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

simulation of excavations in jointed rock masses using a practical equivalent continuum approach a simple practical equivalent continuum numerical model previously presented by sitharam et al int j rock mech min sci 38 2001 437 for simulating the behaviour of jointed rock mass has been incorporated in the commercial finite difference programme fast lagrangian analysis of continua flac this model estimates the properties of jointed rock mass from the properties of intact rock and a joint factor j f which is the integration of the properties of joints to take care of the effects of frequency orientation and strength of joint a fish function has been written in flac specially for modelling jointed rocks this paper verifies the validity of this model for three different field case studies namely two large power station caverns one in japan and the other in himalayas and kiirunavara mine in sweden sequential excavation was simulated in the analysis by assigning null model available in flac to the excavated rock mass in each stage the settlement and failure observations reported from field studies for these different cases were compared with the predicted observations from the numerical analysis in this study the results of numerical modelling applied to these different cases are systematically analysed to investigate the efficiency of the numerical model in estimating the deformations and stress distribution around the excavations results indicated that the model is capable of predicting the settlements and failure observations made in field fairly well results from this study confirmed the effectiveness of the practical equivalent continuum approach and the joint factor model used together for solving various problems involving excavations in jointed rocks

gas geochemistry of the mount elbert gas hydrate stratigraphic test well alaska north slope implications for gas hydrate exploration in the arctic abstract gases were analyzed from well cuttings core gas hydrate and formation tests at the bpxa doe usgs mount elbert gas hydrate stratigraphic test well drilled within the milne point unit alaska north slope the well penetrated a portion of the eileen gas hydrate deposit which overlies the more deeply buried prudhoe bay milne point west sak and kuparuk river oil fields gas sources in the upper 200 m are predominantly from microbial sources c1 isotopic compositions ranging from 86 4 to 80 6 the c1 isotopic composition becomes progressively enriched from 200 m to the top of the gas hydrate bearing sands at 600 m the tested gas hydrates occur in two primary intervals units d and c between 614 0 m and 664 7 m containing a total of 29 3 m of gas hydrate bearing sands the hydrocarbon gases in cuttings and core samples from 604 to 914 m are composed of methane with very little ethane the isotopic composition of the methane carbon ranges from 50 1 to 43 9 with several outliers generally decreasing with depth gas samples collected by the modular formation dynamics testing mdt tool in the hydrate bearing units were similarly composed mainly of methane with up to 284 ppm ethane the methane isotopic composition ranged from 48 2 to 48 0 in the c sand and from 48 4 to 46 6 in the d sand methane hydrogen isotopic composition ranged from 238 to 230 with slightly more depleted values in the deeper c sand these results are consistent with the concept that the eileen gas hydrates contain a mixture of deep sourced microbially biodegraded thermogenic gas with lesser amounts of thermogenic oil associated gas and coal gas thermal gases are likely sourced from existing oil and gas accumulations that have migrated up dip and or up fault and formed gas hydrate in response to climate cooling with permafrost formation

mount elbert gas hydrate stratigraphic test well alaska north slope coring operations core sedimentology and lithostratigraphy abstract in february 2007 bp exploration alaska the u s department of energy and the u s geological survey completed the bpxa doe usgs mount elbert gas hydrate stratigraphic test well mount elbert well in the milne point unit on the alaska north slope the program achieved its primary goals of validating the pre drill estimates of gas hydrate occurrence and thickness based on 3 d seismic interpretations and wireline log correlations and collecting a comprehensive suite of logging coring and pressure testing data the upper section of the mount elbert well was drilled through the base of ice bearing permafrost to a casing point of 594 m 1950 ft approximately 15 m 50 ft above the top of the targeted reservoir interval the lower portion of the well was continuously cored from 606 m 1987 ft to 760 m 2494 ft and drilled to a total depth of 914 m ice bearing permafrost extends to a depth of roughly 536 m and the base of gas hydrate stability is interpreted to extend to a depth of 870 m coring through the targeted gas hydrate bearing reservoirs was completed using a wireline retrievable system the coring program achieved 85 recovery of 7 6 cm 3 in diameter core through 154 m 504 ft of the hole an onsite team processed the cores collecting and preserving approximately 250 sub samples for analyses of pore water geochemistry microbiology gas chemistry petrophysical analysis and thermal and physical properties eleven samples were immediately transferred to either methane charged pressure vessels or liquid nitrogen for future study of the preserved gas hydrate additional offsite sampling analyses and detailed description of the cores were also conducted based on this work one lithostratigraphic unit with eight subunits was identified across the cored interval subunits ii and va comprise the majority of the reservoir facies and are dominantly very fine to fine moderately sorted quartz feldspar and lithic fragment bearing to rich sands lithostratigraphic and palynologic data indicate that this section is most likely early eocene to late paleocene in age the examined units contain evidence for both marine and non marine lithofacies and indications that the depositional environment for the reservoir facies may have been shallower marine than originally interpreted based on pre drill wireline log interpretations there is also evidence of reduced salinity marine conditions during deposition that may be related to the paleo climate and depositional conditions during the early eocene

