age of cu fe au mineralization and thermal evolution of the punta del cobre district chile the punta del cobre belt is located 15 km south of copiapo northern chile it comprises several cu fe au deposits in the punta del cobre and ladrillos districts east of the copiapo river and the ojancos nuevo district with the new candelaria mine and las pintadas district west of the river the mineralization in the punta del cobre belt is characterized by a simple hypogene mineral assemblage of chalcopyrite pyrite magnetite and hematite average ore grades are 1 1 to 2 cu 0 2 to 0 6 g t au and 2 to 8 g t ag massive magnetite occurs as veins and irregularly shaped bodies the ore is spatially associated with alkali metasomatism and in particular with potassic alteration the cu fe au deposits are hosted mainly in volcanic rocks of the punta del cobre formation pre upper valanginian that underlie neocomian limestones of the chanarcillo group this region experienced backarc basin formation in the neocomian uplift and granitoid intrusions in the middle cretaceous and eastward migration of the magmatic front of about 30 km between middle cretaceous and paleocene to determine the timing of ore deposition and to reconstruct parts of the thermal history of the punta del cobre district in the eastern part of the belt we have obtained 40ar 39ar incremental heating and rb sr analyses of mineral and whole rock samples an 40ar 39ar incremental heating experiment on hydrothermal biotite formed synchronous with the cu fe au mineralization yielded an inverse isochron age of 114 9 1 0 ma all errors reported at 2 consistent with a rb sr isochron of 116 8 2 7 ma calculated from 7 whole rock samples these data are interpreted to represent the age of potassic alteration that accompanies mineralization ore formation temperatures of 400 c to 500 c were previously estimated based on paragenetic relationships shearing at the candelaria deposit occurred after ore deposition and before the main stage of batholith emplacement published k ar ages for the middle cretaceous batholith near the punta del cobre belt range from 119 to 97 ma our data suggest that the mineralization is related to the earlier stages of batholith emplacement the biotite age spectrum indicates that the punta del cobre district was not affected by temperatures above 300 c 350 c the closure temperature for argon in biotite during the contact metamorphic overprint produced by later emplaced batholithic intrusions whole rock 40ar 39ar ages are considerably younger incremental heating experiments yielded an inverse isochron age of 90 7 1 2 ma and weighted mean plateau ages of 89 8 0 6 ma and 89 5 0 6 ma these samples are dominantly k feldspar for which we assume an argon closure temperature of 150 c thus they give the age of cooling below 150 c 200 c

simulating seismic chimney structures as potential vertical migration pathways for co2 in the snohvit area sw barents sea model challenges and outcomes carbon capture and storage ccs activities at the snohvit field barents sea will involve carrying out an analysis to determine which parameters affect the migration process of co2 from the gas reservoir to what degree they do so and how sensitive these parameters are to any changes this analysis will aim to evaluate the effects of applying a broad but realistic range of reservoir fault and gas chimney properties on potential co2 leakage at various depths throughout the subsurface fluid flow might take place through parts of or the entire extent of the overburden one of the aims of the analysis is assessing the potential of co2 reaching the seabed using the snohvit gas reservoir and overburden in the barents sea a series of geological models were built using seismic and well log data we then performed numerical simulations of co2 migration in focused fluid flow structures identification of potential migration pathways and their extent such as gas chimneys and faults and their incorporation into these models and simulations will provide a realistic insight into the migration potential of co2 in the simulations the co2 is injected over a 20 year period at a rate of 0 7 mt year and migration is allowed to take place over a 2000 year time frame for domains of approximately 21 km2 for the caprock fault models 24 km2 for the realistic gas chimney models and 35 km2 for the generic gas chimney models in a layered sedimentary succession the total mass of co2 injected in the reservoir during the 20 year injection period is 14 mt there is a strong interaction between the various parameters but the parameter that had the most influence on the co2 migration process was probably the permeability of the reservoirs especially the average permeability k also for the faulted caprock scenarios it should be noted that at near surface depths the permeability of 765 md is already adequate for a good co2 flow at the chimney top level 600 m however a further increase in permeability has an additional effect on improving co2 flow overall considering the slow upward migration velocity of the plume this geological setup can be regarded as a suitable storage site

inferences for sources of oils from the norwegian barents sea using statistical analysis of biomarkers abstract conventional biomarker age indicators may not always give conclusive inferences for the age of an oil s source rock particularly with regard to condensates in which most of the key biomarkers are often too sparse to determine it is possible that other compounds reflecting changes in primary producer assemblages or depositional environment can provide age indications in basins that have experienced a progressive change in conditions the norwegian barents sea provides an opportunity to evaluate this approach although the gradual changes are punctuated by intervals of stratification oaes and extinctions partial least squares analysis was used to identify a number of apparently suitable parameters to establish an age calibration from source rock extracts and then to apply it to a variety of oils and condensates from the barents sea the resulting source age inferences are consistent with conventional age parameters for the normal oils providing a degree of confidence in their applicability to the problematic condensates in the main part of the hammerfest basin oils of jurassic origin dominate whereas contributions from triassic sources are suggested towards the margins particularly in pre jurassic reservoirs to the east on the norsel high and in the nordkapp basin the main oil sources are suggested to be early triassic although a palaeozoic possibly permian source is likely on the margin of the finnmark platform in well 7128 4 1 among the novel parameters the relative abundances of phytanyl arenes and diadrimanes appear to be controlled by diagenetic conditions

