hydrocarbon plumbing systems of salt minibasins offshore angola revealed by three dimensional seismic analysis analysis of three dimensional seismic data from the lower congo basin offshore angola reveals numerous fluid flow features in the miocene to holocene succession and the potential for large shielded traps underneath basinward overhanging salt structures the fluid flow evidence includes present day sea floor pockmarks clustered above salt structures pliocene pleistocene stacked paleopockmarks and miocene pockmark fields other fluid flow features include high amplitude cylindrical pipe structures 60 to 300 m 197 984 ft wide and 25 to 300 m 82 984 ft high within lower and middle miocene strata thick 150 m 492 ft high reflectivity zones within the pliocene succession associated with bottom simulating reflections and subvertical low amplitude chimneys originating from the deeper section 1 km 0 6 mi beneath the sea floor the miocene pockmark fields occur at a specific horizon suggesting a regional fluid expulsion event at ca 12 ma and the miocene fluid flow regime is interpreted to be dominated by thermogenic fluids supplied via carrier beds and leaking vertically above structural highs the pliocene pleistocene fluid flow regime was dominated by short distance vertical fluid migration and expulsion related to early stage diagenetic processes involving biogenic methane and pore water the present day fluid flow regime is inferred to be dominated by thermogenic fluids primarily controlled by kilometer scale salt flank controlled migration the study emphasizes the use of seismically imaged fluid flow features in hydrocarbon systems analysis by documenting the evolution of an overburden plumbing system through time involving several fluid types and flow regimes depending on the spatiotemporal availability of thermogenic and diagenetic fluids and the tectonostratigraphic occurrence of aquifers traps and seals

geophysical characterisation of active thermogenic oil seeps in the salt province of the lower congo basin part i detailed study of one oil seeping site abstract we report the geophysical characterisation of natural oil seep sites through a combination of sea surface evidence of oil leakage from spatial imagery with a large collection of seafloor and subsurface geophysical data this paper provides a detailed characterisation of one selected active seep site and identifies possible specific feature of oil seep sites the oil seep is a complex shaped feature on the seafloor consisting of a cluster of heterometric pockmarks inside a main depression area and peripheral metre scale seafloor mounds a strong deformation related to salt tectonics controls the location of the seafloor source by fracturing the overburden the associated thermal anomaly induces a vertical modification position of the base of the gas hydrate stability zone bghsz that is used as a fluid migration route towards the crest of the diapir the combination of local depressions and seafloor amplitude anomalies linked with vertical high amplitude pipes rooted on the bghsz suggests a focused fluid flow towards the seafloor in peripheral areas the seafloor mounds are linked by shallow faults to buried high amplitude patches on sub bottom profiler sections the combination of restricted size seafloor mounds with a progressive deepening of the high amplitude from the seafloor suggests a substantial decrease of the hydrocarbon flow towards peripheral areas the proximity of actively oil supplying seafloor depressions and seafloor mounds shows that the hydrocarbon flow rapidly decreases laterally the thermogenic seep site is affected by two consistent and sub parallel reflections with negative polarity the first is interpreted as the methane related bghsz the second could correspond to the base of a thermogenic bghsz produced by a mixture of heavier gas the seafloor roughness and double bsr appear to be specific features of oil seep sites the geophysical features revealed at a localised study area will be extrapolated towards a larger province for relevance validation

overdeepened quaternary valleys in the eastern danish north sea morphology and origin abstract a system of 100 350 m deep overdeepened and buried valleys has been mapped in the eastern danish north sea individual valleys can be traced for several tens of kilometres and valleys generally begin and terminate abruptly a correlation to buried valleys onshore southwest denmark is possible the valleys post date glaciotectonic structures and are interpreted to be elsterian and possibly saalian in age the origin of valleys in the eastern danish north sea is explained by repeated cycles of sub glacial down cutting of meltwater channels and channel closure due to ice creep eventually producing deeply incised valleys glacial erosion may have been significant in cases where valleys are broad and shallow the origin of overdeepened quaternary valleys in general can be attributed to a combination of three end member processes i steady state drainage of meltwater ii catastrophic outbursts of meltwater and iii glacial erosion the main requirement for sub glacial valley formation is the presence of a melting ice sheet overlying a poorly consolidated substrate permeability variations of the substrate may produce subregional variations in the pattern of valley incision while pre glacial rivers faults or salt structures are of local importance only

north sea rift system abstract the mesozoic north sea rift forms an integral part of the arctic north atlantic rift system rifting activity in the north sea commenced during the earliest triassic during the mid jurassic the central north sea underwent a temporary doming stage crustal extension peaked during the late jurassic earliest cretaceous abated subsequently and terminated altogether during the paleocene the saucer shaped cenozoic post rift basin straddles the axis of the viking and central grabens this speaks for the applicability of a depth dependent pure shear model rather than a simple shear model geophysical data indicate an important discrepancy between upper and lower crustal attenuation across the north sea rift suggesting that during rifting processes the mono discontinuity was seriously destabilized this requires a basic modification of currently favoured crustal stretching models

imaging through gas filled sediments using marine shear wave data marine multicomponent sea floor data of excellent quality have been acquired over the tommeliten alpha field the most dominating wave modes are interpreted to be conventional compressional pp waves and converted ps waves the most important geophysical problem associated with the tommeliten alpha field is the presence of a gas chimney obscuring the conventional 3 d seismic image of the reservoir zone the converted ps waves effectively undershoot the gas chimney leading to substantially improved images of the reservoir subsequent interpretation indicates the tommeliten alpha structure is a faulted dome

a three dimensional numerical model of the waiotapu waikite and reporoa geothermal areas new zealand abstract a large scale three dimensional numerical model of the waiotapu waikite and reporoa geothermal fields new zealand is presented the model covers an area of 450 km 2 and extends to a depth of about 3 6 km it is based on geological geophysical and geochemical data and related interpretations available in the literature the model has been calibrated by varying its permeability structure and the fluid and heat input at its base so that the temperature distribution in the model associated with the convective and advective fluid flow matches the natural state conditions in the three fields good agreement has been obtained between model results and measured downhole temperature data as well as reproducing the location and magnitude of the surface heat discharge for each field in the best fit model 665 kg s of deep thermal fluid is transferred to the surface and to concealed shallow aquifers the subsurface extent of the geothermal reservoirs can be assessed from model blocks at temperatures greater than 220 c the waiotapu reservoir covers about 30 km 2 at a depth of 1 km below sea level whereas the hot zone in the reporoa caldera associated with the reporoa reservoir extends over about 13 km 2 a separate deep thermal upflow is required in the model in order to get a satisfactory match to temperatures in the reporoa field the modelling study shows that the waikite field is an outflow from the waiotapu field and the high temperature region beneath the waikite field only appears at shallow depths 500 mrl and above the model therefore well defines the waiotapu reporoa geothermal system which hosts the three geothermal fields at waiotapu waikite and reporoa

physical modelling of sand injectites abstract sand injectites are structures that result from intrusion of fluidized sand into fractures we have studied them in the tampen spur area of the north sea and have reproduced them experimentally by driving compressed air through layers of sand glass microspheres and silica powder the silica powder was cohesive and capable of hydraulic fracturing whereas the sand and glass microspheres were almost non cohesive and therefore able to fluidize the models were dynamically similar to their natural counterparts for as long as equilibrium was static when the processes became dynamic so that inertial forces were significant the scaling was approximate and the corresponding reynolds numbers differed the experimental apparatus was a square box 1 m 1 m wide resting on a grid of fluid diffusers during the experiments the fluid pressure increased until it attained and surpassed the weight of overburden flat lying hydraulic fractures containing air formed within cohesive and least permeable layers heterogeneities in material properties and layer thicknesses were responsible for localizing fracture networks when any one network broke through to the surface rapid flow of air through the fractures fluidized the underlying mobile materials and even depleted some of the layers some of the fluidized material extruded at the surface through vents forming volcanoes and sheets the remainder lodged at depth forming sand injectites or laccoliths conical sand injectites formed preferentially where layers had high resistance to bending laccoliths formed nearer the surface where overlying layers had low resistance to bending the experimental sand injectites were broadly similar to those in the tampen spur area of the north sea as well as other areas