deformation characteristics of a roadway in steeply inclined formations and its improved support abstract mining roadways in steeply inclined rock layers commonly experience severe deformation in form of large asymmetric deformation roof subsidence and floor heave which significantly threaten the stability of a roadway using a coal exploration roadway in anhui province china as a case study the deformation characteristics of a roadway in steeply inclined rock formations and the corresponding improved support scheme is analysed by numerical simulation the simulation is performed using a cohesive element to consider the influence of geologic bedding plane around the roadway the results show that due to the spatial relationship of the roadway and the two bedding planes i e interfaces rocks above the roadway move downward along the interface while rocks below the roadway move upward along the interface the maximum deformation occurs along the upper left and lower right sides of the roadway surface which accounts for the large leaning asymmetric deformation of the roadway right inclination an improved support scheme for the roadway is proposed using long cables to restrain severe deformation short cables and enclosed u shaped steel sets to improve the ground stress state the proposed scheme can effectively restrain floor heave manage large asymmetrical deformation compared to the original scheme

rock burst process of limestone and its acoustic emission characteristics under true triaxial unloading conditions abstract the rock failure process is associated with acoustic emission ae hence violent rock failure processes such as rock burst under different stress paths in laboratory can be studied using the ae monitoring technique in this paper single face dynamic unloading tests under true triaxial condition were carried out for paleozonic marine sedimentation limestone samples produced by blocks cored from 1140 m depth in jiahe coal mine of china frequency spectra analysis was conducted for the full wave ae data and figures showing the relationship of frequency amplitude of ae signals in rock burst stages were obtained the dynamical damage process and characteristics of limestone under the test condition are summarized it is found from the fast fourier transformation fft analysis of the ae signals that there exist two main frequency ranges i e lower 60 100 khz and higher 170 190 khz for the samples when the limestone samples are under relatively lower stress the ae signals are characterized by high frequency and low amplitude as the stress increases the ae signals tend to shift more towards a signature of high amplitude near the bursting failure of the rock samples it is observed that there are much higher amplitude and lower frequency events the ae accumulated energy release rapidly increases from the unloading state of the rock samples to its failure the dynamic unloading test facility provides a useful tool to gain an insight into the characteristics of rock bursts

gas hydrate characterization and grain scale imaging of recovered cores from the mount elbert gas hydrate stratigraphic test well alaska north slope abstract using cryogenic scanning electron microscopy csem powder x ray diffraction and gas chromatography methods we investigated the physical states grain characteristics gas composition and methane isotopic composition of two gas hydrate bearing sections of core recovered from the bpxa doe usgs mount elbert gas hydrate stratigraphic test well situated on the alaska north slope the well was continuously cored from 606 5 m to 760 1 m depth and sections investigated here were retrieved from 619 9 m and 661 0 m depth x ray analysis and imaging of the sediment phase in both sections shows it consists of a predominantly fine grained and well sorted quartz sand with lesser amounts of feldspar muscovite and minor clays cryogenic sem shows the gas hydrate phase forming primarily as a pore filling material between the sediment grains at approximately 70 75 saturation and more sporadically as thin veins typically several tens of microns in diameter pore throat diameters vary but commonly range 20 120 microns gas chromatography analyses of the hydrate forming gas show that it is comprised of mainly methane 99 9 indicating that the gas hydrate is structure i here we report on the distribution and articulation of the gas hydrate phase within the cores the grain morphology of the hydrate the composition of the sediment host and the composition of the hydrate forming gas

