the analysis of oil trapped during secondary migration abstract during secondary migration there is an opportunity for oil to be trapped as fluid inclusions fis within framework grains such as quartz and within diagenetic cements that have a crystalline structure oil saturation on migration pathways remains relatively low so typically fewer oil inclusions get trapped compared with samples from an oil column geochemical analysis of the much smaller amounts of inclusion oil present in samples from interpreted oil migration pathways has been attempted for two samples from the champagny 1 and delamere 1 wells in the vulcan sub basin northern offshore australia a combination of petrographic analysis bulk geochemical inclusion analysis and log evaluation confirmed that both samples were from oil migration pathways despite the small number of oil inclusions reliable geochemical data were acquired from both samples that were significantly above the levels detected for the system and outside rinse blanks the fi oil trapped on the interpreted oil migration pathway in champagny 1 was generated from clay rich marine source rock with little terrigenous organic matter input it was generated at peak oil window maturity and correlates best with oils derived from the late jurassic lower vulcan formation in contrast the delamere 1 fi oil contains evidence of greater input of terrigenous organic matter and was generated at early oil window maturity this fi oil also contains a signature of a biodegraded component which could have been generated either from the middle jurassic plover formation or from an older source rock these data indicate that it is feasible to geochemically map migration pathways across prospects or basins and to analyse palaeo oil compositions in oil zones where the few inclusions get trapped this also suggests that the few oil inclusions that sometimes occur in proterozoic or archaean rocks may be analysable in the future which would provide relatively pristine and robust data on the composition and diversity of earth s early biosphere

dynamics of shallow late variscan gold mineralization the le châtelet au arsenopyrite quartz veins massif central france the le ch telet gold deposit is unique among the mined deposits of the french variscan basement in that the gold is not free but caught up in the arsenopyrite crystal lattice microstructural analysis shows that the au arsenopyrite quartz veins are hosted by north trending dextral strike slip faults resulting from nne ssw compression during the early stephanian around 300 ma textural study indicates that vein emplacement was due to sequential dynamics related to spasmodic strike slip movements along these brittle structures seismic regime the classic sequence begins with the slow crystallization of sulphide free comb quartz followed by a co deposition of microcrystalline quartz and needles of au arsenopyrite the rapid crystallization of the au arsenopyrite bearing microcrystalline quartz was due to a sudden drop in fluid pressure the veins correspond to dilational jogs formed by a suction pump mechanism during a late phase of the variscan orogeny they were trapped in migmatite about 1 km below surface

rare earth element mobility at constant inter ree ratios in the alteration zone at the phelps dodge massive sulphide deposit matagami quebec rare earth elements ree from la to ho were mobile and enriched in hydrothermally altered rocks below the archean phelps dodge cu zn volcanogenic massive sulphide deposit in northwestern quebec largest net enrichment was in the moderately altered quartz chlorite zone where la concentration increased six fold and lanybn steepened from 1 9 to 13 0 the intensely altered chloritite zone had both minor net ree enrichment and depletion yb and lu were immobile throughout both zones the mobile ree were added and subtracted in constant chondrite normalized inter ree proportions 1 0 la 0 79 ce 0 57 nd 0 49 sm 0 01 eu 0 10 tb and 0 02 hb small additions of eu relative to generally larger additions of lree and tb produced enhanced negative eu anomalies the ree were mobilized at the hot 300 c core of the alteration system and deposited at the cooler periphery other sites of intense alteration and water rock interaction display similar ree changes indicating that selective ree enrichment at constant inter ree ratios is a widespread phenomenon

the petroleum characteristics and filling history of the froy field and the rind discovery norwegian north sea abstract the brent group reservoirs of the froy field and the rind discovery norwegian north sea show complex distributions of petroleum and aqueous fluids multiple fluid contacts are present in the rind discovery and the fields show various extent of compartmentalisation due to faulting geochemistry data of core extracts indicate that the two fields have different petroleum sources bhullar karlsen holm backer owe tran 1998 late diagenetic modifications of the reservoir quality consist of quartz cementation followed by carbonate and kaolinite cementation and dissolution of k feldspar fluid inclusion results indicate that filling of the reservoirs occurred after the main phase of quartz cementation at pressure temperature conditions close to the present differences in fluid properties between fault compartments in both fields have been identified fluid inclusion data have proved especially valuable for evaluation of the sealing capacity of faults through time and given evidence for the fault lineament north of both fields to be a time integrated pressure seal except for a lower gas condensate zone in the 25 2 13 compartment of rind the present reservoir fluids are volatile oils close to gas saturation the previous presence of an oil in the lower reservoir zone of 25 2 13 has also been demonstrated the fluid inclusion data indicate that the condensate in 25 2 13 represents a second episode of migration filling rather than phase separation

effects of thermal cracking of hydrocarbons on the homogenization temperature of fluid inclusions from the niigata oil and gas fields japan abstract the changes of the homogenization temperature th when hydrocarbons in inclusions were cracked thermally were experimentally evaluated in the experiments the hydrocarbon inclusions in quartz were heated in an autoclave and the th between before and after heating were compared in the experiments the th decreased after heating the amount of decrease became greater as the heating temperature or the duration time or both increased the experiments also revealed that the samples with higher th showed a greater decrease after heating because the experiments have been performed in a closed system mass transfer between inclusions and the enclosing medium was impossible no volumetric changes in the hydrocarbon inclusions were observed after heating therefore the temperature depression after heating should be caused by the pyrolysis of the hydrocarbons in the inclusions in the shin kumoide sk 1d well of the niigata oil and gas field in japan the th of hydrocarbon inclusions decreases from 73 to 30 c between 4040 and 4810 m in depth successively this temperature range is lower than the present formation temperature by from 60 to 140 c and shows a trend opposite to the normal geothermal gradient therefore it should reflect the degree of the thermal cracking after trapping rather than the trapping temperature