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

interlaboratory comparison of magnesium isotopic compositions of 12 felsic to ultramafic igneous rock standards analyzed by mc icpms to evaluate the interlaboratory mass bias for high precision stable mg isotopic analysis of natural materials a suite of silicate standards ranging in composition from felsic to ultramafic were analyzed in five laboratories by using three types of multicollector inductively coupled plasma mass spectrometer mc icpms magnesium isotopic compositions from all labs are in agreement for most rocks within quoted uncertainties but are significantly up to 0 3 in 26mg 24mg 4 times of uncertainties different for some mafic samples the interlaboratory mass bias does not correlate with matrix element mg ratios and the mechanism for producing it is uncertain but very likely arises from column chemistry our results suggest that standards with different matrices are needed to calibrate the efficiency of column chemistry and caution should be taken when dealing with samples with complicated matrices well calibrated standards with matrix elements matching samples should be used to reduce the interlaboratory mass bias

3d basin modelling of the hammerfest basin southwestern barents sea a quantitative assessment of petroleum generation migration and leakage abstract 3d basin modelling of the hammerfest basin southwestern barents sea was performed in order to address the masses of petroleum generated accumulated and lost during the evolution of the basin calibration of the model based on observed maturity vitrinite reflectance and present day temperatures took into account 1 two main erosion episodes an oligocene miocene event due to tectonic uplift and a plio pleistocene glacial erosion event and 2 variable heat flow from late palaeozoic to cenozoic the maturity levels of the main source rocks kobbe snadd and hekkingen formations were reconstructed and show that the highest maturities have been reached in the western and northwestern margin of the basin the beginning of petroleum generation in the kobbe snadd and hekkingen source rocks has been predicted to occur during late triassic early cretaceous and late cretaceous respectively our model reproduces satisfactorily the distribution of the main oil and gas fields and discoveries that have been found in the study area our results indicate that two events of hydrocarbons redistribution occurred in the basin the first event resulted in the main oil redistribution episode which took place during the oligocene miocene associated with tectonic uplift and gas expansion and the second was related to the main gas leakage events that occurred during the pliocene pleistocene glacialinterglacial cycles in general and the episodes of glacial retreat in particular glacial loading and unloading cycles resulted in overpressure fluctuations in the subsurface reservoirs modelling results indicate that during these episodes a portion at least 0 247 gt of thermogenic gas leaked from the main sto formation reservoirs reached the sediment interface and was released to the surface in the hammerfest basin

a new jurassic recent apparent polar wander path for south america and a review of central andean tectonic models abstract the jurassic to recent palaeomagnetic data from the stable cratonic areas of south america and africa are reviewed and evaluated from the combined data set seven mean reference pole positions are calculated for the early middle and late jurassic early and late cretaceous palaeogene and neogene most of these new palaeopoles are well defined and indicate a complex course of apparent polar wander for the south american plate comparison of the palaeomagnetic data from the andean margin with the reference poles indicates vertical axis rotations defining a broad pattern of anticlockwise rotations north of the arica deflection at approximately 19 s and clockwise rotations to the south further analysis indicates however that the distribution and magnitude of rotations is more complicated than this broad division tectonic models proposed to explain the pattern of rotations and the possible origins of the arica deflection are discussed it is suggested that the rotations probably result from localised in situ rotations controlled by strike slip fault systems or thrust sheets rather than large scale rotation mechanisms the broad rotation pattern may result from the influence of pre existing structures in the margin or variations in the flexural rigidity of the brazilian shield behind the deformation zone

identification of a large upper cretaceous polygonal fault network in the hammerfest basin implications on the reactivation of regional faulting and gas leakage dynamics sw barents sea abstract we use a high resolution 3d seismic dataset covering 970 km2 over the snohvit and albatross gas fields of the hammerfest basin in the barents sea in order to investigate the basin fault architecture and identify potential fluid pathways of deeper thermogenic gas and fluids a polygonal fault pf interval not previously published is described in the three non connected blocks within campanian sequences which could imply a permeable complex network of pathways that facilitate the vertical migration of hydrocarbons along the fault planes the dominant orientation of the pfs is similar to the main regional tectonic fault trend ew suggesting a tectonic influence upon the development of polygonal faults although some individual pfs locally seem to develop orthogonally to regional 1st order tectonic faults a lithologic control on the occurrence of pf patterns is evident as none are observed within calcareous low clay sediments the pf networks present three main orientations dominant ene wsw secondary nne ssw and a minor ne sw paleocene early eocene faults peefs prevail above the pf networks with coinciding ene wsw fault strikes interpreted as preferential reactivation of the pf systems numerous amplitude anomalies linked to the escape of thermogenic fluids from the jurassic reservoir were identified we present a conceptual model where the 1st order reactivated faults and peefs acted as pathways for fluids from the deeper hydrocarbon reservoirs the peefs are partially sealing with a lateral migration component interplay between the pfs peefs and the 1st order reactivated faults focuses the fluids vertically along the polygonal fault traces creating a wider diffuse zone which form large gas cloud anomalies in the seismic data

deep seated faults and hydrocarbon leakage in the snohvit gas field hammerfest basin southwestern barents sea abstract high quality 3d seismic data are used to analyze the history of fault growth and hydrocarbon leakage in the snohvit field southwestern barents sea the aim of this work is to evaluate tectonic fracturing as a mechanism driving hydrocarbon leakage in the study area an integrated approach was used which include seismic interpretation fault modeling displacement analysis and multiple seismic attribute analysis the six major faults in the study area are dip slip normal faults which are characterized by complex lateral and vertical segmentation these faults are affected by three main episodes of fault reactivation in the late jurassic early cretaceous and paleocene fault reactivation in the study area was mainly through dip linkage the throw distance plots of these representative faults also revealed along strike linkage and multi skewed c type profiles the faults evolved through polycyclic activity involving both blind propagation and syn sedimentary activity with their maximum displacements recorded at the reservoir zone the expansion and growth indices provided evidence for the interaction of the faults with sedimentation throughout their growth history soft reflections or hydrocarbon related high amplitude anomalies in the study area have negative amplitude reverse polarity and are generally unconformable with structural reflectors the interpreted fluid accumulations are spatially located at the upper tips of the major faults and gas chimneys four episodes of fluid migration are inferred and are linked to the three phases of fault reactivation and neogene glaciations hydrocarbon leakage in the snohvit gas field is driven by tectonic fracturing uplift and erosion the interpreted deep seated faults are the main conduits for shallow hydrocarbon accumulations observed on seismic profiles

