mechanical properties of shale gas reservoir rocks part 1 static and dynamic elastic properties and anisotropy abstractunderstanding the controls on the elastic properties of reservoir rocks is crucial for exploration and successful production from hydrocarbon reservoirs we studied the static and dynamic elastic properties of shale gas reservoir rocks from barnett haynesville eagle ford and fort st john shales through laboratory experiments the elastic properties of these rocks vary significantly between reservoirs and within a reservoir due to the wide variety of material composition and microstructures exhibited by these organic rich shales the static young s modulus and dynamic p and s wave moduli elastic parameters generally decrease monotonically with the clay plus kerogen content the variation of the elastic moduli can be explained in terms of the voigt and reuss limits predicted by end member components however the elastic properties of the shales are strongly anisotropic and the degree of anisotropy was found to correlate with the amount of clay and organic content as well as the shale fab

the 1996 ad delta collapse and large turbidite in lake brienz abstract in spring 1996 ad the occurrence of a large mass transport was detected by a series of events which happened in lake brienz switzerland turbidity increase and oxygen depletion in deep waters release of an old corpse into surface waters and occurrence of a small tsunami like wave this mass transport generated a large turbidite deposit which is studied here by combining high resolution seismic and sedimentary cores this turbidite deposit correlates to a prominent onlapping unit in the seismic record attaining a maximum of 90 cm in thickness it is longitudinally graded and thins out towards the end of the lake basin thickness distribution map shows that the turbidite extends over 8 5 km2 and has a total volume of 2 72 106 m3 which amounts to 8 7 yr of the lake s annual sediment input it consists of normally graded sand to silt sized sediment containing clasts of hemipelagic sediments topped by a thin white clay sized layer the source area the exact dating and the possible trigger of this turbidite deposit as well as its flow mechanism and ecological impact are presented along with environmental data river inflow wind and lake level measurements the combined results indicate that no particular cause i e earthquake explosion flood wind storm lake level change seiche or sediment dredging triggered the 1996 ad large turbidite deposit instead it was due to a delta slope failure most likely caused by normal sediment accumulation

salinity dependence of the complex surface conductivity of the portland sandstone abstractinduced polarization can be used to estimate surface conductivity by assuming a universal linear relationship between the surface and quadrature conductivities of porous media however this assumption has not yet been justified for conditions covering a broad range of fluid conductivities we have performed complex conductivity measurements on portland sandstone an illite and kaolinite rich sandstone at 13 different water salinities nacl over the frequency range of 0 1 hz to 45 khz the conductivity of the pore water w affected the complex surface conductivity mainly by changing the tortuosity of the conduction paths in the pore network from high to low salinities as the fluid conductivity decreases the magnitude of the surface conductivity and quadrature conductivity was observed to decrease at relatively high salinities w 0 01 s m 1 the ratio between the surface conductivity and quadrature conductivity was roughly constant at low salinities w 0 01 s m 1 the ratio decreased s

complex conductivity tomography using low frequency crosswell electromagnetic data abstractthe complex conductivity of partially saturated siliciclastic sediments can now be reasonably predicted through recently developed petrophysical models like the polaris model however classical crosswell induced polarization tomography using a galvanometric approach is characterized by a poor sensitivity map far from the wells and thus other methods should be analyzed for potential improvements the presence of low frequency 1 khz polarization effects in earth porous materials noticeably increases the amplitude and decreases the phase of measured electromagnetic em fields as such the quadrature conductivity directly associated with the low frequency polarization effect yields a significant contribution to the em fields we demonstrate that these contributions can be observed in crosswell em data in terms of signal to noise ratio with a realistic amount of noise we can recover the distribution of the in phase and quadrature conductivities for crosswell em tomography we use an integ

