ice cloud geometrical thickness agree to within 0 05 km at the manus and nauru sites larger differences exist at darwin due to excessive degradation of the mpl output power during our sampling period both sets of observations show thicker clouds during the nighttime which may be real but could also be partially an artifact of the decreased signal to noise ratio during the daytime the number of ice cloud layers per profile are also shown to be consistent after accounting for the difference in spatial resolution for cloud optical depths four different retrieval methods are compared two for each set of observations all products show that the majority of ice cloud optical depths 60 fall below an optical depth of 0 2 for most comparisons all four retrievals agree to within the uncertainty intervals we find that both calipso retrievals agree best to ground based optical depths when the lidar ratio in the latter is retrieved instead of set to a fixed value also thoroughly compared is the cloud properties for the subset of ice clouds which reside in the tropical tropopause layer ttl

chlorobiaceae in palaeozoic seas revealed by biological markers isotopes and geology biomarker hydrocarbons in oils and sediments have considerable potential for assessing the nature of biological processes in the past but only a few can be uniquely related to particular organisms reef hosted oils in the silurian of the michigan basin canada and the devonian of western canada have high abundances of 1 alkyl 2 3 6 trimethylbenzenes their precise structures suggest that they are diagenetic products of aromatic carotenoids of the green sulphur bacteria individual components are enriched in 13c by 7 8 relative to the saturated hydrocarbons of the same oil an isotopic anomaly of this magnitude and direction correlates with a component of photosynthetic carbon assimilation by the reductive tricarboxylic acid cycle these results together with data on palaeoenvironments provide compelling evidence for the existence in ancient restricted seas of microbial communities containing chlorobiaceae organisms with distinctive biochemistry which leave morphologically identifiable remains

cirrus observations in the tropical tropopause layer over the western pacific 1 a polarization lidar was continuously operated aboard the research vessel mirai in the tropical western pacific over three northern winters at 2 0 n 138 0 e during november and december 2001 at 2 0 n 138 5 e during november and december 2002 and at 7 5 n 134 0 e during december 2004 and january 2005 intensive radiosonde soundings were made from the vessel at 3 h intervals during all three campaigns the mechanisms that underlie the observed variations in cirrus in the tropical tropopause layer ttl are discussed from the viewpoint of large scale dynamics and transport during the 2001 campaign the tropopause region was cold but the ttl was often clear with only some subvisual cirrus potential vorticity data and trajectories show that the ttl during this period was strongly affected by dry air transport from the northern midlatitude lower stratosphere during the 2002 campaign a packet of large amplitude equatorial kelvin waves was the primary control on the generation and disappearance of cirrus in the ttl during the 2004 2005 campaign a cold phase of large scale waves resulted in cirrus generation in the ttl in late december of 2004 similar to that observed during the 2002 campaign outflow from the south pacific convergence zone spcz caused optically thick cirrus in the ttl particularly during early january 2005 when we also observed regular diurnal variations in cirrus development within the ttl that is apparent sedimentation during the nighttime we investigated two possible controlling processes namely horizontal advection together with diurnal variations in convective activity within the spcz and diurnal variations in local temperature due to tides and gravity waves in the equatorial western pacific equatorial kelvin waves are the important dynamical process that controls cirrus variations in the ttl dry air horizontal transport from the midlatitude lower stratosphere and wet air vertical transport near the tropical convergence regions should also be considered in fully explaining the cirrus observations in the ttl

aromatic hydrocarbon composition of the permian kupferschiefer in the lower rhine basin nw germany the aromatic hydrocarbon composition of 25 samples of permian kupferschiefer from the lower rhine basin of nw germany has been investigated using gc gc ms and direct probe ms analysis two narrow sampled profiles were investigated with respect to compositional changes during kupferschiefer sedimentation and samples from 13 different wells covering a depth range from 350 to 1000 m were included in order to study temperature sensitive variations in the kupferschiefer trimethyl substituted aryl isoprenoids in the range from c11 to c21 occur these compounds presumably are degradation products of isorenieratane which is also present in the extracts within the profile the amount of a preferentially occuring c29 chroman increases from the bottom to the top of the kupferscheifer by a factor of about 2 5 the chroman distribution observed in the kupferschiefer points towards euhaline to mesohaline seawater during sedimentation moreover in the investigated profiles a terrestrial source input mainly in the bottom most part of the shale is reflected by the occurrence of a monoaromatic c24 chrysene derivative presumably derived from ring a degradation of pentacyclic triterpenes

