high diahopane and neohopane abundances in a biodegraded crude oil from the barrow sub basin of western australia abstract three crude oils from the barrow sub basin of western australia have been analysed for hopanoid biomarkers using gc ms techniques enhanced abundances of nordiahopane and diahopane and norneohopane relative to hopanes have been observed in the most severely biodegraded sample these differences have been attributed to the greater resistance of the diahopanes and norneohopane to microbial degradation

a geochemical reconstruction of oil generation in the barrow sub basin of western australia abstract a suite of crude oils and petroleum source rock extracts from the barrow sub basin of western australia have been analysed for biological marker compounds by capillary gc ms and for volatile hydrocarbons by whole oil capillary gc these analyses were used to calculate values for twenty three biomarker parameters in order to assess aspects of source type maturity migration and biodegradation of the hydrocarbons the crude oils had a source in the upper jurassic dingo claystone formation these hydrocarbons accumulated in the reservoir sands and in some cases were biodegraded several accumulation and biodegradation episodes have been recognised while the basin continued to subside which resulted in a suite of oils showing marked differences in composition

biodegradation and possible source of silurian and carboniferous reservoir bitumens from the halahatang sub depression tarim basin nw china abstract five core samples comprising three silurian and two carboniferous bituminous sandstones from the halahatang sub depression tarim basin nw china were studied to determine the nature and extent of microbial alteration and possible source s of the reservoir bitumens a total of twelve ordovician crude oil samples from this sub depression were also examined for comparative purposes co occurrence of a series of 25 norhopanes nhs c 28 c 34 variable amounts of chromatographically unresolved complex mixture ucm and diminished concentrations of n alkanes below ca c 20 in saturated hydrocarbon fractions of the silurian and carboniferous bitumens indicates that they are mixtures of heavily biodegraded oil from a former charge and slightly biodegraded oil from a later charge the presence of c 28 c 34 25 nhs suggests a biodegradation level of at least pm 6 for these bitumen samples nevertheless minor differences in terpane and sterane distributions between the silurian and carboniferous bitumen samples were observed which can be attributed to small variations in biodegradation levels values for the 25 nh ratio peters et al 1996 gammacerane gammacerane c 30 hopane c 28 25 nh c 29 hopane and c 29 25 nh c 30 hopane ratios indicate slightly higher levels of microbial alteration for the silurian bitumens compared to the carboniferous bitumens although caution must be exercised when comparing the biodegradation intensities using molecular parameters the ordovician crude oil samples appear to be more severely biodegraded than the silurian and carboniferous bitumens as evidenced by higher concentrations of tricyclic terpanes relative to hopanes and pregnanes and diasteranes relative to the regular steranes although thermal maturity effects cannot be ruled out geochemical correlation studies were successfully applied based on carbon isotopes and biomarkers including tricyclic terpanes and triaromatic steroids which are highly resistant to severe biodegradation pm 6 bulk isotopic compositions distribution patterns and certain ratios of these biomarkers indicate that the ordovician crude oils and the silurian and carboniferous bitumens originated from a single source they were probably derived from middle upper ordovician source rocks

analysis of secondary migration of hydrocarbons in the ordovician carbonate reservoirs in the tazhong uplift tarim basin china the process and mechanisms of secondary hydrocarbon migration in the tazhong uplift tarim basin were investigated based on the analysis of the regional structure and by integrating geologic hydrodynamic and geochemical parameters parameters successfully analyzed included the fluid potential fluid properties production outputs and diamantane index the results indicated that hydrocarbons migrated into the tazhong uplift from the northern part of the manjiaer depression through a series of injection points ips during four orogenies that is the early caledonian 510 ma the late caledonian 439 ma the late hercynian indosinian 290 ma and the yanshanian himalayan 208 ma a total of six ips were identified at the intersections of the northeast trending faults and the northwest trending flower strike faults the hydrocarbons migrated from the ips into traps along regional trends from northwest to southeast and from northeast to southwest the hydrocarbon migration process and patterns determined the distribution of hydrocarbon properties and production rates in the tazhong uplift with increasing distance from the ips daily hydrocarbon production decreases and the hydrocarbons become progressively heavier and display lower gas oil ratios

