mount elbert gas hydrate stratigraphic test well alaska north slope overview of scientific and technical program abstract the mount elbert gas hydrate stratigraphic test well was drilled within the alaska north slope ans milne point unit mpu from february 3 to 19 2007 the well was conducted as part of a cooperative research agreement cra project co sponsored since 2001 by bp exploration alaska inc bpxa and the u s department of energy doe in collaboration with the u s geological survey usgs to help determine whether ans gas hydrate can become a technically and commercially viable gas resource early in the effort regional reservoir characterization and reservoir simulation modeling studies indicated that up to 0 34 trillion cubic meters tcm 12 trillion cubic feet tcf gas may be technically recoverable from 0 92 tcm 33 tcf gas in place within the eileen gas hydrate accumulation near industry infrastructure within ans mpu prudhoe bay unit pbu and kuparuk river unit kru areas to further constrain these estimates and to enable the selection of a test site for further data acquisition the usgs reprocessed and interpreted mpu 3d seismic data provided by bpxa to delineate 14 prospects containing significant highly saturated gas hydrate bearing sand reservoirs the mount elbert site was selected to drill a stratigraphic test well to acquire a full suite of wireline log core and formation pressure test data drilling results and data interpretation confirmed pre drill predictions and thus increased confidence in both the prospect interpretation methods and in the wider ans gas hydrate resource estimates the interpreted data from the mount elbert well provide insight into and reduce uncertainty of key gas hydrate bearing reservoir properties enable further refinement and validation of the numerical simulation of the production potential of both mpu and broader ans gas hydrate resources and help determine viability of potential field sites for future extended term production testing drilling and data acquisition operations demonstrated that gas hydrate scientific research programs can be safely effectively and efficiently conducted within ans infrastructure the program success resulted in a technical team recommendation to project management to drill and complete a long term production test within the area of existing ans infrastructure if approved by stakeholders this long term test would build on prior arctic research efforts to better constrain the potential gas rates and volumes that could be produced from gas hydrate bearing sand reservoirs

dynamic in situ imaging of methane hydrate formation and self preservation in porous media abstract we present the results of dynamic in situ 3d x ray imaging of methane hydrates microstructure during methane hydrate formation and dissociation in sand samples short scanning times and high resolution provided by synchrotron x rays allowed for better understanding of water movement and different types of gas hydrate formation complementing previous observations we conclude that the process of gas hydrate formation is accompanied by the water movements caused by cryogenic water suction that happens in sequences of short fast movements with longer equilibrium states in between when the water is immobile based on the 3d microstructure we identified two distinct types of gas hydrate formation i into the gas pockets and ii inside water volumes for both mechanisms we do not see problems in gas or water supply to support the gas hydrate formation the rate of dissociation in the self preservation mode pressure drop at negative temperatures appears to be different for these two types of gas hydrates this means that the history of the gas hydrate formation may influence its behaviour at the dissociation stage e g gas hydrate production

hydrate morphology physical properties of sands with patchy hydrate saturation 1 the physical properties of gas hydrate bearing sediments depend on the volume fraction and spatial distribution of the hydrate phase the host sediment grain size and the state of effective stress determine the hydrate morphology in sediments this information can be used to significantly constrain estimates of the physical properties of hydrate bearing sediments including the coarse grained sands subjected to high effective stress that are of interest as potential energy resources reported data and physical analyses suggest hydrate bearing sands contain a heterogeneous patchy hydrate distribution whereby zones with 100 pore space hydrate saturation are embedded in hydrate free sand accounting for patchy rather than homogeneous hydrate distribution yields more tightly constrained estimates of physical properties in hydrate bearing sands and captures observed physical property dependencies on hydrate saturation for example numerical modeling results of sands with patchy saturation agree with experimental observation showing a transition in stiffness starting near the series bound at low hydrate saturations but moving toward the parallel bound at high hydrate saturations the hydrate patch size itself impacts the physical properties of hydrate bearing sediments for example at constant hydrate saturation we find that conductivity electrical hydraulic and thermal increases as the number of hydrate saturated patches increases this increase reflects the larger number of conductive flow paths that exist in specimens with many small hydrate saturated patches in comparison to specimens in which a few large hydrate saturated patches can block flow over a significant cross section of the specimen

