exploration for gas hydrates in the deepwater northern gulf of mexico part i a seismic approach based on geologic model inversion and rock physics principles this article presents the results of applying a five step process for using high quality seismic data to locate marine gas hydrates the process involved 1 reprocessing of seismic data for higher resolution 2 detailed stratigraphic evaluation and interpretation to locate possible hydrate bearing zones 3 seismic attribute analysis to further delineate these zones 4 seismic inversion to obtain appropriate elastic parameters of these zones in 3d and 5 quantitative estimation of gas hydrate saturation from seismic data using inversion and rock physics principles we used seismic data from keathley canyon 151 and atwater valley 14 in the northern gulf of mexico although careful analysis did indicate the presence of a bottom simulating reflector bsr our study mainly relied on a host of other seismic attributes e g gas chimneys seismically transparent zones other features associated with the petroleum system to characterize the occurrence of gas hydrates in these areas we tested and verified a viable rock model for hydrate bearing sediments using data from the mallik mckenzie delta canada and blake ridge odp leg 164 southeast u s atlantic margin wells and modified it for application in the current area we then used this model to estimate gas hydrate saturation in the host sediments of the northern gulf of mexico focus areas using estimates of p wave and s wave velocities from inversion of reflection seismic data in this paper we present the gas hydrate saturations predicted from the seismic processing methodology prior to 2005 drilling in the focus areas in frontier areas where no well data are available and lithologic heterogeneities are poorly understood implementing a seismic based technique like the one described here to identify potential gas hydrates can provide valuable pre drill information for site selection and for planning future characterization studies of gas hydrate bearing sediments

in situ gas hydrate hydrate saturation estimated from various well logs at the mount elbert gas hydrate stratigraphic test well alaska north slope abstract in 2006 the u s geological survey usgs completed detailed analysis and interpretation of available 2 d and 3 d seismic data and proposed a viable method for identifying sub permafrost gas hydrate prospects within the gas hydrate stability zone in the milne point area of northern alaska to validate the predictions of the usgs and to acquire critical reservoir data needed to develop a long term production testing program a well was drilled at the mount elbert prospect in february 2007 numerous well log data and cores were acquired to estimate in situ gas hydrate saturations and reservoir properties gas hydrate saturations were estimated from various well logs such as nuclear magnetic resonance nmr p and s wave velocity and electrical resistivity logs along with pore water salinity gas hydrate saturations from the nmr log agree well with those estimated from p and s wave velocity data because of the low salinity of the connate water and the low formation temperature the resistivity of connate water is comparable to that of shale therefore the effect of clay should be accounted for to accurately estimate gas hydrate saturations from the resistivity data two highly gas hydrate saturated intervals are identified an upper 43 ft zone with an average gas hydrate saturation of 54 and a lower 53 ft zone with an average gas hydrate saturation of 50 both zones reach a maximum of about 75 saturation

mechanical and electromagnetic properties of northern gulf of mexico sediments with and without thf hydrates using an oedometer cell instrumented to measure the evolution of electromagnetic properties small strain stiffness and temperature we conducted consolidation tests on sediments recovered during drilling in the northern gulf of mexico at the atwater valley and keathley canyon sites as part of the 2005 chevron joint industry project on methane hydrates the tested specimens include both unremolded specimens as recovered from the original core liner and remolded sediments both without gas hydrate and with pore fluid exchanged to attain 100 synthetic tetrahydrofuran hydrate saturation at any stage of loading test results demonstrate the extent to which the electromagnetic and mechanical properties of hydrate bearing marine sediments are governed by the vertical effective stress stress history porosity hydrate saturation fabric ionic concentration of the pore fluid and temperature we also show how permittivity and electrical conductivity data can be used to estimate the evolution of hydrate volume fraction during formation the gradual evolution of geophysical properties during hydrate formation probably reflects the slow increase in ionic concentration in the pore fluid due to ion exclusion in closed systems and the gradual decrease in average pore size in which the hydrate forms during hydrate formation the increase in s wave velocity is delayed with respect to the decrease in permittivity consistent with hydrate formation on mineral surfaces and subsequent crystal growth toward the pore space no significant decementation debonding occurred in 100 thf hydrate saturated sediments during unloading hence the probability of sampling hydrate bearing sediments without disturbing the original sediment fabric is greatest for samples in which the gas hydrate is primarily responsible for maintaining the sediment fabric and for which the time between core retrieval and restoration of in situ effective stress in the laboratory is minimized in evaluating the impact of core retrieval on specimen properties it is also important to consider how far removed hydrate bearing samples are from hydrate stability conditions

