variation of pore fabric across a fold thrust structure variations of pore orientation pore shape porosity and hydraulic permeability within a siltstone unit of a fold thrust structure are determined using magnatic pore fabric analysis mercury injection porosimetry and scanning electron microscopy sem while samples in the foreland show evidence for the preservation of depositional pore geometry the progressively deformed thrust sheet reveals increasingly oblate pore fabric anisotropy with microcrack planes oriented normal to the tectonic transport direction porosity pore throat sizes and permeability show corresponding spatial variations across the structure independent of the deformation state within the thrust sheet pore and magnetic grain fabric correlate closely in orientation

first occurrence of a middle triassic tetrapod ichnofauna from the argana basin western high atlas morocco abstract footprints of early mesozoic terrestrial tetrapods are inadequately known from nw africa despite pervasive and well exposed continental strata of corresponding age in that region here we report on the first occurrence of a tetrapod ichnofauna from the middle part of the triassic timezgadiouine formation in the argana basin central morocco that is outstanding in terms of abundance preservation and diversity footprints of this assemblage are assigned to the ichnotaxa chirotherium barthii isochirotherium coureli synaptichnium isp atreipus grallator rotodactylus isp rhynchosauroides isp and procolophonichnium isp suggesting early archosaurian dinosauromorph lepidosauromorph and possible therapsid or procolophonoid trackmakers based on comparison with the abundant record of early mesozoic vertebrate ichnofossils from europe and north america the ichnofauna presented here indicates a middle triassic anisian ladinian age for the track bearing horizon in the argana basin its clearly euramerican affinity sheds light on the migration and dispersal of early archosaur dominated tetrapod faunas considering that several ichnotaxa of the assemblage are documented from africa for the first time

middle triassic pentasauropus dominated ichnofauna from western gondwana ichnotaxonomy palaeoenvironment biostratigraphy and palaeobiogeography abstract quadruped trackways of large pentadactyl footprints are reported from the middle triassic anisian ladinian cerro de las cabras formation of the cuyo basin mendoza province central western argentina the track bearing strata are interpreted as deposited by sheetfloods in a mixed flat where water was ponded in a playa lake setting the vertebrate trackways are assigned to the ichnogenus pentasauropus originally described from the upper triassic elliot formation of south africa based on the presence of five equally spaced digit imprints that form an anteriorly convex broad arcuate pattern a new ichnospecies pentasauropus argentinae nov isp is erected for the argentinian material because of the distinct heteropody inward rotation of the pes and outward rotation of the manus imprints and the presence of palm sole traces and the diagnosis of the ichnogenus is emended pes manus set arrangement and trackway patterns indicate a sprawling limbed trackmaker with an abducted posture for the fore limbs and at least a semi abducted posture for the hindlimbs which suggests that the trackmaker was a kannemeyeriiform dicynodont associated archosaur ichnotaxa chirotherium barthii chirotherium cf c rex isochirotherium cf i coureli point to a middle triassic age for the trackway bearing strata in agreement with bracketing geochronological data the rare occurrence of the therapsid footprint dicynodontipus isp is also compatible with the inferred age the moderate abundance and oldest occurrence of pentasauropus from three areas in argentina suggest an origin for this ichnogenus in southwestern gondwana and presumably this area was a faunal exchange gate between southeastern and southwestern gondwana and south gondwana and north america

on the impact of forced roll convection on vertical turbulent transport in cold air outbreaks we investigated the impact of roll convection on the convective boundary layer and vertical transports in different cold air outbreak cao scenarios using large eddy simulations les the organization of convection into rolls was triggered by upstream heterogeneities in the surface temperature representing ice and water by changing the sea ice distribution in our les we were able to simulate a roll and a nonroll case for each scenario furthermore the roll wavelength was varied by changing the scale of the heterogeneity the characteristics of the simulated rolls and cloud streets such as aspect ratios orientation of the roll axes and downstream extensions of single rolls agreed closely with observations in cao situations the vertical turbulent fluxes calculated for each simulation were decomposed into contributions from rolls and from unorganized turbulence even though our results confirmed that rolls triggered by upstream heterogeneities can substantially contribute to vertical turbulent fluxes the total fluxes were not affected by the rolls