effects of dissociation on the shear strength and deformation behavior of methane hydrate bearing sediments abstract a series of tests were conducted in order to investigate the shear strength and deformation behavior of methane hydrate bearing sediments during dissociation using the thermal recovery method or depressurization method an innovative temperature controlled high pressure triaxial apparatus which can reproduce the in situ conditions of hydrate reservoirs was used the results indicate that 1 the failure strength of isotropically consolidated methane hydrate bearing sediments which dissociated completely using the thermal recovery method is less than that of pure toyoura sand however the initial stiffness and volumetric strain are higher than that of pure toyoura sand 2 the thermal recovery method will cause the failure of methane hydrate bearing sediments when the axial load is higher than the strength of methane hydrate bearing sediments after dissociation 3 the depressurization method will not cause collapse of methane hydrate bearing sediments during depressurization however water pressure recovery will lead to failure when the axial load is larger than the strength of the methane hydrate bearing sediments after dissociation 4 the depressurization rate shows little effect on the ultimate deformation of methane hydrate bearing sediments while the initial deformation rate increases with increasing depressurization rate 5 the larger the reduction of pore pressure the larger axial strain and volumetric strain

drop size distributions and radar observations of convective and stratiform rain over the equatorial indian and west pacific oceans abstracttwo dimensional video disdrometer 2dvd data were analyzed from two equatorial indian gan and west pacific ocean manus islands where precipitation is primarily organized by the intertropical convergence zone and the madden julian oscillation mjo the 18 3 5 months of 2dvd data from manus gan island show that 1 the two sites have similar drop size distribution dsd spectra of liquid water content median diameter rain rate r radar reflectivity z normalized gamma number concentration nw and other integral rain parameters 2 there is a robust nw based separation between convective c and stratiform s dsds at both sites that produces consistent separation in other parameter spaces the 2dvd data indicate an equatorial maritime average c s rainfall accumulation fraction frequency of 81 19 41 59 at these locations it is hypothesized that convective fraction and frequency estimates are slightly higher than previous radar based studies because the ubiquitous weak shallow convec

mechanical properties of hydrate bearing turbidite reservoir in the first gas production test site of the eastern nankai trough abstract the study of mechanical properties of marine sediments is essential for the prediction of the occurrence of geohazards e g subsea landslides and seafloor subsidence and the design of submarine structures for offshore industry in this study triaxial compression tests of gas hydrate bearing sandy sediments and clayey silty sediments were conducted the sediments were recovered by pressure coring in the eastern nankai trough the area of the first japanese offshore production test soil index properties were measured and revealed porosity of 40 50 with porosity decreasing gradually with greater depth below the seafloor the mean particle size was less than 10 m for clayey silty sediments and approximately 100 m for sandy sediments permeability estimated by a consolidation process of triaxial testing and with x ray diffraction analysis depended on the content of fines which consisted chiefly of mica kaolinite and smectite the results of undrained compression tests for clayey silty sediments showed positive excess pore pressure under all test conditions this mechanical behavior indicates that the core samples are normally consolidated sediments drained compression tests showed that the strength and stiffness of sandy sediments increase with hydrate saturation furthermore the volumetric strain of hydrate bearing sediments changed from compression to dilative this result was obtained for hydrate saturation values sh of more than 70 the shear strength of hydrate bearing turbidite sediments of the eastern nankai trough is shown to be a function of the confining pressure