gas migration pathways and slope failures in the danube fan black sea abstract a large geophysical dataset including bathymetry and 2d and 3d p cable seismic data revealed evidence of numerous gas flares near the s2 canyon in the danube fan northwestern black sea this dataset allows us to investigate potential relationships between gas migration pathways gas vents observed at the seafloor and submarine slope failures vertical gas migration structures as revealed in the seismics appear to be concentrated near submarine slope failure structures where these seismically defined features extend upwards to the seafloor they correlate with the location of gas flares however not all these structures reach the seafloor in some cases because they are capped by overlying sediments a strong correlation is inferred between gas migration pathways heterogeneous mass transport deposits and contacts between adjacent units of contrasting lithology although missing age constrains prevent a final judgement we discuss the potential relationship between submarine slope failures and gas migration in order to determine if gas migration is a precursor to failure or if the presence of slope failures and associated mass transport deposits facilitates the migration of gas our observations indicate that lithological heterogeneity mass transport deposits and minor sediment deformation control gas migration pathways and the formation of gas chimney like features gas migration is focused and gradual resulting in gas flares where the chimney like features extend to the seafloor with no evidence of erosive features such as pockmarks

seismic modeling of gas chimneys we propose a simple acoustic model explaining the main features of gas chimneys the main elements of the model consist of gas diffusing from a connected fracture network and into the surrounding shale creating an inhomogeneous gas saturation the gas saturation results in an inhomogeneous fluctuating compressional velocity field that distorts seismic waves we model the fracture network by a randomwalk process constrained by maximum fracture length and angleofthefracturewithrespecttothevertical thegassaturation is computed from a simple analytical solution of the diffusion equation and pressure wave velocities are locally obtained assuming that mixing of shale and gas occurs on a scalemuchsmallerthanseismicwavelengths syntheticseismic sections are then computed using the resulting inhomogeneous velocity model and shown to give rise to similar deterioration in data quality as that found in data from real gas chimneys also synthetic common midpointcmpgathers show the same distorted and attenuated traveltime curves as those obtained from a real data set the model shows clearly thatthefeaturesofgaschimneyschangewithgeologicaltime a model parameter in our approach the deterioration of seismicwavesbeingsmallestjustafterthecreationofthegas chimney it seems likely that at least some of the features of gas chimneys can be explained by a simple elastic model in combinationwithgasdiffusionfromafracturenetwork

detection of gas migration from a deep source by the use of exploration 3d seismic data abstract periods of sustained gas seepage since mid miocene time is indicated in exploration 3d seismic data from the area of the sleipner fields in the north sea buried mounds suspected to be mud volcanoes may have been generated in association with gas migration in mid miocene time minor faults and fractures are present at the same horizon and the mud volcanoes seem to be distributed along some of these seismic chimneys indicate migration of gas from below this level through the faults and fractures and up to the seabed shallow gas accumulations in late pliocene sands above the mud volcanoes may be a result of the gas migration possible buried craters overlying seismic chimneys may have been generated in a period of sustained gas seepage followed by a less active period during which the craters have been buried a large depression at the seabed overlying seismic chimneys indicates a recent period of sustained gas seepage the gas is believed to have migrated from the sleipner gas reservoirs

heat flow distribution in southeast asia with consideration of volcanic heat abstract as of 1995 in southeast asia from 15 s to 25 n and from 90 to 160 e 2539 heat flow measurements are available despite a recent increase in the number of measurements still important data gaps exist in the region especially around the volcanic regions so far the contribution of heat flux from active volcanoes has largely been overlooked in regional heat flow maps because of uncertainties surrounding it we have tried to estimate the volcanic heat in this region with the assumption that these volcanoes emit a similar amount of heat as those in northeast honshu japan where heat flow studies and seismic tomography enable us to estimate that as a first approximation a volcano can be represented by 140 mw m 2 of heat flow a heat flow map including volcanic heat estimated in this way makes the heat flow in the sunda arc and the philippines where conventional heat flow data are scarce much higher than on a map without the volcanic heat

pleistocene subglacial tunnel valleys in the central north sea basin 3 d morphology and evolution four phases of cross cutting tunnel valleys imaged on 3 d seismic datasets are mapped within the middle late pleistocene succession of the central north sea basin witch ground area in plan the tunnel valleys form complex anastomosing networks with tributary valleys joining main valleys at high angles the valleys have widths ranging from 250 to 2300 m and base to shoulder relief varying between 30 and 155 m with irregular long axis profiles characteristic of erosion by water driven by glaciostatic pressures the youngest phase of tunnel valleys are smaller and have a thinner infill than the older generations the fill of the larger valleys comprises three seismic facies the lowermost of which has high amplitudes and is discontinuous the middle facies consists of wedge shaped packages of low angle dipping reflectors and is overlain by a facies characterised by sub horizontal reflectors which onlap the valley margins the seismic character and comparison with lithologies identified in other northwest european pleistocene tunnel valleys both onshore and offshore suggests that the lower two seismic facies are most likely sand and gravel dominated while the uppermost facies consists of glaciolacustrine and marine muds the 3 d morphology of the valley margins combined with the geometry of the infill packages suggest that episodic discharge of subglacial meltwater was responsible for incising the valleys and depositing at least some of the infill proglacial glaciofluvial deposits are inferred to account for some of the fill overlying the subglacial deposits glaciolacustrine and marine muds filled remaining valley topography as the ice sheet retreated the preserved valley margins are shown to be time transgressive erosion surfaces that record changes in geometry of the tunnel valley system as it evolved through time implying that valleys associated with each ice sheet advance retreat cycle were dynamic and probably long lived within the constraints of the existing stratigraphy the oldest tunnel valleys in the witch ground area of the central north sea are most likely to be marine isotope stage mis 12 elsterian ca 470 ka in age and the youngest pre mis 5e last interglacial ca 120 ka if each tunnel valley phase was formed during the retreat of a major ice sheet then four glaciations with ice coverage of the central north sea are recorded in the pre weichselian middle late pleistocene stratigraphy copyright 2006 john wiley sons ltd

an observational test of the origin of accelerating moment release before large earthquakes 1 a progressive increase of seismic activity distributed over a wide region around a future earthquake epicenter is termed accelerating moment release amr this phenomenon has been observed in several studies over the last 15 years although there is no consensus about the physical origin of the effect in a recent hypothesis known as the stress accumulation sa model the amr is thought to result from the last stage of loading in the earthquake cycle in this view the increasing seismicity is due to minor stress release as the whole region becomes sufficiently stressed for the major event to occur the stress accumulation model makes specific predictions about the distribution of events in an amr sequence because the amr is predicted to be a result of loading on the main fault the precursory activity should be concentrated in the positive lobes of the far field stresses calculated by a backslip dislocation model of the main shock to test this model amr is first found in optimal circular regions around the epicenters of each of the m w 6 5 earthquakes in central and southern california since 1950 a backslip dislocation model is then used to determine which of the precursory events occur in the regions predicted by stress accumulation amr is shown to occur preferentially in the lobes of the backslip stress field predicted by the stress accumulation model