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

chemical and structural characteristics of gas hydrates from the haima cold seeps in the qiongdongnan basin of the south china sea abstract crystalline structure cage occupancy and gas composition are important gas hydrate characteristics which can be used to calculate the gas hydrate s stability and to estimate the energy potential in may and october of 2015 a guangzhou marine geological survey team investigated two sites in the haima cold seeps in the qiongdongnan basin northern south china sea they recovered massive gas hydrate samples by conventional gravity coring after the shenhu sea area and dongsha sea area the qiongdongnan basin became a new area on the northern slope of the south china sea where gas hydrates have been found in order to reveal the structural and geochemical characteristics of the natural gas hydrates samples were analyzed by micro raman spectroscopy and x ray diffraction under ambient pressure and low temperature conditions the results indicate that the gas hydrate samples from the haima cold seeps are typical structure i hydrates with a hydration number of 6 12 6 19 in addition trace amounts of h2s trapped in the hydrate were identified based on its characteristic vibrational signature the gas composition and 13c ch4 of the hydrate bound gas samples were analyzed for gas source correlation all of the gas samples are dominated by methane with small amounts of ethane and propane and had relatively light 13c ch4 indicating that all of the hydrate bound gases are mixtures of biogenic and thermogenic gas the thermogenic gas is inferred to be mainly derived from the coal layers of the late miocene pliocene yacheng formation in the northern lingshui sag

pre and post drill comparison of the mount elbert gas hydrate prospect alaska north slope abstract in 2006 the united states geological survey usgs completed a detailed analysis and interpretation of available 2 d and 3 d seismic data along with seismic modeling and correlation with specially processed downhole well log data for identifying potential gas hydrate accumulations on the north slope of alaska a methodology was developed for identifying sub permafrost gas hydrate prospects within the gas hydrate stability zone in the milne point area the study revealed a total of 14 gas hydrate prospects in this area in order to validate the gas hydrate prospecting protocol of the usgs and to acquire critical reservoir data needed to develop a longer term production testing program a stratigraphic test well was drilled at the mount elbert prospect in the milne point area in early 2007 the drilling confirmed the presence of two prominent gas hydrate bearing units in the mount elbert prospect and high quality well logs and core data were acquired the post drill results indicate pre drill predictions of the reservoir thickness and the gas hydrate saturations based on seismic and existing well data were 90 accurate for the upper unit hydrate unit d and 70 accurate for the lower unit hydrate unit c confirming the validity of the usgs approach to gas hydrate prospecting the mount elbert prospect is the first gas hydrate accumulation on the north slope of alaska identified primarily on the basis of seismic attribute analysis and specially processed downhole log data post drill well log data enabled a better constraint of the elastic model and the development of an improved approach to the gas hydrate prospecting using seismic attributes

effect of sand grain size on simulated mining induced overburden failure in physical model tests abstract to investigate the influence of sand grain size sgs on mining induced overburden failure in physical model tests uniaxial compressive experiments on rock like material with various sgss were performed and two sgss 0 0 5 and 0 5 1 mm were selected the young s modulus uniaxial compressive strength and tangent modulus were larger in rock like material samples with finer sgs and the failure mode changed from mostly shear failure to tensile failure with rising sgs as the mechanical characteristics of coarser sand samples are weaker the overburden breakage distance was shorter in the coarser sand model and the ratio of the average breakage distance between the two models was 1 688 the extent of the overburden fracture was heavier in the coarser sand model and closer pattern to that of the actual coal mine a large database of the heights of the overburden caved zone hcz and fractured zone hfz values with various mining height hm based on previous studies was compiled to obtain best fit parabolic empirical formulas the hcz hm and hfz hm ratios measured in the field were similar to those estimated by the proposed empirical formulas the discrepancy between the physical model test and field measurement may be explained by the fracture pattern in the overburden of the caved zone in the form of layered rectangles unlike the polygonal forms in the coal mine we propose four recommendations to optimize the physical model for such tests from the perspective of sgs the results and recommendations presented here can provide a useful guide for coal mining scientists and engineers designing models for testing of coal mining conditions

a case study on large deformation failure mechanism of deep soft rock roadway in xin an coal mine china abstract large deformation of soft rock roadway has always been a major difficulty in deep mining practices this paper describes a case study of the failure mechanisms and stability control technology of deep roadway with soft rock mass in xin an coal mine in gansu province china rock mass properties around the roadway are evaluated using geological strength index gsi based on the field data and the mechanical properties of intact rock specimens the universal discrete element code udec software program is adopted to establish the numerical model of a ventilation roadway in xin an coal mine and the micro parameter calibration is conducted with the rock mass properties the failure process of roadway under unsupported and primary support conditions is simulated the deformation stress and crack evolution characteristics were clearly illustrated failure first appears around the roadway surface because there is a high stress concentration around the roadway surface after excavation the failure area propagates further into the deep surrounding rock as the stresses applied on the surface gradually decreases finally resulting in a large zone of stress relaxation there exists a large scale of tensile failure in the shallow rock which leads to swelling and fracturing around the roadway the primary support is low in strength with no support in the floor which results in serious floor heave side shrinking and roof subsidence a new bolt cable mesh shotcrete shell combined support is proposed to support the ventilation roadway the monitoring data in the experiment section show that the new support design successfully controls the large deformation of the roadway which can provide helpful references for support designing of engineering in deep soft rock roadway

