biomarker maturity parameters for high maturities calibration of the working range up to the oil condensate threshold abstract in a study of oils and source rocks from the kimmeridge clay united kingdom and the hanifa qatar formations several biomarker maturity parameters with working ranges up to vr e vitrinite reflectance equivalent 1 0 oil condensate threshold have been identified and calibrated this represents a significant improvement compared to commonly used biomarker maturity tools sterane and hopane isomerisation with their maturity maximum of approximately vr e 0 7 early part of oil window these new parameters are 1 the absolute concentrations of steranes and hopanes decreasing gradually with increasing maturity 2 the ratio of tricyclic terpanes tricyclic terpanes hopanes increasing with maturity 3 the ratio of diasteranes 14 h 17 h steranes depending both on maturity and on source rock lithology and 4 the ratio of t s t m 22 29 30 trisnorneohopane 22 29 30 trisnorhopane increasing rapidly at very high maturities during artificial maturation experiments the biomarker maturities described in the natural samples were also known to be time temperature dependent up to rather severe laboratory heating conditions this corresponds with the working range up to high maturity levels as observed in the natural samples

hydrocarbon composition of authigenic inclusions application to elucidation of petroleum reservoir filling history abstract geochemical analysis of petroleum inclusions trapped in authigenic feldspar and quartz in the ula formation in the north sea ula oil field revealed a petroleum of markedly different composition than the oil presently in the reservoir using microthermometry and the burial history as a dating tools it is concluded that the petroleum in the k feldspar inclusions was present in the more porous and permeable parts of the ula formation as early as 45 75 my bp when the field was at a depth of about 1 0 1 5 km as compared with the current depth of 3 4 km this early petroleum which was trapped as inclusions in authigenic k feldspar shows a distinctly different distribution of tricyclic terpanes and pentacyclic triterpanes from that of the current petroleum charge in the ula formation which was derived from the mandal formation source rock in late neogene time molecular parameters show that the oil in the k feldspar inclusions is significantly less mature than the crude oil in the present reservoir the approximate 90 c temperature increase occurring after entrapment of the early petroleum in kfeldspar the field is currently at 143 c appears not to have reset the low maturity signature of the oil in the k feldspar inclusions this could suggest that the temperature in the inclusions is too low for isomerization selective thermal degradation to occur lack of catalysts or that there are other controls on the ratio of some of these parameters still parameters like the ratio of c21 to c28 triaromatic steroids and those based on dimethyl and trimethyl naphthalenes are comparatively similar in both the inclusions and in the reservoir crude the oil inclusions in authigenic quartz and albite formed from about 10 my bp burial depth 2 5 km until the present burial depth 3 4 km are interpreted as representing a palaeo petroleum charge having a composition intermediate between the oil found in k feldspar inclusions and the oil charge in the present reservoir our data suggest strongly that the petroleum trapped in the inclusions in quartz and plagioclase represents progressive dilution of the early reservoired oil now found only in k feldspar inclusions with oil from the mandal formation analysis of solution gas in these inclusions suggests that the first petroleum associated gas to arrive at the trap from the progressively maturing mandal formation had a much wetter composition than the current reservoir solution gas to explain the present comparatively drier and isotopically lighter reservoir solution gas composition the inference is made that there has been a recent during formation of k feldspar inclusions 45 75 my bp maturation of the upper jurassic mandal formation the main source rock in this region was limited possibly to the graben axis this suggests that the petroleum found in the k feldspar inclusions was most likely derived from a deeper post caledonian palaeozoic formation

ti rich komatiites from northern norway komatiites of the karasjok greenstone belt northern norway show two unusual features they have certain compositional differences compared with other komatiites and they are largely volcaniclastic in origin their geological setting suggests that the komatiites were crupted into shallow water thus permitting phreatomagmatic eruption in a small ocean basin that opened in the baltic shield the major oxides except for tio2 the trace elements y sc v heavy rare earth elements hree cr co ni and the platinum group elements pge cover similar ranges to those observed in other komatiites but tio2 sm zr and hf ti associated elements tae are enriched compared with abundances commonly reported for komatiites thus the karasjok komatiites have interelement ratios 2 to 3 times greater than chondritic between the tae and the hree pge sc v y al hre associated elements hae the light rare earth elements lree ta and th are enriched in some samples relative to ti sm zr and hf but are depleted in others one group of rocks that is similar to the karasjok komatiites both in terms of geological setting and geochemistry is the baffin bay picrites the reason for the high concentrations of tae in the karasjok komatiites could be that they formed at lower degrees of partial melting than most komatiites the greater than chondritic tae hae ratios indicate that garnet was a residual phase during their formation requiring that the melt formed at a pressure greater than 40 kb a model involving decompression melting of a mantle plume rising in a rifting environment can explain the main features of the karasjok komatiites