paleogeographic setting and depositional architecture of a sand dominated shelf depositional system miocene utsira formation north sea basin abstract the middle late miocene utsira sandstone of the north sea basin contains a fully preserved regional marine sand deposit that records a stable paleogeographic setting of shelf sand transport and accumulation within an epeiric shelf sea which persisted for ca 8 myr the sediment dispersal system was defined by 1 sediment input through a prograding strandplain platform coast to shelf bypass and regional basin centered transport and deposition within an elongate seaway 2 a high energy marine regime 3 very low rates of sediment supply and accumulation in the accommodation dominated seaway 4 high sediment reworking ratio and consequent abundance of autochthonous sediment 5 regional along strike sediment transport and 6 local to subregional landward sediment transport shelf systems were primarily nourished by sediment reworked from the shetland strandplain which prograded eastward into the central viking trough the viking strait lay between the constructional platform and the nondepositional horda platform southward longshore transport on the high energy shoreface and shallow shelf platform constructed the mounded south viking shelf shoal southward building sandy banner banks that formed along the recurved arc of the platform margin nourished the shoal system low angle sigmoid clinoforms with downstepping aggradational tops are distinctive architectures of the strike fed sand bodies the combination of strong marine currents and slow but continual sand supply from the shetland strandplain created regional sandy shelf depositional systems that individually covered 3500 to 6000 sq km of basin floor defining elements of the shelf shoal systems include their location within the basin axis mounded morphology stratal architecture and construction by amalgamated marine sand facies

comment on relationship between accelerating seismicity and quiescence two precursors to large earthquakes by arnaud mignan and rita di giovambattista

impact of single inclined faults on the fluid flow and heat transport results from 3 d finite element simulations the impact of inclined faults on the hydrothermal field is assessed by adding simplified structural settings to synthetic models this study is innovative in carrying out numerical simulations because it integrates the real 3 d nature of flow influenced by a fault in a porous medium thereby providing a useful tool for complex geothermal modelling the 3 d simulations for the coupled fluid flow and heat transport processes are based on the finite element method in the model one geological layer is dissected by a dipping fault sensitivity analyses are conducted to quantify the effects of the fault s transmissivity on the fluid flow and thermal field different fault models are compared with a model where no fault is present to evaluate the effect of varying fault transmissivity the results show that faults have a significant impact on the hydrothermal field varying either the fault zone width or the fault permeability will result in relevant differences in the pressure velocity and temperature field a linear relationship between fault zone width and fluid velocity is found indicating that velocities increase with decreasing widths the faults act as preferential pathways for advective heat transport in case of highly transmissive faults whereas almost no fluid may be transported through poorly transmissive faults

world s largest extrusive body of sand using three dimensional seismic and well data from the northern north sea we describe a large 10 km 3 body of sand and interpret it as extrusive to our knowledge this is the world9s largest such sandbody it would bury manhattan new york 60 km 2 under 160 m of sand or the whole of london uk 1579 km 2 under 6 m of sand this sand vented to the seafloor when it was more than 500 m deep during the pleistocene glacial period the sandbody 1 covers an area of more than 260 km 2 2 is up to 125 m thick 3 fills low areas around mounds which formed when underlying sand injectites lifted the overburden 4 wedges out away from a central thick zone 5 is locally absent along irregular ditches 20 km long and up to 50 m deep which overlie feeders on the flanks of the mounds and 6 consists of fine grained to medium grained sub rounded to rounded grains we compare the distribution of the sand with the results of scaled physical experiments in our interpretation high fluid pressure fractured the regional hordaland group seal in the study area so that fluidized sand moved rapidly to the seafloor through fissures on the flanks of underlying mounds mixed with seawater and formed lateral gravity currents these transported the sand as much as 8 km away from the blow out fissures and formed extruded sand sheets large extrusive sands represent a new type of economically interesting reservoir

gas hydrate accumulations related to focused fluid flow in the pegasus basin southern hikurangi margin new zealand abstract the hikurangi margin east of the north island of new zealand is known to contain significant deposits of gas hydrates this has been demonstrated by several multidisciplinary studies in the area since 2005 these studies indicate that hydrates in the region are primarily located beneath thrust ridges that enable focused fluid flow and that the hydrates are associated with free gas in 2009 2010 a seismic dataset consisting of 2766 km of 2d seismic data was collected in the undrilled pegasus basin which has been accumulating sediments since the early cretaceous bottom simulating reflections bsrs are abundant in the data and they are accompanied by other features that indicate the presence of free gas and concentrated accumulations of gas hydrate we present results from a detailed qualitative analysis of the data that has made use of automated high density velocity analysis to highlight features related to the hydrate system in the pegasus basin two scenarios are presented that constitute contrasting mechanisms for gas charged fluids to breach the base of the gas hydrate stability zone the first mechanism is the vertical migration of fluids across layers where flow pathways do not appear to be influenced by stratigraphic layers or geological structures the second mechanism is non vertical fluid migration that follows specific strata that crosscut the bsr one of the most intriguing features observed is a presumed gas chimney within the regional gas hydrate stability zone that is surrounded by a triangular in 2d region of low reflectivity approximately 8 km wide interpreted to be the result of acoustic blanking this chimney structure is cored by a 200 m wide low velocity zone interpreted to contain free gas flanked by high velocity bands that are 200 400 m wide interpreted to contain concentrated hydrate deposits

on the origin of multiple bsrs in the danube deep sea fan black sea highlights a stack of four bsrs were identified in levee deposits of the danube deep sea fan the multiple bsrs are not caused by overpressure compartments the multiple bsrs reflect stages of stable sealevel lowstands during glacial times gas underneath the previous ghsz does not start to migrate for thousands of years abstract high resolution 2d seismic data reveal the character and distribution of up to four stacked bottom simulating reflectors bsr within the channel levee systems of the danube deep sea fan the theoretical base of the gas hydrate stability zone ghsz calculated from regional geothermal gradients and salinity data is in agreement with the shallowest bsr for the deeper bsrs bsr formation due to overpressure compartments can be excluded because the necessary gas column would exceed the vertical distance between two overlying bsrs we show instead that the deeper bsrs are likely paleo bsrs caused by a change in pressure and temperature conditions during different limnic phases of the black sea this is supported by the observation that the bsrs correspond to paleo seafloor horizons located in a layer between a buried channel levee system and the levee deposits of the danube channel the good match of the observed bsrs and the bsrs predicted from deposition of these sediment layers indicates that the multiple bsrs reflect stages of stable sealevel lowstands possibly during glacial times the observation of sharp bsrs several 10 000 of years but possibly up to 300 000 yr after they have left the ghsz demonstrates that either hydrate dissociation does not take place within this time frame or that only small amounts of gas are released that can be transported by diffusion the gas underneath the previous ghsz does not start to migrate for several thousands of years

