late holocene erosion in upland britain climatic deterioration or human influence the evidence for enhanced erosion in upland britain during the late holocene is evaluated though there is widespread evidence for recent soil erosion on high plateaux this has not been precisely dated radiocarbon dating confirms the occurrence of late holocene solifluction on high ground but at only one site has evidence been found for recent accelerated activity several areas however have yielded evidence of late holocene debris cone accumulation and parts of the scottish highlands experienced a drastic increase in debris flow activity over the past few centuries climatic deterioration and vegetation degradation resulting from overgrazing or burning are frequently cited as the causes of enhanced erosion but cause and effect are often related only by coincidence of timing in consequence only circumstantial evidence links erosion with climatic deterioration though anthropogenic influences have been more firmly established at a few sites the role of extreme events in initiating phases of uplan

quantitative characterization of connectivity and conductivity of sandstone carriers during secondary petroleum migration applied to the third member of eocene shahejie formation dongying depression eastern china abstract studies on migration pathways remain qualitative albeit extensive quantification of migration forcing in this study hydrocarbon carriers are defined as carrier units and their corresponding carrier beds for the third member of eocene shahejie formation in the dongying depression bohai bay basin eastern china on the basis of their lithofacies and physical properties spatial relationships and data availability secondary migration conduits are then quantified a carrier unit is defined as a stratigraphic unit that contains microscopically porous and permeable carrier beds and is covered by regional seals the carrier beds are macroscopically and physically connected to each other within a carrier unit and are hydrodynamically connected during secondary migration a method of quantifying sandstone carrier units using common physical properties is developed first a carrier unit containing potential carrier beds is identified on the basis of lithofacies and their lateral changes second physical connectivity of sandstone carrier beds is assessed on the basis of percolation theory third the hydrodynamic connectivity of a sandstone carrier unit is analyzed using effective parameters that may reflect the hydraulic circulation in the carrier unit last the conductivity of a sandstone carrier bed is quantitatively characterized using appropriate physical property parameters the results for sandstone carrier units in the third member of the shahejie formation are used in numerical models addressing pleistocene secondary migration the model results explain the discovered accumulation and hydrocarbon shows well and the model predictions on exploration targets have been confirmed by drilling

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

lateglacial and holocene talus slope development and rockwall retreat on mynydd du uk modification of lateglacial and holocene talus sheets by debris flows and gully incision on mynydd du wales has resulted in a convergence of upper slope form characterised by an upper rectilinear slope gradient of 36 3 and a range of concavities of c 0 1 0 2 in most cases gully incision and accumulation of debris cones have led to an increase in slope concavity evidence for talus erosion reworking and redeposition on the upper slope emphasises secondary reworking processes as well as primary talus accumulation on the upper slope and permits construction of a model of talus development at mynydd du on the basis of talus volume calculation of the first rockwall retreat data set for southern britain suggests that c 7 1 m 84 of overall rockwall retreat 8 5 m took place during the lateglacial and only c 1 4 m 16 occurred during the holocene these figures imply that lateglacial retreat rates ranged from 1 01 to 2 44 m ka 1 with an overall mean rate of 1 23 m ka 1 in contrast holocene rockwall retreat rates range from 0 10 to 0 17 m ka 1 with a mean rate of 0 12 m ka 1 approximately 27 of cliff retreat is attributed to microgelivation while similar to holocene and present day alpine environments these lateglacial retreat rates are one order of magnitude higher than most equivalent values for arctic sites this reflects both alpine style diurnal freeze thaw activity on mynydd du during the younger dryas and paraglacial rock mass instability following deglaciation assuming an exponential decline in rockwall sediment release it is estimated that approximately half the talus had accumulated within c 1 ka of deglaciation at one site paraglacial talus accumulation appears to have contributed significantly to the glacial sediment transport system of a subsequent ice advance present day rates of rockwall retreat and talus accumulation by rockfall are estimated to be 0 014 and 0 022 mm yr 1 m ka 1 respectively similar to values for other british sites and markedly lower than holocene rates of cliff recession due to microgelivation by implication the geomorphic significance of microgelivation may have been greatly underestimated in studies of inland rock slope evolution in temperate mid latitude environments

evolution characteristics of transtensional faults and their impacts on hydrocarbon migration and accumulation a case study from the huimin depression bohai bay basin eastern china abstract the study of transtensional faults is significantly important for analysing migration and accumulation of hydrocarbons in petroliferous basins the purpose of this study is to present disparities in the temporal and spatial evolution of two boundary transtensional faults northern linshang fault and southern xiakou fault in the huimin depression by 2d structural restoration and quantitative calculations of fault activity this paper also reveals the controls of transtensional faults on the migration and accumulation of hydrocarbons by considering the stress normal to the fault plane p the shale gouge ratio sgr of the fault zone and models of migration pathways the results show that the transtensional systems within the huimin depression were generated from the reactivation of basement faults under an oblique extensional stress field the linshang fault linked two initially separated segments and then behaved as a single fault since the ek period whereas the xiakou fault retained significant three segment growth properties during the paleogene during the hydrocarbon charging period the weak activity and strong vertical sealing restricted the occurrence of vertical migration around the xiakou fault while the relatively strong movement and weak vertical sealing resulted in multilayer hydrocarbon accumulations around the linshang fault meanwhile the vertically closed fault with high sgr 0 6 acted as barriers and trapped hydrocarbons on the lateral migration pathways whereas the vertically closed fault with low sgr

timing and velocity of petroleum migration in the los angeles basin petroleum in the los angeles basin took a relatively short time to migrate through carrier beds from the deep basin to present day reservoirs we use a numerical model to reconstruct beginning in miocene time subsidence sedimentation compaction thermal evolution and fluid migration in the basin s central block the modeling indicates that the heat flow is currently near the continental average 1 5 hfu but was higher 2 hfu during the early evolution of the basin the thermal history predicted by the model suggests deeply subsided source rocks of late miocene age began to generate oil about 2 2 ma in the simulations compaction slowly drives groundwater from mature source beds toward reservoir rocks these slow rates combined with the low solubility of petroleum in water preclude the possibility that oil migrated by a miscible process instead the oil must have moved as a phase separate from the groundwater the buoyant force acting on the oil phase along the steeply dipping carrier beds was as

molecular memory effects recording the accumulation history of petroleum reservoirs a case study of the heidrun field offshore norway abstract the immobile portion of the oil occupying the pore space of reservoir sandstones which is mostly represented by visible impregnations is shown by the present study to contain geochemical signals that record their filling history the clue to unravelling these signals is sequential extraction of such impregnations of residual oil by a high pressure solvent flow through cell in which the solvent percolates through the intact and primary pore system of the rock sample gas chromatography mass spectroscopy gc ms analysis of residual oils extracted from samples of certain reservoir sandstones within the heidrun field offshore norway reveal significant contrasts in the chemical maturity of the first and the last fractions recovered as high as 0 69 versus 0 50 for the mpi 1 ratio corresponding to 0 79 versus 0 67 rc the hypothesis is proposed that by using this extraction technique oil impregnations from different portions of the pore system i e from large versus small pores are obtained separately this interpretation is especially supported by the regular occurrence of reservoir sandstones in which the residual oil exhibits maturity contrasts between those fractions extracted from large and small pores of the same rock within the heidrun field the distribution of reservoir sandstones with such maturity contrasts is strictly controlled by their position in the oil column and the location of their fault compartment these contrasts are interpreted to reflect the maturity levels of end members of the petroleum charges which have filled this trap during an extended period of geological time reservoir sandstone samples containing such end member charges are limited to the uppermost portion of the oil column lower in the oil column the pore system of all reservoirs contains oil impregnations of a uniform maturity level regardless of their pore size origin this distribution is believed to indicate an early stage of the accumulation history of the heidrun field characterised by the formation of a palaeo oil water contact well above the present one moreover the four fault compartments studied each controlled by bordering faults with different sealing capacities were not filled during the same stages of the accumulation history in summary the present study has shown that oil impregnations depending on their location within the pore system of individual reservoir sandstones can retain molecular memory effects which in turn allow the accumulation history of petroleum fields to be reconstructed