mechanisms of continental growth in extensional arcs an example from the andean plate boundary zone during the late triassic jurassic and early cretaceous an extensional magmatic arc was formed in the andean margin of northern chile plutons emplaced at ramps within a hinterland propagating extensional duplex were fed by dikes that transferred magma through the lower crust from a reservoir in the mantle phases of volcanism separated phases of plutonism and our model demonstrates that plutonism was favored only when upper plate extensional fault systems were active when they were not dikes cut across inactive faults and magma rose directly to the surface during volcanic phases of arc growth

a mesozoic time scale we present an integrated geomagnetic polarity and stratigraphic time scale for the triassic jurassic and cretaceous periods of the mesozoic era with age estimates and uncertainty limits for stage boundaries the time scale uses a suite of 324 radiomenc dates including high resolution 40 ar 39 ar age estimates this framework involves the observed ties between 1 radiometric dates biozones and stage boundaries and 2 between biozones and magnetic reversals on the seafloor and in sediments interpolation techniques include maximum likelihood estimation smoothing cubic spline fitting and magnetochronology

petroleum source maturity alteration and mixing in the southwestern barents sea new insights from geochemical and isotope data the hammerfest basin hb is an important area for petroleum exploration in the southwestern norwegian barents sea this contribution is aimed to characterize oils and condensates hosted in triassic and jurassic reservoirs establish genetic relationships and to assess maturity mixing and petroleum alteration processes the research was based on geochemical as well as bulk and compound specific stable carbon and hydrogen isotope analyses of oil and condensate samples from all major fields and discoveries in the hb including extracts from jurassic and triassic source rocks interpretations of light hydrocarbon composition and isotope data clearly identify four main petroleum groups affected by microbial degradation water washing evaporative fractionation and high thermal maturity level based on polycyclic aromatic hydrocarbons pahs marine and higher plant derived biomarkers and carbon isotopic composition 13c of individual petroleum hydrocarbons four petroleum families i iv are recognized in the hb and a distinction can be made among oils and condensates from different stratigraphic levels and sectors of the basin most oils and condensates from the hb consist of mixtures with small maturity variations however oils from middle triassic reservoirs in the goliat field showed larger maturity variations according to biomarker pah and light hydrocarbon maturity ratios in the hb geochemical and isotopic data allowed unraveling mixtures of hydrocarbons derived mainly from jurassic triassic and paleozoic source rocks

cenozoic erosion and sedimentation in the western barents sea abstract seismic reflection data and well logs are used to interpret cenozoic sedimentary environments in the south western barents sea using volumetric calculations and compaction trend analysis the cenozoic erosion and sedimentation rates have been quantified marine environments ranging from neritic to bathyal water depths dominated the southern barents sea during the late palaeocene at the palaeocene eocene boundary a southwards progradation commenced along the uplifted and eroded loppa and stappen highs during the early eocene to mid miocene sedimentation continued in the intracratonic basins as well as along the newly established continent ocean boundary in the embryonic northern norwegian greenland sea substantial erosion occurred on the westernmost margin particularly on the stappen high during this time interval in the mid miocene during a period of relative lowstand of sea level a system of lowstand fans was deposited west of the stappen high later a pronounced progradation of the shelf edge commenced during the mid miocene to late pliocene the shelf edge prograded between 20 and 40 km during the mid pliocene to early pleistocene the barents sea and adjacent land areas were uplifted a fluvial glaciofluvial drainage system developed on the continental shelf resulting in pronounced erosion there and very high sedimentation rates on the continental margin during the last 0 8 ma several large glaciations on the barents sea shelf proper have resulted in overdeepened troughs and high sedimentation rates at the continental shelfbreak and on the continental slope the overall cenozoic erosion varies spatially as well as temporally in the svalbard area close to 3 km of rocks have been eroded since the oligocene the same amount or more was eroded from the stappen high during the palaeocene and early neogene in the south western areas during the eocene mid miocene erosion occurred along the margin in addition the loppa high and adjacent areas served as sediment source areas during the late pliocene and pleistoncene the average erosion in the south western barents sea amounted to about 600 m erosion was greater in the south east than to the west and north and was more extensive where the former glacial ice streams had flowed

relationship between altered pyroxene diorite and the magnetite mineralization in the chilean iron belt with emphasis on the el algarrobo iron deposits atacama region chile north of el algarrobo one of the four main deposits of the chilean iron belt the iron mineralization magnetite etrmolite actinolite apatite is related to clinoand orthopyroxene diorite intrusions which have crystallized at shallow depth 4km under increasing oxygen fugacities the supercritical fluid phase exsolved during cooling after the consolidation of the plutons 800 900 c results in a h cl and sodic enrichment and in the sequential leaching of fe at less than 700 c then ca and mg between 600 and 500 c from minerals of the primary magmatic diorite assemblage titanomagnetite ilmenite plagioclase an70 40 augite hypersthene as a consequence of the cationic leaching the lower mobility of silica and aluminium and the enrichment in sodium residual altered dioritic rocks present a retromorphic mineral assemblage evolving down to boundary conditions of the greenchist amphibolite facies 450 c fe mg and ca are carried in cationic form associated with cl anions toward cooler rocks where they are precipitated the deposition between 550 and 450 c of magnetite followed iron mineralization paragenesis and occurred in fractured zones located both in altered diorites and contact andesites

