effect of maturity on 13c12c ratios of individual compounds in north sea oils abstract carbon isotope variations in individual compounds are reported for north sea oils of variable thermal maturity using the pristane phytane ratio of the oils as an indication of source facies variation and molecular maturity ratios to determine maturity it is possible to differentiate the two effects in these samples maturity accounts for between 50 and 90 of the observed isotopic variation all values becoming heavier with increasing maturity typically by between 2 and 3 however source differences are also apparent with a terrestrially influenced source possibly the heather formation contributing material to the kimmeridge clay sourced oils the heather contribution is isotopically heavier than the kimmeridge oil for most compounds but is isotopically lighter for the isoprenoid hydrocarbons and some other branched compounds it is also more important for lower molecular weight hydrocarbons than for higher homologues

compositional variation and palaeoenvironment of the volcanolithic fort cooper coal measures bowen basin australia abstract an integrated analysis of megascopic lithotype microscopic maceral and mineral composition stable carbon isotope and interburden sedimentology from a single well was used to interpret the response of the late permian fort cooper coal measures fccm to regional and global environmental influences the fccm are differentiated from underlying relatively high vitrinite moranbah coal measures and overlying higher inertinite rangal coal measures in the bowen basin by their intercalation with abundant tuff and siliciclastic partings and interbeds besides this there is little described about the variation in the organic composition of the fccm and its causes the fccm can be subdivided into a lower aggradational fair hill formation transgressed by the shallow marine derived black alley shale that interfinger with is overlain by the progradational middle main seams and burngrove formation coal measures the coals are dominantly dull with minor bright bands that are more abundant in the burngrove formation representing a change in plant composition the maceral analysis shows that the coals in the fair hill formation and middle main seams are vitrinite rich 80 90 mmf albeit with high mineral matter suggesting the formation of precursory peat under rising water levels and with high sediment tuff influx and preservation the coals in the burngrove formation have an increased inertinite content 30 mmf but are also high in mineral matter suggesting a shift to increased decomposition arising from a fluctuating water table possibly increased aridity and or microbial activity tuffs occur throughout and although their frequency is higher in the lower fair hill formation the preservation of thicker tuffs in the upper burngrove formation indicates increased intensity of volcanism that could have modified the environment variation in carbon isotope compositions show a parabolic trend from around 24 1 in the fair hill formation to more variable values in the middle main seams with an overall 13 c enrichment upwards in the burngrove formation prior to the 13 c values becoming negative depleted between 1 to 4 from the average 24 1 in the top seams and into the overlying rangal coal measures the 13 c depletion trend in the upper part of the section is unexpected in view of corresponding increase in inertinite content of the coals indicating that the 13 c values plant composition and inertinite content are decoupled unless the inertinite origin is from intense microbial decay similar stable carbon isotope depletion trends have been observed elsewhere in an equivalent stratigraphic interval of the bowen basin suggesting that the carbon isotope values are responding to global conditions that cause negative excursions in carbon isotopes before the p t boundary overall the basin was continuously subsiding and peats accumulated with constant interruptions from excessive sedimentation and volcanic eruptions the low proportion of visible thick bright bands coupled with high telovitrinite mmf content suggests a marsh to fen environment with an open canopy and ponding able to preserve volcanic ash falls

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

geochemistry characteristics and genetic types of natural gas in central part of the tarim basin nw china abstract according to the chemical carbon isotopic and hydrogen isotopic compositions and 3 he 4 he ratios of 127 natural gas samples the natural gas in the tarim basin is mainly composed of gaseous alkanes dominated by methane the contents of the gaseous alkanes decrease with the increase of their carbon numbers the 13 c values of ch 4 c 2 h 6 and c 3 h 8 in the platform area of the tarim basin vary in the range of 54 4 24 4 an average value of 39 2 43 1 26 7 an average value of 36 1 and 37 9 21 6 an average value of 31 8 respectively the overall carbon isotopic composition of the alkanes follows the trend of 13 c 1 13 c 2 13 c 3 13 c 4 and in some cases varies with 13 c 1 13 c 2 or 13 c 3 13 c 4 the lower carbon isotope values of methane 13 c 1 13 c 2 may be attributed to thermal sulfate reduction tsr and the higher propane value 13 c 3 13 c 4 was caused by the mixing of the natural gases of the same genetic type formed at different stages the methane hydrogen isotopes 2 h c 1 of the natural gases in the tarim basin are in the range of 195 122 with an average value of 156 the 3 he 4 he ratios of the natural gases are in the range of 2 3 10 8 66 8 10 8 suggesting that there is no deep mantle derived gas in the platform area of the tarim basin the carbon isotope fractionation of alkane gases 13 c 2 13 c 3 1 c 2 vs lnc 2 c 3 and c 2 c 3 vs 13 c 2 13 c 3 of the natural gases indicate that the oil type gas in the tarim basin has different predominant formation processes including kerogen cracking oil cracking oil and gas cracking secondary gas cracking and mixing of the kerogen cracking and oil cracking gases the gas evolved from gas cracking gas to oil and gas cracking gas and oil cracking gas along the direction from the west side of the manjar sag to the central tarim basin the natural gases in some areas of tazhong are the mixtures of the kerogen cracking and oil cracking gases