marine controlled source electromagnetic method used for the gas hydrate investigation in the offshore area of sw taiwan abstract bottom simulating reflectors bsrs high methane flux shallow sulfide methane interfaces fluids venting from the seafloor authigenic carbonates within sediments methane reefs and self biomes are common seafloor features in the area off southwest taiwan the geophysical and geochemical signatures of these features suggest a high potential for gas hydrate gh reservoirs in the region the bsrs are typically interpreted as the boundary between free gases and solid hydrate whereas the upper reaches of the hydrate stability zone and the distribution of gas hydrate in shallow sediments are not well understood this study shows the first results of a marine controlled source electromagnetic survey conducted in the offshore area of sw taiwan in 2010 the survey aimed to provide electrical resistivity information of the shallow sediments three target areas were surveyed 1 an area to the southeast of the xiaoliuchiu island gas seep g96 2 an area in the west of the yung an ridge yar and 3 an area in the northwest of the good weather ridge gwr in total fourteen survey lines with a total length of 72 km were completed our preliminary results show that relatively high resistivity anomalies occur within pockmarks and at gas seepage sites the apparent resistivity is estimated to be about 1 ohm m higher than background in g96 and yar sites while an anomaly up to 2 ohm m is found in the gwr at gas seep site g96 the high resistivity anomaly may be due to the existence of authigenic carbonates whereas the high resistivity anomaly in the nw of the gwr site may also be due to the existence of gas hydrate in the shallow seabed based on the resistivity anomaly the gas hydrate saturation is about 16 in the shallow sediments below the pockmark area in the northwest side of the gwr site

characterization of in situ elastic properties of gas hydrate bearing sediments on the blake ridge during ocean drilling program leg 164 shear sonic velocity and other geophysical logs were acquired in gas hydrate bearing sediments on the blake ridge to characterize the very distinct seismic signature of such formations anomalous low amplitudes overlying a strong bottom simulating reflector bsr a comparison of the bulk moduli derived from the logs to standard elastic consolidation models shows that the sediments are overconsolidated above the bsr at 440 meters below seafloor mbsf because of the presence of hydrates below the bottom of the thermodynamic hydrate stability zone at 520 mbsf the high compressibility of the formation and the attenuation of the monopole sonic waveforms are typical of sediments partially saturated with free gas between these two depths gas hydrate and free gas seem to coexist within the gas hydrate stability zone we estimate the amount of gas hydrates using different models based on theories for wave scattering in multiphase media and for grain cementation in close agreement with measurements made on discrete in situ samples the latter describes most accurately the interactions between the matrix the pore fluids and the hydrates this model indicates that 5 to 10 of the pore space is occupied by hydrates deposited uniformly on the surface of the grains the comparison with gassmann s model also show that the amount of free gas below the bsr never exceeds 5 of the pore space but is high enough to generate the bsr the coexistence of free gas and gas hydrates below the bsr may be explained by capillary effects in the smaller pores or by remaining crystalline structures after partial hydrate decomposition