geophysical characterisation of active thermogenic oil seeps in the salt province of the lower congo basin part ii a regional validation abstract the lower congo basin is known to discharge a substantial volume of oil towards the sea surface from more than one hundred seafloor seep sites distributed throughout the deep province of the lower congo basin a large geochemical coring survey confirmed the presence of oil on the seabed the combination with the seismic data considerably improved the identification of the origin of the oil slicks on the seabed multiple specific geophysical characteristics of thermogenic hydrocarbon seep sites were highlighted in a previous detailed analysis of seismic datasets this study aims to test the characteristics previously identified at regional scale the active discharge zone is limited to the distal province of the basin it is characterised by strong compression shortening due to the sliding of the post salt super sequence resulting in numerous salt diapirs that control the location of seafloor oil seep sites the paper describes the bathymetric reflectivity amplitude and sub bottom profiler characteristics of a group of thermogenic seep sites they correspond essentially to submarine mounds or pockmarks of complex and irregular shape surrounded by hummocky mounds active oil pockmarks are systematically associated with positive amplitude anomalies on the seabed and are linked to vertical high amplitude columns rooted in the seismic reflector and associated with the base of the gas hydrate stability zone the sub bottom profiler data shows that the hummocky mounds are connected by a network of faults to high amplitude bodies buried under a consistent sediment thickness based on the definition of specific geophysical features seafloor mounds complex shape and irregular pockmarks positive anomalies of seafloor amplitude high amplitude vertical pipes we identified a series of potential oil seep sites at basin scale the mounds are particularly recognizable using the seismic curvature attribute we have identified 2946 individual hummocks that are grouped in 50 zones with a density of 35 240 per km2 they are believed to be associated with asphalt storage on the seafloor and related to the biodegradation of heavy oils during hydrocarbon dysmigration through the sedimentary pile unusual double bsrs occur over the study area these are also a specific feature of thermogenic seep sites barely half of the potential sites identified on the seismic datasets are associated with recurrent oil slicks at the sea surface the proportion of remaining anomalies may be associated with inactive seep sites over the period of satellite based monitoring or gas dominated seep sites

the physics of gas chimney and pockmark formation with implications for assessment of seafloor hazards and gas sequestration pockmarks form where fluids discharge through seafloor sediments rapidly enough to make them quick and are common where gas is present in near seafloor sediments this paper investigates how gas might lead to pockmark formation the process is envisioned as follows a capillary seal traps gas beneath a fine grained sediment layer or layers perhaps layers whose pores have been reduced in size by hydrate crystallization gas accumulates until its pressure is sufficient for gas to invade the seal the seal then fails completely a unique aspect of capillary seals releasing a large fraction of the accumulated gas into an upward propagating gas chimney which displaces water like a piston as it rises near the seafloor the water flow causes the sediments to become quick i e liquefied in the sense that grain to grain contact is lost and the grains are suspended dynamically by the upward flow the quickened sediment is removed by ocean bottom currents and a pockmark is formed equations that approximately describe this gas piston water drive show that deformation of the sediments above the chimney and water flow fast enough to quicken the sediments begins when the gas chimney reaches half way from the base of its source gas pocket to the seafloor for uniform near surface sediment permeability this is a buoyancy control not a permeability control the rate the gas chimney grows depends on sediment permeability and the ratio of the depth below seafloor of the top of the gas pocket to the thickness of the gas pocket at the time of seal failure plausible estimates of these parameters suggest gas chimneys at blake ridge could reach the seafloor in less than a decade or more than a century depending mainly on the permeability of the deforming near surface sediments since these become quick before gas is expelled gas venting will not provide a useful warning of the seafloor instabilities that are related to pockmark formation however detecting gas chimney growth might be a useful risk predictor any area underlain by a gas chimney that extends half way or more to the surface should be avoided c 2009 elsevier ltd all rights reserved

quantification of methane emissions at abandoned gas wells in the central north sea as a result of extensive hydrocarbon exploration the north sea hosts several thousand abandoned wells many believed to be leaking methane however how much of this greenhouse gas is emitted into the water column and ultimately reaches the atmosphere is not known here we investigate three abandoned wells at 81 93m water depth in the norwegian sector of the north sea all of which show gas seepage into the bottom water the isotopic signature of the emanating gas points towards a biogenic origin and hence to gas pockets in the sedimentary overburden above the gas reservoirs that the wells were drilled into video analysis of the seeping gas bubbles and direct gas flow measurements resolved initial bubble sizes ranging between 3 2 and 7 4mm in diameter with a total seabed gas flow between 1 and 19 tons of ch4 per year per well estimated total annual seabed emissions from all three wells of 24 tons are similar to the natural seepage rates at tommeliten suggesting that leaky abandoned wells represent a significant source of methane into north sea bottom waters however the bubble driven direct methane transport into the atmosphere was found to be negligible 2 due to the small bubble sizes and the water depth at which they are released

focused fluid flow and the sub seabed storage of co2 evaluating the leakage potential of seismic chimney structures for the sleipner co2 storage operation abstract the integrity of the caprock of a storage formation is the most crucial parameter for the long term performance of a geological co 2 storage site the sleipner area in the southern viking graben hosts the first and longest operating industrial scale co 2 storage project where co 2 is injected in a saline aquifer of the utsira formation time lapse seismic monitoring shows neither that co 2 has left the utsira formation nor indications for fracturing of the caprock by the co 2 injection activity which is in agreement with previous numerical simulations however large chimney structures as close as 7 km from the injection point indicate that the caprock has been breached in the geological past which may raise questions about the integrity of the caprock above the sleipner co 2 storage site here we present seismically constrained numerical fluid flow simulations that evaluate the influence of chimney structures on the long term performance of the co 2 storage operation at sleipner the simulation could reproduce the spreading of the sleipner co 2 plume which is controlled by the anisotropic permeability field of the utsira formation and the regional dip of the formation top we have performed long term plume evolution simulations which show that the injected co 2 will not reach the existing chimney structures assuming a realistic injection duration of 30 years our simulations indicate that an unrealistically long injection period between 92 and 140 years would be required for the co 2 to reach the existing chimney structures in this case a comparably low chimney permeability of 10 md may be sufficient to facilitate co 2 migration from the storage formation to the seafloor once the co 2 has reached a chimney structure however the simulations indicate that it is very unlikely that the co 2 may migrate along existing chimney structures at sleipner our results highlight that the reconstruction of palaeo fluid flow systems and the identification of focused fluid conduits should be considered in the assessment of co 2 storage sites

quaternary glaciations in southern fennoscandia evidence from southwestern norway and the northern north sea region abstract based on records from the northern north sea and southern norway quaternary fennoscandian glaciations are described and discussed maximum glaciation defined as the presence of shelf edge glaciation an ice stream flowing out of the norwegian channel and most likely an ice divide over the central part of fennoscandia sweden gulf of bothnia occurred for the first time in the late cenozoic at ca 1 1 myr the fedje glaciation this glaciation was followed by a ca 600 kyr period with at least two glaciations with ice extension somewhat larger than the younger dryas event in the region the first maximum glaciation of the bruhnes chron was during isotope stage 12 and was followed by repeated maximum glaciations within each of the light isotopic stages until stage 2 during the weichselian the southwestern part of the fennoscandian ice sheet reached maximum position three times sometime between 22 and 28 37 and 50 and 60 and 80 ka limited glaciations probably occurred during stadials between the early and middle weichselian interstadials between 500 ka and 1 1 myr and most likely also prior to 1 1 myr deep norwegian sea ice rafted detritus ird records reflecting contributions from several different ice sheets fennoscandian barents sea iceland and greenland each with large variations in history of ice extent to their respective margins yet to some degree they reflect the glaciation of the northern north sea region with an increasing ird input around 1 1 myr and a relatively low input of north sea components during some cycles around the b m boundary maximum glaciations occurred during insolation minima in the earlier part of the middle pleistocene however not all such minima are reflected by maximum glaciation in southern parts of fennoscandia the relatively poor chronological control and non continuous character of the data on weichselian interstadials stadials precludes a clear relationship to atmospheric changes recorded in greenland ice cores as well as to precession and or obliquity cycles in insolation

improved os isotope stratigraphy of the arctic ocean 1 the history of the arctic ocean remained poorly known until the 2004 iodp coring of lomonosov ridge sediments early studies of the recovered sequence demonstrated the existence of an eocene lake stage prior to the transition to marine conditions the marine stage onset was inferred to be 17 5 million years ma ago thus implying a nearly 26 ma gap between the lacustrine and marine episodes and an unusual tectonic history for lomonosov ridge in order to explain this gap more recently rhenium osmium re os isotope measurements of the transition from the lacustrine to marine sediments suggested a much earlier inception of marine conditions and the absence of any significant gap between both episodes here an improved osmium isotope stratigraphy and re os data concur to assign a late eocene age 36 ma to the marine invasion consistent with a relative change in sea level on top of lomonosov ridge either from tectonic origin or from another cause