simulation and characterization of pathway heterogeneity of secondary hydrocarbon migration carriers are important links between sources and traps for hydrocarbon migration and accumulation in a petroleum system oil and gas commonly migrate along narrow and irregular pathways in porous media even in macroscopically homogeneous media a migration simulator based on the invasion percolation theory which couples the buoyancy of a hydrocarbon column as the driving force with capillary pressure as the resisting force satisfactorily explains migration processes in heterogeneous media in macroscopically homogeneous carriers migration pathways are generally perpendicular to equipotential lines but locally the pathways can be irregular because of the influence of microscopic heterogeneity the degree of irregularity of these pathways depends on the difference between competing driving and resisting forces when numerous pathways form in a migration accumulation system the flux of migrating hydrocarbons may vary among these pathways in macroscopically heterogeneous carriers the irregularity of migration pathways is exacerbated when the driving force is relatively weak hydrocarbons tend to migrate in carriers where the hydraulic conductivity is relatively large these pathways differ from those predicted only on the basis of flow potential simulation of the migration process in the middle jurassic carrier beds of the paris basin demonstrates the characteristics of the migration simulator in the analysis of migration pathway heterogeneity results are comparable to or superior to those achieved with previous simulation approaches

regulation of algal blooms in antarctic shelf waters by the release of iron from melting sea ice during summer 1995 96 we measured iron in the water column and conducted iron enrichment bottle incubation experiments at a station in the central ross sea 76 30 s 170 40 w first in the presence of melting sea ice and 17 days later in ice free conditions we observed a striking temporal change in mixed layer dissolved iron concentrations at this station from 0 72 2 3 nm with sea ice present to 0 16 0 17 nm in ice free conditions these changes were accompanied by a significant drawdown in macronutrients and an approximate doubling of algal diatom biomass our incubation experiments suggest that conditions were iron replete in the presence of sea ice and iron deficient in the absence of sea ice we surmise that bioavailable iron was released into seawater from the melting sea ice stimulating phytoplankton production and the biological removal of dissolved iron from the mixed layer until iron limited conditions developed these observations suggest that the episodic release of bioavailable iron from melting sea ice is an important factor regulating phytoplankton production particularly ice edge blooms in seasonally ice covered antarctic waters

an experimental study of secondary oil migration experiments using long glass columns packed with glass beads or sand have been done to investigate secondary oil migration under hydrostatic conditions different combinations of bead sizes oil densities oil water interfacial tensions and column orientations have been tested in some experiments the oil was replaced by air the observations included the oil migration pathway the minimum oil column height needed for migration and the rate of advance of the migration front migration was found to take place along restricted pathways and an imbibition front often formed at the bottom of the oil zone the minimum oil zone height needed for migration can be predicted accurately if the values of the drainage and imbibition capillary pressures are known for the saturations at which the oil just becomes disconnected in most experiments the migration front advanced at a constant rate which depended on the fluid properties bead size initial oil height and pore structure migration rate is dependent on buoyant and capillary forces but the dependence on capillary forces becomes weaker as the oil length increases column orientation also has been found to affect migration efficiency

large scale sea ice drift and deformation comparison between models and observations in the western weddell sea during 1992 statistical comparisons between numerical sea ice models and an observed large scale strain array in the western weddell sea during 1992 are used to evaluate the performance of three of the more generally utilized sea ice rheology formulations results show that sea ice velocity is reproduced with relatively high accuracy 90 coherence 80 normalized cross correlation in models having high quality atmospheric forcing fields e g the european centre for medium range weather forecasts on the other hand temporal and spatial variability of the velocity field as exemplified by progressive vector plots and ice deformation respectively are reproduced less accurately coherence and normalized cross correlation 50 in terms of model sensitivity this means that deformation and temporal variability are more discriminating in terms of elucidating specifics about the constitutive relation and mechanical properties of sea ice on a large scale for example inclusion of both compressive and shear stresses is important in attaining a proper probability distribution of deformation relative to observations additional analysis shows that adjustments to specific model parameters improve the model results for either drift or select deformation components but no best solution could be found given the models examined here results suggest that inclusion of more physically based processes such as subdaily tidal and inertial oscillations reconsideration of the boundary layer formulation and consideration of anisotropy may be necessary to include in next generation sea ice models especially those that are intended for coupling with high resolution eddy resolving ocean models

fluid pressure and effective stress in sandbox models abstract we have done a series of simple tests on sandpacks involving upward flow of compressed air through the pores and its effect on the yield strength the ultimate objective is to model deformation coupled with fluid flow in sedimentary basins for all tests we used a single batch of fontainebleau sand sieved to a grain size between 0 200 and 0 315 mm poured into a cylindrical container and then fluidized the density of this sand was 1 585 g cm3 irrespective of sand thickness the lithostatic pressure was proportional to the thickness of the sandpack a yield envelope was obtained by shearing the sandpack horizontally compressed air entered the base of the sandpack and flowed upwards through the pore spaces for 69 measurements on air flow without shearing a plot of discharge velocity versus gradient of fluid pressure is close to a straight line verifying darcy s law and yielding an intrinsic permeability of about 1 7 darcy for the sand for 72 tests on simultaneous shearing and fluid flow the estimated effective stress lithostatic stress minus estimated pore fluid pressure ranged from 0 to 1600 pa and the pore fluid ratio between air pressure and lithostatic pressure from 0 0 to 1 0 a plot of shear stress versus effective stress at failure is almost linear verifying terzaghi s principle of effective stress the best fit slope coefficient of internal friction is about 0 55 and the intercept on the shear stress axis cohesion is less than 85 pa the tests show that it is feasible to use compressed air within sandpacks as a means of modelling deformation coupled with fluid flow the next step will be to build sandbox models of layered sequences and to investigate detachments caused by abnormal fluid pressures

differential deformation of gravity driven deep water fold and thrust belts along the passive continental margin of east africa and their impact on petroleum migration and accumulation abstract passive margin deep water fold and thrus belts dwftbs have been the focus of a number of studies in recent decades because many oil and gas fields have been discovered in traps associated with them nevertheless the impact of dwftbs on petroleum plays remains unclear in this study we developed models for petroleum migration and accumulation in the offshore rovuma basin and lamu basin dwftbs located along the passive continental margin of east africa based on an integrated analysis of seismic geochemical and geological data using available high quality seismic data in the depth domain we were able to quantify the evolution of thrust anticline growth by applying the area depth strain ads method our results indicate that the offshore lamu basin dwftb was active from the late cretaceous period to the early miocene period while the offshore rovuma basin dwftb has been active from the oligocene period geochemical parameters and basin modeling show that widespread lower jurassic mudstone is the dominant source of petroleum resources with peaks of oil and gas generation in the cretaceous and cenozoic periods respectively based on this we suggest that the traps within the offshore lamu basin dwftb contain oil generated from lower jurassic sources that migrated along faults and accumulated during the late cretaceous period and gas generated from the same sources during the cenozoic period conversely there is an insufficient amount of oil in the offshore rovuma basin dwftb owing to the absence of oil migration pathways or traps as a result of the dwftb s more recent formation from the oligocene period

secondary migration of hydrocarbons in the zhujiang formation in the huixi half graben pearl river mouth basin south china sea the process and mechanisms of secondary hydrocarbon migration in the huixi half graben pearl river mouth basin were investigated on the basis of geological analysis of the strata and study of the porosity and permeability of the reservoir rocks fluid potential oil properties and geochemistry of oil source correlation the results suggest that the hydrocarbons of the zhujiang formation in the huixi half graben were derived from source rocks of the eocene wenchang formation and the eocene oligocene enping formation in the huizhou sag the hydrocarbons migrated laterally from northeast to southwest the sandstone in the upper member of the zhujiang formation exhibited superior physical properties porosity and permeability and connectivity than the lower member thin sandstone beds with good physical properties and stable distribution in the upper member of the zhujiang formation were the main carrier beds for lateral hydrocarbon migration

late holocene inland dune activity in the uk a case study from breckland east anglia inland dune fields found in breckland east anglia uk have previously been correlated with the widespread late devensian coversands of the region and a seventeenth century sandflood which is known to have inundated the village of santon downham a programme of optically stimulated luminescence and radiocarbon dating undertaken on the dunes at wangford warren and santon downham reveals that episodic aeolian activity has taken place during the last 7000 years five sand depositional phases on breckland dunes are identified c 6500 c 1600 1100 c 500 c 400 335 and from c 200 30 years before present between c 2120 1840 years ago and within the period 1100 300 years ago quiescent periods allowed the development of fen peat and soils local controlling factors on aeolian activity in breckland appear to be related to anthropogenic activities and livestock sheep and rabbits reducing vegetation cover and decreased precipitation and sea levels which led to lowering of water tables breckland aeolian activity when compared to the national and sub continental holocene aeolian activity record shows a high level of concordance the underlying forcing factor for late holocene dune activity in the uk and elsewhere in europe appears to be climatic instability in the north atlantic associated with both the little ice age and previous similar events which led to increased storminess climatic variability and lower temperatures