solute transport through a heterogeneous coupled vadose saturated zone system with temporally random rainfall the transport of nonreactive solutes through a coupled two dimensional randomly heterogeneous vadose saturated zone system subject to temporally random rainfall is predicted by monte carlo simulation and compared with previously published analytic results for three different rainfall patterns the relative contributions of the uncertain inputs i e rainfall and saturated conductivity to the prediction uncertainty of solute transport are quantified in terms of the statistical moments of the pore water velocity the plume spatial moments and solute flux breakthrough curves at downstream control planes results show that the mean and variance of the saturated zone pore water velocity were approximately equivalent for the cases of uniform and random rainfall and were well predicted by the analytical relationships developed by rubin and bellin 1994 as a result the mean plume displacement estimated by the trajectory of the mean plume center of mass was found to be nearly identical for these cases in the temporally random rainfall case the saturated zone mean plume experienced more spread in the direction of mean flow at early times however the asymptotic rates of spatial spreading of the mean solute plumes were found to be approximately equivalent for the uniform and random rainfall cases and well predicted by the approximate expressions for longitudinal macrodispersivity in nonuniform flow proposed by destouni and graham 1995 random rainfall and random soil properties increased prediction uncertainty of the solute plume behavior in the vadose zone by an order of magnitude when compared with the uniform rain and random soil case this effect was reduced considerably when the solute entered the saturated zone where random rainfall produced only slightly larger prediction uncertainty than the uniform rainfall case the analytic model developed by destouni and graham 1995 accurately predicted the temporal breakthrough of the mean solute plume at saturated zone control planes for all cases if transport through the unsaturated zone accounted for the effects of temporally random rainfall using the methodology developed by foussereau et al 2000a 2000b results of this work indicate that for the humid climates studied here uncertain rainfall patterns dominate transport prediction uncertainty in the shallow unsaturated zone while uncertain solute breakthrough to the saturated zone and uncertain hydraulic conductivity dominate prediction uncertainty in the saturated zone

estimate of gas hydrate saturations in the krishna godavari basin eastern continental margin of india results of expedition nghp 02 abstract a total of 25 drill sites were established in the krishna godavari kg and mahanadi basins along the eastern margin of india during the india national gas hydrate program expedition 02 nghp 02 with the goal to identify and characterize gas hydrate occurrences in sand rich reservoir systems the objective of this study is to characterize the gas hydrate bearing zones linked with two seismic inferred horizons r1 and r2 and estimate gas hydrate saturations at two sites in area b of the kg basin sites nghp 02 22 and nghp 02 23 the upper seismic imaged reservoir section reflector r1 contains both pore filling and fracture filling gas hydrate while the lower seismic imaged reservoir section reflector r2 has only pore filling gas hydrate since electrical resistivity seems to be the most pronounced physical response to the presence of gas hydrate we have analyzed the resistivity log data using archie s empirical equation from two sites based on an isotropic reservoir model in order to assess the gas hydrate saturation we have also performed isotropic velocity modelling using the three phase biot equation tpbe and density log derived sediment porosities at site nghp 02 22 the average gas hydrate saturation estimated using the resistivity log data and p wave velocity modelling are 29 and 17 respectively in the depth interval of 207 290 mbsf whereas at site nghp 02 23 the average gas hydrate saturation obtained from resistivity log data and p wave velocity modelling are 25 and 60 respectively in the depth interval of 271 288 mbsf estimated results are further validated with the pressure core derived gas hydrate saturations to ensure their reliability at the respective drill sites it was found that p wave velocity log inferred gas hydrates show a slight mismatch with the pressure core derived hydrate saturations while the electrical resistivity log based result depicts a major mismatch with the pressure core derived hydrate saturations the reason for this discrepancy is likely due to isotropic resistivity analysis of the reservoir section having anisotropic properties