integrated geothermal modeling on different scales in the northeast german basin geothermal modeling is an important part of large scale basin studies based on a new 3d structural model of the northeast german basin the present day regional geothermal field is modeled range and regional trend of the modeled temperature values are in agreement with the published data due to the high spatial resolution the calculated temperature distribution provides additional information with respect to areas where no measured data is available the results are used as input and boundary parameters for small scale models of geothermal energy production in general in many regions not enough data is available to define all necessary physical or chemical parameters for modeling in this context data obtained from the large scale model help to constrain unknown parameters subsequently the small scale model is used to simulate various production schemes focusing on enhanced predictions with respect to the possible lifetime of such installations the simulation results also show the need for elaborated models if reliable predictions of the temperature evolution are required

evidence for late pleistocene ice stream activity in the witch ground basin central north sea from 3d seismic reflection data abstract buried submarine landforms mapped on 3d reflection seismic data sets provide the first glacial geomorphic evidence for glacial occupation of the central north sea by two palaeo ice streams between 58 59 n and 0 1 e streamlined subglacial bedforms mega scale glacial lineations and iceberg plough marks within the top 80 m of the quaternary sequence record the presence and subsequent break up of fast flowing grounded ice sheets in the region during the late pleistocene the lengths of individual mega scale glacial lineations vary from 5 to 20 km and the distance between lineations typically ranges from 100 to 1000 m the lineations incise to a depth of 10 12 m with trough widths of 100 m the most extensive and best preserved set of lineations is attributed to the action of a late weichselian ice stream which either drained the ne sector of the british irish ice sheet or was sourced from the sw within the fennoscandian ice sheet the 30 50 km wide palaeo ice stream is imaged along its flow direction for 90 km trending nw se an older set of less well preserved lineations is interpreted as an earlier weichselian or saalian ice stream and records ice flow in an sw ne orientation cored sedimentary records tied to 3d seismic observations support grounded ice sheet coverage in the central north sea during the last glaciation and indicate that ice flowed over a muddy substrate that is interpreted as a deformation till the identification of a late weichselian ice stream in the witch ground area of the north sea basin provides independent geomorphic evidence in support of ice sheet reconstructions that favour complete ice coverage of the north sea between scotland and norway during the last glacial maximum

seismic chimneys in the southern viking graben implications for palaeo fluid migration and overpressure evolution highlights 3d seismic interpretation reveals 46 large chimney structures in the svg chimneys can be subdivided in three categories based on their seismic appearance seismic appearance of chimneys enables reconstructing formation mechanisms overpressure and seal weakening by deformation control chimney formation fluid flow along chimneys represents an efficient pressure transfer mechanism abstract detailed understanding of natural fluid migration systems is essential to minimize risks during hydrocarbon exploration and to evaluate the long term efficiency of the subsurface storage of waste water and gas from hydrocarbon production as well as co2 the southern viking graben svg hosts numerous focused fluid flow structures in the shallow 1000 m subsurface the seismic expressions of vertical fluid conduits are variously known as seismic chimneys or pipes seismic pipes are known to form large clusters seismic chimneys have so far been described as solitary structures here we show that the study area in the svg hosts more than 46 large scale vertical chimney structures which can be divided in three categories implying different formation processes our analysis reveals that seal weakening formation wide overpressure and the presence of free gas are required to initiate the formation of vertical fluid conduits in the svg the presence of numerous vertical fluid conduits implies inter stratigraphic hydraulic connectivity which significantly affects the migration of fluids in the subsurface chimney structures are important for understanding the transfer of pore pressure anomalies to the shallow parts of the basin

pockmarks in the witch ground basin central north sea marine sediments host large amounts of methane ch4 which is a potent greenhouse gas quantitative estimates for methane release from marine sediments are scarce and a poorly constrained temporal variability leads to large uncertainties in methane emission scenarios here we use 2d and 3d seismic reflection multibeam bathymetric geochemical and sedimentological data to i map and describe pockmarks in the witch ground basin central north sea ii characterize associated sedimentological and fluid migration structures and iii analyze the related methane release more than 1500 pockmarks of two distinct morphological classes spread over an area of 225 km2 the two classes form independently from another and are corresponding to at least two different sources of fluids class 1 pockmarks are large in size 6 m deep 250 m long and 75 m wide show active venting and are located above vertical fluid conduits that hydraulically connect the seafloor with deep methane sources class 2 pockmarks which comprise 99 5 of all pockmarks are smaller 0 9 3 1 m deep 26 140 m long and 14 57 m wide and are limited to the soft fine grained sediments of the witch ground formation and possibly sourced by compaction related dewatering buried pockmarks within the witch ground formation document distinct phases of pockmark formation likely triggered by external forces related to environmental changes after deglaciation thus greenhouse gas emissions from pockmark fields cannot be based on pockmark numbers and present day fluxes but require an analysis of the pockmark forming processes through geological time

seismic evidence of free gas migration through the gas hydrate stability zone ghsz and active methane seep in krishna godavari offshore basin abstract seismic amplitude versus offset avo analysis was performed on the multichannel seismic data in the vicinity of site nghp 01 10 where thick fracture filled gas hydrate is reported to understand the fluid migration in fracture dominated gas hydrate system amplitude preserved common image gathers cig are used in extracting the seismic amplitude with offset for seafloor bottom simulating reflectors bsr and different horizons within the gas hydrate stability zone ghsz the extracted amplitudes are fitted with three term shuey s avo approximation to estimate the intercept and gradient values based on the intercept and gradient values two distinct classes of seismic avo responses are observed class iv avo decreasing negative amplitudes with increasing offsets and class iii avo increasing negative amplitudes with increasing offsets for the bsr and other horizons above the bsr the large negative intercept and gradient values which indicate class iii avo ranges from 0 2 to 1 8 for the inline seismic profile and from 0 01 to 0 3 for the crossline profile the presence of class iii avo anomaly within the gas hydrate stability zone ghsz provides evidence of existence of free gas which may be migrating along the fault system some of the active faults are exposed on the surface and show gas venting signatures such as gas flares and pockmarks in the multibeam data

stratigraphy and facies distribution of the utsira formation and the pliocene sequences in the northern north sea abstract the upper cenozoic deposits of the northern north sea have been analysed in order to establish a regional and detailed stratigraphy the utsira formation is subdivided into four log units and mapped and two main depocentres are outlined the lower part of the utsira formation consists of thick marine mounded sand bodies interpreted as overall stacked lowstand fan deposits while the upper part of the formation consists of more clayey silty intervals indicating increased relative sea level the succeeding progradational pliocene deposits are subdivided into 13 high frequency depositional sequences and are mapped the sequences are grouped into four composite sequences each of the four pliocene composite sequences is composed of one or two rather locally distributed prograding sequences lowstand sequence set succeeded by one or two more widely distributed aggrading prograding sequences transgressive highstand sequence set boundaries between the composite sequences are recorded as marked changes in distribution of depocentres and sequence architecture the regional uplift of scandinavia is believed to be the main control on sediment input feeding the succeeding general prograding pliocene sequences oscillations of the eustatic sea level punctuated the tectonically controlled progradation and affected variations in the accommodation space and thus created the high frequency sequences