role of off shelf to on shelf transitions for east antarctic sea ice dynamics during spring 2003 1 during austral spring 2003 mesoscale sea ice drift and deformation off east antarctica were investigated using in situ data from a nine buoy array upon deployment the array comprised an area of about 4000 km2 with a mean ice concentration of 96 half hourly sea ice velocities were coherent across all buoys at zonal meridional separations of less than 160 km 70 km regional cross spectral correlation was high at synoptic scales and also at semidiurnal periods off the continental shelf atmospheric synoptic scale forcing explained in excess of 85 of the ice drift variability this is significantly more than found in the weddell sea where significant ice drift variability is derived from oceanic forcing peak frequencies of semidiurnal contributions covaried with latitude and are largely associated with the inertial response over the continental shelf coincident diurnal and semidiurnal variances in ice motion arose from tidal forcing net divergence over 37 days resulted in an expansion to 270 of the initial area although regional ice concentration reduced only slightly high frequency processes namely inertial response and to a lesser degree tidal forcing dominated the variability of all deformation parameters in contrast to ice motion low frequency processes played a secondary role in sea ice deformation this high frequency dominance is similar to what has been found in the weddell sea although many observations there were limited to the continental shelf where tidal processes dominate sea ice motion and deformation were not affected by a seasonal transition nor did the regional ice characteristics show any signal of seasonal change instead local ice dynamics were strongly influenced by bathymetrically dependent processes

petroleum migration pathways and charge concentration a three dimensional model petroleum migration pathways through a basin are determined by the three dimensional distribution of discontinuous sealing surfaces which are usually parallel to bedding the petroleum migrates below the sealing surface taking the structurally most advantageous route the three dimensional distribution of migration pathways within the petroleum system can be modeled on a personal computer using a program based on the parameters discussed in this paper application of the model to the paris and williston basins demonstrates that a good correlation between predicted pathways and discovered accumulations can be made using simple models pathways form a dense network overlying generating areas in the central parts of basins toward the basin margins these routes commonly become increasingly focused into discrete pathways by the sealing surface morphologies eventually these pathways may reach the surface as seepages it is important to integrate surface outcrops of migration routes surface seepages into migration modeling deflection of the pathways from the structurally most advantageous route below the sealing surface may be caused by lateral sealing barriers due to facies variation in the carrier rock below the seal fault juxtaposition or cross formational seals such as salt intrusions deflection of pathways also occurs where there are hydrodynamic conditions in response to topography driven groundwater flow zones of vertical migration are associated with facies changes along the horizon of the sealing surface into a nonsealing facies or juxtaposition to nonsealing strata by faults vertical migration from either normally or abnormally pressured strata is most likely to occur into normally or lesser pressured strata at intrabasinal highs where hydrocarbons can be stored and transferred at times of temporary seal rupture reverse modeling of individual pathways from fields and seepages to potential sources is a powerful exploration tool it assists in predicting the boundaries of the leaking accumulations or areas of petroleum expulsion

observation of cyclone induced inertial sea ice oscillation in fram strait 1 in march 2007 the field campaign framzy took place in the region between spitsbergen and greenland one goal of the experiment was the observation of cyclone impact on ice drift by means of autonomous meteorological buoys deployed on sea ice on 23 march an intense cyclone of about 500 km diameter passed with about 20 m s from south to north over the ice covered part of the fram strait and induced strong inertial oscillations of the sea ice ice drift velocity fluctuations abruptly increased by a factor of three to values of more than 1 m s this was caused by a resonant wind forcing for almost three quarters of the inertial oscillation depending on the local ice conditions the oscillations lasted over a two to five days period the inertial oscillations caused ice drift divergence fluctuations of 6 10 6s 1 and a reduction of ice concentration by up to 11

minimum saturations and buoyancy in secondary migration percolation theory it is often argued requires a minimum nonwetting phase saturation of approximately 15 for hydrocarbon migration but field measurements usually fail to find residual oil on the pathway taken during hydrocarbon migration from a source to a reservoir we use numerical simulations and experiments to show that percolation theory when applied to the process of oil invading a pore space leads to the conclusion that field scale saturations in secondary migration can be on the order of 1 or less our capillary invasion experiments on berea sandstone and numerical simulations of fluid invasion on networks show that the minimum saturation for flow of the nonwetting phase decreases as the reciprocal square root of the linear size this result applies to cyli drical samples that have height equal to diameter our numerical simulations include the effects of sample aspect ratio buoyancy and pore size distribution all the numerical results reduce to a single relation between threshold saturations and sample size normalized by a function of the pore size distribution we find that a pore size distribution that has many more small pores than large pores as is typical in rocks and soils substantially reduces the influence of buoyancy on threshold saturations the common practice of using uniform flat pore size distributions to simulate rocks overestimates the effects of buoyancy experiments show that for larger samples the permeability at threshold for flow is higher than conventionally expected in a typical geological situation this h gh permeability is large enough to carry oil to a reservoir over geologic time at saturations of less than 1 of the pore volume our laboratory permeability and saturation experiments confirm the expectations of percolation theory including the fractal dimension of the first invasion path size dependent saturation is the prediction of invasion percolation theory the percolation model is applicable to the secondary migration problem as well as to migration of gas in reservoirs migration of gas or fluids from radioactive waste repositories and migration of nonaqueous phase liquid pollutants in groundwater

secondary migration of oil experiments supporting efficient movement of separate buoyant oil phase along limited conduits geologic note experimental data suggest that the secondary migration of oil in porous permeable sediments probably occurs in most circumstances along restricted pathways or conduits these conduits are formed after the oil has reached a high enough saturation in the reservoir rock for the buoyancy of the oil to overcome the capillary pressure in the pore throats the oil probably moves vertically until it reaches the top of the reservoir interval the oil then moves updip along the top of the reservoir interval via a narrow restricted pathway until it reaches the trap and begins to accumulate depending on the area of the original oil saturation at the bottom of the reservoir unit and the structural geometry multiple conduits may form along which the oil may flow because these conduits are limited in diameter the amount of oil lost during secondary migration could be limited to the irreducible oil saturation left behind in the conduit provided no small scale traps exist along the path to the main trap rates of oil movement are very rapid in a geologic context suggesting that the timing of primary migration is a good indicator of the timing of secondary migration

petroleum migration and accumulation in the bozhong sub basin bohai bay basin china significance of preferential petroleum migration pathways ppmp for the formation of large oilfields in lacustrine fault basins abstract this paper discusses migration styles and primary controls of petroleum migration pathways in heterogeneous carrier beds in bozhong sub basin bohai bay basin modeling of secondary petroleum migration pathways has been conducted using a simple three dimensional model which assumes that the positions of petroleum migration pathways are controlled by the morphology of the sealing surfaces the modeling results have accurately predicted the petroleum occurrences and have been supported by petroleum geochemical studies most commercial petroleum accumulations are on the predicted preferential petroleum migration pathways ppmp formed by focusing of numerous small petroleum streams close to the kitchens and most large fields petroleum reserves greater than 1 10 8 ton have more than one preferential petroleum migration pathway to convey petroleum to the traps the focusing of petroleum originated from a large area of the generative kitchens into restricted channels is essential for the formation of large oilfields the strong porosity and permeability heterogeneities of the carrier beds and the relatively high prediction accuracy by a model that does not take into consideration of the effect of heterogeneity suggest that the positions of petroleum migration pathways in heterogeneous carrier beds in the lacustrine fault basins are determined primarily by the morphology of the sealing surfaces at regional scales

