effective medium theories for fluid saturated materials with aligned cracks there is general agreement between different theories giving expressions for the overall properties of materials with dry aligned cracks if the number density of cracks is small there is also very fair agreement for fluid filled isolated cracks however there are considerable differences between two separate theories for fluid filled cracks with equant porosity comparison with recently published experimental data on synthetic sandstones gives a good fit with theory for dry samples however although the crack number density in the laboratory sample is such that first order theory is unlikely to apply expressions correct to second order in the number density provide a worse fit it also appears that the ratio of wavelength to crack size is not sufficiently great for any detailed comparison with effective medium theories which are valid only when this ratio is large the data show dispersion effects for dry cracks and scattering neither of which will occur at sufficiently long wavelengths data from the water saturated samples indicate that the effect of equant porosity is significant although the two theories differ strongly as to just how significant once again and in spite of the reservations mentioned above a reasonable fit between theory and observation can be shown

spectrum of pore types and networks in mudrocks and a descriptive classification for matrix related mudrock pores matrix related pore networks in mudrocks are composed of nanometer to micrometer size pores in shale gas systems these pores along with natural fractures form the flow path permeability network that allows flow of gas from the mudrock to induced fractures during production a pore classification consisting of three major matrix related pore types is presented that can be used to quantify matrix related pores and relate them to pore networks two pore types are associated with the mineral matrix the third pore type is associated with organic matter om fracture pores are not controlled by individual matrix particles and are not part of this classification pores associated with mineral particles can be subdivided into interparticle interp pores that are found between particles and crystals and intraparticle intrap pores that are located within particles organic matter pores are intrap pores located within om interparticle mineral pores have a higher probability of being part of an effective pore network than intrap mineral pores because they are more likely to be interconnected although they are intrap om pores are also likely to be part of an interconnected network because of the interconnectivity of om particles in unlithifed near surface muds pores consist of interp and intrap pores and as the muds are buried they compact and lithify during the compaction process a large number of interp and intrap pores are destroyed especially in ductile grain rich muds compaction can decrease the pore volume up to 88 by several kilometers of burial at the onset of hydrocarbon thermal maturation om pores are created in kerogen at depth dissolution of chemically unstable particles can create additional moldic intrap pores

seismic evidence for sharp lithosphere asthenosphere boundaries of oceanic plates the mobility of the lithosphere over a weaker asthenosphere constitutes the essential element of plate tectonics and thus the understanding of the processes at the lithosphere asthenosphere boundary lab is fundamental to understand how our planet works it is especially so for oceanic plates because their relatively simple creation and evolution should enable easy elucidation of the lab data from borehole broadband ocean bottom seismometers show that the lab beneath the pacific and philippine sea plates is sharp and age dependent the observed large shear wave velocity reduction at the lab requires a partially molten asthenosphere consisting of horizontal melt rich layers embedded in meltless mantle which accounts for the large viscosity contrast at the lab that facilitates horizontal plate motions

pore connectivity and water accessibility in upper permian transitional shales southern china abstract pore connectivity of shale controls shale gas migration and production behavior the pore connectivity and water accessibility in clay rich upper permian transitional shales remain unclear contrast matching small angle neutron scattering cm sans tests were used to determine the accessibility of water to pores in the transitional shales complementary analyses with sans gas co2 and n2 physisorption isotherm mercury intrusion capillary pressure micp helium ion microscopy him as well as field emission scanning electron microscopy fe sem were conducted to study the pore connectivity and distribution characteristics of closed pores the results show that closed pores inaccessible to nitrogen molecules and mercury are mainly distributed in pore diameters 10 nm and associated with organic pores and interlayer spaces of illite smectite mixed layer mineral the pore volume values obtained from micp and n2 adsorption underestimate the large pores pore diameters 100 nm in shales based on deuterated water cm sans tests 87 98 of the pores 2 200 nm diameters are water connected in transitional samples the low accessibility to water is at pore sizes of 5 10 nm and 20 30 nm results from in situ gas contents show that closed pores have a certain gas bearing capacity but micropores pore diameters 2 nm control the gas occurrence in transitional samples the connectivity of the organic pore network and between organic pores and surrounding interparticle pores is directly supported by fe sem and him imaging overall improving pore fracture connectivity through effective fracturing techniques is a means of mitigating the rapid decline in shale gas production

changes in seismic anisotropy shed light on the nature of the gutenberg discontinuity the boundary between the lithosphere and asthenosphere is associated with a platewide high seismic velocity lid overlying lowered velocities consistent with thermal models seismic body waves also intermittently detect a sharp velocity reduction at similar depths the gutenberg g discontinuity which cannot be explained by temperature alone we compared an anisotropic tomography model with detections of the g to evaluate their context and relation to the lithosphere asthenosphere boundary lab we find that the g is primarily associated with vertical changes in azimuthal anisotropy and lies above a thermally controlled lab implying that the two are not equivalent interfaces the origin of the g is a result of frozen in lithospheric structures regional compositional variations of the mantle or dynamically perturbed lab

multiscale connectivity characterization of marine shales in southern china by fluid intrusion small angle neutron scattering sans and fib sem abstract an evaluation of shale pore connectivity is essential for predicting the production behavior and optimizing the development plan of shale gas to systematically investigate the multiscale connectivity characteristics and controlling factors complementary tests were conducted on four overmature marine shale samples from southern china one each from longmaxi formation and wufeng formation and two from niutitang formation with different maturity and composition the methods included mercury intrusion capillary pressure micp spontaneous imbibition with deionized water and n decane saturated diffusion distribution with seven nano sized tracers n2 physisorption small angle neutron scattering sans and focused ion beam scanning electron microscopy fib sem tomography moreover a novel repeated micp measurement technique was developed and used to evaluate the pore connectivity from the distribution behavior of residual mercury results indicate that the connectivity loss of hydrophilic pore networks owing to an increased maturity and the compaction causes pore shrinkage and bond breakage between pore networks according to the three dimensional reconstruction and pore network extraction of fib sem images pores in organic matter om have a good pore connectivity but the minerals surrounding the om reduce the overall pore connectivity of the shale matrix by evaluating the pore connectivity using different methods the hydrocarbon migration pattern in overmature marine shales was established our results imply that in addition to creating induced fracture networks effectively connecting induced fractures with preexisting microcracks or joint sets between om pore networks and transport pores can also be used to enhance overall pore connectivity microwave heating in shale reservoirs may be an effective way of further improving the production and recovery of hydrocarbons

barnett shale gas production fort worth basin issues and discussion newark east barnett shale field fort worth basin texas is currently the most productive gas field in texas in terms of daily production and is growing at an annual rate of more than 10 however despite the fact that the barnett play has been studied intensely by very capable geologists and engineers from several companies over a period of many years there continues to be several misunderstandings concerning fundamental factors controlling the success of the barnett play of north texas barnett gas production is poorer in areas near faults and structural flexures anticlines and synclines fractures which are most abundant in these structural settings are detrimental to barnett production open natural fractures are rare in the barnett and have little or nothing to do with barnett productivity in areas where barnett shale is thermally mature with respect to gas generation it is slightly overpressured about 0 52 psi ft 11 76 kpa m limestone beds within the barnett formation are the product of debris flows that originated on a carbonate shelf to the north of the present basin center it appears that the barnett can be used as an exploration model for other basins especially analogous basins of the ouachita trend the history of the development of the barnett reservoir in north texas provides an excellent example of how persistence can lead to success in nonconventional gas plays

separating intrinsic and apparent anisotropy abstract seismic anisotropy plays a key role in studies of the earth s rheology and deformation because of its relation to flow induced lattice preferred orientation lpo of intrinsically anisotropic minerals in addition to lpo small scale heterogeneity produces apparent anisotropy that need not be related to deformation in the same way as intrinsic anisotropy quantitative interpretations of observed anisotropy therefore require the separation of its intrinsic and apparent components we analyse the possibility to separate intrinsic and apparent anisotropy in media with hexagonal symmetry typically used in surface wave tomography and sks splitting studies our analysis is on the level of the wave equation which makes it general and independent of specific data types or tomographic techniques we find that observed anisotropy can be explained by isotropic heterogeneity when elastic parameters take specific combinations of values in practice the uncertainties of inferred anisotropy are large enough to ensure that such a combination is always within the error bars it follows that commonly observed anisotropy can always be explained completely by a purely isotropic laminated medium unless all anisotropic parameters are known with unrealistic accuracy most importantly minute changes in the poorly constrained p wave anisotropy and the parameter can switch between the possible or impossible existence of an isotropic equivalent important implications of our study include 1 intrinsic anisotropy over tomographically resolved length scales is never strictly required when reasonable error bars for anisotropic parameters are taken into account 2 currently available seismic observables provide weak constraints on the relative contributions of intrinsic and apparent anisotropy 3 therefore seismic observables alone are not sufficient to constrain the magnitude of mantle flow 4 quantitative interpretations of anisotropy in terms of mantle flow require combined seismic geodynamic inversions as well as the incorporation of additional data such as topography gravity and scattered waves

pore structure and spontaneous imbibition characteristics of marine and continental shales in china the pore structure of shale has a significant effect on hydrocarbon migration and the long term gas supply of shale gas wells the present study investigates the spontaneous imbibition characteristics to evaluate the pore connectivity and wettability of marine longmaxi shale samples from the southeastern chongqing area and continental yanchang shale samples from the ordos basin the pore size distribution obtained from n2 adsorption and mercury intrusion porosimetry field emission scanning electron microscopy and focused ion beam scanning electron microscopy photos are used to interpret the imbibition behaviors our results show that the difference in dominant pore type between marine and continental samples which is dominated by thermal maturity controls on their imbibition behaviors as well as their wettability organic matter om pores within yanchang samples are poorly developed because of their low thermal maturity and a large amount of water wet inorganic pores are preserved in these samples because of relatively weak compaction oil wet om pores are well developed in longmaxi samples with higher thermal maturity and inorganic pores have been largely eliminated because of strong compaction the low pore connectivity to water for both the longmaxi and yanchang samples is indicated by the low water imbibition slopes furthermore the more oil wet property of the longmaxi samples and more water wet characteristics of the yanchang samples are obtained by comparing the directional water oil imbibition slopes in addition the positive meaning of quartz in the protection of pore spaces is found in both the longmaxi and the yanchang samples used in this study

reconstruction of three centuries of annual accumulation rates based on the record of stable isotopes of water from lomonosovfonna svalbard we use the upper 81 in of the record of stable isotopes of water from a 122 in long ice core from lomonosovfonna central spitsbergen svalbard to construct an ice core chronology and the annual accumulation rates over the icefield the isotope cycles are counted in the ice core record using a model that neglects short wavelength and low amplitude cycles we find approximately the same number of delta 18 o cycles as years between known reference horizons and assume these cycles represent annual cycles testing the validity of this assumption using cycles in deltad shows that both records give similar numbers of cycles using the delta 18 o chronology and decompressing the accumulation records using the nye flow model we calculate the annual accumulation for the ice core site back to ad 1715 we find that the average accumulation rate from 1715 to 1950 was on average 0 30 in w e accumulation rates increased about 25 during the later part of the 20th century to an average of 0 41 in w e for the period 1950 97 the accumulation rates show highly significant 2 1 and 21 year periodicities which gives credibility to our time scale