seismic imaging of complex geometry forward modeling of sandstone intrusions abstract sandstone intrusions form large bedding discordant sandstones that intruded into finer grained less permeable host strata they form naturally sand propped hydraulic fractures that constitute a connected network of permeable conduits through which fluids escape to the earth s surface saucer shaped sandstone intrusions are among the largest volume intrusions and are commonly resolved on seismic data outcrop analogues of seismically resolved saucers shaped intrusions reveal that many attendant intrusions in particular dikes are undetected in seismic data seismic forward modeling of a detailed outcrop description of a saucer shaped intrusion demonstrates that intrusions steeper than 45 are undetected and that up to 40 of the entire volume of sandstone intrusions is not seismically imaged wedge geometry associated with discordant contacts between different lithologies causes constructive and destructive amplitude interference creating imaging artefacts of sandstone thickness and geometry comparison of the outcrop seismic models with 3d seismic data from volund oilfield demonstrate both the similarity of the saucer shaped intrusions and the distribution and quantity of dikes that may be undetected ca 78 using subsurface data lack of detection of dikes has direct implications on the valuation of upward migration of fluids and an overestimation of seal capacity this therefore has major implications when using seismic data to evaluate waste sequestration or to execute hydrocarbon or groundwater exploration and production

linking structures with the genesis and activity of mud volcanoes examples from emilia and marche northern apennines italy mud volcanism is known to be strictly linked to tectonic structures since they have the ability to trap hydrocarbon and other fluids and eventually induce them to migrate from a deep reservoir e g sited into an anticline core where large overpressures may be generated to the surface a central theme is how fluids can migrate upward and which is the role in this process of near structures i e structures directly controlling the mud volcano system and far structures i e faults located far away from the mud volcano system in this study we investigate the role of both types of structures in the genesis and evolution of mud volcanoes in particular we investigate six mud volcano case studies from the emilia romagna and marche pede apennine margin in italy through integration of fieldwork interpretation of available seismic reflection profiles and aerial photos the results of these analyses support an intimate link of the investigated mud volcanoes with anticline structures we discuss two different fluid migration settings particularly i mud volcanoes emplaced on outcropping anticlines and ii mud volcanoes located on top of buried structures discerning when fluids are likely to exploit anticline related fracture sets or secondary structures and porosity finally we speculate on how far structures via the seismic triggering may play a role in the occurrence of historical eruption of some of the investigated mud volcanoes

on the origin and evolution of geothermal fluids in the patuha geothermal field indonesia based on geochemical and stable isotope data abstract volcano hosted vapor dominated geothermal systems have great potential for power generation although to date such systems discovered globally remain limited in number understanding of the physical and chemical properties of geothermal fluids water and gas in vapor dominated systems is critical for the sustainable development of geothermal resources this study aims to clarify the origins water rock interactions and chemical evolution of geothermal fluids during migration from a reservoir to the surface by selecting the patuha geothermal field pgf in west java indonesia as a case study the pgf is characterized by a vapor dominated system that originated from the subduction of the indian australian plate beneath the eurasian plate in total 26 water and 12 gas samples from production wells with 1 424 2 004 m depth and fumaroles were analyzed for major anions cations trace elements stable isotopes and gas components to interpret phenomena occurring in deep reservoirs ternary diagrams of cl so4 hco3 ionic compositions suggest that the h2s and co2 gases are condensed near the surface and changed to sulfate and bicarbonate by mixing with groundwater products of water wall rock interactions appeared in the area with acidic water which has mainly leached aluminum accelerated pyrite oxidation and increased iron concentration in the water high fluoride concentration at a fumarole site 95 9 mg l implies hf gas supply from the deep seated magmatic plume that is a geothermal source of the pgf system oxygen and hydrogen isotopes reveal that meteoric water is the main source of this system and na k mg diagrams indicate immaturity of the reservoir water through evaporation and mixing with the magmatic waters the waters have enriched heavy isotopic values ascend along major faults towards the surface and partly discharge at hot springs and fumaroles high temperatures of the reservoir and gas source in the subducted indian australian plate are estimated based on the high co2 and h2s concentrations and the high n2 ar ratios respectively by integrating the analysis results of the water and gas samples the well temperature data and surface geology the volcanic activity under a crater was estimated as the heat source and to have essential functions with the faults in the formation and fluid system of the vapor dominated pgf

distribution of the neogene utsira sand and the succeeding deposits in the viking graben area north sea abstract the sandy quartzose parts of the utsira formation the middle miocene to mid pliocene utsira sand extends north south along the viking graben near the uk norwegian median line for more than 450 km and 75 130 km east west the utsira sand is located in basin restricted seismic depocentres east of and below prograding sandy units from the shetland platform area with hutton sands the utsira sand reaches thicknesses up to ca 300 m in the southern depocentre and 200 m in the two northern depocentres with sedimentation rates up to 2 4 cm ka succeeding plio pleistocene is divided into seismic units including base upper pliocene shale drape prograding complex and pleistocene the units mainly consist of clay but locally minor sands occur especially at toes of prograding clinoforms bottom set sands and in the pleistocene parts and the total thickness covering the utsira sand is in most places more than 800 m but thins towards the margins

1000 m long gas blow out pipes abstract this study presents seismic observation of pipe anomalies from offshore nigeria outcrops of blow out pipes from rhodes greece and geophysical modelling of an acoustic pipe the studies give insight into how pipes form their internal structure the seismic image and geophysical artefacts related to the pipes over one hundred seafloor craters 100 m 700 m wide and up to 30 m deep have been observed on the seafloor offshore nigeria they are underlain by interpreted cones and seismic pipe anomalies that can be traced down to reservoir zones at 1000 m 1300 m below the seafloor the seismic pipe anomalies are 50 m 150 m wide and almost vertical they are interpreted as up scaled pipes found in outcrops on rhodes greece the outcrops show pipe related structures at three levels lowest the reservoir rock contains metre sized cavities which are filled with a mixture of clay derived from the overlying cap rock in the middle several circular to oval structures in plane view of pipes are observed in the lowest part of the cap rock highest 15 m into the clay cap rock strongly sheared country rock forms circular structures with a core of structureless clay based on outcrop observation on rhodes we constructed an acoustic model of a 50 m wide and 1000 m long pipe seismic modelling proves that such pipes would be expressed in seismic data that they are similar to the seismic pipe anomalies offshore nigeria but this study also revealed that prominent intra pipe reflections are artefacts a formation model for the pipes is suggested high fluid overpressure in the reservoir generated hydro fractures from the reservoir to seafloor where a mixture of gas and fluid flowed at high speed to form pipes cones and seafloor craters after hours to weeks of gas and fluid flow through the pipe the pore pressure in the reservoir dropped and the blow out terminated muddy slurry fell back and plugged the cavity in the reservoir and the pipe

a quaternary aminostratigraphy constraining chronology of depositional environments in the north sea basin abstract the aminostratigraphy of up to 1000 m of glacial and interglacial sediments in the north sea basin nsb is compiled from multiple boreholes sites and dated using strontium isotope sr analysis to provide a chronological framework extending throughout the quaternary the quaternary aminostratigraphy within the nsb can be divided into five amino zones az az1 youngest to az5 based on alle ile ratios which are used to correlate depositional events recorded in sedimentary facies from multiple borehole sites the new relative and absolute chronology also ties to seismostratigraphy and multi generational tunnel valley fill early pleistocene sediments produce az5 ratios with sr ages around 1 4 1 5 ma deposited in marine to glacimarine conditions sediments with az4 ratios are constrained by sr ages and magnetic polarity to 1 3 0 9 ma spanning the eccentricity to axial tilt insolation periodicity change of the mid pleistocene transition mpt some coarse grained sedimentary units with az4 ratios may be linked to ice proximal deposition during the mpt sediments with az3 ratios are poorly chronologically constrained to between 1 1 and 0 26 ma at least one episode of diminished coarse clasts and increased foraminiferal diversity during this mid pleistocene time suggests a progression from ice proximal to warmer possibly interglacial conditions furthermore the stratigraphically deepest generation of tunnel valleys cut strata with az3 ratios indicating subglacial conditions at least once during the mid pleistocene sediments with az2 ratios corresponding to mis7 5 are tied to seismic units including a thick up to 40 m deformation till suggesting glacial incursion into the nsb during mis6 followed by tunnel valley cutting of the this till thought to be an mis6 event also the geometry and cross cutting complexities of such tunnel valleys precludes further correlation of this ice extent the youngest aminostratigraphic zone az1 is recognised in all boreholes and well constrained to mis4 2 and the youngest set of tunnel valleys attributed to a single or multiple glacial advances at this time