stable isotope geochemistry of coals humic kerogens and related natural gases isotope systematics are well defined for conventional sapropelic type i ii kerogens and their associated bacterial and thermogenic natural gas products these geochemical tools are used to estimate source type maturity and depositional environment and as a correlation technique in many cases the natural gas signatures in near surface samples and drill cuttings can be used to classify or predict a deeper lying source rock or reservoir corresponding interpretative schemes for coals type iii kerogens and their associated hydrocarbons are progressing quickly the shift in attention to humic sources is driven primarily by depletion of conventional oil and gas resources and the economic and societal requirements of coal and coal bed methane carbon hydrogen and nitrogen stable isotope variations can be large between different coals and humic kerogens these differences can often be recognized in their bulk 13corg dorg and 15norg values isotope signatures of coals can be diagnostic of several factors including deposit age type geographic location maturity and generation history however these characteristic isotopic variations are substantially better defined by the c h and n isotope ratios of the separate maceral groups such as vitrinite exinite and inertinite this new application of stable isotopes at the maceral and compound levels have great potential to improve the interpretative precision over conventional whole coal or bulk techniques hydrocarbon gases including coal gases derived from coals and humic kerogens can be distinguished from type i ii sources based on their molecular rations i e c1 c2 c3 and by comparing their stable isotope compositions especially 13cch4 and dch4 the 13cc2h6 can also be valuable but ethane is generally present in small amount 1 vol and requires

pockmark like depressions near the goliat hydrocarbon field barents sea morphology and genesis abstract pockmarks are observed worldwide along the continental margins and are inferred to be indicators of fluid expulsion in the present study we have analysed multibeam bathymetry and 2d 3d seismic data from the south western barents sea in relation to gas hydrate stability field and sediment type to examine pockmark genesis seismic attributes of the sediments at and beneath the seafloor have been analysed to study the factors related to pockmark formation the seabed depths in the study area are just outside the methane hydrate stability field but the presence of higher order hydrocarbon gases such as ethane and or propane in the expelled fluids may cause localised gas hydrate formation the selective occurrence of pockmarks in regions of specific seabed sediment types indicates that their formation is more closely related to the type of seabed sediment than the source path of fluid venting such as faults the presence of high acoustic backscatter amplitudes at the centre of the pockmarks indicates harder coarser sediments likely linked to removal of soft material the pockmarks show high seismic reflection amplitudes along their fringes indicating deposition of carbonates precipitated from upwelling fluids high seismic amplitude gas anomalies underlying the region away from the pockmarks indicate active fluid flow from hydrocarbon source rocks beneath which is blocked by overlying less permeable formations in areas of consolidated sediments the upward flow is limited to open fault locations while soft sediment areas allow diffused flow of fluids and hence formation of pockmarks over a wider region through removal of fine grained material

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

mesozoic magmatic and tectonic events within the andean plate boundary zone 26 27 30 s north chile constraints from 40 ar 39 ar mineral ages in north chile jurassic cretaceous arc magmatism is represented by several narrow belts of plutons and two separate volcanic sequences new 40 ar 39 ar mineral ages confirm five distinct episodes of magma emplacement as plutonic complexes c 202 188 ma c 160 153 ma c 142 138 ma c 130 127 ma and c 106 103 ma conjugate dike sets were emplaced immediately before periods of plutonism and each distinct episode of magmatism prior to c 127 ma was located successively eastward inboard from the subduction boundary features interpreted to result from regional extension within the magmatic arc steeply dipping ductile mylonitic shear zones were developed in wall rocks along western contacts of late jurassic and early cretaceous plutons steeply plunging mineral stretching lineations and a variety of kinematic indicators record an east side down extension along eastern faults of the atacama fault system steeply dipping ductile mylonitic shear zones display subhorizontal mineral stretching lin

hydrocarbon plumbing systems above the snohvit gas field structural control and implications for thermogenic methane leakage in the hammerfest basin sw barents sea abstract based on the analysis of the high resolution 3d seismic data from the sw barents sea we study the hydrocarbon plumbing system above the snohvit and albatross gas field to investigate the geo morphological manifestation and the dynamics of leakage from the reservoir fluid and gas escape to the seafloor is manifested in this area as mega pockmarks 1 2 km wide large pockmarks

mesozoic fault systems deformation and fault block rotation in the andean forearc a crustal scale strike slip duplex in the coastal cordillera of northern chile abstract in this paper we discuss the evolution and tectonic significance of the mesozoic trench parallel fault systems which affected the coastal cordillera and their relation to magmatism and crustal rotation the oldest extensional fault system separates basement from rift related late triassic and younger sedimentary units this system i subsequently developed into a wider extensional fault system which acted as the locus of magma ascent and emplacement of the coastal batholith during much of the jurassic to earliest cretaceous period this extensional fault system defined the forearc sliver during this period and was the consequence of a retreating subduction boundary during the early cretaceous c 132 125 ma the kinematics of this fault system changed to transtension ii and accommodated a major component of left lateral strike slip motion the principal fault being the atacama fault zone along which plutons continued to be emplaced the final phase of pluton emplacement within the coastal cordillera appears to be c 106 ma after which this magmatic arc and fault system was abandoned an late cretaceous arc and fault system iii developed some 20 ma later and located some 50 km to the east in what is now the central valley of northern chile this paper seeks to show that the coastal cordillera was deformed as a whole by this late cretaceous fault system iii which formed a crustal scale left lateral transpressional duplex during this deformation the thermally weakened crust was dissected into a series of large scale blocks bounded by nw trending left lateral strike slip faults which merge into a nne ssw fault zone which forms the eastern boundary to the duplex we term this eastern boundary zone the central valley fault zone cvfz and this together with the nw trending faults defines the duplex system which we refer to as a whole as the coastal cordillera fault system ccfs iii we have traced the ccfs duplex between 25 s and 29 s and suspect that it continues northward the timing of the deformation is constrained to be post 106 ma the age of coastal cordillera arc abandonment and pre tertiary based on the deformation and pluton emplacement in and along the central valley fault zone palaeomagnetic data from the fault bound blocks within the ccfs duplex indicate 35 45 of post early cretaceous clockwise rotation with no substantial latitudinal motion we suggest that the observed fault kinematics of the ccfs are consistent with this crustal scale duplex model where rotations would have occurred in response to left lateral transpression