geochemistry of paleozoic marine petroleum from the tarim basin nw china part 5 effect of maturation tsr and mixing on the occurrence and distribution of alkyldibenzothiophenes abstract fifty four oils and 20 gas condensates from the cratonic region of the tarim basin nw china were quantitatively analyzed by gas chromatography mass spectrometry to elucidate the influence of thermal maturation multiple charges and mixing and thermochemical sulfate reduction tsr on the relative distributions of alkyldibenzothiophenes dbts vs alkylphenanthrenes which are widely used to interpret depositional environment and lithology concentrations of dbts relative to dbts in the aromatic hydrocarbon fraction and ratios of dibenzothiophene phenanthrene dbt p exhibit wide variations in the studied samples field observations coupled with a suite of oil sand pyrolysis experimental results suggest that dbts are more easily released from kerogen and or asphaltenes and are more easily destroyed in oil than the alkylphenanthrenes the dbt p ratio initially increases during early maturation and then decreases in the post mature stage concentrations of dbts are low in samples from the cratonic region of the tarim basin most samples have dbt p ratios

stable carbon isotope compositions of crude oils application to source depositional environments and petroleum alteration the carbon isotopic composition of the c15 saturate and aromatic hydrocarbon fractions and the gas chromatographs of the c15 saturate fraction of 339 oils were geochemically and statistically evaluated results of this study show that the average isotopic compositions of the c15 aromatic hydrocarbon fractions of oils sourced from terrigenous or marine organic matter are identical the average isotopic composition of the c15 saturate fraction of oils derived from terrigenous organic sources is slightly more negative 0 9 pmil than the average for marine oils but this difference is insufficient to be used as a reliable source indicator reports in the literature stating that marine oils are isotopically more positive than te rigenous oils and that the difference can be utilized to distinguish between the two are therefore not supported by this study the isotopic differences between oils sourced from terrigenous and marine organic matter do not manifest themselves in the range of absolute values of one oil fraction but rather in the isotopic relationship between the saturate and aromatic hydrocarbon fractions the isotopic relationship is the following oils of terrigenous organic source dgr13caro 1 12 dgr13csat 5 45 oils of marine organic source dgr13caro 1 10 dgr13csat 3 75 the difference between the two equations was evaluated statistically and a statistical parameter cv the canonical variable cv 2 53 dgr13csat 2 22 dgr13caro 11 65 was used to distinguish between marine and terrigenous oils cv values larger than 0 47 indicate predominantly a terrigenous organic source for the oil whereas cv values smaller than 0 47 indicate mostly a marine organic source thermal maturity differences in oils and isotopic variations in the source beds can cause as much as 2 pmil variations in the isotopic composition of one family of oils finally stable carbon isotopes can in some situations help correlate biodegraded oils to their nondegraded counterparts

the application of diamondoid indices in the tarim oils this study presents new data for the identification of the source and assessment of the thermal maturity of oils based on the diamondoid indices of oils from the tazhong and luntai uplifts in the tarim basin in northwest china the oil samples were divided into three groups according to biomarker characteristics and the abundance and distribution of diamondoids group i oils are located along the tazhong no 1 fault zone which contained abundant diamondoids and are of high thermal maturity suggesting they are late charged hydrocarbons that were derived from a middle upper ordovician source group ii oils are mainly located in blocks close to the tazhong no 1 fault zone and are dominated by early formed hydrocarbons from cambrian lower ordovician source rocks group iii lacustrine oils comprise relatively low concentrations of diamondoids compared with group i and group ii oils group iii oils were sourced from jurassic or possibly triassic units and are hosted by the low relief yingmaili section of the luntai uplift the thermal maturity of the oils in each group was evaluated using diamondoid parameters a few group i oils exhibit intense thermal cracking to estimate the extent of oil cracking using the concentrations of diamondoids in oils this study proposes a practical approach that facilitates the determination of baseline 4 and 3 methyldiamantane concentrations application of this method indicates that the tarim basin marine oils contain a baseline concentration of approximately 69 ppm

