pore scale evidence of ion exclusion during methane hydrate growth and evolution of hydrate pore habit in sandy sediments abstract hydrate bearing sediments constitute complex hydrological systems within which the pore habit of hydrate significantly affects all physical properties however there is scarce pore scale evidence of the evolution of hydrate growth in porous media and the influence of water salinity in the micro morphology of hydrate in this paper we used x ray computed micro tomography ct to monitor three experiments of methane hydrate growth in sand partially saturated with either nabr or ki brine under excess gas conditions gas brine and hydrate are observed to co exist at the pore scale during the evolution of hydrate pore habit towards three phase equilibrium the experiments and data analysis reveal that 1 hydrate forms as a porous medium mixed with inclusions of brine and gas where hydrate and brine evolve gradually into separate phases as hydrate cages exclude salt ions 2 hydrate growth mobilizes water over fairly long distances resulting in heterogeneous hydrate distribution and 3 hydrate can exhibit interconnecting pore habit at local hydrate saturations higher than 50 even if grown under excess gas conditions the results imply that hydrate micro morphology and pore habit evolve during hydrate formation and we suggest so do the physical properties of hydrate bearing sediments our findings provide new insights into the micro morphology of hydrate and evolution of the properties of hydrate bearing sediments synthesized in the laboratory and in natural systems

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

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

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

the tails of the satellite auroral footprints at jupiter the electromagnetic interaction between io europa and ganymede and the rotating plasma that surrounds jupiter has a signature in the aurora of the planet this signature called the satellite footprint takes the form of a series of spots located slightly downstream of the feet of the field lines passing through the moon under consideration in the case of io these spots are also followed by an extended tail in the downstream direction relative to the plasma flow encountering the moon a few examples of a tail for the europa footprint have also been reported in the northern hemisphere here we present a simplified alfvenic model for footprint tails and simulations of vertical brightness profiles for various electron distributions which favor such a model over quasi static models we also report here additional cases of europa footprint tails in both hemispheres even though such detections are rare and difficult furthermore we show that the ganymede footprint can also be followed by a similar tail finally we present a case of a 320 degrees long io footprint tail while other cases in similar configurations do not display such a length

variationally induced breathing equations of state of pyrope grossular and majorite garnets we have completed the first non empirical fully optimized calculations of the equations of state for pyrope grossular and mgsio3 majorite garnets the static gibbs free energy of the 160 atom unit cell was minimized relative to all 27 structural parameters for the tetragonal structure zero point vibration and thermal effects were estimated with a debye like model and debye temperatures obtained from the equations of state calculated zero pressure densities differ from experimental values by less than 1 while the bulk moduli are systematically larger than those obtained spectroscopically nevertheless the calculations strongly support experimental evidence that the bulk modulus of mgsio3 majorite is close to that of pyrope and further indicate that its kt p o is not distinctly larger than that of other silicate garnets if these properties are close to those of real majorite the steep gradient of the bulk modulus in the transition zone is at best marginally consistent with a iherzolitic composition

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

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

elasticity of a majorite pyrope solid solution the elastic properties of a solid solution consisting of 59 mole percent pyropic garnet and 41 mg sub 4 si sub 4 o sub 12 majorite a high pressure form of pyroxene have been measured by brillouin spectroscopy under ambient conditions values of the adiabatic bulk modulus k sub s 164 plus minus 15 gpa and shear modulus g 89 4 plus minus 3 7 gpa are similar to those for low pressure aluminosilicate garnets the enstatite majorite reaction is characterized by a large 49 increase in k sub s and a much smaller 13 increase in g the properties of low pressure garnets suggest that the contrast in shear moduli for this reaction is probably larger in ca rich systems taken at face value the stp properties of these phases imply that large quantities of ca rich clinopyroxene are needed in order to satisfy seismologically determined shear modulus gradients in the transition zone this suggestion is however subject to considerable uncertainties in the pressure and temperature derivatives of elastic properties for mantle minerals and the velocity structure of the transition zone

the multiple spots of the ganymede auroral footprint 1 the interaction between the moons and the magnetosphere of giant planets sometimes gives rise to auroral signatures in the planetary ionosphere called the satellite footprints so far footprints have been detected for io europa ganymede and enceladus these footprints are usually seen as single spots however the io footprint the brightest one displays a much more complex morphology made of at least three different spots and an extended tail here we present hubble space telescope fuv images showing evidence for a second spot in the ganymede footprint the spots separation distance changes as ganymede moves latitudinally in the plasma sheet as is seen for the io footprint this indicates that the processes identified at io are universal moreover for similar ganymede system iii longitudes the distance may also vary significantly with time indicating changes in the plasma sheet density we identified a rapid evolution of this distance 8 days after the detection of a volcanic outburst at io suggesting that such auroral observations could be used to estimate the plasma density variations at ganymede