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

chemical changes of fluid inclusion oil trapped during the evolution of an oil reservoir jabiru 1a case study timor sea australia abstract this study of the jabiru oil field timor sea australia shows how the variability of visual properties of fluid inclusions in palaeo oil zones can be mapped to identify internal structures that result from fluid interactions in the reservoir variability in the attributes of oil inclusion assemblages oias is greater within an inferred palaeo gas cap zone 1 and current residual zone zone 3 and less within the current oil zone zone 2 in zone 3 where water imbibed a higher proportion of oias with visual white fluorescing oil inclusions correlates with less mono aromatic compounds and a higher abundance of polar compounds determined on a bulk extract of inclusion oil using high performance liquid chromatography hplc the ch 2 ch 3 ratios and water contents determined by fourier transform infrared spectroscopy ft ir are higher in zone 1 where gas drained there is a higher proportion of oias with visual yellow fluorescing oil inclusions and these correlate with low hplc mono aromatic and moderate polar contents and low ft ir ch 2 ch 3 ratios and water contents interpretation of the grains with oil inclusions goi and pressure volume temperature composition pvtx fluid inclusion data suggests that a gas saturated blue fluorescing palaeo oil was present in the three zones at the same pressure temperature fluid inclusion forming event pt 1 lighter gas saturated blue fluorescing oil was present in zone 2 but was rarer in zones 1 and 3 at the later fluid inclusion forming event pt 2 the yellow and white inclusion oils trapped in zones 1 and 3 respectively are gas depleted and interpreted to result from the interaction between non movable residual oil around grains with the surrounding gas and water respectively comparison between the pvtx data and the published burial curve suggests that most of the fluid inclusions were trapped during two different hot fluid flow events the full oil column is interpreted to have been present during early mid tertiary the palaeo oil column was reduced during the late miocene by imbibition of water in the present residual zone and drainage of gas at the top of the reservoir

assessing the maturity of oil trapped in fluid inclusions using molecular geochemistry data and visually determined fluorescence colours abstract the thermal maturity of oils extracted from inclusions and the fluorescence colours of oil bearing fluid inclusions have been measured in 36 sandstone samples from australasian oil fields the inclusion oils were analysed using an off line crushing technique followed by gc ms a maturity assessment was made for each inclusion oil using 25 molecular maturity ratios including a newly defined dimethyldibenzothiophene ratio dmdr each inclusion oil was placed in one of 4 maturity brackets approximately equivalent to early mid peak and post oil generation windows the fluorescence colours of oil inclusions were visually discriminated into blue white and yellow plus orange and their proportions estimated using point counting techniques sixteen samples have 85 of oil inclusions with blue fluorescence whilst other samples have more variable fluorescence colours one sample has 100 of oil inclusions with yellow plus orange fluorescence the results show that samples containing mainly blue fluorescing oil inclusions have thermal maturities anywhere within the oil window in particular the molecular geochemical data strongly suggests that oil inclusions with blue fluorescence can have relatively low maturities calculated reflectance

migration and accumulation of crude oils from permian lacustrine source rocks to triassic reservoirs in the mahu depression of junggar basin nw china constraints from pyrrolic nitrogen compounds and fluid inclusion analysis abstract the geochemical compositions of crude oils and permian source rocks from the mahu depression of the junggar basin were analyzed in this study based on tricyclic terpanes and isoprenoid biomarkers three oil groups i ii and iii can be identified that correspond to different source rock formations and organic facies after examination of the influence of source facies and thermal maturity and selected biomarker ratios based on carbazole isomers such as 1 mc 4 mc 1 8 dmc 2 7 dmc and a a c bc ratios in different oil groups allowed us to determine the direction of hydrocarbon migration in different reservoirs in addition abundant oil inclusions are present with fluorescence colors ranging from yellow to blue white these were analyzed by ftir to distinguish between different sources for the oils fluid inclusion petrography and microthermometry were also used to prove two stages of oil migration and their different sources taking into consideration possible migration pathways and likely driving forces we conclude that abnormally high pressure in the permian sequence acted as the main driving force for oil migration the major migration pathways were vertical faults in the fault belts and slope areas and sand bodies in the deeper areas group i1 oils from p1f carbonate source rocks in the fault belts mainly migrated vertically through the faults and accumulated in t1b reservoirs in the late triassic and were driven by excess formation pressure and buoyancy group i2 oils in the slope areas first migrated vertically within thrust faults from p1f mudstone source rock in the late triassic after which they migrated laterally over short distances to accumulate in t1b sand bodies group ii oils from adjacent p2w source rocks in the center of the depression migrated mainly in the late jurassic due to abnormally high pressure and accumulated in nearby t1b traps some reservoir rocks in the slope area contain two generations of fluid inclusions implying oil mixing from early stage p1f oils and late stage p2w oils resulting in the group iii oils combining these data from biomarkers pyrrolic nitrogen compounds and fluid inclusions allowed us to construct models of migration and accumulation for oils in the mahu depression

