coalbed methane completions a world view abstract cbm wells are cheap because they are usually shallow deeper wells tend to have lower coal permeability and productivity low permeability is the weak point achilles heel for cbm ventures and success will entail finding regions of enhanced permeability utilizing horizontal wells with the option of fracturing these wells and possibly in creating permeability by new paradigm methods such as shear stimulation and branch fracturing this paper discusses the role of permeability in choosing cbm completions as well as examples of those completions from around the world the guidelines offered are new and practical including perm bands and a decision tree and should benefit any cbm completion strategy

volcanic morphology of west mata volcano ne lau basin based on high resolution bathymetry and depth changes high resolution 1 5 m mapping from the autonomous underwater vehicle auv d allan b of west mata volcano in the northern lau basin is used to identify the processes that construct and modify the volcano the surface consists largely of volcaniclastic debris that forms smooth slopes to the nw and se with smaller lava flows forming gently sloping plateaus concentrated along the ene and wsw rift zones and more elongate flows radiating from the summit two active volcanic vents prometheus and hades are located 50 and 150 m wsw of the 1159 m summit respectively and are slightly nw of the ridgeline so the most abundant clastic deposits are emplaced on the nw flank this eruptive activity and the location of vents appears to have been persistent for more than a decade based on comparison of ship based bathymetric surveys in 1996 and 2008 2010 which show positive depth changes up to 96 m on the summit and north flank of the volcano the widespread distribution of clastic deposits downslope from the rift zones as well as from the current vents suggests that pyroclastic activity occurs at least as deep as 2200 m the similar morphology of additional nearby volcanoes suggests that they too have abundant pyroclastic deposits

effect of drilling fluids on coal permeability impact on horizontal wellbore stability the objective of this study was to evaluate a series of mud systems and additives typically used in coalbed methane drilling in terms of formation of an instantaneous filter cake ability of the coal reservoir to rid itself of the filter cake during production and overall impact on coal permeability to achieve this a series of laboratory tests were conducted initially using artificially cleated gypstone rock to simulate coal this was followed by the use of large diameter coal cores which unfortunately did not allow for the tests to be done under in situ confining stress conditions the three mud systems tested against coal xantham gum hec and na cmc did not have a negative impact on coal permeability in contrast to previous laboratory data that showed large decreases two fluid loss control additives which have been used successfully in drilling clastic and carbonate rocks were also tested using a non ionic polymer mud system during simulated drilling these additives flc 2000 and q stop were very effective in building a thin filter cake on the coal surface almost instantaneously to the point that no solids were detected in the downstream fluid accumulator during simulated production a small pressure drop was sufficient to remove the filter cake coal permeability to water returned to its original pre test value which suggested that there was no permanent permeability damage caused by the two additives when coal derived fines were added to the drilling mud in another experiment using the same coal the near wellbore coal permeability was reduced by 87 5 indicating severe damage to the cleat system and in agreement with previously reported laboratory data following the very good performance of flc 2000 and q stop in the laboratory tests these two additives were then used in field applications their presence in the drilling fluid resulted in the successful drilling of 953 m and 1400 m of total horizontal length in the deep mannville coals in alberta at true vertical depth of 1400 m and 1150 m respectively no borehole instability problems were encountered during drilling of the two horizontal wellbores the monitored mud losses were low in both cases with the horizontal well 2 experiencing lower mud loss possibly as a result of the absence of large fractures encountered along the horizontal path horizontal well 1 remained stable which allowed sufficient time to insert a production liner

ultra long range hydroacoustic observations of submarine volcanic activity at monowai kermadec arc monowai is an active submarine volcanic center in the kermadec arc southwest pacific ocean during may 2011 it erupted over a period of 5 days with explosive activity directly linked to the generation of seismoacoustic t phases we show using cross correlation and time difference of arrival techniques that the eruption is detected as far as ascension island equatorial south atlantic ocean where a bottom moored hydrophone array is operated as part of the international monitoring system of the comprehensive nuclear test ban treaty organization hydroacoustic phases from the volcanic center must therefore have propagated through the sound fixing and ranging channel in the south pacific and south atlantic oceans a source receiver distance of 15 800 km we believe this to be the furthest documented range of a naturally occurring underwater signal above 1 hz our findings which are consistent with observations at regional broadband stations and long range acoustic parabolic equation modeling have implications for submarine volcano monitoring

stability analysis of a horizontal coalbed methane well in the rocky mountain front ranges of southeast british columbia canada abstract this study describes a wellbore stability analysis undertaken for a horizontal coalbed methane well in the mist mountain formation se british columbia canada three triaxial compression tests with ultrasonic velocities were conducted on 38 mm diameter core plugs taken from a large fresh block of seam 7 due to the small size of the tested samples the laboratory derived strength values were reduced to reflect the in situ stress conditions considered relevant for a 156 mm diameter horizontal well the vertical stress gradient was calculated by integrating a bulk density log from an offset well horizontal maximum and minimum stresses were estimated from regional stress data whereas formation pressure was estimated on the basis of a local hydrological study the 2d elastoplastic stabview numerical modeling code was used to forecast horizontal wellbore stability the sensitivity of the predicted yielded zone size was examined for varying linear and non linear rock strength criteria horizontal in situ stresses bottom hole pressures formation pressure drilling depth and wall coating efficiency stability analysis was performed at bottom hole pressures ranging from overbalanced to underbalanced in order to simulate the conditions expected during drilling and production the effects of weak bedding planes and varying well trajectories were also investigated when drilling at 650 m depth under underbalanced to slightly overbalanced conditions a high probability of getting the drill pipe stuck was predicted stabview showed that if the 38 mm diameter core plug strengths were used directly for forecasting purposes the predicted yielded zone would be almost 20 overgauge when drilling at balanced conditions when peak cohesion of coal was reduced by 50 to reflect the conditions expected along weak intervals of a horizontal wellbore the predicted enlarged borehole was almost 85 overgauge under the same drilling conditions the most unstable trajectory has n s azimuth which is perpendicular to the maximum horizontal stress in the study area stabview indicates that a production liner should be inserted immediately following the drilling of the horizontal well in this structurally complex geologic setting since pressure drawdown and reservoir pressure depletion would undoubtedly lead to enlarged yielded zones and collapse of the wellbore over time

a method to predict geomechanical properties and model well stability in horizontal boreholes abstract a methodology is proposed to quickly assess the stability risk for horizontal wells drilled in coal seams the first task involves the estimation of strength and deformation parameters of the coal by indirect methods such as the use of core description to assign a geological strength index gsi the second task involves the use of a finite element analysis called flac to investigate factors such as the depth of fluid penetration while drilling the horizontal well and the stability of the wellbore during simulated production these two factors are important because coal fines generated by the drill bit action are carried by the drilling fluid into the cleat system of the coal thereby plugging the permeability pathways and causing formation damage on the other hand a wellbore that may become unstable during pressure drawdown would require a perforated or slotted production liner in this study the conditions of drilling and production necessary for a stable horizontal well drilled into a mannville coal seam at 750 800 m in the central alberta plains were studied modeling showed that the depth of fluid penetration would be at least 2 2 m if there is no filter cake formation while drilling underbalanced drilling fluid penetration would be minimal if a filter cake is formed under overbalanced conditions furthermore flac analysis showed that drilling a smaller diameter hole 5 cm would be preferable because this size results in a stable wellbore during production compared to the standard 15 cm diameter hole

collapse and reconstruction of monowai submarine volcano kermadec arc 1998 2004 monowai submarine volcano is one of the three most historically active volcanoes of the kermadec arc repeat multibeam surveys of monowai cone from september 1998 and september 2004 and t wave data recorded by the reseau sismique polynesien network for the same period document the collapse and subsequent regrowth of the cone within this 6 a period grid differencing of the two bathymetric data sets acquired 6 a apart reveals that a landslide 2230 m long occurred between the surveys within which a postcollapse cone and talus ridge 0 023 km3 in volume subsequently formed the volume of this collapse minus postcollapse construction is 0 085 km3 we interpret an unusual strong amplitude t wave event on 24 may 2002 as recording hot landsliding where the 100 to 160 m thick collapse has unroofed the uppermost parts of the vent conduit with the subsequent explosive interaction and cooling of hot magma and volcaniclastic rubble with ambient seawater this interpretation is consistent with the lack of emergent events sharp onset and large amplitude of the 24 may 2002 t waves the subsequent 2500 t wave events between november 2002 and september 2004 occurred in swarms with emerging and waning activity and with typical explosive volcanic acoustic signatures which are interpreted as recording the regrowth of an 90 m high cone back to a near 1998 elevation at an average rate of 47 m a 1 this study provides 1 a lower bound for frequency magnitude relationships of landsliding for submarine arc volcanoes and 2 estimates of 0 013 km3 a 1 of submarine cone growth during eruptive cycles

seismic precursors and magma ascent before the april 2011 eruption at axial seamount for volcanoes at submarine rift zones a direct link between seismicity seafloor deformation and magma intrusion has not been demonstrated recordings from ocean bottom hydrophones and bottom pressure recorders map an increasing rate of seismicity at axial seamount northeast pacific over several years before its eruption in april 2011