triaxial experiments on the mechanical properties of hydrate bearing marine sediments of south china sea abstract in this paper a series of experiments was conducted on remoulded hydrate bearing marine sediments from a gas hydrate core drilling site located in the pearl river estuary of the south china sea the composition and particle size distribution of marine sediments were analysed and triaxial loading experiments were performed to study the mechanical properties of hydrate bearing marine sediments the strength properties of hydrate bearing marine sediments were compared with those of hydrate bearing kaolin clay ice marine sediment mixtures and hydrate dissociated marine sediments under the same porosity 40 temperature 8 c confining pressures 2 3 and 4 mpa and strain rate 1 min conditions several important results were obtained the composition and particle size distribution analysis indicated the marine sediment and kaolin clay are both sandy clays and the stress strain behaviours and strength properties of hydrate bearing marine sediments are similar to those of hydrate bearing kaolin clay under different confining pressures the failure strengths of all ice marine sediment mixtures were lower than those of methane hydrate bearing sediments confirming that hydrate particles enhance the cementation of sediment particles hydrate dissociation leads to strength reduction of gas hydrate bearing marine sediments as was demonstrated in our previous research of hydrate bearing kaolin clay through the analysis of mohr circles and failure envelopes of three types of mixtures under different confining pressures it can be inferred that the cohesive strength played an important role in the failure strength of hydrate bearing marine sediments following hydrate dissociation

physical properties of hydrate bearing sediments 1 methane gas hydrates crystalline inclusion compounds formed from methane and water are found in marine continental margin and permafrost sediments worldwide this article reviews the current understanding of phenomena involved in gas hydrate formation and the physical properties of hydrate bearing sediments formation phenomena include pore scale habit solubility spatial variability and host sediment aggregate properties physical properties include thermal properties permeability electrical conductivity and permittivity small strain elastic p and s wave velocities shear strength and volume changes resulting from hydrate dissociation the magnitudes and interdependencies of these properties are critically important for predicting and quantifying macroscale responses of hydrate bearing sediments to changes in mechanical thermal or chemical boundary conditions these predictions are vital for mitigating borehole local and regional slope stability hazards optimizing recovery techniques for extracting methane from hydrate bearing sediments or sequestering carbon dioxide in gas hydrate and evaluating the role of gas hydrate in the global carbon cycle

mechanical properties of sand silt and clay containing tetrahydrofuran hydrate 1 the mechanical behavior of hydrate bearing sediments subjected to large strains has relevance for the stability of the seafloor and submarine slopes drilling and coring operations and the analysis of certain small strain properties of these sediments for example seismic velocities this study reports on the results of comprehensive axial compression triaxial tests conducted at up to 1 mpa confining pressure on sand crushed silt precipitated silt and clay specimens with closely controlled concentrations of synthetic hydrate the results show that the stress strain behavior of hydrate bearing sediments is a complex function of particle size confining pressure and hydrate concentration the mechanical properties of hydrate bearing sediments at low hydrate concentration probably 50 of pore space the behaviorbecomesmoreindependentofstressbecausethehydratescontrolbothstiffnessand strength and possibly the dilative tendency of sediments by effectively increasing interparticle coordination cementing particles together and filling the pore space the cementation contribution to the shear strength of hydrate bearing sediments decreases with increasing specific surface of soil minerals the lower the effective confining stress the greater the impact of hydrate formation on normalized strength

strengthening mechanism of cemented hydrate bearing sand at microscales on the basis of hypothetical particle level mechanisms several constitutive models of hydrate bearing sediments have been proposed previously for gas production however to the best of our knowledge the microstructural large strain behaviors of hydrate bearing sediments have not been reported to date because of the experimental challenges posed by the high pressure and low temperature testing conditions herein a novel microtriaxial testing apparatus was developed and the mechanical large strain behavior of hydrate bearing sediments with various hydrate saturation values sh 0 39 and 62 was analyzed using microfocus x ray computed tomography patchy hydrates were observed in the sediments at sh 39 the obtained stress strain relationships indicated strengthening with increasing hydrate saturation and a brittle failure mode of the hydrate bearing sand localized deformations were quantified via image processing at the submillimeter and micrometer scale shear planes and particle deformation and or rotation were detected and the shear band thickness decreased with increasing hydrate saturation