the afar depression transition between continental rifting and sea floor spreading abstract detailed geophysical and geological studies were undertaken in the 1970 s in the afar depression ethiopia in order to study the processes of continental break up occurring in this unique setting the afar is located between the ethiopian and somali plateaus and the red sea we have re evaluated the available seismic refraction and gravity data using modern interpretation techniques and incorporated new information derived from magnetic gravity seismicity and seismic refraction data the results of the re evaluation indicate that the afar depression is a transition zone between the continental rifts of kenya and the present ongoing sea floor spreading of the red sea and the gulf of aden in the depression itself the crust is greatly attenuated and is underlain by a low velocity 7 4 7 5 km s high temperature upper mantle material however it is still a continental crust which thins to the northeast and east towards the red sea and the gulf of aden it is not a newly formed oceanic crust as has been suggested in the past the trends of the areas of crustal thinning are indicated by the gravity anomalies the trend of the ethiopian rift reaches south afar where the trend of crustal thinning changes and becomes parallel to the red sea trend it is offset en echelon from the spreading area of the red sea which is marked by an alignment of gravity maxima the gulf of aden trend continues west towards the ethiopian rift the gravity trends coincide with areas of maximum crustal thinning and may thus suggest a possible triple junction in development

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

multi peak deformation behavior of jointed rock mass under uniaxial compression insight from particle flow modeling abstract evaluation of mechanical properties of jointed rock mass is very important for geological engineering problems related to underground opening slope stability dam foundation and hydraulic fracturing etc it is generally known that both strength and deformability of rock mass may change with joint geometry and arrangement by pfc particle flow code modeling this paper aims at understanding the damage mechanism of the multi peak deformation behavior of jointed rock mass with different joint orientations and continuity factors under uniaxial compression observed in the physical model tests with the smooth joint contact model not only has the inherent roughness in conventional joint model been avoided but also we can monitor the joint aperture number of closed joints and forces acting on the joints during the damage process it is shown that mobilization of joint strength plays an important role in the multi peak deformation behavior of rock mass if the joint strength is slightly mobilized or immobilized i e most joints keep open during the test strain softening occurs however if the joint strength is significantly or fully mobilized yielding platform or strain hardening may happen

physical modeling of an underground roadway excavation in geologically 45 inclined rock using infrared thermography abstract physical modeling of excavation of a roadway tunnel in the geologically 45 inclined rock strata by using a newly developed physical modeling approach the so called physically finite elemental slab assemblage pfesa together with infrared ir thermography were conducted for visualization and observation of the progressive development of the excavation damaged zone edz the excavation was schemed as two phases i e phase 1 the full face excavation and phase 2 the staged excavation the experiment was performed under unbalanced confinement found in underground coal mining the relative temperatures of the excavation zone were mapped by the ir camera in real time and over the entire field into thermography series which were processed using such procedures as statistics noise removal and spectral frequency analysis for image feature extraction irt defined as the statistical mean of the thermography matrix was used as a measure of rock responses characterizing the full face excavation and the staged excavation as a multi linearity and nonlinearity processes respectively by its time marching scheme the temporal and spatial evolutions of the edz were described in detail by the denoised thermographies directional propagations of the excavation induced stress wave were characterized by the spectral frequency analysis of the resultant thermographies

study on deformation failure mechanism and support technology of deep soft rock roadway abstract the roadway support has always been a difficult problem in the mining engineering especially in the deep soft rock roadway whether it can provide endurable and effective support directly affects the safety production and sustainable development of the mine in order to solve the supporting issues it is necessary to make the deformation failure mechanism of deep soft rock roadway clear this paper describes a case study of the deformation failure mechanism and support technology of deep roadway with soft rock mass in no 2 mine zone of jinchuan mine that is located in gansu province china based on a detailed field investigation and previous research experience the modes influencing factors laws and mechanisms of deformation failure in the roadway are summarized then the primary combined supporting scheme double layer bolt mesh shotcrete and u shaped steel is evaluated through numerical simulation calculation and onsite experiments to make up for the shortcomings of the primary support an improved combined supporting scheme double layer long bolt mesh shotcrete and cfst concrete filled steel tube is proposed the results of numerical simulation field monitoring and economic analysis show that the new support can control the deformation of the roadway effectively and has a high cost performance finally several suggestions for supporting in deep soft rock roadway are put forward aiming at serve as a reference for other engineering

