faulting of rocks in three dimensional strain fields i failure of rocks in polyaxial servo control experiments abstract the dependence of the number of sets of faults and their orientation on the intermediate strain axis is investigated through polyaxial tests reported here and theoretical analysis reported in an accompanying paper in the experiments cubic samples of berea sandstone sierra white and westerly granites and candoro and solnhofen limestones were loaded on their three pairs of faces by three independent mutually perpendicular presses at room temperature two of the presses were servo controlled and applied constant displacement rates throughout the experiment most samples display three or four sets of faults in orthorhombic symmetry these faults form in several yielding events that follow a stage of elastic deformation in many experiments the maximum and the intermediate compressive stresses interchange orientations during the yielding events where the corresponding strains are constant the final stage of most experiments is characterized by slip along the faults

permeability evolution of shale under anisotropic true triaxial stress conditions abstract although permeability data for shale have been reported previously and permeability models have been proposed studies on permeability for shale under anisotropic true triaxial stress conditions are lacking in this work the permeability of shale under true triaxial stress conditions was measured using a newly developed true triaxial geophysical apparatus the permeability always decreased with increasing principal stress the permeability variations induced by varying each principal stress were distinct the greatest permeability reductions were observed with increasing stress normal to the bedding planes based on a consideration of shale anisotropy a permeability model was established to be applicable to shale under anisotropic true triaxial stress conditions ttp model this model was verified by matching the permeability data in our experiments it was found that a more accurate match could be obtained using the ttp model which showed advantages in reflecting the permeability changes related to increments in each principal stress

an analytical coal permeability model for tri axial strain and stress conditions coal permeability is sensitive to the effective stress and is therefore coupled to the geomechanical behaviour of the seam during gas migration as coal shrinks with gas desorption and swells with adsorption understanding this coupling to geomechanical behaviour is central to interpreting coal permeability existing coal permeability models such as those proposed by shi and durucan 2004 and palmer and mansoori 1996 simplify the geomechanical processes by assuming uni axial strain and constant vertical stress however it is difficult to replicate these conditions in laboratory tri axial permeability testing and during laboratory core flooding tests for enhanced coal bed methane often laboratory tests involve a hydrostatic stress state where the pressure in the confining fluid within the tri axial cell is uniformly applied to the sample exterior in this experimental arrangement the sample is allowed to undergo tri axial strain this paper presents two new analytical permeability model representations derived from the general linear poroelastic constitutive law that include the effects of tri axial strain and stress for coal undergoing gas adsorption induced swelling a novel approach is presented to the representation of the effect of coal sorption strain on cleat porosity and thus permeability this involves distinguishing between the sorption strain of the coal matrix the pores or cleats and the bulk coal the developed model representations are applied to the results from a series of laboratory tests and it is shown that the models can predict the laboratory permeability data as part of this characterisation the various sorption strains are identified and it is shown that the pore strain is significantly larger than approximately 50 times the bulk sorption strain the models also provide further insight into how coal permeability varies with coal shrinkage and swelling and how the permeability rebound pressure depends upon the effective stress applied

influence of specimen height to width ratio on the strainburst characteristics of tianhu granite under true triaxial unloading conditions strainbursts occur frequently near excavation boundaries posing a significant threat to the safety of workers and stability of underground structures a better understanding of the strainburst phe

co2 ecbm field tests in the ishikari coal basin of japan abstract the feasibility of extracting gas from coal seam while storing carbon dioxide underground was evaluated in japan a co2 ecbm project had begun near the town of yubari on the island of hokkaido in northern japan the primary coal seam of interest was a 5 6 m thick yubari coal seam located at the depth of 900 m a micro pilot test with a single well and multi well co2 injection tests involving an injection and production wells were carried out in the period between may 2004 and october 2007 there were a variety of tests conducted in the injection well including an initial water injection fall off test and a series of co2 injection and fall off tests although gas production rate was obviously enhanced by co2 injection water production rate was not clearly affected by co2 injection several injection tests suggested that injectivity of co2 into the virgin coal seam saturated with water was eventually increased as the water saturation near the injector was decreased by the injected co2 it was estimated that low injectivity of co2 was caused by the reduction in permeability induced by coal swelling n2 flooding test was performed in 2006 to evaluate the effectiveness of n2 injection on improving well injectivity the n2 flooding test showed that daily co2 injection rate was boosted but only temporarily moreover the permeability did not return to the initial value after co2 and n2 were repeatedly injected it was also indicated that the coal matrix swelling might create a high stress zone near to the injection well

ekman heat transport for slab oceans a series of schemes designed to include various representations of the ekman driven heat fluxes in slab ocean models is introduced they work by computing an ekman mass flux then deducing heat fluxes by the surface flow and an opposite deep return flow the schemes differ by the computation of the return flow temperature either diagnosed from the sst or given by an active second layer both schemes conserve energy and use as few parameters as possible simulations in an aquaplanet setting show that the schemes reproduce well the structure of the meridional heat transport by the ocean compared to a diffusive slab ocean the simulated sst is more flat in the tropics and presents a relative minimum at the equator shifting the itcz into the summer hemisphere in a realistic setting with continents the slab model simulates correctly the mean state in many regions especially in the tropics the lack of other dynamical features such as barotropic gyres means that an optimal mean state in regions such as the mid latitudes will require additional flux corrections 2011 springer verlag

swelling induced volumetric strains internal to a stressed coal associated with co2 sorption abstract it is generally accepted that typical coalbed gases methane and carbon dioxide are sorbed both adsorbed and absorbed in the coal matrix causing it to swell and resulting in local stress and strain variations in a coalbed confined under overburden pressure the swelling interactions of gases within the coal matrix and the resultant changes in the permeability sorption gas flow mechanics in the reservoir and stress state of the coal can impact a number of reservoir related factors these include effective production of coalbed methane degasification of future mining areas by drilling horizontal and vertical degasification wells injection of co2 as an enhanced coalbed methane recovery technique and concurrent co2 sequestration such information can also provide an understanding of the mechanisms behind gas outbursts in underground coal mines the spatio temporal volumetric strains in a consolidated pittsburgh seam coal sample were evaluated while both confining pressure and carbon dioxide co2 pore pressure were increased to keep a constant positive effective stress on the sample the changes internal to the sample were evaluated by maps of density and atomic number determined by dual energy x ray computed tomography x ray ct early time images as soon as co2 was introduced were also used to calculate the macroporosity in the coal sample scanning electron microscopy sem and photographic images of the polished section of the coal sample at x ray ct image location were used to identify the microlithotypes and microstructures the co2 sorption associated swelling and volumetric strains in consolidated coal under constant effective stress are heterogeneous processes depending on the lithotypes present in the time scale of the experiment vitrite showed the highest degree of swelling due to dissolution of co2 while the clay kaolinite and inertite region was compressed in response the volumetric strains associated with swelling and compression were between 15 depending on the location although the effective stress on the sample was constant it varied within the sample as a result of the internal stresses created by gas sorption related structural changes sem images and porosity calculations revealed that the kaolinite and inertite bearing layer was highly porous which enabled the fastest co2 uptake and the highest degree of compression

permeability anisotropy and its relations with porous medium structure 1 the complete permeability tensor of 18 porous rock cores was determined by means of x ray tomography monitoring during the displacement of a salty tracer to study the effect of the pore space geometry on the anisotropy of permeability we compared the three dimensional shape of the invasion front with the x ray porosity maps obtained before injection the samples clean and shale bearing sandstones limestones and volcanic rocks belong to a broad variety of granulometry and pore space geometry their porosity ranges from 12 to 57 and their permeability ranges from 1 5 10 14 to 4 10 12 m2 for sandstones the permeability anisotropy is well correlated with the presence of bedding for volcanic rocks it is clearly related to the orientation of vesicles or cracks however for limestones no evident link between the geometry of the porous network and the permeability anisotropy appears probably because of the influence of the nonconnected porosity that does not contribute to the hydraulic transport this systematic work evidences the ability and the limitations of the tracer method to characterize the anisotropy of permeability in the laboratory in a simple and rapid way

carbon dioxide gas permeability of coal core samples and estimation of fracture aperture width abstract the structure of cleats or natural fractures in coal seams is an important factor affecting gas permeability coal seam permeabilities have been classified into fracture and matrix flows however fractures in coal seams are generally not regular and usually are discontinuous in addition it is difficult to definitively distinguish the fracture and matrix permeabilities and to measure the fracture widths or other necessary properties of fractures for permeability estimation typically gas permeability has been determined by using the darcy equation for incompressible fluid flow and homogeneous porous media even if the gas flow through fractures has different characteristics with respect to effective stress which is given by the confined stress minus the gas pressure in this study permeability measurements were carried out with a new procedure and methodology to estimate the fracture width in coal core samples this measurement method is an improvement on conventional permeability measuring methods in this research it was identified that fracture permeability can be estimated from measurements of gas flow rates in a limited small area using a pipe attachment on the end of the surface of the core finally a linear equation composed of fracture permeability and matrix permeability is presented