fluid flow features in hydrocarbon plumbing systems what do they tell us about the basin evolution abstract fluid flow features such as sandstone intrusions mud volcano systems and pockmarks represent well known geological structures generated due to flow of fluids in the subsurface however the integration of fluid flow features in quantitative and qualitative basin analysis is still in its infancy this study presents a review and a qualitative integration of fluid flow features in basin analysis of the danish north sea area and of salt mini basins offshore angola based on results from six case studies focusing on the detection mapping and evaluation of features related to focused fluid flow in these areas in the study the diversity of seismically imaged fluid flow features in hydrocarbon plumbing systems is reviewed and their utility is demonstrated this is done by focusing on the aspects of fluid flow related features that can be integrated into basin analysis studies and how these may help us increase the understanding of basin evolution and to achieve the major goals of basin analysis such as understanding the depositional and tectonic context of the basin and the presence and extent of hydrocarbons particularly concerning the determination of fluid flow timing triggers sources and routes fluid flow features represent a major but underused tool in basin analysis

improved tests reveal that the accelerating moment release hypothesis is statistically insignificant 1 we test the hypothesis that accelerating moment release amr is a precursor to large earthquakes using data from california nevada and sumatra spurious cases of amr can arise from data fitting because the time period area and sometimes magnitude range analyzed before each main shock are often optimized to produce the strongest amr signal optimizing the search criteria can identify apparent amr even if no robust signal exists for both 1950 2006 california nevada m 6 5 earthquakes and the 2004 m9 3 sumatra earthquake we can find two contradictory patterns in the pre main shock earthquakes by data fitting amr and decelerating moment release we compare the apparent amr found in the real data to the apparent amr found in four types of synthetic catalogs with no inherent amr when spatiotemporal clustering is included in the simulations similar amr signals are found by data fitting in both the real and synthetic data sets even though the synthetic data sets contain no real amr these tests demonstrate that apparent amr may arise from a combination of data fitting and normal foreshock and aftershock activity in principle data fitting artifacts could be avoided if the free parameters were determined from scaling relationships between the duration and spatial extent of the amr pattern and the magnitude of the earthquake that follows it however we demonstrate that previously proposed scaling relationships are unstable statistical artifacts caused by the use of a minimum magnitude for the earthquake catalog that scales with the main shock magnitude some recent amr studies have used spatial regions based on hypothetical stress loading patterns rather than circles to select the data we show that previous tests were biased and that unbiased tests do not find this change to the method to be an improvement the use of declustered catalogs has also been proposed to eliminate the effect of clustering but we demonstrate that this does not increase the statistical significance of amr given the ease with which data fitting can find desired patterns in seismicity future studies of amr like observations must include complete tests against synthetic catalogs that include spatiotemporal clustering

self organizing maps in geothermal exploration a new approach for understanding geochemical processes and fluid evolution understanding geochemical processes is an important part of geothermal exploration to get information about the source and evolution of geothermal fluids however in most cases knowledge of fluid properties is based on few parameters determined in samples from the shallow subsurface this study presents a new approach that allows to conclude from the combination of a variety of these data on processes occurring at depth in a geothermal reservoir the neural network clustering technique called self organizing maps soms successfully distinguished two different geothermal settings based on a hydrochemical database and disclosed the source evolution and flow pathways of geothermal fluids scatter plots as shown in this study are appropriate presentations of element concentrations and the chemical interaction of water and rock at depth one geological setting presented here is marked by fault dominated fluid pathways and minor influence of volcanic affected fluids with high concentrations of hco3 ca and sr the second is a magmatically dominated setting showing strong alteration features in volcanic rocks and accommodates acidic fluids with high so4 and si concentrations former studies i e giggenbach 1988 suggested cl hco3 and so4 to be generally the most important elements for understanding hydrochemical processes in geothermal reservoirs their relation has been widely used to classify different water types in geothermal fields however this study showed that non standard elements are at least of same importance to reveal different fluid types in geothermal systems therefore this study is an extended water classification approach using som for element correlations som have been proven to be a successful method for analyzing even relatively small hydrochemical datasets in geothermal applications

ice load induced tectonics controlled tunnel valley evolution instances from the southwestern baltic sea abstract advancing ice sheets have a strong impact on the earth s topography for example they leave behind an erosional unconformity bulldozer the underlying strata and form tunnel valleys primarily by subglacial melt water erosion and secondarily by direct glacial erosion the conceptual models of the reactivation of faults within the upper crust due to the ice sheets load are also established however this phenomenon is also rather under explored here we propose a causal link between ice load induced tectonics the generation of near vertical faults in the upper crust above an inherited deep rooted fault and the evolution of tunnel valleys the kossau tunnel valley in the southeastern bay of kiel has been surveyed by means of high resolution multi channel seismic and echosounder data it strikes almost south to north and can be mapped over a distance of ca 50 km it is 1200 8000 m wide with a valley of up to 200 m deep quaternary deposits fill the valley and cover the adjacent glaciogenic unconformity a near vertical fault system with an apparent dip angle of 80 which reaches from the top zechstein upwards into the quaternary underlies the valley the fault partially pierces the seafloor and growth is observed within the uppermost quaternary strata only consequently the fault evolved in the late quaternary the fault is associated with an anticline that is between 700 and 3000 m wide and about 20 40 m high the fault anticline assemblage neither resembles any typical extensional compressional or strike slip deformation pattern nor is it related to salt tectonics based on the observed position and deformation pattern of the fault anticline assemblage we suggest that these structures formed as a consequence of the differential ice load induced tectonics above an inherited deep rooted sub salt fault related to the gluckstadt graben lateral variations in the ice load during the ice sheet s advance caused differential subsidence thus rejuvenating the deep rooted fault as a result the inherited fault propagated upwards across the zechstein and post permian overburden and further grew during the ice sheet s retreat the developing fault and anticline system under the ice sheet created a weakness zone that facilitated erosion by pressurized glacial and subglacial melt water as well as by the glaciers themselves near vertical faults cutting through the post permian are abundant in the southwestern baltic realm which implies that the ice load induced tectonic activity described above was not an isolated incident

seismic evidence for repeated vertical fluid flow through polygonally faulted strata in the canterbury basin new zealand abstract seismic imaging techniques are widely used to determine fluid migration pathways in the subsurface understanding the timing and distribution of focused fluid migration pathways is important for assessing reservoir seal quality and hydrocarbon exploration risk as well as seafloor biogeochemical processes in the case of fluid venting from the seafloor the frontier canterbury basin southeast of new zealand is well studied but questions remain regarding the dynamic movement of fluids through the basin using 3d seismic data combined with high resolution boomer seismic data we characterise focused fluid migration and sediment remobilisation events in the canterbury basin we show how polygonal fault formation and nucleation is affected in the vicinity of vertically ascending fluids and sediments a cylindrical region devoid of polygonal faulting around the feeder system of a buried sediment volcano points to the possible existence of an axisymmetrical stress field induced by upward migrating fluids and sediments sediment remobilisation and intrusions of permeable stingers i e sand injectites could enable dewatering of their host strata and thereby prevent polygonal faults from nucleating amplitude variations with angle ava and a detailed analysis of two tiers of polygonal faults reveal three phases of fluid migration and sediment remobilisation and intrusion through and into low permeability sediments our integrated conceptual model provides insights into vertical fluid migration mechanisms and the implications for polygonal fault formation