genesis and development mechanisms of a polar mesocyclone over the japan sea abstracta polar mesocyclone pmc observed over the japan sea on 30 december 2010 was studied using a nonhydrostatic mesoscale numerical model with a horizontal resolution of 2 km the numerical simulation successfully reproduced the observed life cycle of the pmc the results of the numerical simulation suggest that the life cycle of the pmc may be divided into three stages an early development stage in which a number of small vortices appear in a shear zone a late development stage which is characterized by the merger of vortices and the formation of a few larger vortices and a mature stage in which only a single pmc is present during the early development stage vortices are generated in the shear zones of strong updrafts in discrete cumulus convection cells in contrast during the late development stage the vortices develop as a result of barotropic instability in the shear zone a cloud free eye and spiral cloud bands accompany the mature stage of a simulated pmc a warm core structure also

complex resistivity measurements of confined rock complex resistivity was measured for samples of westerly granite and berea sandstone saturated with 0 01 m kclaq a four electrode technique was employed to make measurements over a frequency range of 10 3 to 106 hz and a confining pressure range of 0 2 to 200 mpa when the electrical response was analyzed in terms of equivalent conductivity and relative permittivity k both of these quantities varied more with confining pressure for the granite samples than they did for the sandstone in addition both rock types exhibited large low frequency dispersion of permittivity while previous studies have measured the response of near dc conductivity to changes in pressure measurements of pressure dependence of the full complex resistivity provide greater insight into earthquake related phenomena as well as induced polarization measurements and other remote sensing techniques

step drawdown test as a tool for the assessment of the nubia sandstone aquifer in east el oweinat area egypt the cretaceous nubia sandstone aquifer is the main aquifer in east el oweinat area along the egyptian sudanese borders and in ne africa east el oweinat project has been recently considered one of the main agricultural projects in the southwest of the egyptian western desert so the hydrogeological assessment for the nubia aquifer in east el oweinat area has been done through studying and characterising the hydraulic parameters and step drawdown test the well and aquifer losses coefficients c and b respectively the specific capacity and the well efficiency as well as the aquifer and aquitard thickness have been estimated and traced through a total of 46 wells that have been distributed through the study area in two sectors southern and northern for the purpose of further exploration the effective porosity hydraulic conductivity k and transmissivity t have been estimated for the wells in the northern sector in addition an aquifer assessment quality index has been introduced to assess and to rank the studied aquifer therefore it is concluded that the hydraulic and the step draw down parameters as well as the aquifer and aquitard thicknesses are prospective for further exploration to the north and the east of the northern sector in the study area the well efficiency is mostly affected by the studied parameters particularly the well loss coefficient the hydraulic parameters and the well design as well gis approach and arcgis software have been applied to delineate the spatial distribution of the well performance characteristics in order to compare between the studied groundwater wells and to integrate the different acquired data a set of isocontour maps have been introduced to match the lateral variation of the studied parameters and the aquifer potential to refer to the best direction for further underground water exploration

petrophysical and magnetic pore network anisotropy of some cretaceous sandstone from tushka basin egypt summary pore magnetic fabric is a well established technique for the determination of pore elongation and preferred directions for migration of the interstitial fluids this study further exemplify this technique on a set of the nubia sandstones through a comparison with the pore anisotropy obtained from measuring permeability in three orthogonal directions in a gaz permeameter the nubia sandstones are represented in tushka area south egypt by quartz arenite of large porosity 29 40 per cent which was measured on thin sections parallel and perpendicular to the bedding plane and petrophysically by helium pycnometry and ferrofluid injection at 1 bar pressure petrographically there is a detectable difference between the porosity values in the bedding plane and in the perpendicular direction indicating inhomogeneity in the pore space network distribution the petrophysical studies indicate large porosity and permeability values with some differences between the helium and ferrofluid porosity due to presence of micro pore spaces not accessible for the ferrofluid molecules having relatively high diameters and injected at low pressure an overall agreement is observed between the permeability anisotropy and the magnetic grain and pore fabrics magnetic anisotropy measured before and after ferrofluid injection the three fabrics are mainly dominated by a bedding parallel foliation in a few cases maximum permeability appears to be perpendicular to bedding within the bedding plane maximum pore elongation direction from ferrofluid injection is nnw for adindan and kesieba formations and nw for abu simbil formation the maximum pore elongation direction for abu ballas samples showed a direction fluctuating around the e w direction the main fault trends in tushka area the pore fabric of abu ballas formation seems therefore to be structurally controlled while it would be originated from palaeocurrent directions in the other formations