pore types and pore network evolution in upper devonian lower mississippian woodford and mississippian barnett mudstones insights from laboratory thermal maturation and organic petrology abstract pore evolution models from immature organic matter om rich barnett 0 42 r o and woodford 0 49 r o mudstones were compared with models previously developed from low maturity om lean boquillas eagle ford equivalent mudstones to investigate whether 1 different mineralogy siliceous vs calcareous exerts different catalytic and sorption effects and influences om pore origin and evolution and 2 different types of macerals show different om pore evolution history laboratory gold tube pyrolysis scanning electron microscopy sem and thin section petrography organic petrography and geochemical characterization were used to investigate the role of bulk mineralogy maceral type and thermal maturation on om pore evolution results suggest that mineralogy has little impact on om pore development and evolution macerals identified using both sem platy om particulate om organic mineral admixtures tasmanites and organic petrology vitrinite inertinite amorphous organic matter aom bituminite telalginite leiosphaeridia tasmanites do affect the origin and evolution of om pores owing to differences in chemical compositions generation kinetics and activation energy distributions between tasmanites matrix bituminite and other types of macerals leiosphaeridia and tasmanites in woodford mudstone samples exhibit a delay in onset and a shorter period of petroleum generation and pore development compared to the matrix bituminite in the barnett and woodford mudstone samples pre oil solid bitumen was observed to have migrated into initial primary mineral pore networks at the bitumen generation stage in both barnett and woodford samples at higher levels of thermal maturation the volume of primary mineral pores decreases and the pore volume composed of modified mineral pores and om pores becomes greater pore evolution and pore type heterogeneity in these mudstones is a function of the initial mineral pore network types of kerogen and macerals and generation kinetics of individual macerals upon thermal maturation

climatic signals in multiple highly resolved stable isotope records from greenland abstract twenty ice cores drilled in medium to high accumulation areas of the greenland ice sheet have been used to extract seasonally resolved stable isotope records relationships between the seasonal stable isotope data and greenland and icelandic temperatures as well as atmospheric flow are investigated for the past 150 200 years the winter season stable isotope data are found to be influenced by the north atlantic oscillation nao and very closely related to sw greenland temperatures the linear correlation between the first principal component of the winter season stable isotope data and greenland winter temperatures is 0 71 for seasonally resolved data and 0 83 for decadally filtered data the summer season stable isotope data display higher correlations with stykkisholmur summer temperatures and north atlantic sst conditions than with sw greenland temperatures the linear correlation between stykkisholmur summer temperatures and the first principal component of the summer season stable isotope data is 0 56 increasing to 0 66 for decadally filtered data winter season stable isotope data from ice core records that reach more than 1400 years back in time suggest that the warm period that began in the 1920s raised southern greenland temperatures to the same level as those that prevailed during the warmest intervals of the medieval warm period some 900 1300 years ago this observation is supported by a southern greenland ice core borehole temperature inversion as greenland borehole temperature inversions are found to correspond better with winter stable isotope data than with summer or annual average stable isotope data it is suggested that a strong local greenland temperature signal can be extracted from the winter stable isotope data even on centennial to millennial time scales

accumulation storage and release of atmospheric mercury in a glaciated arctic catchment baffin island canada abstract part of the mercury hg entering arctic ecosystems is believed to be delivered from the atmosphere in snow but this source is difficult to quantify due to limited spatial coverage of hg data in snow here we evaluate the atmospheric deposition storage and release of total hg thg and monomethyl mercury mehg on penny ice cap baffin island this is the first such study in the baffin region thg levels in snow and firn mean 0 61 ng l 1 are comparable to those on high arctic glaciers but mehg levels are noticeably higher mean 0 11 ng l 1 we find little evidence of springtime enhancement of hg deposition in snow attributable to atmospheric mercury depletion events estimated accumulation rates of thg and mehg in firn are 0 33 and 0 03 g m 2 a 1 higher than on high arctic glaciers possibly due to higher precipitation on southern baffin island the estimated net annual release of thg by glacial snow and ice melt is small thg 1 86 kg mehg 0 18 kg in the study area geogenic hg contributions from sediment loaded glacial meltwater could be as large or larger than those from melting ice mehg levels are very low in meltwater fed streams and lakes 0 01 ng l 1 suggesting that mehg is released early in the snowmelt season and or quickly removed from meltwater by various processes summer melt and percolation on penny ice cap remobilise hg in firn after deposition and this imposes resolution limits of at least 3 years on depositional trends inferred from ice cores

petrological constraints on seismic anisotropy the purpose of this paper is to investigate the correlations between anisotropic parameters for different orientations and mineralogies for realistic mineralogical and petrological models of the upper mantle such correlations make it possible to reduce the number of independent parameters required in seismic modelling of the upper mantle the variation with depth and with degree of random orientation is also investigated it is shown that the anisotropic combinations involved in an equivalent transversely isotropic medium azumithally averaged velocities with a vertical symmetry axis are strongly correlated but the combinations involved in azimuthal anisotropy are more weakly correlated comparison with available seismic data does not yet allow discrimination based on anisotropy between different petrological models it is shown that even if a proportion of random orientation is introduced it should be possible to achieve petrological discrimination from seismic data for some orientation configurations if the inverse problem is well posed i e takes account of the correlations between anisotropic parameters these correlations are incorporated in an inversion process to show that it is possible to explain the dataset used to derive the prem by alternative anisotropic models for the uppermost 220 km

organic matter hosted pore system marcellus formation devonian pennsylvania the marcellus formation of pennsylvania represents an outstanding example of an organic matter om hosted pore system most pores detectable by field emission scanning electron microscopy fe sem are associated with om instead of mineral matrix in the two wells studied here total organic carbon toc content is a stronger control on om hosted porosity than is thermal maturity the two study wells span a maturity from late wet gas vitrinite reflectance ro 1 0 to dry gas ro 2 1 samples with a toc less than 5 5 wt display a positive correlation between toc and porosity but samples with a toc greater than 5 5 wt display little or no increase in porosity with a further increasing toc in a subset of samples 14 across a range of toc 2 3 13 6 wt the pore volume detectable by fe sem is a small fraction of total porosity ranging from 2 to 32 of the helium porosity importantly the fe sem visible porosity in om decreases significantly with increasing toc diminishing from 30 of om volume to less than 1 of om volume across the range of toc the morphology and size of om hosted pores also vary systematically with toc the interpretation of this anticorrelation between om content and sem visible pores remains uncertain samples with the lowest om porosity higher toc may represent gas expulsion pore collapse that was more complete as a consequence of greater om connectivity and framework compaction whereas samples with higher om porosity lower toc correspond to rigid mineral frameworks that inhibited compactional expulsion of methane filled bubbles alternatively higher toc samples may contain om low initial hydrogen index relatively unreactive that is less prone to development of fe sem detectable pores in this interpretation om type controlled by sequence stratigraphic position is a factor in determining pore size distribution

pyroxene orientation within the upper mantle petrofabric analyses of orthopyroxene and olivine for a suite of rocks from the bay of islands ophiolite newfoundland show systematic relationships between the minerals9 fabrics the plane of the mohorovicic discontinuity determined from the contact of the gabbro and ultramafic sections and the spreading direction inferred from the attitude of the sheeted dikes the orthopyroxene c crystallographic axes maxima which are aligned subparallel to the spreading direction coincide with olivine a axes maxima the orthopyroxene b axes and olivine c axes also lie approximately within the plane of the mohorovicic discontinuity but parallel the ridge whereas the orthopyroxene a axes maxima and olivine b axes maxima are approximately perpendicular to the mohorovicic discontinuity using olivine and orthopyroxene elastic constants and their pressure derivatives velocities have been calculated from composite petrofabric data and contoured for varying proportions of olivine and pyroxene the results of these calculations show that within a vertical direction compressional wave velocities change only slightly with increasing pyroxene content whereas parallel to the mohorovicic discontinuity velocities decrease with increasing pyroxene content anisotropy decreases from 4 for a rock with 100 olivine to 2 6 for a rock with 50 olivine and 50 orthopyroxene also within the plane of mohorovicic discontinuity the maximum and minumum velocities occur at approximately the same azimuth for differing percentages of orthopyroxene a comparison of the calculated anisotropy and the observed seismic anisotropy off the coast of california shows a striking agreement from this comparison it is estimated that the percentage of orthopyroxene within the upper mantle of this region varies between 0 and 30

recovery rates of fracturing fluids and provenance of produced water from hydraulic fracturing of silurian qusaiba hot shale northern saudi arabia with implications on fracture network geochemical fingerprinting of produced water from hydraulic fracturing projects is an essential tool to trace their provenance during the postfracturing period to quantify recovery rates and volumes of fracturing fluids and to visualize the geodynamic structure of natural or induced fracture networks a total of 41 produced water samples from an exploration well in the northern arabia exploration area in saudi arabia were collected daily from the fracture stimulated qusaiba hot shale and analyzed for major ions and trace elements and partially for environmental isotopes the postfracturing period shows an initial return of supply water and potassium chloride brine subsequently replaced by the inflow of sodium chloride type formation water with a stable plateau salinity of 50 000 mg l less than 10 of the total injected fracturing fluids were recovered during postfracturing whereas 78 8 vol of the total recovered fluid is composed of formation water 20 843 out of 26 446 bbls during the study period coinciding values between logged reservoir temperature and calculated geothermometers confirm the provenance of pore water from the qusaiba hot shale or from nearby units the recharge of the silurian sequence with meteoric surface water occurred during the early holocene 6 6 7 ka as evidenced by geochronological dating with the 14c method and 18o 2h values close to the global meteoric water line the inflow of formation water into the stimulated shale layer in the postfracturing stage could be originated by the natural occurrence of pore water within a naturally fractured black shale layer or more likely by the rise of groundwater from the underlying sarah sandstones via migration pathways of natural or newly formed vertically induced hydraulic fractures for this particular well site and the specific hydraulic fracturing project chemical and isotopic fingerprinting confirms the absence of ascending migration pathways from the silurian qusaiba hot shale toward a shallower groundwater system which are isolated through a lithological set of more than 900 m 3000 ft of impermeable mudstone from the qusaiba member

comparative study on micro pore structure of marine terrestrial and transitional shales in key areas china abstract the purpose of this article is to make a comparative study on the pore structure of different sedimentary facies shales developed in typical areas china results show that the surface area sa and pore volume pv of the over mature marine shales are in the range of 17 83 29 49 m 2 g and 3 65 18 26 ml kg respectively which are much higher than that of the highly mature transitional and less mature terrestrial shales in the range of 0 9 1 9 m 2 g and 2 5 10 9 ml kg respectively in the view of the pore size distribution psd marine shales concentrate at the fine mesopores