displacement transfer from fault bend to fault propagation fold geometry an example from the himalayan thrust front abstract the leading edge of the ene trending himalayan thrust front in pakistan exhibits along strike changes in deformational style ranging from fault bend to fault propagation folds although the structural geometry is very gently deformed throughout the salt range it becomes progressively more complex to the east as the leading edge of the emergent salt range thrust becomes blind surface geology seismic reflection petroleum well and chronostratigraphic data are synthesized to produce a 3 d kinematic model that reconciles the contrasting structural geometries along this part of the himalayan thrust front we propose a model whereby displacement was transferred across a newly identified lateral ramp from a fault bend fold in the west to fault propagation folds in the east and comparable shortening was synchronously accommodated by two fundamentally different mechanisms translation vs telescoping however substantially different shortening distribution patterns within these structurally contrasting segments require a tear fault which later is reactivated as a thrust fault the present geometry of this s shaped displacement transfer zone is a combined result of the nw se compression of the lateral culmination wall and associated tear fault and their subsequent modification due to mobilization of underlying ductile salt

behaviour of rare earth elements during hydrothermal alteration at the buena esperanza copper silver deposit northern chile abstract a study of the ree behaviour in alteration zones of the buena esperanza subvolcanic cu ag deposit located in the coastal range of northern chile reveals that the elements are mobile in the rocks during alteration the ore forming process developed in three different stages of alteration mineralization the hydrothermal alteration of the early and middle stages affected basaltic fragments of a breccia pipe la and ce were leached from the rock fragments located at the bottom and at the middle part of the breccia pipe and partly redeposited at the top during alteration sm eu and tb were released selectively and the heavy ree behaved as relatively immobile elements sericite is the most important alteration mineral for fixing the ree during this stage the incoming fluids had low ree contents the late stage of hydrothermal alteration happened simultaneously with the intrusion of a gabbroic volcanic neck affecting mainly these subvolcanic rocks ree patterns of samples from the top and bottom of the alteration zone exhibit roughly parallel trends but are systematically enriched in ree in comparison to unaltered samples this enrichment seems to be more intensive at the top of the altered area coinciding with the enrichment of rb k and cu in these rocks epidote plays the most important role for fixing this hydrothermal input of ree during the latest stage of alteration

assessment of fluid contacts and compartmentalization in sandstone reservoirs using fluid inclusions an example from the magnus oil field north sea location of an oil water contact is crucial for estimating reserves and for designing production strategies identifying hydrodynamic barriers or baffles is also important for optimizing both recovery and flow rates in some oil fields identifying fluid contacts and barriers is not always possible using conventional wireline and formation testing methods

petroleum inclusions atop unayzah gas condensate reservoir signpost for an undocumented chapter of the arabian basin filling history abstract the carboniferous permian unayzah gas condensate reservoir of the ghazal field in eastern saudi arabia contains abundant oil inclusions indicative of a palaeo oil column the molecular composition of a fluid inclusion rich zone at the top of the reservoir revealed a mid mature biomarker distribution 0 80 vitrinite reflectance equivalent vre that is considerably lower than that of the co occurring reservoired fluid 1 41 vre side chain cracking of the triaromatic steroids evident in the produced condensate is significantly less advanced in the inclusion oil as is also reflected in their alkylnaphthalene distributions the lower maturity signal in the inclusion oil is combined with calcareous related biomarkers that include relatively abundant 30 nor 17 hopane c24 tetracyclic terpane and alkyldibenzothiophenes in contrast to the reservoir hydrocarbon fluid derived from the lower silurian qusaiba shale inclusion gas is enriched in the higher hydrocarbons which might be attributed to a high proportion of oil or wet gas inclusions fluid inclusion ethane and propane 13c are very close to the mean of the produced gases but carbon dioxide 13c is about 5 and methane 13c 2 less negative than the average of the produced ghazal gases which may signify more than one hydrocarbon generation population within the fluid inclusions an earlier contribution into the unayzah reservoir from a non qusaiba source may therefore be inferred to have had preceded the volumetrically more significant and more mature qusaiba charges further research is needed to elucidate the source of this oil charge and its extent which could include deep cambrian or neoproterozoic sources that might be present in the region

authigenic albite formation due to water rock interactions case study magnus oilfield uk northern north sea abstract it is the aim of this contribution to test whether organic inorganic interactions could induce the formation of authigenic albite this concept and related results are being compared with modelling scenarios which are purely based on inorganic geochemical reactions in order to unravel the pathway of authigenic albite formation this paper presents results of a multidisciplinary study from imaging geochemistry mineralogy and hydrogeochemical modelling the jurassic reservoir sandstones of the magnus oilfield uk north sea were chosen as a test site albite occurs with 4 18 wt in the magnus sandstones and its contents vary with depth however albite contents increase with increasing k feldspar contents and decreasing grain size it occurs in three forms 1 as lamellae in perthite 2 as overgrowth on in corroded feldspar and 3 as cloudy replacing albite patches in k feldspar the albite overgrowth has the highest chemical purity 100 albite whilst albite lamellae and replacing albite patches are slightly less pure containing 1 4 anorthite albite appears non altered and has a euhedral morphology and dull cathodoluminescence it commonly co occurs with corroded k feldspar grains the precipitation of diagenetic albite in the magnus sandstones is attributed to deep burial 80 ma ago and may have continued until today at temperatures between 90 120 c the results of hydrogeochemical modelling offer two possible pathways for the authigenic albite formation 1 dissolution of unstable minerals such as kaolinite and chalcedony coupled to reduction of ferric iron minerals by products generated during oil generation migration and degradation 2 dissolution of non end member feldspar such as k feldspar with 10 albite coupled to illite formation can account for trace amounts of albite due to an elevated na k activity ratio in the pore water

