gas origin and migration in the ulleung basin east sea results from the second ulleung basin gas hydrate drilling expedition ubgh2 abstract we have investigated the gas chemistry of marine sediments up to 250 m below seafloor m bsf recovered during the second ulleung basin gas hydrate drilling expedition ubgh2 to identify and compare the gas origin and its migration at seismically non chimney truncated chimney and chimney sites in this basin the molecular and isotopic data c1 c2 ratios 300 13 c ch 4 d ch 4 kim et al 2012 and thought to reflect two phase methane transport processes in chimney sites deep sourced methane migrates independently of the carbon dioxide which remains dissolved in the aqueous phase leading to the extremely low c values observed in the upper 30 m bsf upward methane diffusion at non chimney sites may also add a transport induced fractionation as evidenced in mixing diagrams but this process does not significantly affect the c values 13 c co 2 shows usually minimum values at the sulfate methane transition zone smtz at all sites however in chimney sites these values have a much more depleted signature indicating faster rates of methane consumption by anaerobic oxidation of methane aom supported by the higher methane flux moreover here the massive hydrate that forms in shallow sediments incorporates gases with a lower c1 c2 ratio higher c2 c1 than the surrounding sediment as documented in hydrate bound gas bg and void gas vg samples gas hydrate dissociation during the core recovery is released enriched ethane c2h6 trapped in gas cage which leads to have high c2h6 in vg samples

marine silicate weathering in the anoxic sediment of the ulleung basin evidence and consequences marine silicate weathering msiw in anoxic sediments has been recently shown to be a significant sink for co2 generated by methanogenesis independently the roles of clay dehydration illitization in producing water and driving upward fluid advection have been well established in deep marine sediments but to date the k source required for the reaction has not been established here we present chemical and strontium isotope properties of pore fluids from seven cores in the ulleung basin which show radiogenic 87sr 86sr values up to 0 71045 very high alkalinity values maximum 130 mm and enrichment in h4sio4 na k and mg2 consistent with msiw this reaction consumes co2 generates alkalinity and acts as a k source for illitization water released from msiw supported illitization drives upward fluid flow our results highlight the importance of msiw along continental margins and its underappreciated role in carbon cycling silicate diagenesis and hydrogeology of marine systems

migration and venting of deep gases into the ocean through hydrate choked chimneys offshore korea it has recently been recognized that in addition to low concentrations of widespread natural gas hydrate associated with bottomsimulating seismic refl ectors highly concentrated hydrate can occur in local seafl oor fl uid venting structures such structures extend upward into the regional gas hydrate stability fi eld and sometimes allow gases to escape into the overlying ocean these hydrate choked chimneys are especially prospective as an energy resource because they contain high hydrate concentrations furthermore they may be one of the most important conduits into the ocean atmosphere system for deep methane we present an analysis of two dimensional seismic refl ection data from offshore korea that give a complete picture of gas migrating from a deep source zone to feed hydrate choked vent structures at the seafl oor the gases migrate upward through networks of fractures imaged as steep amplitude striations in both diffuse and concentrated distributions we present an example of a high fl ux gas vent fed through fracture swarms emanating from a 10 15 km wide catchment zone of source gases residing 3 4 km below the seabed the geological context and the inferred distribution of hydrate within this feature are consistent with recent models in which seabed gas venting is a consequence of elevated pore fl uid salinities that are produced by a high fl ux of gases migrating independently of the pore water in contrast a nearby vent that is not plumbed into the same high fl ux system appears to be dominated more by gas rich liquids we present these two vent structures as type cases for high and lowfl ux fl uid escape systems in the seabed furthermore we suggest that since the amount of gas trapped as hydrate within the vents is small compared with the amount in the underlying reservoir the greatest risk for increased methane input to the atmosphere associated with climate driven oceanic warming is not the melting of hydrate but an increase in the number of deep reservoirs able to vent gases through the seabed that occurs as the regional gas hydrate stability zone thins

investigation of in situ salinity and methane hydrate dissociation in coarse grained sediments by slow stepwise depressurization abstract slow 8 15 day stepwise degassing of synthesized methane hydrate bearing sand packs was used to determine in situ salinity to within 0 5 wt rebounds in pressure during shut in intervals between degassing steps record gradual hydrate dissociation during successive dissociation steps and pressure rebounds the pressure decreases more than predicted for a sample with homogenous salinity and temperature at thermodynamic equilibrium we interpret that hydrate dissociation is limited by local pore water freshening and endothermic cooling around the dissociating hydrate these results suggest that during production hydrate dissociation in a reservoir will occur along the freshwater phase boundary even though the bulk salinity of the system may be higher pore pressure rebound during shut in is more rapid in freshwater experiments than in brine experiments which indicates that salt diffusion plays a role in limiting recovery to homogenous bulk equilibrium during hydrate dissociation we demonstrate that it is possible to interpret the in situ salinity from the temperature and pressure at the onset of dissociation this approach can be applied to actual hydrate bearing pressure core samples and the results will assist our understanding of how these hydrates form depressurization experiments with controlled shut in periods provide insight into the role of salt and heat diffusion on dissociation in coarse grained sediments particularly relevant to pauses in production and in regions of a hydrate reservoir near the hydrate phase boundary