application of diamondoids to distinguish source rock facies abstract diamondoid distributions in solvent extracts from marine siliciclastic shales marine carbonates and coals of a wide variety of maturities were determined by gc msd for this sample set published diamondoid maturity parameters did not change systematically throughout the oil window it was found that several novel diamondoid ratios were indicative of source it was possible to distinguish between terrigenous marine carbonate and marine siliciclastic facies the proposed dimethyl diamantane facies ratios are virtually unaffected by maturity while the ethyl adamantane ratio appears to be affected by maturity in the late gas window range

the abundance and distribution of diamondoids in biodegraded oils from the san joaquin valley implications for biodegradation of diamondoids in petroleum reservoirs abstract the biodegradability of diamondoids was investigated using a collection of crude oil samples from the san joaquin valley california that had been biodegraded to varying extent in the reservoir our results show that diamondoids are subjected to biodegradation which is selective as well as stepwise adamantanes are generally more susceptible to biodegradation than other diamondoids such as diamantanes and triamantanes we report a possible pathway for the microbial degradation of adamantane this cage hydrocarbon possibly breaks down to a metabolic intermediate through the action of microbes at higher levels of biodegradation in petroleum reservoirs microbial alteration has only a minor effect on diamondoid abundance in oil at low levels of biodegradation our results suggest that most diamondoids with the exception of adamantane are resistant to biodegradation like the polycyclic terpanes e g c19 c24 tricyclic terpanes hopanes gammacerane oleananes ts tm c29 ts steranes and diasteranes microbial alteration of diamondoids has a negligible impact on the quantification of oil cracking achieved using the diamondoid biomarker method

evaluating the recharge mechanism of the lower kuiseb dune area using mixing cell modeling and residence time data summary a mixing cell approach was extended by a method incorporating mean cell residence times derived from 14c to further constrain and validate the modeling results this extended approach was used to model the groundwater system of the lower kuiseb dune area in namibia the kuiseb river is a 560 km long ephemeral river that crosses the namib desert from east to west transmission losses from the riverbed during flood events are an important source of groundwater recharge to the underlying aquifer system the lower kuiseb area is located in a hyper arid region with annual precipitation less than 25 mm yr hydrochemical data from 13 wells in the area were used in the mixing cell model mcm end members were identified as sources for the groundwater found in the lower kuiseb including inflow from the crystalline basement plateau north of the kuiseb as well as floodwater from the kuiseb river a conceptual groundwater recharge and flow model was developed and then inverse mixing cell modeling was carried out using hydrochemical tracers this approach generally allows for several possible solutions after completing the inverse modeling a forward mixing cell model was developed by varying the mean residence time of each cell to fit calculated 14c data to the measured 14c data this new approach joins previously developed methods solely based on conservative mixing or residence time optimization based on the results of the model the fraction of floodwater in different sections of the lower kuiseb groundwater systems was calculated ranging from 61 to 98 2 in addition to floodwater groundwater inflow from the crystalline basement north of the kuiseb was shown to contribute to the lower kuiseb aquifer accounting for salinization during periods without flooding

identifying multiple sources of petroleum fluids in browse basin accumulations using diamondoids and semi volatile aromatic compounds abstract hydrocarbon fluid correlation studies often rely on compounds that are source specific but only represent a minor fraction of the bulk fluid e g steranes the correlation in the present study utilises compounds that represent a significant proportion of the bulk fluid namely semi volatile aromatics sva and diamondoids comprehensive two dimensional gas chromatography coupled to time of flight mass spectrometry gc gc tofms was used to analyse diamondoids and sva in whole oil condensate samples from the browse basin north west shelf australia together with aromatic maturity ratios and the stable carbon isotopic composition for selected diamondoids and alkylbenzenes these analyses demonstrate that numerous accumulations within the browse basin contain hydrocarbons from mixed sources the diamondoid and sva data provides further information on the current hydrocarbon fluid discrimination which is primarily based on saturated biomarker compositions results of this study reveal a complex fill history by identifying the presence of a high maturity fluid s in the biodegraded accumulations on the yampi shelf i e in the greater cornea field and at gwydion 1 this high maturity fluid is most likely derived from the lower middle jurassic plover formation j10 j20 supersequences in the greater cornea area and in the case of gwydion 1 additional hydrocarbons may also be derived from the upper jurassic vulcan formation j30 k10 supersequences other accumulations that comprise mixtures include mimia 1 and concerto 1 st1 deep located to the north of the ichthys field and could represent charge from several jurassic source rocks the most mature fluids analysed in this basin are family ii plover sourced and reservoired condensates from kronos 1 dinichthys north 1 and gorgonichthys 1 as demonstrated by their elevated concentrations of the methyladamantanes and methyldiamantanes the dinichthys north 1 and gorgonichthys 1 condensates also show a significant enrichment in the 13c compound specific values of the di tri and tetra methylbenzenes whereas the kronos 1 condensate does not suggesting derivation from different source kitchens