composition volume changes during hydrothermal alteration of andesite at buttercup hill noranda district quebec abstract hydrothermally altered andesites in the upper member of the amulet formation at buttercup hill noranda quebec represent part of the aquifer and cap of a self sealing geothermal system that focussed the discharge of hydrothermal fluids during the formation of massive cu zn sulfide deposits five alteration facies are recognized 1 pervasive greenschist facies regional metamorphism least altered andesite 2 epidotization silicification 3 albitization silicification 4 chloritization 5 sericitization silicification alteration is localized on permeable zones such as amygdules fractures flow tops discordant breccia dikes and conformable breccia horizons epidotized silicified andesite is enriched in ca sr eu and depleted in mg and first transition series metals ftsm relative to least altered andesite albitized silicified andesite is significantly enriched in na and depleted in most ftsm relative to least altered andesite the abundances and inter element ratios of the rare earth elements ree and most high field strength elements hfs y zr th u hf ta are similar in least altered epidotized silicified and albitized silicified andesites the most silicified andesites are strongly enriched in na si strongly depleted in mg and divalent ftsm and slightly but systematically depleted in ree and most hfs elements serialized andesites were previously silicified they are very strongly enriched in k rb cs ba very strongly depleted in na ca sr eu and slightly depleted in light ree relative to silicified andesite chloritized andesitic rocks exhibit heavy ree and hfs element ratios similar to those of leastaltered andesite but are relatively strongly enriched in mg and divalent ftsm strongly depleted in si and large ion lithophile lil elements and slightly depleted in light ree the coupled behavior of the heavy ree and most hfs elements during epidotization albitization silicification chloritization and serialization suggests that they were inert during hydrothermal modification of the andesite mass balance calculations suggest that volume was conserved during epidotization silicification and albitization silicification but that intense silicification was accompanied by volume increases up to 30 percent

classification and thermal history of petroleum based on light hydrocarbons abstract classifications of oils and kerogens are described two indices are employed termed the heptane and isoheptane values based on analyses of gasoline range hydrocarbons the indices assess degree of paraffinicity and allow the definition of four types of oil normal mature supermature and biodegraded the values of these indices measured in sediment extracts are a function of maximum attained temperature and of kerogen type aliphatic and aromatic kerogens are definable only the extracts of sediments bearing aliphatic kerogens having a specific thermal history are identical to the normal oils which form the largest group 41 in the sample set this group was evidently generated at subsurface temperatures of the order of 138 149 c 280 300 f defined under specific conditions of burial history it is suggested that all other petroleums are transformation products of normal oils

the organic geochemistry of petroleum reservoirs abstract the organic constituents of petroleum reservoirs frequently show measurable compositional variations both laterally between wells and vertically within a single well the pattern of variation is controlled by the geological setting of the reservoir which influences the way in which migrating petroleum fills the reservoir from one or more source kitchens having achieved a high petroleum pore saturation the reservoir fluids may then redistribute themselves at rates are often comparable to geological time periods mass transfer by diffusion and density driven convection must be considered and their timescales compared with the elapsed time since the accumulation was filled in many cases the compositional variations inherited from the filling process persist to the current day this paper outlines the mechanisms by which reservoirs fill and mix and describes how this can lead to observable lateral differences in composition the relationship between certain engineering parameters particularly the gas oil ratio and reservoir fluid density reservoir rock description and geochemical parameters will be stressed the goal being to improve the characterisation of petroleum reservoirs by combining geochemical and engineering data into a scientifically consistent framework many aspects of the geochemistry of petroleum reservoirs have only recently begun to be researched it is hoped that the recent advances in the geochemical characterisation of oils and gases will be increasingly applied to the problems of reservoir and petroleum engineering this should lead to improvements in the efficiency with which petroleum is recovered from the subsurface

variability of petroleum inclusions in vein fossil and vug cements a geochemical study in the barrandian basin lower palaeozoic czech republic abstract although no commercial oil or gas occurrences have been found in the barrandian basin residual oils and petroleum inclusions give evidence about the petroleum history of this lower palaeozoic basin petroleum inclusions are hosted in six generations of calcite and quartz cements that can be attributed to different stages of a basinal cycle and associated diagenetic events they were analysed using an on line crushing and an off line crush and leach approach five different groups pi a to pi e and intermediate mixtures pi m could be differentiated based on the relative distribution of n alkanes all oils had a calculated aromatic maturity rc ranging between 0 9 and 1 6 pi a shows a molecular weight maximum in the range of n c8 11 with a constant attenuation towards higher carbon numbered n alkanes this distribution is interpreted as the pristine precursor oil for other petroleum inclusion groups pi b has a maximum weight abundance at n c15 20 the genetic relationship between pi b and pi a can tentatively be explained by mixing effects or by gas stripping pi c is bimodal and characterised by a molecular weight maximum at n c32 34 and also a molecular weight maximum at n c15 20 similar to that of group pi b pi d shows a normally distributed molecular weight maximum in the range n c25 28 and is interpreted as a wax precipitate from ascending gas saturated in n alkanes pi e contains predominantly gaseous compounds with only a few higher hydrocarbons thompson s aromaticity values are elevated for condensates of group pi e and also for group pi c that is dominated by long chained n alkanes this gives evidence that fault bound petroleum migration in the barrandian basin was associated with evaporative fractionation for group pi c and pi e samples of group pi e yielded gas range compounds only and all come from a last generation of vein filling whitish calcite that was formed in a late uplift phase of the basin for other petroleum inclusion groups only a vague preferential occurrence in specific mineralisation phases or stratigraphic intervals of the host rock has been found this reflects the predominance of fracture bound migration in the barrandian basin aromatic maturity values also showed no correlation between either crystal type or pi group in six of the investigated petroleum inclusion samples alk 1 enes are present these terminal olefins are interpreted to be the result of the natural pyrolysis of petroleum due to the intrusion of volcanic dykes or hydrothermal processes an artificial generation of olefins during sample work up and analysis is unlikely the preservation of alk 1 enes from palaeozoic times was possible due to the protecting environment of petroleum inclusions