measurements of elastic and electrical properties of an unconventional organic shale under differential loading abstractwe have developed an experimental approach to simultaneously measure the stress dependence of ultrasonic wave velocities at 1 mhz and therefore the components of the undrained elastic stiffness tensor as well as the components of the complex conductivity tensor in the frequency range from 100 mhz to 10 hz we performed the experiments on a cylindrical core sample from the haynesville formation porosity of approximately 0 08 bound water excluded and clay content mostly illite approximately 30 40 wt we performed experiments under controlled confining and pore fluid pressures achieving differential pressure states representative of autochthonous reservoir conditions directional measurements were made using independent acquisition arrays piezoelectric crystals and nonpolarizing electrodes distributed azimuthally on the core sample external surface the bedding plane being along the axis of the cylindrical core sample ultrasonic waveforms were recorded on a high resolution oscilloscope

estimation of the anisotropy parameters of transversely isotropic shales with a tilted symmetry axis summary this paper reports a new approach for the estimation of thomsen anisotropy parameters and symmetry axis orientation from ultrasonic p wave traveltime measurements on transversely isotropic shale samples of arbitrary geometry this approach can be used for core samples cut in any direction with respect to the bedding plane because no a priori assumption regarding the symmetry axis orientation is made this orientation is rather part of the solution of the inverse problem together with the anisotropy parameters themselves very fast simulated reannealing is used to search for the best possible estimate of the model parameters the methodology is applied to spherical and cylindrical anisotropic shale samples

laboratory determination of the full electrical resistivity tensor of heterogeneous carbonate rocks at elevated pressures we describe a measurement system capable of determining the full resistivity tensor of core samples at elevated geologically representative pressures using a galvanic method it is suitable for heterogeneous rocks where it is difficult to measure tensorial resistivity without bias from sample selection and heterogeneity we demonstrate the efficacy of the system using both synthetic data and measurements on carbonate rock core samples the apparatus employs a computer controlled array of 16 electrodes to inject current into and measure boundary voltages on a 5 cm diameter cylindrical sample a computationally efficient fe algorithm is used to retrieve the full resistivity tensor from the measured voltages the algorithm uses isotropic finite element code to calculate anisotropic solutions for samples of arbitrary geometry initial results from jurassic limestone and triassic dolomite samples reveal cm scale heterogeneity and significant bulk anisotropy consistent with rock fabric observed in x ray computed tomography scan images

impact of fabric microcracks and stress field on shale anisotropy summary few data are available on shales in terms of seismic to ultrasonic properties and anisotropy although all are important with regards to imaging problems often encountered in such lithologies additionally mechanisms causing changes in these properties are not well documented due to the fine grain size of such materials and time required for testing under controlled pore pressure conditions the results presented here are derived from a set of experiments run on muderong shale with pore pressure control in order to evaluate the effect of stress magnitude and stress anisotropy on ultrasonic response this shale was noted to have a linear velocitymean effective stress response and extremely high anisotropy both likely the result of the presence of fluid filled cracks in a low permeability porous medium changes in velocity and vp vs ratios are dependent on both stress and smectite content s wave velocity is significantly affected by the presence of smectite in this and other shales and at low stress 20 mpa is less sensitive to stress change than p wave velocity vp vs ratios are noted to increase in this shale up to 20 mpa effective stress then decrease slightly due to stress induced loss of interlayer water in smectite intrinsic anisotropy comes from composition a strong compaction fabric and the presence of microfractures changes to ultrasonic anisotropy are the result of the magnitude of the stresses their orientation with respect to the fractures and the degree of stress anisotropy