entrainment induced by near inertial drift of sea ice and its impact on under ice biogeochemical processes in marginal ice zones abstract mooring observation of hydrography hydrodynamics and suspended particles distribution under a drifting sea ice revealed the mixing and entrainment pattern in the upper mixed layer ml of the marginal ice zone the ice floe where the mooring system was installed drifted as near inertial motion with approximately 12 h cycle the mixing pattern induced by this near inertial drift can be divided into two distinct regimes first simple entrainment upward fluxes from the seasonal pycnocline to sea ice water boundary are induced by shear across ml and seasonal pycnocline during the period when ice floes drift toward pack ice the entrainment speed was in the range of 0 25 2 m h 1 which matches well with thickening and thinning of the ml during a near inertial period turbulent wakes on the boundary between sea ice and open water occurred behind the advancing edge of ice in the second regime when ice floes drift toward open ocean the turbulent wakes at the advancing edge of ice are combined with the entrainment caused by near inertial motion which results in a complex mixing pattern of both upward and downward fluxes in the ml the echo intensity observed by the acoustic doppler current profiler and beam attenuation from transmissometer revealed the elevated concentration of suspended particulate materials in the ml which can be direct evidence visualizing the mixing pattern results suggest that the mixing and entrainment found in our study sustain particulate matters in suspension within upper ml for a few months this may provide a potential mechanism to sustain abundant organic particulates in the ml and upper pycnocline for months after under ice bloom under strong wind events like storms the entrainment induced by near inertial motion may also get enhanced which causes elevated supply of nutrients from the deeper permanent pycnocline to the ml

interactions between near inertial mixed layer currents and the mesoscale the importance of spatial variabilities in the vorticity field abstract satellite tracked mixed layer drifter data from the 1987 ocean storms experiment in the northeast pacific are used to study the temporal and spatial variability in the near inertial currents of the surface mixed layer the data suggest that the near inertial currents interact with the mesoscale vorticity to explore the exact nature of this relationship an asymptotic analysis is extended to include the mesoscale and it is shown that not only gradients in the planetary vorticity but also the gradients in the mesoscale vorticity affect the generation and evolution of near inertial mixed layer currents while the effect is relevant for the large scale evolution of the near inertial currents the vorticity gradients of the mesoscale field determine the local behavior of near inertial currents using a three dimensional model it is shown that areas of large gradients in the mesoscale vorticity coincide with areas of low near inertial energy the smaller spatial scales in the near inertial energ

impacts of the tectonic stress field on natural gas migration and accumulation a case study of the kuqa depression in the tarim basin china stress fluid and temperature are three of the major factors that impact natural gas migration and accumulation in order to study the influences of tectonic stress field on natural gas migration and accumulation in low permeability rocks we take the kuqa depression as an example and analyze the evolution of the structure and tectonic stress field at first then we study the influences of tectonic stress field at different tectonic episodes on fractures and fluid potentials through the numerical simulation method on the section across the kl2 gas field we summarize two aspects of the impact of the tectonic stress field on natural gas migration and accumulation firstly under the effects of the tectonic stress field the rock dilation increases with the added stress and strain and when the shear stress of rock exceeds its shear strength the shear fractures are well developed on one hand the faults which communicate with the hydrocarbon source rocks become the main pathways for natural gas migration on the other hand these positions where fractures are well developed near faults can become good reservoirs for natural gas accumulation secondly because fluid potentials decrease in these places near the faults where fractures are well developed natural gas can migrate rapidly along the faults and accumulates the impact of tectonic stress fields on natural gas migration and accumulation allows for hydrocarbon migration and accumulation in the low permeability rocks in an active tectonic compressive setting

an experimental study of secondary oil migration in a three dimensional tilted porous medium a three dimensional physical experiment was conducted to study secondary oil migration under an impermeable inclined cap light colored oil was released continuously at a slow rate of about 0 1 ml min from a point at the base of an initially water saturated porous model with buoyancy as a primary driving force a vertical cylindrical shape of an oil migration pathway was observed first and then a layer shaped lateral migration pathway was observed beneath the top inclined sealing plate once the oil cluster had reached the top cap magnetic resonance imaging was used to observe the migration processesmdashfor example morphology of the migration pathway intermittency of oil bubbles and variation of oil saturation within the migration paths results show that the snap off phenomenon related to fast local imbibition processes occurred more commonly during vertical migration than it did during lateral migration the lateral migration pathway that parallels to the top inclined cap has a typical vertical thickness of 2 to 4 cm 0 8ndash1 6 in i e roughly 40ndash80 pores this thickness is consistent with the prediction derived from scaling laws related to pore size and bond number along the lateral migration direction the sectional area and the horizontal width of the migration pathway fluctuate significantly although the average oil saturation along the pathway remains almost the same after stopping the initial oil injection the sectional area of the migration pathway shrinks significantly therefore we believe that this significant shrinking of the migration pathway is the main reason why only a relatively small volume of oil and gas has been lost during secondary migration

water mass properties and circulation on the west antarctic peninsula continental shelf in austral fall and winter 2001 abstract hydrographic measurements made during the us southern ocean global ocean ecosystem dynamics cruises which took place from april to june and july to september 2001 provide a description of changes in water mass distributions and circulation patterns in the marguerite bay region of the west antarctic peninsula continental shelf that result from seasonal variability and offshore forcing by the southern boundary of the antarctic circumpolar current acc the primary seasonal change in water mass properties is the reduction in antarctic surface water and replacement by a thick winter water layer the primary effect of the acc is to pump warm 1 5 c salty 34 65 34 7 and nutrient rich circumpolar deep water cdw onto the continental shelf below 200 m at specific sites that correspond to bathymetric features such as marguerite trough the cdw intruded onto the continental shelf moved across shelf and entered marguerite bay this flow pattern was observed during both cruises suggesting that onshelf intrusions of cdw are a regular occurrence on this shelf the number of cdw intrusions observed suggests that 4 6 events can occur in a year regions where cdw intrusions occur are characterized by surface waters that are above freezing in winter diffusive heat fluxes based on estimated diffusivities are insufficient for the observed rate of temperature decay of cdw intrusions localized bathymetrically controlled vertical mixing is suggested as the primary heat transfer mechanism the hydrographic and acoustic doppler current profiler measurements show a southwesterly flowing coastal current along adelaide island that enters the north side of marguerite bay and exits around alexander island this current which may result from seasonal coastal buoyancy forcing was present in fall and winter but was better developed in fall this current may be part of a larger cyclonic gyre that overlies the northern part of the area surveyed during the two cruises

buoyancy and interfacial force effects on two phase displacement patterns an experimental study modeling secondary migration of oil currently is difficult because the physics governing the movement is complex and information on heterogeneity of carrier beds is always incomplete to better understand the basic physical process of secondary migration we discuss displacement patterns based on relative magnitudes among buoyancy interfacial and viscous forces using the results of one dimensional vertical oil water displacement experiments oil was injected at a constant rate from the lower inlet of a glass tube packed with sorted glass beads the injection pressure and oil outflow rate were measured while we observed the displacement pattern runs were done using different grain sizes and injection rates two displacement patterns were recognized during the experiments type a consisted of stable piston like displacement and type b consisted of capillary fingering the difference coincided with the relative magnitudes of the driving forces which can be characterized by the dimensionless modified bond bo and capillary ca numbers type a pattern was produced for high ca bo ratios and type b pattern for low ca bo ratios a flow regime diagram showing the regions of the two displacement patterns was constructed in ca bo space including the effects of gravity our results also showed that excess pressure for the nonwetting phase fluid to intrude into a porous medium was rate dependent

petroleum secondary migration and accumulation in the central junggar basin northwest china insights from basin modeling the timing of petroleum generation migration and accumulation in the central junggar basin has been evaluated using basin modeling technology to decipher the processes of petroleum secondary migration and accumulation in the jurassic carrier beds during the yanshan and himalayan orogenies during the early yanshan orogeny j2 j3 crude oils sourced mainly from the permian source rocks migrated laterally from depocenters to adjacent structural high points during the late yanshan orogeny cretaceous eocene the hydrocarbon secondary migration pattern changed significantly specifically in the cretaceous a large scale regional second phase of generation and migration occurred in the western part of the central junggar basin in the eastern part of the central junggar basin crude oils emplaced in the depressions migrated mainly to the eastern uplifts in the early tertiary oils in the source kitchens generally began migrating to the north and mixed with the jurassic generated hydrocarbons during the himalayan orogeny neogene quaternary this migration was strengthened continually the modeled results agree with migration associated geochemical information of the jurassic accumulations integration of the regional geological setting and some petroleum geology data suggest that the jurassic tectonic high points and facies change and unconformity associated subtle traps are of crucial importance for current oil exploration both overpressured bodies in the triassic and permian systems and volcanic rock reservoirs of the carboniferous basement in the uplifts have important implications for future natural oil and gas exploration this work should help reduce exploration risk in this region