an olivine fabric database an overview of upper mantle fabrics and seismic anisotropy we present a unique database of 110 olivine petrofabrics and their calculated seismic properties the samples come from a variety of the upper mantle geodynamic environments ophiolites subduction zones and kimberlites with a wide range of micro structures a phenomenological relationship is established between p and s wave seismic anisotropy and the degree of crystal alignment fabric strength seismic anisotropy increases rapidly at low fabric strength before reaching a near saturation level of 15 to 20 for p waves and 10 to 15 for s waves despite a large variation in the symmetry of fabric patterns the average seismic properties of the different fabric micro structural and geodynamic settings have similar anisotropies in both magnitude and symmetry hence it would seem possible to determine some measure of fabric strength from seismic anisotropy if the dimensions of the anisotropic region are known but not geodynamic environment or details of the petrofabric pattern a simple pattern of seismic anisotropy characterises the average sample of the database which has the following features the polarisation plane of the fastest s wave is parallel or sub parallel to the foliation plane the maximum shear wave splitting is parallel to the y structural direction in foliation plane and normal to the lineation the maximum of the p wave velocity is parallel to the high concentration of 100 axes which is sub parallel to the lineation the 100 orientation distribution has the greatest influence on the p wave seismic anisotropy the 100 and 001 orientation distributions have the greatest influence on the symmetry of s wave anisotropy although the magnitude of anisotropy is influenced by the distribution of all three principal axes although the database only contains olivine petrofabrics this statistical study clearly shows that seismic anisotropy can be used to deduce the orientation of the structural frame in the upper mantle 1998 elsevier science b v all rights reserved

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

magnitude and symmetry of seismic anisotropy in mica and amphibole bearing metamorphic rocks and implications for tectonic interpretation of seismic data from the southeast tibetan plateau we calibrated the magnitude and symmetry of seismic anisotropy for 132 mica or amphibole bearing metamorphic rocks to constrain their departures from transverse isotropy ti which is usually assumed in the interpretation of seismic data the average bulk vp anisotropy at 600 mpa for the chlorite schists mica schists phyllites sillimanite mica schists and amphibole schists examined is 12 0 12 8 12 8 17 0 and 12 9 respectively most of the schists show vp anisotropy in the foliation plane which averages 2 4 for phyllites 3 3 for mica schists 4 1 for chlorite schists 6 8 for sillimanite mica schists and 5 2 for amphibole schists this departure from ti is due to the presence of amphibole sillimanite and quartz amphibole and sillimanite develop strong crystallographic preferred orientations with the fast c axes parallel to the lineation forming orthorhombic anisotropy with vp x vp y vp z effects of quartz are complicated depending on its volume fraction and prevailing slip system most of the mica or amphibole bearing schists and mylonites are approximately transversely isotropic in terms of s wave velocities and splitting although their p wave properties may display orthorhombic symmetry the results provide insight for the interpretation of seismic data from the southeast tibetan plateau the n s to nw se polarized crustal anisotropy in the sibumasu and indochina blocks is caused by subvertically foliated mica and amphibole bearing rocks deformed by predominantly compressional folding and subordinate strike slip shear these blocks have been rotated clockwise 70 90 around the east himalayan syntaxis without finite eastward or southeastward extrusion in responding to progressive indentation of india into asia

experimental investigations on the geometry and connectivity of pore space in organic rich wufeng and longmaxi shales abstract the nano scale pore systems of organic rich shale reservoirs were investigated from upper ordovician wufeng and lower silurian longmaxi formations in southeast sichuan basin these two formations are the most important target plays of shale gas development in china the purpose of this article is to assess the geometry and connectivity of multi scale pore systems and to reveal the nature and complexity of pore structure for these over mature gas shales to achieve these objective total organic carbon mineralogy image analyses by focused ion beam sem low pressure nitrogen adsorption mercury injection capillary pressure micp and spontaneous fluid deionized di water and n decane imbibition were performed most of the visible pores from sem work in wufeng and longmaxi shales are within nm and m size regimes and belong to organic matter om pores the shapes of om pore in longmaxi samples are elliptical bubble like irregular or rounded wufeng pores are mainly irregular linear and faveolated even though two shales have small depth difference as well as similar thermal maturity kerogen type and toc content nano scale pores in longmaxi are mainly associated with narrow platelike or slitlike pores with pore size of 3 50 nm while inkbottle pores are dominant in wufeng samples and over 88 of the pore volume is contributed by pores with diameter

annual accumulation over recent centuries at four sites in central greenland 1 accurate accumulation records are fundamental to understanding mass balance of the greenland ice sheet ice cores can provide multicentury high resolution ground based point estimates of water accumulation in 2003 and 2004 four new ice cores were collected in the central western d4 and d5 and summit sandy and katie regions of greenland annual layer counting based on multiple glaciochemical parameters primarily hydrogen peroxide sea salt and dust proxies was used to date the ice cores resulting in annual dating the bottom depth ages for d4 d5 sandy and katie were estimated at 1738 1673 1844 and 1934 a d with mean annual accumulation rates of 41 4 35 2 22 4 and 22 4 cmweq yr 1 respectively these new records were in good agreement with previous accumulation maps and four previously published records from nearby multicentury ice cores spatial variability was quantified through an analysis of variance thereby allowing for more meaningful comparisons to atmospheric processes more regionally representative accumulation records were constructed for the central western and summit regions spanning recent centuries using a principle component analysis of both the new and previously reported ice core measurements these regional records exhibited 6 7 interannual variability 1 standard deviation of the mean and had lower spatial variability uncertainties than individual accumulation records correlations indicate that 20 of the variance in the central western region was explained by the north atlantic oscillation nao and suggests that an array of more northern ice cores may correlate more closely with nao

local to regional scale variability of annual net accumulation on the greenland ice sheet from parca cores a suite of spatially distributed cores collected under the program for arctic regional climate assessment parca provides an unprecedented opportunity to assess local to regional variability of annual accumulation rates over the greenland ice sheet parca cores are unique in their broad spatial distribution and accurate dating of annual layers using multiple seasonally varying indicators the core data provide 1 a more rigorous evaluation of spatial and temporal variations in accumulation rates 2 critical input to ice sheet mass balance estimates 3 ground truth measurements for satellite observations and climate model based precipitation estimates and 4 important constraints on paleoclimatic interpretations from ice cores multiple closely spaced cores demonstrate that signals of high frequency annual to possibly decadal scale climate variability preserved in the ice sheet are partially masked by glaciological noise two 350 year accumulation histories one from northwest greenland and one from the summit area reveal significant multidecadal variability the regional trends show long periods 60 90 years of strong positive correlation and an equally long period of strong negative correlation since 1940 the trends have been decoupled this spatial variability reflects the strong modulation of greenland precipitation and the climate information it contains by changes in north atlantic atmospheric circulation patterns proxy records from the parca cores document that climate reconstructions from a single core must be interpreted cautiously with application of appropriate filters to reduce local noise and careful extrapolations from local to regional scales richer more robust ice core derived data sets should result from combining multiple more widely spaced cores to produce regional stacked records

mass balance and surface movement of the greenland ice sheet at summit central greenland during the grip deep drilling in central greenland the ice sheet topography and surface movement at summit has been mapped with gps measurements of the surface velocity are presented for a strain net consisting of 13 poles at distances of 25 60 km from the grip site some results are the grip site is located approximately 2 km nw of the topographic summit the surface velocity at the gisp 2 site is 1 7 m yr in the w direction the present mass balance at summit is calculated to be 0 03 0 04 m yr i e close to steady state this result is the best now available for summit a small thinning rate might be a transient response of the greenland ice sheet due to the temperature increase at the wisconsin holocene transition

upper mantle anisotropy a preliminary model seismic anisotropy in the upper mantle can be explained by crystallographic mineral alignment achieved through dislocation motion the physical mechanism of mineral alignment requires upper mantle shear flow which reorients and aligns minerals by dislocation glide and climb governed by the dominant glide system of each mineral the dominant glide systems are assumed to be 100 0l0 for olivine and 001 100 for the pyroxenes these yield a predominantly orthorhombic fabric with the olivine 100 and the pyroxene 001 axes aligned in the upper mantle flow direction and the olivine 010 and the pyroxene 100 axes aligned normal to the upper mantle flow plane these glide systems have a threshold temperature of enhanced mobility of 1100 1200 k which yields a solid state thermally defined lithosphere asthenosphere boundary in an olivine pyroxene mantle consistent with recent seismic determinations of the thickness of the lithosphere mantle anisotropy due to mineral alignment is then actively maintained below this boundary asthenosphere and mesosphere and is a fossil state above this boundary lithosphere we use the dominant glide systems to establish the crystallographic orientation of olivine and pyroxene in calculating the maximum seismic anisotropy of two petrologic models pyrolite and piclogite for the upper mantle by an extrapolation of single crystal anisotropic mineral elastic properties to a depth of 400 km the real earth seismic anisotropy will be bound by the limits of maximum anisotropy from perfect mineral alignment and minimum anisotropy isotropy from random mineral alignment the seismic anisotropy of the upper 220 km is best represented by the pyrolite model which reduces to quasi hexagonal symmetry with the unique axis in the direction of mantle flow the lehmann discontinuity is conjectured to be due to a change in composition from pyrolite to piclogite and therefore may represent a change in anisotropy the piclogite model has orthorhombic symmetry distinctly different from that of the pyrolite the piclogite anisotropy model can appear quasi isotropic when measured by transverse isotropy parameterization if the mantle flow is mainly horizontal with a horizontal shear plane that is the shear flow gradient duh dr dominates

quantifying seismic anisotropy induced by small scale chemical heterogeneities observations of seismic anisotropy are usually used as a proxy for lattice preferred orientation lpo of anisotropic minerals in the earth s mantle in this way seismic anisotropy observed in tomographic models provides important constraints on the geometry of mantle deformation associated with thermal convection and plate tectonics however in addition to lpo smallscale heterogeneities that cannot be resolved by long period seismic waves may also produce anisotropy the observed i e apparent anisotropy is then a combination of an intrinsic and an extrinsic component assuming the earth s mantle exhibits petrological inhomogeneities at all scales tomographic models built from long period seismic waves may thus display extrinsic anisotropy in this paper we investigate the relation between the amplitude of seismic heterogeneities and the level of induced s wave radial anisotropy as seen by long period seismic waves we generate some simple 1 d and 2 d isotropic models that exhibit a power spectrum of heterogeneities as what is expected for the earth s mantle that is varying as 1 k with k the wavenumber of these heterogeneities the 1 d toymodels correspond to simple layeredmedia in the 2 d case our models depict marble cake patterns in which an anomaly in shear wave velocity has been advected within convective cells the long wavelength equivalents of these models are computed using upscaling relations that link properties of a rapidly varying elastic medium to properties of the effective that is apparent medium as seen by long period waves the resulting homogenized media exhibit extrinsic anisotropy and represent what would be observed in tomography in the 1 d case we analytically show that the level of anisotropy increases with the square of the amplitude of heterogeneities this relation is numerically verified for both 1 d and 2 d media in addition we predict that 10 per cent of chemical heterogeneities in 2 d marble cake models can induce more than 3 9 per cent of extrinsic radial s wave anisotropy we thus predict that a non negligible part of the observed anisotropy in tomographic models may be the result of unmapped small scale heterogeneities in the mantle mainly in the form of fine layering and that caution should be taken when interpreting observed anisotropy in terms of lpo and mantle deformation this effect may be particularly strong in the lithosphere where chemical heterogeneities are assumed to be the strongest the authors 2017