district scale alteration associated with massive sulfide deposits in the mount read volcanics western tasmania the distribution of secondary mineral assemblages in six mineralized areas of the mount read volcanics defines a district wide zonation which is subconformable with massive sulfide host horizons and the contacts of sill like granitoids where present the relationships between alteration patterns and elements of cambrian geology strongly suggest that the alteration is related to cambrian hydrothermal circulation responsible for massive sulfide mineralization there is a later greenschist facies metamorphic overprint the major components of the principal assemblages are quartz albite chlorite epidote quartz albite chlorite calcite quartz sericite chlorite and quartz k feldspar chlorite several complex assemblages involving the above minerals biotite magnetite pyrite and tourmaline are characteristic of granite contacts secondary biotite is also present sporadically in the rosebery area probably related to devonian granitoids at depth there is a districtwide zonation of sodic or calcic versus nonsodic noncalcic assemblages in felsic volcanic rocks in preore volcanics nonsodic noncalcic assemblages occur immediately beneath the host horizon and may persist several hundred meters before passing into a zone including granite contacts where calcium minerals and albite occur sporadically the nonsodic noncalcic assemblages are predominantly sericitic but assemblages with prominent k feldspar occur locally in postore volcanics sericitic non sodic noncalcic assemblages may persist up to 200 m above the ore horizon before passing into relatively fresh volcanics with common albite and calcic greenschist minerals preore assemblages probably largely reflect downward circulation upwelling zones are characterized by intense sericite chlorite or chlorite development with or without k feldspar lateral spreading of solutions immediately beneath the ore horizon is common chlorite compositions preserve local patterns due to cambrian hydrothermal processes but they do not vary systematically with alteration assemblages throughout the province chlorite mg to fe ratios appear to have been preserved through metamorphism a combination of structural and alteration data is useful to mapping in the mount read volcanics this approach indicates that most syngenetic deposits and sedimentary lenses in the rosebery hercules area may lie on a single host horizon and suggests a continuity of geology from mount farrell through red hills to mount sedgwick

applications of petroleum geochemistry to exploration and reservoir management abstract petroleum geochemistry improves exploration efficiency by accounting for many of the variables that control the volumes of crude oil and natural gas available for entrapment including source rock distribution richness and quality thermal maturity and the timing of generation migration accumulation relative to trap formation it is most powerful when used with other disciplines such as seismic sequence stratigraphy and reservoir characterization four key technology milestones form the basis for most modern applications of geochemistry to exploration these are the concepts and applications of 1 petroleum systems and exploration risk 2 biomarkers stable isotopes and multivariate statistics for genetic oil oil and oil source rock correlation 3 calibrated three dimensional thermal and fluid flow modeling and 4 controls on petroleum composition by secondary processes petroleum geochemistry offers rapid low cost evaluation tools to aid in understanding development and production problems some technology milestones in reservoir geochemistry include 1 assessment of vertical and lateral fluid continuity 2 determination of proportions of commingled production from multiple zones and leaky casing 3 prediction of oil quality in reservoir zones and 4 prediction of gas oil and oil water contact locations as described in the conclusions future research will continue a trend toward predictive geochemistry examples of predictive tools that draw major research support include piston core surveys to assess deepwater petroleum systems prior to drilling and three dimensional basin modeling to predict the regional timing of generation migration and accumulation of petroleum among other research objectives models are needed to better predict the distribution and quality of petroleum in reservoirs

simulations of the effects of diagenesis on the evolution of sandstone porosity abstract automated image analysis and image processing techniques make possible the simulation of sandstone diagenesis and prediction of pore system modification diagenetic processes in real rocks are simulated using a combination of element x ray maps and backscattered electron images processes can also be simulated for computer generated sand packs by image analysis and image processing compaction is simulated by moving grain centers closer together overgrowth type cementation is simulated by dilation of free grain surfaces mineral dissolution is simulated by selective removal of specific minerals identified by the combination of element x ray maps and backscattered electron images the original and modified images can be processed and analyzed to reveal all the parameters needed to predict permeability using a kozeny carman type equation the computer modeling and image analysis approach can also be used to determine the specific effects of various diagenetic processes on porosity the results are encouragingly realistic by reference to the few available well characterized empirical datasets

metamorphic veining and mass transfer in a chemically closed system a case study in alpine metabauxites western vanoise in western vanoise french alps karstic pockets of triassic to jurassic metabauxites embedded in carbonate rocks and containing several generations of metamorphic veins were studied during blueschist facies metamorphism a cumulative amount of 13 vol of water is inferred to have been produced locally by successive dehydration reactions and part of this fluid remained in the bauxitic lenses during most of the metamorphic cycle field and geochemical evidence show that these rocks have been isolated from large scale fluid flow closed system behaviour it is proposed that the internally derived fluid has promoted the opening of fluid filled open spaces as attested by the euhedral habits of vein minerals and served as medium for mass transfer from rock to vein indeed the vein infill is obviously the result of chemical interactions at the millimetre to centimetre scale between the rock minerals and the locally produced aqueous fluid two vein types can be distinguished based on mineralogical and textural features i some veins are filled with newly formed products of either prograde chloritoid or retrograde chlorite metamorphic reactions in this case fluid filled open spaces seem to offer energetically favourable nucleation growth sites ii the second vein type is infilled with cookeite or pyrophyllite that were present in the host rock prior to the vein formation in this closed chemical system the components for the vein infill minerals have been transferred from rock to vein through the fluid in a dissolution transport precipitation process possibly stress assisted these different vein generations all contain al rich mineral infills suggesting that al was a mobile element cm scale during metamorphism in these hp rocks fluid flow may have been restricted and if so mass transfer occurred by diffusion in an almost stagnant fluid metamorphic veins can be seen as witnesses of fluid and mass redistribution that partly accommodate the rock deformation lateral segregation