origin of the unusually high dibenzothiophene oils in tazhong 4 oilfield of tarim basin and its implication in deep petroleum exploration abstract unusually high dibenzothiophene dbt concentrations are present in the oils from the tazhong 4 oilfield in the tazhong uplift tarim basin positive ion electrospray ionization fourier transform ion cyclotron resonance mass spectrometry ft icr ms was used in combination with conventional geochemical approaches to unravel the enrichment mechanisms significant amounts of s1 species with relatively low dbe values 0 8 i e sulfur ethers mercaptans thiophenes and benzothiophenes were detected in three lower ordovician oils with high thermal maturity which were suggested to be the products of thermochemical sulfate reduction tsr in the reservoir the occurrence of tsr was also supported by the coexistence of thiadiamondoids and abundant h2s in the gases associated with the oils obviously low concentrations of the dbe 9 s1 species mainly equivalent to c0 c35 dbts compared to its homologues were observed for the three oils which were probably altered by tsr indicating that no positive relationship existed between tsr and dbts in this study the sulfur compounds in the tazhong 4 oils are quite similar to those in the majority of lower ordovician oils characterized by high concentrations of dbts and dominant dbe 9 s1 species with only small amounts of sulfur compounds with low thermal stability dbe 0 8 suggesting only a small proportion of sulfur compounds were derived from tsr it is thermal maturity rather than tsr that has caused the unusually high dbt concentrations in most of the lower ordovician oils we suggest that the unusually high dbt oils in the tazhong 4 oilfield are caused by oil mixing from the later charged lower ordovician or perhaps even deeper with high dbt abundances from the earlier less mature oils which was supported by our oil mixing experiments and previous relevant investigations as well as abundant authigenic pyrite of hydrothermal origin we believe that tsr should have occurred in the tazhong uplift based on our ft icr ms results however normal sulfur compounds were detected in most oils and no increase of 13c2h6 13c4h10 was observed for the gas hydrocarbons suggesting only a slight alteration of the oils by tsr currently and or recently we suspect that the abnormal sulfur compounds in the lower ordovician oils might also be a result of deep oil mixing which might imply a deeper petroliferous horizon i e cambrian with a high petroleum potential this study is important to further deep petroleum exploration in the area

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

molecular and isotopic evidence for mixed source oils in subtle petroleum traps of the dongying south slope bohai bay basin abstract subtle traps have become an important petroleum play type for exploration in the dongying depression bohai bay basin eastern china the majority of the oil pools are in the middle interval of the es3 member e s 3 m of the eocene oligocene shahejie formation with the subtle traps being primarily in the lenticular basin floor turbidite sands enclosed within basin floor mudstones detailed geochemical investigation of 68 oil and rock samples from the depression reveals that in contrast to previous models the oils from the subtle traps correlate poorly with the surrounding e s 3 m source rocks while the high pristane phytane pr ph 1 and low gammacerane c30 hopane ratios in these source rocks represent a freshwater lacustrine setting the oils feature low pr ph ratios e s 4 u source rocks deposited in a brackish lacustrine setting the compound specific isotope ratios of n alkanes in the oils have intermediate values between those observed in extracts from the lower es3 e s 3 l and upper es4 e s 4 u source rocks consequently the oils in the e s 3 m subtle traps were most likely derived from mixed e s 3 l and e s 4 u sources with the contribution from the e s 4 u source rocks being predominant the oils generated from the e s 4 u source rocks must have migrated through a thick interval of the e s 3 l source rocks to reach the subtle traps in the e s 3 m through which there are no apparent structural nor stratigraphic pathways the traditional migration and accumulation model i e indigenous crude oil with short migration distance to lenticular oil pools should be revised to account for the charging of oils from e s 4 u source rocks

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

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

relationship between petroleum composition and depositional environment of petroleum source rocks crude oils of nonmarine source can be distinguished from those of marine shale source and from oils originating in marine carbonate sequences by using a battery of geochemical parameters as demonstrated with a sample suite of nearly 40 oils a novel parameter based on the presence of c30 steranes in the oil was found to be a definitive indication of a contribution to the source from marine derived organic matter a second novel parameter based on monoaromatized steroid distributions was effective in helping to distinguish nonmarine from marine crudes and can be used to gauge relative amounts of higher plant input to oils within a given basin sterane distributions were similarly useful for detecting higher plant input but were less effective than monoaromatize steroid distributions for making marine versus nonmarine distinctions concentrations of high molecular weight paraffin can also be effective nonmarine indicators but are influenced by maturation and biodegradation processes certain algal derived nonmarine oils may show little high molecular weight paraffin response oils from carbonate sources with a few exceptions can be distinguished by having low pristane phytane ratios low carbon preference indexes and high sulfur contents gammacerane indexes and carbon isotope ratios of the whole crude are not effective in distinguishing these types of environmental differences on a global basis

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

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

geochemical characteristics and genetic types of the crude oils from the iranian sector of the persian gulf abstract comprehensive geochemical study shows genetic relationships among 33 crude oils from iranian sector of the persian gulf and suggests the ages and paleoenvironments of their source rocks the samples were collected from jurassic to tertiary reservoirs of 17 developed oil fields where about 15 billion barrels of recoverable oil have been reserved the oil density varies in rather wide range between 12 2 and 39 2 api asphaltene contents ranged from 0 8 18 5 and the maltene fractions are dominated by saturated hcs 29 3 70 9 with subordinate proportions of aromatic hcs 22 30 38 30 and polar compounds 7 15 70 pristane to phytane pr ph ratios are variable 0 67 1 41 sulfur content in crude oil samples are highly variable 0 65 3 7 according to the tissot and welte s classification most of the oils can be classified as high sulfur oils statistical and geochemical results indicate that the studied oils belong to four main genetic groups group i oils jurassic to early cretaceous reservoirs of the dorood kharg aboozar and foroozan oil fields in the nw part of the persian gulf originated from jurassic or older carbonate rich source rocks deposited in an anoxic environment group ii oils jurassic to early cretaceous reservoirs of the salman resalat reshadat and balal oilfields in the eastern part of the persian gulf were sourced from jurassic or older carbonate source rocks deposited in a relatively oxic environment group iii oils late cretaceous to tertiary reservoirs of the aboozar bahregansar souroush nowrouz dorood and kharg oilfields in the north north west part of the persian gulf were probably sourced from middle cretaceous calcareous shales group iv oils late cretaceous reservoir of the sirri a sirri c sirri d sirri e resalat and reshadat oilfields in the eastern part of the persian gulf probably originated from mid to late cretaceous source rock

hydrochemical properties of transition zone between fresh groundwater and seawater in karst environment of the adriatic islands croatia eastern coast of the adriatic sea consists of karstified carbonates it belongs to the well known dinaric karst region the coast is extremely indented and there are 718 islands with numerous rock crags and reefs some of the inhabited islands use their own water resources for public water supply or plan to do it in the future since karst rocks are extremely permeable the seawater intrudes into underground water resources thereby forming the wedge a wide transition zone occurs between this seawater wedge and fresh water aquifers consequently island groundwater reserves turn brackish to a certain extent in this study 77 water samples were collected from a wide variety of water resources comprehensive statistical and mathematical multivariate analysis of these data was performed simple statistical approach showed several useful correlations among some parameters and more complex multivariate techniques extracted three factors in connection with three natural processes 1 mixing with the seawater 2 carbonate dissolution and 3 human influence pollution and nitrogen transformation processes the results of this study demonstrate that in situ measurement of electrical conductivity is adequate for the very rough field estimation of numerous parameters