permeability of coals and characteristics of desorption tests implications for coalbed methane production abstract desorption tests conducted before development drilling can predict early production rates of coalbed methane wells in this study results from 136 desorption tests from 30 coreholes are compared to subsequent production histories of surrounding wells coals studied are from the carboniferous pottsville formation in the black warrior basin of alabama usa the investigation indicates that the best predictor for gas production is gas yield at 120 days divided by sample depth this quotient has a higher correlation with actual gas production than other variables examined including original reserves in place gas content of coal generally increases with depth however coal permeability and hence the recovery factor tends to decrease with depth therefore coalbed methane exploration should focus on finding the optimal balance between gas yield and depth commercially successful wells are characterized by coals with high gas yields at shallow depths desorption tests especially of slowly desorbing coals should be run for a minimum of 120 days or else should be extrapolated to that time if tests are terminated earlier

coal bed reservoir simulation with geostatistical property realizations for simultaneous multi well production history matching a case study from illinois basin indiana usa abstract coal seam degasification is a means to recover energy from the methane gas retained in coal and is also a supplementary measure to ventilation which is proven to be one of the most effective ways to reduce methane emissions to a safe level in coal mines reservoir simulation is probably the most effective way to assess the coal seam as a gas reservoir and thereby its fluid storage and flow related properties this objective is achieved by taking advantage of history matching of wellbore production reservoir simulation with multi well history matching is a tedious process as important coal properties that affect wells production characteristics are spatially variable across the seam the common practice is to change various properties at the well blocks during the history matching process and assume that they are uniform across the domain of interest this process however often does not produce realistic and effective results for well or coal reservoir management in this work a multi level approach to coal bed reservoir simulation is demonstrated for a group of coalbed methane wells in the illinois basin producing from the seelyville coal member of the linton formation of the carbondale group pennsylvanian in indiana this approach includes in order gas and water deliverability analyses of wells geostatistical simulation and co simulation and coal bed reservoir simulation it is shown that a reservoir model which utilizes the geostatistical maps of important coal properties is effective for simultaneous history matching of all wells and eliminates the need for guessing and changing values of coal properties at and around individual well blocks this methodology also provides realistic distributions of reservoir parameters and how they change during gas depletion and thus aids in coal seam and coal gas management

elastic wave velocities and permeability of cracked rocks abstract cracks play a major role in most rocks submitted to crustal conditions mechanically cracks make the rock much more compliant they also make it much easier for fluid to flow through any rock body relying on fracture mechanics and statistical physics we introduce a few key concepts which allow to understand and quantify how cracks do modify both the elastic and transport properties of rocks the main different schemes which can be used to derive the elastic effective moduli of a rock are presented it is shown from experimental results that an excellent approximation is the so called non interactive scheme the main consequences of the existence of cracks on the elastic waves is the development of elastic anisotropy due to the anisotropic distribution of crack orientations and the dispersion effect due to microscopic local fluid flow at a larger scale macroscopic fluid flow takes place through the crack network above the percolation threshold two macroscopic fluid flow regimes can be distinguished the percolative regime close to the percolation threshold and the connected regime well above it experimental data on very different rock types show both of these behaviors

effect of pore geometry on vp vs from equilibrium geometry to crack seismic wave velocities of melt or aqueous fluid containing systems are studied over a wide range of pore shapes including oblate spheroids tubes cracks and an equilibrium geometry controlled by a dihedral angle the relative role of liquid compressibility and pore geometry on the v p v s velocity ratio is clarified the result clearly indicates that p and s velocity structures determined by seismic tomography can be used to verify whether interfacial energy controlled melt or fluid geometry equilibrium geometry is achieved relationships between the diverse models are clearly established by relating each model to the oblate spheroid model in terms of the equivalent aspect ratio as a function of the aspect ratio a significant effect of pore geometry on d in v s d in v p the ratio of the fractional changes in v s and v p is shown equilibrium geometry of the partially molten rocks characterized by a dihedral angle of 20 40 corresponds to an aspect ratio of 0 1 0 15 the value of d in v s d in v p expected for the texturally equilibrated partially molten rocks is shown to be 1 1 5 which is much smaller than that expected for cracks and dikes with an aspect ratio of 10 2 10 3 in the upper mantle low velocity regions the seismologically obtained value of d in v s d in v p is within this range beneath the bolivian andes 1 1 1 4 but is as high as 2 beneath iceland 1 7 2 3 and beneath northeastern japan 2 0 the former region can be regarded as a region where equilibrium geometry is achieved and the latter regions can be regarded as regions where dikes and veins typical of a system far from the textural equilibrium dominate

south atlantic response to el nino southern oscillation induced climate variability in an ocean general circulation model 1 the response of the south atlantic ocean to el nino southern oscillation enso is investigated by means of an ocean general circulation model orca2 forced with national centers for environmental prediction ncep reanalyses for the 1948 1999 period seasonal enso composites suggest that the enso induced wind anomalies play a major role in driving upper ocean temperatures by altering the net surface heat fluxes the meridional ekman heat transport and ekman pumping model diagnostics indicate that the ekman heat transport changes are in better agreement with the upper ocean temperature anomalies during the first half of the enso event whereas in the latter half the surface heat flux anomalies agree better in general the atmospheric forcing tends to lead to a coherent ocean response with a time lag of about one season subsurface temperatures evolve more slowly in response to enso forcing than the upper ocean they receive time filtered enso signals from mainly ekman pumping suction and variations in thermocline depth that result in the poleward and equatorward margins of the subtropical gyre exhibiting temperature anomalies of the same sign but opposite to those in the central regions of the gyre

characteristics and origins of coal cleat a review abstract cleats are natural opening mode fractures in coal beds they account for most of the permeability and much of the porosity of coalbed gas reservoirs and can have a significant effect on the success of engineering procedures such as cavity stimulations because permeability and stimulation success are commonly limiting factors in gas well performance knowledge of cleat characteristics and origins is essential for successful exploration and production although the coal cleat literature spans at least 160 years mining issues have been the principal focus and quantitative data are almost exclusively limited to orientation and spacing information few data are available on apertures heights lengths connectivity and the relation of cleat formation to diagenesis characteristics that are critical to permeability moreover recent studies of cleat orientation patterns and fracture style suggest that new investigations of even these well studied parameters can yield insight into coal permeability more effective predictions of cleat patterns will come from advances in understanding cleat origins although cleat formation has been speculatively attributed to diagenetic and or tectonic processes a viable mechanical process for creating cleats has yet to be demonstrated progress in this area may come from recent developments in fracture mechanics and in coal geochemistry

weichselian palynostratigraphy palaeovegetation and palaeoenvironment the record from lago grande di monticchio southern italy abstract the palynostratigraphic record from lago grande di monticchio s italy is presented an independent sedimentation rate based chronology provides an age of 101 530 calendar years bp for the lowermost sediments sampled this chronology enables assessment of the rapidity of vegetation changes during the last glacial contrary to widely held views the vegetation showed numerous large magnitude changes in periods of

from sub rayleigh to supershear ruptures during stick slip experiments on crustal rocks supershear earthquake ruptures propagate faster than the shear wave velocity although there is evidence that this occurs in nature it has not been experimentally demonstrated with the use of crustal rocks we performed stick slip experiments with westerly granite under controlled upper crustal stress conditions supershear ruptures systematically occur when the normal stress exceeds 43 megapascals mpa with resulting stress drops on the order of 3 to 25 mpa comparable to the stress drops inferred by seismology for crustal earthquakes in our experiments the sub rayleigh to supershear transition length is a few centimeters at most suggesting that the rupture of asperities along a fault may propagate locally at supershear velocities in turn these sudden accelerations and decelerations could play an important role in the generation of high frequency radiation and the overall rupture energy budget