modeling dynamic marine gas hydrate systems dynamically changing marine gas hydrate systems are the subject of this study the changes may result from varying pressure or temperature at the seafloor exploration and exploitation operations rapid sedimentation or wasting at the seafloor etc pressure and temperature may not be used as independent state variables at the same time to specify the overall state of such dynamic systems consequently a pressure enthalpy gas concentration salinity phase balance model is constructed for calculating phase distribution and transition of the system of marine gas hydrate which is assumed to contain a liquid phase consisting of water gas and salt a vapor phase consisting of gas only solid halite and solid gas hydrate consisting of gas and water calculations of phase transition processes demonstrate various dynamic feedback mechanisms involved in dynamically evolving marine gas hydrate systems a comprehensive model of fluid flow and transport of heat water salt and gas in marine sediment is developed simulations show that gas hydrate dissociation resulting from increasing temperature or decreasing pressure at the seafloor may lead to the development of a three phase zone with coexistent gas hydrate free gas and liquid solution and excess pore pressure in marine gas hydrate systems the changes considered in this study are rapid 5 years with respect to the geological time scale but are sufficiently slow 10 2 years to allow thermodynamic equilibrium throughout the applicable pressure temperature and salinity ranges for the calculations used in this study are sufficiently wide to cover those likely occurring in gas hydrate bearing marine sediments

tides for a convective earth in this paper we give values of the tidal gravimetric factor as well as of the love numbers for the tidal surface displacement and for the tidal mass redistribution potential that are consistent with the presently adopted definitions we present analytical expressions for these quantities and compute numerical values for two rotating nonspherical earth models in the first model the earth is everywhere in hydrostatic equilibrium and the inner core and mantle are both elastic in the second model the earth is ellipsoidal with an inelastic mantle and with a nonhydrostatic initial state for which the effects of mantle convection and its associated boundary deformations are considered this latter model is constrained to reproduce the observed free core nutation period and global earth dynamical flattening

a seafloor long baseline tiltmeter long term monitoring of seismicity and deformation has provided constraints on the eruptive behavior and internal structure and dynamics of subaerial volcanoes but until recently such monitoring of submarine volcanoes has not been feasible little is known about the formation of oceanic crust or seamounts and we have therefore developed a stand alone long baseline tiltmeter to record deformation on active seafloor volcanoes the instrument is a differential pressure two fluid sensor adapted for use on the seafloor combined with an autonomous data logger and acoustic navigation release system the tiltmeter can be installed without use of remotely operated vehicles or manned submersibles and to first order is insensitive to noise driven by temperature or pressure gradients we recorded 65 days of continuous data from one of these tiltmeters on axial seamount on the juan de fuca ridge during a multidisciplinary experiment that included ocean bottom seismographs magnetotelluric instruments and short baseline tiltmeters after instrument equilibration the 100 m iono tiltmeter provided a record with long term drift rates of 0 5 5 rad day and higher frequency variations of the order of 5 10 rad comparison with records of subaerial volcanic tilt shows that this instrument can discriminate volcanic deflation events though none occurred during our deployment a conclusion supported by nearby short baseline tilt and bottom pressure recordings the short and long baseline data constrain volcanic inflation of axial seamount to be below 0 5 1 rad day 1 during mid 1994 analysis of the long baseline tilt data in conjunction with electric field temperature and short baseline tiltmeter data shows that high frequency signals are largely driven by ocean currents improved coupling between the tiltmeter and seafloor should reduce this noise improve stability and drift and further enhance our ability to record tilt related to active submarine volcanism

tidal modulation of temperature oscillations monitored in borehole yaxcopoil 1 yucatan mexico abstract for better understanding of temperature state in the subsurface temperature depth logs can be suitably completed by high resolution long run temperature time monitoring at selected depths the results of temperature monitoring at three depth levels in borehole yaxcopoil 1 chicxulub impact structure mexico april may 2006 proved that even when a borehole is in fully stabilized conditions temperature may exhibit certain unrest resembling irregular oscillations in the order of hundredths or in the extreme case even first tenths of degree two novel methods for detection of the weak fingerprints of stable periodic components in long noisy records namely the rqi recurrence quantification interval analysis and the hicum histograms cumulation were used to isolate the constituents with tidal periodicities from temperature oscillations measured in borehole yaxcopoil 1 both analyses revealed that temperature series contain perceptible tidal component the field data were correlated with the simulated synthetic tides the comparison of staked hicum records for the theoretical gravity tide and monitored temperature shows significant positive linear correlation between both variables there is a small lag between two signals corresponding to 25 min phase difference