pore scale investigation of permeability evolution during hydrate formation using a pore network model based on x ray ct abstract permeability in hydrate bearing sediment critically governs fluid flow and determines hydrate nucleation growth and distribution making it important to characterize the evolution of permeability with respect to water and gas during hydrate formation this study uses ct scanning of krypton hydrate formation in silica sand using the excess gas method together with a pore network model to investigate variations in hydrate morphology and associated permeation the results show that during hydrate formation the growth habit mainly varies from grain coating to patchy with an increase in hydrate saturation however at relatively low saturation hydrate preferentially grows as a grain cementing habit theoretical models of a capillary tube and of a kozeny grain both predict that permeability in grain coating hydrates will be higher than in patchy hydrates we thus recognise a correlation of permeability and hydrate saturation for multiple growth habits that is of interest for gas production from hydrate reservoirs under lower water saturation there is a decrease in relative permeability to water but an increase in relative permeability to gas due to the reduction in pore shape factors conversely an upward shift in relative permeability to water and a downward shift in relative permeability to gas is found with hydrate formation under higher water saturation owing to the jamin effect steeper curves of relative permeability to gas and water with increasing hydrate saturation resulted in a reduction of the co cementation zone for water and gas even if or though no gas migrates the results suggest that due to the low relative permeability of gas higher water saturation sediments result in an excess water yield accompanied by low gas production that is not desirable for natural gas hydrate production therefore improving the permeability and weakening the jamin effect are critical for gas production in marine hydrate reservoirs especially in low permeability sediments

estimating pore space gas hydrate saturations from well log acoustic data relating pore space gas hydrate saturation to sonic velocity data is important for remotely estimating gas hydrate concentration in sediment in the present study sonic velocities of gas hydrate bearing sands are modeled using a three phase biot type theory in which sand gas hydrate and pore fluid form three homogeneous interwoven frameworks this theory is developed using well log compressional and shear wave velocity data from the mallik 5l 38 permafrost gas hydrate research well in canada and applied to well log data from hydrate bearing sands in the alaskan permafrost gulf of mexico and northern cascadia margin velocity based gas hydrate saturation estimates are in good agreement with nuclear magneto resonance and resistivity log estimates over the complete range of observed gas hydrate saturations

physical properties of sediment from the mount elbert gas hydrate stratigraphic test well alaska north slope this study characterizes cored and logged sedimentary strata from the february 2007 bp exploration alaska department of energy u s geological survey bpxa doe usgs mount elbert gas hydrate stratigraphic test well on the alaska north slope ans the physical properties program analyzed core samples recovered from the well and in conjunction with downhole geophysical logs produced an extensive dataset including grain size water content porosity grain density bulk density permeability x ray diffraction xrd mineralogy nuclear magnetic resonance nmr and petrography this study documents the physical property interrelationships in the well and demonstrates their correlation with the occurrence of gas hydrate gas hydrate gh occurs in three unconsolidated coarse silt to fine sand intervals within the paleocene and eocene beds of the sagavanirktok formation unit d gh 614 4 m 627 9 m unit c gh1 649 8 m 660 8 m and unit c gh2 663 2 m 666 3 m these intervals are overlain by fine to coarse silt intervals with greater clay content a deeper interval unit b is similar lithologically to the gas hydrate bearing strata however it is water saturated and contains no hydrate in this system it appears that high sediment permeability k is critical to the formation of concentrated hydrate deposits intervals d gh and c gh1 have average plug intrinsic permeability to nitrogen values of 1700 md and 675 md respectively these values are in strong contrast with those of the overlying gas hydrate free sediments which have k values of 5 7 md and 49 md respectively and thus would have provided effective seals to trap free gas the relation between permeability and porosity critically influences the occurrence of gh for example an average increase of 4 in porosity increases permeability by an order of magnitude but the presence of a second fluid e g methane from dissociating gas hydrate in the reservoir reduces permeability by more than an order of magnitude published by elsevier ltd

stability assessment of an ancient landslide crossed by two coal mine tunnels abstract in 2005 when two main tunnels were excavated in faer coal mine guizhou province china an unknown ancient landslide subsequently named dazhai landslide was encountered roof caving large convergence and severe support damage in the tunnels as well as several ground subsidence occurred the two tunnels have been kept stable after an inner supporting treatment in 2008 however since a heavy rainfall in july 2010 some transverse cracks were observed at the landslide toe determining significant additional costs over the normal administration of the mine invited by the owner we performed a comprehensive investigation to evaluate the stability of dazhai landslide crossed by two main tunnels firstly field surveys and mappings were completed to obtain a preliminary delineation of the landslide surface and a geological drilling along the central landslide axis was accomplished to depict the sliding surface after that a monitoring system containing a gps rtk network and six observation sections in one tunnel were established and a 12 month monitoring was conducted moreover to obtain an overall comprehension numerical simulations were carried out by using geostudio and flac 3d software the results from site drilling monitoring and simulations indicate that the dazhai landslide is stable as a whole and only local shallow landslides might occur the local instability of dazhai landslide has limited impact on the safety of the two main tunnels this conclusion has led to a budget savings of over rmb 40 million