mechanical behavior of structurally reconstructed irregular columnar jointed rock mass using 3d printing abstract baihetan hydropower station is one the most famous hydroelectric projects in china the columnar jointed rock mass cjrm is widely distributed in this area such as at the dam site and drainage tunnel the rocks surrounding cjrm are usually unstable due to its discontinuity therefore the investigation of mechanical properties of cjrm is essential to designing relevant structures in recent years several previous studies have been conducted to determine the mechanical properties of regular cjrm reconstructed using the mixture of water cement and sand however few studies have been conducted on the irregular cjrms formed in nature because of their structural uniqueness in this study the mechanical properties of irregular cjrms reconstructed using 3d printing technology was investigated and verified through laboratory test first the sampling window method was adopted to obtain the structural characteristics of columnar jointed basalts cjbs after this the mechanical properties i e uniaxial compressive strength ucs uniaxial tensile strength uts peak shear strength residual shear strength failure mode and acoustic emission ae characteristics of the reconstructed and natural cjbs in the laboratory tests were compared based on the similarity constant the results show that the mechanical properties of irregular cjrm reconstructed using 3d printing are consistent with the in situ specimens when considering the similarity constant finally based on a detailed discussion of the reconstructed and original irregular cjrm a new method to accurately reconstruct the structure of irregular cjrms using 3d printing is suggested and verified this method could be used to design irregular cjrms in rock engineering

three dimensional effects of hydraulic conductivity enhancement and desaturation around mined panels changes in the three dimensional hydraulic conductivity field that accompany undermining by a longwall panel are evaluated to define the potential for changes in flow patterns and desaturation relations linking changes in conductivity with the mining induced strain field that develops around the advancing face are defined through the assumption of an equivalent porous medium with the strain partition between fractures and matrix apportioned relative to respective deformation constants model results are validated against behavior recorded at a well instrumented field site replicating the complex steady flow pattern that develops around an advancing longwall face significant hydraulic conductivity increases are restricted to strata at shallow depth ahead of the advancing face and to deep zones behind the face particularly in the caving zone and abutment shear zones these very large increases in conductivity at depth that include the out of section conductivity enhancement that develops along the panel rib exercise primary control on induced water level changes and the potential for saturation zones of desaturation are readily defined with these enabling locations of well vulnerability to water loss to be identified these zones of vulnerability are directly above the panel with their extent potentially modulated by the presence and the location of flatlying layers of low conductivity the complex response recorded in the near face region mandates use of three dimensional models to adequately represent observed behavior

compressibility of porous rocks four compressibilities are defined for porous rock relating changes in the bulk and pore volumes to changes in the pore and confining pressures using a micromechanical theory based on classical linear elasticity three relations are found between these compressibilities two of these relations are verified experimentally for berea and bandera sandstone bounds are derived for these compressibilities involving only the porosity and the elastic moduli of the rock forming minerals for the strains to be unique functions of the stresses the compressibilities must be functions only of the difference between the confining and pore pressures this dependence is verified for berea bandera and boise sandstone while the strains cannot be expressed as functions of an effective stress regardless of how it is defined the elastic volumetric behavior of porous rocks can be studied through tests conducted at zero pore pressure

rapid environmental changes in southern europe during the last glacial period oxygen isotope records from greenland ice cores1 2 indicate numerous rapid climate fluctuations during the last glacial period north atlantic marine sediment cores show comparable variability in sea surface temperature and the deposition of ice rafted debris3 4 5 in contrast very few continental records of this time period provide the temporal resolution and environmental sensitivity necessary to reveal the extent and effects of these environmental fluctuations on the continents here we present high resolution geochemical physical and pollen data from lake sediments in italy and from a mediterranean sediment core linked by a common tephrochronology our lacustrine sequence extends to the past 102 000 years many of its features correlate well with the greenland ice core records demonstrating that the closely coupled ocean atmosphere system of the northern hemisphere during the last glacial4 extended its influence at least as far as the central mediterranean region numerous vegetation changes were rapid frequently occurring in less than 200 years showing that the terrestrial biosphere participated fully in last glacial climate variability earlier than 65 000 years ago our record shows more climate fluctuations than are apparent in the greenland ice cores together the multi proxy data from the continental and marine records reveal differences in the seasonal character of climate during successive interstadials and provide a step towards determining the underlying mechanisms of the centennial millennial scale variability

premonitory acoustic emissions and stick slip in natural and smooth faulted westerly granite 1 a stick slip event was induced in a cylindrical sample of westerly granite containing a preexisting natural fault by loading at constant confining pressure of 150 mpa continuously recorded acoustic emission ae data and computer tomography ct generated images of the fault plane were combined to provide a detailed examination of microscale processes operating on the fault the dynamic stick slip event considered to be a laboratory analog of an earthquake generated an ultrasonic signal that was recorded as a large amplitude ae event first arrivals of this event were inverted to determine the nucleation site of slip which is associated with a geometric asperity on the fault surface ct images and ae locations suggest that a variety of asperities existed in the sample because of the intersection of branch or splay faults with the main fault this experiment is compared with a stick slip experiment on a sample prepared with a smooth artificial saw cut fault surface nearly a thousand times more ae were observed for the natural fault which has a higher friction coefficient 0 78 compared to 0 53 and larger shear stress drop 140 compared to 68 mpa however at the measured resolution the ultrasonic signal emitted during slip initiation does not vary significantly between the two experiments suggesting a similar dynamic rupture process we propose that the natural faulted sample under triaxial compression provides a good laboratory analogue for a field scale fault system in terms of the presence of asperities fault surface heterogeneity and interaction of branching faults

acoustic emissions associated with the formation of fracture sets in sandstone under polyaxial stress conditions a polyaxial true triaxial stress loading system developed originally for determining all nine components of p and s wave velocities and attenuation and fluid permeability for 50 8 mm side cubic rock specimens tested to failure has been modified to permit the measurement of acoustic emission events associated with the failure process results are reported for crosland hill sandstone tested to failure under loading conditions leading to the formation of sets of aligned microcracks achieved by maintaining the minor principal stress at a low value while increasing the two other principal stresses until failure of the rock an ultrasonic survey associated with the test has been employed to map the transversely isotropic velocity structure created by through going parallel fractures resulting from the sets of aligned microcracks this velocity structure has then been employed to locate acoustic emission events recorded during the test by four acoustic emission sensors located in each of the six specimen loading platens a selection of acoustic emission events associated with one of the fractures has been processed for moment tensor analysis information in order to determine the source type and orientation of microcracking as the fracture grows the mechanisms indicate tensile behaviour during initial fracture propagation shear failure however appears to dominate as the fracture finally approaches the opposite face of the cubic specimen the work presented here has in part led to the development of new rock testing systems and geophysical monitoring and processing technologies that will enable laboratory study of rock behaviour under conditions better resembling those experienced in situ

millstone coastal quarries of the mediterranean a new class of sea level indicator abstract the coasts of italy still preserve several remnants of coastal quarries built in antiquity that now provide insights into the intervening sea level changes occurred during the last millennia in this paper we show and discuss a new class of sea level indicator consisting of millstones carved along the rocky coast of southern italy since 2500 bp that are currently submerged they were extracted from beachrocks sandstones or similar sedimentary rocks easier for carving by ancient carving tools our study focuses on 10 coastal sites located at capo d orlando avola and letojanni in sicily soverato tropea and capo dell armi in calabria castellabate palinuro and scario in campania and polignano san vito in apulia unfortunately only limited archaeological information is available for these anthropic structures scario one of these millstone quarries discussed here has been dated through independent archaeological remains allowing us to restrict the exploitation age to the end of xvii century present day elevations of these coastal sites were obtained through geo archaeological surveys calibrated using the nearest tidal stations together with geomorphological and tectonic interpretations data were compared against the latest sea level predictions based on glacio hydro isostatic models our results allow proposal of the age range of these millstone quarries and to estimate the intervening relative sea level changes since the time when they were carved

eddy heat flux across the antarctic circumpolar current estimated from sea surface height standard deviation eddy heat flux ehf is a predominant mechanism for heat transport across the zonally unbounded mean flow of the antarctic circumpolar current acc observations of dynamically relevant divergent four year mean ehf in drake passage from the cdrake project as well as previous studies of atmospheric and oceanic storm tracks motivates the use of sea surface height ssh standard deviation h as a proxy for depth integrated downgradient time mean ehf ehf in the acc statistics from the southern ocean state estimate corroborate this choice and validate throughout the acc the spatial agreement between h and ehf seen locally in drake passage eight regions of elevated ehf are identified from nearly 23 5 years of satellite altimetry data elevated cross front exchange usually does not span the full latitudinal width of the acc in each region implying a hand off of heat between acc fronts and frontal zones as they encounter the different ehf hot spots along their circumpolar path integrated along circumpolar streamlines defined by mean ssh contours there is a convergence of ehf in the acc 1 06 pw enters from the north and 0 02 pw exits to the south temporal trends in low frequency ehf are calculated in a running mean sense using h from overlapping 4 year subsets of ssh significant increases in downgradient ehf magnitude have occurred since 1993 at kerguelen plateau southeast indian ridge and the brazil malvinas confluence whereas the other five ehf hot spots have insignificant trends of varying sign