gas hydrate saturations estimated from fractured reservoir at site nghp 01 10 krishna godavari basin india 1 during the indian national gas hydrate program expedition 01 nghp 01 one of the richest marine gas hydrate accumulations was discovered at site nghp 01 10 in the krishna godavari basin the occurrence of concentrated gas hydrate at this site is primarily controlled by the presence of fractures assuming the resistivity of gas hydrate bearing sediments is isotropic the conventional archie analysis using the logging while drilling resistivity log yields gas hydrate saturations greater than 50 as high as 80 of the pore space for the depth interval between 25 and 160 m below seafloor on the other hand gas hydrate saturations estimated from pressure cores from nearby wells were less than 26 of the pore space although intrasite variability may contribute to the difference the primary cause of the saturation difference is attributed to the anisotropic nature of the reservoir due to gas hydrate in high angle fractures archie s law can be used to estimate gas hydrate saturations in anisotropic reservoir with additional information such as elastic velocities to constrain archie cementation parameters m and the saturation exponent n theory indicates that m and n depend on the direction of the measurement relative to fracture orientation as well as depending on gas hydrate saturation by using higher values of m and n in the resistivity analysis for fractured reservoirs the difference between saturation estimates is significantly reduced although a sizable difference remains to better understand the nature of fractured reservoirs wireline p and s wave velocities were also incorporated into the analysis

revisiting the origin of organic matter and depositional environment of sediment in the central ulleung basin east sea since the late quaternary abstract by analyzing sedimentary geochemical data from three piston cores in the central ulleung basin east sea we discuss the origin of organic matter and the depositional environment of sediments from marine isotope stage mis 3 to 1 downcore profiles show that the values of toc total organic carbon tn total nitrogen and 13corg are the lowest values during mis 2 and the highest during mis 1 the relationship between toc tn and 13corg shows that most data fall in the region of the marine algae irrespective of mis stage which illustrates that the organic matter has been predominantly produced by a marine source rather than by a terrestrial source since the late quaternary however depleted 13corg values are discretely observed during mis 2 and mis 3 particularly in dark laminated mud dlm which appears to reflect the influence of episodic event by the east asian monsoon rather than the organic matter source changing by lower sea level previous sedimentological studies in the ulleung basin reported that the depositional environment of sediment in mis 2 was more reducing than during mis 1 and mis 3 but our geochemical data do not support this interpretation the abundance of most redox sensitive trace elements e g mn v u and mo has not significantly varied from mis 3 to mis 1 in addition the ratios of redox sensitive trace elements e g ni co v cr v ni u th and v v ni indicate a predominantly oxic or suboxic environment the bottom water condition was similarly oxic to suboxic during times of sediment deposition since the late quaternary the sedimentary layers containing tephra and foraminiferal shell fragments illustrate abnormal element al ratios suggesting that these allochthonous sediment sources are one of important factors controlling the geochemical composition of sediments in the ulleung basin

multiple origins of methane in the earth methane occurrences in the earth s crust are predominantly of biogenic origin i e their ultimate source is biologically formed organic matter methane can also form through inorganic reactions and is consequently termed abiogenic biogenic methanes can either form through bacterial or thermogenic processes bacterial processes follow a co2 reduction and or fermentation pathway the fermentation processes are quantitatively more important in recent fresh sediments and swamps methane formed by co2 reduction however is most common in older sediments and commercial gasfields temperature organic substrate and age may be the major factors controlling the relative importance of the two pathways stable isotope concentrations in thermogenic methanes seem to be controlled by the extent of conversion of organic matter the timing of gas expulsion and trapping the different character of methane in individual sedimentary basins may be a result of the geologic history geothermal methanes are most likely derived from pyrolysis of organic matter abiogenic methane occurs in hydrothermal vents and ophiolite complexes inorganic reactions either surficial or deep seated are the likely source of such methanes a uniform mantle origin of methane is not supported by the observed isotope variations in naturally occurring methanes

sediment mounds and other sedimentary features related to hydrate occurrences in a columnar seismic blanking zone of the ulleung basin east sea korea abstract a mound related to a cold vent in a columnar seismic blanking zone csbz was formed around site ubgh1 10 in the central ulleung basin 2077 m water depth east sea korea the mound is 300 400 m wide and 2 3 m high according to multi beam bathymetry 2 7 khz sub bottom profiler data and multi channel reflection seismic data seafloor topography and characteristics were investigated using a remotely operated vehicle rov around site ubgh1 10 which is located near the northern part of the mound the origin of the mound was investigated through lithology mineralogy hydrate occurrence and sedimentary features using dive cores piston cores and a deep drilling core the csbz extends to 265 ms two way traveltime twt below the seafloor within a mass transport deposit mtd unit gas hydrate was entirely contained 6 141 m below the seafloor mbsf within hemipelagic deposits intercalated with a fine grained turbidite htd unit characteristically associated with high resistivity values at site ubgh1 10 the hydrate is commonly characterized by veins nodules and massive types and is found within muddy sediments as a fracture filling type methane has been produced by microbial reduction of co2 as indicated by c1 c2 13 c ch 4 and d ch 4 analyses the bowl shaped hydrate cap revealed at 20 45 ms twt below the seafloor has very high resistivity and high salinity suggesting rapid and recent gas hydrate formation the origin of the sediment mound is interpreted as a topographic high formed by the expansion associated with the formation of the gas hydrate cap above the csbz the lower sedimentation rate of the mound sediments may be due to local enhancement of bottom currents by topographic effects in addition no evidence of gas bubbles chemosynthetic communities or bacterial mats was observed in the mound suggesting an inactive cold vent