stress relief coalbed methane drainage by surface vertical wells in china abstract this paper summarizes the status of engineering practice technology and research related to stress relief coalbed methane cbm drainage using surface wells in china during the past 10 years comments are provided on the theory and technical progress of this method in high gas mining areas such as the huainan huaibei and tiefa mining areas characterized by heavily sheared coals with relatively low permeability stress relief cbm surface well drainage has been successfully implemented and has broad acceptance as a cbm exploitation technology the fundamental theories underpinning stress relief cbm surface well drainage were established in china and include elements relating to 1 rock layer deformation theory vertical zoning and horizontal partitioning and the change in the stress condition in mining stopes 2 a theory regarding an abscission circle in the development of mining horizontal abscission fracture and vertical broken fracture in overlaying rocks and 3 the theory of stress relief inducing permeability increase in protected coal seams during mining and the gas migration accumulation theory of stress relief cbm surface well drainage three kinds of technical drainage modes are described protected seam surface well drainage in areas influenced by mining represented mainly in the huainan mining area gob surface well drainage most prominently in the tiefa mining areas and the multipurpose surface well drainage used in the huaibei mining areas serial well allocation in which wells are used for different purposes as extraction and mining proceeds and well bore configurations and designs suitable for this purpose are described the development and utilization of cbm is significant to energy saving emission reduction and to ensure safety in coal production

an analytical model of coal wellbore stability based on block limit equilibrium considering irregular distribution of cleats abstract an analytical model of coal wellbore stability is established based on the block limit equilibrium method taking the irregular distribution of cleats into account because coal seam is cut into discontinuous blocks with different shapes and sizes block slip can be treated as the symbol of coal wellbore instability according to the geometric characteristic of blocks blocks surrounding the wellbore can be divided into 3 categorizes type i type ii and type iii to evaluate the block slip the stress distribution near the wellbore is determined based on the continuous medium mechanics and the fracture mechanics using mohr coulomb criterion and limit equilibrium method the critical conditions of block slip are derived by defining the failure coefficient including type i type ii and type iii the proposed model is verified by comparison of the obtained results from the proposed analytical method with the discrete element method as well as the actual drilling it can be proved that the proposed model can predict accurately block slip additionally the effect of drilling fluid pressures on the wellbore stability is specially investigated the results show that with the increasing of drilling fluid pressure the degree of wellbore collapse may be more severe meanwhile the analysis method of reasonable drilling fluid pressure for coal drilling is proposed based on the interval theory combining the slip area of blocks finally the parametric study is focused on investigating the effects of the internal friction angle of face cleats the cohesion of face cleats and the tensile strength of butt cleats on the failure coefficients of blocks

stratigraphy and structure of coalbed methane reservoirs in the united states an overview stratigraphy and geologic structure determine the shape continuity and permeability of coal and are therefore critical considerations for designing exploration and production strategies for coalbed methane coal in the united states is dominantly of pennsylvanian cretaceous and tertiary age and to date more than 90 of the coalbed methane produced is from pennsylvanian and cretaceous strata of the black warrior and san juan basins investigations of these basins establish that sequence stratigraphy is a promising approach for regional characterization of coalbed methane reservoirs local stratigraphic variation within these strata is the product of sedimentologic and tectonic processes and is a consideration for selecting completion zones coalbed methane production in the united states is mainly from foreland and intermontane basins containing diverse compressional and extensional structures balanced structural models can be used to construct and validate cross sections as well as to quantify layer parallel strain and predict the distribution of fractures folds and faults influence gas and water production in diverse ways however interwell heterogeneity related to fractures and shear structures makes the performance of individual wells difficult to predict

on the mechanism of conversion of seismic waves to and from t waves in the vicinity of island shores high frequency seismic records from the polynesian seismic network are used to investigate in detail the processes of conversion of acoustic t wave energy from and to seismic waves at island shores on the source side we study the seismic to acoustic conversion based on t phases from hawaiian events recorded at polynesian stations located on the coral platter on the receiver side we study the acoustic to seismic conversion based on t phases from marine sources recorded across the polynesian islands in both instances our results underline the importance of steep slopes typically 50 in allowing an efficient conversion between p waves in the island structure and t waves in the water column these slopes can be coral reefs or the heads of young presumably unconsolidated basalt flows under this geometry modeling based on raytracing indicates that the seismic record of the t phase consists of a p wave at distances from the conversion point greater than 9 km at shorter distances s waves and surface waves are generated in the absence of a steep slope only surface waves are present these models can be used to compute precise and predictable travel time station corrections allowing the use of seismometers located inland to exploit the superb detection and location capabilities of t waves

cyclic eruptions and sector collapses at monowai submarine volcano kermadec arc 1998 2007 1 repeated multibeam bathymetric surveys at monowai cone a shallow submarine basaltic volcano and part of the monowai volcanic center in the northern kermadec arc were conducted in 1998 2004 and 2007 these surveys document dramatic depth changes at the volcano including negative changes up to 176 m from two sector collapses and positive changes up to 138 m from volcanic reconstruction near the summit and debris avalanche deposits downslope of the slide scars one sector collapse occurred on the se slope between 1998 and 2004 with a volume of 0 09 km3 and another occurred on the sw slope between 2004 and 2007 with a volume of 0 04 km3 the volume of positive depth change due to addition of volcanic material by eruption is of the same order 0 05 km3 between 1998 and 2004 and 0 06 km3 between 2004 and 2007 during these time intervals monitoring by the polynesian seismic network detected frequent t wave swarms at monowai indicative of explosive eruptive activity every few months an unusual t wave swarm on 24 may 2002 was previously interpreted as the collapse event between the 1998 and 2004 surveys but no similarly anomalous t waves were detected between 2004 and 2007 probably because the polynesian seismic network stations were acoustically shadowed from the second slide event we interpret that the sector collapses on monowai are caused by the unstable loading of fragmental erupted material on the summit and steep upper slopes of the volcano 20 moreover there appears to be a cyclic pattern in which recurrent eruptions oversteepen the cone and periodically lead to collapse events that transport volcaniclastic material downslope to the lower apron of the volcano volumetric rate calculations suggest that these two processes may be more or less in equilibrium the repeated collapses at monowai are relatively modest in volume involving only 0 1 0 5 of the edifice volume have occurred much more frequently than is estimated for larger debris avalanches at subaerial volcanoes and may be characteristic of how persistently active shallow submarine arc volcanoes grow

empirical and numerical approaches for geomechanical characterization of coal seam reservoirs abstract the effects of fractures or joints on geomechanical properties of coal when transitioning from small samples to larger field scales have long been recognized two geomechanical characterization methodologies for of a coal seam for reservoir engineering are presented which attempt to account for these scale effect the first is a well established empirical rock mass classification method the geological strength index gsi the second is a newly developed numerical technique termed the synthetic rock mass srm gsi was developed to empirically account for the influence of rock joint density and joint surface conditions on the behaviour of the rock mass the established gsi to strength and deformation theories are reviewed and an approach to account for joint stiffness based on the minimum confining stress is presented the srm approach to jointed rock mass geomechanical characterization is a numerical modeling technique which combines the bonded particle model for rock and discrete fracture network simulation the intact or matrix of the srm is calibrated to laboratory data the dfn inserted creating a numerical representation of the rock mass which can then be tested at any scale in each case the approaches attempt to geomechanically characterize strength modulus etc the large scale behaviour of the coal seam where the properties can then be used for continuum type simulation reservoir simulation borehole stability etc

direct video and hydrophone observations of submarine explosive eruptions at nw rota 1 volcano mariana arc 1 extraordinary video and hydrophone observations of a submarine explosive eruption were made with a remotely operated vehicle in april 2006 at a depth of 550 560 m on nw rota 1 volcano in the mariana arc the observed eruption evolved from effusive to explosive while the eruption rate increased from near zero to 10 100 m3 h during the peak in activity cyclic explosive bursts 2 6 min long were separated by shorter non eruptive pauses lasting 10 100 s the size of the ejecta increased with the vigor of the explosions a portable hydrophone deployed near the vent recorded sounds correlated with the explosive bursts the highest amplitudes were 50 db higher than ambient noise at frequencies between 10 and 50 hz the acoustic data allow us to quantify the durations amplitudes and evolution of the eruptive events over time the low eruption rate high gas lava ratio and rhythmic eruptive behavior at nw rota 1 are most consistent with a strombolian eruptive style we interpret that the eruption was primarily driven by the venting of magmatic gases which was also the primary source of the sound recorded during the explosive bursts the rhythmic nature of the bursts can be explained by partial gas segregation in the conduit and upward migration in a transitional regime between bubbly flow and fully developed slug flow the strongest explosive bursts were accompanied by flashes of red glow and oscillating eruption plumes in the vent apparently caused by magma seawater interaction and rapid steam formation and condensation this is the first time submarine explosive eruptions have been witnessed with simultaneous near field acoustic recordings

assessing the mechanical stability of horizontal boreholes in coal horizontal wells are used in some geological settings in the petroleum industry to produce methane from coal seams horizontal directional drilling is used in the mining industry to enhance the effectiveness of coal degasification procedures and to aid in the delineation of coal reserves coals tend to be mechanically weak hence they are prone to borehole instability related problems during drilling completion and production operations this paper includes a review of the mechanical properties of selected coals and provides two empirical cross plots that can be used for estimating coal strength from index tests and geophysical logs linear elastic borehole stability models are demonstrated to be appealing because they are easily implemented require a minimum of input data and are well suited to rapid parameter sensitivity analyses using experience obtained drilling vertical wells in a given setting a methodology is described for calibrating linear elastic models to provide realistic borehole stabil