alkylbiphenyls and alkyldiphenylmethanes as indicators of petroleum biodegradation abstract gas chromatographic mass spectrometric analyses of alkylbiphenyls and alkyldiphenylmethanes have been performed on a series of crude oils reservoired in the gippsland basin australia as well as in some marine coastal sediments contaminated with a condensate changes in the isomeric distribution of the alkylbiphenyls and alkyldiphenylmethanes with increasing biodegradation were investigated the relative abundance and distributions of the isomers were found to change significantly with increasing biodegradation isomers with the 4 substituent s generally increase in abundance relative to isomers that lack this feature thus alkylbiphenyl and alkyldiphenylmethane isomeric distributions are useful indicators of the extent of petroleum biodegradation in reservoirs and surface sediments it is suggested that geosynthetic processes and or relative susceptibilities of certain isomers to microbial attack can account for changes in the isomeric distribution of these components with increasing biodegradation significant differences in the relative abundances of the methylbiphenyls are apparent and are probably due to variations in the conditions that the petroleum had been subjected to in the two contrasting environments

25 norhopanes formation during biodegradation of petroleum in the subsurface abstract quantitative data from petroleum systems in china liaohe basin and canada athabasca tar sands support the theory that 25 norhopanes are produced during biodegradation of petroleum in the subsurface within a single oil column both case histories showed increasing severity of degradation indicated by destruction of hopanes and production of 25 norhopanes downward to the oil water contact in the athabasca samples between the peters k e moldowan j m 1993 the biomarker guide interpreting molecular fossils in petroleum and ancient sediments prentice hall englewood cliffs new jersey p 363 scale of biodegradation levels 5 9 concentrations of c 28 20s triaromatic steroids and other biodegradation resistant compounds increased by 35 reflecting a concentration effect as a consequence of removal of more degradable compounds over the same interval the concentrations of c 28 17 25 norhopane and c 29 17 25 norhopane increased by an order of magnitude thus requiring that the balance be met by their net production during degradation a detailed molecular investigation of the athabasca bitumen revealed that c 30 17 hopane degrades faster than c 29 17 hopane whilst the rate of formation of both c 29 17 25 norhopane and c 28 17 25 norhopane are similar complicating a straightforward interpretation of demethylation of hopanes to form 25 norhopanes hopane degradation in the athabasca tar sand may also occur without the production of 25 norhopanes the results show that even within a single petroleum accumulation a number of mechanisms control changes in the abundance and composition of hopanes and 25 norhopanes

diamondoid hydrocarbon ratios novel maturity indices for highly mature crude oils abstract diamondoid hydrocarbons have been identified in oil and source rock samples from the tarim yinggehai qiongdongnan and other chinese basins two diamondoid hydrocarbon ratios have been used as novel high maturity indices to evaluate the maturation and evolution of crude oils and condensates in these chinese basins the two ratios 1 ma 1 ma 2 ma mai methyl adamantane index and 4 md 1 md 3 md 4 md mdi methyl diamantane index were found to increase with increasing vitrinite reflectance the initial values for the ratios are ca 50 and 30 respectively diamondoid hydrocarbons are products of rearrangement of polycyclic hydrocarbons and their ratios are found to be affected by organic input to a minor extent based on this study crude oils from the tarim basin are generally believed to be very mature ro 1 1 the cambrian ordovician source beds are the major source rocks of crude oils and natural gases in this basin condensates from the tarim yinggehai and qiongdongnan basins have higher maturities equivalent to ro values of 1 6 2 0 gases and condensates from the yinggehai and qiongdongnan basins are generated mainly from tertiary source rocks below 4000 5000 m