laser ablation gc ms analysis of oil bearing fluid inclusions in petroleum reservoir rocks abstract the hydrocarbon composition of co occurring blue and yellow fluorescing fluid inclusions fis in ordovician reservoirs of the tarim basin nw china have been separately analyzed by laser microprobe gas chromatography mass spectrometry gc ms using a 193 nm excimer laser to drill through the host quartz a newly designed gc inlet system enabled detection of c4 c30 hydrocarbons extending the molecular weight significantly beyond the c21 limit of previous online laser based hydrocarbon analysis of oil inclusions the blue fluorescing inclusions contain notably higher proportions of aliphatic hydrocarbons e g n alkanes cycloalkanes and gaseous range products whereas the yellow fluorescing inclusions contain relatively more aromatic hydrocarbons e g alkylnaphthalenes hydrocarbon based parameters also indicate that the blue fluorescing inclusions are of higher thermal maturity than the yellow fluorescing inclusions consistent with maturity estimates based on fluorescence colors the compositional differences of the co occurring inclusions are indicative of different oil types and charge events this highlights the capacity of the new laser ablation technology to separately analyse specific inclusions amongst a mixture of inclusions of different fluorescing colors in the future integration of this new compositional detail with other inclusion and reservoir data will help reconstruct the oil charge history of the tarim basin

recurrent mesolithic neolithic occupation at sise western latvia and shoreline displacement in the baltic sea basin a major assemblage of mesolithic and neolithic wooden artefacts has been recovered from the bed of the river u ava at sise in the coastal belt of western latvia new archaeological investigation h

hydrocarbon downward accumulation from an upper oil source to the oil reservoir below in an extensional basin a case study of chezhen depression in the bohai bay basin abstract there is a disputable theory that hydrocarbon can be injected into the reservoir and migrate downward in an oil reservoir with an upper oil source which is still questioned now however although some examples are previously found questions still remain about the theory regarding oil sources oil migration pathways and migration forces that related to downward hydrocarbon migration for this reason the chezhen graben in the bohai bay basin is selected to study all the problems above geo chemical evidence show that lower es3 source rock t6 in seismic profiles has a close genetic relationship with the underlying es4 t7 in seismic profiles and ordovician oil therefore the upper source lower reservoir type can be formed inside the lower gentle slopes and sag zones and inside the cambrian and permian reservoirs the fluid inclusion experiment shows that the lower es3 source rock underwent 3 over pressure evolution stages meanwhile there is a huge pressure difference between the lower es3 source rock and underlying es4 reservoirs which is the migration force of downward migration in the lower areas of gentle slopes and sags the early generated and early ended faults are terminated at the source rock of es3 member and can be re opened under the over pressure influence of the source rock and regional tensile stress then they become the pathways of the so called downward migration the distance of downward migration can be calculated through the accumulation dynamic which is obtained by hydrocarbon pressure subtracting the reservoir hydrostatic pressure pressure attenuation and displacement pressure the research result on downward migration process is of great significance to broaden the hydrocarbon exploration fields

oleanane or lupane reappraisal of the presence of oleanane in cretaceous tertiary oils and sediments nonpolar gc columns are normally used for gc ms analysis of saturate fractions from crude oils under these conditions lupane coelutes with oleananes and some minor c30 compounds of non terrigenous origin having lupane like mass spectra because any peak eluting fractionally earlier than 17 21 h hopane in the m z 191 mass chromatogram is routinely assigned to oleanane the presence of lupane may sometimes have been overlooked lupane and oleananes are easily separated using reverse phase hplc triterpane concentrates from 10 crude oils known to contain oleananes were hplc separated lupane was unambiguously identified in six of the oils by full scan gc ms analysis of fractions having the hplc retention time of authentic lupane gc separation of lupane and oleananes is possible using polar gc columns having a polyethylene glycol stationary phase organic geochemistry 23 1995 21 allowing estimation of the lupane lupane oleanane ratio high ratios were measured in the marraat oil west greenland 0 8 and the amauligak oil from the beaufort mackenzie delta 0 26 the results suggest that lupane may be more frequently occurring than previously thought and that this compound is preferably associated with high latitude samples high concentrations of 28 nor and 24 28 bisnortriterpanes oleananes lupanes and taraxastanes were detected in the marraat oil

application of aromatic compounds as maturity indicators in source rocks and crude oils concentration ratios of aromatic compounds such as naphthalenes phenanthrenes and dibenzothiophenes are at present attracting increasing attention as maturity indicators in sedimentary rocks and crude oils generally these indicators rely either on an increase with maturity in the degree of alkylation of a given parent compound or a shift in the isomer distribution of alkyl aromatic homologues towards thermally more stable isomers a combination of both concepts in the methylphenanthrene index mpi resulted in an excellent maturity parameter as demonstrated for rock extracts by an improved correlation with mean vitrinite reflectance rm between 0 65 and 1 4 i e in the zone of oil formation in cases that rm measurements were ambiguous this empirical relationship has proved useful in the calculation of theoretical vitrinite reflectance rc values from the mpi on the other hand for potential petroleum source rocks reaching maturity at relatively low temperatures the influence of the organic matter type on the aromatic distributions cannot be neglected consequently organic facies effects should be taken into account in the interpretation of aromatic distributions of such source rocks and related crude oils since the impact of the organic facies is strongly reduced with increasing maturity aromatic maturity parameters are particularly useful in the maturity evaluation of post mature crude oils and condensates in contrast to biological markers substantially higher concentrations of the key alkyl aromatics persist at elevated maturation levels thus aromatic maturity parameters should be considered as versatile tools in organic maturation studies and can complement established maturity indicators based on steranes and terpanes