gas hydrate systems at hydrate ridge offshore oregon inferred from molecular and isotopic properties of hydrate bound and void gases abstract we report and discuss molecular and isotopic properties of hydrate bound gases from 55 samples and void gases from 494 samples collected during ocean drilling program odp leg 204 at hydrate ridge offshore oregon gas hydrates appear to crystallize in sediments from two end member gas sources deep allochthonous and in situ as mixtures of different proportions in an area of high gas flux at the southern summit of the ridge sites 1248 1250 shallow 0 40 m below the seafloor mbsf gas hydrates are composed of mainly allochthonous mixed microbial and thermogenic methane and a small portion of thermogenic c2 gases which migrated vertically and laterally from as deep as 2 to 2 5 km depths in contrast deep 50 105 mbsf gas hydrates at the southern summit sites 1248 and 1250 and on the flanks of the ridge sites 1244 1247 crystallize mainly from microbial methane and ethane generated dominantly in situ a small contribution of allochthonous gas may also be present at sites where geologic and tectonic settings favor focused vertical gas migration from greater depth e g sites 1244 and 1245 non hydrocarbon gases such as co2 and h2s are not abundant in sampled hydrates the new gas geochemical data are inconsistent with earlier models suggesting that seafloor gas hydrates at hydrate ridge formed from gas derived from decomposition of deeper and older gas hydrates gas hydrate formation at the southern summit is explained by a model in which gas migrated from deep sediments and perhaps was trapped by a gas hydrate seal at the base of the gas hydrate stability zone ghsz free gas migrated into the ghsz when the overpressure in gas column exceeded sealing capacity of overlaying sediments and precipitated as gas hydrate mainly within shallow sediments the mushroom like 3d shape of gas hydrate accumulation at the summit is possibly defined by the gas diffusion aureole surrounding the main migration conduit the decrease of gas solubility in shallow sediment and refocusing of gas by carbonate and gas hydrate seals near the seafloor to the crest of the local anticline structure

pore fluid chemistry from the second gas hydrate drilling expedition in the ulleung basin ubgh2 source mechanisms and consequences of fluid freshening in the central part of the ulleung basin east sea during the second gas hydrate drilling expedition in the ulleung basin ubgh2 pore fluids were collected from sites that sampled sediments from the continental slope to the basin center and included locations within and outside seismic identified chimney like features at five non chimney sites established during the ubgh2 discrete excursions to low cl concentrations within the gas hydrate occurrence zone ghoz are associated with water enriched in d and 18o as expected from gas hydrate dissociation during core recovery estimates of gas hydrate saturation values sh based on cl and d values are in good agreement and show that when gas hydrate occurs in discrete horizons or within strata bound fractures throughout the ghoz it occupies 5 65 of the pore space fluids recovered from three sites characterized by seismic inferred chimneys show massive hydrate accumulation near the seafloor accompanied by the formation of shallow cl rich brines with d and 18o values lower than seawater chemical and isotopic data from fluids sampled at all drilled sites reveal significant fluid freshening below the gas hydrate stability zone ghsz the distribution of cl k and d indicate that the observed freshening is predominantly caused by clay mineral dehydration illitization previously reported heat flow values in the center of the basin indicate that the sediments deeper than 800 mbsf meter below seafloor are warm enough to expect clay diagenesis with the onset of smectite to illite transformation source fluid temperatures 70 c are confirmed through the use of na li and mg2 li geothermometry based on these observations we propose the following scenario for the evolution of formation fluids in the ulleung basin where high formation temperatures and rapid sedimentation at the basin center led to sediment compaction and clay dehydration reactions that result in fluid overpressures and associated fracturing of the formation sediment fractures and fluid possible gas migration in the chimney features imaged in seismic records are consistent with our postulated upward transport of fluids from 800 m depth though the ghsz and to the seafloor

seismic indicators of gas hydrate and associated gas in the ulleung basin east sea japan sea and implications of heat flows derived from depths of the bottom simulating reflector abstract analysis of multi channel seismic reflection data from the ulleung basin east sea japan sea reveals various seismic indicators of gas hydrate and associated gas including the bottom simulating reflector bsr enhanced reflections below the bsr and seismic chimneys the recent recovery of massive gas hydrate by drilling together with these seismic indicators strongly suggests favorable conditions for the formation of gas hydrate in the area the bsr is most common and of a wide range of amplitude and continuity seismic chimneys characterized by columnar zones of amplitude reduction terminate mostly within the gas hydrate stability zone ghsz but a few extend to pockmarks or mounds on the seafloor seismic chimneys with seafloor expressions probably represent vertical vents for gas originating from below the ghsz the increase in the degree of amplitude reduction in seismic chimneys with increasing seismic frequency may be due to seismic attenuation by gas bubbles trapped in hydrate filled coated fractures in the ghsz bsr derived heat flows range from about 65 to over 115 mw m2 comparable to those from direct measurements heat flows in the northern part of the study area are very high for the age of the basin suggesting hotter than normal mantle temperature the area of high 105 mw m2 heat flows also coincides largely with the distribution of the presumed incipient oceanic crust formed during the earliest stage of seafloor spreading