aryl isoprenoids and diaromatic carotenoids in paleozoic source rocks and oils from the western canada and williston basins abstract aryl isoprenoids in the range c13 c31 have been identified in source rock bitumens and oils from several paleozoic age petroleum systems in the western canada and williston basins the principal compounds possess the 2 alkyl 1 3 4 trimethyl substitution pattern characteristic of diaromatic carotenoids found in the chlorobiaceae family of photosynthetic sulfur bacteria two c40 perhydrodiaromatic carotenoids which are structurally related to the presumed precursors of the aryl isoprenoids have also been identified in oils and source rock bitumens of the duvernay late devonian petroleum system pyrolysis gas chromatograms of kerogens isolated from several paleozoic source rocks show an unusual abundance of 1 2 3 4 tetramethylbenzene it is proposed that this compound arises from cleavage of diaromatic carotenoid moieties which have been incorporated into the kerogen structure with increasing maturation concentrations of the aryl isoprenoids in duvernay source rock bitumens increase to a point whereas the c40 perhydrodiaromatic carotenoids decrease steadily previous studies have suggested that aryl isoprenoids may be indicators of enhanced salinity environments this is not supported by the present work which shows high concentrations in source rocks associated with presumed normal marine salinities there is however a general association with intervals of condensed clastic or mixed clastic carbonate sedimentation within carbonate depositional systems from the association found and from parallels to modern habitats of photosynthetic bacteria it can be inferred that these biomarkers indicate prolific bacterial growth in a stratified water column at and below the oxic anoxic boundary layer in sub tropical to tropical marine environments

new investigations in southwestern guinea consequences for the rokelide belt west africa the southern guinean terranes belong to the rokelide belt that is located in the southwestern part of the west african craton senegal to liberia field investigations and k ar and 40ar 39ar radiometric analysis performed on samples collected from southern guinea provide a new interpretation for metamorphic terranes not yet dated a k ar whole rock age of a gneiss and 40ar 39ar plateau ages of amphiboles separated from a mylonitic gneiss of the ouankifondi formation and a gneiss from the kissi kissi formation yield several pan african metamorphic ages at circa 650 560 and 530 ma respectively field investigations show that these formations are unconformably capped by the kolente group the previous structural framework and the geodynamic evolution of the rokelide belt based on the coeval evolution of the ouankifondi and kissi kissi formations and the kolente group are reassessed the rokelide belt is linked to the bassaride belt correlations with adjacent sierra leonean terranes and with northern guinea and senegal are considered