combining impedance inversion and seismic similarity for robust gas hydrate concentration assessments a case study from the krishna godavari basin east coast of india abstract gas hydrate saturations were calculated based on archie s relation and rock physics modeling utilizing log measurements of electrical resistivity and p wave velocity through the gas hydrate stability zone ghsz at two sites in the krishna godavari kg basin off the east coast of india acoustic impedance inversion was then performed around the well sites for regional extrapolation of the borehole data well log based gas hydrate concentration estimates and core data are in general agreement with the seismic impedance inversion results at the individual well sites however the correlation with seismic data and thus the confidence in the extrapolation decreases with distance from the well site to address the general problem of unknown regional confidence limits in the extrapolation and aid in regional gas hydrate assessment analyses a new approach is introduced by calculating the running sum of the seismic similarity attribute across the gas hydrate stability zone the running sum of the similarity attribute can be used locally on a 2d seismic line or 3d seismic volume for defining the limit of well data extrapolation around a given well site by normalizing the running sum of the similarity attribute from all available 2d seismic data in the kg basin a regional map was generated yielding effective confidence limits for extrapolation of well log data such maps of regional confidence limits can be used strategically in basin wide gas hydrate assessments as they provide a measure of probability to find a given gas hydrate concentration and may also offer a guide for defining a minimum regional spacing between well sites to address the overall structural complexity of the basin which is reflected in the similarity of the seismic data

mixing rates and vertical heat fluxes north of svalbard from arctic winter to spring mixing and heat flux rates collected in the eurasian basin north of svalbard during the n ice2015 drift expedition are presented the observations cover the deep nansen basin the svalbard continental slope and the shallow yermak plateau from winter to summer mean quiescent winter heat flux values in the nansen basin are 2 w m 2 at the ice ocean interface 3 w m 2 in the pycnocline and 1 w m 2 below the pycnocline large heat fluxes exceeding 300 w m 2 are observed in the late spring close to the surface over the yermak plateau the data consisting of 588 microstructure profiles and 50 days of high resolution under ice turbulence measurements are used to quantify the impact of several forcing factors on turbulent dissipation and heat flux rates wind forcing increases turbulent dissipation seven times in the upper 50 m and doubles heat fluxes at the ice ocean interface the presence of warm atlantic water close to the surface increases the temperature gradient in the water column leading to enhanced heat flux rates within the pycnocline steep topography consistently enhances dissipation rates by a factor of four and episodically increases heat flux at depth it is however the combination of storms and shallow atlantic water that leads to the highest heat flux rates observed ice ocean interface heat fluxes average 100 w m 2 during peak events and are associated with rapid basal sea ice melt reaching 25 cm d

characterization and rheology of krishna godavari basin sediments abstract the krishna godavari offshore basin to the east of india is a proven reserve rich in natural gas hydrate the impact of sediment characteristics on the hydrate formation has already been well established in open literature in the present study we have attempted to investigate the mineralogy of sediments collected from kg basin by elemental analysis energy dispersive spectroscopy and x ray diffraction various physicochemical characteristics of the clayey sediments such as tds salinity ph conductivity and resistivity were analysed at various concentrations and compared together also this paper highlights the rheological behavior of the sediment samples with concentrations of 20 35 and 50 wt at different experimental temperatures 278 15 k 283 15 k and 288 15 k viscosity measurements were performed for a wide range of shear rates for all concentrations and comparative studies have been conducted on their exhibited behavior the viscosity of sediment sample were found to be varying from 76 3 to 0 003 pa s depending on the sediment concentration temperature and shear rate in addition viscoelastic measurements were carried out at various angular frequencies for all the sediment samples the work aims to characterise the sediments of kg basin and analyse the rheological behavior of sediment solution which has not yet been reported in open literature this will provide vital information for possible methane recovery from kg basin hydrate reservoir by manipulating the host sediment behavior

extending nmr data for permeability estimation in fine grained sediments abstract we combine nuclear magnetic resonance nmr transverse relaxation time data and gamma ray data to estimate lithology dependent permeability in silt and clay rich sediments this approach extends the utility of the schlumberger doll research sdr permeability equation from reservoirs to aquicludes and seals and thus improves the value and robustness of nmr data data from keathley canyon northern gulf of mexico show that nmr data can be used to define permeability from 10 18 to 10 14 m 2 0 001 10 millidarcies as calibrated and tested by direct measurements on core samples we performed uniaxial constant rate of strain consolidation experiments on sediments from keathley canyon to determine core scale permeability permeabilities from these experiments were compared to permeabilities calculated from logging while drilling data a better fit between log derived permeability and laboratory measured permeability was obtained using the sdr equation with a variable coefficient a rather than a constant a as is typically used we show how a is a function of lithology and can be modeled from gamma ray data the relationship between a and gamma ray values suggests that variations in a are caused by platy clay minerals and the effect they have on the pore system our results provide improved means for permeability estimation for application in basin flow modeling hydrocarbon migration modeling and well completion design