origins and fates of h2s in the cambrian and ordovician in tazhong area evidence from sulfur isotopes fluid inclusions and production data abstract gases oils solid bitumen samples and fluid inclusions were analyzed for chemical composition and 13 c and 34 s values and production data were collated to elucidate the origin and fates of the h 2 s in the tazhong area the h 2 s in the ordovician was measured to have 34 s values from 12 1 to 23 4 which are significantly lighter than the counterpart in the cambrian 33 0 indicating that the h 2 s did not migrate from the cambrian but may have been derived from thermochemical sulfate reduction in situ as partially supported by 12 c rich co 2 in fluid inclusions and tsr calcites with 13 c values from 3 6 to 17 7 in the ordovician the h 2 s rich gas subsequently mixed with h 2 s poor 13 c rich methane dominated gas as indicated by the roughly negative correlations of h 2 s content to dryness and gas oil ratio and ch 4 from fluid inclusions having 13 c values 1 2 3 6 lighter than the associated free gas the h 2 s has been dissolved in formation water precipitated as pyrite and incorporated into oils and solid bitumens resulting in the generation of alkylthiolanes alkylthiols and alkyl 2 thiaadamantanes and increase in 34 s values and s c ratios of the solid bitumen the content of h 2 s produced from the water intervals or petroleum water transition zones is significantly contributed from exsolved gas and thus higher than that of the gas cap gas in the reservoirs thus h 2 s contents cannot be used to indicate tsr extents in the ordovician however in the cambrian whole oil and saturates show positive shifts in 13 c values with increasing h 2 s contents indicating that the h 2 s in the cambrian was derived from tsr by liquid hydrocarbons

the complexity secondary geochemical process genetic mechanism and distribution prediction of deep marine oil and gas in the tarim basin china abstract most paleozoic marine craton basins in china are rich in natural gas except the tarim basin where both oil and gas are prolific various hydrocarbon types have been found in this basin including deep ultra heavy oil heavy oil normal oil volatile oil condensate and natural gas petroleums with diverse types even coexist within a single reservoir generally the ordovician and cambrian reservoirs are deeply buried 5500 8000 m and intensively altered after initial oil and gas accumulations bringing challenges to physical property prediction before drilling and evaluation of exploration targets based on recent exploration discoveries and experimental data we systematically analyzed the origin of oil and gas demonstrated the mechanisms and processes of secondary geochemical alteration e g biodegradation gas washing fractionation tsr and high temperature cracking moreover the preservation mechanism of ultra deep normal oil was also clarified and the distribution patterns of oil and gas were predicted tarim basin has been uplifted and shallowly buried in the early accumulation stage then rapidly and deeply buried in the late stage resulting in various geochemical alteration processes at different burial stages through the reconstruction of complex deep strata oil and gas accumulation histories the spatial distribution of deep petroleum types were predicted this review has provided detailed assessment with case studies in the tarim basin and shed light on the preservation mechanisms and the alteration processes of deep liquid petroleums in addition to massive gas accumulations liquid oils still have great exploration potential in strata deeper than 8000 m in the tarim basin

bakken madison petroleum systems in the canadian williston basin part 2 molecular markers diagnostic of bakken and lodgepole source rocks abstract the uppermost devonian mississippian bakken formation black shale and the mississippian lodgepole formation carbonate represent two of the most important source rocks in the canadian williston basin quantitative analyses of both saturated and aromatic hydrocarbon fractions reveal significant differences in the relative distributions and absolute concentrations for a wide range of molecular markers between the extracts of the two source units among others the bakken shales are characterized by their high relative abundance of trimethyl aryl and diaryl isoprenoids likely derived from green sulfur bacteria chlorobiaceae in contrast the lodgepole carbonates at similar maturity levels display a c35 homohopane prominence and abundant benzohopanes ring d monoaromatic 8 14 secohopanes and a tetracyclic monoaromatic hydrocarbon the distinctive nature of molecular marker fingerprints diagnostic of the two source rocks is clearly related to their different organic inputs and depositional environments additionally the large difference in the absolute concentrations of these compounds observed in both source units may potentially lead to biased geochemical interpretations if strictly conventional saturate based biomarker approaches were used for oil oil and oil source correlation

conditions for shallow geothermal energy utilization in dinaric karst terrains in croatia hydrogeological and thermogeological properties of the shallow subsurface in the dinaric karst area of croatia were investigated in the context of its utilization for ground and water source heat pumps gshps and wshps the research encompassed four 100 m deep boreholes with gshp installations in both coastal and inland dinaric karst different limestones and evaporitic rocks at one location and a set of six exploratory boreholes abstraction and reinjection wells for wshp heating and cooling using seawater on the coast fractured and karstified limestones it was determined that rock thermal conductivities are favourable for gshp utilization but dependent on the wider rock mass characteristics which are hard to predict size of karst voids and their saturation status in addition wells with high enough yield and stabile seawater or groundwater temperatures for wshp utilization can be designed in appropriate structural settings tensional fractures and fracture set intersections advantages and disadvantages of the utilized methodology have been pointed out as well as methods which should prove useful in the future especially if larger systems are planned hydrogeological geotechnical and thermal risks expected during the drilling installation and operational phases have also been identified presented case studies have given the insight into heat pump installation options and conditions in croatian part of the dinarides but can be useful to other researchers and engineers both in the dinarides and in similar karst regions