precursors for rock fracturing and failure part i irr image abnormalities abstract there are many precursors including the abnormality of infrared radiation irr for rock fracturing and failure as the comprehensive effect of rock thermoelasticity and rock friction the study of the irr abnormality of loaded rock as one of the important issues of remote sensing rock mechanics rsrm is facilitated by the fast development of ir remote sensing imaging technology in view of energy input and consumption by the loading system comprised of loader rock and air the mechanism of surface irr from loaded rock is studied the concepts that surface irr is the comprehensive effect of a series of physical mechanical processes inside loaded rock and that the thermoelastic effect and the frictional thermal effect are two of the main mechanisms are presented here based on retrospective investigation of the fundamental experiments on rsrm during the past decade it is concluded that there are two kinds of irr abnormality as precursors of rock fracturing and failure irr image abnormality and irr temperature curve abnormality the spatial temporal evolution of abnormal surface irr images of loaded rock in a condition of uniaxial stress compressive shear biaxial stress frictional slide and impact is systematically analyzed the fact that large irr can occur in the fracturing center of compressively loaded and shearing fractured strong and brittle rock is also revealed finally the relation between rock stress and irr temperature are studied based on thermomechanical coupling theory for solid materials it is concluded that irr image abnormalities are important precursors for rock fracturing and meaningful for the forecast of rockbursts and tectonic earthquakes

an application of the response function technique to profiles of bathymetry and gravity in the gulf of aden summary the relationship between bathymetry and gravity in the eastern and the western gulf of aden is analysed by computing response functions the form of the response functions indicates that the short wavelength topography is isostatically compensated the most appropriate mechanism of compensation is one in which the topography is not locally compensated but regionally compensated by flexure of the lithosphere though the sets of profiles from the eastern and the western gulf of aden are separated by only 500 750 km the observed response functions are very different the lithosphere in the eastern gulf of aden can be modelled by an elastic plate 15 3 km thick whereas an elastic plate 3 2km thick is probably an appropriate model for the lithosphere in the western gulf of aden a different mechanism of isostasy the pratt operates in the compensation of the long wavelength topography of the mid ocean ridge in the gulf of aden a larger negative broad bouguer gravity anomaly across the western gulf of aden than across the east indicates that upper mantle temperatures increase from east to west the long wavelength shallowing of the gulf of aden and increasing elevation of the adjacent continents from east to west are therefore probably mainly the result of thermal uplift the subdued nature of the median valley and consequently other short wave length topography in the west can be explained by hot low viscosity asthenosphere and the inferred thin lithosphere in the west also suggests high temperature mantle finally a magnetic anomaly superimposed on the axial anomaly which is probably related to the depth of the curie temperature is more common in the western gulf of aden than in the east and this is also consistent with upper mantle temperatures increasing to the west there are a number of similarities between the mid ocean ridge in the western gulf of aden and the reykjanes ridge it is suggested that the western gulf of aden is anomalous because of its proximity to the afar hot spot in the same way that the reykjanes ridge is often considered to be anomalous because of its proximity to the iceland hot spot

infrared radiation of rock impacted at low velocity impact is one of the issues in dynamic mechanics the impacting velocities ranging from low to hypervelocity usually the reaction of the impacted material is the main purpose of research on high velocity or hypervelocity impacts 1 3 such as piercing and blasting recent research on low velocity impact emphasizes the dynamic change of material parameters and the transient processes 4 however research on solid impact whatever the velocity has common features