distinguishing high surf from volcanic long period earthquakes repeating long period lp earthquakes are observed at active volcanoes worldwide and are typically attributed to unsteady pressure fluctuations associated with fluid migration through the volcanic plumbing system nonvolcanic sources of lp signals include ice movement and glacial outburst floods and the waveform characteristics and frequency content of these events often make them difficult to distinguish from volcanic lp events we analyze seismic and infrasound data from an lp swarm recorded at pagan volcano on 12 14 october 2013 and compare the results to ocean wave data from a nearby buoy we demonstrate that although the events show strong similarity to volcanic lp signals the events are not volcanic but due to intense surf generated by a passing typhoon seismo acoustic methods allow for rapid distinction of volcanic lp signals from those generated by large surf and other sources a critical task for volcano monitoring

a decade of volcanic construction and destruction at the summit of nw rota 1 seamount 2004 2014 arc volcanoes are important to our understanding of submarine volcanism because at some sites frequent eruptions cause them to grow and collapse on human timescales this makes it possible to document volcanic processes active submarine eruptions have been observed at the summit of nw rota 1 in the mariana arc we use remotely operated vehicle videography and repeat high resolution bathymetric surveys to construct geologic maps of the summit of nw rota 1 in 2009 and 2010 and relate them to the geologic evolution of the summit area over a 10 year period 2004 2014 we find that 2009 and 2010 were characterized by different eruptive styles which affected the type and distribution of eruptive deposits at the summit year 2009 was characterized by ultraslow extrusion and autobrecciation of lava at a single eruptive vent producing a large cone of blocky lava debris in 2010 higher energy explosive eruptions occurred at multiple closely spaced vents producing a thin blanket of pebble sized tephra overlying lava flow outcrops a landslide that occurred between 2009 and 2010 had a major effect on lithofacies distribution by removing the debris cone and other unconsolidated deposits revealing steep massive flow cliffs this relatively rapid alternation between construction and destruction forms one end of a seamount growth and mass wasting spectrum intraplate seamounts which tend to grow larger than arc volcanoes experience collapse events that are orders of magnitude larger and much less frequent than those occurring at subduction zone settings our results highlight the interrelated cyclicity of eruptive activity and mass wasting at submarine arc volcanoes

the stability of methane capture boreholes around a long wall coal panel this paper describes the application of computational modelling to the prediction of the stability of methane drainage boreholes during the extraction life of an active long wall coal panel within a united kingdom coal mine the modelling was undertaken to investigate the affects that changes in the roof geology and roadway support system may have on the deformation and closure of the gas drainage boreholes drilled from the tailgate across the goaf of an active long wall panel the paper also outlines the development of an analytical model to estimate the bending deformation axial strain and the rupture of borehole casing due to rock shear this model was used in conjunction with the geomechanical strata models to predict the distance behind the face line at which excessive borehole deformation and closure would occur this method was used to evaluate the optimum roadway support system and spacing between boreholes to maintain effective borehole drainage subject to the range of geological conditions encountered during the panel retreat a good correlation was obtained between the model predictions and the geomechanical and gas drainage data measured at a uk colliery

geodynamics of rifting and implications for hydrocarbon habitat abstract rifting activity is probably mainly governed by frictional forces exerted on the base of the lithosphere by the convecting sub lithospheric upper mantle combined with deviatoric tensional stresses developing over upwelling branches of the asthenospheric convection system and by far filed stresses controlling the interaction of lithospheric plates moving relative to each other mantle plumes rising from the deep mantle do not appear to be a major driving force of rifting therefore it is questioned whether a distinction between active and passive rifts is still justified lithospheric extension triggers by decompression partial melting of the lower lithosphere and upper asthenosphere magmatic processes contribute materially to thinning of the subcrustal lithosphere and probably also of the lower crust this could explain the frequently observed discrepancy between upper crustal extension by faulting and lower crustal attenuation as defined by refraction and deep reflection seismic data the duration of the rifting stage of palaeorifts and passive margins is highly variable depending on plate interaction crustal separation can be achieved after as little as 7 ma and as much as 280 ma of rifting activity the availability of crustal discontinuities does not appear to play a significant role in the time required for crustal separation to be achieved the structural style of rifts is controlled by the physical state of the lithosphere the mode and amount of its extension and the lithological composition of pre and syn rift sediments subsidence of rift basins is controlled by the balance between isostatic adjustment of the crust to lithospheric stretching and uplift induced by mechanical and thermal attenuation of the subcrustal lithosphere post rift basin subsidence is mainly governed by the decay of rift induced thermal anomalies densification of the lower crust and intra plate stresses provide overprinting effects in view of this it is unlikely that quantitative analyses of post rift basin subsidence give a direct measure of lithospheric extension tectonically active rifts palaeorifts and passive margin basins contain major hydrocarbon provinces their hydrocarbon charge can rely exclusively on pre rift syn rift or post rift sedimentary sequences or a combination thereof maturation of source rocks can be achieved during the syn and or post rift stage of basin evolution during rifting conductive and convective heat transfer accounts for elevated geothermal gradients these play an important role in the maturation of pre and syn rift source rocks thermal gradients decrease asymptotically during the post rift stage

variations in mixed layer illite smectite diagenesis in the rift and post rift sediments of the jeanne d arc basin grand banks offshore newfoundland canada mixed layer illite smectite i s clays were analyzed from 22 deep exploration wells from the jeanne d arc basin on the grand banks offshore newfoundland the host of large commercial hydrocarbon accumulations discovered in the last two and a half decades the fine fraction of the clays 0 1 m consists mainly of mixed layer i s with minor amounts of kaolinite illite and chlorite smectite and or smectite rich i s clays were supplied to the jeanne d arc basin from upper jurassic to tertiary times smectite rich i s clays occur only in shallow samples irrespective of geologic age the proportion of illite in i s mixed layers as well as the degree of ordering increase with depth and temperature indicating that smectite rich i s clays have been progressively illitized in both rift and post rift sediments of the jeanne d arc basin during burial the transition from random to r1 ordered i s occurs between subsurface depths of 1940 and 3720 m and crosses major stratigraphic boundaries the transition fr

hydroacoustic detection of submarine landslides on kilauea volcano landslides produced at the site where lava flows intothe o cean at kilauea vo lcanohave been detected hy droacoustically up to 10 landslides per day were detected by a hydrophone on the hawaii undersea geo observatory hugo located 50 km south of the entry site the largest of these landslides partly subaerial events known as bench collapses were detected by a network of hydrophones in the eastern pacific 5000 7000 km away from the source the landslides display a characteristic spectral signature eas ily recognizable among other signals such as earthquake t phases and anthropogenic noises the fact that signals are detected at great distances suggests that hydroacoustic de tection of landslides could be a powerful tool in tsunami monitoring and modeling efforts

seismic and hydroacoustic effects of the may 29 2010 submarine south sarigan volcanic explosion energy release and interpretation abstract the may 2010 submarine volcanic crisis of the shallow south sarigan seamount marianas arc ended on may 29 by a violent explosion that emitted a 12 km high atmospheric plume and created a crater 350 m in diameter the application of the multiphase localization method to the pg p t phases of this explosion allows us to refine considerably mainly based on the intense and impulsive t phases the location of their source that fits the position of the newly formed south sarigan crater we highlight the numerous similarities of this final explosion with artificial underwater explosions conventional or nuclear tests of known energy especially the explosive nature of the source in the volcanic basement is confirmed by the similarity of the p phases with those of underground nuclear tests and the application of discriminating criteria ms mb the explosive nature of the source in the water is also confirmedby the application of the identification criteria for hydroacoustic sources and the t phases exceptionally impulsive and of short durations these similarities allow us to provide a rough evaluation of the energy released by the south sarigan final explosion using the methods commonly applied to man generated explosions we estimate a minimal released energy of 1 kt 4 2 1012 j for the seismic effects of the shock and ca 1 t of equivalent tnt i e 4 2 109 j for the hydroacoustic effects of the explosive source in the water the processes leading to this final explosion are discussed on the basis of the sequence of the earlier seismic and eruptive events within the comprehensive nuclear test ban treaty framework this explosion that affected concomitantly the solid liquid and subaerial media is the first well documented one having generated intense waves p hydroacoustic t acoustic infrasounds and tsunamis

geology of coalbed methane reservoirs in the southeast qinshui basin of china abstract the no 15 coal seam of the pennsylvanian taiyuan formation and the no 3 coal seam of the permian shanxi formation in the southeast qinshui basin are relatively thick 3 m laterally continuous and are of anthracite rank ro 2 2 4 5 the depth of these coal seams is generally between 200 and 700 m a tectonic thermal event during the jurassic to cretaceous yanshanian orogeny controlled coalification and thermogenic hydrocarbon generation because the generation of late stage bacterial gas coalbed methane in the southeast qinshui basin occupies two zones which are the mixed thermogenic and late stage bacterial gas zone near the basin margins and the dominantly thermogenic gas zone in the structurally deep part of the basin basin hydrodynamics causes low gas content in the shallow subsurface 20 m3 t because cleats are rare and are mostly filled with calcite the permeability of the coalbed methane reservoir is controlled by shear fractures the recharge and flow of groundwater not only control gas content but also control reservoir pressure abnormally high pressure reservoir in the deep stagnant zone is a favorable area for coalbed methane exploration and development the current coalbed methane wells are generally completed in the deep stagnant zone