laboratory characterisation of fracture compressibility for coal and shale gas reservoir rocks a review abstract unconventional natural gas including coalbed methane and shale gas has become important natural gas resources coal and shale reservoirs are characterised by low porosity and low permeability and difficult for gas production these reservoirs are also considered as fractured reservoirs i e the natural fracture cleat system in coals and bedding direction microfractures in shales permeabilities of these reservoirs are sensitive to stress change during gas production the pressure drawdown significantly increases effective stress and thus decreases the absolute permeability the relationship between permeability and stress is characterised by fracture compressibility which is difficult and costly to be obtained from the field but can be acquired easily from laboratory measurement in this review article the laboratory methods to obtain fracture compressibility were reviewed literature data on fracture compressibility for coals and shales were collated and the relationships between fracture compressibility and pressure stress and rock properties were discussed it is found that fracture compressibility is higher for coals than for shales and the fracture compressibility for proppant supported fracture is even lower than that for the same shale or coal moreover fracture compressibility is variable depending on gas type gas pressure and stress fracture compressibility has no correlation with absolute permeability in general but has a weak positive correlation for the same sample

meridional ekman heat fluxes for the world ocean and individual ocean basins abstract monthly climatological estimates of wind stress and sea surface temperature are used to compute meridional ekman heat fluxes in the world ocean qualitatively the annual cycles of the atlantic and pacific oceans are quite similar but quantitatively the pacific estimates are up to several times larger than the atlantic estimates the indian ocean exhibits an annual mean southward flux over nearly all of the 24 5 n 31 5 s latitude belt which qualitatively supports an annual mean net southward heat flux for this region as determined by surface heat balance requirements a large southward heat flux in the indian ocean centered at about 7 5 n during northern hemisphere summer is responsible for a global ekman heat flux distribution with an annual cycle in the tropics that qualitatively resembles the results of oort and vonder haar

the grotta grande of scario salerno italy archaeology and environment during the last interglacial mis 5 of the mediterranean region abstract archeological and paleo environmental researches carried on the grotta grande site illustrate the importance of a multidisciplinary approach among archeologists palynologists and paleontologists the archaeology fauna pollen and micro charcoal recovered in two short sedimentary successions trenches a f located close to the entrance of the cave are discussed the cave opens directly on the tyrrhenian sea 2 km from scario salerno campania southern italy the morphology of the cave and sedimentary processes were controlled by eustatic fluctuations during the late middle pleistocene and the early late pleistocene the sea repeatedly occupied the cave the cave was frequented by humans of middle palaeolithic culture archaeological and faunal record of the two trenches can be positioned within the climatic fluctuation posterior to the warm interglacial mis 5e peak pollen have been retrieved in the older series b c of trench a referable to mis 7 6 the most important archaeological finds are the occurrence of structures that indicate the living space trench f together with hearths and lithic industry the latter is characterised by the presence of the levallois system and by the prevalence of sidescrapers among tools the systematic use of limestone is observed only in trench f large and small mammal remains recovered within the two trenches show that in the neighbourhood of the site a diversified assemblage occurred including eleven large mammals among which the hippo the straight tusked elephant and the narrow nosed rhino are noteworthy and fourteen small mammal taxa mainly rodents with a significant amount of glirids the fauna is indicative of a temperate forested mediterranean environment variation of faunal composition suggests that environments underwent some minor fluctuations towards cooler and or drier landscapes pollen indicates vegetation organized in different belts mainly mediterranean evergreen forest maquis and mixed forest with conifers and deciduous broadleaved trees fresh water plant communities are mainly represented in trench a some records of tertiary taxa suggest stands of survival of these plants in the surroundings of the cave over the time span the landscape become more open due to some episodes of steppe vegetation spread caused by variation in temperature and humidity deposit of this age are rather uncommon even in the italian peninsula and therefore the integration of sedimentological archaeological faunal and palynological data provides an important piece of information to the puzzling reconstruction of the late pleistocene mediterranean environments before the onset of the glaciation

coupled flow and geomechanical processes during gas production from coal seams abstract permeability in coal seams is sensitive to stress and pore pressure changes an additional influence on this behaviour is the nature of the coal matrix to shrink with gas desorption and swell with adsorption concise relationships for permeability have been developed which incorporate these mechanisms some of which are derived from a geomechanical basis such as the shi durucan model and the palmer mansoori model while these expressions are attractive approaches for defining coal permeability during gas migration the geomechanical behaviour has been simplified by assuming uni axial strain and constant vertical stress in this paper a coupled numerical model is developed and used to investigate the applicability of these geomechanical assumptions for gas drainage from coal seams the modelling approach involved coupling the existing coal seam gas reservoir simulator simed ii with the geomechanical simulator flac3d while simed ii was used to simulate gas migration in a hypothetical coal seam and a series of production scenarios flac3d simulated the geomechanical response of the coal and the adjacent non coal geological formations to fluid pressure and gas content changes imported from simed ii the simulations which considered a range of property values relevant to the san juan basin found that while the assumption of uni axial strain introduced negligible discrepancy the assumption of constant vertical stress leads to significant differences between the shi durucan permeability estimate and that calculated from the simed flac3d simulation especially at early times during production these differences were a result of the pressure and sorption strain changes induced by production leading to arching of stresses in the vicinity of the production well the mechanism was shown to produce significant differences in the calculated gas rate particularly at early times during production

duration of last interglacial conditions in northwestern greece a new astronomical calibration method for long pollen records from southern europe is applied to the last interglacial interval of the ioannina sequence northwest greece this shows that the last interglacial in this region as defined by the presence of forest communities lasted c 15 500 years from 127 300 to 111 800 yr b p interglacial conditions developed within marine isotope sub stage mis 5e and persisted into mis 5d lagging changes in global ice volume

detailed analysis of acoustic emission activity during catastrophic fracture of faults in rock abstract the detailed time space distribution of acoustic emission ae events during the catastrophic fracture of rock samples containing a pre existing joint or potential fracture plane is obtained under triaxial compression using a high speed 32 channel waveform recording system and the results are discussed with respect to the prediction and characterization of catastrophic fault failure ae activity is modeled quantitatively in terms of the seismic b value of the magnitude frequency relation the self excitation strength of the ae time series and the fractal dimension of ae hypocenters consistent with previous studies on rock samples containing a fracture plane with several asperities the present analyses reveal three long term phases of ae activity associated with damage creation on heterogeneous faults each clearly identifiable based on the above parameters a long term decreasing trend and short term fluctuation of the b value in the phase immediately preceding dynamic fracture are identified as characteristic features of the failure of heterogeneous faults based on the experimental results it is suggested that precursory anomalies related to earthquakes and other events associated with rock failure are strongly dependent on the heterogeneity of the fault or rock mass a homogeneous fault or rock mass appears to fracture unpredictably without a consistent trend in precursory statistics while inhomogeneous faults fracture with clear precursors related to the nature of the heterogeneity

permeability changes in coal analytical modeling abstract permeability changes can be very large during depletion of coalbed methane wells up to 100 times in the san juan basin analytic models of permeability increase during depletion are accessible easy to use and practical they are more transparent and less complicated than coupled numerical models however there are minor differences between the analytic models and these are reviewed here there are also discrepancies in attempting to match field data which is the final test of a model and these are discussed two different sets of san juan data have been modeled after suppressing the pressure dependent permeability with reasonably consistent reservoir parameters the matching parameters appear to be justifiable the small porosities do not seem to be ruled out by reservoir experts and the changes of elastic parameters including pore volume compressibility with depletion do not seem unreasonable the analytic models are used in reservoir simulators to model and predict injection of greenhouse gases in coal seams only when we can match the permeability increase of coalbed methane wells during depletion will we have the confidence to use the analytic models in reservoir simulators to match or predict sequestration of greenhouse gases such as co2