pore habit of methane hydrate and its evolution in sediment matrix laboratory visualization with phase contrast micro ct abstract describing the pore habit of methane hydrate in sediment matrices is essential for understanding natural distribution of methane hydrate methane trace transport and solidification in the hydrate stability zone physical properties of hydrate bearing sediments and the associated influence on potential gas production pore habit visualization in natural media at pore scale even with laboratory synthesized cores has been challenging due to the similar densities of methane hydrate from pore liquid in this work we used phase contrast assisted micro ct with potassium iodine doped brine to visualize four phases sand particles pore fluid methane hydrate and methane gas this study visualizes the pore habit of methane hydrate at various stages including during hydrate formation in excess gas systems its evolution after brine injection to replace pore fluid and hydrate formation in excess water systems hydrate tends to adopt round and smooth surfaces when in contact with water while exhibits relatively angular interfaces when in contact with methane gas hydrate formation in excess gas systems results in a partial cementing and partial mineral coating pore habit while hydrate in excess water systems develops mainly as pore filling and locally cementing or mineral coating where big gas pockets exist at the initial state pore liquid replacement from methane gas to brine triggers a shift of hydrate pore habit towards pore filling methane hydrate evolution over time produces bigger hydrate particles but with less contact area with sand particles the effects of hydrate pore habit become less important as hydrate particle size exceeds the pore size additionally hydrate formation could trap residual methane gas and brine as inclusions

load bearing characteristic of methane hydrate within coarse grained sediments insights from isotropic consolidation abstract gas hydrate as a solid pore constituent can potentially share external load with sediment matrix and critically impact geological evolution of its hosting sediments well integration and sediment settlement during gas production depending on its contribution to support external loading we aim to address the question of whether hydrate shares the load with the soil skeleton through isotropic consolidation experiments our results highlight the formation of methane hydrate does not affect the integrity of sediment skeletons if the effective stress previously applied on the skeleton remains constant which indicates that methane hydrate would not actively support the load subsequent external load applied to the sediments after hydrate formation can be supported by hydrate secondly hydrate as well as hydrate bearing sediments exhibit creep behavior as hydrate creeps the load transfers to the sediment skeleton with time and hydrate gradually retreats from the status of load bearing when hydrate saturation is low and the coexisting pore fluid can percolate through sediments the local deformation of hydrate due to sediment consolidation induces excess pore pressure which dissipates by pushing out the pore fluid when the coexisting pore fluid is enclosed in hydrate mass in high hydrate saturation environments the dissipation of excess pore pressure relies on the viscous flow of hydrate this pressure dissipation could last for millions of years according to analytical analysis based on terzaghi s consolidation theory during which hydrate cannot completely escape the status of load bearing these observations conclude that load bearing is a dynamic status rather than a stagnant pore habit countering conventional thinking that load bearing joins grain coating cementing and pore filling as a pore habit of gas hydrate

anisotropy of magnetic susceptibility ams records synsedimentary deformation kinematics at pico del aguila anticline pyrenees spain