modeled variations of precipitation over the greenland ice sheet abstract a parameterization of the synoptic activity at 500 hpa and a simple orographic scheme are used to model the spatial and temporal variations of precipitation over the greenland ice sheet for 1963 88 from analyzed geopotential height fields produced by the national meteorological center nmc model coefficients are fitted to observed accumulation data primarily from the summit area of the ice sheet all major spatial characteristics of the observed accumulation distribution are reproduced apart from the orographic accumulation maximum over the northwestern coastal slopes the modeled time averaged total precipitation amount over greenland is within the range of values determined by other investigators from surface based observations a realistic degree of interannual variability in precipitation is also simulated a downward trend in simulated ice sheet precipitation over the 26 years is found this is supported by a number of lines of evidence it matches the accumulation trends during this peri

seismic observations of large scale deformation at the bottom of fast moving plates abstract we present a new tomographic model of azimuthal anisotropy in the upper mantle dr2012 and discuss in details the geodynamical causes of this anisotropy our model improves upon dkp2005 seismic model debayle et al 2005 through a larger dataset expanded by a factor 3 7 and a new approach which allows us to better extract fundamental and higher mode information our results confirm that on average azimuthal anisotropy is only significant in the uppermost 200 250 km of the upper mantle where it decreases regularly with depth we do not see a significant difference in the amplitude of anisotropy beneath fast oceanic plates slow oceanic plates or continents the anisotropy projected onto the direction of present plate motion shows a very specific relation with the plate velocity it peaks in the asthenosphere around 150 km depth it is very weak for plate velocities smaller than 3 cm yr 1 increases significantly between 3 and 5 cm yr 1 and saturates for plate velocities larger than 5 cm yr 1 plate scale present day deformation is remarkably well and uniformly recorded beneath the fastest moving plates india coco nazca australia philippine sea and pacific plates beneath slower plates plate motion parallel anisotropy is only observed locally which suggests that the mantle flow below these plates is not controlled by the lithospheric motion a minimum plate velocity of around 4 cm yr 1 is necessary for a plate to organize the flow in its underlying asthenosphere the correlation of oceanic anisotropy with the actual plate motion in the shallow lithosphere is very weak a better correlation is obtained with the fossil accretion velocity recorded by the gradient of local seafloor age the transition between frozen in and active anisotropy occurs across the typical age isotherm that defines the bottom of the thermal lithosphere around 1100 c under fast continents mostly under australia and india the present day velocity orients also the anisotropy in a depth range around 150 200 km depth which is not deeper than what is observed under oceans

three dimensional variations in love and rayleigh wave azimuthal anisotropy for the upper 800 km of the mantle we present a new mantle model yb14shani of azimuthal anisotropy for horizontally polarized shear waves sh in parallel with our previously published vertically polarized shear wave sv anisotropy model yb13svani yb14shani was obtained from higher mode love wave phase velocity maps with sensitivity to anisotropy down to 1200 km depth sh anisotropy is present down to the mantle transition zone mtz with an average amplitude of 2 in the upper 250 km and 1 in the mtz consistent with yb13svani changes in sv and sh anisotropy were found at the top of the mtz where olivine transforms into wadsleyite which might indicate that mtz anisotropy is due to the lattice preferred orientation of anisotropic material beneath oceanic plates sv fast axes become subparallel to the absolute plate motion apm at a depth that marks the location of a thermally controlled lithosphere asthenosphere boundary lab in contrast sh anisotropy does not systematically depend on ocean age moreover while upper mantle sv anisotropy is anomalously high in the middle of the pacific as seen in radial anisotropy models sh anisotropy amplitude remains close to the average for other oceans based on the depth at which sv fast axes and the apm direction begin to align we also found that the average thickness of cratonic roots is 250 km consistent with yuan and romanowicz 2010 for north america here we add new constraints on the nature of the cratonic lab and show that it is characterized by changes in both sv and sh anisotropy 2014 american geophysical union all rights reserved

on the relation between seismic anisotropy and finite strain because seismic anisotropy in the upper mantle is due primarily to lattice preferred orientation lpo of olivine crystals induced by deformation observations of anisotropy can provide constraints on mantle deformation and flow in this paper we use a previously published theory for deformation induced lpo ribe and yu 1991 to quantify the relation between seismic anisotropy and deformation for two model compositions a pure olivine dunite aggregate and a harzburgite comprising 70 olivine and 30 enstatite analytical and numerical solutions of the governing equations show that the predicted lpo and hence also the seismic anisotropy depends only on the finite strain and not on the deformation path by which that strain is produced the magnitude of the anisotropy depends only on the ratios c1 c2 and c2 c3 where c1 c2 c3 are the lengths of the principle axes of the finite strain ellipsoid and the directions of maximum and minimum compressional wave velocity vp coincide with the axes c1 and c3 respectively we calculate the percent anisotropies for compresional and shear waves propagating along the three principle axes of the finite strain ellipsoid as functions of the axial ratios c1 c2 and c2 c3 for our two model compositions however inferences of the magnitude of finite strain obtained using these results are likely to be minimum estimates because our theory neglects the effects of dynamic recrystallization finally we present as a byproduct of this study a new direct method for calculating the finite strain produced by an arbitiary deformation history

is there seismic attenuation in the mantle article history the small scale heterogeneity of the mantle is mostly due to the mixing of petrological heterogeneities by a smooth but chaotic convection and should consist in a laminated structure marble cake with a power spectrums k varying as 1 k w herekis the wavenumber of the anomalies this distribution of heterogeneities during convective stirring with negligible diffusion called batchelor regime is documented by fluid dynamic experiments and corresponds to what can be inferred from geochemistry and seismic tomography this laminated structure imposes density seismic velocity and potentially anisotropic heterogeneities with similar 1 kspectra a seismic wave of wavenumberk 0 crossing such a medium is partly reflected by the heterogeneities and we show that the scattered energy is proportional tok 0 s 2k 0 t he reduction of energy for the propagating wave appears therefore equivalent to aq uality factor 1 q k 0 s 2k 0 w ith the specif ic 1 kspectrum of the mantle the resulting apparent attenuation should therefore be frequency independent we show that the total contribution of 6 9 rms density velocity and anisotropy would explain the observed s and p attenuation of the mantle although these values are large they are not unreasonable and we discuss how they depend on the range of frequencies over which the attenuation is explained if such a level of heterogeneity were present most of the attenuation of the earth would be due to small scale scattering by laminations not by intrinsic dissipation intrinsic dissipation must certainly exist but might correspond to a larger yet unobservedq this provocative result would explain the very weak frequency dependence of the attenuation and the fact that bulk attenuation seems negligible two observations that have been difficult to explain for 50 years

a review of shale wettability characterization using spontaneous imbibition experiments abstract wettability is an important reservoir property that can affect the distribution and migration of geofluids within shale reservoirs which significantly influences the occurrence state of methane in shale pore systems and the selection of fracturing fluids during shale gas exploitation the wettability characteristics of organic matter om rich shale are much more complicated than those of conventional reservoir rocks with a relatively homogeneous composition in addition the low porosity and extremely low permeability as well as the strong heterogeneity of shale complicate the evaluation of shale wettability as a result traditional wettability tests including contact angle measurements and oil water displacement experiments are inapplicable for shale samples consequently spontaneous imbibition experiments become a practical and effective way to establish the wettability characteristics of different shales this paper reviews shale wettability characterization using spontaneous imbibition experiments and discusses the close relationship between shale wettability and pore structure as reported in the literature most shale samples can imbibe both water and oil which indicates the co existence of water wet and oil wet connected pore spaces and the mixed wet property of shales however different shales show a range of oil and water imbibition behaviors indicating the wettability differences amongst them this review reveals that the development degrees of water and oil wet pores within shale determine its wettability as well as its imbibition behaviors and four simplified pore network models are proposed for more water wet more oil wet mixed wet and intermediate wet shale samples respectively this work also shows the pronounced effects of thermal maturity on shale pore structure development and shale wettability characteristics consequently a simplified and empirical wettability evolution model with four stages only considering the effect of thermal maturity is established in this study

nitrogen rich gas shale logging evaluation and differential gas bearing characterization of lower cambrian formation in northern guizhou south china abstract there are significant differences in the gas content between the two sets of lower paleozoic shale in south china the nitrogen content of the lower silurian shale gas that has been commercially developed is very low whereas that of the lower cambrian shale lcs is relatively high shale has complex gas bearing mechanistic characteristics the genesis of nitrogen is complex and sources are diverse a gas containing high nitrogen and low hydrocarbons increases the risk and difficulty of developing a shale gas resource based on the key geological parameters of the lcs in the northern guizhou area nga this study investigates the characteristics of nitrogen in the highly mature shale and discusses the logging evaluation method for nitrogen bearing shale gas reservoirs in this complex tectonic area changes in the gas bearing characteristics of the lcs in the study area are complex the shale gas composition was found to vary widely due to differential enrichment the methane content was between 1 2 and 82 4 and the nitrogen content was between 0 03 and 97 4 the nitrogen rich shale formations exhibited a high compensation density 2 46 2 58 g cm3 high compensation neutron 10 2 17 9 and low acoustic time difference 192 230 s m there were two different types of resistivity responses in nitrogen bearing shale gas reservoirs which had distribution characteristics of 21 56 m and 100 1000 m with these response characteristics the logging evaluation of nitrogen bearing shale gas reservoirs was interpreted by selecting differential gas sensitive parameters and different gas bearing types were divided into dry nitrogen mixed and methane gas layers furthermore the identification and computational evaluation of the gas composition methane nitrogen and content were carried out quantitatively differential gas bearing property was characterized and that is beneficial to the exploration practice in the study area