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

mixing of thermogenic natural gases in northern appalachian basin stable isotopic studies were undertaken to investigate the origin of 20 oil associated and non associated gases from western and central new york state in the northern appalachian basin gas wetness c2 c5 c1 c5 methane dgr13c and methane dgrd values range from 0 8 to 26 9 47 9 to 30 7 pmil and 305 to 143 pmil respectively corresponding ethane and propane dgr13c values range from 40 9 to 32 0 pmil and 34 9 to 27 9 pmil these data are interpreted to indicate a thermogenic origin with source rock maturities ranging from early mature equivalent vitrinite reflectance ro approximately 0 5 to post mature equivalent ro 2 0 inferred gas maturities generally in rease with increasing reservoir age from late to middle devonian marcellus and overlying rocks middle devonian to latest silurian oriskany onondaga akron silurian lockport herkimer medina to ordovician queenston and black river oil and gas in many late to middle devonian reservoirs may have migrated from interbedded organic rich shales in other reservoirs particularly those of ordovician and silurian age unusual isotopic reversals methane dgr13c ethane dgr13c suggest that gas generated locally from equivalent age rocks within the oil window mixed with post mature gas migrated from deeply buried sources to the south and southeast the post mature gas was probably sourced from middle to late ordovician shales regional migration of middle ordovician gas may have occurred along the middle ordovician knox unconformity gas was presumably channeled into overlying silurian and devonian reservoirs along faults and fractures

mixed oils derived from multiple source rocks in the cainan oilfield junggar basin northwest china part i genetic potential of source rocks features of biomarkers and oil sources of typical crude oils abstract there are four generative hydrocarbon source rocks of carboniferous permian triassic and jurassic age in the east of the junggar basin geochemical study of these has shown that permian source rocks which contain high abundances of organic matter with good genetic potential are the best hydrocarbon source rocks in this area triassic source rocks are shown to be next best in these aspects the abundance of mainly type iii organic matter in jurassic and carboniferous source rocks varies greatly and the genetic potential of these rocks is lower than that of permian and triassic rocks these four source rock units in the fukang sag all reach a mature to highly mature stage of thermal generation and have generated large amounts of oil permian extracts are isotopically light with 13 c ratios generally less than 29 they have low pr ph ratios are rich in carotane tricyclic terpanes gammacerane and c 28 and c 29 steranes contain almost no diasteranes and have a low content of c 27 steranes the carbon isotopic composition of the triassic extracts is similar to that of the permian but they are characteristically rich in ts c 29 ts and diahopanes and have low gammacerane contents the carbon isotopic composition of jurassic extracts is noticeably heavier than that of permian and triassic extracts with 13 c being generally greater than 28 jurassic source rocks have pr ph ratios generally 3 0 and are rich in pentacyclic hopanes and c 29 steranes but poor in tricyclic terpanes gammacerane and c 27 and c 28 steranes using carbon isotopic and biomarker data the crude oils in this area can be divided into five groups the first group of crude oils a is derived from the permian the second group b from the triassic and the third group c from the jurassic source rocks the geochemical properties of the fourth group d of oils are intermediate between the properties of typical permian triassic and jurassic oils and they are interpreted as mixed oils derived from multiple source rocks including the permian triassic and jurassic the fifth group of crude oils e is particularly isotopically heavy and originates from carboniferous source rocks

tectono thermal evolution of cambrian ordovician source rocks and implications for hydrocarbon generation in the eastern tarim basin nw china abstract the tectono thermal evolution is an important control on petroliferous basin development however this evolution is difficult to reconstruct in sedimentary basins subjected to multiple tectono thermal events the tarim basin is the largest petroliferous basin in northwestern china and hosts a complex oil gas system comprising several sets of source reservoir and cap rocks that have experienced multiple tectonic thermal and sedimentary events large oil and gas reserves have been discovered in the central and northern tarim basin during the last 30 years but none in the eastern part of the basin this is generally attributed to the high thermal maturity reached by source rocks during the late ordovician and subsequent hydrocarbon loss therefore reconstructing the cambrian ordovician tectono thermal evolution is critical in facilitating successful oil and gas exploration in this region we compiled equivalent vitrinite reflectance data n 178 of source rocks from seven wells in the tarim basin which for cambrian ordovician source rocks are 1 3 beyond the hydrocarbon generation threshold and in the main gas and dry gas generation stages the cambrian ordovician source rocks experienced rapid burial and heating during the caledonian period entered the hydrocarbon generation stage during the middle late ordovician and reached peak hydrocarbon generation at the end caledonian period they might have experienced secondary hydrocarbon generation after the jurassic homogenization temperatures of fluid inclusions n 616 from wells gc4 lx1 md1 and yd2 as well as the modeled thermal evolution reveal a main hydrocarbon generation event during the caledonian period and a secondary event in the yanshanian and himalayan period in other wells lx1 md1 and yd2 hercynian and indosinian uplift and exhumation in the eastern tarim basin controlled the main structures and faulting created favorable conditions for secondary hydrocarbon generation and migration at this time since the yanshanian and himalayan the tarim basin has experienced further sedimentation and heating and the tectono thermal evolution might have been related to the formation of the tibetan plateau in summary our reconstruction of the tectono thermal evolution of cambrian ordovician strata and the hydrocarbon generation history of the tarim basin suggests that the eastern tarim basin may also have hydrocarbon generation potential and can guide future oil and gas exploration

genetic origin of sour gas condensates in the paleozoic dolomite reservoirs of the tazhong uplift tarim basin abstract twenty gas condensates six oils and their associated formation water from the tazhong uplift in the tarim basin nw china were characterized for their molecular and isotopic compositions and water chemistry to elucidate the origins of the sour condensates thermochemical sulfate reduction tsr is the main secondary alteration process relevant to the generation of sour gas condensates those condensates are slightly heavier than regular condensates with a wide range of physical property and chemical composition variations the hydrogen sulfide h 2 s concentrations in gas phase show a strong positive correlation to gas oil ratio organosulfur compound osc concentrations in the liquid phase while methane isotopic values are mainly controlled by thermal maturity wet gas components show unusual 13 c enrichment at a low degree of thermal cracking geochemical anomalies occur mainly in the lower ordovician yingshan fm where more h 2 s has been discovered while the upper ordovician lianglitage fm shows less irregularity and h 2 s concentration is much lower generation of sour gas condensate is most likely caused by tsr alteration which could oxidize liquid hydrocarbons and form a large quantity of oscs isotopic enrichment of 34 s in formation water sulfate and elevated osc concentrations provide supplemental evidence of tsr alteration both burial history reconstructions based on fluid inclusion analysis and pvt simulation indicate that in situ tsr reactions mainly occurred around last 10 ma during the late himalayan orogeny and overall tsr extent is relatively low in the tazhong uplift