springtime ice motion in the western antarctic peninsula region abstract oscillatory motion of sea ice is examined using two ice drifting buoys separated by 1 latitude near 66 s during the winter to spring transition in the marguerite bay region west of the antarctic peninsula the buoys motions exhibit spectrally distinct periods 12 87 0 04 and 13 03 0 04 h respectively despite highly correlated motion between them r2 is 0 62 and 0 81 for u and v respectively the periods shift with latitude and nearly match the local inertial periods 13 00 and 13 10 h respectively the oscillations are further examined with respect to the kinematics involved in the breakup process of sea ice these include hourly resolved manifestations of circular trajectories semi circular oscillations with compressed trajectory cusps and accordion like compressions along straight line trajectories oscillations are found in all trajectory types over the lifetime of both buoys several months traditional circular and semi circular oscillations are particularly prominent during two episodes one of which is preceded by strong wind events and a substantial decrease in ice thickness and concentration these episodes combine with seasonally warming temperatures to break up and melt the sea ice cover we discuss potential relationships between the degradation of the ice pack during spring breakup and the increase in energy at near inertial frequencies including the appearance of a non linear cascade of energy within the ice from the low frequencies commensurate with storms and fortnightly tides to semi diurnal frequencies we further comment on the implications this type of high frequency motion has on local biological ecosystems specifically we find that sea ice semi diurnal oscillations are at their peak during the final decay of sea ice just before springtime primary productivity begins hence the oscillatory motion of sea ice not only serves as an effective mixing agent within the ice ocean mixed layer but also serves as an effective seeding platform for distributing phyto and zooplankton overwintering within and around the ice floes

estimating the annual cycle of sea ice thickness and volume in the ross sea antarctic sea ice thickness and concentration derived from satellite based ice charts are compared to contemporaneous ship based estimates of the same parameters collected in the ross sea between 130 w and 160 e from 1995 to 1998 thickness variability exists on the scale of individual ice chart polygons tens of kilometers but found compatible with wmo thickness ranges except in areas with high concentration of ridging very good agreement is found between the thickness distributions on the regional scale of the ross sea with an annual climatological average thickness of 0 65 m for the ice charts in comparison to 0 76 m for the ship based measurements given these analyses we proceed by examining resulting annual cycle and interannual sea ice thickness and volume estimates for the ross sea region resolved to weekly time intervals the weekly thickness estimates show the influence of thicker ice advected from the amundsen sea new ice produced adjacent to ross ice shelf and changes in the ross sea polynya the relationship between weekly ice extent and volume indicate a lag one to nine weeks of volume mass due to thickness processes during the growth season which differs from lateral extent in 1996 1998 while both extent and volume are more similar during the melt season the maximum extent and volume occur simultaneously in 1995 1997 but in 1998 the volume peak lags extent by almost 5 weeks moreover thickness variability is found to be more sensitive than extent to climate events during the 1996 la nina and 1997 98 el nino episodes we postulate therefore that ice thickening processes evolve somewhat independent of sea ice extent these results contradict some existing model studies which show that sea ice thickness and extent co vary hence the thickness estimates here demonstrate the importance of measured ice thickness which responds distinctly different from extent in response to dynamic and thermodynamic processes during the annual cycle

subsynoptic scale spatial variability of sea ice deformation in the western weddell sea during early summer 1 ice station polarstern ispol deployed in the western weddell sea from november 2004 to january 2005 included a study of subsynoptic scale variability in sea ice velocity and deformation using an array of 24 buoys upon deployment the ispol buoy array measured 70 km in both zonal and meridional extent and consisted of subarrays that resolved sea ice deformation on scales from 10 to 70 km across the ispol array divergence varied and did not show a distinct coherent length scale spectral analysis of divergence and shear of subarrays revealed that deformation did not vary smoothly across the array this indicates variability of internal ice stress on the scale of 10 km ice conditions within the ispol array encompassed two distinct regimes separated by shear along the continental shelf break differences in spectral power of the tidal and inertial bands across the two regions do not mirror expected differences due to spatial variability of tide induced deformation on the shelf break instead they indicate that the pack ice s internal stress behaved anisotropically on the scale of the shear zone across the buoy array 70 km

holocene landscape change at carn dubh near pitlochry perthshire scotland detailed palynological analyses including pollen preservation and charcoal counts and sedimentological analyses loss on ignition percentage dry weight dry bulk density and humification supported by 15 14c dates were applied to a small upland 350 m od peat basin near pitlochry east central grampians scotland stratigraphical analyses and radiocarbon dating were also undertaken on the valley peat surrounding the basin organic sediment began to accumulate in the basin and on the valley floor at ca 9800 yr bp recurrence surfaces within the valley floor peat correlate with the end of a trend to increased aridity in the deep basin from 8900 to 8500 yr bp pine may have colonised the hills with birch before the migration of hazel at 9150 yr bp from around 8000 yr bp elm grew on the base rich soils alder may have been present by 7000 yr bp but it did not expand until immediately after the first major anthropogenic disturbance at 4800 yr bp above 8000 yr bp silt was commonly deposited in the basin by streams but several phases of exceptionally intense inwashing are identified and at least two of these correlate with periods of increased precipitation grazing pressure during the elm decline marks the beginning of a long history of generally low intensity pastoralism interspersed with periods of heightened anthropogenic activity

cosmogenic cl 36 dating of postglacial landsliding at the storr isle of skye scotland major postglacial rock slope failures are a common feature of the scottish highlands and other mountainous areas that were deglaciated at the end of the pleistocene but evaluation of the causes and triggers of failure has been hindered by a lack of reliable dating evidence we report the result of a pilot study designed to establish the absolute age of a large postglacial rotational rockslide at the storr on the isle of skye scotland using 36cl surface exposure dating exposure ages of 6 3 0 7 cal ka bp and 6 6 0 8 cal ka bp were obtained for rock samples from two separate landslide blocks giving an overall age estimate of 6 5 0 5 cal ka bp for rock slope failure at this site this date is consistent with ams radiocarbon dating of windblown sand derived from the failure scarp and with previous inferences based on relative dating evidence concerning an early holocene age for most rock slope failures in the scottish highlands the long time lag 7 ka between deglaciation and failure sugge

quantitative assessment of petroleum loss during secondary migration in the yaojia formation ne songliao basin ne china abstract in the nw songliao basin ne china petroleum is produced from fluvio deltaic sandstones in the upper cretaceous yaojia formation source rocks are dark colored lacustrine shales of the qinshankou formation in this paper two models were developed to characterize the petroleum migration pathways in the lower member member 1 of the yaojia formation in the first model which applies to the northern region of the study area petroleum migrates only in the lowermost carrier bed in member 1 immediately above the area of the source kitchen and later in multiple carrier beds outside this area in the second model which represents migration patterns in the central and southern regions of the study area petroleum migrates in multiple carrier beds both within and outside the area of the source kitchen pressures in the yaojia formation were inferred to be hydrostatic while petroleum expulsion and migration took place therefore seven migration accumulation i e local palaeo drainage systems were defined according to the fluid potential gradients migration loss was found to vary markedly between migration accumulation systems in the study area and was controlled by factors including the shape width and area of the effective source rocks the thickness and distribution of carrier beds inside the source area the migration distance outside the source area and the number of carrier beds involved in petroleum migration using these two models petroleum loss during secondary migration was estimated the loss during secondary migration was approximately 5 21 billion bbl of petroleum which is approximately 6 of the petroleum expelled into the first member of the yaojia formation nearly 80 of the total migration loss occurred in all the carrier beds above the source area

modeling the high frequency component of arctic sea ice drift and deformation abstract buoy observations of sea ice drift show that sea ice motion and deformation contain substantial high frequency variability at subdaily timescales however numerical simulations of the sea ice dynamics normally do not include processes on such short timescales instead by applying traditional water drag formulations for the ocean sea ice boundary layer the inertial frequencies tend to be omitted in the spectra of modeled sea ice motion and deformation due to fictitious ocean damping here a dynamic thermodynamic sea ice model is presented that includes inertial embedding of the sea ice into the oceanic boundary layer to reproduce sea ice motion and deformation not only at daily and lower frequencies but also at subdaily frequencies up to 2 cycles per day and higher comparison with buoy data shows that the embedded model much more successfully simulates the observed sea ice motion in regard to the high frequency component the results demonstrate that both inertial embedding of the sea ice oc