effect of grain scale alignment on seismic anisotropy and reflectivity of shales the elastic properties and anisotropy of shales are strongly influenced by the degree of alignment of the grain scale texture in general an orientation distribution function odf can be used to describe this alignment which in practice can be characterized by two legendre coefficients we discuss various statistical odfs that define the alignment by spreading from a mean value in particular the gaussian fisher and bingham distributions we compare the statistical models with an odf resulting from pure vertical compaction no shear strain of a sediment the compaction odf may be used to estimate how the elastic properties and anisotropy evolve due to burial of clayey sediments our study shows that the three statistical odfs produce almost identical correspondence between the two legendre coefficients as a function of the spreading parameter so that the spreading parameter of one odf can be converted to the spreading parameter of another odf in most cases it is then sufficient to apply the spreading parameter for the odf instead of the two legendre coefficients the effect of compaction on the odf gives a slightly different correspondence between the two legendre coefficients from that for the other models in principle this opens up the possibility of distinguishing anisotropy effects due to compaction from those due to other processes we also study reflection amplitudes versus angle of incidence ava for all wave modes where shales having various odfs overlie an isotropic medium the ava responses are modelled using both exact and approximation formulae and their intercepts and gradients are compared the modelling shows that the s wave velocity is sensitive to any perturbation in the spreading parameter while the p wave velocity becomes increasingly sensitive to a perturbation of a less ordered system similar observations are found for the ava of the p p and p sv waves modelling indicates that a combined use of the amplitude versus offset of p p and p sv reflected waves may reveal certain grain scale alignment properties of shale like rocks

sphericity as a characteristic of solids from fossil fuel burning in a lake michigan sediment abstract the property of sphericity is used to identify some anthropogenic particles in a lake michigan sediment three classes of products from high temperature processes primarily fossil fuel burning have been isolated charcoals iron oxides and aluminosilicates the morphologies structures and surface characteristics are indicative of the combustion process

induced polarization of shaly sands equations have been developed that relate induced polarization ip in shaly sands to measurable petrophysical parameters the induced polarization process has been modeled in terms of two mechanisms clay counterion displacement and membrane blockage the resulting equations can be used to determine shaliness brine conductivity and oil saturation from in phase and out of phase conductivities laboratory measurements have confirmed the ip dependence on these variables as well as on temperature

pore scale simulations of electrical and elastic properties of shale samples based on multicomponent and multiscale digital rocks abstract the special intrinsic characteristics of shale formations such as multiscale pore systems and complex mineral components make the simulation of shale properties more difficult than that of sandstone properties as such one prerequisite of numerically predicting the physical properties of shale samples is to construct accurate shale models that include those special features to this end the study presents a novel hybrid stochastic modeling algorithm called dem qsgsa which integrates the discrete element method dem and the quartet structure generation set algorithm qsgsa to build the necessary multicomponent and multiscale shale models to investigate the effects of the components on the shale properties the dem qsgsa was used to generate a dozen digital shale models with different mineral components containing quartz feldspar calcite clay minerals pyrite and organic matter the accuracy of the models was verified by comparing the characteristics of pore systems and the percentages of mineral components of the generated models with the ones of the sem images of real shale samples the electrical resistivity bulk modulus and shear modulus of these shale models were obtained using fem the results of electrical and elastic properties of these digital rocks indicate that the increase in abundance of the organic matter om pores intraparticle intrap pores clay minerals or om results in a decrease in the electrical resistivity and elastic moduli when the pore systems of shale models are saturated with water however when the volume fraction of pyrite becomes larger the elastic moduli increases and electrical resistivity decreases moreover comparison of the sensitivity indices of the variables shows that pyrite has the largest effect on the electrical and elastic properties of shale samples whilst clay minerals exert a moderate impact on them

pressure effects on the joint elastic electrical properties of reservoir sandstones we conducted a laboratory study of the joint elastic electrical properties of sixty three brine saturated sandstone samples to assess the likely impact of differential pressure confining minus pore fluid pressures in the range 8 60 mpa on the joint interpretation of marine seismic and controlled source electromagnetic survey data the samples showed a wide range of petrophysical properties representative of most sandstone reservoirs we found that a regression equation comprising both a constant and an exponential part gave a good fit to the pressure dependence of all five measured geophysical parameters ultrasonic p and s wave velocity attenuation and electrical resistivity electrical resistivity was more pressure sensitive in clay rich sandstones with higher concentrations of low aspect ratio pores and micropores than in clean sandstones attenuation was more pressure sensitive in clean sandstones with large open pores macropores than in clay rich sandstones pore shape did not show any influence on the pressure sensitivity of elastic velocity as differential pressure increases the effect of the low aspect ratio pores and micropores on electrical resistivity becomes stronger than the effect of the macropores on attenuation further analysis of correlations among the five parameters as a function of pressure revealed potentially diagnostic relationships for geopressure prediction in reservoir sandstones