isotopic diffusion in polar firn implications for interpretation of seasonal climate parameters in ice core records with emphasis on central greenland if it were possible to properly extract seasonal information from ice core isotopic records paleoclimate researchers could retrieve a wealth of new information concerning the nature of climate changes and the meaning of trends observed in ice core proxy records it is widely recognized however that the diffusional smoothing of the seasonal record makes a proper extraction very difficult in this paper we examine the extent to which seasonal information specifically the amplitude and shape of the seasonal cycle is irrecoverably destroyed by diffusion in the firn first we show that isotopic diffusion firn is reasonably well understood we do this by showing that a slightly modified version of the whillans and grootes 1985 theory makes a tenable a priori prediction of the decay of seasonal isotopic amplitudes with depth at the gisp2 site though a small adjustment to one parameter significantly improves the prediction further we calculate the amplitude decay at various other ice core sites and show that these predictions compare favorably with published data from south pole and locations in southern and central greenland and the antarctic peninsula we then present numerical experiments wherein synthetic ice core records are created diffused sampled reconstituted and compared to the original these show that alter diffusive mixing in the entire fini column seasonal amplitudes can be reconstructed to within about 20 error in central greenland but that all information about sub annual signals is permanently lost there furthermore most of the error in the amplitude reconstructions is due to the unknowable variations in the sub annual signal finally we explore how these results can be applied to other locations and suggest that dye 3 has a high potential for meaningful seasonal reconstructions while siple dome has no potential at all an optimal ice core site for seasonal reconstructions has a high accumulation rate and a low temperature

a search in north greenland for a new ice core drill site a new deep ice core drilling site has been identified in north greenland at 75 12 n 42 30 w 316 km north northwest nnw of the grip drill site on the summit of the ice sheet the ice thickness here is 3085 m the surface elevation is 2919 m the north grip ngrip site is identified so that ice of eemian age 115 130 ka bp calendar years before present is located as far above bedrock as possible and so the thickness of the eemian layer is as great as possible an ice flow model similar to the one used to date the grip ice core is used to simulate the flow along the nnw trending ice ridge surface and bedrock elevations surface accumulation rate distribution and ratio echo sounding along the ridge have been used as model input the surface accumulation rate drops from 0 23 m ice equivalent year 1 at grip to 0 19 m ice equivalent year 1 50 km from grip over the following 300 km the accumulation is relatively constant before is starts decreasing again further north ice thickness up to 3250 m bring the temperature of the basal ice up to the pressure melting point 100 250 km from grip the ngrip site is located 316 km from grip in a region where the bedrock is smooth and the accumulation rate is 0 19 m ice equivalent year 1 the modeled basal ice here has always been a few degrees below the pressure melting point internal radio echo sounding horizons can be traced between the grip and ngrip sites allowing us to date the ice down to 2300 m depth 52 ka bp an ice flow model predicts that the eemian age ice will be located in the depth range 2710 2800 m which is 285 m above the bedrock this is 120 m further above the bedrock and the thickness of the eemian layer of ice is 20 m thicker than at the grip ice core site

fluid distribution and gas adsorption behaviors in over mature shales in southern china abstract to better understand the mechanism of hydrocarbon accumulation and fluid migration in chinese shales several samples from two leading marine shales longmaxi and niutitang were collected for geochemical and mineral analysis the characterization of pore structure preliminary studies on fluid flow and the distribution and investigation of different methane adsorption behaviors firstly the longmaxi and niutitang marine shales were found to be in an over matured stage and dry gas window pore structures and connectivity were characterized by field emission scanning electron microscopy fe sem the sem images showed that the micro fracture interparticle pores and organic pores had better connectivity than intraparticle pores results from contact angles indicated that the longmaxi and niutitang shales tended to have higher affinities for oil rather than for water the connectivity of pores distribution of fluids water and gas and fluid flow behaviors in the over matured shale were analyzed using spontaneous imbibition si and tracer diffusion tests it was found the tracer fluids flow in the way of network flow inside of shale matrix the connected pore network may be the main path for fluid migration in shale additionally a gravimetric isothermal adsorption experiment was applied to assess methane adsorption capacity in shale shale samples with higher total organic carbon toc contents had higher methane adsorption capacities organic matter including kerogen and bitumen had much greater adsorption capabilities than inorganic minerals quartz clay and others finally the fluid distribution patterns in over matured marine shale were studied shale gas was originally generated in organic matter and then migrated out through connected pores under differential pressure between internal and external organic matter hydrocarbon generation areas these hydrocarbons replaced the water in the pores therefore shale gas may adsorb in organic pores and is freely stored in connected inorganic pores with bound water whereas isolated pores are saturated with water two different adsorption patterns on mineral surfaces organic matters and inorganic minerals were established to explain the different shale gas adsorption behaviors in organic pores and connected pores with bound water

pore structure characterization for the longmaxi and niutitang shales in the upper yangtze platform south china evidence from focused ion beam he ion microscopy nano computerized tomography and gas adsorption analysis abstract pore structure is of great importance in the occurrence of shale gas in this study pores in shale samples from the lower silurian longmaxi and lower cambrian niutitang shales in chongqing in the upper yangtze platform south china were examined using focused ion beam he ion microscopy fib him nano computerized tomography nano ct and gas adsorption analysis the results show that most pores in measured samples of the niutitang shale are mineral matrix pores and have poor connectivity including both intraparticle and interparticle pores organic matter pores in measured samples of the niutitang shale are rare and have small diameters in measured samples of the longmaxi shale om pores mostly macropores and large mesopores are the most abundant the nano ct results revealed that the abundance of om pores led to good pore connectivity in the longmaxi shale samples whereas the prevalence of mineral matrix pores resulted in poor connectivity in the niutitang shale samples n2 and co2 adsorption analyses showed that the mean value of micropore mesopore volumes in the niutitang and longmaxi shales samples are 0 0332 ml g and 0 0261 ml g respectively the mean values of micropores mesopores surface area in the niutitang and longmaxi shales samples are 33 84 m2 g and 32 46 m2 g respectively thus there is little difference between measured samples of the longmaxi and niutitang shales in terms of volume and surface area of micropores mesopores the equal vitrinite reflectance equal ro values of measured samples of the longmaxi shale are lower than those of the niutitang shale samples over maturity equal ro 3 resulted in a reduction of the number of pores in organic matter small pore size and poor connectivity in measured samples of the niutitang shale relatively low maturity 2

effective media for transversely isotropic models based on homogenization theory with applications to borehole sonic logs sonic log records including measurements of wave speeds in boreholes provide critical input to the geological geophysical and petrophysical studies of a region under exploration 1d background models are routinely built based on sonic log records for applications such as seismic imaging of hydrocarbon reservoirs and microseismic source inversions smoothing or upscaling techniques are required to produce models in coarser scales than the very fine layers in the raw log data in this paper we follow the recently popular homogenization theory derive its application to the special case of 1d ti models for both p sv and sh waves and show that it is consistent with the backus averaging technique commonly used to upscale 1d fine layered models we examine a study case of sonic log data from a well in the horn river basin in northeastern british columbia a region known for its tight shale gas deposit we demonstrate the computational accuracy and efficiency gained by proper upscaling procedures for spectral element simulations of seismic wave propagation and discuss the effect of control parameters on wavefield recovery

radial anisotropy and prior petrological constraints a comparative study click here journal of geophysical research vol 115 b03303 doi 10 1029 2008jb005842 2010 for full article radial anisotropy and prior petrological constraints a comparative study c beghein 1 received 31 may 2008 revised 8 september 2009 accepted 6 october 2009 published 6 march 2010 1 radial seismic anisotropy models are traditionally obtained using empirical constraints based on laboratory experiments and petrological considerations we tested the hypothesis that such petrological constraints affect the uppermost mantle models of s wave anisotropy using a statistical approach in addition we were able to determine which model features are constrained by the data and which are dominated by the prior we focused on large scale models and found that the most likely models obtained in both cases are highly correlated this demonstrates that for the best data fitting solution the geometry of uppermost mantle radial anisotropy is not strongly affected by prior petrological constraints the amplitude of the anomalies however can change significantly the best data fitting model obtained without petrological constraints displays stronger amplitudes than the one obtained with prior this could become an issue when quantitatively interpreting seismic anisotropy models and thus emphasizes the importance of accurately accounting for parameter uncertainties and trade offs and of understanding whether the seismic data or the prior constraints the model we showed that model uncertainties are strongly affected by the prior as the relative rms uncertainties were reduced by a factor of 2 in addition we showed that while the model distributions are not necessarily gaussian a priori imposing petrological constraints can force the distributions to be narrower and more gaussian like as expected from inverse theory finally we demonstrated that the age dependence of seismic wave velocities is robust and independent of prior constraints a similar age signal exists for anisotropy but with larger uncertainties without prior constraints citation beghein c 2010 radial anisotropy and prior petrological constraints a comparative study j geophys res 115 b03303 doi 10 1029 2008jb005842 1 introduction 2 accurately modeling mantle seismic anisotropy that is the dependence of seismic wave velocity with the direction of propagation or polarization can help us under stand mantle deformation karato and toriumi 1989 kendall 2000 becker et al 2003 the coupling between lithosphere and asthenosphere silver and holt 2002 becker et al 2006b mantle composition montagner and anderson 1989 rheology becker et al 2008 and the net rotation of the lithosphere becker 2008 however despite numerous efforts to model mantle seismic anisotropy over the past 20 years uncertainties remain on its exact depth extent and lateral variations in the uppermost mantle on its presence in the transition zone and on its global nature in the d 00 layer fouch and fischer 1996 montagner and kennett 1996 ekstro m and dziewonski 1998 lay et al 1998 trampert and van heijst 2002 wookey et al 2002 gung et al 2003 panning and romanowicz 2006 earth and space sciences department ucla los angeles california usa copyright 2010 by the american geophysical union 0148 0227 10 2008jb005842 09 00 beghein and trampert 2004a 2004b beghein et al 2006 panning and romanowicz 2006 zhou et al 2006 marone et al 2007 nettles and dziewonski 2008 beghein et al 2008 3 discrepancies between models can arise for a variety of reasons to fully describe earth s elastic properties one would ideally want to determine the 21 independent ele ments of the fourth order elastic stiffness tensor at a given time and location inside earth in practice this is challeng ing because seismic data are only sensitive to subsets of those 21 elements tanimoto 1986 chen and tromp 2007 beghein et al 2008 and different types of data depend on different subsets of elastic coefficients see summary tables in chen and tromp 2007 and beghein et al 2008 in addition while some data such as shear wave splitting measurements can provide precise constraints on lateral changes in seismic anisotropy their depth resolution is very poor surface wave and free oscillation data are better suited to constrain depth changes in structure but their lateral resolution is lower than that of body waves this can yield apparent discrepancies and make model comparisons diffi cult moreover three dimensional models of seismic anisot ropy are typically obtained by data inversion which is often an ill posed and ill conditioned problem this means that b03303 1 of 17

surface roughness on the greenland ice sheet from airborne laser altimetry high resolution airborne laser altimetry is used to determine the small scale surface relief in central greenland and estimate the contribution from spatial noise to stratigraphic records the standard deviation of the surface roughness is 1 6 cm water equivalent corresponding to a standard deviation of annual layer thickness of 2 3 cm we this estimate agrees with an independent assessment of the spatial variability 2 5 cm we based on nine shallow ice cores the agreement suggests that the statistical nature of the surface in central greenland remains unchanged throughout the year by conducting airborne altimetry around proposed drilling sites the expected noise level in the core can be evaluated and sites selected where this level is lowest

porosity of devonian and mississippian new albany shale across a maturation gradient insights from organic petrology gas adsorption and mercury intrusion the evolution of porosity in shales with increasing maturity was examined in a suite of five new albany shale samples spanning a maturity range from immature vitrinite reflectance ro 0 35 to postmature ro 1 41 devonian to lower mississippian new albany shale samples from the illinois basin used in this study contain marine type ii kerogen having total organic carbon contents from 1 2 to 13 0 wt organic petrology co2 and n2 low pressure adsorption and mercury intrusion capillary pressure techniques were used to quantify pore volumes pore sizes and pore size distributions increasing maturity of the new albany shale is paralleled by many changes in the characteristics of porosity the total porosity of 9 1 vol in immature new albany shale decreases to 1 5 vol in the late mature sample whereas total pore volumes decrease from 0 0365 to 0 0059 cm3 g in the same sequence reversing the trend at even higher maturity the postmature new albany shale exhibits higher porosity and larger total pore volumes compared to the late mature sample with increasing maturity changes in total porosity and total pore volumes are accompanied by changes in pore size distributions and relative proportions of micropores mesopores and macropores porosity related variances are directly related to differences in the amount and character of the organic matter and mineralogical composition but maturity exerts the dominant control upon these characteristics we conclude that organic matter transformation due to hydrocarbon generation and migration is a pivotal cause of the observed porosity differences