the seismic structure of thinned continental crust in the northern bay of biscay summary the stretching and thinning of the continental crust which occurs during the formation of passive continental margins may cause important changes in the velocity structure of such crust further crust attenuated to a few kilometres thickness can be found underlying oceanic water depths this paper poses the question of whether thinned continental crust can be distinguished seismically from normal oceanic crust of about the same thickness a single seismic refraction line shot over thinned continental crust as part of the north biscay margin transect in 1979 was studied in detail tau p inversion suggested that there are differences between oceanic and continental crust in the lower crustal structure this was confirmed when synthetic seismograms were calculated the thinned continental crust p 7 0 exhibits a two gradient structure in the non sedimentary crust with velocities between 5 9 and 7 4 km s l an upper 0 8 s l layer overlies a 0 4 s l layer no layer comparable to oceanic layer 3 was detected the uppermost mantle also contains a low velocity zone

extensional tectonics in the jeanne d arc basin offshore newfoundland implications for the timing of break up between grand banks and iberia

hydroacoustic investigation of submarine landslides at west mata volcano lau basin submarine landslides are an important process in volcano growth yet are rarely observed and poorly understood we show that landslides occur frequently in association with the eruption of west mata volcano in the ne lau basin these events are identifiable in hydroacoustic data recorded between 5 and 20 km from the volcano and may be recognized in spectrograms by the weak and strong powers at specific frequencies generated by multipathing of sound waves the summation of direct and surface reflected arrivals causes interference patterns in the spectrum that change with time as the landslide propagates observed frequencies are consistent with propagation down the volcano s north flank in an area known to have experienced mass wasting in the past these data allow us to estimate the distance traveled by west mata landslides and show that they travel at average speeds of 10 25 m s

a numerical study on optimization of multilateral horizontal wellbore patterns for coalbed methane production in southern shanxi province china abstract china s southern shanxi province contains thick gassy coals of anthracite rank these high methane content higher than 500 ft 3 ton coals necessitate pre mining methane drainage to enhance the health and safety of underground coal workers both traditional vertical wells and multilateral horizontal wells which were shown to perform better have been drilled in the area in order to effectively reduce the gas content of coals however optimization of well drilling patterns is crucial to improve the gas drainage by boosting well performance and resulting in significant additional recovered gas in a cost effective manner in this study exploration borehole data from an undeveloped coalbed methane field in china s qinshui basin was obtained where permeability is expected to range from 0 1 to 10 md reservoir modeling conducted in this study concludes that in the presence of low permeability coals less than 1 0 md well patterns can be optimized to maintain high methane production rates in this work relationships to determine combinations of horizontal lateral spacing and permeability that yield similar production curves were developed in order to maximize production pinnate wells with laterals spaced at 600 ft intervals in reservoirs with 2 0 md permeability performed similar to those with 200 ft lateral intervals in 0 5 md reservoirs additional similar relationships were drawn for reservoirs ranging from 0 1 to 8 0 md furthermore because of the qinshui basin s potential high stress regime pitchfork and pinnate horizontal well patterns were analyzed based on their potential for catastrophic wellbore failure at well junctions and producing well branches analyses concluded that pitchfork wells had a significantly lower risk for significant wellbore loss due to borehole collapse while providing the opportunity for higher gas recovery in reservoirs exhibiting directional permeability

multi branched horizontal wells for coalbed methane production field performance and well structure analysis abstract horizontal wells such as multi lateral and multi branched horizontal wells mbhws have been effectively used in the development of coalbed methane cbm fields especially for coal beds with very low permeability and low compressive strength in which the performance of conventional fracture stimulated vertical wells is ineffective in this study the performance of mbhws in the liulin block of the ordos basin in central north china is analyzed and compared to that of hydraulically fractured vertical wells the field pilot data show that the gas production rate of most fractured vertical wells decreased rapidly after a short period of time far below expectation while the performance of mbhws is satisfactory and relatively stable during 3 years of production a numerical simulation model was established based on the coal reservoir characteristics the productivities of different well types are predicted and compared to the field data the poor performance of the fractured vertical wells is thought to be caused by the early closure of the fractures and proppant embedded in the coal matrix or by a poor proppant delivery inside the fractures the high and stable productivity of the mbhws is attributed to their large drainage volume and to the stability of the wellbores simulation results show that the parameters of a mbhw such as the branch angle length and spacing can be optimized to maximize its productivity though the drilling cost of a mbhw is relatively high in comparison to vertical wells its high and stable productivity can compensate for the drilling cost therefore mbhws are thought to be more appropriate than vertical wells for the successful exploitation of the cbm resource potential in the liulin block and surrounding area

hydrothermal activity and volcano distribution along the mariana arc 1 submarine volcanic arcs extend for fully a third of the length of the mid ocean ridge system but systematic investigation of hydrothermal venting on those arcs is sparse here we report on the distribution of hydrothermal activity along the intraoceanic mariana arc we identify 76 volcanic edifices along 1370 km of arc grouped into 60 volcanic centers of which at least 26 20 submarine are hydrothermally or volcanically active the overall volcanic center density is 4 4 100 km of arc and that of active centers is 1 9 100 km an equal length of the tonga kermadec arc holds fewer centers 2 9 100 km but a similar density of active centers 1 8 100 km the lower percentage of active centers on the mariana arc results from its having both fewer caldera volcanoes since on both arcs calderas are twice as likely as cones to be active and a lower percentage of active calderas and cones active centers are found from 80 to 230 km above the subducting pacific slab and a quarter lie behind the arc front the frequency distribution of center spacing along the arc front peaks between 20 and 30 km and shows the asymmetric long tail shape typical for many other arcs especially those with volcano populations 20 there is no evidence for a regular spacing of volcanic centers using the new mariana data and recent data from the tonga kermadec arc we estimate that all intraoceanic arcs combined may contribute hydrothermal emissions equal to 10 of that from the global mid ocean ridge

submarine volcanic activity ocean acoustic waves and internal ocean tides 1 submarine volcanic event often generates acoustic waves t waves traveling over long distances through the low velocity channel sofar of the ocean by a method of coherent stacking of t waves from a submarine volcanic activity in northern mariana we found a significant semidiurnal variation of t wave travel times the amplitude of variation is an order of larger than those reported in the previous ocean sound transmission experiments ray theoretical consideration for the numerically simulated ocean tides indicates that such large t phase travel time variation is a consequence of large up and down movement of seawater around the axis of the sofar channel due to the m2 internal tide effectively converted from external tidal forcing t phases a ubiquitous feature of the ocean acoustic noise field can be used to infer internal tidal motion and the associated ocean mixing

integration of vertical and in seam horizontal well production analyses with stochastic geostatistical algorithms to estimate pre mining methane drainage efficiency from coal seams blue creek seam alabama coal seam degasification and its efficiency are directly related to the safety of coal mining degasification activities in the black warrior basin started in the early 1980s by using vertical boreholes although the blue creek seam which is part of the mary lee coal group has been the main seam of interest for coal mining vertical wellbores have also been completed in the pratt mary lee and black creek coal groups of the upper pottsville formation to degasify multiple seams currently the blue creek seam is further degasified 2 3 years in advance of mining using in seam horizontal boreholes to ensure safe mining the studied location in this work is located between tuscaloosa and jefferson counties in alabama and was degasified using 81 vertical boreholes some of which are still active when the current long mine expanded its operation into this area in 2009 horizontal boreholes were also drilled in advance of mining for further degasification of only the blue creek seam to ensure a safe and a productive operation this paper presents an integrated study and a methodology to combine history matching results from vertical boreholes with production modeling of horizontal boreholes using geostatistical simulation to evaluate spatial effectiveness of in seam boreholes in reducing gas in place gip results in this study showed that in seam wells boreholes had an estimated effective drainage area of 2050 acres with cumulative production of 604 mmscf methane during 2 years of operation with horizontal borehole production gip in the blue creek seam decreased from an average of 1 52 mmscf to 1 23 mmscf per acre it was also shown that effective gas flow capacity which was independently modeled using vertical borehole data affected horizontal borehole production gip and effective gas flow capacity of coal seam gas were also used to predict remaining gas potential for the blue creek seam

active submarine eruption of boninite in the northeastern lau basin subduction of oceanic crust and the formation of volcanic arcs above the subduction zone are important components in earth s geological and geochemical cycles subduction consumes and recycles material from the oceanic plates releasing fluids and gases that enhance magmatic activity feed hydrothermal systems generate ore deposits and nurture chemosynthetic biological communities among the first lavas to erupt at the surface from a nascent subduction zone are a type classified as boninites these lavas contain information about the early stages of subduction yet because most subduction systems on earth are old and well established boninite lavas have previously only been observed in the ancient geological record here we observe and sample an active boninite eruption occurring at 1 200 m depth at the west mata submarine volcano in the northeast lau basin southwest pacific ocean we find that large volumes of h2o co2 and sulphur are emitted which we suggest are derived from the subducting slab these volatiles drive explosive eruptions that fragment rocks and generate abundant incandescent magma skinned bubbles and pillow lavas the eruption has been ongoing for at least 2 5 years and we conclude that this boninite eruption is a multi year low mass transfer rate eruption thus the lau basin may provide an important site for the long term study of submarine volcanic eruptions related to the early stages of subduction boninite lavas are erupted during the early stages of subduction however they have previously been found only in the ancient geological record discovery of an active boninite eruption shows that abundant volatile gases derived from the subducting slab drive this violent eruptive activity even in the deep sea