radius rapid particle analysis of digital images by ultra high resolution scanning of thin sections radius is a newly developed particle size measurement technique based on evaluation of digital images of thin sections analyses are performed with sub millimetre sample resolution and are thus designed to work on a single lamina of laminated sediments the method covers grain sizes from medium silt to coarse sand the application contains pattern recognition modules that allow the detection of typical particle distributions of loess organic detritus turbidites and tephra layers cutting and hiding effects of particles on thin sections are corrected by empirical correction matrices the calculated analysis results are compared with manually counted and measured samples to calibrate the application settings the method can be applied to all fine grained clastic sediments particularly to laminated lake sediments

a biomass burning record from the west equatorial pacific over the last 360 ky methodological climatic and anthropic implications abstract to reconstruct past fire activity in the west pacific east asian region we investigate a 360 ky pelagic sedimentary record from the caroline basin in the western pacific warm pool wpwp core md97 2140 2547 m water depth in the lack of standard protocol and terminology for the determination of combustion derived products in sedimentary archives three proxies were compared with other paleoceanographic proxies oxidation resistant elemental carbon orec black carbon bc and microcharcoal the mineral caco3 and organic carbon corg records of core md97 2140 generally covary with the oxygen isotope record suggesting that glacial interglacial changes in ice volume and sea level control the preservation of caco3 and terrigeneous inputs of corg in the deep sea sediments of the caroline basin the changes in orec are primarily connected to the changes in corg record in contrast the bc and charcoal records which better reflect the input of biomass burning products are tightly connected with changes in the precession band 23 ky likely through low latitude atmospheric circulation patterns a peculiar control by the competing influence of the long term el nino southern oscillation enso like forcing and the glacial interglacial cycle on the east asian summer monsoon 30 19 11 and 6 ky periods is suggested in addition large increases in bc and charcoal are observed between ca 53 43 and 12 10 ky bp these events strikingly correspond to the main late pleistocene and early holocene periods of human colonization in the region likely suggesting an additional anthropic impact on the fire activity

charcoal and fly ash particles from lake lucerne sediments central switzerland characterized by image analysis anthropologic stratigraphic and environmental implications abstract in order to link the charcoal record from sedimentary archives with the combustion processes that reflect past anthropogenic activity a novel method based on automated image analysis was developed it allows a detailed quantification and morphological analysis of the combustion derived products that were emitted in the area of lake lucerne central europe throughout the last 7200 years charcoal particle distribution reconstructed from the composite sedimentary record shows that the charcoal input is primarily linked to redistribution of detrital m size charcoal degradation products from surface runoff into the large lake basin however the independent distribution of the coarser charcoal fraction 38 m exhibits four major periods of large scale fire activity around 5500 3300 2400 and 530 cal bp these events are synchronous with major anthropogenic changes lake dwellings land use changes technological innovations although it is possible that these major fire episodes could have been indirectly triggered by climatic deterioration and unfavorable environmental conditions during the late nineteenth century a great increase in slag particles and magnetic spherules of fly ash occurred due to the steamboat navigation on lake lucerne the successive burning of wood after ad 1838 coal after ad 1862 and diesel after ad 1931 by the steamboat traffic produced specific particle shapes providing valuable chronological markers for dating the recent sediments and a proxy for fossil fuel combustion