the origin and charging directions of neogene biodegraded oils a geochemical study of large oil fields in the middle of the shijiutuo uplift bohai sea china abstract two large oil fields qhd32 6 and qhd33 1 located in the middle part of the shijiutuo uplift have generally suffered mild biodegradation based on multivariate statistical analysis of the biomarker parameters this study discussed the origin and charging directions for these two oil fields in contrast to ed 3 derived oil all available oil samples from these two large oil fields displayed low c 19 c 23 c 24 c 26 and high g h and 4 msi which are attributed to the mixtures of oils derived from the shahejie es 1 and es 3 source rocks oils in qhd32 6 which contain relatively more es 3 derived oil are called group i oils and most oils in qhd33 1 which share relatively more es 1 derived oil are called group ii oils our mixed oil experiments reveal the predominant es 3 and es 1 derived oil contribution for group i and group ii oil groups respectively however the selection of end member oils warrants further research based on comparisons of biomarker parameters the qhd32 6 oil field was mainly charged in the north by oil generated from shahejie formation source rocks in the bozhong depression however oils from the north of qhd32 6 field display a remarkable difference to the oils in the south of this field which may indicate that a charging pathway exists from the qhd33 1 field considering the variations in biomarker compositions in the west to east and northwest to southeast sections across the qhd33 1 and qhd32 6 oil fields it can be deduced that es 3 sourced oil migrated westward to the qhd32 6 traps and then charging by es 1 oil from the bozhong sag resulted in the qhd33 1 oil field being characterized by the mixture of es 3 and es 1 sourced oil moreover migration of es 1 derived oil from the qinnan sag was not identified implying that the qhd33 1 oil field is mainly charged from the northeast of the bozhong sag

parameter estimation for a karst aquifer with unknown thickness using the genetic algorithm method the thickness of an aquifer b is a critical hydrogeologic parameter in understanding groundwater system especially in a karst aquifer where the high heterogeneity in this parameter brings more uncertainty to the evaluation of groundwater resources in this study the genetic algorithm ga method was used to estimate b as well as five other parameters including k r horizontal hydraulic conductivity k z vertical hydraulic conductivity s storativity s y specific yield and delayed coefficient of a karst aquifer based on a pumping test the search bounds of the six parameters for the ga method were obtained from numerous hypothetic numerical tests the feasibility of the ga method for parameter estimation was verified by the results obtained from the gradient method in terms of a pumping test conducted in the platte river valley in nebraska then this approach was used to estimate the hydraulic parameters in a karst aquifer with unknown aquifer thickness based on a pumping recovery test conducted in the houzhai karst basin southwestern china the results show that the k r k z and the anisotropy ratio of k r to k z are strongly affected by b the differences between the estimated parameter values at two observation wells indicate the existence of high heterogeneity in the karst aquifer the parameter b has the highest absolute normalized sensitivity among these variables implying that the estimated b may be more reliable as compared to other parameters this study demonstrates that the ga method is an alternative method of parameter estimation with the unknown aquifer thickness

origin of beatrice oil by co sourcing from devonian and middle jurassic source rocks inner moray firth united kingdom commercial hydrocarbons in the moray firth area of the north sea occur in reservoirs ranging in age from devonian to tertiary with the bulk of the reserves located in upper jurassic and lower cretaceous clastic rocks most hydrocarbon discoveries in this area have been made in the outer moray firth primarily in the witch ground graben a single oil field beatrice has been developed in the inner moray firth area the unusual location and chemical composition of beatrice compared to piper and other north sea oils generated from the kimmeridge clay have contributed to the longstanding controversy on its origin oil source potential in the inner moray firth has been recognized in lacustrine devonian dolomitic siltstones middle jurassic paralic coals upper jurassic marine shales and other rocks however prior to this study only the upper jurassic kimmeridge clay was recognized as a significant effective source rock in the main graben area of the north sea biomarker and stable carbon isotope analyses conclusively show that beatrice oil could not have been generated from the classic kimmeridge clay source rock but is a mixture of products derived from effective devonian and middle jurassic source rocks this work demonstrates the power of a multiparameter geochemical approach in solving this difficult oil to source rock correlation problem use of this approach can lead to the recognition of new exploration plays in previously well explored basins

a review of possible eustatic isostatic and tectonic contributions in eight late holocene relative sea level histories from the mediterranean area abstract this paper consists of a comparison between eight late holocene sea level histories investigated by the author in different mediterranean areas and sea level predictions in the same areas made by global isostatic models the areas include three regions that are generally considered as tectonically relatively stable 1 the southern coast of france 2 sardinia and 3 the southern coasts of tunisia where late holocene evidence may be either of submergence or of emergence also considered are 4 a subsidence region in the northern adriatic and actively uplifting areas 5 in calabria and 6 in nisyros island greece lastly case studies in areas affected by repeated coseismic vertical displacements include 7 western crete and antikythira island in the hellenic arc and 8 the levant coasts of turkey syria and the lebanon in each case the question of whether the evidence available may or may not be consistent with gradual isostatic or eustatic displacements has been explored it appears that in non tectonic areas the hydro isostatic effects have been overestimated sardinia or underestimated southern tunisia by the same models in the northern adriatic the closest mediterranean area to the former scandinavian ice sheet glacio eustatic effects are suspected to be almost absent our analysis failed to quantify isostatic effects in areas of rapid tectonic uplift calabria and nisyros but rejected predictions of significant isostatic subsidence in the hellenic arc and on the levant coast finally several data from tectonic and non tectonic areas are consistent with nearly stable global eustasy since 6000 bp thus challenging the assertion of significant additional melting of antarctica after the complete melting of the former northern hemisphere ice caps