a new method of drilling long boreholes in low permeability coal by improving its permeability abstract when drilling holes for gas pre extraction from soft coal seams having low permeability phenomena such as hole collapse and drill pipe sticking can occur these problems are due to the coal s low intensity and high gas pressure both of which severely limit the efficiency of gas extraction based on an analysis of borehole collapse in soft seams and on a study of the pore formation mechanism in stiff layers this paper proposes a new drilling technique that uses a high pressure pulsed water jet this technique can be used to drill holes in stiff layers of the roof floor until the soft layers of the coal seam are reached this method can improve the gas extraction rate according to damage models for rock a theoretical analysis and numerical simulation was performed for a high pressure pulsed water jet this analysis examined the instantaneous dynamic loads the damage features when using a flexible impact regime the changes in fracture field patterns and the high pressure pulsed water jet s oscillatory effect upon the gas flow of coal mass the impact and vibration effects of a high pressure pulsed water jet could effectively contribute to crushing of the coal to improvement of the coal s cracking and connectivity rate and to improvement in the permeability of the coal additionally the high pressure pulsed water jet s dynamic pressure and flow rate must be calculated for breaking rock during drilling and slotting the developed system was applied in the sanhui mine of sichuan province china the hole drilled by the new method is 2 7 times deeper than that of the hole drilled in the coal seam in the yutianbao mine the average length was 148 m when drilling between the roof and the seam and this value was more than 2 4 times deeper than that previously drilled in the coal seam the gas flow was about 1 06 m 3 min per meter which is more than 5 times that of a traditional hole

the newfoundland basin ocean continent boundary and mesozoic seafloor spreading history the ocean continent boundary in the newfoundland basin is defined as the seaward limit of a continental margin magnetic smooth zone east of the grand banks this boundary is marked by a prominent nne trending magnetic anomaly that is correlated with the j anomaly 115 m y south of flemish cap the smooth zone boundary strikes approximately 060 and is approximately 15 m y younger magnetic anomaly trends suggest two directions of motion during separation of iberia and north america the first phase of motion commencing at j anomaly time with a spreading center strike of 015 produced a rifted margin along the grand banks south of the newfoundland seamounts no spreading occurred north of the seamounts during this phase implying a counter clockwise rotation of iberia and no grand banks galicia bank separation the second phase began at about 102 m y with a shift of the pole of rotation to a location near paris producing a ridge orientation of approximately 060 this spreading center extended north and east into the northern newfoundland basin and bay of biscay producing a rifted margin south of flemish cap and opening of biscay this ridge geometry produced a component of extension across the newfoundland fracture zone and the southeastward migration of the resultant leaky transform fault between 102 m y and the next pole shift produced the volcanic edifice of the southeast newfoundland ridge fracture zone trends during this phase also exerted strong control on volcanism within the newfoundland seamount province this activity ceased at about 97 m y the date at which the second phase ended is not well defined by presently available data a rrr triple junction existed in the northeastern newfoundland basin western biscay region for a short time prior to anomaly33 34 80 m y which marks the inception of a continuous mid atlantic ridge spreading center between the newfoundland and charlie gibbs fracture zones

current status and geological conditions for the applicability of cbm drilling technologies in china a review abstract coalbed methane cbm drilling technology is critical in achieving efficient cbm development the geological conditions for cbm development in china are complex including special terrain high rank coal areas deep coal seams multiple superposed coal seams and coal measure gas symbiosis areas steeply inclined coal seam areas and tectonic coal seam areas therefore it is critical to apply the optimum drilling technology in each different area this paper first reviews the current cbm drilling technologies and gas production behaviors in china it is found that although vertical wells and cluster well groups are common well types for cbm development in china u v and l shaped horizontal wells and multilateral horizontal wells have been favored for cbm development in recent years the paper then discusses the applicability of different well types to geological conditions and proposes a modification method for well design in various geologic conditions this method uses the coal structure ro in situ stress and ratio of critical desorption pressure to the reservoir pressure as the main inputs

30 years in the life of an active submarine volcano a time lapse bathymetry study of the kick em jenny volcano lesser antilles effective monitoring is an essential part of identifying and mitigating volcanic hazards in the submarine environment this is more difficult than onshore because observations are typically limited to land based seismic networks and infrequent shipboard surveys since the first recorded eruption in 1939 the kick em jenny kej volcano located 8km off northern grenada has been the source of 13 episodes of t phase signals these distinctive seismic signals often coincident with heightened body wave seismicity are interpreted as extrusive eruptions they have occurred with a recurrence interval of around a decade yet direct confirmation of volcanism has been rare by conducting new bathymetric surveys in 2016 and 2017 and reprocessing 4 legacy datasets spanning 30 years we present a clearer picture of the development of kej through time processed grids with a cell size of 5m and vertical precision on the order of 1 4m allow us to correlate t phase episodes with morphological changes at the volcano s edifice in the time period of observation 7 09x106 m3 of material has been added through constructive volcanism yet 5 times this amount has been lost through landslides limited recent magma production suggests that kej may be susceptible to larger eruptions with longer repeat times than have occurred during the study interval behavior more similar to sub aerial volcanism in the arc than previously thought t phase signals at kej have a varied origin and are unlikely to be solely the result of extrusive submarine eruptions our results confirm the value of repeat swath bathymetry surveys in assessing submarine volcanic hazards

rheological modelling and deformation instability of lithosphere under extension summary continental break up which precedes oceanic accretion probably results from an unstable extension of the lithosphere analogous to necking of metals when they are submitted to tension by reason of complexity of the rheology no conclusion about lithospheric extension stability may be reached by an a priori analysis we thus examine directly the evolution when the lithosphere is stretched of lateral inhomogeneities represented in our example by small scale variations of thickness the rheological model is derived from the hypotheses of brace kohlstedt 1980 and is consistent with the results of rock mechanics the lithosphere consists of three or four layers of varying thicknesses and mechanical properties the brittle upper crust and eventually the brittle part of the mantle are assimilated to perfectly plastic media and are described in a state of uniform extension by a constant viscosity in the lower crust and ductile mantle lithosphere the effective viscosity is supposed to be exponential the mechanical model relies on a perturbation method developed by fletcher hallet 1983 among others contrary to previous published results no unstable behaviour of the lithosphere is observed unless the latter is more dense than the asthenosphere in which case a gravitational instability may develop this discrepancy can be explained by differences in assumptions concerning the variation of strength in the lithosphere as yet poorly constrained by the data we observe a great sensitivity of the results to the strength stratification and to the artificial discontinuities of density or viscosity implied by the models

seismic and hydroacoustic observations of the 2016 17 bogoslof eruption in mid december 2016 bogoslof volcano alaska began an 8 5 month long eruption that produced at least 70 explosions and three lava domes bogoslof is an emergent submarine volcano with only the very top forming a small island so the eruptive activity mostly occurred from a vent submerged beneath a bay or lagoon the bogoslof eruption was recorded on regional seismic and infrasound arrays as well as by a hydrophone that was deployed locally during the second half of the eruption since few emergent volcanic eruptions have seismo acoustic recordings these observations taken in context with satellite and other observations provide an opportunity to greatly improve our understanding of the seismo acoustic signals produced by these eruptions the instruments detected a range of activity including earthquakes tremor and mass flow events earthquakes occurred before during after and unassociated with explosions and also often occurred in swarms the 47 seismically detected swarms and 27 additional hydroacoustically detected swarms can be further broken into four types precursory post eruptive general and tremor dominated most seismic swarms were less than 10 h long had fewer than 50 earthquakes and had average earthquake rates below 20 h for the explosions we calculate a tremor magnitude frequency index and average frequency the tremor magnitudes determined from the hydrophone data show a roughly linear relation to explosion plume height though this relation was not clear in the more limited seismic data lastly we categorize the activity into five eruption phases based on seismo acoustic character precursory opening explosive i pause and explosive ii

the 2013 eruption of pavlof volcano alaska a spatter eruption at an ice and snow clad volcano the 2013 eruption of pavlof volcano alaska began on 13 may and ended 49 days later on 1 july the eruption was characterized by persistent lava fountaining from a vent just north of the summit intermittent strombolian explosions and ash gas and aerosol plumes that reached as high as 8 km above sea level and on several occasions extended as much as 500 km downwind of the volcano during the first several days of the eruption accumulations of spatter near the vent periodically collapsed to form small pyroclastic avalanches that eroded and melted snow and ice to form lahars on the lower north flank of the volcano continued lava fountaining led to the production of clastogenic lava flows that extended to the base of the volcano about 3 4 km beyond the vent the generation of fountain fed lava flows was a dominant process during the 2013 eruption however episodic collapse of spatter accumulations and formation of hot spatter rich granular avalanches was a more efficient process for melting snow and ice and initiating lahars the lahars and ash plumes generated during the eruption did not pose any serious hazards for the area however numerous local airline flights were cancelled or rerouted and trace amounts of ash fall occurred at all of the local communities surrounding the volcano including cold bay nelson lagoon sand point and king cove

hydroacoustic infrasonic and seismic monitoring of the submarine eruptive activity and sub aerial plume generation at south sarigan may 2010 abstract explosive submarine volcanic processes are poorly understood due to the difficulties associated with both direct observation and continuous monitoring in this study hydroacoustic infrasound and seismic signals recorded during the may 2010 submarine eruption of south sarigan seamount marianas arc are used to construct a detailed event chronology the signals were recorded on stations of the international monitoring system which is a component of the verification measures for the comprehensive nuclear test ban treaty numerical hydroacoustic and infrasound propagation modelling confirms that viable propagation paths from the source to receivers exist and provide traveltimes allowing signals recorded on the different technologies to be associated the eruption occurred in three stages separated by three hour periods of quiescence 1 a 46 h period during which broadband impulsive hydroacoustic signals were generated in clusters lasting between 2 and 13 min 95 of the 7602 identified events could be classified into 4 groups based on their waveform similarity the time interval between clusters decreased steadily from 80 to 25 min during this period 2 a five hour period of 10 hz hydroacoustic tremor interspersed with large amplitude broadband signals associated infrasound signals were also recorded at this time 3 an hour long period of transient broadband events culminated in two large amplitude hydroacoustic events and one broadband infrasound signal a speculative interpretation consistent with the data suggests that during phase 1 transitions between endogenous dome growth and phreatomagmatic explosions occurred with the magma ascent rate accelerating throughout the period during phase 2 continuous venting of fragmented magma occurred and was powerful enough to breach the sea surface during the climactic phase 3 discrete powerful explosions occurred and sufficient seawater was vaporised to produce the contemporaneous 12 km altitude steam plume