origin and occurrence of 25 norhopanes a statistical study abstract the alkane fraction of more than 200 rocks biodegraded oils and non biodegraded oils have been analysed by means of computerized gc ms in order to investigate the effect of natural biodegradation on the occurrence of demethylated hopanes i e 17 25 norhopanes the results obtained indicate that 25 norhopanes are preexisting biomarkers the concentration of which is enhanced by selective biodegradation of more readily degradable homologs i e regular hopanes rather than by demethylation of hopanes in reservoirs however the use of 25 norhopane enrichment as a palaebiodegradation indicator in apparently non biodegraded oils is still valuable providing the initial background content in the corresponding source rocks is known furthermore 25 norhopanes appear to be diagnostic of specific environmental conditions marine and lacustrine source rocks dysoxic and not very hypersaline lastly one other novel bacterially resistant rearranged hopanoic compound namely a c29 neohopane is applicable for both biodegradation and maturation evaluation

lacustrine source rock deposition in response to co evolution of environments and organisms controlled by tectonic subsidence and climate bohai bay basin china three paleogene syn rift intervals from the bohai bay basin the most petroliferous basin in china were analyzed with sedimentological and geochemical techniques to characterize the lateral source rock heterogeneities to reveal the environmental and ecological changes through geologic time and to construct depositional models for lacustrine source rocks under different tectonic and climatic conditions the third es3 and first es1 members of the eocene shahejie formation and the oligocene dongying formation ed display widely variable total organic carbon contents hydrogen indices and visual kerogen compositions suggesting changes in organic facies from deep to marginal sediments carefully selected deep lake facies samples from any interval however display fairly uniform biomarker composition these three intervals have distinctly different biomarker assemblages which indicate weakly alkaline freshwater lakes with a moderately deep thermocline during es3 deposition alkaline saline lakes with shallow chemocline during es1 deposition and acidic freshwater lakes with deep unstable thermocline during the deposition of the dongying formation such environmental changes corresponded to changes in subsidence rate and paleoclimate from rapid subsidence and wet climate during es3 deposition through slow subsidence and arid climate during es1 deposition to rapid subsidence and wet climate during ed deposition and resulted in synchronous changes in terrigenous organic matter input phytoplankton community and primary productivity the co evolution of environments and organisms controlled by tectonic subsidence and climate accounted for the deposition and distribution of high quality lacustrine source rocks with distinctly different geochemical characteristics most rift basins experienced changes in subsidence rates and possibly changes in climates during their syn rift evolutions the models constructed in this paper may have important implications for source rock prediction in other lacustrine rift basins

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

p t conditions in the south wales coalfield evidence from coexisting hydrocarbon and aqueous fluid inclusions siderite nodules in the carboniferous coal measures of south wales contain cavities which are often infilled with quartz carbonates sulphides and hydrocarbons the quartz contains a mixture of hydrocarbon and aqueous fluid inclusions the aqueous fluid inclusions consist of a dilute brine 3 wt nacl equivalent and have homogenization temperatures in the range 97 212 oc mean 143 oc the hydrocarbon fluid inclusions are dominated by methane with a small component of higher order hydrocarbons their homogenization temperatures are in the range 35 78 c mean 54 c it is assumed that the two fluids were trapped simultaneously during growth of the quartz and thus a p t estimate of entrapment can be obtained by graphical intersection of the hydrocarbon isochores and the aqueous fluid bubble point homogenization temperatures assuming hydrocarbon saturation this method gives temperatures between 130 and 160 oc and pressures between 40 and 55 mpa the timing of mineralization is uncertain but it is suggested that it took place during burial and low grade metamorphism of the subsiding sedimentary basin i e in the upper carboniferous the hydrothermal fluids were probably derived from evolved meteoric or connate waters expelled during subsidence and sediment compaction

origin of giant vein type bitumen deposits in the northwestern junggar basin nw china implications for fault controlled hydrocarbon accumulation abstract giant vein type bitumen deposits in the wuerhe region within the northwestern junggar basin of nw china are representative examples of similar bitumen deposits that are found in a number of other locations in both china and elsewhere these deposits can provide information on regional tectonics as well as insights into hydrocarbon and bitumen exploration but the origin of the deposits remains unclear this study focuses on determining the origin of the wuerhe bitumen deposit using field petrological and geochemical data results show that the bitumen veins are generally hosted by shallow high angle fault systems located within the nose of the wuerhe fault fold the bitumen is of low maturity and has an organic origin having formed by secondary alteration most likely biodegradation of crude oil sourced from the lower permian fengcheng formation p1f the bitumen contains high concentrations of carotane and gammacerane low concentrations of ts and diasteranes and comprises in ascending order of concentration c20 c21 c23 tricyclic terpanes and c27 c28 c29 regular steranes the bitumen was most likely formed during the early cretaceous under the control of faults a fault controlled model is presented for hydrocarbon migration and accumulation and the subsequent formation of this bitumen within the northwestern junggar basin this model suggests that future hydrocarbon exploration should focus on the cores of fault fold noses and areas of minor fold nose near deep seated fault zones especially where these areas correspond to potential moderate to shallow depth jurassic cretaceous reservoirs the new model should be able to guide exploration in other basins with similar tectonic settings of this study i e superimposed thrusting compression and transtension