diagenetic pore waters stratified for at least 35 million years magnus oil field north sea isotopically distinct pore waters remained stratified in the upper jurassic magnus sandstone reservoir for the magnus oil field in the northern north sea throughout diagenesis a petrographic and isotopic study of the reservoir sandstones in three wells indicates that a similar suite of diagenetic quartz overgrowths kaolinite magnesian siderite ankerite and illite developed across the field however the oxygen isotope ratios delta 18 o recorded in these diagenetic minerals from the crest of the field are consistently more negative by about 3 o oo than those from the downdip flank we propose that this consistent difference in delta 18 o values records the persistence of isotopically different and stratified pore waters in the magnus sandstones the sandstones w re deposited as marine turbidites but were subaerially exposed during periods of structural uplift and tilting during the early and middle cretaceous meteoric water entered the structural crest resulting in pore water stratification deposition of thick upper cretaceous mudstones and marls sealed the magnus structure during subsequent rapid burial diagenetic minerals in the crest of the oil field grew in a pore water with significantly more meteorically derived water than those downdip assuming that each diagenetic phase developed at a similar temperature in each well the pore waters remained stratified for at least 35 m y from middle cretaceous approximately 90 ma subaerial erosion of the sandstone until reservoir charging at 55 ma the sandstones and mudstones of the kimmeridge clay formation behaved essentially as a closed system during diagenesis in contrast to the open system concept envisaged in most other diagenetic reconstructions

fracture controlled antimony quartz mineralization lake george deposit new brunswick mineralogy geochemistry alteration and hydrothermal regimes veins are of two orientations 000 degrees 35 degrees e lawrence vein and 090 degrees 33 degrees n hibbard and prout veins to date approximately 1 million short tons of ore grading 3 0 to 3 5 percent sb have been mined from hibbard the dominant vein two way chemical mass balance reveals that wall rock alteration accompanying stibnite quartz vein emplacement involved major additions of sb as s and volatiles with minor introduction of k 2 o rb and si fe 2 o 3 mgo cao and na 2 o along with co ni ba and zn were stripped whereas sc ti and al behaved essentially isochemically the argillic alteration developed at 360 degrees to 490 degrees c from fluids with a delta 18 o 10 per mil the hibbard vein was precipitated at 325 degrees to 350 degrees c from a saline hydrothermal fluid with a delta 18 o value of 11 to 12 per mil and a delta d value of 20 to 30 per mil undergoing transient boiling at a pressure of 270 to 420 bars salinity is estimated at 38 to 40 weight percent nacl hematitic alteration was formed at 200 degrees to 350 degrees c in the presence of a fluid with a delta 18 o value of 2 to 8 per mil the ore forming solutions may have been a late stage magmatic fluid evolved off a high 18 o granitic intrusion modified journal abstract

implications of outcrop geology for reservoirs in the neogene productive series apsheron peninsula azerbaijan the neogene sediments of eastern azerbaijan and western turkmenistan contain significant hydrocarbon reserves in deltaic reservoirs sedimentary logging of these reservoirs at outcrop in azerbaijan has outlined four facies associations that encompass a range of paleoenvironments from alluvial braided river sandstones and conglomerates to delta front siltstones and mudstones the facies associations suggest a river dominated braid delta and are arranged into an architecture controlled by base level changes parasequences parasequence sets and sequence boundaries are key elements the facies associations and stratigraphic architecture together with outcrop observations of cementation and faulting are summarized in terms of four idealized reservoir models fluvial delta plain proximal delta front and distal delta front each reservoir model has distinctive grain size and shale distributions comparison of nearby oil fields with the studied outcrops suggests that the outcrops form good analogs from which to model reservoir architecture barriers and baffles to fluid flow reservoir heterogeneity and reservoir quality variations

petroleum migration faults and overpressure part ii case history the haltenbanken petroleum province offshore norway abstract petroleum inclusion and geochemical data from core extracts were applied to deduce a model for oil migration overpressure development and palaeo leakage of oil from currently dry structures in the haltenbanken vest area the existence of fluorescent oil type inclusions in quartz in the smorbukk asgard 2 field suggest that oil migrated into this structure 70 50 million years before present ma bp this is also the case for the dry structures 6506 12 4 6506 11 3 and 6506 11 1 west of the main smorbukk fault zone black oil inclusions with medium gas oil ratio gor occur in these fields together with condensate type petroleum inclusions this suggests that the dry structures transformed from containing oil to condensate before leakage petroleum extracted from inclusions in these structures and in nearby fields have identical marine type ii kerogen signatures source rocks at the spekk formation level in the current drainage area of smorbukk and these dry structures were immature 70 50 ma bp and the smorbukk sor asgard 3 field did not fill at this early time thus oil must initially have entered into smorbukk from areas to the w sw through the currently pressure sealing smorbukk fault zone which today marks the westward limit of the smorbukk field diagenesis in this fault zone caused the much later overpressure development and petroleum was lost from the 6506 12 4 6506 11 3 and 6506 11 1 structures as overpressure built up regionally petroleum loss from these structures with their often thick seals must have occurred via self propagating open fracture induced mechanisms lack of petroleum in the cretaceous strata above these structures suggests that leakage occurred to even shallower strata this could imply that the cretaceous strata in halten vest were overpressured at the time of leakage in contrast the oil in the cretaceous lysing and lange formation above the jurassic reservoirs in smorbukk and smorbukk sor most likely originated based on geochemistry and gors from the jurassic reservoirs below and not from cretaceous strata this migration event would have been facilitated if it occurred before these sands became overpressured as they are today modelling suggests that the spekk formation became mature in the smorbukk sor region