postglacial vegetation climate and fire history along the east side of the andes lat 41 42 5 s argentina abstract the history of the low elevation forest and forest steppe ecotone on the east side of the andes is revealed in pollen and charcoal records obtained from mid latitude lakes prior to 15 000 cal yr bp the vegetation was characterized by steppe vegetation with isolated stands of nothofagus the climate was generally dry and the sparse vegetation apparently lacked sufficient fuels to burn extensively after 15 000 cal yr bp a mixture of nothofagus forest and shrubland steppe developed fire activity increased between 13 250 and 11 400 cal yr bp contemporaneous with a regionally defined cold dry period huelmo mascardi cold reversal the early holocene period was characterized by an open nothofagus forest shrubland mosaic and fire frequency was high in dry sites and low in wet sites the data suggest a sharp decrease in moisture eastward from the andes a shift to a surface fire regime occurred at 7500 cal yr bp at the wet site and at 4400 cal yr bp at the dry site preceding the expansion of austrocedrus by 1000 1500 yr the spread of austrocedrus is explained by a shift towards a cooler and wetter climate in the middle and late holocene the change to a surface fire regime is consistent with increased interannual climate variability and the onset or strengthening of enso the present day mixed forest dominated by nothofagus and austrocedrus was established in the last few millennia

downhole geophysical logging downhole geophysical logging is the method of making geophysical measurements in drill holes and interpreting these measurements for evaluation of geological properties of the subsurface the downhole measurements can be made with great spatial resolution with a single sonde containing both source and receivers which are separated by 10 cm to tens of meters measurements can be repeated every few centimeters as the sonde moves upward or downward in the borehole this technique is called well logging it is also possible to make downhole measurements with the sensor in the borehole at depth and the source at the surface when the sensor package is moved to a different depth the source signal is repeated when these measurements are made with seismic waves the process is called vertical seismic profiling vsp in vsp the surface source can be any appropriate system that would generate a seismic pulse dynamite air gun or a sinusoidal wave vibroseis and the downhole sensor can be a hydrophone or borehole geophone vertical seismic profiling is a rapidly expanding technique and some of its applications are described in a series of recent books gal perin 1974 hardage 1983 balch lee 1984 toksoz stewart 1984 another method of downhole measurement is possible when closely spaced drill holes are available with the source placed in one drill hole and the detector receiver in another this technique called cross

on the long term context for late twentieth century warming 1 previous tree ring based northern hemisphere temperature reconstructions portray a varying amplitude range between the medieval warm period mwp little ice age lia and present we describe a new reconstruction developed using largely different methodologies and additional new data compared to previous efforts unlike earlier studies we quantify differences between more traditional std and regional curve standardization rcs methodologies concluding that rcs is superior for retention of low frequency trends continental north american versus eurasian rcs series developed prior to merging to the hemispheric scale cohere surprisingly well suggesting common forcing although there are notable deviations e g fifteenth to sixteenth century results indicate clear mwp warm lia cool and recent warm episodes direct interpretation of the rcs reconstruction suggests that mwp temperatures were nearly 0 7c cooler than in the late twentieth century with an amplitude difference of 1 14c from the coldest 1600 1609 to warmest 1937 1946 decades however we advise caution with this analysis although we conclude as found elsewhere that recent warming has been substantial relative to natural fluctuations of the past millennium we also note that owing to the spatially heterogeneous nature of the mwp and its different timing within different regions present palaeoclimatic methodologies will likely flatten out estimates for this period relative to twentieth century warming which expresses a more homogenous global fingerprint therefore we stress that presently available paleoclimatic reconstructions are inadequate for making specific inferences at hemispheric scales about mwp warmth relative to the present anthropogenic period and that such comparisons can only still be made at the local regional scale