paleo heat flow of eastern canada s passive margins abstract tectonic subsidence rates derived from several wells in the labrador sea and offshore nova scotia and newfoundland were used to estimate the paleo heat flow along the margins of eastern canada if tectonic subsidence is caused by the cooling of the lithosphere only the transient component of the heat flow i e the heat flow in excess of background heat flow can be estimated directly from subsidence data for the nova scotia and the labrador sea margins the analysis shows that the transient component of the heat flow decreased markedly from 28 56 mw m 2 immediately after rifting to a present value between 7 and 14 mw m 2 depending on boundary conditions the analysis shows a distinctive difference between the evolution of the labrador sea and that of the northeastern newfoundland margin where it is estimated that the transient component of the heat flow exceeded 100 mw m 2 after rifting and dropped rapidly to very low values the study suggests that the subsidence of the newfoundland margin was not caused by cooling only but required an additional mechanism such as lower crustal phase transformations or continuing extension after continental breakup with ductile deformation in the lower crust and upper mantle the estimated transient heat flow was used to calculate the average present surface heat flow in eastern canada s margins which is the sum of heat flow from the mantle crustal heat production and the transient cooling of the lithosphere the calculated heat flow compares well with heat flow density data obtained from bottom hole temperature measurements

coal permeability improving mechanism of multilevel slotting by water jet and application in coal mine gas extraction multilevel slotting by water jet is one of the effective methods used to improve the coal seam permeability as the example of the 1603 working face of guhanshan coalmine first using acoustic emission technology we analyzed the mechanical properties and crack propagation characteristics of the multilevel slotting coal under the condition of uniaxial loading then using the particle flow software pfc2d we numerically simulated the fracture stress and porosity evolutions of the multilevel slotting coal and analyzed the coal permeability improving mechanism of the slot crack network meanwhile the borehole gas extraction slotted by water jet underground was field tested the study found that the coal s body strength could be weakened significantly when the number of slots was increased and the multilevel distribution of the slots induced a great amount of crack growth and extension which formed the slot crack network reduced the stress concentration and increased the coal porosity field tests demonstrated that the gas extraction effect underground was significantly improved the ability of gas extraction of multilevel slotting borehole was enhanced by 5 10 times compared with the conventional borehole and the coal permeability coefficient was increased by about six times

magma water interactions in subaqueous and emergent basaltic in the subaqueous growth and emergence of a basaltic volcano clasts are formed by one or a combination of 1 explosive release of magmatic volatiles 2 explosive expansion and collapse of steam formed at magma water contact surfaces 3 explosive expansion of steam following enclosure of water in magma or entrapment of water close to magma and 4 cooling contraction these processes named respectivelymagmatic explosivity contact surface steam explosivity bulk interaction steam explosivity andcooling contraction granulation can be enhanced by mutual interaction and feedback the first three explosive processes are limited at certain water depths hydrostatic pressures and become increasingly vigorous at shallower levels the depth of onset of magmatic explosivity depends largely on juvenile volatile content it is up to 200 m for tholeiitic magmas and up to 1 km for alkalic magmas at the depth where formation of clastic deposits becomes predominant over effusion of lavas magmatic explosivity is subordinate to steam explosivity as a clast forming process the upward transition to accumulation of dominantly clastic deposits is not simply related to the onset of substantial exsolution of magmatic volatiles and can occur without it contact surface explosivity commonly requires initiation by a vigorous impact between magma and water and although no certain depth limit is known likelihood of such explosivity decreases rapidly with depth clast generation by bulk interaction explosivity appears to be restricted to depths much shallower than that of the critical pressure of water which in sea water is at about 3 km cooling contraction granulation can occur in any depth of water but at shallow levels may be replaced by contact surface explosivity during continuous eruption under water tephra can be ejected and deposited within a cupola of steam such that rapid quenching does not occur emergent volcanoes are characterized by distinctive steam explosive activity that results primarily from a bulk interaction between rapidly ascending magma and a highly mobile slurry of clastic material water and steam the water gets into the vent by flooding across or through the top of the tephra pile and violent explosions cease when this access is sealed the eruptions during emergence of surtsey and capelinhos typify the distinctive explosive activity the style and controls of which are different from those of maar volcanoes

long term explosive degassing and debris flow activity at west mata submarine volcano west mata is a 1200 m deep submarine volcano where explosive boninite eruptions were observed in 2009 the acoustic signatures from the volcano s summit eruptive vents hades and prometheus were recorded with an in situ 25 m range hydrophone during rov dives in may 2009 and with local 5 km range moored hydrophones between december 2009 and august 2011 the sensors recorded low frequency 1 40 hz short duration explosions consistent with magma bubble bursts from hades and broadband 1 5 min duration signals associated with episodes of fragmentation degassing from prometheus long term eruptive degassing signals recorded through may 2010 preceded a several month period of declining activity degassing episodes were not recorded acoustically after early 2011 although quieter effusive eruption activity may have continued synchronous optical measurements of turbidity made between december 2009 and april 2010 indicate that turbidity maxima resulted from occasional south flank slope failures triggered by the collapse of accumulated debris during eruption intervals

tectonics global changes in sea level and their relationship to stratigraphical sequences at the us atlantic continental margin of geological the principal factors that control the extent of seas through geological time are vertical movements of the lithosphere and global changes in sea level the relative height of the sea surface determines the facies and the thickness of sediments that can accumulate in a sedimentary basin backstripping studies show that the primary factors affecting the subsidence of rifted sedimentary basins are thermal contraction following heating and thinning of the lithosphere at the time of rifting and sedimentary loading factors such as compaction palaeobathymetry erosion and global sea level changes also contribute but their combined affects are small compared to those of thermal contraction and sedimentary loading simple models have been constructed which combine the effects of sedimentary loading and thermal contraction with those of compaction sub aerial erosion and global changes in sea level in the models it was assumed that the lithosphere was heated and thinned by stretching at the time of rifting sedimentary loading occurs by flexure of a lithosphere that progressively increases its flexural rigidity with age following rifting and that sediment compaction and bathymetry change across a basin but do not vary significantly with geological time furthermore different assumptions were made on the magnitude of curves of global sea level changes and the relationship between denudation rate and regional elevation the models show that tectonics in the form of thermal contraction of the lithosphere and flexure and slowly varying global changes in sea level can explain a number of the stratigraphic features of the us atlantic continental margin in this paper some of the implications of these results are examined for studies of a sea level changes through geological time and b the maturation history of continental margin basins

eruptive modes and hiatus of volcanism at west mata seamount ne lau basin 1996 2012 we present multiple lines of evidence for years to decade long changes in the location and character of volcanic activity at west mata seamount in the ne lau basin over a 16 year period and a hiatus in summit eruptions from early 2011 to at least september 2012 boninite lava and pyroclasts were observed erupting from its summit in 2009 and hydroacoustic data from a succession of hydrophones moored nearby show near continuous eruptive activity from january 2009 to early 2011 successive differencing of seven multibeam bathymetric surveys of the volcano made in the 1996 2012 period reveals a pattern of extended constructional volcanism on the summit and northwest flank punctuated by eruptions along the volcano s wsw rift zone wswrz away from the summit the volumetrically largest eruption during the observational period occurred between may 2010 and november 2011 at 2920 m depth near the base of the wswrz the nearly equally long ene rift zone did not experience any volcanic activity during the 1996 2012 period the cessation of summit volcanism recorded on the moored hydrophone was accompanied or followed by the formation of a small summit crater and a landslide on the eastern flank water column sensors analysis of gas samples in the overlying hydrothermal plume and dives with a remotely operated vehicle in september 2012 confirmed that the summit eruption had ceased based on the historical eruption rates calculated using the bathymetric differencing technique the volcano could be as young as several thousand years

coalbed methane from hazard to resource abstract coalbed gas which mainly consists of methane has remained a major hazard affecting safety and productivity in underground coal mines for more than 100 years coalbed gas emissions have resulted in outbursts and explosions where ignited by open lights smoking or improper use of black blasting powder and machinery operations investigations of coal gas outbursts and explosions during the past century were aimed at predicting and preventing this mine hazard during this time gas emissions were diluted with ventilation by airways e g tunnels vertical and horizontal drillholes shafts and by drainage boreholes the 1970 s energy crisis led to studies of the feasibility of producing the gas for commercial use subsequent research on the origin accumulation distribution availability and recoverability has been pursued vigorously during the past two decades since the 1970 s research investigations on the causes and effects of coal mine outbursts and gas emissions have led to major advances towards the recovery and development of coalbed methane for commercial use thus coalbed methane as a mining hazard was harnessed as a conventional gas resource