characterizing the shale gas resource potential of devonian mississippian strata in the western canada sedimentary basin application of an integrated formation evaluation devonian mississippian strata in the northwestern region of the western canada sedimentary basin wcsb were investigated for shale gas potential in the subsurface thermally mature strata of the besa river horn river muskwa and fort simpson formations attain thicknesses of more than 1 km 0 6 mi encompassing an area of approximately 125 000 km2 48 300 mi2 and represent an enormous potential gas resource total gas capacity estimates range between 60 and 600 bcf section of particular exploration interest are shales and mudrocks of the horn river formation including the laterally equivalent lower besa river mudrocks muskwa formation and upper besa river formation which yield total organic carbon toc contents of up to 5 7 wt fort simpson shales seldom have toc contents above 1 wt horn river and muskwa formations have excellent shale gas potential in a region between longitudes 122w and 123w and latitudes 59n and 60n national topographic system nts 94o08 to 94o15 in this area which covers an areal extent of 6250 km2 2404 mi2 average toc contents are higher 3 wt as determined by wire line log calibrations and have a stratal thickness of more than 200 m 656 ft gas capacities are estimated to be between 100 and 240 bcf section and possibly greater than 400 tcf gas in place a substantial percentage of the gas capacity is free gas caused by high reservoir temperatures and pressures muskwa shales have adsorbed gas capacities ranging between 0 3 and 0 5 cm3 g 9 6 16 scf t at reservoir temperatures of 60 80c 140 176f whereas besa river mudrocks and shales have low adsorbed gas capacities of less than 0 01 cm3 g 0 32 scf t liard basin region because reservoir temperatures exceed 130c 266f potential free gas capacities range from 1 2 to 9 5 cm3 g 38 4 to 304 scf t when total pore volumes 0 4 6 9 are saturated with gas the mineralogy has a major influence on total gas capacity carbonate rich samples indicative of adjacent carbonate platform and embayment successions commonly have lower organic carbon content and porosity and corresponding lower gas capacity 1 toc and 1 porosity seaward of the carbonate slave point edge muskwa and lower besa river mudrocks can be both silica and toc rich up to 92 quartz and 5 wt toc and most favorable for shale gas reservoir exploration because of possible fracture enhancement of the brittle organic and siliceous rich facies however an inverse relation between silica and porosity in some regions implies that zones with the best propensity for fracture completion may not provide optimal gas capacity and a balance between favorable reservoir characteristics needs to be sought

the effects of stress and fracturing on permeability of coal abstract this paper examines the changes in structure and permeability of coal under the stress conditions experienced around longwall faces the effect of fracturing on permeability of coal is discussed and the stress permeability relationship for fractured coal is compared with that of non fractured coal an empirical relationship between stress and permeability for coal is derived from the experimental data which relates the stress permeability behaviour of coal to its rank through the compressibility of the coal itself

the role of spatial variability in coal seam parameters on gas outburst behaviour during coal mining abstract gas outburst is recognized as a potentially fatal hazard to be managed during the mining of gassy coal seams gas outbursts in australian coal mines have been associated with the presence of geological structures in the coal and surrounding rocks having a range of spatial scales from millimetres to metres the contributing mechanisms are influenced by coal gas reservoir variables including gas composition fluid pressure desorption pressure and rate porosity intrinsic permeability and relative permeability they are also influenced by geomechanical variables such as strength in situ stress and mining induced stress the work described here concerns the influence of variability of permeability and strength on outburst behaviour key coal properties are characterised for a field site in an operational underground coal mine and then used in a series of hypothetical simulations of outburst initiation at the field site an array of horizontal holes was cored in seam well tests for permeability and stress were performed in the holes and recovered core was tested in the laboratory for permeability strength and sorption properties for permeability and strength sufficient numbers of measurements were obtained to describe these properties statistically assuming that the measurements are uncorrelated spatially analysis of the cumulative probability distributions of the field and laboratory permeability data shows a strong size effect that cannot be linearly up scaled using monte carlo techniques these statistical descriptions are used to generate realisations of property values across the model grid used in the simulation analyses the stochastic model approach demonstrates that the variability of the permeability and strength fields can lead to both outburst and non outburst outcomes from the same measured input data depending on the corresponding spatial distribution of permeability and strength at the face these results suggest the potential application of this approach as a tool for outburst risk analysis and assessment

deformation and permeability evolution of coals considering the effect of beddings abstract coal belongs to sedimentary rock with obvious bedding planes the existence of bedding weakens the continuity and integrity of coal deformation and permeability anisotropy of coals to a certain extent is attributed to the bedding planes we performed experiments of deformation and permeability evolution of coals under true triaxial stress conditions the experimental results indicate that the volumetric strain and bedding jointly affect permeability an analytical model for stress strain relationship of coals containing beddings is developed to quantify the bedding effects under true triaxial stress conditions in the model the deformation and permeability of the bedding and non bedding are separated through bedding ratio and bedding elastic modulus the bedding ratio is defined as the ratio of the total length of bedding to the total length of coal normal to bedding planes which is a parameter closely related to the porosity the elastic modulus is divided into four parts a bedding elastic modulus and a non bedding elastic modulus in the direction normal to bedding planes and two elastic moduli in the direction parallel to bedding planes the four elastic moduli are calculated by the analytical model the bedding elastic modulus is relatively small which shows that the bedding effect cannot be ignored the permeability is highly sensitive to the bedding of coal with low stress in the direction normal to the bedding the bedding ratio always affects the volumetric strain the permeability of the coal is divided into bedding and non bedding permeability the ratio of the bedding permeability to the total permeability is different due to different stresses in the direction normal to bedding planes which is linking with the compression of bedding a permeability model which can reflect the different effects of beddings and non beddings to the total permeability is proposed and verified

stress dependence of the permeability and porosity of sandstone and shale from tcdp hole a abstract we utilize an integrated permeability and porosity measurement system to measure the stress dependent permeability and porosity of pliocene to pleistocene sedimentary rocks from a 2000 m borehole experiments were conducted by first gradually increasing the confining pressure from 3 to 120 mpa and then subsequently reducing it back to 3 mpa the permeability of the sandstone remained within a narrow range 10 14 10 13 m2 the permeability of the shale was more sensitive to the effective confining pressure varying by two to three orders of magnitude than the sandstone possibly due to the existence of microcracks in the shale meanwhile the sandstone and shale showed a similar sensitivity of porosity to effective pressure whereby porosity was reduced by about 10 20 when the confining pressure was increased from 3 to 120 mpa the experimental results indicate that the fit of the models to the data points can be improved by using a power law instead of an exponential relationship to extrapolate the permeability or porosity under larger confining pressure e g 300 mpa using a straight line in a log log plot might induce unreasonable error but might be adequate to predict the stress dependent permeability or porosity within the experimental stress range part of the permeability and porosity decrease observed during loading is irreversible during unloading

modelling permeability for coal reservoirs a review of analytical models and testing data abstract as with other reservoir types permeability is a key controlling factor for gas migration in coalbed methane reservoirs the absolute permeability of coal reservoirs changes significantly during gas production often initially decreasing but then increasing as the reservoir pressure and gas content is drawn down it has also been observed to decrease markedly during co2 injection to enhance coalbed methane recovery in order to predict gas migration models for coal permeability must represent the mechanisms leading to these observed behaviours the permeability of coal reservoirs behaves in a similar fashion to other fractured reservoirs with respect to effective stress decreasing exponentially as the effective stress increases however a unique effect of coal is that it shrinks with gas desorption and swells with adsorption within the reservoir this swelling shrinkage strain leads to a geomechanical response changing the effective stress and thus the permeability modelling coal permeability incorporating the impacts from both effective stress and coal swelling shrinkage dates back about 25 years since then a number of permeability models have been developed in recent years this topic has seen a great deal of activity with a growing body of research on coal permeability behaviour and model development this article presents a review of coal permeability and the approaches to modelling its behaviour as an important part of this the field and laboratory data used to test the models are reviewed in detail this article also aims to identify some potential areas for future work

coupled flow and geomechanical processes during enhanced coal seam methane recovery through co2 sequestration abstract the sensitivity of coal permeability to the effective stress means that changes in stress as well as pore pressure within a coal seam lead to changes in permeability in addition coal swells with gas adsorption and shrinks with desorption these sorption strains impact on the coal stress state and thus the permeability therefore the consideration of gas migration in coal requires an appreciation of the coupled geomechanical behaviour a number of approaches to representing coal permeability incorporate the geomechanical response and have found widespread use in reservoir simulation however these approaches are based on two simplifying assumptions uniaxial strain i e zero strain in the horizontal plane and constant vertical stress this paper investigates the accuracy of these assumptions for reservoir simulation of enhanced coalbed methane through co 2 sequestration a coupled simulation approach is used where the coalbed methane simulator simed ii is coupled with the geomechanical model flac3d this model is applied to three simulation case studies assembled from information presented in the literature two of these are for 100 co 2 injection while the final example is where a flue gas 12 5 co 2 and 87 5 n 2 is injected it was found that the horizontal contrast in sorption strain within the coal seam caused by spatial differences in the total gas content leads to vertical stress variation thus the permeability calculated from the coupled simulation and that using an existing coal permeability model the shi durucan model are significantly different for the region in the vicinity of the production well the coupled permeability is greater than the shi durucan model in the vicinity of the injection well the permeability is less than that calculated using the shi durucan model this response is a function of the magnitude of the strain contrast within the seam and dissipates as these contrasts diminish