geochemically driven exploration models in uplifted areas examples from the norwegian barents sea the norwegian barents sea with multiple source rock intervals represents a prime example of an overfilled petroleum system however several episodes of uplift and erosion from the paleocene until the pliocene pleistocene have caused the depletion of hydrocarbon accumulations in the region these uplift events were not only potentially catastrophic but have also caused the redistribution of the remaining oil and gas over laterally large distances in the barents sea region this redistribution directed petroleum to distal parts of the various hydrocarbon generating basins thus charging traps which otherwise would not have been reached therefore we expect that discoveries will be made in distal basin settings particularly in traps with partly leaking cap rocks which can bleed off gas and thereby retain oil many oil accumulations in the region represent various mixtures of oils from several different stratigraphic source intervals this suggests that triassic and paleozoic oils may be trapped below the presently drilled targets which are mostly jurassic in the hammerfest basin and older to the north and east deeper exploration targets also stand a higher chance of containing oil because the amount of gas being released from oil during uplift erosion and subsequent pressure release is lower uplift and erosion are followed by a reduction in temperature this is why hydrocarbon generation is believed to have ended in uplifted areas some discoveries in this data set suggest however a significant fresh gas charge

development and applications of light hydrocarbon based star diagrams two star diagrams multivariate plots in polar coordinates have been developed to assess subtle chemical differences among oils the diagrams are based on analysis of c7 hydrocarbons of crude oils separated by gas chromatography the first of the c7 diagrams is used for distinguishing variations in oils caused by transformation e g water washing biodegradation and evaporation eight ratios are plotted on this diagram in order of decreasing sensitivity to biodegradation the ratios are designated tr1 through tr8 and the diagram is referred to as the c7 oil transformation star diagram c7otsd a second c7 based diagram consists of five ratios composed of compounds that are very resistant to the effects of transformation and thus are useful for correlation these ratios designated c1 through c5 are plotted on the c7 oil correlation star diagram c7ocsd this diagram can be used to correlate both transformed and primary oils based on source related chemical differences a task not easily accomplished through most conventional geochemical techniques for example condensates often contain no biomarkers due to their advanced maturity and therefore cannot be correlated with lower maturity oils however both condensates and oils usually contain light ends allowing correlation by c7 based star diagrams the division of star diagrams into two types allows one to assess the relative degrees of transformation among a set of oils that have been found to correlate based on the c7ocsd these microscale correlations detect small chemical differences between oils and therefore allow even slight variations among oils within the same reservoir to be recognized the technique has many applications that concern both exploration and production production related uses include reservoir compartmentalization studies investigating reservoir extent and connectivity determining the source of casing leakage and determining the extent of commingling of oils from different reservoirs in multicompletion wells or leaky single completion wells exploration problems that can be addressed are mechanisms and models of field fill history and evaluation of oil quality in untested pay zones most of these problems can be addressed through simple cost effective analyses on produced or tested crude oils for example a large advantage in production applications is the ability to assess reservoir connectivity without halting production from any well an additional use of the technique is for investigating contaminants or incompletely refined crudes in refinery streams in this paper i present several case studies that have already been done at saudi aramco these studies include three examples of behind casing leakage two examples of oil differentiation and a single example each of correlation of condensates and refinery contaminant tracing

petroleum system analysis of the hammerfest basin southwestern barents sea comparison of basin modelling and geochemical data abstract exploration in the hammerfest basin southwestern barents sea has proven several petroleum systems and plays with the presence of multiple source rocks of mainly jurassic and triassic age to date several fields and discoveries have been found and are described to mainly contain gaseous hydrocarbons with the presence in some cases of an oil leg our 3d hammerfest basin model shows that the jurassic hekkingen formation and the triassic snadd and kobbe formations reached high maturity levels gas window in the western and the northwestern margin at the same time this model reproduces the main hydrocarbon accumulations that have been found in the basin an analysis of the volumetrics and the proportion of oil and gas contributions to each field and discovery suggests that the gas contribution stems mainly from triassic source rocks while the oil phases contain variable proportions from the jurassic hekkingen formation and triassic source rocks gas isotope and maturity related biomarker ratios confirm the maturity trends derived from the basin modelling results light hydrocarbons indicate the influence of secondary processes biodegradation and long distance migration in the petroleum from the goliat field and the tornerose discovery age related biomarker ratios such as the etr extended tricyclic terpane ratio and the c28 c29 steranes ratio did not provide a clear separation when evaluating a contribution from jurassic vs triassic source rocks