middle triassic archosaur population structure interpretation based on isochirotherium delicatum fossil footprints southern alps italy abstract well preserved archosaur footprints have recently been found on a single bedding plane in the italian alps the tracks are referable to isochirotherium delicatum courel and demathieu 1976 a form that was identified for the first time at the anisian ladinian boundary in the area of argentiere ardeche france the isochirotherium delicatum footprints and trackways from gampenpass represent a possible social group or herd estimating the age of the trackmakers from the examination of the footprints is difficult and complicated by the fact that the sample can be divided into two groups of tracks distinguishable by the l w cross axis and interdigital angle the diversity of the tracks is here interpreted as an indication of sexual dimorphism

the advection of mesoscale atmospheric vortices over reykjavik abstracton 12 august 2009 a series of satellite images revealed asymmetric shedding of atmospheric vortices in the lee of mt snaefellsjokull and their passage a distance of 120 km across faxafloi bay and over the city of reykjavik in west iceland after landfall the vortices were detected by a network of surface weather stations these observations are presented and with the aid of a numerical simulation they are discussed in view of existing theories of orographic wakes and vortex shedding in general the flow is in line with existing knowledge but there is a remarkable absence of vortices with anticyclonic rotation atmospheric conditions for vortices of this kind are most often favorable in late winter and spring and they are a forecasting challenge

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

the structure of strongly stratified flow over hills dividing streamline concept in stably stratified flow over a three dimensional hill we can define a dividing streamline that separates those streamlines that pass around the hill from those that pass over the hill the height hs of this dividing streamline can be estimated by sheppard s simple energy argument fluid parcels originating far upstream of a hill at an elevation above hs have sufficient kinetic energy to rise over the top whereas those below hs must pass around the sides this prediction provides the basis for analysing an extensive range of laboratory observations and measurements of stably stratified flow over a variety of shapes and orientations of hills and with different upwind density and velocity profiles for symmetric hills and small upwind shear sheppard s expression provides a good estimate for hs for highly asymmetric flow and or in the presence of strong upwind shear the expression provides a lower limit for hs as the hills become more nearly two dimensional these experiments become less well defined because steady state conditions take progressively longer to be established the results of new studies are presented here of the development of the unsteady flow upwind of two dimensional hills in a finite length towing tank these measurements suggest that a very long tank would be required for steady state conditions to be established upstream of long ridges with or without small gaps and cast doubt upon the validity of previous laboratory studies

low froude number flow past three dimensional obstacles part i baroclinically generated lee vortices abstract we study the flow of a density stratified fluid past a three dimensional obstacle using a numerical model our special concern is the response of the fluid when the froude number is near or less than unity linear theory is inapplicable in this range of froude number and the present numerical solutions show the rich variety of phenomena that emerge in this essentially nonlinear flow regime two such phenomena which occupy parts i and ii of this study are the formation of a pair of vertically oriented vortices on the lee side and a zone of flow reversal on the windward side of the obstacle the ice vortices have been explained as a consequence of the separation of the viscous boundary layer from the obstacle however this boundary layer is absent by design in the present experiments and lee vortices still occur we argue that a vertical component of vorticity develops on the lee side owing to the tilting of horizontally oriented vorticity produced baroclinically as the isentropes deform in r