comment on seismic chimneys in the southern viking graben implications for palaeo fluid migration and overpressure evolution by karstens and berndt

increased fluid flow activity in shallow sediments at the 3 km long hugin fracture in the central north sea the north sea hosts a wide variety of seafloor seeps that may be important for transfer of chemical species such as methane from the earth s interior to its exterior here we provide geochemical and geophysical evidence for fluid flow within shallow sediments at the recently discovered 3 km long hugin fracture in the central north sea although venting of gas bubbles was not observed concentrations of dissolved methane were significantly elevated up to six times background values in the water column at various locations above the fracture and microbial mats that form in the presence of methane were observed at the seafloor seismic amplitude anomalies revealed a bright spot at a fault bend that may be the source of the water column methane sediment porewaters recovered in close proximity to the hugin fracture indicate the presence of fluids from two different shallow 500m sources i a reduced fluid characterized by elevated methane concentrations and or high levels of dissolved sulfide up to 6 mmol l 1 and ii a low chlorinity fluid cl 305 mmol l 1 that has low levels of dissolved methane and or sulfide the area of the seafloor affected by the presence of methane enriched fluids is similar to the footprint of seepage from other morphological features in the north sea

fluid source and methane related diagenetic processes recorded in cold seep carbonates from the alvheim channel central north sea integrated petrography mineralogy geochronology and geochemistry of cold seep carbonate crusts and free gas from the alvheim channel elucidate diagenetic carbonate precipitation and related seepage histories in the central north sea free gas isotope characteristics coupled with carbonate 13c values as low as 66 vpdb indicate a predominantly microbial methane source with minor thermogenic contribution we estimate that 70 of the carbon sequestered into carbonate precipitates was derived from local oxidation of methane the early stage of crust growth is represented by microcrystalline aragonite and mg calcite 10 to 40 mol mgco3 cementing seafloor sediments consisting of clays quartz feldspar and minor detrital low mg calcite and dolomite typical association of aragonite cement with coarse grained detritus may reflect elevated fluid flow and flushing of fine particles prior to cementation close to the seafloor middle rare earth element enrichment in early generation microcrystalline cements containing framboidal pyrite indicates diagenetic precipitation within the zone of anaerobic methane oxidation contiguous to iron reduction the later generation diagenetic phase corresponds to less abundant radial fibrous and botryoidal aragonite which lines cavities developed within the crusts in contrast to early generation cements late generation cavity infills have rare earth elements and y patterns with small negative ce anomalies similar to seawater consistent with carbonate precipitation in a more open seawater dominated system aragonite u th ages indicate carbonate precipitation between 6 09 and 3 46 kyr bp in the northern part of the channel whereas in the southern part precipitation occurred between 1 94 and 0 81 kyr bp reflecting regional changes in fluid conduit position

removal of overburden velocity anomaly effects for depth conversion a method of compensating for the presence of discrete overburden velocity anomalies during depth conversion of time horizons interpreted on conventional post stack time migrated seismic data is presented positive and negative time delays are estimated either from the push down or pull up of reflectors directly beneath the anomalies or from interpreted time thickness of the anomalous body and interval velocities estimated from well data the critical steps are pre stack simulation of seismic acquisition across the velocity anomalies incorporating the effects of a fresnel volume which changes its width as a function of depth and simulation of commonmidpoint cmp stacking using a linear regression of time delay at versus offset squared x 2 the time correction method predicts the time distortion for any target horizon and the distortion is removed as a correction in time depth conversion is then performed using a background velocity function the final average velocity map is calculated from the resulting depth structure and the raw times at the target horizon the method is implemented by manipulating time grids within an industry standard mapping package the final average velocity map shows steep lateral velocity gradients which are constrained by the interpreted boundaries of the velocity anomalies

permeability distribution in the lahendong geothermal field a blind fault captured by thermal hydraulic simulation subsurface fluid flow of reservoirs in active tectonic regions is mainly controlled by permeability of fault zones therefore the characterization of fault zones is an important step toward performance assessment of a reservoir the fluid flow is controlled also by pressure and temperature conditions in this context we simulated pressure and temperature fields to elaborate on the influence of permeability on subsurface fluid flow in the lahendong geothermal reservoir thermal hydraulic simulation is performed using a finite element approach adjusting the permeability through 370 different cases modeling results converged to the observed data within a misfit range of 0 7 the best fitting models identified a deep seated fault that has previously not been traced at the surface simulated temperature distribution suggests a prominent convective heat flow driven by an upward migrating and sw ne oriented fluid flow this hydraulic gradient causes a pressure drop along the reservoir high pressure patterns are used to constrain recharge areas in addition to infiltration measurements discharge flow occurs from sw to ne migrating also upward toward the hot springs in that frame thermal hydraulic simulations identified previously unresolved subsurface faults which now allow a better understanding of the subsurface permeability and its influence on fluid flow

pressure significance of gas chimneys abstract analysis was carried out of part of the northern north sea to test what the presence and style of gas chimneys indicate about fluid pressure p f within hydrocarbon reservoirs previous results suggest that broad chimneys above a trap and thin chimneys on the flanks indicate the presence of hydrocarbons whilst thin chimneys in the crest suggest the hydrocarbons have escaped each type of gas chimney is usually associated with overpressure within mesozoic reservoirs but the water leg is hydrostatically pressured in most cenozoic reservoirs this indicates a gas leaking from a trap does not necessarily cause p f to become hydrostatic b overpressure may not be necessary for the expulsion of gasses through seal units to create the chimneys c although gas chimneys indicate the existence of an active hydrocarbon system their presence does not appear to indicate anything significant about present day p f

elongate fluid flow structures stress control on gas migration at opouawe bank new zealand highlights elongated fault structures are conduits for focused fluid flow gas migration occurs only along a sub set of faults across opouawe bank stress state deduced from 3d fault structures appears partially stratigraphically controlled abstract high resolution 2d and 3d seismic data from opouawe bank an accretionary ridge on the hikurangi subduction margin off new zealand show evidence for exceptional gas migration pathways linked to the stress regime of the ridge although the ridge has formed by thrusting and folding in response to a sub horizontal principal compressive stress 1 it is clear that local stress conditions related to uplift and extension around the apex of folding i e sub vertical 1 are controlling shallow fluid flow the most conspicuous structural features are parallel and horizontally elongated extensional fractures that are perpendicular to the ridge axis at shallower depth near the seafloor extensional fractures evolve into more concentric structures which ultimately reach the seafloor where they terminate at gas seeps in addition to the ridge perpendicular extensional fractures we also observe both ridge perpendicular and ridge parallel normal faults this indicates that both longitudinal and ridge perpendicular extension have occurred in the past the deepest stratigraphic unit that we image has undergone significant folding and is affected by both sets of normal faults shallower stratigraphic units are less deformed and only host the ridge parallel normal faults indicating that longitudinal extension was limited to an older phase of ridge evolution present day gas migration has exploited the fabric from longitudinal extension at depth as the gas ascends to shallower units it self generates its flow pathways through the more concentric structures near the seafloor this shows that gas migration can evolve from being dependent on inherited tectonic structures at depth to becoming self propagating closer to the seafloor