characteristic of source rocks and origin of crude oils in the raoyang sag and baxian sag bohai bay basin china insights from geochemical and geological analyses abstract three potential source rock intervals were evaluated based on the results of rock eval pyrolysis on nearly 700 rock samples and the origin of the twenty two oil fields was studied by the biomarker analysis on 62 source rock samples and 93 oil samples in the raoyang sag and baxian sag bohai bay basin the first member of the shahejie formation es was deposited in an anoxic and salted water column with the dominant contribution of algal organic matters reflected by its rock samples with high gammacerane c30 hopane high etr high c35 c34 hopane high steranes hopanes low pristane phytane low c27 diasterane c27 sterane and low c19 c23 tricyclic terpane characterized by higher c19 c23 tricyclic terpane higher pristane phytane lower steranes hopanes and lower c35 c34 hopane than the es1 rock samples the biomarkers of rocks suggest that the third and forth members of the es were deposited in the sub oxic to anoxic environments with a significant terrestrial organism input further studies suggest that the best source rock interval for oil generation is the es1 source rock interval in the raoyang sag and is the es3 source rock interval in the baxian sag by organic facies analysis of source rocks three source related oil groups have been identified there are two oil groups for the discovered oils in the raoyang sag group i oil dominated by the es1 derived oils has been found in all the oil fields in the raoyang sag and group ii oil mainly derived from the es3 source rock interval only distributes in the north east area and in the south end of the raoyang sag however the three oil groups have been found in the baxian sag but the es3 derived oils are dominant in them and have been found in the major oil fields in the east area and the wen an slope in the west area furthermore the es4 derived oils group iii oil mainly distribute in the baxian sag without any findings in the raoyang sag because of the absence of the es4 source rocks as our studies oils almost accumulate near their source rocks without a long distance migration except the slope areas in the raoyang sag and baxian sag therefore the source rock distribution is a key factor to oil accumulations in the raoyang sag and baxian sag especially the efficient source rock distributions which mainly developed in the organic facies a and b based on the geochemical and geological researches

geophysical evidence for structurally controlled authigenic carbonate cementation in the laminaria high bonaparte basin northwest shelf of australia abstract 3d seismic reflection data are used to investigate the processes which have led to the development of amplitude anomalies on reflectors in the faulted cenozoic overburden on the laminaria high northwest shelf of australia amplitude and root mean square rms attributes are mapped on two reflectors seabed and horizon h9 that were deposited synchronous with fault activity and are located adjacent to predominantly ene wsw striking fault traces on the seabed the main anomaly is located on the up dip side of the fault trace and is elongated parallel to the local time structure contours these observations are consistent with the anomalies having developed in response to structurally controlled fluid seepage along and up dip migration away from the fault trace the other amplitude anomalies associated with the h9 reflector are also located adjacent to fault traces but are discordant to the local time structure contours the latter observation is inconsistent with the migration of buoyant fluid at the present day instead it suggests that the anomalies may be due to cemented hardgrounds that formed due to seepage when the faults intersected the palaeo seafloor but were subsequently buried and deformed during ongoing sedimentation and fault growth linkage prominent anomalies mapped on reflectors within the pre faulting succession h10 are located adjacent to and are elongated along sub seismic scale nw se striking faults or as in the case of a deeper horizon h13 show no clear relationship with the faults we conclude that there is no relationship between the occurrence of anomalies and the magnitude of throw or the duration of activity along the cenozoic faults the results suggest that whilst fluid seepage and cementation were structurally controlled these processes were also influenced by permeability variations that cannot be resolved by seismic interpretation methods

organic geochemistry and mineralogy i characterisation of organic matter associated with metal deposits abstract as geochemical appraisals of mineral regions of commercial prospectivity evolve the organic matter associated with metal rich ores has attracted greater attention petroleum basin and modern seafloor hydrothermal vent studies have suggested that organic matter can have a significant influence on the behaviour of mineralising fluids there have been many isolated reports of certain organic compositional or morphological e g pyrobitumen features showing an apparent relationships with hydrothermal fluids or minerals raising expectations that organic based parameters might be useful to mineral exploration however the understanding of organic inorganic relationships in earth systems is far from complete for example the detailed mechanics of the interaction of organics with hydrothermal fluids over geological time remain largely undefined organic geochemistry studies have traditionally involved the measurement and interpretation of the hydrocarbon composition of sedimentary rocks here we review the types of aliphatic hydrocarbons aromatic hydrocarbons and metalloporphyrins often detected from organic geochemical investigations in mineral rich regions such molecular data can be particularly diagnostic of biochemical sources and the palaeo environments at the time mineral associated organic matter was deposited sub surface trends of hydrocarbon alteration may also reflect major biogeochemical processes such as thermal maturity and biodegradation organic geochemistry data can also occasionally provide information about the nature e g origin composition temperatures and migration pathways of hydrothermal fluids and can make a contribution to holistic ore genesis models the well preserved organic matter associated with the economic here s your chance pb zn ag mine paleoproterozoic barney creek formation mcarthur basin australia and the transition metal rich early permian kupferschiefer formation germany poland have attracted significant attention a more detailed summary of the organic character of these deposits is provided to highlight the contribution organic geochemistry can make to understanding mineralisation processes most organic geochemical studies of highly mineralised regions however have not adequately addressed the significance of organic matter to mineralisation a slightly different analytical focus than traditionally used for exploration appraisal of petroleum hydrocarbons may be required to properly evaluate the significance of organic species to the mobilisation transport and deposition of ore metals the characterisation and subsequent thermodynamic modeling of organic substances and complexes within metalliferous hydrothermal systems will contribute to a better understanding of the nature and role of organic inorganic fluids or other affiliated organics in ore systems