complex electrical conductivity changes associated with hydrous pyrolysis maturation of the woodford shale abstracthydrous closed system pyrolysis experiments were performed on five pairs of chert cubes from the woodford shale aliquots under uniaxial confinement at various prescribed thermal maturities these thermal maturities represent each of the phases of organic matter om catagenesis under hydrous conditions immature kerogen at low thermal stress 125 c for 72 h low and peak bitumen generation with increasing thermal stress 300 c and 330 c for 72 h cracking of bitumen to oil and gas at higher thermal stresses 330 c and 360 c for 72 h and cracking of some oil at the highest experimental conditions 400 c for 72 h we measured the spectra of the complex electrical conductivity tensor in the frequency range 10 mhz to 45 khz of these 10 aliquots to capture the effects of thermal maturation by hydrous pyrolysis results indicate that surface conduction of polar rich bitumens has a significant effect on their complex electrical conductivity the om of a source rock is considered a negligible cause

synchronous holocene climatic oscillations recorded on the swiss plateau and at timberline in the alps eight synchronous pre roman cold phases were found at 9600 9200 8600 8150 7550 6900 6600 6200 5350 4900 4600 4400 3500 3200 and 2600 2350 radiocarbon years bp by reconstructing past climate at two sites on the swiss plateau and at timberline in the alps the cooling events during the early and mid holocene represent temperature values similar to today and apparently the onset of cooling events represents a deviation from today s mean annual temperature of about 1 c and is triggered at a 1000 year periodicity at wallisellen langachermoos 440 m a former oligotrophic lake near zurich the correlation between sum mertime lake levels and the seed production of the amphi atlantic aquatic plantnajas flexilis was used to reconstruct lake levels over a 3000 year period during the first part of the holocene at lake seedorf on the western swiss plateau 609 m the sedimentological palynological and macrofossil record revealed fluctuations of lake levels for the complete holocene from lago basso in the

dating of recent lake sediments in the united kingdom and ireland using spheroidal carbonaceous particle scp concentration profiles spheroidal carbonaceous particles scps produced from fossil fuel combustion are found in lake sediments and provide a historical record of atmospheric pollutant deposition the sediment record of these particles is remarkably consistent and the main features are now seen throughout europe and beyond once the scp record from a region has been established using accurately dated cores scp profiles can be used to determine dates at other sites in the region this technique was developed in sweden brit until recently has had limited use in the uk and ireland as the most useful dating feature the subsurface peak was not present in all cores in recent cores this can now almost always be observed dating features for uk and irish cores are found to differ slightly between regions the potential exists for extra dates to be allocated to a profile by using characterisation of scp surfaces to determine changes in fuel type use dates could then be allocated to these changes using documentary sources to derive combustion histories in future years scp dating will become increasingly valuable especially for mid to late nineteenth century sediments as continual decay renders 210 pb progressively less useful for this time interval

characterization of gas shale pore systems by porosimetry pycnometry surface area and field emission scanning electron microscopy transmission electron microscopy image analyses examples from the barnett woodford haynesville marcellus and doig units the nanometer scaled pore systems of gas shale reservoirs were investigated from the barnett marcellus woodford and haynesville gas shales in the united states and the doig formation of northeastern british columbia canada the purpose of this article is to provide awareness of the nature and variability in pore structures within gas shales and not to provide a representative evaluation on the previously mentioned north american reservoirs to understand the pore system of these rocks the total porosity pore size distribution surface area organic geochemistry mineralogy and image analyses by electron microscopy were performed total porosity from helium pycnometry ranges between 2 5 and 6 6 total organic carbon content ranges between 0 7 and 6 8 wt and vitrinite reflectance measured between 1 45 and 2 37 the gas shales in the united states are clay and quartz rich with the doig formation samples being quartz and carbonate rich and clay poor higher porosity samples have higher values because of a greater abundance of mesopores compared with lower porosity samples with decreasing total porosity micropore volumes relatively increase whereas the sum of mesopores and macropore volumes decrease focused ion beam milling field emission scanning electron microscopy and transmission electron microscopy provide high resolution 5 nm images of pore distribution and geometries image analysis provides a visual appreciation of pore systems in gas shale reservoirs but is not a statistically valid method to evaluate gas shale reservoirs macropores and mesopores are observed as either intergranular porosity or are confined to kerogen rich aggregates and show no preferred orientation or align parallel with the laminae of the shale networks of mesopores are observed to connect with the larger macropores within the kerogen rich aggregates