formation of apollo 17 orange and black glass beads size frequency distributions of the cross sections of orange and black glass beads in the 125 250 m fraction of soil 74220 have been determined cross section medians of black vitrophyric and orange glassy beads in the 125 250 m fraction are 0 16 mm and 0 14 mm respectively the vitrophyric beads contain skeletal olivine crystals mantled by ilmenite some beads contain fragments and euhedral crystals of endogeneous olivine free flight cooling rates and the critical cooling rate for crystallization have been determined with a synthetic melt of orange glass composition the critical cooling rate is approximately 100 c s the free flight cooling rate of droplets 0 16 mm in diameter is approximately 1080 c s it is inferred that apollo 17 orange melt droplets were erupted together with a large mass of hot gas and or formed a dense cloud of heat radiating droplets

towards quantifying the reaction network around the sulfate methane transition zone in the ulleung basin east sea with a kinetic modeling approach abstract we present a kinetic model based upon pore water data collected from eight sites drilled during the second ulleung basin gas hydrate drilling expedition ubgh2 in 2010 three sites were drilled at locations where acoustic chimneys were identified in seismic data and the rest were drilled on non chimney i e background environments our model coupled a comprehensive compositional and isotopic data set is used to illustrate the different biogeochemical processes at play in those two environments in terms of reactions around the sulfate methane transition zone smtz organic matter decomposition is an important process for production of methane dissolved inorganic carbon dic and consumption of sulfate in the non chimney sites whereas anaerobic oxidation of methane aom dominates both carbon and sulfur cycles in the chimney environment different sources of methane mediate aom in the two settings internally produced methane through co 2 reduction cr and methanogenesis fuels aom in the non chimney sites whereas aom is sustained by methane from external sources in the chimney sites we also simulate the system evolution from non chimney to chimney conditions by increasing the bottom methane supply to a non chimney setting we show that the higher ch 4 flux leads to a higher microbial activity of aom and more organic matter decomposition through methanogenesis a higher methanogenesis rate and a smaller cr contribution relative to aom in the chimney sites is responsible for the isotopically light dic and heavy methane in this environment relative to the non chimney sites

tectonic history of ulleung basin margin east sea sea of japan a geologic history analysis of an exploratory well drilled on the southern margin of the ulleung back arc basin east sea western part of the sea of japan reveals that tectonic force and sedimentary loading played a major role in the subsidence of the paleo ulleung basin where a thick clastic sequence was deposited during the neogene initial subsidence was most likely caused by a tectonic force related to the back arc rifting and spreading associated with convergent processes the southern margin underwent regional deformation uplift faulting and folding toward the late miocene this event was probably due to back arc deformation caused by changes both in plate motions and in subduction mode at the convergent zones

thermal instability of the fluid column in a borehole application to the yaxcopoil hole mexico observational evidence proved that even when a borehole is in fully stabilized conditions temperature data may exhibit certain unrest resembling irregular oscillations in the order of hundredths or in the extreme case even tenths of degree temperature was monitored in complicated hydrogeological conditions in the yaxcopoil 1 hole chicxulub impact structure mexico two experiments are reported a 20 day monitoring when a logger was located in the center of the high temperature gradient anomaly produced by the cold wave slowly propagating downwards and b simultaneous three loggers 18 day monitoring with loggers located above in and below the anomaly all observed temperature time series displayed intermittent oscillations of temperature with sharp gradients and large fluctuations over all observed time scales while the upper and lower records revealed quasi periodic temperature variations the central record shows fast temperature oscillations with strong up and down reversals all with amplitudes up to a few tenths of degree the observed temperature time series were processed by recurrence and recurrence interval quantification as well as by spectral analyses it is shown that fluid in a borehole subject to thermal gradient is stable as far as the gradient remains below a certain critical value at higher rayleigh numbers the periodic character of oscillations typical for quiescent regime is superseded by stochastic features this oscillatory convection occurs due to instability of the horizontal boundary layers in the specific case of the yaxcopoil hole the time series above and below the cold wave characterized by relatively lower temperature gradients between 20 and 50 mk m contain a clear low frequency component produced by tidal forcing this component dominates over the high frequency domain periods from 10 15 to 1 min which exhibit a scaling behavior this pattern conspicuously changes in the center part of the cold wave where the local temperature gradient exceeds 200 mk m and where tidal forcing composes only 3 of the signal