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

quantitative evaluation of the oil leg potential in the oliver gas field timor sea australia oil bearing fluid inclusions in sandstone cores and cuttings represent hidden oil shows the frequency of quartz grains containing these inclusions the goi number reflects the maximum paleo oil saturation experienced in a sandstone reservoir irrespective of the present fluid phase samples that have been exposed to high oil saturation have goi numbers at least one order of magnitude greater than samples that have demonstrably low oil saturation in this way these fluid inclusion data can be used to identify paleo oil columns and to map original oil water contacts in wells where oil has been displaced by a later gas charge moreover the use of detailed goi mapping to accurately define the location of the original oil water contact allows the height of the paleocolumn to be determined and an estimate to be made of original oil in place the oliver oil and gas discovery located in the timor sea australia presently contains a hydrocarbon column of 178 5 m composed of 164 m of gas over a 14 5 m oil leg and is filled to spillpoint in well oliver 1 goi mapping has delineated a gross paleo oil column of between 99 and 132 m within the present gas leg this corresponds to original oil in place of up to 200 million bbl considerably greater than the 45 million bbl of oil presently reservoired the displacement of up to 155 million bbl of oil from this structure has high graded the prospectivity of tilted fault blocks updip from the oliver structure goi mapping is an innovative approach to reservoir characterization that can reliably detect paleo oil accumulation in hydrocarbon traps that are presently filled by gas these data allow the oil leg potential of both gas discoveries and nearby untested structures to be addressed in a quantitative manner before additional drilling is commissioned

the occurrence of bisnorhopane trisnorhopane and 25 norhopanes as free hydrocarbons in some australian shales abstract the triterpenoid hydrocarbons of some west australian shales have been examined by gc ms in addition to the common 17 h 21 h hopanes 17 h 21 h hopanes and 17 h 21 h moretanes 28 30 bisnorhopane 25 28 30 trisnorhopane and 25 norhopanes were identified in the organic extracts in contrast pyrolysates of the solvent extracted sediments contained only the common hopane and moretane series indicating that 28 30 bisnorhopane 25 28 30 trisnorhopane and 25 norhopanes are not bonded to kerogen but rather are present in the sediments as free hydrocarbons

30 norhopanes their occurrence in sediments and crude oils abstract sediments and crude oils have been analysed using gc ms techniques and shown to contain two homologous series of hopanes namely 30 nor 17 h hopanes and 25 30 bisnor 17 h hopanes as well as the common 17 h hopanes homologues c28 to c34 of the 30 nor 17 h hopane series have been identified in crude oils associated with carbonate source rocks the abundances of these hopanes relative to the 17 h hopanes in the soluble organic matter from carbonate sediments has been shown to depend upon sample maturity the more mature samples having higher relative abundances of these norhopanes a comparison of the relative abundances of the norhopanes in the soluble organic matter of sediments and in the hydrocarbon fraction released when the extracted sediments were pyrolysed showed that the 30 nor 17 h hopanes were more abundant in the pyrolysis product these observations indicate that the proportion of norhopanes relative to normal 17 h hopanes in bound form in the kerogen is greater than that present in the soluble form and so kerogen cracking proceeds with increased maturity of the sediments and a relative enrichment of these norhopanes occurs in the soluble fraction the series of 25 30 bisnor 17 h hopanes has been identified in a severely biodegraded crude oil from a putative carbonate source this observation together with the reported occurrence of enriched 25 norhopanes in severely biodegraded crude oils suggests that 25 30 bisnor 17 h hopanes may be biomarkers for severely biodegraded crude oils from carbonate rich source rocks

trimethylnaphthalenes in crude oils and sediments effects of source and maturity abstract three sedimentary sequences and a number of crude oils have been analysed for trimethylnaphthalenes tmns using gas chromatography the sediments were found to contain enhanced relative abundances of 1 2 5 tmn and 1 2 7 tmn in samples of cretaceous age and younger this was especially pronounced in lower maturity sediments containing type iii organic matter older samples containing type iii organic matter were found to contain enhanced relative abundances of 1 2 5 tmn and lower relative abundances of 1 2 7 tmn 1 2 7 tmn appears to be derived directly from the structural degradation of oleanane type triterpenoids present in angiosperms and as such is proposed as a marker for this class of plant and indirectly therefore also for samples deposited since the early cretaceous the crude oils have been classified according to their trimethylnaphthalene compositions this classification enables crudes of higher plant origin to be identified and to be further classified according to whether the organic matter pre dated or post dated the evolution of angiosperms