gas hydrate saturation in the krishna godavari basin from p wave velocity and electrical resistivity logs abstract during the indian national gas hydrate program nghp expedition 01 a series of well logs were acquired at several sites across the krishna godavari kg basin electrical resistivity logs were used for gas hydrate saturation estimates using archie s method the measured in situ pore water salinity seafloor temperature and geothermal gradients were used to determine the baseline pore water resistivity in the absence of core data arp s law was used to estimate in situ pore water resistivity uncertainties in the archie s approach are related to the calibration of archie coefficient a cementation factor m and saturation exponent n values we also have estimated gas hydrate saturation from sonic p wave velocity logs considering the gas hydrate in frame effective medium rock physics model uncertainties in the effective medium modeling stem from the choice of mineral assemblage used in the model in both methods we assume that gas hydrate forms in sediment pore space combined observations from these analyses show that gas hydrate saturations are relatively low s h 15 20 in two zones between 168 and 198 mbsf site nghp 01 05 s h 35 38 in two discrete zone between 70 and 90 mbsf and site nghp 01 07 shows the gas hydrate saturation more than 25 in two zones between 75 and 155 mbsf a total of 10 drill sites and associated log data regional occurrences of bottom simulating reflectors from 2d and 3d seismic data and thermal modeling of the gas hydrate stability zone were used to estimate the total amount of gas hydrate within the kg basin average gas hydrate saturations for the entire gas hydrate stability zone seafloor to base of gas hydrate stability sediment porosities and statistically derived extreme values for these parameters were defined from the logs the total area considered based on the bsr seismic data covers 720 km 2 using the statistical ranges in all parameters involved in the calculation the total amount of gas from gas hydrate in the kg basin study area varies from a minimum of 5 7 trillion cubic feet tcf to 32 1 tcf

exploration for gas hydrates in the deepwater northern gulf of mexico part ii model validation by drilling this study examines the accuracy of the predictions of gas hydrate saturations made based on five step analysis of 3d seismic data prior to 2005 drilling logging conventional coring and pressure core sampling through the gas hydrate stability zone at two focus sites in the northern gulf of mexico these predictions are detailed in part i 2008 here we conduct a detailed analysis of the gas hydrate saturation using both resistivity and p wave velocity log data and analyze the pre drilling predictions which were made almost exclusively on the basis of seismic data with no local logging control well log measurements core data analysis and pressure core degas experiments all indicated general agreement with the pre cruise analysis regarding the location and approximate concentration of gas hydrates in the sediments we find that seismic predictions are generally consistent with log based estimates after upscaling to seismic frequencies we recalibrated the pre drill model based on the new field data so that a refined version of the model could be used for future work