scaled physical model of secondary oil migration a scaled physical model was constructed to simulate gravity and capillary controlled flow of oil into a water saturated sand during secondary hydrocarbon migration the model provided both visualization of the flow patterns and estimates of hydrocarbon transport rates and efficiencies the dimensions and physical properties of the model were designed so the balance of gravity capillary and viscous forces was the same in the model as in the geologic system the physical model was a sand pack between glass plates the pack was 52 cm high 100 cm long 2 5 cm thick and inclined at a 5 dip its porosity was 42 and its permeability was 7 0 10 10 m2 710 d it modeled a geologic carrier bed 27 m thick with 20 porosity and 9 9 10 14 m2 100 md permeability overlying a source rock a dyed oil was injected into the lowest corner at a rate of 1 cm3 day and it exited the highest corner at atmospheric pressure oil movement was followed both visually and by ultrasonic velocity measurements the behavior of fluids in the model led us to the following conclusions for oil transport through water wet homogeneous carrier beds the rate limiting step in charging a trap is not secondary migration but rather the rate of oil release from the source rock high hydrocarbon loss may occur during vertical migration when the carrier bed lies above the source because of extensive dispersion losses during lateral migration are probably minimal because flow is concentrated below the top seal

barents sea tidal and inertial motions from argos ice buoys during the coordinated eastern arctic experiment a harmonic analysis constrained to estimate separately ice motions forced by tides and inertial oscillations was applied to observed positions of argos buoys deployed on drifting multiyear sea ice in the eastern arctic ocean and barents sea during the coordinated eastern arctic experiment 1988 1989 individual tidal components were estimated at 15 day intervals and inertial oscillations were estimated at 3 day intervals the s2 tidal component was distinguishable from inertial motions south of 79 n and the m2 tidal component was distinguishable from the inertial motion north of 77 5 n computed ice velocities of up to 70 cm s 1 for m2 tidal motion over spitsbergen bank southeast of svalbard agreed reasonably well with the regional tidal models no ice cover of gjevik and of kowalik regional differences in the energy distribution in the arctic basin low barents shelf high and spitsbergen bank extreme were emphasized by this technique the m4 tidal component in the ice motion was typically as large over the barents shelf as the inertial oscillation

coarse cliff top aeolian sedimentation in northern gaspesie quebec canada this paper deals with the effects of wind on rockwall dynamics on 5 and 6 january 1988 very strong northwest winds blizzard were blowing onto the rockwall of mount saint pierre alt 424 m gaspesie quebec canada the most violent recorded squall reached 99 4 km h 1 during this event the summit plateau received a large amount of aeolian sediments originating from the shale rockwall that forms the mountain s northwest side in the 15 to 20 m wide by 75 m long belt located along the top of the rockwall over a 1200 m2 area a continuous layer of debris completely covered the snow this layer of debris had a mean thickness of 11 4 mm which represents an accumulated volume in the order of 13 m3 largely dominated by sand and granules 2 4 mm the 28 samples collected for grain size analysis also contained numerous thin shale flakes many of which were longer than 10 mm the largest flake measured had a width of 134 mm and a weight of 164 3 g six available 14c dates provide information concerning mean cliff top aeolian sedimentation rate for the last thousand years c 1 8 mmyr 1

time dependent pore filling this research was funded by the kaust endowment j jang was supported in part by the u s geological survey s gas hydrates projects g abelskamp edited the manuscript data sets presented in this study are available from the kaust repository http hdl handle net 10754 627427

aeolian deposits on a scottish mountain summit characteristics provenance history and significance the summit plateau of the storr 719 m in northern skye is mantled by a sheet of aeolian sediment up to 2 9 m thick covering an area of 33 000 m2 with a volume of 41 000 m3 the deposits are of massive poorly sorted sand with significant components of silt and fine gravel and contain clasts up to 109 mm in length the thickness and coarseness of the deposits decline westwards and northwards away from the highest cliffs implying that the sediment comprises particles dislodged from rockwalls and blown upwards in an accelerating vertical or near vertical airflow settling through a lower velocity flow onto the plateau surface where they are trapped by vegetation radiocarbon dating of soils buried under and within the deposits suggests that accumulation began after 7 2 6 9 calendar ka bp but before 5 6 5 3 calendar ka bp and was probably initiated by exposure of the present rockwall by a massive landslide at c 6 5 0 5 calendar ka bp pollen analyses of buried organic horizons suggest that a vegetation mat dominated by grasses and sedges was present throughout the period of sediment deposition sediment accumulation over much of the plateau averaged 10 20 mm per century throughout the late holocene but reached c 60 mm per century in the area of the thickest deposits the volume of the deposits implies the removal of 420 480 mm of rock averaged over the face during the late holocene and suggests that small scale granular disaggregation and release of small clasts constitute a major component of rockwall retreat under present conditions the origin of the storr deposits suggests that plateau top aeolian sediments on other scottish mountains accumulated in a similar way but have been eroded and redeposited on lee slopes following breakage of vegetation cover 1998 john wiley sons ltd

sub daily sea ice motion and deformation from radarsat observations 1 we find a persistent level of oscillatory sea ice motion and deformation superimposed on the large scale wind driven field in may 2002 spring and february 2003 mid winter in the high arctic over a region centered at 85 n 135 w at this latitude the radarsat wide swath sar coverage provides 4 5 sequential observations every day for ice motion retrieval with a sampling interval at the orbital period of 101 minutes periodic correlations in ice motion and deformation can be seen in length scales from 10 km and above and suggest a 12 hr oscillation that is more likely associated with inertial rather than tidal frequencies divergence convergence of 0 1 0 2 peak to peak or rates of 10 7 s is seen in both datasets with the mid winter dataset having smaller values these observations are remarkable in that short period ice motion is previously believed to be inhibited by the strength of the ice pack in the high arctic during winter new ice production due to the recurrent openings and closings at these temporal scales if ubiquitous could be significant within the winter pack

late quaternary aeolian dunes on the presently humid blue mountains eastern australia abstract sand dunes on the newnes plateau 1000 m a s l west of sydney were active during the last glacial maximum the scattered sand dunes are forested under the modern humid temperate climate regime dune types range from parabolic to transverse lee dunes and sand sheets or patches all point to the presence of conditions marginal for aeolian activity made possible through wind acceleration on windward slopes ready sand supply from the weathered sandstone of the plateau and sparse vegetation cover modern climate envelopes of sand dune activity in australia predict that unrealistically drier conditions are necessary to allow wind transport at this site only additional impediments to plant growth such as lower temperature and lower atmospheric carbon dioxide concentrations appear to allow the necessary conditions for dune formation these observations and conclusions extend our understanding of the extremes of the lgm climate in humid eastern australia confirming that the widespread treeless vegetation was also sparse even in areas that today have annual rainfall above 1000 mm

development of a cliff top dune indicated by particle size and geochemical characteristics rubjerg knude denmark particle size and geochemical data have been used to investigate the development of a large cliff top dune at rubjerg knude located on the western coast of jutland denmark textural parameters and geochemical ratios provided useful indicators of the dune sediment provenance and mode of evolution of the dune the dune sediments themselves showed no significant spatial particle size trends and reflect a number of processes including grainfall wind ripple migration and avalanching grainflow which formed a high proportion of the deposits on both the stoss and lee sides of the present dune fine grainfall sediments which have accumulated to form a sandplain in the lee of the dune show fining and improved sorting with distance and extend more than 2 km downwind of the dune crest comparison of the textural and geochemical data from rubjerg knude and other locations on the jutland coast indicates that although there is a contribution of sand to the dune from local marine sources the main source of sand to the cliff top dune and sand plain sediments has been provided by the wind erosion of the underlying cliffs which are composed of weichselian age sandy glaciofluvial and glaciolacustrine deposits optically stimulated luminescence dating indicated an apparent age for the sand at the base of 274 14 years if this date is reliable it suggests that accumulation of the aeolian sand in this area began within approximately the last 300 years map and photographic evidence indicate that the modern high dune only began to form after 1885 apparently associated with an acceleration in the rate of coastal cliff retreat