multiple episodes of fluid flow in the sw barents sea loppa high evidenced by gas flares pockmarks and gas hydrate accumulation abstract gas and gas hydrates have gained considerable attention in the last 20 yr due to their possible impact on global climate change from methane escalations our study area the sw barents sea is unique in its evolution due to the effect of glaciations which removed thick layers of sediment from the seabed unloading due to erosion and deglaciation resulted in opening of pre existing faults and creation of new ones facilitating fluid migration and eventually escape into the water from the subsurface expressions of hydrocarbon gas accumulation and fluid flow such as gas hydrates and pockmarks are widely distributed in the barents sea several gas flares some of them 200 m high in echograms occur along a segment of the ringvassoy loppa fault complex indicating open fractures and active fluid flow observation of gas flares along regional fault complexes outside pockmark regions indicates that present gas escape occurs along faults only the pockmark formation and gas flares belong to different episodes of fluid flow the pockmarks are absent outside soft sediment depocentres indicating that their existence is related to the presence of recording medium the thin sediment cover in pockmarks and their penetration down into glaciomarine sediments indicate that they formed after deposition of these sediments and that fluid escape was active to the very recent past methane hydrate stability zone mhsz modelling shows that after the last glacial maximum 18 000 20 000 14c years ago the mhsz has thinned from 600 m to zero in most parts of the sw barents sea the fluid expulsion probably happened after retreat of the glaciers causing release of methane from dissociation of methane hydrates through fluid escape processes which lasted until recently bottom simulating reflectors bsr observed are probably due to structure ii hydrates formed from gas containing higher order hydrocarbon components such as ethane propane etc along with methane the study area falls close to the new gigantic oil discoveries skrugard and havis and north of the snohvit hydrocarbon field

palaeomagnetism applied to magnetic anomaly interpretation a new twist to the search for mineralisation in northern chile the chilean iron belt is an important location for fe and cu fe au deposits and includes the recently developed candelaria deposit which is located some 20 km south of the city of copiapo in northern chile this mine is now a major cu producer in chile but its discovery in the late 1980s was relatively fortuitous the exploration programme included a ground magnetic survey from which lessons can be learnt in the search for further such deposits palaeomagnetic studies throughout the northern part of the chilean iron belt indicate major crustal rotation of the region probably related to oblique convergence and transpression at the andean margin the application of palaeomagnetic techniques to a magnetite apatite deposit mina fresia indicates that magnetite rich ores in this area are capable of maintaining a significant remanence component which will contribute to their magnetic anomaly as with the volcanics intrusives and sediments of the region this remanence is clearly rotated clockwise using 2 5d and 3d magnetic modelling it is demonstrated that the magnetic anomaly associated with the candelaria deposit is also dominated by a remanence component which is significantly rotated but of reversed polarity recognition of clockwise rotated remanence dominated anomalies should provide a new key to the search for deposits in this part of chile and elsewhere an example of an unexplored anomaly showing this key feature of a clockwise rotated remanence component dominating over the induced component is presented modelling of this anomaly indicates a pair of sources which are either ten times as big or ten times as magnetic as the candelaria deposit it is suggested that the low cost of palaeomagnetic study of an exploration target should be a prerequisite to magnetic anomaly interpretation of targets in tectonic areas where vertical axis crustal rotations may be a significant element of the overall deformation pattern

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

cenozoic erosion and the preglacial uplift of the svalbard barents sea region abstract the creation of the huge fans observed in the western barents sea margin can only be explained by assuming extremely high glacial erosion rates in the barents sea area glacial processes capable of producing such high erosion rates have been proposed but require the largest part of the preglacial barents sea to be subaerial to investigate the validity of these proposals we have attempted to reconstruct the western preglacial barents sea our approach was to combine erosion maps based on prepublished data into a single mean valued erosion map covering the whole western barents sea and consequently use it together with a simple airy isostatic model to obtain a first rough estimate of the preglacial topography and bathymetry of the western barents sea margin the mean valued erosion map presented herein is in good volumetric agreement with the sediments deposited in the western barents sea margin areas and as a direct consequence of the averaging procedures employed in its construction we can safely assume that it is the most reliable erosion map based on the available information by comparing the preglacial sequences with the glacial sequences in the fans we have concluded that 1 2 to 2 3 of the total cenozoic erosion was glacial in origin and therefore a rough reconstruction of the preglacial relief of the western barents sea could be obtained the results show a subaerial preglacial barents sea thus during interglacials and interstadials the area may have been partly glaciated and intensively eroded up to 1 mm y while during relatively brief periods of peak glaciation with grounded ice extending to the shelf edge sediments have been evacuated and deposited at the margins at high rates the interplay between erosion and uplift represents a typical chicken and egg problem initial uplift is followed by intensive glacial erosion compensated by isostatic uplift which in turn leads to the maintenance of an elevated and glaciated terrain the information we have on the initial tectonic uplift suggests that the most likely mechanism to cause an uplift of the dimensions and magnitude of the one observed in the barents sea is a thermal mechanism

south american reference pole for the mid cretaceous further constraints in the interpretation of andean paleomagnetic data a paleomagnetic study of the aptian cerro barcino formation in central patagonia showed the presence of a stable magnetization with a positive tilt test the obtained pole position lat 85 s long 181 e 95 5 6 n 11 differs from reliable early and late cretaceous south american cratonic poles the cerro barcino pole overlaps coeval poles from the chilean andean fore arc previously interpreted to record crustal block rotations this new result indicates that previously published andean tectonic models must be reviewed

tectonostratigraphic modelling of cenozoic uplift and erosion in the south western barents sea abstract cenozoic subsidence patterns in the south western barents sea punctuated by periods of uplift and erosion deviate from thermal subsidence patterns predicted by stretching models of basin formation three regional seismic lines crossing the south western barents sea show that a substantial amount of erosion occurred at the shelf whereas at the margin a thick wedge of cenozoic sediments has been observed quantitative basin modelling of the profiles allows different mechanisms for erosion and uplift to be tested the modelling shows that the palaeocene early eocene flank uplift during rifting and late neogene intraplate stresses superimposed on a middle miocene sea level change and pliocene quaternary de glaciation play a major role in the development of the late cenozoic stratigraphy stress induced uplift of flank areas could augment the regional uplift of scandinavia possibly leading to climatic changes such as the onset of cooling and glaciation intraplate stresses related to plate boundary processes in the north atlantic realm also have important implications for the depth of the hydrocarbon window in the south western barents sea