dinosterane and other steroidal hydrocarbons of dinoflagellate origin in sediments and petroleum abstract the steroidal alkanes of a selection of sediments and oils have been examined by gc ms with multiple metastable reaction monitoring specific 4 methyl sterane isomers have been identified by comparison with isomers synthesized from sterols isolated from dinoflagellates an immature marine oil shale and two mature marine oils of triassic to early cretaceous age contained high concentrations of c30 steranes comprising desmethyl 24 ethyl 4 methylcholestane and 4 23 24 trimethylcholestane dinosterane isomers an immature non marine oil shale and two non marine oils of cretaceous to eocene age contained stereoisomers of 24 ethyl 4 methylcholestane as the dominant c30 steranes reaction monitoring analyses in gc ms are particularly suited to unravelling complex distributions of homologous and stereoisomeric steroids encountered in oils and their source rocks

fluid inclusion evidence for an early marine sourced oil charge prior to gas condensate migration bayu 1 timor sea australia the distribution of oil bearing fluid inclusions fi in currently gas bearing jurassic reservoir sandstones from bayu 1 northern bonaparte basin timor sea is consistent with the bayu gas condensate field originally containing a palaeo oil column beneath a thick palaeo gas cap in order to assess the origin of the oil trapped in the fis and its relationship if any to the gas condensate a detailed molecular geochemical study was carried out on a fi oil extract and a condensate sample recovered from a similar interval by modular formation dynamics tester mdt compared to the condensate the fi oil was generated from a more marine influenced less clay rich source rock or source facies which was deposited in a less oxic environment with greater eukaryotic input the source rock of the condensate was more terrigenous and had greater microbial input the bayu fi oil contains a greater amount of c28 and c29 tricyclic terpanes than the bayu condensate and particularly compared to the elang plover sourced oils from further to the northwest e g corallina and laminaria which are more terrestrially dominated the bayu condensate has previously been attributed to either the marine cretaceous echuca shoals formation or mixed sourcing from the less terrestrially influenced facies of the jurassic elang and plover formations together with the marine flamingo group analysis of the fi oil confirms a more marine influenced source facies of the palaeo oil with the echuca shoals formation being the most likely source based on oil oil and oil source correlations the fi oil appears to represent a marine source end member and it is likely that mixing of this oil sourced from the echuca shoals formation with hydrocarbons sourced from the more terrestrially dominated plover elang source facies could account for the intermediate composition of the currently reservoired condensate a discrete flamingo group is not required and this oil family may not be present in the bayu area the differences are nevertheless subtle and a contribution from the flamingo group cannot be completely discounted the fi oil has a mid oil window maturity 0 75 vitrinite reflectance equivalent vre whereas the currently reservoired condensate has a higher maturity 0 9 vre these maturity data are consistent with early expulsion from the more labile marine derived organic matter in the echuca shoals formation followed by expulsion of large amounts of condensate from the more terrestrially dominated elang and plover formations three possible transition mechanisms from gas over oil to condensate are consistent with the fi petrographical and geochemical data the first charge may have 1 been lost by breaching of the seal 2 been displaced by the condensate or 3 been partly dissolved in the later condensate charge a combination of factors 2 and 3 is considered most likely but further investigation is required to assess these options the fi oil at bayu 1 predominantly represents a different hydrocarbon charge compared to the condensate liquid and so by analogy the large residual oil columns that are observed elsewhere in the northern bonaparte basin are unlikely to be due to water washing of a pre existing gas condensate column similar to bayu undan

origin of petroleum accumulation in the chaheji gaojiapu structural belt of the baxian sag bohai bay basin china insights from biomarker and geological analyses abstract the origin of petroleum accumulations in the chaheji gaojiapu structural belt of the baxian sag bohai bay basin was evaluated based on the results of rock eval pyrolysis on 135 samples and a biomarker analysis on 26 source rock samples and 33 oil samples the four possible source rock intervals have different biomarker assemblages and were deposited in different environments for example pristane phytane c27 diasterane c27 sterane and c19 c23 tricyclic terpane ratios show an increasing trend but c28 c29 tricyclic terpane c28 c29 tricyclic terpane ts and steranes hopanes parameters display a decreasing trend among the lower part of the first member es1l and the middle es3m and lower part es3l of the third member of the eocene shahejie formation this finding indicates that a decreasing anoxic and alkaline environment with an increasing input of terrigenous organic matter developed during the deposition of the es1l es3m and es3l source rocks however the biomarker parameters of the forth member es4 of the eocene shahejie formation display highly similar characteristics with the es3l source rocks except for the c29 sterane 20s 20s 20r and c27 diasterane c27 sterane ratios which show obviously higher than the other source rock values the es3 derived oils are absolutely dominant in the chaheji gaojipu structural belt based on the biomarker analysis of saturated hydrocarbon with slight or no contributions from the es1l and es4 source rocks because of the low maturation for the es1l source rock and the absence of vertical migrating channels for the es4 source rock faults are vital to petroleum migration and accumulation in this area and demonstrate the following double effects 1 the deep faults cutting off the es3 source rocks are the key channels for oil vertical migration 2 the shallow faults entrap oil and finally form the commercial oil pools as a result the fault block reservoir is the major oil reservoir type in the chaheji gaojiapu structural zone and the lithologic reservoir is another oil reservoir type in this area based on 1d burial and thermal history modelling the e3 and e4 source rocks reached the oil generation peak at approximately 5 ma and 20 ma respectively but the es1l source rock is still in the low mature stage therefore the process of the large oil migration and accumulation for the es3 source rocks occurred during the late neogene quaternary through this research there are two considerable exploration potentials for this area including condensate reservoirs in the deep strata and low mature reservoirs in the es1 stratum interval