confocal microscopy of fluid inclusions reveals fluid pressure histories of sediments and an unexpected origin of gas condensate we present two examples of how fluid inclusion data can be used to determine geologic pressure histories and to quantify the compositional evolution of petroleum in oil reservoirs volumetric liquid vapor ratios generated with a confocal laser scanning microscope are used along with pressure vapor temperature p v t modeling software to estimate the composition p t phase envelope and isochore of single petroleum inclusions in the north sea9s judy and alwyn fields in both cases the gas condensates currently in the reservoirs formed by the emplacement of gas into preexisting oil accumulations pressure histories of individual units in each field are also revealed providing the kind of data needed to determine the permeability and fluid flow histories of sedimentary basins

a geologic deconstruction of one of the world s largest natural accumulations of co2 moxa arch southwestern wyoming geologic sequestration of anthropogenic carbon dioxide co2 is one of the most promising approaches to safely and effectively reduce emissions of co2 created through the oxidation of fossil fuels methods used by the petroleum industry in the characterization of hydrocarbon accumulations can be used to assess potential subsurface traps for sequestration purposes in this article we use these approaches to evaluate the characteristics of a naturally occurring accumulation of co2 in western wyoming the moxa arch is a 200 km 124 mi long basement involved anticline the mississippian madison formation and the ordovician bighorn dolomite contain the most co2 within the structure relict anhydrite in these and other paleozoic units was an important factor in evolving hydrocarbons into co2 through inorganic thermal sulfate reduction and more importantly in creating a seal to hold large columns of buoyant gas fluid inclusion data sets have been particularly useful in understanding the sealing characteristics of the units within the moxa arch and affirming that the devonian jefferson mississippian amsden and triassic dinwoody and woodside formations have been very effective seals existing pressure data reveal that the two gas columns in the madison and bighorn formations lie on a similar gradient and share a common gas water contact yet are likely not in hydraulic communication currently all available data suggest that both reservoirs share a fault dependent spill point by reconciling the spill points of the gas in the madison and bighorn reservoirs their compositions their initial and current pressures their seal and the uncertainties associated with injection of co2 can be identified and potentially derisked with additional information if the madison and bighorn are filled to their fault dependent spill point it implies that additional storage capacity in the reservoir can only be obtained by production of the original gas column this uncertainty may be abated if data from future drilling demonstrates that neither the madison formation nor the bighorn dolomite have a fault dependent spill point suggesting that these structures are underfilled with respect to their closure and possess additional storage capacity

le chaˆtelet gold bearing arsenopyrite deposit massif central france mineralogy and geochemistry applied to prospecting abstract the abundant data available on the geochemistry and mineralogy of the herynian gold deposit of le cha telet massif central france formed the basis for an analysis of the complex signature of a gold deposit and its hydrothermal alteration haloes this study describes the deposit and its environment at various scales the sulfide paragenesis of the le cha telet deposit resulted from several stages one of which was an event responsible for the deposition of au bearing arsenopyrite quartz veins the au is contained within the arsenopyrite lattice hydrothermal activity associated with these veins produced two superimposed alteration haloes an outer halo of kaolinite tosudite siderite alteration that developed at the expense of the plagioclase minerals and an inner halo of illite siderite alteration that affected all the minerals the hydrothermal alteration was followed by silicification of the wall rocks and then deposition of the au bearing arsenopyrite the hydrothermal alteration related to the event also generated geochemical signatures such as li b lree as sb au and w anomalies mineralogical studies and geochemical analyses of the hydrothermal facies show that 1 the anomalous li is trapped mainly in the tosudite lattice and to a lesser degree in the illite lattice and 2 the b is probably located in tosudite and illite lattices arsenic sb and au are contained in the arsenopyrite lattice during weathering the lithochemical signatures determined by the analytical techniques used in this study lose some of their specific characteristics depending on the original concentrations at deposit scale 0 25 1 0 km 2 b and li in the soill profiles indicate zones of hydrothermal alteration whereas as and au indicate zones of mineralization at a regional scale the association of au li and b in stream sediments is characteristics of this type of mineralization therefore in the hydrothermal setting described at le cha telet au as li and b appear at all scales to be dependable pathfinders for au bearing hydrothermal systems of possible economic interest

rare earth element distributions among minerals in a granodiorite and their petrogenetic implications a study of the distribution of lanthanide rare earths in a granodiorite from the eastern peninsular ranges batholith southern california reveals that a large fraction of the ree in this rock resides in the accessory phases sphene and allanite the minerals plagioclase alkali feldspar biotite epidote and apatite each contribute approximately 1 or less of each ree to the whole rock with the exception of eu for which plagioclase contributes 7 sphene and allanite together contain 80 to 95 of each ree each of these phases is zoned in ree concentration with substantial decreases from core to margin textural observations argue for relatively early saturation and precipitation of sphene and allanite in the magma ree zoning trends in sphene and allanite and unexpectedly low ree concentrations in largely later crystallizing minerals such as feldspar indicate that the precipitation of sphene and allanite significantly reduced ree concentrations in residual melts these results illustrate the potential that sphene and allanite have for controlling the behavior of ree in granitic magmas available information collectively suggest that the sampled granodiorite existed as a complete melt that the ree contained in the assemblage of phases were derived by direct crystallization from the melt and that the melt behaved essentially as a closed system once crystallization of the phases now present began close correspondences between the major and trace element chemistries of the granodiorite and phenocryst poor lavas from similar tectonic settings support these conclusions the ree pattern of the granodiorite melt appears to have originated at depth and is characteristic of its source regions and derivation mechanism the high liquidus temperature of a granodiorite melt 1000 c indicates the importance of mantle derived components within the sources of batholithic magmas in the peninsular ranges