oil families and their inferred source rocks in the barents sea and northern timan pechora basin russia a geochemical study of 34 oil samples was conducted to understand the types and distributions of effective source rocks and evaluate the geographic extent of the petroleum systems in the barents sea and northern timan pechora basin taxon specific age related and source related biological markers biomarkers and isotope data provided information on the depositional environment of the source rock source input and source age of the oil samples a relationship between biomarker and diamondoid concentration was used to identify mixed oils having both oil window and highly cracked components compound specific isotope analyses of diamondoids and n alkanes were used to deconvolute cosourced oils and identify deep source rocks in the basin results suggest five major source rocks in the barents sea and the northern timan pechora basin upper jurassic shale lower middle jurassic shale triassic carbonate and shale devonian marl and devonian carbonate the upper and lower middle jurassic source rocks are dominant in the barents sea triassic source rock consists of carbonate in the onshore part of northern timan pechora basin and marine shale in the barents sea the devonian domanik formation carbonate source rock extends offshore into the southern barents sea the high maturity domanik formation could also be a secondary source rock for most of the mixed oils in the northern timan pechora basin this detailed geochemical study provides a new and detailed understanding of petroleum systems in the barents sea and northern timan pechora basin

from petroleum type organofacies to hydrocarbon phase prediction the organic facies concept states that kerogen abundance and composition are relatable to depositional settings this link has been extended using open system pyrolysis methods to include major petroleum types whose gross compositions are inherently defined by source rock kerogens and hence to petroleum composition which directly controls the physical response of fluids to changing pressure and temperature conditions during secondary migration the possibility to model petroleum composition during hydrocarbon generation as well as the phase behavior of the fluids during migration is now available in modern basin modeling software however whereas pyrolysis methods can accurately reconstruct hydrocarbon gas oil ratios and liquid compositions they are inherently incapable of correctly reproducing the gas composition of natural fluids and because the gas composition dominantly controls the phase behavior of petroleums multicompound compositional kinetic predictions based on pyrolysis results alone are inappropriate for the prediction of phase behavior the new phasekinetics approach described here combines open and closed system pyrolysis techniques to characterize the compositional evolution of the fluids generated as a function of increasing thermal stress as well as correcting experimentally determined gas compositions and therefore overcomes these deficiencies it has been used to develop compositional kinetic schemes capable of predicting natural petroleum phase behavior for different organofacies types the methodology uses a compositional description of the generated fluids similar to that used in pressure volume temperature pvt simulation selected studies in the norwegian north sea brazil and mexico demonstrate the quality of the tuned compositional predictions for different organic facies types

severity and timing of cenozoic exhumation in the southwestern barents sea the juxtaposition of the north atlantic rift system with the borderlands of the eurasian arctic shelf has resulted in an unusual basin evolution in the southwestern barents sea exploration has concentrated on the mesozoic sandstone plays of the hammerfest basin these have yielded abundant gas and very little oil such findings are typical of peripheral north atlantic margin basins that have undergone cenozoic exhumation this is generally thought to have occurred during the palaeocene oligocene miocene or pleistocene hammerfest basin erosion is widely estimated to be in the range of 500 1500 m however the relative severity of individual episodes and impact on fluid dynamics within the basin are poorly constrained we apply basin modelling tools to establish the sensitivity of the petroleum system to three cited scenarios for cenozoic exhumation vitrinite reflectance and temperature data constrain burial and thermal histories calibration is not possible using heat flow variations alone erosion timing and magnitude are required to match available data the calibrated model indicates a significant thermal disequilibrium in the hammerfest basin at the present day resulting from late cenozoic exhumation forward modelling of pleistocene ice sheets allows for an estimation of pressure and temperature fluctuations in response to glacial interglacial cycles

major crustal rotations in the andean margin paleomagnetic results from the coastal cordillera of northern chile paleomagnetic analyses of mesozoic lavas and dike swarms from the northern chilean coastal cordillera between 25 4 s and 26 4 s reveal a clockwise rotation of about 42 magnetizations from lava flows of andesitic basaltic composition of the middle jurassic la negra formation pass both fold and reversal tests and are interpreted as prefolding remanences five dike swarms of middle jurassic to early cretaceous age yield similar directions to that obtained from the la negra formation four of the five swarms have mixed polarity suggesting that they too carry a primary or very early remanence the structural setting of the dikes suggests that they have not suffered any substantial tilting about nonvertical axes since acquisition of the remanence the clockwise rotation of the area is believed to have been the consequence of transpressional deformation of mid late cretaceous age post 100 ma associated with abandonment of the jurassic early cretaceous magmatic arc in this region and its eastward migration to form a new mid late cretaceous magmatic arc in the former back arc region this younger arc is located east of the coastal cordillera and lies in the central valley region the clockwise sense of rotation is consistent with other paleomagnetic data from northern chile and southern bolivia south of the arica deflection in the andean margin although it is the largest yet reported to the north of the arica deflection paleomagnetic studies report counterclockwise rotations and several large scale models have been proposed to explain the overall pattern of rotations models include oroclinal bending of an originally straight margin differential shortening across the margin at a preexisting bend which is subsequently tightened by the passive rotation of the limbs of the bend and distributed shear throughout the margin as a consequence of oblique convergence at a preexisting bend in contrast to these models several workers have argued that rotation is better explained in terms of localized in situ rotations we review these models in light of our results and present a domino type model with blocks bounded by left lateral faults and rotating clockwise in response to mid late cretaceous transpression within a crustal scale shear zone this is consistent with the observed strike slip fault systems identified in the coastal cordillera