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

the influence of thermochemical sulphate reduction on hydrocarbon composition in nisku reservoirs brazeau river area alberta canada abstract the upper devonian nisku formation reservoirs of the brazeau river area of west central alberta canada produce oil and sweet and sour gas condensate generally oil pools are located updip in the study area and sour 6 31 h2s gas condensate downdip h2s in the study area is formed by thermochemical sulphate reduction tsr all liquid hydrocarbons probably have one source with the duvernay formation being the most likely candidate assessing the relative maturity of the oils and condensates is difficult because of the wide variation in thermal maturity and the effects of tsr but the ratio of pristane n heptadecane does appear to decrease with increasing maturity for this sample set with increasing tsr the following changes were noted decrease in the saturate aromatic hydrocarbon ratio increase in the relative abundance of organo sulphur compounds e g benzothiophenes 34s values of liquid hydrocarbon samples approached the values for anhydrite of the nisku formation in the study area and an increase in 13c of the saturate fraction h2s concentrations in hydrodynamically isolated pools provide a good estimate of the extent of tsr in these reservoirs however other pools have anomalously high h2s concentrations for their depth suggesting that the h2s was generated at greater depths and migrated updip into these pools

rapid least squares inversion of apparent resistivity pseudosections by a quasi newton method1 a fast inversion technique for the interpretation of data from resistivity tomography surveys has been developed for operation on a microcomputer this technique is based on the smoothness constrained least squares method and it produces a two dimensional subsurface model from the apparent resistivity pseudosection in the first iteration a homogeneous earth model is used as the starting model for which the apparent resistivity partial derivative values can be calculated analytically for subsequent iterations a quasi newton method is used to estimate the partial derivatives which reduces the computer time and memory space required by about eight and twelve times respectively compared to the conventional least squares method tests with a variety of computer models and data from field surveys show that this technique is insensitive to random noise and converges rapidly this technique takes about one minute to invert a single data set on an 80486dx microcomputer

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 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

mixed oils derived from multiple source rocks in the cainan oilfield junggar basin northwest china part ii artificial mixing experiments on typical crude oils and quantitative oil source correlation abstract there are five groups of crude oils in the east junggar basin four of which are derived from single sources viz permian triassic jurassic and carboniferous the crude oils in the cainan field are of a special type in that they have little correlation with any of the four known source rocks in the basin based on their distribution in the reservoir formations and their carbon isotopic and biomarker compositions it is concluded that these crude oils are mixtures of hydrocarbons from permian triassic and jurassic source rocks a mixing calculation using whole oil stable carbon isotope ratios of typical end member crude oils suggests that the contribution of jurassic source rocks to the cainan crude oils averages 50 65 a second calculation based on absolute concentrations of biomarkers indicates that the jurassic contribution averages 62 while those of the triassic and permian source rocks average 15 and 23 respectively artificial laboratory mixing of three typical permian triassic and jurassic oils indicates that the average contribution of the jurassic source rocks is 65 whereas those of the triassic and permian rocks are around 15 and 20 respectively in summary using whole oil stable carbon isotope ratios and biomarker parameters it can be concluded that the jurassic source makes a contribution of 55 70 while the triassic and permian sources each contribute 10 30 therefore the crude oils in the cainan oilfield are mainly derived from jurassic source rocks in the fukang sag

estimating recharge thresholds in tropical karst island aquifers barbados puerto rico and guam the hydrology and geochemistry of groundwater in tropical island aquifers such as barbados guam and puerto rico are significantly influenced by tropical climatic conditions recharge to these aquifers is the product of regional and local climate patterns that control rainfall oxygen isotopes can be used to estimate the amount and timing of recharge on these islands because seasonal fluctuations of rainwater oxygen isotopic compositions are related to the amount of rainfall the karst aquifers on barbados guam and puerto rico have similar rainwater and groundwater oxygen isotopic compositions comparison of groundwater and rainwater oxygen isotopic compositions in the three aquifers indicates that 1 recharge occurs by rapid infiltration with little evaporation prior to recharge and 2 recharge is associated with similar monthly rainfall thresholds of 190 200 mm these rainfall thresholds are remarkably similar for three aquifers in different geographic locations differences between the spatial variations of groundwater oxygen isotopic compositions on barbados and puerto rico can be attributed to the more complex groundwater flow system on puerto rico the surprising similarities of hydrologic conditions under which recharge will take place can be attributed to similarities in climate and geologic conditions such as soils and limestone bedrock that exist on the three islands we therefore speculate that similar recharge rainfall thresholds may be observed in other tropical karst aquifers q 2003 elsevier science b v all rights reserved

an assessment of hydrogeological parameters on the karstic island of dugi otok croatia summary extensive explorations have been performed in the northern part of the island of dugi otok in the adriatic sea croatia with the purpose of extraction of fresh and or brackish water the island is predominantly composed of karstified carbonate rocks of the cretaceous age the explorations included geological and hydrogeological mapping of the area geophysical surveys by means of the geoelectric tomography method electrical resistivity sounding and surface seismic refraction exploratory core drilling hydrochemical in situ and laboratory explorations and the pumping test with the calculation of rock mass parameters based on the obtained results it was concluded that it is possible to exploit the groundwater with a pumping quantity of 5 l s without intrusion of salt water into the fresh water lens choosing a pumping regime based on the parameters of the aquifer rock mass hydraulic conductivity order of magnitude 10 4 10 6 m s and knowing the parameters of the well as well as the tidal efficiency should reduce the possibility of intrusion to the minimum because of the systematic quality of the performed explorations and obtained results the island of dugi otok can serve as a typical example for such kinds of exploration works on other karstic islands hydrogeological composition behaves partly according to ghyben herzberg s law but because of the nature of the karstic hydrogeological system such a statement needs to be accepted approximately because of the highly complicated relationships

the ratios of dibenzothiophene to phenanthrene and pristane to phytane as indicators of depositional environment and lithology of petroleum source rocks abstract the ratio of dibenzothiophene to phenanthrene and the ratio of pristane to phytane when coupled together provide a novel and convenient way to infer crude oil source rock depositional environments and lithologies such knowledge can significantly assist in identifying the source formation s in a basin thereby providing valuable guidance for further exploration the ability to infer this information from analysis of a crude oil is especially valuable as frequently the earliest samples in a new area may be shows and or drill stem test samples from exploratory wells which are characteristically drilled on structural highs stratigraphically remote from the source formation s a cross plot of dibenzothiophene phenanthrene versus the pristane phytane ratios measured on seventy five crude oils from forty one known source rocks ranging in age from ordovician to miocene consistently classified the oils into the following environment lithology groups marine carbonate marine carbonate mixed and lacustrine sulfate rich lacustrine sulfate poor marine and lacustrine shale and fluvial deltaic carbonaceous shale and coal the dibenzothiophene phenanthrene ratio alone is an excellent indicator of source rock lithology with carbonates having ratios 1 and shales having ratios the dibenzothiophene to phenanthrene and the pristane to phytane ratios can also be used to classify source rock paleodepositional environments the classification scheme is based on the premise that these ratios reflect the different eh ph regimes resulting from the significant microbiological and chemical processes occurring during deposition and early diagenesis of sediments the dibenzothiophene phenanthrene ratio assesses the availability of reduced sulfur for incorporation into organic matter and the pristane phytane ratio assesses the redox conditions within the depositional environment interpretation of these ratios has been aided by quantitative biomarker analysis and by carbon isotope data for pristane and phytane obtained by gas chromatography isotope ratio mass spectrometry