the stability and equation of state of majoritic garnet synthesized from natural basalt at mantle conditions the high pressure stability and equation of state of majoritic garnet synthesized from natural basalt have been determined using the laser heated diamond cell and x ray diffraction natural mid ocean ridge basalt morb and tholeiitic basalt transform from a garnet dominated mineral assemblage to a silicate perovskite dominated mineralogy near 42 3 gpa static compression data at 300 k for the majoritic garnet synthesized from the natural tholeiitic basalt yields an isothermal bulk modulus k0t of 226 2 9 3 gpa with dk0t dp constrained to be 4 an equally acceptable fit to the data is obtained if k0t is constrained to be 180 gpa and dk0t dp is 7 1 using our new equation of state and phase stability results for basaltic majorite structured garnet we calculate density models for the subducting oceanic crust at mantle pressures and temperatures and find that the basaltic crust is 0 4 g cm 9 less dense than the lower mantle at 660 km depth if we assume that the subducted crust can delaminate from the underlying lithosphere a simple buoyancy model for the crustal portion of subducting slabs indicates that basaltic crust may not sink below 660 km in depth

imaging of oil layers curvature and contact angle in a mixed wet and a water wet carbonate rock we have investigated the effect of wettability of carbonate rocks on the morphologies of remaining oil after sequential oil and brine injection in a capillary dominated flow regime at elevated pressure the wettability of ketton limestone was altered in situ using an oil phase doped with fatty acid which produced mixed wet conditions the contact angle where oil contacted the solid surface measured directly from the images 180 while brine filled regions remained water wet whereas the untreated rock without doped oil was weakly water wet 47 9 using x ray micro tomography we show that the brine displaces oil in larger pores during brine injection in the mixed wet system leaving oil layers in the pore corners or sandwiched between two brine interfaces these oil layers with an average thickness of 47 17 m may provide a conductive flow path for slow oil drainage in contrast the oil fragments into isolated oil clusters ganglia during brine injection under water wet conditions although the remaining oil saturation in a water wet system is about a factor of two larger than that obtained in the mixed wet rock the measured brine oil interfacial area of the disconnected ganglia is a factor of three smaller than that of oil layers

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

an experimental investigation of the pyroxene garnet transformation in a pyrolite composition and its bearing on the constitution of the mantle abstract the pyroxene garnet transformation in a model pyrolite composition has been investigated over the pressure interval 4 0 to 17 5 gpa at temperatures of 1200 1400 c the transformation is largely completed in the pressure interval 14 16 gpa and a single phase aluminum deficient garnet majorite becomes stable above 16 gpa the mineral assemblages and the density and seismic velocity distributions for pyrolite are calculated as a function of depth on the basis of this and other recent experimental data density and seismic velocity profiles calculated for pyrolite are consistent with models based on seismic observations to a depth of 550 km if the existence of a high density velocity gradient between 550 km and 650 km is confirmed the presence of further phase transformations in majorite and or some degree of chemical heterogeneity in this depth interval would be indicated

transformation of enstatite diopside jadeite pyroxenes to garnet the high pressure stability of enstatite en diopside di jadeite jd pyroxenes has been investigated experimentally with a split sphere anvil apparatus ussa 2000 on the enstatite pyrope join the compositions of garnet coexisting with enstatite were determined at 100 165 kbar and 1450 1850 c the results indicate complete solubility between enstatite and pyrope in the system cao mgo al2o3 sio2 cmas the compositions of coexisting pyroxenes and garnet were determined at 100 165 kbar and 1250 1750 c at 157 kbar 1650 c garnet with the composition en79di21 mol forms on the en di join in the system na2o mgo al2o3 sio2 nmas the compositions of coexisting pyroxenes and garnet were determined at 60 160 kbar and 1200 1850 c on the en jd join the first garnet has the composition en48jd52 at 135 kbar 1650 c and en53jd47 at 140 kbar 1500 c on the di jd join the first garnet with the composition di63jd37 forms around 170 kbar 1650 c in the en di jd system the first appearance of garnet with the composition en42di9jd49 is estimated at 133 kbar 1650 c the new pyroxene with the composition namg0 5si2 5o6 napx transforms to garnet at 154 kbar 1650 c the experimental results indicate that the transformation of a twopyroxene assemblage to garnet and residual pyroxene in the en di jd system could occur at pressures consistent with the 400 km seismic discontinuity and in a pressure interval of 0 3 kbar

auroral evidence of io s control over the magnetosphere of jupiter 1 contrary to the case of the earth the main auroral oval on jupiter is related to the breakdown of plasma corotation in the middle magnetosphere even if the root causes for the main auroral emissions are io s volcanism and jupiter s fast rotation changes in the aurora could be attributed either to these internal factors or to fluctuations of the solar wind here we show multiple lines of evidence from the aurora for a major internally controlled magnetospheric reconfiguration that took place in spring 2007 hubble space telescope far uv images show that the main oval continuously expanded over a few months engulfing the ganymede footprint on its way simultaneously there was an increased occurrence rate of large equatorward isolated auroral features attributed to injection of depleted flux tubes furthermore the unique disappearance of the io footprint on 6 june appears to be related to the exceptional equatorward migration of such a feature the contemporary observation of the spectacular tvashtar volcanic plume by the new horizons probe as well as direct measurement of increased io plasma torus emissions suggest that these dramatic changes were triggered by io s volcanic activity