hydrodynamics of coalbed methane reservoirs in the black warrior basin key to understanding reservoir performance and environmental issues abstract the black warrior basin of the southeastern united states hosts one of the world s most prolific and long lived coalbed methane plays and the wealth of experience in this basin provides insight into the relationships among basin hydrology production performance and environmental issues along the southeast margin of the basin meteoric recharge of reservoir coal beds exposed in an upturned fold limb exerts a strong control on water chemistry reservoir pressure and production performance fresh water plumes containing na hco3 waters with low tds content extend from the structurally upturned basin margin into the interior of the basin northwest of the plumes coal beds contain na cl waters with moderate to high tds content carbon isotope data from produced gas and mineral cements suggest that the fresh water plumes have been the site of significant bacterial activity and that the coalbed methane reservoirs contain a mixture of thermogenic and late stage biogenic gases water produced from the fresh water plumes may be disposed safely at the surface whereas underground injection has been used locally to dispose of highly saline water wells in areas that had normal hydrostatic reservoir pressure prior to development tend to produce large volumes of water and may take up to 4 a to reach peak gas production in contrast wells drilled in naturally underpressured areas distal to the fresh water plumes typically produce little water and achieve peak gas rates during the first year of production environmental debate has focused largely on issues associated with hydrologic communication between deep reservoir coal beds and shallow aquifers in the coalbed methane fields of the black warrior basin a broad range of geologic evidence suggests that flow is effectively confined within coal and that the thick intervals of marine shale separating coal zones limit cross formational flow

permeability of illite bearing shale 1 anisotropy and effects of clay content and loading direction relative to bedding clay content 40 65 and effective pressure pe 2 12 mpa permeability k is anisotropic at low pe measured k values for flow parallel to bedding at pe 3 mpa exceed those for flow perpendicular to bedding by a factor of 10 both for low clay content lc and high clay content hc samples with increasing pe k becomes increasingly isotropic showing little directional dependence at 10 12 mpa permeability depends on clay content k measured for lc samples exceed those of hc samples by a factor of 5 permeability decreases irreversibly with the application of pe following a cubic law of the form k k0 1 pe p1 m 3 where k0 varies over 3 orders of magnitude depending on orientation and clay content m is dependent only on orientation equal to 0 166 for bedding parallel flow and 0 52 for flow across bedding and p1 18 27 mpa appears to be similar for all orientations and clay contents anisotropy and reductions in permeability with pe are attributed to the presence of crack like voids parallel to bedding and their closure upon loading respectively index terms 5114 physical properties of rocks permeability and porosity 5139 physical properties of rocks transport properties 5112 physical properties of rocks microstructure 1832 hydrology groundwater transport keywords permeability shale connected pore space

variation in permeability with lithotype and maceral composition of cretaceous coals of the canadian cordillera abstract the permeability of high and medium volatile bituminous cretaceous coal at the megascopic and microscopic scale is investigated utilizing a pressure decay permeameter the order of decreasing permeability with lithotype is bright average 4 1 md banded 0 79 md fibrous 0 50 md banded dull 0 14 md and dull 0 016 md bright coals are the most permeable because of associated macro fracturing cleat banded dull coal permeability generally increases with increasing vitrinite content the lowest permeabilities occur in dull coals with a high mineral and inertinite content fibrous coal has a higher permeability than dull coal of the same rank due to the abundance of macroporous fusinite in fibrous coal dull coal permeability decreases with an increase in rank but these results are overshadowed by compositional variability between samples pressure decay measurements are more reliable for dull lithotypes as these lithotypes do not fracture as easily during sample preparation although measured permeabilities are optimistic due to the relaxation of stress upon exposure of coal to atmospheric pressure the results obtained are representative of the range of permeabilities of coal lithotypes and provide insight into the variability in permeability that may exist at high effective stress in the subsurface

source analysis of acoustic emissions in aue granite cores under symmetric and asymmetric compressive loads the effect of stress anisotropy on the brittle failure of granite is investigated under uniaxial compression non standard asymmetric compression tests are performed on cores of aue granite diameter 52 mm length 100 mm in which 20 per cent of the core top surface remains unloaded the edge of the asymmetric steel loading plate acts as a stress concentrator from where a shear rupture is initiated the propagation of the fracture related process zone from top to bottom of the core is mapped by microcrack induced acoustic emissions compared to standard uniaxial tests with symmetric loading in the asymmetric tests both a greater quantity and more localized distributions of emission event hypocentres are observed the maximum event density doubles for asymmetric 20 events per 10 6 m3 compared to symmetric tests the cluster correlation coefficient a measure of strain localization in the faulting process reaches 0 15 for symmetric and 0 30 for asymmetric tests the clustering of events however is found post failure only three different amplitudes are used to determine b values discussed as a possible failure precursor focal amplitudes determined at a 10 mm source distance and maximum amplitudes measured at eight piezoceramic sensors lead to b values that drop before rock failure first pulse amplitudes automatically picked from emission wavelets show no anomaly first motion polarity statistics of amplitudes indicate that a shear crack type radiation pattern is responsible for 70 per cent of the failure of granite irrespective of stress boundary conditions for type s events with an equal percentage of dilatational and compressional first motions focal mechanisms are determined by fitting measured first pulse amplitudes to an assumed double couple radiation pattern while hypocentres of large type s events align parallel to the later fracture plane their fault plane solutions show no coherent pattern spatial views of fracture planes reconstructed from x ray computed tomograms reveal local small scale changes in fracture plane orientation nodal planes from average fault plane solutions of the microscopic acoustic emission events coincide with the overall orientation of the macroscopic fracture plane azimuth strike angle determined from thin sections and tomograms

abrupt temperature changes in the western mediterranean over the past 250 000 years a continuous high resolution western mediterranean sea surface temperature sst alkenone record spanning the past 250 000 years shows that abrupt changes were more common at warming than at cooling during marine isotope stage mis 6 sst oscillated following a stadial interstadial pattern but at lower intensities and rates of change than in the dansgaard oeschger events of mis 3 some of the most prominent events occurred over miss 5 and 7 after prolonged warm periods of high stability climate during the whole period was predominantly maintained in interglacial interstadial conditions whereas the duration of stadials was much shorter

neanderthal firewood management evidence from stratigraphic unit iv of abric del pastor eastern iberia abstract this paper presents anthracological data from abric del pastor alcoi spain a middle paleolithic rock shelter site analysis of 1077 wood charcoal remains from stratigraphic unit iv s u iv collected within archaeological combustion structures and from loose sediment outside of structures allowed us to characterise the local landscape as well as to approach the interaction between neanderthal groups and their local environment taxonomic identification suggests that firewood was gathered from nearby sources with predominance of juniper juniperus sp followed by thermophilous shrubby taxa additional analysis focussing on post depositional processes affecting charcoal have shown features indicative of biodegradation and mechanical action the results of this study contribute significant anthracological data towards our understanding of late pleistocene mediterranean landscapes and neanderthal forest management in this region

failure properties of cubic granite marble and sandstone specimens under true triaxial stress abstract cubic specimens of granite marble and sandstone with side lengths of 50 mm were prepared in the laboratory true triaxial compression tests were conducted on each rock type with minor principal stress 3 magnitudes of 10 20 30 50 and 100 mpa and the intermediate principal stress 2 varying from 2 3 to 2 1 where 1 represents the major principal stress the experimental results demonstrated that the failure strength fracture dip angle non linear behavior and failure mode of these rocks under true triaxial conditions were affected by both 2 and 3 as well as by the rock lithology when 3 was kept constant and 2 increased failure strength showed an initial increase followed by a decrease whereas the fracture dip angle increased monotonically the non linear behavior before the peak strength point of granite became more apparent by the increase of 3 whereas 2 had an opposite effect on the non linear behavior of granite under high 3 e g 100 mpa the non linear behavior before the peak strength point was always found in marble and sandstone for all of the stress state conditions analyses of fracture dip angle and failure mode showed that when 3 10 20 and 30 mpa and 2 3 5 7 5 and 10 respectively the failure mode of granite changed from shear to slabbing whereas marble and sandstone always fractured in the shear direction this study confirms that rocks may experience slabbing failure under true triaxial stress and slabbing failure mode is likely to be induced in high strength and brittle rocks under low 3 with the stress ratio of 2 3 exceeding a particular threshold value