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

engineering characterization of hydraulic properties in a pilot rock cavern for underground lng storage abstract feasibility of storing lng in a lined rock cavern was evaluated using a pilot cryogenic rock cavern constructed in daejeon korea the pilot program included hydrogeological and engineering characterization of the rock mass around the cavern design and construction of a drainage system and pilot operation of the cryogenic cavern an appropriate drainage system is most important to protect the containment system of lng from thermal shocks due to ice lenses and hydrostatic pressure of groundwater as a part of the pilot program this study focused on the evaluation of hydraulic and engineering properties of the rock mass around the cavern for this purpose engineering logging of the rock cores single and cross hole hydraulic tests and recharge drainage tests were performed using seven drilled holes with different trends and plunges three main joint sets were found from the logging of the rock cores acoustic borehole televiewer and window mapping the orientations of the three major joint sets were 60 209 40 171 and 29 331 which can provide the main groundwater flow paths mean rqd values ranged from 56 to 88 which were classified as fair and good although varying with depth along single boreholes hydraulic conductivity from the single and cross hole hydraulic tests estimated in the order of 10 6 or 10 7 m s and corresponding transmissivity ranged between 10 5 and 10 6 m2 s permeable intervals identified from the hydraulic tests were mostly located above the cavern roof below the roof the permeable zone was difficult to observe according to the hydraulic communication tests performed for some designated intervals hydraulic connection between boreholes was highly varied with depth or location which indicated a very different distribution of water conducting joint sets along the boreholes when water was injected at r1 with constant or varying flow rates monotonous and stable seepage was observed at observation boreholes from this some stable drainage was expected even in relatively heavy rainfalls when designing the drainage system of the cavern the drainage holes should be orientated to maximize frequency of encountering the major joint sets and the permeable intervals identified from this study

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

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

impacts of source input and secondary alteration on the extended tricyclic terpane ratio a case study from palaeozoic sourced oils and condensates in the tarim basin nw china abstract a suite of oils and condensates from cambrian ordovician sources in the cratonic region of the tarim basin nw china has been characterized by gas chromatography mass spectrometry with a focus on factors affecting the extended tricyclic terpane ratio etr c28 c29 tt ts these oils and condensates show etr values ranging from 0 3 to 12 4 suggesting variable source contributions deposited under different environmental conditions coupled with tri and tetracyclic terpane distributions etr can be used as an organofacies discriminator most of the samples have high etr values 2 0 a low relative abundance of the c19 tricyclic terpane c19tt and the c24 tetracyclic terpane c24tet characteristic of a clastic marine depositional environment possibly with upwelling conditions a specific organofacies for a few samples is characterized by low etr values 0 8 and c24tet c26tt 1 0 ratios reflecting deposition under dysoxic conditions however various other alteration processes such as thermal maturity thermochemical sulfate reduction tsr biodegradation and in reservoir mixing probably have a significant impact on this parameter which makes understanding the meaning of the etr complicated the effect of thermal maturity on etr is minimal in the oil generation window but the etr values decrease dramatically at the post oil generation stage tsr seems to preferentially lead to the loss of the c28tt and c29tt before the 18 h 22 29 30 trisnorneohopane ts and thus the etr value decreases as tsr progresses while the dibenzothiophene phenanthrene ratio can help to differentiate tsr alteration from thermal cracking processes the etr is no longer a valid geochemical parameter when these two processes occur etr also increases with biodegradation the c28 and c29tt are more resistant to biodegradation than ts supporting evidence can be derived from a positive correlation between etr and c29 25 norhopane to c30 hopane ratio in reservoir mixing is another important alteration process which normally results in lower etr values after a fresh charge is mixed with a biodegraded charge in a reservoir evaporative fractionation may also have an impact on etr values some unusually high etr values might be attributed to evaporative fractionation the etr values from our case study suggests that the etr parameter is much more complicated than just being an age diagnostic parameter maturation and secondary alteration processes need to be fully accounted for before the etr can be properly applied to interpretations of depositional environment conditions such as upwelling

characteristics of selected petroleum source rocks xianjiang uygur autonomous region northwest china 1 the sedimentary basins of xinjiang uygur autonomous region china are moderately to poorly explored for petroleum volumetric adequacy of petroleum source rocks is a critical exploration risk in these basins particularly because source rock data are limited this study provides new source rock data and speculatively assesses the source rock potential of xinjiang basins the junggar zhungaer basin the best explored of the xinjiang basins and containing a giant oil field is underlain in many areas by an upper permian lacustrine oil shale sequence remarkable for its organic richness and oil source quality depending on its position in the basin the permian section ranges from immature to overmature and is inferred to be the principal source of oil in the basin upper triassic middle jurassic coal measures including lacustrine rocks constitute a secondary source rock sequence in the basin the smaller intermontane turpan tulufan basin contains a very similar upper triassic middle jurassic sequence which where sufficiently buried probably comprises the only significant oil source sequence in the basin the vast tarim talimu basin offers the greatest variety of potential source rocks of all xinjiang basins but remains the least well documented from limited but geologically planned and focused sampling cambrian carboniferous and permian strata are not considered major oil contributors in the dominantly shallow marine paleozoic section of the northern tarim basin only ordovician black shales appear to have significant potential the upper triassic middle jurassic sequence of the northern tarim basin is similar to that of the junggar and turpan basins a section rich in coal and lacustrine shale that constitutes another potentially significant oil source due to the size stratigraphic packaging and structural relief of the northern tarim basin paleozoic and mesozoic potential il source beds range from immature to overmature