petroleum charge and entrapment along active faults study of the accumulation mechanism of the qinhuangdao 29 oil field on the slope of the shijiutuo uplift bohai sea in the qinhuangdao 29 qhd29 oil field oil generated from the first member of the shahejie source rocks is mainly contained in paleogene reservoirs whereas deeper oil sourced from the third member of the shahejie es3 source rocks is generally accumulated in neogene reservoirs the present study was undertaken to better understand the differences in petroleum accumulation in the qhd29 oil field and to provide suggestions for future petroleum exploration on the shijiutuo uplift laser raman spectroscopy reveals that carbon dioxide co2 exists with hydrocarbon gas in the same fluid inclusions measured homogenization temperatures of aqueous inclusions range from 80 c to 160 c 176 f to 320 f indicating late stage rapid petroleum accumulation with a charging time of no earlier than 5 1 ma the results of grains containing oil inclusions measurements reveal the presence of paleo oil accumulation in the current natural gas column in terms of the boundary fault activity rate far co2 distribution is quite relevant to the late stage activity of boundary faults with high content of co2 corresponding to the section of the f1 fault with high intensity activity higher far values both neogene and paleogene reservoirs in well a1 contained predominantly es3 derived oil and were accompanied by abundant mantle co2 this reveals the segmented vertical transport of petroleum in the fault both the mantle derived co2 and hydrocarbons vertically migrated and accumulated in shallower reservoirs in the high activity intensity section of the boundary fault this may account for the occurrence of predominantly es3 derived oil in the reservoirs near the section of the fault with high activity intensity in the eastern part of the qhd29 oil field vertical migration may have been limited because of the relatively low intensity of fault activity and the distribution of sandstones seems to dominate the petroleum accumulation our research reveals that lithologic traps in the es3 stratum may still have great potential for exploration along the slope of the shijiutuo uplift

geochemical comparison of oil bearing fluid inclusions and produced oil from the toro sandstone papua new guinea abstract a detailed study was carried out to compare the geochemistry of the crude oil in the lower cretaceous toro sandstone reservoir in the iagifu 7x well with oil trapped in fluid inclusions in this sandstone in the iagifu 7x and p nyang 2x wells in the papuan fold belt the drill stem test dst oils and the oils trapped in fluid inclusions show different source and maturity dependent geochemical parameters biomarkers suggest that the dst oils at iagifu 7x were derived from clay rich mixed marine terrestrial source rocks deposited under oxic conditions probably middle to late jurassic mudstones the fluid inclusion oils were derived from a less terrestrially influenced marine source rock deposited under less oxic conditions the fluid inclusion oils contain 1 2 7 trimethylnaphthalene and oleanane biomarkers indicative of angiosperm input and a cretaceous or younger source rock these oils are more mature calculated reflectance rc 1 02 than the reservoired oil at iagifu 7x rc 0 84 and condensate at p nyang 2x rc 0 84 source and thermal maturity parameters for all three fluid inclusion samples are similar suggesting that they were derived from similar source rock facies furthermore samples with predominantly blue vs white fluorescing oil inclusions have no discernible geochemical maturity difference suggesting that the use of fluorescence colours as a qualitative guide to the maturity of the trapped oil is not valid in this case fluid inclusion oils were trapped prior to charge of the reservoir with oil at the iagifu 7x and gas condensate at the p nyang 2x wells the fluid inclusion oils therefore represent an early oil charge from a deeply buried probably cretaceous source rock which started migrating into the toro sandstone during the miocene at iagifu this early oil was probably diluted by a larger volume of jurassic oil generated at the end of the miocene the absence of fluid inclusions with compositions like the currently reservoired oil is interpreted to be due to oil charging an already oil saturated zone when diagenesis is likely to have been inhibited at the p nyang well the transition from oil as represented by the oil inclusions to gas condensate was most likely caused by gas displacement

the origin and distribution of crude oil in zhu iii sub basin pearl river mouth basin china abstract the origin of thirteen major oil fields in zhu iii sub basin pearl river mouth basin was studied by using the results of rock eval pyrolysis on 340 samples and biomarker analysis on 18 source rock samples and 33 oil samples the two possible source rock intervals have different biomarker assemblages and were deposited in different environments the eocene wenchang formation e2w 49 5 35 ma is characterized by high hopane sterane ratio 37 84 high 4 methyl sterane index 0 28 1 06 low gammacerane index 0 10 high bicadinane c30 hopane up to 73 62 but low hopane sterane ratio