geologic implications of gas hydrates in the offshore of india krishna godavari basin mahanadi basin andaman sea kerala konkan basin gas hydrate resource assessments that indicate enormous global volumes of gas present within hydrate accumulations have been one of the primary driving forces behind the growing interest in gas hydrates gas hydrate volumetric estimates in recent years have focused on documenting the geologic parameters in the gas hydrate petroleum system that control the occurrence of gas hydrates in nature the primary goals of this report are to review our present understanding of the geologic controls on the occurrence of gas hydrate in the offshore of india and to document the application of the petroleum system approach to the study of gas hydrates national gas hydrate program of india executed the national gas hydrate program expedition 01 nghp 01 in 2006 in four areas located on the eastern and western margins of the indian peninsula and in the andaman sea these areas have experienced very different tectonic and depositional histories the peninsular margins are passive continental margins resulting from a series of rifting episodes during the breakup and dispersion of gondwanaland to form the present indian ocean the andaman sea is bounded on its western side by a convergent margin where the indian plate lithosphere is being subducted beneath southeast asia nghp 01 drilled logged and or cored 15 sites 31 holes in the krishna godavari basin 4 sites 5 holes in the mahanadi basin 1 site 2 holes in the andaman sea and 1 site 1 hole in the kerala konkan basin holes were drilled using standard drilling methods for the purpose of logging while drilling and dedicated wireline logging as well as through the use of a variety of standard coring systems and specialized pressure coring systems nghp 01 yielded evidence of gas hydrate from downhole log and core data obtained from all the sites in the krishna godavari basin the mahanadi basin and in the andaman sea the site drilled in the kerala konkan basin during nghp 01 did not yield any evidence of gas hydrate most of the downhole log inferred gas hydrate and core recovered gas hydrate were characterized as either fracture filling in clay dominated sediments or as pore filling or grain displacement particles disseminated in both fine and coarse grained sediments geochemical analyses of gases obtained from sediment cores recovered during nghp 01 indicated that the gas in most all of the hydrates in the offshore of india is derived from microbial sources only one site in the andaman sea exhibited limited evidence of a thermogenic gas source the gas hydrate petroleum system concept has been used to effectively characterize the geologic controls on the occurrence of gas hydrates in the offshore of india

paleogene building of the bolivian orocline tectonic restoration of the central andes in 2 d map view using available information on the magnitude and age of tectonic shortening as well as paleomagnetically determined tectonic rotations we have run a series of 2 d map view restorations of the central andes neogene shortening in the foreland belt induced only slight orogenic curvature of the central andes the constraints on the ages of the large observed fore arc rotations average of 37 counterclockwise in southern peru and 29 clockwise in northern chile indicate that the bolivian orocline formed during the eocene oligocene as a consequence of differential shortening focused in the eastern cordillera to minimize local block rotations along the fore arc the restoration that best fits the central andean rotation pattern requires about 400 km of total paleogene plus neogene shortening near the arica bend this value corresponds to the upper bound of estimates of maximum horizontal shortening for the central andes along strike variations in horizontal shortening in the back arc induced bending of the continental margin block rotations with fore arc along strike extension and or orogen parallel transport of upper crustal material toward the symmetry axis of the orocline

pressure core based study of gas hydrates in the ulleung basin and implication for geomechanical controls on gas hydrate occurrence pressure coring technology enables the recovery of natural gas hydrate bearing sediments without pressure release and thus without gas hydrate dissociation a total of 21 pressure cores were successfully recovered from the ulleung basin east sea korea during the second gas hydrate drilling expedition in the ulleung basin ubgh2 recovered pressure core samples were utilized to characterize hydrate occurrences and formation mechanisms with non destructive physical property scans x ray ct scans and controlled degassing experiments findings include 1 the p wave velocity in mud rich sediments with grain displacing hydrate increases with decreasing bulk density since hydrate displaces sediment grains and lowers the bulk density 2 the p wave velocity in sand with pore filling hydrate is mostly affected by hydrate saturation rather than bulk density 3 the p wave velocity trend with hydrate saturations for pore filling hydrates follows pore filling model at low hydrate saturations and gradually deviates from pore filling model toward cementation model as hydrate saturation increases 4 gas recovery times during controlled core degassing experiments are proportional to both hydrate saturations and porosities 5 at site ubgh2 3 the thickness of both sub horizontal and sub vertical grain displacing hydrates decreases with depth while the number of sub vertical hydrates does not decrease with depth implying that the formation mechanisms of sub horizontal and sub vertical hydrates differ while growth mechanisms are similar to each other in different growth directions 6 the angle and thickness of grain displacing hydrate bearing fractures are a function of the overburden stress and the hydraulic conductivity but the main governing factor is the overburden stress