2d and 3d nanopore characterization of gas shale in longmaxi formation based on fib sem abstract studying complex pore structures is the key to understanding the mechanism of shale gas accumulation fib sem focused ion beam scanning electron microscope is the mainstream and effective instrument for imaging nanopores in gas shales based on this technology 2d and 3d characteristics of shale samples from lower silurian longmaxi formation in southern sichuan basin were investigated 2d experimental results show that the pores in shale are nanometer sized and the structure of those nanopores can be classified into three types organic pores inorganic pores and micro fractures among the three types organic pores are dominantly developed in the om organic matter with three patterns such as continuous distributed om om between clay minerals and om between pyrite particles and the size of organic pores range from 5 nm to 200 nm inveresly inorganic pores and micro fractures are less developed in the longmaxi shales 3d digital rocks were reconstructed and segmented by 600 continuous images by fib cutting and sem imaging simultaneously the pore size distribution and porosity can be calculated by this 3d digital core showing that its average value is 32 nm and porosity is 3 62 the 3d digital porosity is higher than its helium porosity which can be regarded as one important parameter for evaluation of shale gas reserves the 2d and 3d characterized results suggest that the nanometer sized pores in organic matter take up the fundamental storage space for the longmaxi shale these characteristics have contributed to the preservation of shale gas in this complex tectonic area

interannual variations of snow accumulation on the greenland ice sheet 1985 1996 new observations versus model predictions newly measured time series of net water equivalent accumulation from ice cores are reported for 11 sites located near the 2000 m contour of the greenland ice sheet many of these sites are located in regions where accumulation has not been previously measured we compared these new time series of annual accumulation with previously reported modeled precipitation covering the same time range because ice core accumulation records include both regional and local accumulation components we used adjacent ice core records at six multiple core sites to estimate the local component and extrapolated these results to the five single core sites we investigated the impact of this short scale spatial variability in accumulation on statistical comparisons between the observed accumulation and model precipitation although sealers were required to match the 12 year mean modeled precipitation to the mean observed accumulation a high degree of correspondence between observed interannual accumulation and scaled modeled precipitation was found at 7 of 11 locations the need for scaling and the low correspondence between model simulations and observations at some sites clearly indicate that model improvements are needed although very encouraging a more spatially distributed array of ice core accumulation measurements spanning the same time period as the precipitation modeling is necessary for continued model improvement and validation in agreement with earlier studies the large temporal variability in snow accumulation predicted by modeling and confirmed by ice cores indicates that the ice sheet elevation varies by tens of centimeters from year to year simply because of changing accumulation

pore structure of cambrian shales from the sichuan basin in china and implications to gas storage abstract the microstructure of black siliceous shale from the lower cambrian niutitang formation sichuan basin in china was investigated by the combination of field emission scanning electron microscope fe sem and argon ion beam milling the nanometer to micrometer scale pore systems of shales are an important control on gas storage and fluid migration in this paper the organic porosity in shale samples within oil and gas window has been investigated and the formation mechanism and diagenetic evolution of nanopores have been researched fe sem reveals five pore types that are classified as follows organic nanopores pores in clay minerals nanopores of framework minerals intragranular pores in microfossils and microfractures numerous organic nanopores are observed in shales in the gas window whereas microfractures can be seen within the organic matter of shales in the oil window microfractures in oil window shales could be attributed to pressure buildup in the organic matter when incompressible liquid hydrocarbon are generated and the orientation of microfractures is probably parallel to the bedding and strength anisotropy of the formation pores in clay minerals are always associated with the framework of clay flakes and develop around rigid mineral grains because the pressure shadows of mineral grains protect pores from collapse and the increasing of silt content would lead to an increase in pressure shadows and improve porosity nanopores of rock framework are probably related to dissolution by acidic fluids from hydrocarbon generation and the dissolution related pores promote permeability of shales porosity in the low toc low thermal maturity shales contrast greatly with those of high toc high thermal maturity shales while the high toc shales contain abundant organic microporosity the inorganic pores can contribute a lot to the porosity of the low toc shales

synchronous deposition of volcanic ash and sulfate aerosols over greenland in 1783 from the laki eruption iceland 1 sulfate aerosols from the 1783 1784 a d laki eruption are widely used as a reference horizon for constraining greenland ice core time scales yet the timing of the arrival of the sulfate remains under discussion two ice cores from western greenland analyzed with high temporal resolution confirm that sulfate aerosols arrived over greenland late in 1783 concomitant with the tephra elevated concentrations of cd bi and tl all indicators of volcanic emissions and with a short lived rare earth elements anomaly thereafter sulfate deposition declined rapidly very modest concentrations of sulfate in 1784 snowfall evident in six greenland cores suggest a relatively short less than 1 year atmospheric residence time and an injection height limited to the lower stratosphere an improved estimate of the associated stratospheric sulfate burden is calculated and provides an important input for models assessing climatic impacts of this volcanic eruption

mineral controlled nm μm scale pore structure of saline lacustrine shale in qianjiang depression jianghan basin china abstract the pore structure of the saline lacustrine shales in the eq3 unit of the qianjiang formation was characterized for pore space of m nm scales through a combined study of mercury injection capillary pressure micp and small ultra small angle neutron scattering sans and usans x ray diffraction xrd and total organic carbon toc content tests as well as field emission scanning electron microscopy fe sem imaging are also employed to obtain the mineralogical composition organic richness as well as the general pore types and sizes of the selected qianjiang shale samples in these samples three major rock types are identified 1 silica rich carbonate mudstone 2 carbonate siliceous mudstone and 3 salt the porosity as well as pore size and pore throat size distributions generated from both sans usans and micp techniques indicate a porous rock matrix and well connected pore networks in the two mudstone rock types meanwhile an averaged toc of around 3 5 wt for eq3 unit exhibits a good quality for oil generation potential this study primarily provides new insights into the pore structure of the qianjiang shales across a wide measurable range for both pore and pore throat sizes and correlates the pore structure and mineral compositions at different scales

global azimuthal seismic anisotropy and the unique plate motion deformation of australia differences in the thickness of the high velocity lid underlying continents as imaged by seismic tomography have fuelled a long debate on the origin of the roots of continents1 2 3 4 5 some of these differences may be reconciled by observations of radial anisotropy between 250 and 300 km depth with horizontally polarized shear waves travelling faster than vertically polarized ones2 this azimuthally averaged anisotropy could arise from present day deformation at the base of the plate as has been found for shallower depths beneath ocean basins6 such deformation would also produce significant azimuthal variation owing to the preferred alignment of highly anisotropic minerals7 here we report global observations of surface wave azimuthal anisotropy which indicate that only the continental portion of the australian plate displays significant azimuthal anisotropy and strong correlation with present day plate motion in the depth range 175 300 km beneath other continents azimuthal anisotropy is only weakly correlated with plate motion and its depth location is similar to that found beneath oceans we infer that the fast moving australian plate contains the only continental region with a sufficiently large deformation at its base to be transformed into azimuthal anisotropy simple shear leading to anisotropy with a plunging axis of symmetry may explain the smaller azimuthal anisotropy beneath other continents

mechanisms of shale gas storage implications for shale gas exploration in china this article reviews the mechanisms of shale gas storage and discusses the major risks or uncertainties for shale gas exploration in china at a given temperature and pressure the gas sorption capacities of organic rich shales are primarily controlled by the organic matter richness but may be significantly influenced by the type and maturity of the organic matter mineral composition especially clay content moisture content pore volume and structure resulting in different ratios of gas sorption capacity gsc to total organic carbon content for different shales in laboratory experiments the gsc of organic rich shales increases with increasing pressure and decreases with increasing temperature under geologic conditions assuming hydrostatic pressure gradient and constant thermal gradient the gsc increases initially with depth due to the predominating effect of pressure passes through a maximum and then decreases because of the influence of increasing temperature at greater depth this pattern of variation is quite similar to that observed for coals and is of great significance for understanding the changes in gsc of organic rich shales over geologic time as a function of burial history at an elevated temperature and pressure and with the presence of moisture the gas sorption capacities of organic rich shales are quite low as a result adsorption alone cannot protect sufficient gas for high maturity organic rich shales to be commercial gas reservoirs two models are proposed to predict the variation of gsc and total gas content over geologic time as a function of burial history high contents of free gas in organic rich shales can be preserved in relatively closed systems loss of free gas during postgeneration uplift and erosion may result in undersaturation the total gas contents lower than the sorption capacity and is the major risk for gas exploration in marine organic rich shales in china

age independent seismic anisotropy under oceanic plates explained by strain history in the asthenosphere the depth of the oceanic lithosphere asthenosphere boundary lab as inferred from shear wave velocities increases with lithospheric age in agreement with models of cooling oceanic lithosphere on the other hand the distribution of radial anisotropy under oceanic plates is almost age independent in particular radial anisotropy shows a maximum positive gradient at a depth of 70 km which if used as a proxy indicates an age independent lab depth these contrasting observations have fueled a controversy on the seismological signature of the lab to better understand the discrepancy between these observations we model the development of lattice preferred orientation lpo in upper mantle crystal aggregates and predict the seismic anisotropy produced by plate driven mid ocean ridge flows the model accounts for the progressive cooling of the lithosphere with age and can incorporate both diffusion and dislocation creep deformation mechanisms we find that an age independent distribution of radial anisotropy is the natural consequence of these simple flows the depth and strength of anisotropy is further controlled by the deformation regime dislocation or diffusion creep experienced by crystals during their ascent towards and subsequent motion away from the ridge axis comparison to surface wave tomography models yield constraints on rheological parameters such as the activation volume although not excluded additional mechanisms proposed to explain some geophysical signatures of the lab such as the presence of partial melt or changes in water content are not required to explain the radial anisotropy proxy our prediction that the age independent radial anisotropy proxy marks the transition to flow induced asthenospheric anisotropy provides a way to reconcile thermal mechanical and seismological views of the lab