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

the structure and sedimentology of relict talus trotternish northern skye scotland sections up to 3 5 m deep cut through the upper rectilinear segment of relict vegetated talus slopes at the foot of the trotternish escarpment reveal stacked debris flow deposits intercalated with occasional slopewash horizons and buried organic soils radiocarbon dating of buried soil horizons indicates that reworking of sediment by debris flows predates 5 9 5 6 cal ka bp and has been intermittently active throughout the late holocene particle size analyses of 18 bulk samples from these units indicates that c 27 30 per cent of the talus deposit is composed of fine 2 mm sediment sedimentological comparison with tills excludes a glacigenic origin for the talus debris and the angularity of constituent clasts suggests that in situ weathering has been insignificant in generating fine material we conclude that the fine sediment within the talus is derived primarily by granular weathering of the rockwall with syndepositional accumulation of both fine and coarse debris implying that c 27 30 per cent of rockwall retreat since deglaciation reflects granular weathering rather than rockfall the abundance of fines within the talus deposits is inferred to have been of critical importance in facilitating build up of porewater pressures during rainstorms leading to episodic failure and flow of debris on the upper parts of the slope a wider implication of these findings is that the mechanical properties of talus slopes cannot be regarded as those of free draining accumulations of coarse clasts and that models that treat talus slopes as such have limited value in explaining their form and evolution our findings lend support to models that envisage the upper straight slope on talus accumulations as the product of mass transport as well as rockfall and indicate that episodic debris flow has been the primary agent of mass transport at this site 1998 john wiley sons ltd

age and significance of aeolian sediment reworking on high plateaux in the scottish highlands holocene aeolian sand sheets at the margins of high level deflation surfaces in the scottish highlands commonly comprise two units a lower weathered unit representing slow accumulation through out much or all of the holocene and an upper unit of structureless sand that is inferred to represent recent erosion of aeolian deposits and aeolisols from adjacent plateaux osl dating of samples from above and below the upper lower unit contact at three sites in nw scotland places the onset of upper unit sediment accumulation within the interval ad 1550 1700 accumulation rates calculated from osl ages confirm rapid accumulation of upper unit deposits the timing of the onset of upper unit sand accumulation excludes expansion of sheep grazing intrinsic instability and atmospheric pollution as triggers of plateau surface vegetation degradation and consequent erosion but favours climatic deterioration increased wind stress and possibly prolonged snow lie during the little ice age as the likely cause this explanation does not however apply in all cases at an osl dated site in the grampian highlands upper unit aeolian sand accumulation commenced around ad 1900

gibbsitic soils on former nunataks implications for ice sheet reconstruction x ray diffraction analyses of soils above and below a periglacial trimline developed across the basalts of the trotternish escarpment isle of skye scotland demonstrate that gibbsite is restricted to soils above the trimline this suggests that the gibbsite is a relict of pre late devensian weathering and that the trimline did not develop after the last ice sheet achieved its maximum thickness the sharpness of the boundary between frost weathered regolith and gibbsitic soils upslope and ice scoured bedrock associated with gibbsite free soils downslope suggests that the trimline represents the altitude of the last ice sheet at its maximum thickness rather than a former boundary between passive cold based ice and erosive warm based ice these findings illustrate how identification of high level periglacial trimlines and associated contrasts in clay mineralogy provide a means for constraining reconstructions of the form of the last ice sheets

principles of geochemical prospect appraisal our current understanding of the geochemical processes responsible for the creation of commercial accumulations of oil and gas can be reduced to simple rules and equations to allow the petroleum geologist to use geochemistry to estimate before drilling the likely volumes and compositions of oil and gas delivered to the trap in most sedimentary basins oil is expelled from source rocks between 120 and 150 c whereas most gas and gas condensate are released between 150 and 230 c when the initial potential of source rocks exceeds 10kg mt oil expulsion efficiencies are between 60 and 90 expelled oil and gas migrate as petroleum rich phases driven by fluid potential gradients most flow is laterally updip in beds with effective horizontal permeabilities greater than 1 md in lower permeability rocks the petroleum fluids move vertically up or down along the path of least resistance i e the most permeable or thinnest beds separating them from a high permeability lateral carrier bed the residual saturations of petroleum left behind along the migration pathway are of the order of a few percent of the porosity geochemical analysis of source rocks helps determine the yields and compositions of petroleum fluids expelled in the catchment area of a prospect these fluid masses are converted to volumes from knowledge of the phase relations and densities of petroleum fluids evaluation of the total volume of rock through which the petroleum potentially can migrate and the mean porosity of the rocks that constitute the migration pathway allow migration losses to be assessed these losses constrain both the range of migration of petroleum fluids away from the mature source rock and the volumes of petroleum remaining for entrapment in the prospect

utility of goi qgf and qgf e for interpreting reservoir geohistory and oil remigration in the hudson oilfield tarim basin northwest china abstract the physical mechanisms responsible for hydrocarbon migration in carrier beds are well understood however secondary migration is one of poorly understood facets in petroleum system the carboniferous donghe sandstone reservoir in the tarim basin s hudson oilfield is an example of a secondary or unsteady reservoir that is oil in this reservoir is in the process of remigration making it a suitable geologic system for studying hydrocarbon remigration in carrier beds experimental methods including grains containing oil inclusions goi quantitative grain fluorescence qgf and quantitative grain fluorescence on extract qgf e together with the results from drilling logging and testing data were used to characterize the nature of oil remigration in the donghe sandstone the results show that 1 significant differences exist between paleo and current oil reservoirs in the donghe sandstone which implies that oil has remigrated a significant distance following primary accumulation 2 due to tectonic inversion oil remigration is slowly driven by buoyancy force but the oil has not entered into the trap entirely because of the weak driving force oil scarcely enters into the interlayers where the resistance is relatively large 3 the oil remigration pathway located in the upper part of the donghe sandstone is planar in nature and oil moving along this pathway is primarily distributed in those areas of the sandstone having suitable properties residual oil is also present in the paleo oil reservoirs which results in their abnormal qgf e a better understanding of the characteristics of oil remigration in the donghe sandstone in the hudson oilfield can contribute to more effective oil exploration and development in the study area

ancient and modern cold climate aeolian sand deposition a review although partly active aeolian sand sheets and dunes cover large areas in the zones of dis continuous permafrost little precise information is available about the influence of cold climate conditions on modern aeolian processes this means that palaeoenvironmental reconstructions in the stabilised mainly late pleistocene dune fields and cover sand regions in the sand belts of the european lowlands and the northern great plains of the usa and canada are necessarily still based on ancient evidence cold climate wind deposits are typically derived from areas of abundant sediment supply like unvegetated flood plains glacial outwash plains till plains and lake shores the common parabolic and transverse dune forms resemble those observed in temperate regions although a variety of periglacial features has been identified in late pleistocene dune and cover sands none of them indicate that permafrost is crucial to aeolian activity specific structures in aeolian strata permit tentative interpretation of the moisture content of depositional sand surfaces the nature of annual sedimentation cycles and the processes by which strata were deposited and or contorted but surprisingly little is known about the role of vegetation in the process of sand accumulation dunes are most informative with respect to reconstructions of past wind regimes which offer important data for verification of palaeoclimatic simulations

modeling m2 tidal variability in arctic sea ice drift and deformation semi diurnal oscillations are a ubiquitous feature of polar sea ice motion over much of the arctic basin inertial and semi diurnal tidal variability have similar frequencies so that periodicity alone is inadequate to determine the source of oscillations we investigate the relative roles of tidal and inertial variability in arctic sea ice using a barotropic ice ocean model with sea ice embedded in an upper boundary layer results from this model are compared with levitated ice ocean coupling used in many models in levitated models the mechanical buoyancy effect of sea ice is neglected so that convergence of ice for example does not affect the oceanic ekman flux we use rotary spectral analysis to compare simulated and observed results this helps to interpret the rotation sense of sea ice drift and deformation at the semi diurnal period and is a useful discriminator between tidal and inertial effects results indicate that the levitated model generates an artificial inertial resonance in the presence of tidal and wind forcing contrary to the embedded sea ice model we conclude that sea ice mechanics can cause the rotational response of ice motion to change sign even in the presence of strong and opposing local tidal forcing when a physically consistent dynamic ice ocean coupling is employed

drifter measurements of surface currents near marguerite bay on the western antarctic peninsula shelf during austral summer and fall 2001 and 2002 abstract we deployed 24 satellite tracked surface drifters near marguerite bay on the western antarctic peninsula shelf during march may 2001 and february april 2002 the woce style drifters featured holey sock drogues centered at 15 m and were located about 20 times per day by service argos analyses of the drifter tracks show a coastal current that flows toward the southwest along the west coast of adelaide island and into marguerite bay near the southern tip of adelaide island then flows clockwise around the bay near the coast and finally exits the bay near alexander island this coastal current flowed along the eastern boundary of marguerite bay in 2001 but across the central part of the bay in 2002 due to the early presence of sea ice in the southern half of the bay the outflow from the bay continued along the coast of alexander island toward the southwest in 2001 but was directed northwestward across the shelf in 2002 due to the sea ice coverage to the south a mean drifter current speed of about 10 cm s 1 was observed in the coastal current with a maximum speed of about 20 cm s 1 during periods of strong wind stress an intermittent northeastward current was observed near the shelf break the drifter tracks also show that intermittent near inertial currents are common in marguerite bay and over the adjacent shelf during ice free conditions these counterclockwise oscillations had periods near the local inertial period roughly 13 0 h and speeds of 5 20 cm s 1 with a tendency for smaller amplitudes within marguerite bay