auriferous mineralization in some shear zones a three stage model of metallogenesis studies of numerous shear zones hosting auriferous quartz veins suggest a three stage model of formation for such veins these stages are indicative of the progressive increase of the gold concentration with the evolution of the shear zone and comprise an early stage with invisible gold an intermediate stage with finegrained gold and a late stage with gold nuggets the early stage consisting of two consecutive episodes comprises the development of the shear zone sensu stricto which results in the formation of a structure characterized by mylonite this structure subsequently acts as a drain for hydrothermal fluids under the combined action of deformation and hydrothermal circulation the rocks in this structure undergo mineralogical transformations that depend on the initial composition of the rock these phenomena occur with increasing intensity towards the cores of the structures the sites of substantial silicification and sulfidation gold is first fixed in the crystal lattice of pyrrhotite up to 30 ppm of gold disseminated throughout the structure as a whole in the core it is destabilized to pyrite marcasite during the second episode of this early stage and the gold thus freed is trapped in the lattice of locally abundant ferriferous sulfides pyrite arsenopyrite up to 1 6 wt gold and berthierite at the intermediate stage again consisting of two consecutive episodes the shear zone can generate openings allowing the emplacement of lenses and veins of milky white quartz when these various veins are in turn crushed by continuing tectonic activity microsaccharoidal quartz forms by cataclasis and acts as a receptacle for the gold mineralization therefore textbook auriferous quartz veins are only one particular aspect of this stage characterized by the appearance of visible native gold caused by destabilization of the auriferous sulfides of the early stage this gold is generally very fine grained several micrometres and relatively silverfree the late stage i e the fifth episode in a brittle domain can occur within a structure of the early or intermediate stage it corresponds to a stage of opening during which stockworks of quartz or of quartz and carbonate form causing in situ remobilization of the auriferous mineralization from the earlier stages this phenomenon is accompanied by the appearance of gold nuggets several millimetres in size very often rich in silver electrum

interpretation and visualization of thrust sheets in a triangle zone in eastern potwar pakistan triangle zone plays are common in the potwar area of pakistan the potwar basin figure 1 is one of the oldest oil provinces it is located in the western foothills of the himalayas in northern pakistan it includes the potwar plateau the salt range and the jhelum plain the khairi murat thrust dhurnal backthrust triangle zone in the northern potwar deformed zone npdz and the joya mair triangle zone in the southern potwar platform zone sppz are also well documented today these tectonic settings hold several billion barrels of reserves and significant amounts of hydrocarbons are being produced we interpreted the domeli dil jabba triangle zone geometry which is the result of tertiary himalayan collision between indian and eurasian plates the thrust and backthrust phases in the eastern potwar are the result of a northwest southeast himalayan compression this is the regional triangle zone in the eastern edge of potwar which is the result of large regionally extensive convergent thrust sheets

drilling conditions making wells unsuitable for fluid inclusion studies on drill cuttings a fluid inclusion study conducted on a well in the northern north sea showed a remarkable correlation between fluid inclusion stratigraphy responses and depths of drilling bit changes further investigation of the well data suggested that extreme temperatures occasionally had been generated at the bit sediment interface during drilling cracking of larger organic molecules to an abundance of smaller ones and trapping of these in inclusions formed by supercooling of partly melted sediment explain the correlation not all wells are consequently suitable for fluid inclusion screening analyses thus before initiating fluid inclusion studies wells that have experienced intense heat during drilling should be identified and avoided

quantitative fluorescence techniques for detecting residual oils and reconstructing hydrocarbon charge history abstract two new fluorescence techniques quantitative grain fluorescence qgf and quantitative grain fluorescence on extract qgf e can detect palaeo oil zones and current residual oil zones in petroleum wells respectively qgf and qgf e measure the fluorescence emission spectra of trace fluorescence from reservoir grains and their extracts qgf is measured on dry disaggregated reservoir grains after a cleaning procedure involving solvent hydrogen peroxide and acid whereas qgf e is measured on the solvent extract from the qgf cleaned grains palaeo oil zones have distinct qgf spectra with spectral peaks between 375 and 475 nm and elevated fluorescence intensities compared with spectra for rocks that have always been water saturated current and residual oil zones have distinct qgf e spectra with spectral peaks at around 370 nm and elevated qgf e intensities compared with that for current water zones both qgf and qgf e responses increase upwards from the palaeo oil water and residual oil water contacts respectively an oil producing well from timor sea nw australia was investigated in detail using the qgf and qgf e techniques to illustrate how they can be used to reconstruct hydrocarbon migration history

using petroleum inclusions to trace petroleum systems a review abstract petroleum bearing fluid inclusions are small encapsulations of oil and gas that offer an invaluable opportunity to better constrain the evolution of petroleum systems insights into palaeo fluid compositions complement observations on present day fluid compositions which represent only the end point of complex cumulative processes throughout basin history in this contribution we review a wide range of approaches used to extract geochemical information from petroleum inclusions and how these can be used to better constrain petroleum systems these techniques can be grouped into optical spectrographic and thermometric non destructive methods or destructive chemical analyses of bulk samples or individual inclusions typically optical methods documenting the distribution and visual properties of petroleum inclusions are used to provide petrographic context for subsequent specialised geochemical analyses of petroleum inclusions additional non destructive techniques such as raman spectroscopy can then be applied to provide some further insights into the composition of the trapped fluids although the complex nature of petroleum generally requires direct access to the fluid for a more complete understanding of geochemical aspects a variety of destructive techniques have been developed initially to analyse bulk samples released by mechanical crushing and more recently through ablation type techniques that allow the composition of individual inclusions to be characterised screening geochemical techniques that utilise mechanical crushing of bulk samples to analyse petroleum inclusions using mass spectrometry without prior chromatographic separation have become routine analyses other geochemical techniques more geared towards detailed molecular information such as biomarkers utilise chromatographic separation prior to mass spectrometry evaluation of the isotopic composition of petroleum inclusions is also possible for both bulk samples and compound specific analyses the use of lasers to open individual inclusions allows the released contents to be analysed by thermal extraction gas chromatography mass spectrometry gc ms or mass spectrometric mapping of minerals using time of flight secondary ion mass spectrometry tof sims a surface sensitive analytical method that uses ion beams to ablate into minerals the continued evolution of techniques to analyse the incredibly small volume of hydrocarbons trapped within fluid inclusions has progressed to a point where there is little that can be done to evaluate a live oil or gas sample that cannot be achieved for a fluid inclusion sample the full power for tracing petroleum systems is however only realised where there is an effective integration of fluid inclusion data with a more conventional approach to petroleum systems analysis