interpretation and mathematical modeling of temporal changes of temperature observed in borehole yaxcopoil 1 within the chicxulub impact structure mexico summary geothermal research of the chicxulub impact structure on the yucatan peninsula mexico included repeated temperature logs following 0 3 0 8 15 24 34 and 50 months after shut in of drilling operations at the 1 5 km deep yaxcopoil 1 borehole a gradual distortion of the linear temperature profile by a cold wave propagating downward from 145 m to 317 m was detected within the observational period of 49 months march 2002 april 2006 the amplitude of the cold wave was increasing with depth and time in the range of 0 8 1 6 c as an explanation of this unusual phenomenon the hypothesis of downward migration of a large volume of drilling mud reported lost during drilling within the overlying and cooler highly porous and permeable karstic rocks has been proposed the thermal effects of the migrating fluid have been evaluated by solving numerically the heat conduction convection equation in appropriate geothermal models the best coincidence between the observed data and the simulations was yielded by the model of the drilling mud migrating as a large body parameters of this model are constrained by the measured temperature logs relatively tightly i the vertical extent of the downward migrating fluid body is about 5 10 m possibly increasing within the observational period of 49 months by a factor of 2 ii the horizontal extent of the body must be at least 15 20 m i e by order s of magnitude larger than the diameter of the borehole iii the average speed of the migration is about 5 metres per month and iv the fluid must migrate through a highly porous rock 80 porosity or more this high porosity which is necessary for the model to fit the observed data and the observed relatively stable velocity of the migration indicate the existence of a well developed system of interconnected cavities down to more than 300 m about 150 m more than the deepest cave system known in yucatan yet

molecular and stable isotope compositions of natural gas hydrates a revised global dataset and basic interpretations in the context of geological settings abstract a global dataset of molecular and stable isotope compositions of gases released from 209 different specimens of natural gas hydrate is presented and discussed the 26 hydrate bearing areas from 21 geographic regions are grouped into high gas flux hgf settings low gas flux lgf settings and hydrated gas accumulations hga methane ch4 is the most abundant hydrate bound gas while co2 and c2 hydrocarbon gases are frequently present in small amounts non hydrocarbon gases such as h2s are uncommon the stable isotope composition of hydrate bound gases varies significantly e g 13c of ch4 from 74 7 to 39 6 suggesting that gases of both microbial and thermogenic origin form gas hydrates hydrate bound gases are derived from autochthonous located predominantly within the gas hydrate stability zone ghsz and allochthonous located in deep sediments sources the occurrence and concentration of gas hydrates in sediments are controlled not by the origin of gases but rather by their sources which in turn strongly depend on geological setting allochthonous gases microbial and or thermogenic dominate in hgf and hga settings where they are focused in the shallow ghsz along faults within mud volcanoes in permeable carrier beds and other geological features from underlying petroleum systems relatively high concentrations of gas hydrate average 5 15 of pores and locally up to 100 of volume occurring over small areas are typical of hgf and hga settings in contrast autochthonous and diffuse allochthonous gases mostly microbial occur in stratigraphically and structurally simple lgf settings and result in relatively low concentrations of gas hydrate average 2 of pores in the ghsz spread over large areas the major implication of this finding is that successful prediction of resource and geohazard potential of gas hydrates is possible only if regional petroleum systems extending well below the ghsz are properly evaluated in addition to the diagnosis of origins and sources of hydrate bound gases molecular and isotopic data help to better identify hydrate bearing intervals and provide valuable insights into the dynamics of hydrate bearing sites

methane sources and production in the northern cascadia margin gas hydrate system abstract the oceanographic and tectonic conditions of accretionary margins are well suited for several potential processes governing methane generation storage and release to identify the relevant methane evolution pathways in the northern cascadia accretionary margin a four site transect was drilled during integrated ocean drilling program expedition 311 the 13c values of methane range from a minimum value of 82 2 on an uplifted ridge of accreted sediment near the deformation front site u1326 1829 mbsl meters below sea level to a maximum value of 39 5 at the most landward location within an area of steep canyons near the shelf edge site u1329 946 mbsl an interpretation based solely on methane isotope values might conclude the 13c enrichment of methane indicates a transition from microbially to thermogenically sourced methane however the co existing co2 exhibits a similar trend of 13c enrichment along the transect with values ranging from 22 5 to 25 7 the magnitude of the carbon isotope separation between methane and co2 ec 63 8 5 8 is consistent with isotope fractionation during microbially mediated carbonate reduction these results in conjunction with a transect wide gaseous hydrocarbon content composed of 99 8 by volume methane and uniform dch4 values 172 8 that are distinct from thermogenic methane at a seep located 60 km from the expedition 311 transect suggest microbial co2 reduction is the predominant methane source at all investigated sites the magnitude of the intra site downhole 13c enrichment of co2 within the accreted ridge site u1326 and a slope basin nearest the deformation front site u1325 2195 mbsl is 5 at the mid slope site site u1327 1304 mbsl the downhole 13c enrichment of the co2 is 25 and increases to 40 at the near shelf edge site u1329 this isotope fractionation pattern is indicative of more extensive diagenetic alteration at sites with greater 13c enrichment the magnitude of the 13c enrichment of co2 correlates with decreasing sedimentation rates and a diminishing occurrence of stratigraphic gas hydrate we suggest the decreasing sedimentation rates increase the exposure time of sedimentary organic matter to aerobic and anaerobic degradation during burial thereby reducing the availability of metabolizable organic matter available for methane production this process is reflected in the occurrence and distribution of gas hydrate within the northern cascadia margin accretionary prism our observations are relevant for evaluating methane production and the occurrence of stratigraphic gas hydrate within other convergent margins