migration behaviour of petroleum associated short chain organic acids abstract in order to increase our understanding of the origin of the short chain organic acids sca found in oilfield waters peoperties that influence the possible mechanisms for migration from source rock to reservoir have been examined the preferential partition of sca between a synthetic formation water and a modified crude oil has been measured and shows the dominance of water solubility the flooding of a modified petroleum containing sca through a water saturated core of reservoir type rock shows that the pore water has a great capacity for extracting the sca from the migrating oil phase these factors make long distance transport of sca dissolved in oil from source rock to reservoir improbable also focused water flow or diffusion processes are not considered realistic mechanisms for long distance transport in situ sources of sca are required and hydrous pyrolysis of crude oil mixed with reservoir type minerals shows that significant amounts of sca can be generated and that the emplaced petroleum could thus be the source of the sca found in oilfield waters

oil migration through preferential petroleum migration pathway ppmp and polycyclic faults a case study from the shijiutuo uplift bohai bay basin china abstract the shijiutuo uplift is an oil enriched uplift in the offshore bohai bay basin petroleum migration is a key factor for oil enrichment in neogene reservoirs far away from the hydrocarbon kitchen in this article an integration of geological geophysical and geochemical analyses are employed to investigate the petroleum migration and accumulation on the shijiutuo uplift hydrocarbons in the qhd32 6 and qhd33 oilfields are mainly originated from the third e 2 s 3 and first e 2 s 1 member of the shahejie formation the shallow traps have significant contributions of late stage e 2 s 1 derived oil lateral petroleum migration is a major mechanism forming large oilfields on the shijiutuo uplift the large oilfields have multiple hydrocarbon kitchens multiple source rocks and numerous preferential petroleum migration pathways ppmps once petroleum arrives at the structural highs on the shijiutuo uplift through the guantao formation n 1 g carrier beds neotectonic faults cutting through guantao n 1 g and minghuazhen n 1 m l formations could serve as effective conduits for vertical petroleum migration neotectonic faults have experienced polycyclic fault activities fluid inclusions indicate episodic hydrocarbon charging crude oils display duplex properties of biodegradation and non biodegradation which is strong evidence for multiple and episodic oil charging on the shijiutuo uplift finally episodic petroleum charging along polycyclic neotectonic faults causes the late stage e 2 s 1 derived oils to occur in the shallow reservoirs

notes on southern ocean hydrography sea ice and bottom water formation abstract the southern ocean circulation and sea ice distribution is briefly described the formation of extremely cold bottom water in the weddell sea and its relation to the floating ronne filchner ice shelves is discussed it is shown that a concentrated swift eroding bottom current with anomalous low 18 o ratio transports the cold and dense ice shelf water from the shelf towards large depths comments are made on possible implications of this process for the large scale deep water circulation and for the interpretation of sediment cores

scaled physical model of secondary oil migration discussion thomas and clouse have presented results of a detailed laboratory model of secondary oil migration using a sand pack and then used scaling group theory to extrapolate their observations to field scale source rock carrier bed reservoir systems they conclude that for water wet homogeneous systems the charging of traps is not controlled by secondary migration rates or losses but by the rate of primary migration from the source rock although this conclusion is compatible with the observation that estimates of field charging times are broadly similar to estimates of the time interval for a source rock to mature and expel oil we feel that several of their arguments about real secondary migration processes are misleading and require further discussion

coincident buoy and sar derived surface fluxes in the western weddell sea during ice station weddell 1992 propagation shows lower agreement for divergence 47 4 rmse 7 46 10 8 s 1 but we find these results sufficient for integrated surface flux comparisons using a toy model we test the effects of aliasing in surface flux determination the results show that variability associated with storms ocean tides inertial oscillations and other highfrequency forcing affects integrated sea ice growth rates along this continental slope location integrated salt and new ice production rates computed from buoys are found to be two times larger than those computed from ers 1 sar motion products we show that these differences in salt and ice production rates result primarily from inadequate temporal resolution of heat flux variability and sea ice divergence comparison with other studies shows that the problem is widespread thereby impacting the modeling of sea ice mass balance and variability the small scale processes cited here have significant ramifications for larger scales and the global thermohaline circulation

simulating transient ice ocean ekman transport in the regional arctic system model and community earth system model this work evaluates the fidelity of the polar marine ekman layer in the regional arctic system model rasm and community earth system model cesm using sea ice inertial oscillations as a proxy for ice ocean ekman transport a case study is presented that demonstrates that rasm replicates inertial oscillations in close agreement with motion derived using the gps this result is obtained from a year long case study pre dating the recent decline in perennial arctic sea ice using rasm with sub hourly coupling between the atmosphere sea ice and ocean components to place this work in context the rasm coupling method is applied to cesm increasing the frequency of oceanic flux exchange from once per day in the standard cesm configuration to every 30 min for a single year simulation this change causes a considerable increase in the median inertial ice speed across large areas of the southern ocean and parts of the arctic sea ice zone the result suggests that processes associated with the passage of storms over sea ice e g oceanic mixing sea ice deformation and surface energy exchange are underestimated in earth system models that do not resolve inertial frequencies in their marine coupling cycle

flow regime associated with vertical secondary migration secondary migration is defined as the movement of hydrocarbons through relatively permeable rocks from source to trap a two phase flow within a porous medium depending on the geometry and capillary pressure distributions of carrier beds secondary migration has both vertical and lateral components the present paper focuses on that part of the migration where the movement is mainly vertical its objective is to propose a description of the dynamics governing the vertical part of secondary migration based on the main physical aspects of two phase flow in a homogeneous porous medium the study is illustrated by laboratory observations performed in a vertical 2 d hele shaw cell filled with a transparent porous medium where the flow of dyed oil invading a wetting fluid is visually observed these observations help us to understand the effect of buoyant capillary and viscous forces on the resulting flow the relative importance of which is characterized by non dimensional numbers extrapolating these observations to natural media it is proposed that vertical secondary migration can be described as a percolation of disconnected and vertically elongated stringers these stringers do not move continuously but as a succession of snap off and re feeding events which result in a jerky upward movement using parameters characterizing the physical properties of the fluid and of the porous medium the geometry and the dynamic behavior of the stringers are estimated the width of stringers occurring during secondary migration in geological media is centimetric and their vertical size ranges from several centimeters to a few meters an upper limit of the mean upward velocity of stringers is proposed as well as an estimate of their spatial density and of the minimum average horizontal distance decametric between two stringers the stringers are sparsely distributed resulting in a low average oil loss and a high efficiency of the vertical migration process

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

petroleum migration and accumulation modeling and applications subsurface hydrocarbon observations at any scale serve as critical clues to understand and reconstruct migration pathways and charge histories through geological time to assess the risk of petroleum exploration targets hydrocarbon migration commonly occurred millions of years ago and the pathways can rarely be observed in wells or in outcrops therefore hydrocarbon migration modeling tools are important to test and quantify the processes and elements which impact hydrocarbon migration this paper presents a new method of analyzing migration in superimposed basins which have experienced multiple stages of basin subsidence and inversion during which multiple episodes of hydrocarbon generation migration and accumulation occurred the new modeling method first identifies the character of the migration and accumulation units by synthesizing geological factors such as heterogeneity of carrier beds and reservoirs second hydrocarbon migration is analyzed as a geologic process for which the invasion percolation ip migration method seems to be most suitable the ip migration method demonstrates a good relationship between migration driving and resisting forces along pathways and thus can be used to reasonably model hydrocarbon migration processes at any scale of units in a basin the new migration method provides insights into quantitative methods that can be applied to petroleum system analysis the new method has been applied to several chinese basins and has proven to be useful for defining exploration targets and resource assessments in mature frontier and especially tectonically complex basins a case study of the upper triassic chang 7 and chang 8 units in the southern ordos basin central china is presented to demonstrate a multistage hydrocarbon accumulation unit modeling results show that the same pairs of reservoir seal sets contained different accumulation units in the geological past with different styles of hydrocarbon migration and different accumulation patterns it can be concluded that the style and character of early hydrocarbon migration have significantly affected the more recent hydrocarbon migration and the present day distribution of hydrocarbons