physical analog centrifuge model investigation of contrasting structural styles in the salt range and potwar plateau northern pakistan abstract we use scaled physical analog centrifuge modeling to investigate along and across strike structural variations in the salt range and potwar plateau of the himalayan foreland fold thrust belt of pakistan the models composed of interlayered plasticine and silicone putty laminae comprise four mechanical units representing the neoproterozoic salt range formation basal detachment cambrian eocene carapace sequence and rawalpindi and siwalik groups neogene molasse on a rigid base representing the indian craton pre cut ramps simulate basement faults with various structural geometries a pre existing north dipping basement normal fault under the model foreland induces a frontal ramp and a prominent fault bend fold culmination simulating the salt range the ramp localizes displacement on a frontal thrust that occurs out of sequence with respect to other foreland folds and thrusts with a frontal basement fault terminating to the east against a right stepping east dipping lateral ramp deformation propagates further south in the east strata to the east of the lateral ramp are telescoped in ene trending detachment folds fault propagation folds and pop up structures above a thick basal detachment salt range formation in contrast to translated but less deformed strata with e w trending salt range structures to the west the models are consistent with salt range potwar plateau structural style contrasts being due to basement fault geometry and variation in detachment thickness

archean gold bearing quartz veins at the sigma mine abitibi greenstone belt quebec part ii vein paragenesis and hydrothermal alteration the sigma deposit consists of an archean gold bearing vein system in deformed volcanic rocks intruded by two generations of porphyries the veins cut all rock types and wall rock alteration is superposed on greenschist facies metamorphic assemblages there are two related vein sets subvertical veins in ductile shears and subhorizontal veins in extensional fractures between shear zones this paper reports on the paragenesis of extensional veins and related hydrothermal alteration tension veins are composed chiefly of quartz and tourmaline and subordinate amounts of carbonates chlorite pyrite pyrrhotite scheelite and free gold the veins formed by one or more episodes of open space filling the paragenetic sequence consists essentially of successive deposition of carbonate scheelite tourmaline pyrite pyrrhotite carbonate chlorite and quartz most of the gold and tellurides was introduced into fractures and along grain boundaries of recrystallized vein minerals during a postfilling episode of deformation veins are surrounded by zoned alteration envelopes consisting of an outer zone of cryptic alteration characterized by a chlorite carbonate white mica assemblage and an inner zone of visible alteration characterized by a carbonate white mica outer subzone and a carbonate albite inner subzone alteration zones represent reaction fronts advancing into the wall rocks and resulted from progressive interaction of wall rocks with a single hydrothermal fluid the chlorite carbonate white mica zone is characterized by replacement of epidote by calcite and white mica accompanied by fixation of co 2 and k and by release of small amounts of si in carbonate white mica and carbonate albite subzones of visible alteration chlorite biotite and white mica were replaced by calcite albite and quartz variable amounts of gold tourmaline pyrite pyrrhotite and ilmenite were also introduced visible alteration zones are characterized by additions of ca co 2 na b s p and au and by important losses of mg fe al and h 2 o mass balance calculations show that ca na si co 2 s and b in vein minerals were contributed from the hydrothermal fluid whereas fe mg and al were derived from the walls the development of alteration envelopes began with the infiltration of hydrothermal fluids into open extensional fractures and it ceased before complete filling of the veins when continuous mineral coatings formed along vein walls deposition of carbonate accompanied development of cryptic alteration including initial co 2 additions to the wall rocks subsequent deposition of tourmaline pyrite and pyrrhotite carbonate chlorite accompanied the progressive development of visible alteration which encroached on cryptically altered rocks visible alteration is characterized by additions of ca and co 2 to the wall rocks and by release of mg fe and al later bulk quartz deposition which filled the vein openings generally took place after complete development of the alteration envelopes except for this late quartz deposition of vein minerals is attributed to chemical changes in the fluid resulting from progressive wall rock alteration bulk quartz deposition is attributed to progressive cooling of the hydrothermal fluid

modelling of thermal convection in sedimentary basins and its relevance to diagenetic reactions abstract mathematical calculations of thermal convection have been carried out using a porous three player model to simulate pore water flow in a sedimentary basin with layers of different permeabilities the calculated flow lines demonstrate that even very thin layers eg around salt domes and igneous or hydrothermal intrusions analyses of formation waters from sedimentary basins like the north sea often show evidence of a crude stratification of the pore water with respect to salinity and isotopic composition this is evidence suggesting that large scale convection or other types of mixing does not take place and positive salinity depth gradient may help to physically stabilize the formation water the fact that many of the shallow reservoir rocks from the north sea have formation water with low salinity and negative 18 o values suggest that this is modified meteoric water and that migration of petroleum from deeper parts of the basin occurred as a separate phase along restricted migration pathways and was not associated with a high flux of pore water in the absence of thermal convection the total pore water flux through sandstones will be rather small except locally where we may have focused compactional flow through small cross sections diagenetic reactions will therefore normally be relatively isochemical during deeper burial