finite element analysis and ray tracing modeling of petroleum migration separate phase flow is the dominant transport mechanism for secondary migration of petroleum phases commonly two different methods are used for the modeling of separate phase flow full 3d modeling finite element analysis which leads to the physically best description but can only be performed on low resolution grids and flowpath modeling ray tracing which can be performed on high resolution grids but is based on simplified physical assumptions a new approach that integrates both methods allows a physically realistic description without losing any of the original geometric information this new approach cuts processing times considerably

investigations on the use of triaromatic dimethylcholesteroids as age specific biomarkers in bitumens and oils from arctic norway abstract triaromatic dimethylcholesteroid ta dmc and triaromatic dinosteroids ta dinosteroids derive from dinoflagellates and are considered age specific biomarkers that have some potential to distinguish between petroleum generated from paleozoic vs mesozoic strata still some ambiguity remains concerning a gradational or abrupt paleozoic vs mesozoic phylogenetic change in the precursor bio molecule for these biomarkers our examination of ta dmc in a series of 112 sedimentary rock samples and oils from the barents sea svalbard the norwegian sea and novaya zemlya ranging from the silurian to the cretaceous could shed light on these issues ta dmc together with ta dinosteroids occur locally in upper permian source rocks of the orret formation while the upper permian roye formation did not reveal any occurrences the abundance of both compound classes in permian sediments might either suggest the presence of dinoflagellates in palaeo niche environments during the late permian in the studied area or hint towards the occurrence of related ancestors among acritarchs or non calcifying haptophytes ta dmc and ta dinosteroid were found in lower induan rocks from the haltenbanken area which implies the occurrence of ta dmc and ta dinosteroid producing organisms in the early triassic however the appearance of ta dmc and ta dinosteroids in lower to middle triassic sediments from the svalis dome sw barents sea increases during the anisian while no ta dmc have been found in early triassic olenekian sequences which is in accordance with global observations based on these results it could be concluded that the 7324 8 1 wisting central oil discovery was generated from olenekian intervals of the lower triassic steinkobbe formation

cu mn and ag mineralization in the quebrada marquesa quadrangle chile the talcuna and arqueros districts the quebrada marquesa quadrangle in chile exhibits a series of mineralizations comprising manto type manganese and copper deposits of lower cretaceous age and copper and silver veins of tertiary age the deposits are hosted by volcanic and volcaniclastic units of the arqueros hauterivian barremian and quebrada marquesa barremian albian formations three episodes of manganese mineralization mn1 3 are recognized within the study area hydrothermal activity leading to episodes 1 and 3 was of minor importance while the second one mn2 gave rise to major manto type deposits of both manganese and copper in the talcuna mining district extensional faulting during tertiary time resulted in block faulting and the unroofing of the oldest andesitic volcanics and marine sediments arqueros formation this episode was accompanied by magmatic and hydrothermal activity leading to vein formation in the arqueros ag and talcuna cu districts the latter veins cross cut the previous manto type copper deposits ore mineralogy is similar in both styles of mineralization manto and vein type and consists mainly of chalcopyrite and bornite with variable amounts of galena tetrahedrite vein related chalcocite sphalerite pyrite hematite digenite and covellite alteration processes at talcuna can be divided into two categories those related to the lower cretaceous manto type episode lk alteration chlorite epidote calcite albite prehnite zeolite and those associated with the locally mineralized normal faults of tertiary age tt alteration chlorite calcite sericite the arqueros silver veins display an ore mineralogy consisting of arquerite argentite native silver polybasite cerargyrite and pyrargyrite proustite associated alteration includes strong chloritization of the country rock the manto type deposits formed from fluids of salinity between 11 and 19 wt nacl equivalent and temperatures between 120 and 205 c mineralizing fluids during the vein type stage circulated at lower temperatures between 70 and 170 c with salinity values in a wide range from 3 to 27 wt nacl equivalent this distribution of salinities is interpreted as the result of the complex interplay of two different processes boiling and fluid mixing the former is considered to control the major mineralogical textural and fluid inclusion features of the vein type deposits we suggest that the lower cretaceous mineralization manto type stage developed in response to widespread hydrothermal activity geothermal field type involving basinal brines

regional petroleum alteration trends in barents sea oils and condensates as a clue to migration regimes and processes to date most condensates and gases found in the hammerfest basin exist in distal central basin settings in traps with tight cap rocks of class 1 traps whereas low gas oil ratio gor oils occur systematically in proximal basin settings where cap rocks of class 3 traps prevail multiple fill spill events resulted in the redistribution of oils toward structurally higher basin margins in a systematic evaluation of light hydrocarbon parameters from condensates and oils it was found that oils in general exhibit more traceable alteration effects than do condensates whereas 75 of condensate and 13 3 of oil samples are fractionated 6 25 and 10 respectively show signs of biodegradation long distance migration is indicated for 12 5 of condensate and 50 of oil samples in addition clear evidence is shown for the mixing of recently migrated high gor petroleum phases with older low gor paleo oils in general variation in source specific parameters is surprisingly less pronounced decreasing thermal maturity of entrapped petroleum from the eastern part of the tromso basin toward the masoy nysleppen fault complex is observed whereas high maturities are shown for the nordkapp basin and the finnmark platform in the eastern part of the study area low to medium maturities are recorded for oils from the basin margins of the hammerfest basin alterations in the composition of the petroleums by physiochemical processes and distribution patterns of the petroleums are closely associated with uplift and erosion