discussion on the rising segment of the mercury extrusion curve in the high pressure mercury intrusion experiment on shales abstract in order to explain the rising segment of the mercury intrusion curve in the high pressure 60 000 psi mercury intrusion tests on shales this study implemented a series of analyses on 7 lower silurian longmaxi formation shale samples from 4 wells in the sichuan basin china including helium based porosity toc abundance and x ray diffraction two pressure balance time values namely 30 s and 60 s were used in the high pressure mercury intrusion tests according to the results the compressibility of shales instead of the pressure balance time was identified as the main contributor to the rising segment in the mercury extrusion curve further it was proposed based on the helium based porosity and mercury intrusion porosity that the pore space could be compressed to about half of the original in the high pressure condition the pseudo compression ratio was found to be mainly affected by the bulk density which was further influenced by the contents of quartz and feldspar results of this study were expected to provide a better insight into the influence of rock compression and deformation during the mercury intrusion and subsequently the calibration of the mercury intrusion method

evaluation of recent precipitation studies for greenland ice sheet the retrieval of an accurate spatial and temporal record of contemporary greenland precipitation is a uniquely challenging task because of the extreme variability in both atmospheric processes and the resulting precipitation distribution over relatively small spatial scales a comparison of precipitation data sets composed of monthly mean values from recent studies shows a convergence on the general features of the long term spatial patterns but substantial disagreement on the temporal variability both regionally and for all of greenland there is general agreement on a long term greenland average of about 35 cm yr 1 and on long term values for regional scales although differences for outlying data sets exceed 50 of the observed glaciological estimate for particular regions a fundamental problem is the inadequate topographic representation of greenland in the numerical analyses nearly all of the data sets are overly dry for high elevation areas as seen from comparisons with glaciological observations from summit the east central region of greenland is found to be particularly susceptible to the temporal discontinuities in data sets which employ operational analyses in contrast there is strong agreement among all methods on the temporal variability for the west central region over a 15 year period from the comparison it is concluded that none of the data sets is able to capture all of the regional scale features in general however the deficiencies of each data set are readily identifiable from comparison and evaluation in the context of circulation features agreement among the methods on particular regions and timescales gives increased confidence in drawing conclusions related to aspects of greenland s precipitation climatology in particular an enhanced precipitation retrieval method is found to be less susceptible to data artifacts than other methods using operational analyses in the north anomalously high precipitation is associated with cyclonic development near the fram strait for west central greenland the close agreement among methods is related to the dominant contribution of the mean circulation

where can seismic anisotropy be detected in the earth s mantle in boundary layers during the last 30 years considerable evidence of seismic anisotropy has accumulated demonstrating that it is present at all scales but not in all depth ranges we detail which conditions are necessary to detect large scale seismic anisotropy firstly minerals must display a strong anisotropy at the microscopic scale and or the medium must be finely layered secondly the relative orientations of symmetry axes in the different crystals must not counteract in destroying the intrinsic anisotropy of each mineral and there must be efficient mechanisms of orientation of minerals and aggregates finally the strain field must be coherent at large scale in order to preserve long wavelength anisotropy part of shallow anisotropy can be related to the past strain field frozen in anisotropy however the deep anisotropy is due to the present strain field all these conditions are fulfilled only in boundary layers of convective mantle we review in this paper the seismic data sets which provide insight into the location at depth of large scale anisotropy from the d layer up to the lithosphere in addition to the well documented seismic anisotropy in the lithosphere and asthenosphere there is new evidence of seismic anisotropy in the upper 400 660 km and lower 660 900 km transition zones and in the d layer nonetheless the bulk of the lower mantle seems close to isotropy if we assume the hypothesis that seismic anisotropy is associated with boundary layers in convective systems these observations strongly suggest that the transition zone is a boundary layer which makes the pasage of matter between the upper and the lower mantle difficult however this general statement does not rule out flow circulation between the upper and lower mantles finally the geophysical mineral physics and geological applications are briefly reviewed an intercomparison between surface wave anisotropy and body wave anisotropy data sets is presented we discuss the scientific potential of seismic anisotropy and how it makes it possible to gain more insight into continental root deformation and geodynamics processes

the impact of composition on pore throat size and permeability in high maturity shales middle and upper devonian horn river group northeastern british columbia canada abstract shale reservoirs of the middle and upper devonian horn river group provide an opportunity to study the influence of rock composition on permeability and pore throat size distribution in high maturity formations sedimentological geochemical and petrophysical analyses reveal relationships between rock composition pore throat size and matrix permeability in our sample set measured matrix permeability ranges between 1 69 and 42 81 nanodarcies and increases with increasing porosity total organic carbon toc content positively correlates to permeability and exerts a stronger control on permeability than inorganic composition a positive correlation between silica content and permeability and abundant interparticle pores between quartz crystals suggests that quartz may be another factor enhancing the permeability pore throat size distributions are strongly related to toc content in organic rich samples the dominant pore throat size is less than 10 nm whereas in organic lean samples pore throat size distribution is dominantly greater than 20 nm sem images suggest that in organic rich samples organic matter pores are the dominant pore type whereas in quartz rich samples the dominant type is interparticle pores between quartz grains in clay rich and carbonate rich samples the dominant pore type is intraparticle pores which are fewer and smaller in size high permeability shales are associated with specific depositional facies massive and pyritic mudstones rich in toc and quartz have comparatively high permeability laminated mudstone bioturbated mudstone and carbonate facies which are relatively enriched in clay or carbonate have fairly low permeability

pore structure characteristics of lower silurian shales in the southern sichuan basin china insights to pore development and gas storage mechanism abstract silurian shale in sichuan basin is currently the most important target zone for shale gas exploration and development in china pore structure characteristics of lower silurian longmaxi shales from southern sichuan basin were investigated the combination of field emission scanning electron microscope fe sem and argon ion beam milling was utilized to describe the nanometer to micrometer scale 1 2 nm pore systems the shales were characterized by organic geochemical and mineralogical analyses total porosity pore size distribution psd specific surface area and gas content were determined controls of organic matter richness thermal maturity and mineralogy on porosity were examined the contribution of individual mineral components to total porosity was analyzed quantitatively total gas contents of the shales determined from canister desorption data were compared with theoretical sorptive and volumetric gas storage capacities the total organic carbon toc content of the shale samples ranges between 0 1 and 8 0 wt and helium porosity varies between 0 7 and 5 7 maturity in terms of equivalent vitrinite reflectance of bitumen reqv ranges from 1 8 to 3 2 toc content is a strong control for the pore system of these shales and shows a positive correlation with porosity porosity increases with increasing thermal maturity when reqv is less than 2 5 but decreases for higher thermal maturity samples fe sem reveals four pore types related to the rock matrix that are classified as follows organic matter om hosted pores pores in clay minerals pores of framework minerals and intragranular pores in microfossils pores in clay minerals are always associated with the framework of clay flakes and develop around rigid mineral grains because the pressure shadows of mineral grains prevent pores from collapsing pores of framework minerals are probably related to dissolution by acidic fluids and the dissolution related pores promote porosity of shales a unimodal psd exists in the micropore range of toc rich samples while the psd of carbonate rich samples are bimodal a psd maximum in the micropore range is attributed by om and another maximum in the range of mesopore macropores is probably caused by the dissolution of carbonate minerals quantitative evaluation of the contribution of individual mineral components to porosity shows that the organic matter contributes approximately 62 to the total porosity framework minerals quartz feldspar and carbonates et al and clay minerals contribute 25 and 13 respectively the total gas content of these shales ranges from 0 4 to 6 2 m3 t and the total gas contents of selected samples determined from canister desorption tests agree with the theoretically estimated original gas in place ogip om hosted pores are the main space for gas storage and accounted for about 78 55 adsorbed gas plus 23 free gas of the ogip while pores in the inorganic matter accommodate 22 free gas of the ogip

nanoscale pore characteristics of the lower cambrian niutitang formation shale a case study from well yuke 1 in the southeast of chongqing china the lower cambrian niutitang formation shale is one of the most important shales being studied for unconventional development in china in this work we focused on 21 core samples of niutitang shale from well yuke 1 in the southeast of chongqing to better understand their vertical reservoir characteristics and pore evolution using complementary approaches of x ray diffraction n2 and co2 adsorption petrology microscope and field emission scanning electron microscopy we conducted a series of analyses for pore volume pore size distribution surface area fractal characterization organic geochemistry petrology and mineralogy results indicate that most micropores 50 nm are composed of organic pores and inorganic pores meso macropore volume per unit of total organic carbon toc content dramatically decreases with an increase of maturity and extent of diagenesis meanwhile the toc normalized micropore volume also rapidly declines after maturity ro values were higher than 3 13 the surface fractal dimension d1 for relative n2 pressure p p0 0 5 with capillary condensation and surface fractal dimension d2 for p p0 0 5 with mono and multi layer adsorption derived from n2 sorption isotherms can be used to indicate the pore characteristics d1 is controlled by the percentages of micropore volume d2 seems to be affected by the clay mineral contents and thermal maturity

intrinsic versus extrinsic seismic anisotropy the radial anisotropy in reference earth models 1 seismic anisotropy usually arises from different mechanisms which include lattice or crystallographic preferred orientation lpo cpo alignment of cracks with or without fluid inclusions fine layering or partial melting this makes the interpretation of anisotropy in terms of intrinsic produced by lpo cpo versus extrinsic produced by other mechanisms properties difficult and nonunique the radial anisotropy in the one dimensional global spherically symmetric reference earth is usually claimed to be intrinsic here we explore whether the radial anisotropy in one dimensional reference earth models including preliminary reference earth model prem and the constrained reference earth model acy400 contains extrinsic anisotropy especially in relation to fine layering we conclude that as well as intrinsic anisotropy extrinsic anisotropy introduced by finely layered models can be considered to explain the lithospheric anisotropy in prem but cannot explain alone its asthenospheric anisotropy we also find that radial anisotropy in model acy400 is mainly intrinsic due to its petrological constraints