extension of continental crust at the margin of the eastern grand banks newfoundland seismic and gravity observations from the rifted margin of the eastern grand banks newfoundland support a new model for extension of the continental crust from the shelf edge to odp site 1277 where mantle rocks are exhumed we find that the largest decrease in crustal thickness from about 28 km to 6 km occurs beneath the continental slope of the grand banks over a distance of just 20 km this rapid decrease in crustal thickness coincides with anomalously high seismic velocities 7 0 7 2 km s 1 in the lower crust of the shelf edge the thin crust of the continent ocean transition cot in this area has a smooth basement surface void of upper crustal blocks and prerift sediments we compare our geophysical results with a geodynamical model that represents rifting of a relatively hot continental lithosphere and with another numerical model that represents rifting of a cold lithosphere both geodynamic models suggest that crustal thinning beneath the continental slope was achieved by extensional faulting in the upper crust and ductile shear zones in the middle crust the geodynamic models provide an explanation for the formation of distinct continental slopes at rifted margins beneath the continental shelf of the grand banks the moho and the strong lower crust rotated upwards toward to a 50 dip without visible internal deformation the presence of these strong lower crustal rocks at shallow depth in the rift flank subsequently helped to localize the extension farther seaward with ongoing extension some high angle normal faults may have rotated to a sub horizontal orientation which would explain the lack of brittle deformation visible in the seismic reflection data the two geodynamic models produce different amounts of extension of continental crust in the distal margins the hot rifting model localizes strain much more rapidly leaving narrow zones of extended continental crust and it produces a relatively large amount of melt 30 in the final stages of rifting continental breakup may occur rapidly in hot lithosphere 5 myr on the other hand a cold extension model extends the continental crust to a thickness smaller than 10 km over a width of 50 km in the distal margin similar to what we inferred at the eastern grand banks the cold lithospheric model requires about 23 myr of extension before continental breakup and it predicts much less melting in the mantle 13 the long rift duration wide zones of thinned continental crust and small amount of magmatism make the cold rifting model the most applicable to newfoundland iberia rift

anomalous seaward dip of the lithosphere asthenosphere boundary beneath northeastern usa detected using differential array measurements of rayleigh waves summary rayleigh wave phase velocities and azimuth anomalies in the period range of 30 100 s are measured for a set of four triangular arrays of broad band seismometers in coastal northeastern usa this is a region in which a strong upper mantle slow shear velocity anomaly a new england anomaly crosses the continental margin earthquakes from a wide range of directions are used to detect the variation of parameters with azimuth of propagation no lateral heterogeneity in phase velocity is detected at these periods between stations at the centre and the edge of the anomaly however large 10 20 per cent azimuthal variations occur and have a cos 1 dependence which is indicative of a dipping structure in the upper mantle corresponding azimuth variations with a magnitude of 5 are also detected this behaviour is consistent with a southeasterly n150 e dip of the lithosphere asthenosphere boundary beneath new england this dip is associated with the shoaling of the new england anomaly beneath the adirondack mountains west of the array it is opposite to the dip associated with lithospheric thickening toward the interior of the craton

thinned and subsided continental crust on the rifted margin of eastern canada crustal structure thermal evolution and subsidence history summary seismic refraction measurements were carried out using ocean bottom seismometers over foundered continental crust in orphan basin and flemish pass on the continental margin north east of newfoundland tau p travel time inversion synthetic seismogram analysis and conventional layered model calculations were applied to the data the results show that these outer regions of the margin are underlain by thinned continental crust with a total depth to the m discontinuity of about 22 km there are two main crustal layers with p velocities of about 6 1 and 7 0 km s 1 which appear to be homogenous and separated by sharp interfaces these are overlain by a layer in which p velocities are about 5 5 km s 1 this is interpreted to be precambrian or palaeozoic basement mesozoic and cenozoic sediments cover the basement rocks and are over 4 km thick the results imply that crustal thinning to about 50 per cent of the original crustal thickness occurred the gravity anomaly data show that the thin crust has a maximum horizontal extent of about 450 km from the ocean continent boundary near orphan knoll landward to the outer continental shelf the subsidence history and thermal evolution of the region was computed assuming that the observed thinning is produced by horizontal extension of the lithosphere it is suggested that extension can only satisfy the observed crustal structure and elevation of the margin during the rift phase if more extension took place in the lower lithosphere than in the upper lithosphere the computed subsidence is compared to the observed subsidence and the total amounts of subsidence are similar however the shape of the observed subsidence curves measured in deep exploratory wells differs significantly from the predicted subsidence assuming cooling began when final continental breakup occurred in the late cretaceous the temperature distribution within the lithosphere due to extension may be related to the flexural rigidity of the plate as a function of both time and position across the margin therefore it is suggested that the response of the lithosphere to sediment loading and the large amplitude of the gravity shelf edge anomalies are directly related to the thermal history of the region

hydraulic fracturing and wellbore completion of coalbed methane wells in the powder river basin wyoming implications for water and gas production excessive water production more than 7000 bbl month per well from many coalbed methane cbm wells in the powder river basin of wyoming is also associated with significant delays in the time it takes for gas production to begin analysis of about 550 water enhancement activities carried out during well completion demonstrates that such activities result in hydraulic fracturing of the coal water enhancement activities as the operators in the basin call this procedure consists of pumping 60 bbl of water min into the coal seam during approximately 15 min this is done to clean the wellbore and to enhance cbm production hydraulic fracturing is of concern because vertical hydraulic fracture growth could extend into adjacent formations and potentially result in excess cbm water production and inefficient depressurization of coals analysis of the pressure time records of the water enhancement tests enabled us to determine the magnitude of the least principal stress s3 in the coal seams of 372 wells these data reveal that because s3 switches between the minimum horizontal stress and the overburden at different locations both vertical and horizontal hydraulic fracture growth is inferred to occur in the basin depending on the exact location and coal layer relatively low water production is observed for wells with inferred horizontal fractures whereas all of the wells associated with excessive water production are characterized by inferred vertical hydraulic fractures the reason wells with exceptionally high water production show delays in gas production appears to be inefficient depressurization of the coal caused by water production from the formations outside the coal to minimize cbm water production we recommend that in areas of known vertical fracture propagation the injection rate during the water enhancement tests should be reduced to prevent the propagation of induced fractures into adjacent water bearing formations in areas where s3 is unknown a minifrac should be done to determine the magnitude of s3 to know whether fracture propagation will be vertical or horizontal so the water enhancement activities at the time of well completion are done to minimize water production and optimize gas production

the crustal structure of the rockall trough differential stretching without underplating the crustal structure along the axis of the rockall trough in the north atlantic has been studied along a 600 km refraction wide angle reflection transect containing three lines each 200 to 250 km long using explosives and ocean bottom seismometers one dimensional inversions of each section were made using the p method and forward modeling of the observed travel times in the next stage travel times and amplitudes were modeled using ray tracing techniques through two dimensional heterogeneous structures the results indicate that there are three sedimentary layers with velocities ranging from 2 km s to 4 5 km s the whole sedimentary section is up to 6 km thick and interpreted as late paleozoic to tertiary in age a two layer continental crust 5 to 7 km thick occurs along the length of the profile the upper crust 6 0 6 3 km s is circa 2 km thick and the lower crust 6 6 6 9 km s is circa 3 km thick a moho transition zone approximately 1 km thick lies at the base of the crust velocities in this transition zone increase from 6 9 km s up to 7 8 km s along the profile the underlying upper mantle has a laterally variable velocity between 7 6 and 7 8 km s unstretched crust onshore in ireland comprises a three layered crust with each layer approximately 10 km thick and a moho transition zone which is about 3 km thick the two upper layers in the onshore region are interpreted as corresponding to the upper crust in the rockall trough and indicate a stretching factor of 8 10 the velocity pattern in the lower crust in the rockall trough and under ireland are similar suggesting significantly less stretching 2 3 the differential stretching model is supported by the presence of the moho transition zone which is stretched by a similar factor to the lower crust the bulk stretching factor for the crust as a whole is in the range of 4 6 if this represents the lithospheric stretching factor significant underplating would be expected however if the stretching factor for the lower crust in the differential stretching model is more representative of overall lithospheric stretching little or no underplating is predicted the velocity patterns observed in the rockall trough indicate the absence of any significant underplating at the base of the crust such as that observed at the continental margin west of the hatton basin

rapid rates of growth and collapse of monowai submarine volcano in the kermadec arc most of earth s volcanoes are under water as a result of their relative inaccessibility little is known of the structure and evolution of submarine volcanoes advances in navigation and sonar imaging techniques have made it possible to map submarine volcanoes in detail and repeat surveys allow the identification of regions where the depth of the sea floor is actively changing here we report the results of a bathymetric survey of monowai submarine volcano in the tonga kermadec arc which we mapped twice within 14 days we found marked differences in bathymetry between the two surveys including an increase in seafloor depth up to 18 8 m and a decrease in depth up to 71 9 m we attribute the depth increase to collapse of the volcano summit region and the decrease to growth of new lava cones and debris flows hydroacoustic t wave data reveal a 5 day long swarm of seismic events with unusually high amplitude between the surveys which directly link the depth changes to explosive activity at the volcano the collapse and growth rates implied by our data are extremely high compared with measured long term growth rates of the volcano demonstrating the pulsating nature of submarine volcanism and highlighting the dynamic nature of the sea floor