geochemistry of paleozoic marine oils from the tarim basin nw china part 4 paleobiodegradation and oil charge mixing abstract fifty three oil samples from paleozoic marine reservoirs of the tarim basin were analyzed by gc fid and gc ms to elucidate the influence of biodegradation and mixing on molecular compositions biodegradation has a major impact on many classes of compounds but the ultimate compositions and physical properties of the oil are influenced strongly by mixing with late oil charge subsequent to the process of biodegradation almost all samples display biodegradation signatures characterized by variable size of the unresolved complex mixture ucm and variable amounts of 25 norhopanes 25 nhs and 17 nortricyclic terpanes 17 nts the ubiquitous occurrence of n alkanes suggests that the petroleum accumulated in these fields is mainly a mixture of previously biodegraded oils with later migrated fresh oils the unaltered late charge of oil which has commingled with the initial biodegraded charge gives the wide range of oil gravities and asphaltene contents observed most commonly used maturity and depositional environment diagnostic parameters in the saturated hydrocarbon fraction are affected by biodegradation based on the intensity of 25 nhs and 17 nts oils from the tabei uplift appear to have experienced a much greater degree of biodegradation than those from the tazhong uplift however we caution against the simplistic use of molecular indicators to define a specific level of biodegradation in this case study as it may be somewhat misleading for physical property prediction a wide range of estimated maturity values from different components provides an important clue for multiple charge and mixing interpretations the relationship between the absolute concentrations of compound class and peak hump ratios of the samples can potentially qualitatively differentiate the pulse of inputs to the mixed oils the positive correlation between the concentrations of a given compound class and peak hump ratios may suggest that that class of compounds is most likely derived from the late charge after biodegradation while the negative correlation may indicate compounds largely inherited from the early charge before biodegradation some compounds show almost no correlation between their concentrations and peak hump ratios implying more similar intensity of charge inherited from early pulse and amalgamated from later pulses in some extremely biodegraded cases where ucm hump can also be diminished not in present case study the correlation between compound class concentrations and peak hump ratios will be more complicated

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

chemometric recognition of genetically distinct oil families in the los angeles basin california the prolific los angeles basin in california may be the most petroliferous province on earth per volume of sedimentary fill however because most exploration in the basin occurred prior to the advent of modern geochemical methods genetic relationships among the various petroleum accumulations and their source rocks have remained speculative a training set of 24 source related biomarker and stable carbon isotope ratios for 111 non or mildly biodegraded oil samples from the basin was used to construct a chemometric multivariate statistics decision tree the decision tree allows genetic classification of additional oil or source rock extract samples that might be collected the decision tree identifies 6 tribes and a total of 12 genetically distinct oil families the families have different bulk properties such as api gravity and sulfur content which were previously explained as resulting from secondary processes including thermal maturity or biodegradation however the chemometric assignments are based on genetic properties that reflect distinct organofacies the oil families occur in different locations and reservoir intervals in the basin consistent with their origins from different organofacies of active source rock the source rock depositional environment for each oil family can be inferred using biomarker and isotope ratios the samples show stable carbon isotope ratios for saturate and aromatic hydrocarbons that indicate different organofacies of miocene marine source rocks tribes 1 and 2 straddle the central trough mainly occur east of the newport inglewood fault zone nifz and show evidence of proximal clay rich source rock deposited under suboxic conditions with elevated angiosperm input tribes 3 6 occur west of the nifz and show evidence of more distal clay poor source rock deposited under anoxic conditions geochemistry and stratigraphy of the oil tribes 1 6 below suggest the following source rock organofacies

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

effects of source thermal maturity and biodegradation on the distribution and isomerization of homohopanes in petroleum abstract the distributions of c31 c35 17 21 h homohopanes in marine petroleums can be used to describe redox conditions in the source rock depositional environment for example high c35 homohopane indices c35 c31 c35 are typical of petroleums generated from source rocks deposited under anoxic marine conditions where the c35 backbone of the precursor bacteriohopanetetrol is preferentially preserved homohopane distributions have been used to distinguish petroleums from different organic facies of the same source rock homohopane distributions are altered by secondary processes for example the c35 homohopane index decreases with increasing api gravity and thermal maturity of related oils from the monterey formation offshore california similar decreases in the homohopane index are observed for expelled oils from monterey source rock during hydrous pyrolysis biodegradation can result in selective loss of high or low molecular weight homologs apparently depending on the bacterial population in the reservoir bacterial demethylation of homohopanes appears necessary to explain 25 norhopanes in at least one biodegraded oil hydrous pyrolysis studies of the phosphatic and siliceous members in the monterey formation show that identical heating conditions result in different homohopane c 22 epimer ratios furthermore a reversal in the trend of the epimer ratio at high experimental temperatures is observed for the phosphatic but not for the siliceous lithology this could be caused by the combined effects of isomerization and differential thermal destruction of epimers at high temperatures possibly mediated by rock mineralogy