geochemical constraints on the origin of the pore fluids and gas hydrate distribution at atwater valley and keathley canyon northern gulf of mexico abstract pore fluids from atwater valley at 13 14 and keathley canyon kc 151 in the northern gulf of mexico are surprisingly similar with respect to ionic concentrations and oxygen and strontium isotope values as well as hydrocarbon geochemistry suggesting that these widely separated localities share common deep subsurface fluid origins seafloor mounds with focused fluid migration pathways and inferred near seafloor gas hydrates characterize the at 13 14 region whereas the kc 151 region has a bottom simulating reflector bsr at 310 mbsf which is rather uncommon in the gulf of mexico gom at these sites seafloor gas hydrates were not observed but the sediment surface in the vicinity and particularly at the mounds is populated with chemosynthetic communities that are commonly associated with seafloor gas emission the geochemical results together with the pressure core data suggest that at the at region methane hydrate mostly occurs in near surface sediments at mounds consistent with focused migration pathways in the kc region methane hydrate mostly occurs deeper in the section in highly fractured silty clayey sediments from 220 to 300 mbsf the pore fluids at the at mounds and kc 151 are characterized by higher than seawater salinity the more saline pore fluids at the at mound and at kc151 sites located 350 km apart are almost chemically indistinct ionic ratios indicate that this distinct high salinity fluid is not from in situ salt dome halite dissolution rather this fluid is a subsurface brine derived from jurassic or cenozoic evaporite formation modified by fluid sediment reactions and migrated to the two sites analyzed despite porewater salinities elevated above that of seawater the sediment temperatures are within the range of methane hydrate stability for each of the sites based on cl dilutions the maximum gas hydrate pore volume occupancy at the at mound sites would be 9 at kc cl concentrations in pressure cores imply that in situ hydrate is unevenly distributed with pore volume occupancy of 1 12 significant variations in sulfate gradients were observed with the sulfate to methane transition zone smtz at or near the seafloor at the at mound sites at at 13 2 the well defined smtz is at 8 mbsf and at kc 151 3 it is at 9 mbsf there is no coincidence between the steepness of the sulfate gradients and the presence or depth of a bsr suggesting that the smtz interfaces are measuring different aspects of the subsurface methane hydrology at both at and kc the 13 c dic values clearly indicate that anaerobic oxidation of methane aom is the dominant reaction responsible for sulfate reduction and the increased alkalinities observed the most negative 13 c dic values obtained are 46 3 and 49 6 at the smtzs at at 13 2 and kc 151 3 respectively

origin and evolution of fracture hosted methane hydrate deposits 1 fracture hosted methane hydrate deposits exist at many sites worldwide these sites often have hydrate present as vein and fracture fill as well as disseminated through the pore space we estimate that thousands to millions of years are required to form fracture systems by hydraulic fracturing driven by occlusion of the pore system by hydrate this time scale is a function of rates of fluid flow and permeability loss low permeability layers in a sedimentary column can reduce this time if the permeability contrast with respect to the surrounding sediments is of order 10 or greater additionally we find that tensile fracturing produced by hydrate heave around hydrate lenses is a viable fracture mechanism over all but the lowermost part of the hydrate stability zone with our coupled fluid flow hydrate formation model we assess fracture formation at four well studied hydrate provinces blake ridge offshore south carolina hydrate ridge offshore oregon keathley canyon block 151 offshore louisiana and the krishna godavari basin offshore india we conclude that hydraulic fracturing due to pore pressure buildup is reasonable only at hydrate ridge and the krishna godavari basin owing to sediment age constraints and that hydrate filled fractures observed at blake ridge and keathley canyon block 151 are formed either by hydrate heave or in preexisting fractures our findings offer new insight into the processes and time scales associated with fracture hosted hydrate deposits which help further our understanding of hydrate systems

quantitative characterization of gas hydrate bearing sediment using elastic electrical rock physics models abstract successful evaluation of reservoir resources in gas hydrate bearing sediments depends on the accurate estimation of reservoir parameters such as hydrate saturation porosity and clay content elastic and electrical measurements are affected by several rock and fluid properties and their joint interpretation can provide complementary information and improve the accuracy of reservoir characterization results in this work we propose a new rock physics inversion workflow based on 3d rock physics template of elastic and electrical attributes for the direct estimation of reservoir parameters we first conduct a quantitative analysis of the available well log data and core data to understand the morphology of gas hydrate within the marine sediment and choose the appropriate elastic rock physics model then we construct the 3d rock physics template by discretizing the 3d space of reservoir parameters and implementing the suitable elastic and electrical models to calculate the poisson s ratio p wave impedance and electrical resistivity for each combination of values of rock and fluid properties finally we superimpose the measurements on the templates and use a grid searching method to find the nearest gridded node to the data point and minimize the objective function of the mismatch between data and model predictions to investigate the feasibility of our proposed inversion scheme we test a rock physics model based on effective medium theory and a modified archie s equation and invert for reservoir parameters of gas hydrate bearing sediments at well 1250f and 1247b in hydrate ridge the good match between inversion results and core data suggests that the proposed inversion scheme is applicable to real data and allows combining elastic and electrical data for reservoir parameter estimation of gas hydrate bearing sediments