first chirothere and possible grallatorid footprint assemblage from the upper triassic baoding formation of sichuan province southwestern china abstract trackways of archosaurs have recently been discovered in sandstones of the upper triassic norian rhaetian baoding formation of panzhihua city in southern sichuan province china based on their overall morphology pes imprints are of characteristic chirotheriid shape showing a compact and symmetrical anterior group of digit traces ii iv with the trace of digit iii being the longest and a posterolaterally positioned long and slender trace of digit v imprints of digit i and the manus are not preserved this could be related to substrate conditions and the relatively shallow impressions even if peculiarities in the gait such as overstep of the manus by the pes or bipedal movement cannot completely be excluded ichnotaxonomically the imprints are assigned tentatively to cf chirotherium there are some similarities with the type ichnospecies c barthii from the middle triassic that has a global distribution and that was described also from the guanling formation middle triassic of adjacent guizhou province however the long and slender digit v that lacks a distinct large oval basal pad the relatively short stride step length the low pace angulation and the slight inward rotation of the imprints toward the midline are different the peculiar shape of digit v and the lack of digit i in all imprints also preclude an assignment to the common late triassic ichnogenus brachychirotherium or similar ichnotaxa such as pseudotetrasauropus an isolated tridactyl footprint on the same surface is different in shape from the chirotheriid ones by the stronger mesaxony and narrower digit divarication it is considered here as a possible large grallatorid this is the first occurrence of tetrapod footprints in the baoding formation of sichuan province and the second record of chirotheriids in the triassic of china the baoding formation has also yielded a characteristic upper triassic flora with cycads filicopsids gingkos and conifers as well as bivalve fossils the depositional environment can be designated as fluvial lacustrine with occasional opening to marine areas considering biostratigraphic and palaeobiogeographic aspects the late occurrence of chirotheriids cf chirotherium in china supports the view that basal crown group archosaurs with a distinct tendency toward a functionally tridactyl pes developed and dispersed in parallel to typical tridactyl dinosaurs

atmospheric karman vortex shedding from jeju island east china sea a numerical study abstracta mesoscale atmospheric numerical model is used to simulate two cases of karman vortex shedding in the lee of jeju island south korea in the winter of 2013 observed cloud patterns associated with the karman vortex shedding are successfully reproduced when the winter monsoon flows out from the eurasian continent a convective mixed layer develops through the supply of heat and moisture from the relatively warm yellow sea and encounters jeju island and dynamical conditions favorable for the formation of lee vortices are realized vortices that form behind the island induce updrafts to trigger cloud formation at the top of the convective boundary layer a sensitivity experiment in which surface drag on the island is eliminated demonstrates that the formation mechanism of the atmospheric karman vortex shedding is different from that behind a bluff body in classical fluid mechanics

anomalous electrical resistivity anisotropy in clean reservoir sandstones we report novel laboratory measurements of the full electrical resistivity tensor in reservoir analogue quartzose sandstones with clay contents less than 1 5 we show that clean homogeneous visually uniform sandstone samples typically display between 15 and 25 resistivity anisotropy with minimum resistivity normal to the bedding plane thin section petrography analysis of fabric anisotropy and comparison to finite element simulations of grain pack compaction show that the observed anisotropy symmetries and magnitudes can be explained by syn depositional and post depositional compaction processes our findings suggest that electrical resistivity anisotropy is likely to be present in most clastic rocks as a consequence of ballistic deposition and compaction compaction may be deduced from measurements of electrical anisotropy and the anisotropy observed at larger scales in well logging and controlled source electromagnetic data with maximum resistivity normal to bedding is most likely the result of meso scale 10 1 m 101 m periodic layering of electrically dissimilar lithologies

archosaur footprints cf brachychirotherium with unusual morphology from the upper triassic fleming fjord formation norian rhaetian of east greenland the orsted dal member of the upper triassic fleming fjord formation in east green land is well known for its rich vertebrate fauna represented by numerous specimens of both body and ichnofossils in particular the footprints of theropod dinosaurs have been described recently an international expedition discovered several slabs with 100 small chirotheriid pes and manus imprints pes length 4 4 5 cm in siliciclastic deposits of this unit they show strong similarities with brachychirotherium a characteristic upper triassic ichnogenus with a global distribution a peculiar feature in the fleming fjord specimens is the lack of a fifth digit even in more deeply impressed imprints therefore the specimens are assigned here tentatively to cf brachychirothe rium possibly this characteristic is related to the extremely small size and early ontogenetic stage of the trackmaker the record from greenland is the first evidence of this morphotype from the fleming fjord formation candidate trackmakers are crocodylian stem group archosaurs how ever a distinct correlation with known osteological taxa from this unit is not currently possible while the occurrence of sauropodomorph plateosaurs in the bone record links the greenland assemblage more closer to that from the germanic basin of central europe here the described foot prints suggest a pangaea wide exchange supplementary material three dimensional model of cf brachychirotherium pes manus set from mguh 31233b from the upper triassic fleming fjord formation norian rhaetian of east greenland as pdf ply and jpg files 3d model created by oliver wings photographs taken by jesper milan is available at https doi org 10 6084 m9 figshare c 2133546