20 years of excavation response studies at aecl s underground research laboratory incremental development of a rock mechanics rock fracturing and excavation stability knowledge base has been ongoing at atomic energy of canada limited s aecl s underground research laboratory url since shaft excavation commenced in 1982 excavation response experiments conducted as part of shaft construction recorded displacements shaft convergence stress changes and microseismic events in the rock as excavation progressed an excavation response test at the 240 level of the url involved similar monitoring as well as pore pressure measurements of a horizontal tunnel excavated through a subvertical water bearing fracture these precursor studies led to a series of experiments in the more highly stressed rock at the 420 level of the url to investigate the formation of rock damage around tunnels and to assess the factors that influence the stability of excavations the first of these experiments was the mine by experiment an excavation response study involving a mechanically excavated cylindrical tunnel in a pre instrumented rock volume the heated failure tests were subsequently conducted in the same rock volume to assess the influence of thermal loading on damage development these investigations were complemented by studies of borehole breakouts in adjacent excavations the excavation stability study which involved excavating ten tunnel segments of different geometry to assess the effects of excavation design on stability and damage development followed these experiments the tunnel sealing experiment focused on developing sealing technologies also provided insight into the excavation response of the rock mass the excavation response experiments at the url culminated in the thermal mechanical stability study tmss a comprehensive study to link characterization numerical modeling monitoring and design of underground excavations this paper provides an overview of the various experiments and studies leading up to the tmss highlighting the advances in our fundamental understanding of rock mechanics related to underground excavations and in our means of designing stable underground openings with minimal excavation damage

mapping the crust mantle boundary beneath afar depression abstract the funnel shaped afar depression in the horn of africa situated at the separation zones of the nubian somalian and arabian plates represents a triple junction between the main ethiopian rift the red sea and gulf of aden rifts this depression occupies an important place in that it is the only emerged triple junction in the world assuming that the mechanism of compensation is one in which the topography is regionally compensated by the flexuring of the elastic plate and that linear relationship exists between the gravity field of the compensation and the topography isostatic correction isostatic anomaly and moho depth maps are computed for the depression the results show that nonlinear elements are small in afar and hence the crust mantle interface beneath afar modelled using admittance technique compares very well with the existing seismic results the results also show that there is crustal attenuation to the north and east and that there is an under compensation in the north that may be due to the upwelling of mantle material along the active axis

energy resource potential of natural gas hydrates the discovery of large gas hydrate accumulations in terrestrial per mafrost regions of the arctic and beneath the sea along the outer continental margins of the world s oceans has heightened interest in gas hydrates as a possible energy resource however significant to potentially insurmountable technical issues must be resolved be fore gas hydrates can be considered a viable option for affordable supplies of natural gas the combined information from arctic gas hydrate studies shows that in permafrost regions gas hydrates may exist at subsurface depths ranging from about 130 to 2000 m the presence of gas hydrates in offshore continental margins has been inferred mainly from anomalous seismic reflectors known as bottom simulating reflectors that have been mapped at depths below the sea floor ranging from about 100 to 1100 m current estimates of the amount of gas in the world s marine and permafrost gas hydrate accumulations are in rough accord at about 20 000 trillion m3 disagreements over fundamental issues such as the volume of gas stored within delineated gas hydrate accumulations and the concentration of gas hydrates within hydrate bearing strata have demonstrated that we know little about gas hydrates recently however several countries including japan india and the united states have launched ambitious national projects to further examine the resource potential of gas hydrates these projects may help answer key questions dealing with the properties of gas hydrate reservoirs the design of production systems and most important the costs and economics of gas hydrate production

the gravity field of the red sea and east africa abstract reevaluation of all gravity data from the red sea the gulf of aden and east africa permitted the compilation of a new bouguer anomaly map the intensity of the gravity field and its regional pattern correlate closely with the topographic features of the region the maximum bouguer values 100 mgal are located over the median troughs of the red sea and gulf of aden dense juvenile oceanic crust in these rifts and intruding magmas in stretched continental areas produce excess mass responsible for the anomaly highs in the red sea the orientation of the gravity highs is nw se in the south turning to ne sw in the north almost parallel to the aqaba dead sea strike this pattern reveals that the present basin axis is not identical with that which formed the tertiary coastal margins and the pre red sea zones of crustal weakness in the gulf of aden new oceanic crust along the tadjura trench and its eastward extension is also expressed in the bouguer anomaly map by gravity highs and a sharp bending of the isolines a maximum of approx 150 mgal is located over the central section of the sheba ridge bouguer gravity values over the east african and yemen plateaus are of the order of 180 to 240 mgal indicating significant crustal thickening on the somali plateau the marda fault also has a strong gravity signature that can be traced towards somalia by constraining crustal thickness and structure with seismic data and density values from the velocity distribution by means of the nafe drake and birch relationships we computed density models for the crust and upper mantle the crustal thickness is of the order of 40 km beneath the plateaus and only 5 to 6 km at the oceanized parts in the central and southern portions of the red sea median trough the flanks of the southern red sea and the corresponding arabian side are underlain by 12 to 16 km thick stretched continental type crust oceanization offshore sudan and egypt is asymmetrical the continental crust terminates abruptly at about 20 km off the coastline followed by an oceanic crust of early miocene age that was produced in pull apart basins by contrast the eastern side of the red sea trough offshore saudi arabia is floored by stretched continental crust that extends far into the sea seafloor spreading and the generation of oceanic crust in organized spreading centres are limited to the median troughs off sudan and the northern part of ethiopia and commenced approx 5 m y bp they are absent in the northern red sea where crustal fracturing occurs only in pull apart basins of dead sea aqaba orientation distributed in en echelon pattern