a new approach for deriving pseudovelocity logs from resistivity logs1 this paper describes a method of generating pseudovelocity logs using measurements of electrical resistivity a theoretical relation between electrical resistivity and transit time which is applicable to a wide range of lithologies has been developed the application of this relation using a method which defines lithoresistivity zones as lithological intervals related to the same formation and showing small resistivity variations has been tested in the reconcavo sedimentary basin in bahia brazil a comparison of derived pseudovelocity logs with actual sonic logs for five wells shows the validity of the present approach

elastic velocities of partially gas saturated unconsolidated sediments abstract fluid in sediments significantly affects elastic properties of sediments and gas in the pore space can be identified by a marked reduction of p wave velocity or a decrease of poisson s ratio the elastic properties of gas saturated sediments can be predicted by the classical biot gassmann theory bgt however parameters for the bgt such as the biot coefficient or moduli of dry frame of unconsolidated and high porosity sediments are not readily available dependence of velocities on differential pressure or porosity for partially gas saturated sediments is formulated using properties derived from velocities of water saturated sediments laboratory samples for unconsolidated and consolidated sediments and well log data acquired for unconsolidated marine sediments agree well with the predictions however because the p wave velocity depends highly on how the gas is saturated in the pore space such as uniform or patch the amounts of gas estimated from the p wave velocity contains high uncertainty the modeled vp vs ratio of partially gas saturated sediment using the patch distribution is usually greater than 1 6 whereas the ratio modeled assuming a uniform distribution is about 1 6 thus poisson s ratio or vp vs ratio may be used to differentiate patch from uniform saturation but differences between various models of patch saturation cannot be easily identified

integrated analysis of well logs and seismic data to estimate gas hydrate concentrations at keathley canyon gulf of mexico abstract accurately detecting and quantifying gas hydrate or free gas in sediments from seismic data require downhole well log data to calibrate the physical properties of the gas hydrate free gas bearing sediments as part of the gulf of mexico joint industry program a series of wells were either cored or drilled in the gulf of mexico to characterize the physical properties of gas hydrate bearing sediments to calibrate geophysical estimates and to evaluate source and transport mechanisms for gas within the gas hydrates downhole acoustic logs were used sparingly in this study because of degraded log quality due to adverse wellbore conditions however reliable logging while drilling lwd electrical resistivity and porosity logs were obtained to tie the well log information to the available 3 d seismic data in this area a velocity log was calculated from the available resistivity log at the keathley canyon 151 2 well because the acoustic log or vertical seismic data acquired at the nearby keathley canyon 151 3 well were either of poor quality or had limited depth coverage based on the gas hydrate saturations estimated from the lwd resistivity log the modified biot gassmann theory was used to generate synthetic acoustic log and a synthetic seismogram was generated with a fairly good agreement with a seismic profile crossing the well site based on the well log information a faintly defined bottom simulating reflection bsr in this area is interpreted as a reflection representing gas hydrate bearing sediments with about 15 saturation overlying partially gas saturated sediments with 3 saturation gas hydrate saturations over 30 40 are estimated from the resistivity log in two distinct intervals at 220 230 and 264 300 m below the sea floor but gas hydrate was not physically recovered in cores it is speculated that the poor recovery of cores and gas hydrate morphology are responsible for the lack of physical gas hydrate recovery