joint elastic electrical properties of reservoir sandstones and their relationships with petrophysical parameters we measured in the laboratory ultrasonic compressional and shear wave velocity and attenuation 0 7 1 0 mhz and low frequency 2 hz electrical resistivity on 63 sandstone samples with a wide range of petrophysical properties to study the influence of reservoir porosity permeability and clay content on the joint elastic electrical properties of reservoir sandstones p and s wave velocities were found to be linearly correlated with apparent electrical formation factor on a semi logarithmic scale for both clean and clay rich sandstones p and s wave attenuations showed a bell shaped correlation partial for s waves with apparent electrical formation factor the joint elastic electrical properties provide a way to discriminate between sandstones with similar porosities but with different clay contents the laboratory results can be used to estimate sandstone reservoir permeability from seismic velocity and apparent formation factor obtained from co located seismic and controlled source electromagnetic surveys

characterization of electrical properties of organic rich shales at nano micro scales abstract a new experimental protocol is explored to characterize electrical properties of hydrocarbon bearing mudrocks at nano micro scales two current flow regimes of peak force tunneling atomic force microscopy pf tuna have been used 1 the vertical out of plane current regime with hundred micrometer diameter top electrodes obtains homogenized conductivity quantitatively 2 the horizontal in plane current regime was shown powerful to visualize the conductive paths related to connectivity and tortuosity for heterogeneous and anisotropic shales results show that the approach works well with one to two layers of adsorbed water 25 55 relative humidity under low frequency 0 5 20 hz for shale rocks current maps with sub nanometer resolution emphasize the dominant role of hydrated ions associated with the hydrophilic clay minerals in driving the dielectric response of shales while conductivity of pyrite and kerogen cannot be neglected for mature organic rich shale conductive network the acquired i v curves at microscale provide a reliable mean to evaluate homogenized conductivity of such multiscale multi component heterogeneous material under controlled environmental conditions the procedure discussed herein serves as a complement for fine grained rocks and minerals of ionic electronic hybrid conductive mechanism under partially water saturation these results can be used to develop accurate electrical models specifically for shale rocks with heterogeneous and sophisticated microstructure the methodology can be also extended to other micro or meso porous geomaterials such as cementitious and bituminous nanoporous media

velocity anisotropy in shales a petrophysical study using ultrasonic velocity and anisotropy measurements on a variety of shales with different clay and kerogen content clay mineralogy and porosity at a wide range of effective pressure we find that elastic anisotropy of shales increases substantially with compaction the effect is attributed to both porosity reduction and smectite to illite transformation with diagenesis a means of kerogen content mapping using velocity versus porosity crossplot for shales is shown matrix anisotropy of shales dramatically increases with kerogen reaching the maximum values of about 0 4 at total organic carbon toc 15 20 a strong chemical softening effect was found in shales containing even minor amounts of swelling smectite clay when saturated with aqueous solution this effect results in a significant p wave anisotropy reduction as compared to dry and oil saturated shales since mature black shales are normally oil wet this effect can only have a local significance restricted to the wellbore wall accurate measurements of phase velocities including velocities at a 45 direction to the bedding plane allow us to immediately calculate elastic stiffnesses and anisotropic parameters intrinsic high pressure properties of shales display an e 0 relation introduction of the bedding parallel microcracks in overpressured shales results in a decrease when fully fluid saturated and a increase when partially gas saturated with a characteristic effect on the shape of the p wave velocity surface at small angles of incidence filtering the contribution of the intrinsic anisotropy of shales it is possible to estimate the pore fluid phase microcrack density and aspect ratio parameters using seismic anisotropy measurements