examination of core samples from the mount elbert gas hydrate stratigraphic test well alaska north slope effects of retrieval and preservation abstract collecting and preserving undamaged core samples containing gas hydrates from depth is difficult because of the pressure and temperature changes encountered upon retrieval hydrate bearing core samples were collected at the bpxa doe usgs mount elbert gas hydrate stratigraphic test well in february 2007 coring was performed while using a custom oil based drilling mud and the cores were retrieved by a wireline the samples were characterized and subsampled at the surface under ambient winter arctic conditions samples thought to be hydrate bearing were preserved either by immersion in liquid nitrogen ln or by storage under methane pressure at ambient arctic conditions and later depressurized and immersed in ln eleven core samples from hydrate bearing zones were scanned using x ray computed tomography to examine core structure and homogeneity features observed include radial fractures spalling type fractures and reduced density near the periphery these features were induced during sample collection handling and preservation isotopic analysis of the methane from hydrate in an initially ln preserved core and a pressure preserved core indicate that secondary hydrate formation occurred throughout the pressurized core whereas none occurred in the ln preserved core however no hydrate was found near the periphery of the ln preserved core to replicate some aspects of the preservation methods natural and laboratory made saturated porous media samples were frozen in a variety of ways with radial fractures observed in some ln frozen sands and needle like ice crystals forming in slowly frozen clay rich sediments suggestions for hydrate bearing core preservation are presented

theoretical modeling insights into elastic wave attenuation mechanisms in marine sediments with pore filling methane hydrate the majority of presently exploitable marine methane hydrate reservoirs are likely to host hydrate in disseminated form in coarse grain sediments for hydrate concentrations below 25 40 disseminated or pore filling hydrate does not increase elastic frame moduli thus making impotent traditional seismic velocity based methods here we present a theoretical model to calculate frequency dependent p and s wave velocity and attenuation of an effective porous medium composed of solid mineral grains methane hydrate methane gas and water the model considers elastic wave energy losses caused by local viscous flow both i between fluid inclusions in hydrate and pores and ii between different aspect ratio pores created when hydrate grows the inertial motion of the frame with respect to the pore fluid biot s type fluid flow and gas bubble damping the sole presence of pore filling hydrate in the sediment reduces the available porosity and intrinsic permeability of the sediment affecting biot s type attenuation at high frequencies our model shows that attenuation maxima due to fluid inclusions in hydrate are possible over the entire frequency range of interest to exploration seismology 1 106 hz depending on the aspect ratio of the inclusions whereas maxima due to different aspect ratio pores occur only at sonic to ultrasound frequencies 104 106 hz this frequency response imposes further constraints on possible hydrate saturations able to reproduce broadband elastic measurements of velocity and attenuation our results provide a physical basis for detecting the presence and amount of pore filling hydrate in seafloor sediments using conventional seismic surveys

quantitative description theory of water migration in rock sites based on infrared radiation temperature abstract in order to solve the problem of quantitative description of water migration in a stone artifacts site we have investigated the dynamic migration process of water and established a quantitative descriptive theory system based on infrared radiation temperature through the infrared thermal imaging method we propose the criterion of water movement initiation based on entropy theory a quantitative relationship equation between infrared radiation temperature and water content is established using the first law of thermodynamics a method of identifying the moisture migration wetting front is proposed the above theory is verified by laboratory experimental thermal imaging results of moisture migration of siltstone from the mogao grottoes cliff therefore our method can quantitatively describe the start and migration of water at a rock site using our theoretical system and infrared thermography in a non destructive and real time manner here we provide a new method for quantitative description of moisture migration in a stone artifacts site

physical property changes in hydrate bearing sediment due to depressurization and subsequent repressurization physical property changes in hydrate bearing sediment due to depressurization and subsequent repressurization w f waite 1 t j kneafsey 2 w j winters 1 d h mason 1 u s geological survey 384 woods hole road woods hole ma 02543 usa lawrence berkeley national laboratory 1 cyclotron rd ms 90r1116 berkeley ca 94720 usa