stable volume and heat transports of the north pacific subtropical gyre revealed by identifying the kuroshio in synoptic hydrography south of japan 1 we conducted synoptic hydrographic surveys three times under distinctly different conditions of the kuroshio in the region off the southern coast of japan the large meander october 2004 and non large meander september 2005 and september 2006 states as a result of the water mass analysis we could separate the volume and heat transports of the north pacific subtropical gyre from the local recirculation gyre and mesoscale eddies despite the different flow conditions of the kuroshio the volume transport and the volume transport averaged temperature of the subtropical gyre fluctuate within the ranges of 23 3 29 0 106 m3 s 1 and 17 3 17 6 c respectively which are quite stable with respect to those for the kuroshio south of japan estimated in the past studies taking into account the decrease in the volume transport averaged temperature in the north pacific interior region the net heat transport of the subtropical gyre across the latitude of 30 n was estimated to be between 0 19 and 0 22 1015 w

volumetric strain associated with methane desorption and its impact on coalbed gas production from deep coal seams the permeability of deep 1000 m 3300 ft coal seams is commonly low for deep coal seams significant reservoir pressure drawdown is required to promote gas desorption because of the langmuir type isotherm that typifies coals hence a large permeability decline may occur because of pressure drawdown and the resulting increase in effective stress depending on coal properties and the stress field during production however the permeability decline can potentially be offset by the permeability enhancement caused by the matrix shrinkage associated with methane desorption the predictability of varying permeability is critical for coalbed gas exploration and production well management we have investigated quantitatively the effects of reservoir pressure and sorption induced volumetric strain on coal seam permeability with constraints from the adsorption isotherm and associated volumetric strain measured on a cretaceous mesaverde group coal piceance basin and derived a stress dependent permeability model our results suggest that the favorable coal properties that can result in less permeability reduction during earlier production and an earlier strong permeability rebound increase in permeability caused by coal shrinkage with methane desorption include 1 large bulk or young s modulus 2 large adsorption or langmuir volume 3 high langmuir pressure 4 high initial permeability and dense cleat spacing and 5 low initial reservoir pressure and high in situ gas content permeability variation with gas production is further dependent on the orientation of the coal seam the reservoir stress field and the cleat structure well completion with injection of n2 and displacement of ch4 only results in short term enhancement of permeability and does not promote the overall gas production for the coal studied

experimental study of fluid transport processes in the matrix system of the european organic rich shales ii posidonia shale lower toarcian northern germany abstract a laboratory study has been conducted to investigate the transport of gases he ar ch 4 and water in the matrix of lower toarcian posidonia shale samples from three shallow boreholes in northern germany the maturity of the organic matter of the shale samples ranged between 0 53 and 1 45 vitrinite reflectance vr r the measurements were performed at effective stresses ranging between 6 and 37 mpa and a temperature of 45 c the effects of different controlling factors including permeating fluid maturity anisotropy moisture content and effective stress on the fluid conductivity were analyzed and discussed permeability coefficients measured perpendicular and parallel to bedding 3 10 22 to 9 7 10 17 m 2 were within the range previously reported for other shales and mudstones they exhibited a strong dependence on permeating fluid maturity anisotropy moisture content and effective stress the permeability coefficients measured with helium as permeate were consistently higher up to two times than those measured with argon and methane permeability coefficients measured with water were up to three orders of magnitude lower than klinkenberg corrected gas permeability coefficients measured with helium and methane under similar experimental conditions among the samples studied the lowest porosity and permeability coefficients were measured on samples of intermediate thermal maturity 0 88 vr r oil window permeability coefficients he ch 4 measured parallel to bedding were up to more than one order of magnitude higher than those measured perpendicular to bedding permeability coefficients measured with he and ch 4 on a dry sample were up to two times higher than those measured on a sample with the as received moisture content all samples showed a nonlinear reduction in permeability parallel to bedding with increasing effective stress 6 37 mpa the permeability anisotropy and stress dependence of permeability were controlled by the mineralogy

influence of temperature on the strainburst characteristics of granite under true triaxial loading conditions abstract the experimental study of the strainburst on granite treated with different high temperatures was conducted using a novel true triaxial rockburst test system during the test process a loading path was given by keeping one free face and then loading on other five faces the strainburst process the failure patterns the peak stress the acoustic emission ae signal characteristics the fragment characteristics and the kinetic energy of the ejected fragments were analyzed by employing the stress strain curves the high speed camera system and the ae technology the experimental results show that temperature has significant influences on the strainburst the critical temperature of these specimens is 300 c with the temperature increasing from 30 c to 300 c the peak stress the peak strain and the ae process exhibit a slight variation while the kinetic energy of the ejected fragments rapidly increases when the temperature increases from 300 c to 700 c the peak stress and the kinetic energy apparently decrease but the peak strain swiftly rises the time of the ae quiet period and the fragmentation increase with rising temperature compared with the specimens at 30 c the specimens treated with temperatures from 100 c to 500 c have more intense rockburst while the specimens treated with temperatures from 600 c to 700 c have a lesser kinetic energy of the ejected fragments

nature and origin of fractures in permian coals from the bowen basin queensland australia a field investigation into the development of cleat and other fractures within permian coal measures was undertaken in the bowen basin of eastern queensland australia to provide predictive information on coal permeability for use in coalbed methane exploration data were collected from five open cut and three underground mines in the southern and central bowen basin covering the upper permian german creek formation and rangal coal measures fractures noted in the coals fall readily into the four categories of faults and shear zones extension and compression related joint sets mining induced fractures and coal cleats four geometric varieties of coal cleats were identified class a orthogonal sets class b sinusoidal sets class c polygonal sets and class d chaotic sets superimposed or overprinted type a sets were also observed locally on a regional scale the cleats typically parallel dip face cleats and strike butt cleats but local departures from this pattern occur in proximity to faults where face and butt cleat directions were often reversed rotated or multimodal field data suggest that coal cleats of classes a b and c were formed by brittle fracturing of the coal during burial wheras class d and superimposed cleats were formed during later compressional events constraints on the timing of deformation events affecting the bowen basin and geochemical data provided by other workers indicate that the cleats were formed within 5 ma of formation of precursor peats but were in many instances modified by later structural events

a directional crack damage memory effect in sandstone under true triaxial loading crack damage leading to failure in rocks can be accumulated through cyclic stressing in the crust however the vast majority of experimental studies to investigate cyclic stressing apply conventional triaxial stress states 1 2 3 while in nature the state of stress in the crust is generally truly triaxial 1 2 3 furthermore the magnitude of these crustal stresses can vary over time and their orientations can also rotate over time generating multiple crack populations and bulk anisotropic crack damage we investigate the evolution of crack damage under both conventional and true triaxial stress conditions by sequentially and cyclically varying stresses in all three principal directions on cubic samples of dry sandstone using independently controlled stress paths we have measured simultaneously with stress the bulk acoustic emission output as a proxy for crack damage we report a directionally controlled crack damage memory effect which has implications for the approach to failure in complex tectonic stress environments

3 d transport and acoustic properties of fontainebleau sandstone during true triaxial deformation experiments abstract fontainebleau sandstone specimens have been tested in a true triaxial geophysical imaging cell under hydrostatic 1 2 3 traditional triaxial 1 2 3 and true triaxial 1 2 3 stress regimes the research objectives are to recognize the effect of various stress ratios 2 3 under varying magnitudes of 2 and 3 on 3 d stress strain responses 3 d transport 3 d ultrasonic wave velocities and acoustic emission properties comparison of the variation of 3 d directional permeability between the specimens shows that higher magnitude of 3 and 2 disrupts the 3 d interconnectivity of the pore spaces and intergranular cracks irrespective of the magnitude of applied stress ratio 2 3 the observed permeability anisotropy between the two specimens is a function of inherent oriented pores and cracks stress ratio 2 3 and the magnitude of applied 3 and 2 stresses temporal and spatial evolution of the ae hypocenter locations combined with the examination of micro ct and thin section images shows the timely development of polymodal fault systems during peak to post peak stresses and validates the development of the source mechanism inferred from the acoustic emission events

modulation of monsoon circulations by cross equatorial ocean heat transport abstractmotivated by observations of southward ocean heat transport oht in the northern indian ocean during summer the role of the ocean in modulating monsoon circulations is explored by couplin