a diverse pleistocene marsupial trackway assemblage from the victorian volcanic plains australia abstract a diverse assemblage of late pleistocene marsupial trackways on a lake bed in south western victoria provides the first information relating to the gaits and morphology of several megafaunal species and represents the most speciose and best preserved megafaunal footprint site in australia the 60 110 ka volcaniclastic lacustrine sedimentary rocks preserve trackways of the diprotodontid diprotodon optatum a macropodid probably protemnodon sp and a large vombatid perhaps ramsayia magna or phascolomys medius and possible prints of the marsupial lion thylacoleo carnifex the footprints were imprinted within a short time period demonstrating the association of the taxa present rather than the time averaged accumulations usually observed in skeletal fossil deposits individual manus and pes prints are distinguishable in some trackways and in many cases some digital pad morphology is also present several parameters traditionally used to differentiate ichnotaxa including trackway gauge and the degree of print in turning relative to the midline are shown to be subject to significant intraspecific variation in marsupials sexual dimorphism in the trackway proportions of diprotodon and its potential for occurrence in all large bodied quadrupedal marsupials is identified here for the first time

the dynamics of orographic wake formation in flows with upstream blocking the development of orographic wakes and vortices is revisited from the dynamical perspective of a three dimensional 3d vorticity vector potential formulation particular emphasis is given to the role of upstream blocking in the formation of the wake scaling arguments are first presented to explore the limiting form of the 3d vorticity inversion for the case of flow at small dynamical aspect ratio it is shown that in the limit of small the inversion is determined completely by the two horizontal vorticity components that is the part of the velocity induced by the vertical component of vorticity vanishes in the small limit this result leads to an approximate formulation of small fluid mechanics in which the three governing prognostic variables are the two horizontal vorticity components and the potential temperature the remainder of the study then revisits the problem of orographic wake formation from the perspective of this small vorticity dynamics framework previous studies have suggested that one of the potential routes to stratified wake formation is through the blocking of flow on the upstream side of the barrier this apparent link between blocking and wake formation is shown to be relatively straightforward in the small vorticity context in particular it is shown that blocking of the flow inevitably leads to a horizontal vorticity distribution that favors deceleration of the leeside flow at the ground this process of leeside flow deceleration as well as the subsequent time evolution of the wake is illustrated through a series of numerical initial value problems involving flows past 2d and 3d barriers it is proposed that the initiation of the wake flow in these stratified problems resembles the flow produced by a retracting piston in shallow water theory

pore throat characterization in highly porous and permeable sandstones several methods have been developed to characterize the pore spaces in sandstone reservoirs using data on the pore throat size distribution obtained from mercury injection tests the winland equation the threshold pressure the displacement pressure and pittman s equation are mostly used for this purpose to delineate the stratigraphic traps and seals this study examines the reliability of these methods applied to the highly permeable nubia sandstones in their type section in southern egypt these sandstones are composed mainly of siliceous sandstones and constitute the main paleozoic cretaceous aquifers and reservoirs in egypt routine core analysis and mercury injection tests were conducted to delineate the pore network characteristics for these rocks the relationships between helium porosity and the uncorrected air permeability from the routine core analysis and the various parameters derived from mercury injection capillary pressure curves were established using multiple regressions this study indicates the high reliability of the displacement pressure at 10 mercury saturation and also reveals the apex of pittman s hyperbole at 45 mercury saturation as a complexity apex at which the pore network becomes highly chaotic despite the great benefits of such types of measurements they are not commonly used because of their high cost this study introduces a series of empirical equations for constructing a partial pore aperture size distribution curve from routine core analysis for the highly permeable rocks

an observational study of vortex spacing in island wake vortex streets abstract vortex streets are a frequent occurrence in stratocumulus topped flow downwind of mountainous islands theoretical studies dating back to von karman supported by laboratory and numerical studies have yielded similarity theories for the size and spacing of these vortices behind bluff bodies despite dynamical differences between such two dimensional flows and the three dimensional flow past isolated islands satellite case studies suggest these geometric similarities may also hold for the atmospheric case in this study two of the resulting dimensionless ratios are measured using satellite imagery one is the aspect ratio between cross street and along street spacing of the vortices the second is the ratio of the cross street spacing to the crosswind width of the island a 30 image sample from the aqua and terra moderate resolution imaging spectroradiometer satellites is analyzed to obtain these ratios the resulting set of values for the two dimensionless ratios is tested against the values f