quantitative diamondoid analysis indicates oil cosourcing from a deep petroleum system onshore niger delta basin the niger delta basin is one of the most prolific hydrocarbon provinces in the world yet the origin of the vast amounts of oil and gas found in the numerous sub basins across the delta remains contested a total of 180 oil samples from more than 40 oil fields in the niger delta were analyzed by gas chromatography gc gc mass spectrometry gc ms and selected samples by gc tandem mass spectrometry gc msms the interpreted thermal maturity and source depositional environments of these hydrocarbons show significant variation depending on the components analyzed and allow no clear correlation to a single source rock but rather imply extensive mixed contributions diamondoid hydrocarbon parameters were used for the first time on these paleogene neogene reservoired oils to investigate source thermal maturity and mixing effects and to perform cross correlations of these oils the diamondoid abundances and distributions support the hypothesis of co sourcing of oil from a thermally cracked sub delta type ii marine source which was then mixed with oils of relatively lower maturities in the paleogene neogene reservoirs future geochemical interpretations should treat the niger delta oils as potential mixtures of oils of variable maturities from different sources often with the most important source biomarkers depleted because of the extent of thermal cracking

reservoir alteration of crude oils in the junggar basin northwest china insights from diamondoid indices abstract reservoir alteration of crude oils is ubiquitous in petroleum reservoirs alteration can change the composition and physicochemical properties of crude oils and complicate oil source correlations and origin studies of crude oils thus the identification and assessment of reservoir alteration could provide a better understanding of the formation and evolution of crude oils in this study the effects of reservoir alteration e g biodegradation gas washing water washing and mixing on oils in the junggar basin northwest china were identified and assessed by combining diamondoid indices with other commonly studied crude oil properties the results indicate that 1 diamondoid indices can be used to evaluate the intensity of reservoir alteration on oils e g slight biodegradation and water washing has no effect on diamondoids moderate biodegradation and water washing can result in a marked increase in diamondoid concentrations severe biodegradation and water washing significantly changes diamondoid concentration and isomerization ratios 2 diamondoid indices can assist in determining the type of reservoir alteration of oils e g condensate formed by gas washing has a lower diamondoid concentration than that generated by thermal cracking differing from biodegradation and water washing gas washing can affect diamondoid ratios mixing can be identified by a combination of diamondoid concentrations and other parameters such as api gravity and biomarker indices in oils therefore diamondoids provide specific information as to the reservoir alteration of oils which is useful in further understanding of the origin and evolution of crude oils in the junggar basin

source and thermal maturity of crude oils in the junggar basin in northwest china determined from the concentration and distribution of diamondoids abstract here we discuss three types of diamondoid parameters for oils from the junggar basin these are absolute concentrations concentration ratios and isomerization ratios according to the absolute diamondoid concentrations the oils collected from different areas of the basin were broadly divided into three maturity stages 1 low mature 1000 ppm adamantanes 50 ppm diamantanes the oils in the northwestern region of the junggar basin are in the low mature to mature stages based on a combination of diamondoid concentration ratios and biomarker indices these oils can be divided into three groups i e group i oils in the wuxia zone derived from the lower permian fengcheng formation p1f group ii oils in the kebai zone sourced from middle permian lower wuerhe formation p2w and group iii oils in the mahu depression generated from more mature source rocks of jiamuhe formation p1j or the p1f diamondoid concentrations and isomerization ratios were used to precisely evaluate the thermal maturity of mature oils and highly mature condensates respectively our results indicate that the oils in the central part of the basin have decreasing thermal maturity from south to north whereas the oils in the kelameili area display increasing thermal maturity from east to west in this study we found that different diamondoid indices are useful only in certain thermal maturity ranges therefore at least for the junggar basin it is crucial to know which thermal region one is in before using diamondoid ratios for maturity assessment