permeability and porosity of hydrate bearing sediments in the northern gulf of mexico abstract hydrate bearing sands are being actively explored because they contain the highest concentrations of hydrate and are the most economically recoverable hydrate resource however relatively little is known about the mechanisms or timescales of hydrate formation which are related to methane supply fluid flux and host sediment properties such as permeability we used logging while drilling data from locations in the northern gulf of mexico to develop an effective medium theory based model for predicting permeability based on clay sized sediment fraction the model considers permeability varying between sand and clay endpoint permeabilities that are defined from laboratory data we verified the model using permeability measurements on core samples from three boreholes and then used the model to predict permeability in two wells drilled in walker ridge block 313 during the gulf of mexico gas hydrate joint industry project leg ii expedition in 2009 we found that the cleanest sands clay sized fraction

erratum invasion of drilling mud into gas hydrate bearing sediments part i effect of drilling mud properties fulong ning 1 2 keni zhang 3 4 nengyou wu 2 ling zhang 1 gang li 2 guosheng jiang 1 yibing yu 1 li liu1 and yinghong qin1 1faculty of engineering china university of geosciences wuhan hubei 430074 china e mail nflzx cug edu cn 2guangzhou center for gas hydrate research chinese academy of sciences guangzhou 510640 china 3earth system division lawrence berkeley national laboratory berkeley ca 94720 usa 4college of water sciences beijing normal university beijing 100875 china

imaging methane hydrates growth dynamics in porous media using synchrotron x ray computed microtomography commercial scale methane ch4 extraction from natural hydrate deposits remains a challenge due to among other factors a poor understanding of hydrate host sediment interactions under low temperature and high pressure conditions that are conducive to their existence we report the use of synchrotron x ray computed microtomography cmt to image for the first time time resolved pore scale methane ch4 hydrate growth from an aqueous solution containing 5 wt barium chloride bacl2 and pressurized ch4 hosted in glass beads all contained in an aluminum cell with an effective volume of 3 5 ml multiple two dimensional 2 d cross sectional images show ch4 hydrates with 7 5 m resolution distributed in patches throughout the system without dependence on distance from the cell walls the time resolved three dimensional 3 d images constructed from the 2 d slices exhibited pore filling hydrate formation from dissolved ch4 gas similar to natural ch4 hydrates si in the marine environment furthermore the 3 d images show that the aqueous phase was the wetting phase of the glass beads i e the host and the formed hydrate were separated by an aqueous layer these results provide some fundamental understanding of the nucleation phenomenon of gas hydrate formation at the pore scale pore filling ch4 hydrate growth is likely to result in a reduced bulk modulus and thus could affect seafloor stability during the reverse phenomenon i e dissociation of natural hydrate deposits

pore water sulfate alkalinity and carbon isotope profiles in shallow sediment above marine gas hydrate systems a numerical modeling perspective 1 both the concentration and the carbon isotope composition of dissolved inorganic carbon dic vary considerably across the sulfate methane transition smt in shallow marine sediment at locations with gas hydrate this variability has led to different interpretations for how carbon including ch4 cycles within gas charged sediment sequences over time we extend a one dimensional model for the formation of gas hydrate to account for downhole changes in dissolved ch4 so42 dic and ca2 and the 13c of dic the model includes advection diffusion and two reactions that consume so42 degradation of particulate organic carbon poc and anaerobic oxidation of methane aom using our model and site specific parameters steady state pore water profiles are simulated for two sites containing gas hydrate but different carbon chemistry across the smt site 1244 hydrate ridge dic 38 mm 13c of dic 22 5 pdb and site keathley canyon kc 151 3 gulf of mexico dic 16 mm 13c of dic 49 6 pdb the simulated profiles for ch4 so42 dic ca2 and 13c of dic resemble those measured at the sites and the model explains the similarities and differences in pore water chemistry at both sites an upward flux of ch4 consumes most net so42 at a shallow smt and calcium carbonate removes a portion of dic at this horizon however a large flux of 13c enriched hco3 enters the smt from depth at site 1244 but not at site kc151 3 this leads to a high concentration of dic with a 13c much greater than that of ch4 even though aom causes the smt the addition of hco3 from depth impacts the slope of certain concentration crossplots crucially neither the dic concentration nor its carbon isotope composition at the smt can be used to discriminate between sulfate reduction pathways