comparison of the anisotropic behaviour of undeformed sandstones under dry and saturated conditions abstract this article presents a systematic analysis of the anisotropic behaviours of the bentheim and rothbach sandstones using ultrasonic p wave velocity electrical conductivity and magnetic susceptibility measurements for each sandstone the data were obtained from three core samples drilled perpendicularly to each other and tested in dry and water saturated conditions for acoustic and magnetic investigations the same statistical analysis was applied in order to present the data on comparable stereoplots surprisingly the bentheim sandstone which appeared homogeneous at macroscopic scale showed a stronger elastic and electrical anisotropy than the rothbach sandstone in which cross laminations were clearly identified as confirmed by a sedimentary magnetic fabric a discussion on the velocity contrasts between dry and saturated samples led us to consider two different origins for the observed anisotropies first by comparing electrical and acoustic properties in the bentheim sandstone we conclude that the nature of the anisotropic behaviour is linked to the anisotropy of pore shape the inclusion model developed by kachanov kachanov m 1993 elastic solids with many cracks and related problems advances in applied mechanics vol 30 academic press boston ma pp 259 445 accounts for our observations if one considers that the pore space is made of parallel flat pores with moderate pore aspect ratio second acoustic electrical and magnetic properties indicate that the observed anisotropy in the rothbach sandstone can be attributed to the matrix and more specifically to cementation we modified the dvorkin and nur geophysics 61 5 1996 1363 model of cemented granular media by introducing a spatially variable contact length and the model suggests that a very small variability of cemented contact length is enough to account for the observed p wave velocity anisotropy we emphasise the fact that combining several kinds of measurements is of great help in capturing the nature of the anisotropic behaviour of porous rocks

the alps with little ice evidence for eight holocene phases of reduced glacier extent in the central swiss alps glacially deformed pieces of wood organic lake sediments and clasts of reworked peat have been collected in front of alpine glaciers since ad 1990 the palaeoglaciological interpretation of these organic materials is related to earlier phases of glacier recession surpassing that of today s shrunken glaciers and to tree growth and peat accumulation in the valleys now occupied by the glaciers glacial transport of the material is indicated by wood anatomy incorporated silt sand and gravel particles missing bark and deformed treerings a total of 65 samples have been radiocarbon dated so far and clusters of dates provide evidence of eight phases of glacier recession 9910 9550 9010 7980 7250 6500 6170 5950 5290 3870 3640 3360 2740 2620 and 1530 1170 calibrated years bp allowing for the timelag between climatic fluctuations glacier response and vegetation colonization these recession phases may lag behind climatic changes by 100 200 years

experimental laboratory determination of the dynamic elastic properties of wet drained shales the ultrasonic anisotropic elastic properties of drained saturated shales were measured as a function of confining pressure two shales were characterized in this study a jurassic outcrop shale retrieved under the sea in a saturated state and a kimmeridge clay shale cut from a north sea borehole both shales were highly anisotropic both texturally as revealed by scanning electron microscopy analysis and elastically as measured ultrasonically in the laboratory the strongest anisotropy was seen in the kimmeridge clay shale where up to 38 compressional wave anisotropy thomsen s parameter e and up to 58 shear wave anisotropy thomsen s parameter were observed in addition for both shales e and were found to decrease as a function of increasing confining pressure with the pore pressure drained to atmosphere while the anellipticity deviation of the slowness surfaces from ellipses was found to be positive and decreased as a function of increasing confining pressure accompanying these changes in elastic properties was a decrease in porosity with increasing confining pressure from 10 5 to 8 5 for the jurassic shale the decrease in overall anisotropy of the shales with increasing confining pressure was found to be consistent with theoretical modeling of shale properties where the shale anisotropy and anellipticity were predicted to decrease as a function of decreasing fluid filled porosity