precise temperature monitoring in boreholes evidence for oscillatory convection part 1 experiments and field data temperature was monitored in two boreholes in kamchatka russia in years 2001 2003 ten min reading sampling interval was selected for the first half year run followed by shorter 12 days experiment with 5 s reading interval a similar experiment was repeated later in the test borehole sporilov prague czech republic where four temperature time series were performed with reading intervals varying from 1 to 20 s all temperature time series except the record from the bottom of the hole displayed intermittent non periodic oscillations of temperature of up to several hundredths of degree with sharp gradients and large fluctuations over all observed time intervals no such oscillation was detected at the bottom of the hole the spectral analysis revealed a high level of stochasticity in the measured signal calculated spectra showed band pass behavior without any definite peaks which might characterize certain periodicity local growth of the second moment technique revealed the presence of at least two distinct temperature forming processes one of them can be related to heat transfer in the structurally and compositionally complex subsurface the second process which presents the bulk of the measured signal probably reflects certain intra hole convection we hypothesized that the oscillatory regime of such convection is responsible for the stochastic nature of measured temperatures results of numerical modeling describing the fluctuation of water cells in a vertical slot support the idea of thermally unstable water column in a hole the instability of which produces a complex oscillation system model solutions and their discussion is presented in part ii of this work

geotechnical properties of deep oceanic sediments recovered from the hydrate occurrence regions in the ulleung basin east sea offshore korea abstract this study presents comprehensive geotechnical data of the natural marine sediments cored from the hydrate occurrence regions during the ulleung basin gas hydrate expedition 1 ubgh1 east sea offshore korea in 2007 geotechnical soil index properties of the ulleung basin sediments including grain size distribution porosity water content atterberg limits specific gravity and specific surface area were experimentally determined these soil index properties were correlated to geotechnical engineering parameters e g shear strength and friction angle by using well known empirical relationships by performing standard consolidation tests on both undisturbed specimens as recovered from the original core liner after hydrate dissociation and remolded specimens stress dependent mechanical and hydraulic properties e g compressibility and hydraulic conductivity were measured the experimental results provide important engineering parameters and demonstrate the effect of hydrate presence and consequential dissociation to index properties engineering parameters and innate sediment structures

depressurization experiment of pressure cores from the central ulleung basin east sea insights into gas chemistry abstract we performed depressurization experiments on pressure cores pcs recovered from holes ubgh1 10b and ubgh2 11b which were drilled during two separate expeditions in the ulleung basin ubgh1 and ubgh2 various lines of evidence such as convex curvature in the p v curves obtained by depressurization as well as x ray images and resistivity at bit rab data point to the presence of gas hydrates at these holes we estimated gas hydrate saturation sh at these holes to range from 5 23 based on the amount of gas released from pcs these sh values are in agreement with those reported at other high gas flux settings molecular c1 c2 and isotopic 13cch4 dch4 13cc2h6 indicators delineate a microbial source for the ch4 and c2h6 in core ubgh1 10b 5r the carbon isotopic fractionation factor between co2 and ch4 ec 13cco2 13cch4 was observed to increase from 50 to 68 as pressure was reduced during our experiments these changes illustrate the isotope fractionation that results from the preferential release of 13c depleted co2 during the early stages of depressurization the constant carbon isotope separation 10 20 between co2 in void gases and in the dissolved inorganic carbon dic pool shown in cores from the ulleung basin has also been observed in gas hydrate bearing sediments elsewhere it is important to consider this effect when using carbon isotopic data in carbon cycling models specifically when unraveling metabolic pathways of methane generation in situations where partial co2 degassing of a core is suspected we recommend the use of the carbon isotope ratio of dic instead of the gas measurements to best delineate the methane cycling pathways in marine systems