phase relations in the transition zone phase relations in the systems mgo al2o3 sio2 and cao mgo sio2 have been investigated experimentally at 166 226 kbar pressures and 1350 2500 c temperatures with a split sphere anvil apparatus ussa 2000 mgsio3 ilmenite is stable to lower pressures 175 kbar than found previously casio3 perovskite forms at p bar 15t c 151 000 three new high pressure phases are reported a phase with the diopsidic composition the cm phase a high pressure polymorph of al2o3 and superphase b with the tentative composition mg10si3o14 oh f 4 the invariant point for coexisting majorite mg4si4o12 perovskite mgsio3 beta phase mg2sio4 and liquid has been located at 224 kbar 2430 c with the eutectic melt composition on the enstatite forsterite join at 40 44 wt of forsterite the melting temperature of mgsio3 perovskite at 225 kbar is predicted to be 2600 c the new data made possible the calculation of a temperature pressure phase diagram for the system cao mgo al2o3 sio2 cmas in the pressure range 0 280 kbar the mineralogy of the earth s mantle and the possible mechanisms for producing large seismic velocity gradients in the transition zone are discussed on the basis of the derived phase relations

elastic wave velocities of a pyrope majorite garnet to 3 gpa abstract the pressure dependence of the elastic wave velocities for a polycrystalline specimen 100 theoretical density of majorite pyrope garnet py 62 mj 38 has been determined at room temperature to 3 gpa by ultrasonic phase comparison interferometry pressure derivatives of the adiabatic bulk modulus dk s dp 5 3 and shear modulus dgdp 2 0 are derived from the travel times of the compressional p and shear s waves these derivatives clearly demonstrate that pressure has a more pronounced effect on the elasticity of the majorite rich garnet than on the pure pyrope end member presumably in response to the coupled substitution of si and mg for al on the octahedral site in the garnet structure when combined with plausible values for the as yet unmeasured temperature derivatives these new data can be used to calculate velocity depth profiles along a 1400 c adiabat for the range of depths in which majorite is expected to be stable in the transition zone of the earth s mantle 450 600 km for shear waves these majorite gradients match those from regional seismic models much better than those for a pure olivine mantle more reliable calculations of elastic wave velocities at mantle temperatures and pressures await measurement of the temperature derivatives of elastic modulus

thermodynamic properties and phase relations in mantle minerals investigated by first principles quasiharmonic theory this research has been motivated by geophysics and materials physics the objective of this research has been to advance materials theory and computations for high pressure and high temperature applications to the point that it can make a difference in our understanding of the earth understanding of the mineralogy composition and thermal structure of the earth evolves by close interaction of three fields seismology geodynamics and mineral physics earth s structure is imaged by seismology which obtains body wave velocities and density throughout the earth s interior fig 1 interpretation of this data relies on knowledge of aggregate properties of earth forming materials either measured in laboratory or calculated in many cases by both however the conditions of the earth s interior especially at the core may be challenging for important experiments and materials computations have emerged to contribute decisively to this field earth s evolution is simulated by geodynamics but these simulations need as input information about rheological and thermodynamic properties of minerals including phase transformation properties such as clapeyron slopes our research has concentrated on the phases of the earth s mantle particularly the deep mantle whose conditions are more challenging for experiments the mantle accounts for 83 of the earth s volume in this article we will review the essential first principles approach used to investigate solids at high temperatures and pressures summarize their performance for mantle minerals fig 2 and point to critical results that have stirred us in the current research path the success is remarkable but some limitations point the way to future developments in this field figure 1 a velocities and density profiles kennett et al 1995 b earth s cross section and c composition and mineralogy of earth s layers figure 2 phases proportions versus depth and or pressure ol mg fe 2sio4 olivine also known as phase mg fe

upper mantle p velocity structure of the canadian shield waveform modeling of the phases pnl p and pp is used to determine the p wave upper mantle structure beneath the canadian shield long period recordings at world wide standard seismograph network long range seismic measurement and canadian network stations in north america are used with earthquakes within and just outside the shield as sources the p data set is incomplete due to the scarcity of large events within the shield and the inclusion of pp provides much more data using the wkbj approach to calculate the mantle response the pp waveforms can be modeled almost as well as the p the phase pnl persists to large distances in shield regions and the interference of pnl with triplication range p helps constrain the structure in the upper 400 km important features of our model which is designated s25 are 1 a thick high q high velocity lid to 165 km 2 a deep low velocity zone and 3 discontinuities of 5 at 405 km and 4 at 660 km the lid and low velocity zone create an unusual b branch arrival not seen in other regions which persists well beyond 30 only slight lateral variation is noted within the shield region the major features of the model are similar to those of grand and helmberger s s wave model for the canadian shield