production characteristics and the key factors in high rank coalbed methane fields a case study on the fanzhuang block southern qinshui basin china abstract the temporal and spatial production characteristics of coalbed methane cbm wells in the fanzhuang block of the southern qinshui basin the first commercial cbm producing basin in china were studied to determine the dominant factors the study indicates that gas production differs significantly in different wells adjacent to or located in different tectonic areas in combination with the production characteristics in the temporal and spatial variations the impact of seven factors burial depth thickness of coal gas content porosity permeability effect of fracturing structural setting and hydrogeological conditions on the gas production was analyzed based on bivariate correlation analysis and gray system theory which are suitable for solving the complex interrelationships between multiple factors and variables the results indicate that hydraulic fracturing is an effective guarantee of high production cbm wells in the first several months during a high rank cbm field development however the effect of hydraulic fracturing on enhancing the gas production of cbm wells decreases with time because the initial reservoir permeability lower than the hydraulic fracture permeability limits the adsorption diffusion and flow of cbm this limitation inevitably leads to a slow gas production rate when the adsorbed cbm from the initial reservoir becomes the main gas source instead of the fracturing affected zone gas content and permeability are two key factors that dominate cbm well productivity because they perform elementary roles in controlling the volume of gas sources and conductivity respectively the structural setting and hydrogeological condition are also two important factors that dominate cbm well productivity because they can influence the spatial distribution of permeability and gas content as well as other factors such as aquifers

long period seismicity and very long period infrasound driven by shallow magmatic degassing at mount pagan mariana islands long period lp seismicity and very long period infrasound ivlp were recorded during continuous degassing from mount pagan mariana islands in july 2013 to january 2014 the frequency content of the lp and ivlp events and delay times between the two arrivals were remarkably stable and indicate nearly co located sources using phase weighted stacking over similar events to dampen noise we find that the lp source centroid is located 60 m below and 180 m west of the summit vent the moment tensor reveals a volumetric source modeled as resonance of a subhorizontal sill intersecting a dike we model the seismoacoustic wavefields with a coupled earth air 3 d finite difference code the ratios of pressure to velocity measured at the infrasound arrays are an order of magnitude larger than the synthetic ratios so the ivlp is not the result of lp energy transmitting into the atmosphere at its epicenter based on crater shape and dimensions determined by structure from motion we model the ivlp as acoustic resonance of an exponential horn the source of the continuous plume from gas analysis is shallow magmatic degassing which repeatedly pressurized the dike sill portion of the conduit over the 7 months of observation periodic gas release caused the geologically controlled sill to partially collapse and resonate while venting of gas at the surface triggered resonance in the crater lp degassing only accounts for 12 of total degassing indicating that most degassing is relatively aseismic and that multiple active pathways exist beneath the vent

hydroacoustic records and a numerical model of the source mechanism from the first historical eruption of anatahan volcano mariana islands abstract anatahan volcano in the commonwealth of the northern mariana islands cnmi erupted for the first time in recorded history on 10 may 2003 the underwater acoustic records t waves of earthquakes explosions and tremor produced during the eruption were recorded on a sound channel hydrophone deployed in february 2003 acoustic propagation models show that the seismic to acoustic conversion at anatahan is particularly efficient aided by the upward slope of the seamount toward the hydrophone the hydrophone records confirm the onset of earthquake activity between 0100 and 0200z on 10 may with a substantial increase in seismicity beginning at 0620z in addition the onset of continuous low frequency 3 40 hz acoustic energy that is likely volcanic tremor related to magma intrusion was also observed at 0620z the hydrophone recorded 1401 earthquakes during the first 3 days of the eruption a histogram of seismicity indicates two main periods of explosion eruption activity the first beginning at 0620z on 10 may and the second at 0000z on 11 may relative earthquake depth estimates indicate that both eruption periods were accompanied by earthquake activity from deep within the anatahan volcanic edifice a numerical representation of the anatahan volcano seismic source was developed to examine the character of acoustic signals generated from the eruption governed by the geometry of the source and the physical properties of the magma a magma pipe source mechanism is used to compute the seismo acoustic wavefield on the flank of the anatahan volcanic edifice on the seafloor and in the water column due to mode conversion by roughness scattering a fluid filled pipe model was chosen because it allows for a more straightforward relation between volcano geometry and spectral features of harmonic tremor as well as its morphologic similarity to a submerged volcanic edifice

underwater records of submarine volcanic activity el hierro canary islands 2011 2012 eruption abstract we present the monitoring of a submarine volcanic eruption that took place near the southernmost emerged land of el hierro island canary islands spain from october 2011 to february 2012 right after the onset of the eruption in mid october 2011 we deployed an offshore geophone array for the purpose of monitoring the submarine eruptive activity signals it acquired continuous data from october 2011 to may 2012 sometime after the end of the eruption the array consisted of 8 high frequency 3 component geophones assembled into a cable string with 6 m of separation the geophone string was installed in la restinga harbor at a distance of less than 2 km from the volcanic edifice the dataset acquired with the array is a unique continuous acoustic record of the activity associated with this eruption we analyzed the continuous signal of the eruptive activity with special interest in those events reflecting the eruption dynamics our results show that the geophone array was recording acoustic waves from a back azimuth source corresponding to the position of the submarine vent traveling at a speed of 1510 m s compatible with the speed of sound in water acoustic data shows a good correlation with the seismic data recorded on land for the case of earthquake occurrence in addition it provides relevant information towards the understanding of the eruptive surface activity therefore this methodology can be successfully used in cases of submarine eruptions

the use of numerical simulation in predicting coalbed methane producibility from the gates coals alberta inner foothills canada comparison with mannville coal cbm production in the alberta syncline abstract two medium to low volatile bituminous rank coals in the lower cretaceous gates formation mannville equivalent inner foothills of alberta were cored as part of a coalbed methane exploration program the target seams seam 4 and seam 10 were intersected at 652 m and 605 m respectively the coals were bright banded relatively competent and reasonably cleated with cleat spacing between 5 20 mm the fmi formation micro imaging log identified two primary fracture directions corresponding to both face and butt cleats which were developed almost equally in some coal intervals the amount of shearing was limited in spite of the presence of numerous thrust faults and fold structures in the corehole vicinity total gas content was high with an average of 17 7 cm 3 g arb 568 1 scf t an adsorption isotherm of the thick seam 4 showed gas saturation levels of 90 at in situ reservoir conditions methane content was 92 96 and carbon dioxide levels were less than 2 isotopic studies on the methane confirmed the thermogenic origin of the gas as anticipated based on the coal rank the coal seams were fracture stimulated using 50 50 nitrogen and fresh water along with 9 to 12 tons of 12 20 mesh sand used as a proppant it is believed that the coals were not stimulated properly because of the small proppant volume and the complex and often unpredictable fracture pattern in coals particularly in the inner foothills region that has high stress anisotropy an injectivity test showed coal absolute permeability to be less than 1 md the skin to be 2 indicating a slightly damaged coal and water saturation in the cleats to be 90 a four month production test was conducted gas rates declined from 930 to 310 m 3 d 33 to 11 mcfd and water rates were low constructive interference in depressurizing the coal reservoirs and accelerating gas production over short periods of time was demonstrated coal quality data from a nearby underground mine shows that drilling horizontal wellbores in the gates coals would be challenging because of unfavourable geomechanical properties such as low cohesion and unconfined compressive strength values and structural complexity

three distinct regimes of volcanic tremor associated with the eruption of shishaldin volcano alaska 1999 tremor signals associated with the eruption of shishaldin volcano on 19 and 23 april 1999 were the strongest recorded anywhere in the aleutian arc by the alaska volcano observatory avo in its 10 year history reduced displacements dr reached 23 cm2 on 19 april and 43 cm2 on 23 april during the activity dr and spectral data with a frequency resolution of 0 1 hz were computed and put on the world wide web every 10 min these data are analyzed here the general temporal patterns of seismicity of these eruption events were similar but the eruptions and their effects quite different the 19 april event is known to have culminated in a sub plinian phase which ejected ash to an altitude of 16 km despite higher amplitudes and the largest hotspot from satellite data the 23 april event produced little ash reaching only 6 km altitude for several hours prior to the sub plinian phase on 19 april tremor with a peak frequency of 1 3 hz intensified during the sub plinian phase the peak frequency increased to 4 8 hz however in 15 h after the eruption three episodes of stronger tremor occurred with a lower 1 0 hz peak alternating with weaker tremor with a 1 3 hz peak these transitions correspond to dr 8 cm2 although these strong tremor episodes produced higher dr levels than the sub plinian phase data from a pressure sensor show that only strong strombolian explosions occurred the suite of observations suggests three distinct tremor regimes that may correspond to slug flow bubbly flow and sustained strong eruptions or a cyclic change in source parameters e g geometry sound speed or ascent rate this behavior occurred at shishaldin only during the april 1999 sequence and we are not aware of similar behavior at other volcanoes

crustal structure of the newfoundland rifted continental margin from constrained 3 d gravity inversion the rifting history of the atlantic continental margin of newfoundland is very complex and so far has been investigated at the crustal scale primarily with the use of 2 d seismic surveys while informative the results generated from these surveys cannot easily be interpreted in a regional sense due to their sparse sampling of the margin a 3 d gravity inversion of the free air data over the newfoundland margin allows us to generate a 3 d density anomaly model that can be compared with the seismic results and used to gain insight into regions lacking seismic coverage results of the gravity inversion show good correspondence with moho depths from seismic results a shallowing of the moho to 12 km depth is resolved on the shelf at the northern edge of the grand banks in a region poorly sampled by other methods comparisons between sediment thickness and crustal thickness show deviations from local isostatic compensation in locations which correlate with faults and rifting trends such insights must act as constraints for future palaeoreconstructions of north atlantic rifting