molecular and isotopic partitioning of low molecular weight hydrocarbons during migration and gas hydrate precipitation in deposits of a high flux seepage site detailed knowledge of the extent of post genetic modifications affecting shallow submarine hydrocarbons fueled from the deep subsurface is fundamental for evaluating source and reservoir properties we investigated gases from a submarine high flux seepage site in the anoxic eastern black sea in order to elucidate molecular and isotopic alterations of low molecular weight hydrocarbons lmwhc associated with upward migration through the sediment and precipitation of shallow gas hydrates for this near surface sediment pressure cores and free gas venting from the seafloor were collected using autoclave technology at the batumi seep area at 845 m water depth within the gas hydrate stability zone vent gas gas from pressure core degassing and from hydrate dissociation were strongly dominated by methane 99 85 mol of c1 c4 co2 molecular ratios of lmwhc c1 c2 c3 1000 and stable isotopic compositions of methane 13c 53 5 v pdb d h around 175 smow indicated predominant microbial methane formation c1 c2 ratios and stable isotopic compositions of lmwhc distinguished three gas types prevailing in the seepage area vent gas discharged into bottom waters was depleted in methane by 0 03 mol c1 c4 co2 relative to the other gas types and the virtual lack of 14c ch4 indicated a negligible input of methane from degradation of fresh organic matter of all gas types analyzed vent gas was least affected by molecular fractionation thus its origin from the deep subsurface rather than from decomposing hydrates in near surface sediments is likely as a result of the anaerobic oxidation of methane lmwhc in pressure cores in top sediments included smaller methane fractions 0 03 mol c1 c4 co2 than gas released from pressure cores of more deeply buried sediments where the fraction of methane was maximal due to its preferential incorporation in hydrate lattices no indications for stable carbon isotopic fractionations of methane during hydrate crystallization from vent gas were found enrichments of 14c ch4 1 4 pmc in short cores relative to lower abundances max 0 6 pmc in gas from long cores and gas hydrates substantiates recent methanogenesis utilizing modern organic matter deposited in top sediments of this high flux hydrocarbon seep area

geotechnical characterization of marine sediments in the ulleung basin east sea the geotechnical characteristics of ulleung basin sediments are explored using depressurized samples obtained at 2100 m water depth and 110 m below the sea floor geotechnical index tests x ray diffraction and sem images were obtained to identify the governing sediment parameters chemical composition and mineralogy we use an instrumented multi sensor oedometer cell to determine the small strain stiffness zero lateral strain compressibility and electromagnetic properties and a triaxial device to measure shear strength sem images show a sediment structure dominated by microfossils with some clay minerals that include kaolinite illite and chlorite the preponderant presence of microfossils determines the high porosity of these sediments defines their microstructure and governs all macroscale properties the shear wave velocity increases as the vertical effective stress increases on the other hand porosity permittivity electrical conductivity and hydraulic conductivity decrease with increasing confinement all these parameters exhibit a bi linear response with effective vertical stress due to the crushable nature of microfossils well established empirical correlations used to evaluate engineering parameters do not apply for these diatomaceous sediments which exhibit higher compressibility than anticipated based on correlations with index properties settlements will be particularly important if gas production is attempted using depressurization because this approach will cause both hydrate dissociation and increase in effective stress

tidal pumping of fluids within and from the oceanic crust new observations and opportunities for sampling the crustal hydrosphere abstract seven boreholes established by the ocean drilling program in sedimented ridge crest and ridge flank environments have been sealed to stop the exchange of formation water and seawater via the holes after drilling and instrumented to allow long term hydrologic monitoring records of seafloor and basement fluid pressures in these holes document tidal frequency formation pressure variations that are attenuated and phase shifted relative to variations at the seafloor spatial variations in the response to seafloor tidal loading create oscillatory pressure gradients which drive fluid flow within the crust and tidal pressure differentials between the crust and the water column modulate flow through the seafloor both may have significant geochemical and biological consequences the magnitude of the tidal pressure differential observed across sediment sections is in many instances larger than the average differential pressure created by hydrothermal buoyancy forces and this causes the pressure difference across fluid sampling ports incorporated in the borehole seals to reverse sign periodically this can create a problem for obtaining undiluted crustal fluid samples at the seafloor from moderately overpressured holes but it also provides an opportunity for fluids to be pumped passively from moderately underpressured holes through the use of uni directional valves potential production rates estimated using pre and post seal thermal fluid flow and pressure data indicate that significant fluid fluxes can be established of the order of 10 m 3 typically one hole volume per month

evidence of gas hydrate from downhole logging data in the ulleung basin east sea the gas hydrate research and development organization ghdo of korea successfully accomplished both coring hydraulic piston and pressure coring and logging logging while drilling lwd and wireline logging to investigate the presence of gas hydrate during the first deep drilling expedition in the ulleung basin east sea of korea referred to as ubgh1 in 2007 the lwd data from two sites ubgh1 9 ubgh1 10 showed elevated electrical resistivity 80 m and p wave velocity 2000 m s values indicating the presence of gas hydrate during the coring period the richest gas hydrate accumulation was discovered at these intervals based on log data the occurrence of gas hydrate is primarily controlled by the presence of fractures the gas hydrate saturation calculated using archie s relation shows greater than 60 as high as 90 of the pore space although archie s equation typically overestimates gas hydrate saturation in near vertical fractures the saturation of gas hydrate is also estimated using the modified biot gassmann theory bgtl by lee and collett 2006 the saturation values estimated rom bgtl are much lower than those calculated from archie s equation based on log data the hydrate bearing sediment section is approximately 70 m ubgh1 9 to 130 m ubgh1 10 in thickness at these two sites this was further directly confirmed by the recovery of gas hydrate samples and pore water freshening collected from deep drilling core during the expedition lwd data also strongly support the interpretation of the seismic gas hydrate indicators e g vent or chimney structures and bottom simulating reflectors which imply the probability of widespread gas hydrate presence in the ulleung basin