molecular correlation of free oil adsorbed oil and inclusion oil of reservoir rocks in the tazhong uplift of the tarim basin china the free adsorbed and inclusion oils were recovered by sequential extraction from eleven oil and tar containing reservoir rocks in the tazhong uplift of tarim basin the results of gas chromatography gc and gc mass spectrometry analyses of these oil components and seven crude oils collected from this region reveal multiple oil charges derived from different source rocks for these oil reservoirs the initially charged oils show strong predominance of even over odd n alkanes in the range n c12 to n c20 and have ordinary maturities while the later charged oils do not exhibit any predominance of n alkanes and have high maturities the adsorbed and inclusion oils of the reservoir rocks generally have high relative concentrations of gammacerane and c28 steranes similar to the cambrian lower ordovician source rocks in contrast the free oils of these reservoir rocks generally have low relative concentrations of gammacerane and c28 steranes similar to the middle upper ordovician source rocks there are two interpretations of this result 1 the initially charged oils are derived from the cambrian lower ordovician source rocks while the later charged oils are derived from the middle upper ordovician source rocks and 2 both the initially and later charged oils are mainly derived from the cambrian lower ordovician source rocks but the later charged oils are contaminated by the oil components from the silurian tar sandstones and the middle upper ordovician source rocks

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

saturate biomarkers and aromatic sulfur compounds in oils and condensates from different source rock lithologies of kazakhstan japan and russia abstract representative petroleums from the seven basins of kazakhstan russia and japan were analyzed using gas chromatography with dual fid fpd and gc ms the present study has shown that the deviation in relative concentrations of aromatic sulfur compounds in petroleums could be related to the type of source rock all oil samples were classified into three groups on the basis of the relative abundance of aromatic sulfur compounds biomarker distribution and lithology of source rock the first group of oils derived from carbonate source rocks is rich in aromatic sulfur compounds such as methylbenzothiophenes mbt and methyldibenzothiophenes mdbt and poor in dibenzothiophene dbt compared to methylated homologs the second group derived from siliceous and siliceous carbonate source rocks contains various types of benzothiophenes and dibenzothiophenes including dbt the third group originating from argillaceous rocks has lower concentrations of aromatic sulfur compounds and especially of methylated benzothiophenes

hydrological modeling in the karst area rižana spring catchment slovenia karst aquifers are known for their heterogeneity and irregular complex flow patterns which make them more difficult to model and demand specific modeling approaches this paper presents one such approach which is based on a conceptual model the model was applied in a karst area of the catchment of ri ana spring 200 km it is based on the mike she code and incorporates the main hydrological processes and geological features of the karst aquifer diffuse and concentrated infiltration allogenic recharge quick and slow groundwater flow shifting groundwater divides and groundwater outflow from the catchment area modeling of evapotranspiration and flow in the upper part of the unsaturated zone is more detailed for the modeling of groundwater flow in the karst aquifer a conceptual model was applied which uses drainage function for the simulation of groundwater flow through large conduits karst channels and large fissures the model was calibrated and validated against the observed ri ana spring discharge which represents a measured response of the aquifer the results of validation show that the model is able to adequately simulate temporal evolution of the spring discharge measured by nash sutcliffe coefficient 0 82 as well as overall water balance

source characterization of highly mature pyrobitumens using trace and rare earth element geochemistry sinian paleozoic paleo oil reservoirs in south china abstract understanding the relationships between migrated hydrocarbons and source rocks under highly mature conditions i e pyrobitumen source correlation is a critical and challenging issue in the field of petroleum geology and geochemistry based on a case study of three sinian paleozoic paleo oil reservoirs from yunan and guizhou provinces south china we attempt to provide further understanding of this issue using trace and rare earth element ree geochemistry which can characterize the depositional setting organic input and rock provenance of source rocks results show that the bitumens from the three paleo oil reservoirs can be distinguished from each other using post archean australian shale paas normalized trace element distribution patterns ree distribution patterns hierarchal cluster analysis of element concentrations and redox and provenance sensitive elemental ratios e g v ni ni co ni mo zr cr la sc and la co pyrobitumen in the devonian xiaocaoba paleo oil reservoir is derived primarily from devonian source rocks representing a self sourced petroleum system and one stage hydrocarbon charging similarly pyrobitumen in the sinian jinsha yankong paleo reservoir also received a single fluid charge but the source is different and likely generated by contributions from both lower cambrian and sinian sources in contrast the bitumen in ordovician kaili luomian paleo reservoirs are indicated to have contributions from two different hydrocarbon sources and thus experienced two stages of hydrocarbon charging an early charge from lower cambrian source rocks and a later charge from permian source rocks the new trace and rare earth element method used in this study appears to be effective at providing a better understanding of the hydrocarbon source correlation under highly mature conditions the results improve our understanding of the complex hydrocarbon accumulation alteration evolution in the marine strata of south china which is a potential target for petroleum exploration

estimating recharge in a tropical karst aquifer unique constraints on seasonal and spatial variations in recharge to the pleistocene limestone aquifer of barbados are obtained from the analysis of oxygen isotopic compositions of groundwater and rainwater conventional methods of estimating recharge are based on groundwater chloride variations coastal groundwater discharge and potential evapotranspiration these methods typically yield estimates of recharge for barbados that range from 9 to 20 of average annual rainfall with significant uncertainties that arise from poorly constrained model input parameters owing to the low relief and tropical climate of barbados variations in rainwater and groundwater 18o values are primarily influenced by the amount of rainfall with negligible temperature or altitude effects composite monthly rainwater 18o values are inversely related to rainfall while groundwater 18o values show little seasonal variability rainwater 18o values are equivalent to groundwater values only at the peak of the wet season by using mass balance the difference between groundwater and weighted mean rainwater 18o values gives recharge values these values are in general agreement with estimates by conventional methods 10 20 and provide unique additional information including the following 1 recharge is restricted to the wettest 1 3 months of the year and 2 there is less recharge at higher elevations the effective shift in 18o values between contemporaneous rainwater and groundwater via recharge is a useful tool for estimating temporal and spatial variability in recharge and must be considered in paleoclimatic studies where climate inferences are based on groundwater 18o values preserved in the geologic record

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