sampling and preparation of c 200 mm diameter cylindrical rock samples for geomechanical experiments abstract experimental investigation of rock mechanical properties of real and artificial samples often requires much care and attention to detail during sample preparation this especially applies to high fidelity state of the art complex experimental apparatuses where sample tolerance is low due to the complexity of the measuring and stress control devices as well as the nature of the experiments to be conducted although sometimes mundane the sample preparation methodology is as equally important as the experimental apparatus itself and can require several new technological developments the methodology and technical developments required to prepare realistic heterogeneous fractured and natural reservoir analogue rock samples for coupled thermo hydro mechanical chemical process experimental investigation is described here we present the sample recovery and preparation procedures for large c 200 mm diameter cylindrical samples of 200 mm 5 mm length with variable composition and mechanical properties e g rock strength existing fractures fracture networks macro porosity or lithic fragments although the technology demonstrated is for a specific application the procedures developed equipment and methodology are applicable to multiple sizes of sample requirements

the return to the iberian peninsula first quaternary record of muscardinus and a palaeogeographical overview of the genus in europe abstract although the earliest record of the genus muscardinus dates from the middle miocene in spain no mention has been reported since the lower pliocene in the iberian peninsula in this paper quaternary fossil remains of a hazel dormouse muscardinus avellanarius are described for the first time in the iberian peninsula these remains constitute the south westernmost record of the genus in the eurasian continent during the late pleistocene the fossils one first upper molar m1 and two second upper molars m2 come from lezetxiki ii cave an early late pleistocene site in northern spain the presence of the hazel dormouse agrees with the abundance of rodent species indicative of woodland suggesting mild climatic conditions and a landscape formed by deciduous forest this assemblage has been arguably assigned to warm and humid conditions related to an interstadial period in mis 5 we also present an overview of the palaeogeography of the genus in europe the identification of this dormouse reinforces the idea of biological corridors between western iberia and the rest of europe during the pleistocene

geomechanical properties and permeability of coals from the foothills and mountain regions of western canada abstract static and dynamic geomechanical properties and hydraulic permeability were determined for six large blocks of bituminous coal sampled from active mines in the foothills and mountain regions of western canada testing showed a nonlinear shear strength envelope and brittle failure during triaxial loading the dominant failure mode was along distinct shear planes effective compressive strengths increased from 8 6 mpa to 80 8 mpa with increasing confining pressure the mohr coulomb failure criterion showed that the coals had friction angle of 29 8 to 39 8 and cohesion ranging between 3 4 mpa and 8 0 mpa with increasing confining stress the non linear hoek brown failure envelope was also fit to the data which provided a better estimation of the strength values for static young s modulus ranged from 1119 mpa to 5070 mpa and poisson s ratio ranged from 0 26 to 0 48 also varying with the confining stress concurrent ultrasonic measurements indicate that the values for dynamic moduli are consistently higher than those obtained from quasi static measurements permeability of the coals tested at simulated in situ stress conditions and parallel to bedding surfaces was highly variable ranging from 2 09 md in seam 3 greenhills mine to less than 0 001 md in seam 10 elkview mine this variation may be rationalized based on variations in maceral composition stress history degree of shearing and the mode of deformation brittle or ductile of the coal seams in these tectonically complex regions

dynamic in situ three dimensional imaging and digital volume correlation analysis to quantify strain localization and fracture coalescence in sandstone advances in triaxial compression deformation apparatus design dynamic x ray microtomography imaging data analysis techniques and digital volume correlation analysis provide unparalleled access to the in situ four dimensional distribution of developing strain within rocks to demonstrate the power of these new techniques and acquire detailed information about the micromechanics of damage evolution deformation and failure of porous rocks we deformed 3 cm scale cylindrical specimens of low porosity fontainebleau sandstone in an x ray transparent triaxial compression apparatus and repeatedly recorded three dimensional tomograms of the specimens as the differential stress was increased until macroscopic failure occurred experiments were performed at room temperature with confining pressure in the range of 10 20 mpa distinct grayscale subsets indicative of density enabled segmentation of the three dimensional tomograms into intact rock matrix pore space and fractures digital volume correlation analysis of pairs of tomograms provided time series of three dimensional incremental strain tensor fields throughout the experiments after the yield stress was reached the samples deformed first by dilatant opening and propagation of microfractures and then by shear sliding via grain rotation and strain localization along faults for two samples damage and dilatancy occurred by grain boundary opening and then a sudden collapse of the granular rock framework at failure for the third sample a fault nucleated near the yield point and propagated in the sample through the development of transgranular microfractures the results confirm findings of previous experimental studies on the same rock and provide new detailed quantifications of 1 the proportion of shear versus dilatant strain in the sample 2 the amount of dilatancy due to microfracture opening versus pore opening when a fault develops and 3 the role of grain boundaries and pore walls in pinning microfracture propagation and slowing down the rate of damage accumulation as failure is approached our study demonstrates how the combination of high resolution in situ dynamic x ray microtomography imaging and digital volume image correlation analysis can be used to provide additional information to unravel brittle failure processes in rocks under stress conditions relevant to the upper crust

acoustic emission monitoring of hydraulic fracturing laboratory experiment with supercritical and liquid co2 1 carbon dioxide co2 is often used for enhanced oil recovery in depleted petroleum reservoirs and its behavior in rock is also of interest in co2 capture and storage projects co2usually becomes supercritical sc co2 at depths greater than 1 000 m while it is liquid l co2 at low temperatures the viscosity of l co2is one order lower than that of normal liquid water and that of sc co2is much lower still to clarify fracture behavior induced with injection of the low viscosity fluids we conducted hydraulic fracturing experiments using 17 cm cubic granite blocks the ae sources with the sc and l co2injections tend to distribute in a larger area than those with water injection and furthermore sc co2tended to generate cracks extending more three dimensionally rather than along a flat plane than l co2 it was also found that the breakdown pressures for sc and l co2 injections are expected to be considerably lower than for water

micromechanics of asperity rupture during laboratory stick slip experiments 1 acoustic emissions and tremor like signals are widely recorded in laboratory experiments we are able to isolate the physical origins of these signals using high resolution nanoseismic analysis the use of a picometer sensitive wide band sensor array permits us to determine force time functions and focal mechanisms for discrete events found amid the noise of friction similar to how low frequency earthquakes are found buried within tremor we interpret these localized events to be the rupture of m sized contacts known as asperities we performed stick slip experiments on plastic plastic and rock rock interfaces and found a systematic difference between the nano earthquakes the rock interface produces very rapid 1 s implosive forces indicative of brittle failure and fault gouge formation while rupture on the plastic interface releases only shear force and produces a nano quake more similar to earthquakes commonly recorded in the field the difference between the mechanisms is attributed to the vast differences in the hardness and melting temperatures of the two materials which affect the distribution of asperities as well as their failure behavior with proper scaling the strong link between material properties and laboratory earthquakes will aid in our understanding of fault mechanics and the generation of earthquakes and tectonic tremor

the last 1 35 million years at tenaghi philippon revised chronostratigraphy and long term vegetation trends abstract in addition to being of interest to ancient greek and roman historians the site of philippi ne greece has long been noted in quaternary circles for providing the longest continuous european pollen record spanning the last one million years here the original age model is re evaluated and a new marine terrestrial correlation is proposed an astronomical calibration procedure based on a correspondence between changes in certain vegetation elements and march and june perihelion configurations suggests that the base of the sequence extends back to 1 35 million years ago the revised chronological framework for the tenaghi philippon sequence provides an opportunity to examine the long term behaviour of individual taxa and vegetation trends within the context of global climate changes comparisons reveal a close correspondence between the terrestrial and marine records in terms of orbital and suborbital variability however joint time frequency analysis of the arboreal pollen record shows that the obliquity and eccentricity precession signals persist into the 100 kyr and 41 kyr worlds respectively suggesting the operation of additional climate mechanisms that are independent of high latitude glacial interglacial effects unlike ice core and marine sequences no change in the magnitude of interglacial tree population expansions is observed after the mid brunhes event instead the tenaghi philippon record suggests a major shift in the vegetational composition of interglacials after mis 16 with the establishment of forests of reduced diversity and a modern appearance

laboratory simulation of volcano seismicity the physical processes generating seismicity within volcanic edifices are highly complex and not fully understood we report results from a laboratory experiment in which basalt from mount etna volcano italy was deformed and fractured the experiment was monitored with an array of transducers around the sample to permit full waveform capture location and analysis of microseismic events rapid post failure decompression of the water filled pore volume and damage zone triggered many low frequency events analogous to volcanic long period seismicity the low frequencies were associated with pore fluid decompression and were located in the damage zone in the fractured sample these events exhibited a weak component of shear double couple slip consistent with fluid driven events occurring beneath active volcanoes