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

diamondoid hydrocarbon ratios as indicators of biodegradation in australian crude oils the effect of biodegradation on diamondoid distributions in petroleum has been investigated on a series of crude oils reservoired in two australian sedimentary basins the gippsland basin and the carnarvon basin the ratio of methyladamantanes to adamantane rises with increasing biodegradation significant changes in the ratio occur at extreme levels indicating that diamondoids can be indicators of petroleum biodegradation especially when most other hydrocarbons have been removed the methyladamantane adamantane ratio can also be used to assess the composition of crude oils that are comprised of a mixture of severely biodegraded and non biodegraded oil

generation and evolution of diamondoids in source rock abstract thermal maturation related variations in the abundance and distribution of diamondoids in source rocks were investigated by thermal simulation experiments on extracts and kerogen obtained from a same marine shale and by quantitative analysis of diamondoids within pyrolysates using highly sensitive and selective gas chromatography triple quadrupole mass spectrometry gc ms ms the results indicate that diamondoids within the marine shale are generated mainly during 0 8 1 7 easyro generally deriving from extractable organic matter within source rocks and are destroyed after 1 7 easyro to be entirely removed by ca 3 0 easyro ternary plots of the relative distribution of diamondoids and bivariate diagrams for diamondoid parameters e g dma md vs dmai 1 and dma md vs tmai 1 show systematic changes in diamondoids with increasing thermal maturity expressed as easyro

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

comparison of crustal velocity profiles determined by seismic refraction and teleseismic methods recently two diverse seismic techniques were applied independently to the study of the crustal structure of the cumberland plateau eastern tennessee one involved a reinterpretation of a refraction experiment performed in 1965 by the u s geological survey consisting of two 400 km long reversed refraction lines the other entailed the inversion of broadband teleseismic p waveforms recorded at a single three component broadband station rscp located at the intersection of the two refraction profiles a comparison of the two sets of velocity profiles revealed many similarities and some significant differences both sets of velocity models consist of three major crustal layers 1 an upper crust vp 6 1 6 4 km s down to about 17 km 2 a mid crust vp 6 7 6 9 km s between 17 and 40 km depth 3 a lower crust vp 7 2 7 4 km s from 40 to 51 km depth the refraction models have linear transition zones up to 11 km thick at the base of each layer whereas the teleseismic models have more irregular transition zones at the base of the mid and lower crust the differences in the results of these studies are attributed to the differing frequency bandwidths of the data sets the predominant sensitivity of the teleseismic data to shear velocities compared to compressional velocities for the refraction data and the different analysis procedures involved in each method nevertheless the similarities indicate that the teleseismic waveform method with broadband data is capable of retreiving comparable crustal information as the cumberland plateau refraction survey in addition it provides the kind of complementary information required to constrain the composition of the continental lower crust and uppermost mantle

the origin and accumulation of multi phase reservoirs in the east tabei uplift tarim basin china abstract a giant deep strata oil gas field with complex fluid characteristics was recently discovered in the hade yuke area of the east tabei uplift tarim basin nw china the deep fluids show a lateral co existence of several gas condensate and oil phase reservoirs characterized through the integration of complimentary geochemical e g bulk composition biomarker and stable carbon isotope and geological data typical features of the gas and condensate reservoirs which were mainly distributed in the eastern parts of the study site included high gor gas to oil ratio hydrocarbon gases with relatively heavy 13c values and crude oils with high wax content in contrast oil reservoirs which mostly occurred in more westerly locations had lower gor values lighter 13c values and lower wax content indicating gradual change of fluid characters the petroleum accumulations derive from two hydrocarbon charge events an early oil charge in the late hercynian and a later gas charge in the late himalayan which migrated from east to west leading to a gradual variation in fluid phase and characteristics alteration of paleo oil reservoirs by this secondary gas charge was therefore primarily responsible for the complex fluid character and multi phase reservoirs presently in place secondary condensates were formed from the retrograde condensation of paleo reservoirs our re construction of the hydrocarbon accumulation process encourages future exploration endeavours to target commercially viable gas accumulations in the deep east strata and oil reservoirs in the west