three age groups of ornithopods inferred from footprints in the mid cretaceous dakota group eastern colorado north america abstract ornithopod population structure is inferred from a large sample of footprints from the mid cretaceous dakota group of colorado new mexico and oklahoma allometric analyses and size frequency distributions suggest size age classes or recruitments for tracks identified as caririchnium leonardii ornithopoda from sequence 3 of the mid cretaceous dakota group of the rocky mountain front range high plains region five hundred ninety eight footprints from 284 trackways were used in the statistical analysis tests were conducted that revealed no significant difference between analyses of right and left footprints or between casts and molds allometric analysis suggests a growth curve that can be subdivided into three segments corresponding to foot lengths of 16 5 21 7 21 7 29 3 and 29 3 55 0 cm respectively these are interpreted as juvenile possibly yearlings subadults and adults the former two categories may correspond to animal recruitments n n 1 whereas the latter category may represent several recruitments n 2 n 3 n 4 etc once ornithopod growth curves of the type proposed for maiasaura are established there is considerable potential for estimating dinosaur age from footprints in the meantime however large track samples can be analyzed for the size class information they contain

laboratory determined transport properties of berea sandstone we report laboratory measurements of electrical resistivity water permeability k and compressional wave velocity vp for both intact and fractured berea sandstone samples as functions of temperature from 20 c to 200 c and effective pressure pe from 2 5 mpa to 50 mpa for the intact sample vp increases from 3 52 km s to 4 16 km s as pe goes from 3 to 50 mpa with increasing temperature vp decreases at rates of about 3 percent per 100 c at pe of 5 mpa and about 1 5 percent per 100 c at pe of 38 mpa data from the fractured sample are qualitatively similar but velocities are about 10 percent lower for both intact and fractured samples increases less than 15 percent as pe increases from 2 5 mpa to 50 mpa although both samples show a larger decrease in resistivity with increasing temperature most of this change is attributed to the decrease in resistivity of the pore fluid over that temperature range for both samples k decreases with increasing pressure and temperature the intact sample permeabi

an unusual aerial photograph of an eddy circulation in marine stratocumulus clouds abstractan aerial photograph of a cyclonic von karman like vortex in the marine stratocumulus clouds off the california coast taken by a commercial pilot near grover beach is presented it is believed that this is the first photograph of such an eddy taken from an airplane to appear in publication the eddy occurred with a strong inversion above a shallow marine boundary layer in the lee of high inversion penetrating terrain tower and surface wind measurements plotted on satellite imagery demonstrate that the grover beach eddy was not just a cloud level feature but extended through the marine atmospheric boundary layer mabl to the surface evolution of the flow during the formation of the eddy appears similar to idealized numerical simulations of blocked mabl flow from the literature the tower measurements sampled the northern part of the eddy circulation during its formation just offshore the 2 3 c temperature increases and then decreases during and after the eddy passage may be indicative o

electric pore fabric of the nubia sandstones in south egypt characterization and modelling summary this study testifies the reliability of the electric pore fabric technique applied on the nubia sandstones in south egypt through a comparison with pre assigned magnetic pore fabric and permeabilityalreadymeasuredforthreeperpendiculardirectionsintheserocks discrepancies between the different techniques were attributed to the fact that the magnetic pore fabric technique has the ability to detect and define accurately the pore volume distribution in 3 d whereas the electric pore fabric technique has the ability to detect the shortest paths for the electric current fluid flow although the magnetic pore fabric is a bulk property the permeability measurements and the electric pore fabric are quantifying transport properties both the magnetic and electric pore fabrics refer mostly to slightly and moderately anisotropic fabrics the integration between both techniques revealed two main directions for fluid migration swinging to the n s and the e w directions one difficulty of the electric pore fabric technique is due to the surface conductivity effects either from the presence of some clay minerals or cracks therefore interpreting the obtained electric pore fabric must be carried out in care for the cracked and clayey rocks the surface conductivity effect could be accounted for by using the true formation factor for calculating the electric pore fabric parameters the electric pore fabric technique can be compared to the 3 d permeability measurements which show very similar directions

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