mantle dynamics and seismic anisotropy abstract observations of seismic anisotropy yield some of the most direct constraints available on both past and present day deformation in the earth s mantle insight into the character of mantle flow can also be gained from the geodynamical modeling of mantle processes on both global and regional scales we highlight recent progress toward understanding mantle flow from both observations and modeling and discuss outstanding problems and avenues for progress particularly in the integration of seismological and geodynamical constraints to understand seismic anisotropy and the deformation that produces it to first order the predictions of upper mantle anisotropy made by global mantle circulation models match seismological observations well beneath the ocean basins but the fit is poorer in regions of greater tectonic complexity such as beneath continental interiors and within subduction systems in many regions of the upper mantle models of anisotropy derived from surface waves are seemingly inconsistent with shear wave splitting observations which suggests that our understanding of complex anisotropic regions remains incomplete observations of anisotropy in the d layer hold promise for improving our understanding of dynamic processes in the deep earth but much progress remains to be made in characterizing anisotropic structure and relating it to the geometry of flow geochemical heterogeneity or phase transitions major outstanding problems related to understanding mantle anisotropy remain particularly regarding the deformation and evolution of continents the nature of the asthenosphere subduction zone geodynamics and the thermo chemical state of the lowermost mantle however we expect that new seismological deployments and closer integration of observations with geodynamical models will yield rapid progress in these areas

on the relationship between azimuthal anisotropy from shear wave splitting and surface wave tomography 1 seismic anisotropy provides essential constraints on mantle dynamics and continental evolution one particular question concerns the depth distribution and coherence of azimuthal anisotropy which is key for understanding force transmission between the lithosphere and asthenosphere here we reevaluate the degree of coherence between the predicted shear wave splitting derived from tomographic models of azimuthal anisotropy and that from actual observations of splitting significant differences between the two types of models have been reported and such discrepancies may be due to differences in averaging properties or due to approximations used in previous comparisons we find that elaborate full waveform methods to estimate splitting from tomography yield generally similar results to the more common simplified approaches this validates previous comparisons and structural inversions however full waveform methods may be required for regional studies and they allow exploiting the back azimuthal variations in splitting that are expected for depth variable anisotropy applying our analysis to a global set ofskssplitting measurements and two recent surface wave models of upper mantle azimuthal anisotropy we show that the measures of anisotropy inferred from the two types of data are in substantial agreement provided that the splitting data is spatially averaged so as to bring it to the scale of long wavelength tomographic models and reduce spatial aliasing observed and tomography predicted delay times are significantly correlated and global angular misfits between predicted and actual splits are relatively low regional anisotropy complexity notwithstanding our findings imply that splitting and tomography yield a consistent signal that can be used for geodynamic interpretation

fractured shale gas systems the first commercial united states natural gas production 1821 came from an organic rich devonian shale in the appalachian basin understanding the geological and geochemical nature of organic shale formations and improving their gas producibility have subsequently been the challenge of millions of dollars worth of research since the 1970s shale gas systems essentially are continuous type biogenic predominant thermogenic or combined biogenic thermogenic gas accumulations characterized by widespread gas saturation subtle trapping mechanisms seals of variable lithology and relatively short hydrocarbon migration distances shale gas may be stored as free gas in natural fractures and intergranular porosity as gas sorbed onto kerogen and clay particle surfaces or as gas dissolved in kerogen and bitumen five united states shale formations that presently produce gas commercially exhibit an unexpectedly wide variation in the values of five key parameters thermal maturity expressed as vitrinite reflectance sorbed gas fraction reservoir thickness total organic carbon content and volume of gas in place the degree of natural fracture development in an otherwise low matrix permeability shale reservoir is a controlling factor in gas producibility to date unstimulated commercial production has been achievable in only a small proportion of shale wells those that intercept natural fracture networks in most other cases a successful shale gas well requires hydraulic stimulation together the devonian antrim shale of the michigan basin and devonian ohio shale of the appalachian basin accounted for about 84 of the total 380 bcf of shale gas produced in 1999 however annual gas production is steadily increasing from three other major organic shale formations that subsequently have been explored and developed the devonian new albany shale in the illinois basin the mississippian barnett shale in the fort worth basin and the cretaceous lewis shale in the san juan basin in the basins for which estimates have been made shale gas resources are substantial with in place volumes of 497 783 tcf the estimated technically recoverable resource exclusive of the lewis shale ranges from 31 to 76 tcf in both cases the ohio shale accounts for the largest share

pore characteristics of longmaxi shale gas reservoir in the northwest of guizhou china investigations using small angle neutron scattering sans helium pycnometry and gas sorption isotherm abstract small angle neutron scattering sans helium pycnometry and low pressure gas sorption isotherm experiments were used to investigate the pore characteristics of longmaxi shale the leading producing formation in china this work is the first microstructural study of chinese marine shales by neutron scattering technique the polydisperse spheres model pdsp was used for sans data analysis to obtain porosity and pore size distribution psd and the results were compared with those from gas co2 n2 adsorption and helium pycnometry by evaluating the difference of porosities determined from these methods the closed fraction of shale pores are derived and discussed moreover the porosity has a positive correlation with total organic carbon toc in longmaxi shale samples the fractal dimension of shale samples was derived and results indicated that longmaxi shale is a mass fractal a lower mass fractal dimension means less closed pores with correspondingly more open structures

nano scale pore structure and fractal dimension of organic rich wufeng longmaxi shale from jiaoshiba area sichuan basin investigations using fe sem gas adsorption and helium pycnometry abstract much attention have been recently paid to the upper ordovician wufeng shale o3w and lower silurian longmaxi shale s1l in the jiaoshiba area of sichuan basin which is now the largest producing shale gas field in china field emission scanning electron microscopy fe sem low pressure gas n2 and co2 adsorption helium pycnometry x ray diffraction and geochemical analyses were performed to investigate the pore structure and fractal dimension of the pores in o3w s1l shale formation in the jiaoshiba area fe sem images show that organic matter om pores are dominant in the organic rich samples and these pores are often irregular bubble like elliptical and faveolate in shape while in organic poor samples limited and isolated interparticle interp intraparticle intrap and om pores are observed reversed s shaped isotherms obtained from nitrogen adsorption are type and hysteresis loops indicate that the shape of micropore in the samples is slit or plate like bet surface areas and total pore volume vary from 12 2 to 27 1 m2 g and from 1 8 10 2 to 2 9 10 2 cm3 g with an average of 19 5 m2 g and 2 3 10 2 cm3 g respectively adsorption volume from both n2 and co2 adsorption increases with respect to toc contents porosities obtained from helium porosimetry are comparable with these from gas co2 and n2 adsorption in o3w s1l shale however porosity determined by quantitative fe sem analysis is much smaller which is mainly related to limited resolution and the small areas of investigation based on the frenkel halsey hill fhh model of low pressure n2 adsorption fractal dimensions of the pores varied from 2 737 to 2 823 relationships between pore structure parameters and toc content mineral composition and fractal dimension reveal that the fractal dimension is mainly associated with micropores samples with higher toc content higher quartz content and lower clay content tend to contain more heterogeneous micropores resulting in higher fractal dimensions and more complicated pore structure in shales therefore fractal dimension is an effective parameter to reflect the complexity of pore structure and the degree of micropore development in o3w s1l shale

seasonal and interannual variations of firn densification and ice sheet surface elevation at the greenland summit seasonal and interannual variations in surface elevation at the greenland summit are modeled using a new temperature dependent formulation of firn densification and are compared with elevations from european remote sensing satellite ers 1 2 radar altimetry the rate constant and activation energy usually set as constants in the arrhenius type relation are strongly temperature dependent based on measurements of crystal growth rates a multiplicative factor in the densification rate accounts for differences between densification and grain growth rates and is chosen to match the modeled and measured density profiles from 0 to 40 m the stronger temperature dependence produces a significant seasonal cycle in the densification rate in the upper firn much of the densification and consequent surface lowering occur within 3 months in late spring early summer followed by a build up from accumulation modeled elevation changes using automatic weather station measurements of temperature and accumulation and modeled precipitation agree well with observations the respective seasonal amplitudes are 18 and 25 cm peak to peak with minima in mid summer the minimum elevation in 1995 is driven mainly by a temporary accumulation decrease and secondarily by warmer temperatures increased compaction driven by a summer warming trend decreases the modeled elevation 1992 99 by 20 cm but accumulation increases in latter years dominate the overall 4 2 cm a 1 trend

heterogeneous nanoporosity of the silurian longmaxi formation shale gas reservoir in the sichuan basin using the qemscan fib sem and nano ct methods abstract nanoporosity of a shale gas reservoir provides essential information on the gas accumulation space and controls the gas reserves the characteristics of heterogeneous nanoporosity of four shale samples are analyzed by combining quantitative evaluation of minerals by scanning electronic microscopy qemscan focused ion beam scanning electron microscopy fib sem and nano ct the representative elementary area rea is proposed by qemscan to detect the imaging area that can represent the overall contents of minerals and organic matter combined with the statistics of pores in minerals and organic matter by fib sem the quantitative nanoporosity is obtained the nano ct is used to compare the total nanoporosity that was obtained by fib sem the results show that shale has distinct characteristics in nanoporosities due to the variation in organic matter and mineral content the major pore sizes of the organic matter and clay minerals are smaller than 400 nanometers nm and the pore sizes of feldspar and pyrite are mainly 200 600 nm the pore sizes for pores developed in quartz and carbonate minerals range from a few nanometers to 1000 nm furthermore pores smaller than 400 nm mainly provide the total nanoporosity the nanoporosities in the organic matter are approximately 17 21 since the organic matter content 0 54 6 98 is low the organic matter contributes approximately 5 33 of the total nanoporosity in shale conversely the nanoporosities in quartz and clay are generally lower than 3 since the mineral content 93 02 99 46 is obviously higher than the organic matter content the minerals contribute approximately 67 95 of the total nanoporosity in shale

sks splitting in the western indian ocean from land and seafloor seismometers plume plate and ridge signatures we present sks splitting measurements in the western indian ocean recorded on 20 land and 57 seafloor seismometers deployed by the rhum rum experiment reunion hotspot and upper mantle reunions unterer mantel we discuss our splitting observations within their geodynamic settings and compare them to sks splitting parameters predicted from an azimuthally anisotropic rayleigh wave tomography model that includes the rhum rum data we find that anisotropic directions poorly correlate with the present day motion of the somali plate which at 2 6 cm yr may be too slow to cause strongly sheared fabric in the asthenosphere fast split directions between la reunion and the central indian ridge cir trend e w and provide strong first seismological evidence for near horizontal flow in the asthenosphere that connects the reunion mantle upwelling with the cir supporting a long standing hypothesis on plume ridge interaction in the vicinity of the reunion hotspot we observe a seismic anisotropy pattern indicative of a parabolic asthenospheric flow controlled by the reunion mantle upwelling and its consecutive asthenospheric spreading we furthermore observe ridge normal along the cir and ridge parallel along the southwest indian ridge swir both mainly attributed to asthenospheric mantle flows in the mozambique channel between east africa and madagascar we attribute e w trending to frozen lithospheric structures recording the paleo orientation of the spreading ridges that enabled madagascar s separation away from africa based on the synopsis of this and previous sks splitting studies at mid ocean ridges we propose that ridge normal may develop at fast and intermediate spreading ridges e g cir and east pacific rise and ridge parallel could be characteristic to slow spreading ridges e g swir mid atlantic ridge and the paleo ridges in the mozambique channel