a volumetric approach for the resistivity response of freshwater shaly sandstones the dc electrical response of freshwater saturated shaly sandstone is analyzed on the basis of effective volume conductivity concepts for a concentrated mixture of solid grains in a continuous electrolyte the bulk conductivity of this model is physically controlled by 1 the effective porosity and the average electrical tortuosity of its free pore electrolyte and 2 the amount and concentration of bound water that coats charged solid surfaces mainly of clays and a corresponding averaged electrical surface tortuosity the latter is combined in an equivalent volume conductivity that is mainly due to the electrical double layers of charges developed at the clay electrolyte interfaces analytical expressions based on effective medium and general mixture theories are developed to describe both the whole rock conductivity and the specific conductivities of its constituent elements the derived equations for the bulk conductivity of the system describe with sufficient precision experimental core dat

a simple effective medium model for water saturation in porous rocks a general equation for water saturation is derived from effective medium theory a simpler low frequency equation is also derived both equations are directly solvable for water saturation the model should be applicable to any granular water wet formation additional relationships are derived specifically for application to shaly sandstones but the model should be applicable to a wide range of rock types water conductivities and tool frequencies in the derivation hydrocarbons are included in the matrix component of the equation and the combined matrix elements are treated as resistors in parallel the low frequency equation is compared to various approaches to calculation of water saturation such as dual water waxman smits and bussian the general equation is compared to three component effective medium porosity index and complex refractive index models crim the model is proven to work on experimental data under a wide range of frequencies and water conductivities it is recommended that

a modified archie s law for two conducting phases abstract many types of mixing model are used widely within the earth sciences to determine the electrical properties of porous media consisting of solid and fluid phases of known conductivities volume fractions and distributions i e phase connectivities most models are valid for two or more conducting phases however of the simple models only archie s law includes a variable term the archie cementation exponent m that describes the connectivity of the phases unfortunately archie s law is only valid for one conducting phase distributed within a non conducting phase which makes it inapplicable in instances where the rock matrix has a significant conductivity such as for clay rich rocks and in calculations involving partial melting more complex models exist which account for multiple conducting phases and control over phase conductivity we have adapted the conventional archie s law to produce a simple modified archie s law that can be used with two conducting phases of any conductivity and any volume fraction while retaining the ability to model variable connectivities within those phases that result from variations in their distribution the modified model has two exponents m and p that describe the connectivity of each of the two phases the exponents are related through an equation that depends also on the volume fractions of the two phases the modified and the conventional versions of archie s law have been tested on a granular analogue porous medium with a conducting matrix and a pore space saturated with a range of saline fluids with different salinities and conductivities the new model describes the experimentally determined electrical behaviour of the system extremely well improving greatly on the conventional archie s law

the bedrock electrical conductivity structure of northern ireland an airborne geophysical survey of the whole of northern ireland has provided over 4 8 m estimates of the bedrock conductivity over the wide range of geological formations present this study investigates how such data can be used to provide additional knowledge in relation to existing digital geological map information a by product of the analysis is a simplification of the spatially aggregated information obtained in such surveys the methodology used is a gis based attribution of the conductivity estimates using a lithological classification of the bedrock formations a 1 250k geological classification of the data is performed leading to a 56 unit lithological and geostatistical analysis of the conductivity information the central moments medians of the classified data are used to provide a new digital bedrock conductivity map of northern ireland with values ranging from 0 32 to 41 36 ms m 1 this baseline map of conductivities displays a strong correspondence with an existing 4 quadrant chrono geological description of northern ireland once defined the baseline conductivity map allows departures from the norm to be assessed across each specific lithological unit bulk electrical conductivity is controlled by a number of petrophysical parameters and it is their variation that is assessed by the procedures employed the igneous rocks are found to display the largest variability in conductivity values and many of the statistical distributions are multi modal a sequence of low value modes in these data are associated with intrusives within volcanic complexes these and much older neoproterzoic rocks appear to represent very low porosity formations that may be the product of rapid cooling during emplacement by way of contrast extensive flood basalts the antrim lavas record a well defined and much higher median value 12 24 ms m 1 although they display complex spatial behaviour in detail sedimentary rocks appear to follow the broad behaviours anticipated by standard theoretical descriptions of rock electrical properties that allow for a term due to grain surface conduction e g the presence of clay single lithology sedimentary rocks are represented by an increasing set of conductivities through the sequence sandstone 4 91 ms m 1 limestone 8 41 ms m 1 and mudstone 17 85 ms m 1 with argillaceous rocks providing a conductivity of 41 1 ms m 1 in the case of both sandstone and limestone the single lithology conductivities are significantly less than their mixed lithology counterparts mudrocks display a bimodal statistical distribution and an extended analysis of these rocks is carried out across a carboniferous basin the results clearly indicate that non shale mudstones are distinctly less conductive than their shale counterparts shale formations display rapid and large movements in conductivity and it is suggested that the observed sensitivity may be due to competing surface conduction effects due to clay and organic material a study of the variation of conductivity with geological period is also performed both a decreasing trend with age and a modulation that peaks in the triassic period are observed

consistent joint elastic electrical differential effective medium modelling of compacting reservoir sandstones abstract improved reservoir characterization and monitoring can be achieved by combining seismic and controlled source electromagnetic techniques this requires developing coherent rock physics descriptions in this paper we demonstrate consistent joint elastic electrical modelling according to the differential effective medium theory we test our modelling against data from a compaction experiment on a set of 11 sandstone core samples from the same quarry location the presented approach is analogous to calibrating a rock physics model to a particular reservoir based on data from possible well logs and core samples for simplicity we choose to use multivariable non linear regression in the inversion it shows that this technique is able to identify solutions that are physically sound however a more rigorous inversion method might be considered in future implementations to identify the critical parameters we test the elastic electrical sensitivity of the various unknown variables involved the most sensitive parameters identified are then perturbed during the modelling the mineralogy consists mainly of quartz which we assume to be spherical and kaolinite we use the resistivity to calibrate the aspect ratio of the clay grains and estimate the porosity reduction due to compaction these values are in turn used in inverse modelling of the bulk and shear moduli the solid minerals make up the inclusion material in the differential effective medium modelling for both the elastic and electrical properties hence this formulation constitutes a consistent joint elastic electrical modelling scheme we achieve good fits between the model results and the laboratory measurements for most of the samples the reason for the less good fit with some of the samples might be due to measurement errors in the laboratory this is supported by the observed abnormal stiffness compaction trends associated with those samples

validation of temperature precipitation based aridity index paleoclimatic implications abstract water availability in the ecosystem is one of the most crucial environmental factors that determines global terrestrial biome distribution however aridity humidity conditions in the geologic past are difficult to quantify mainly owing to the lack of a proper parameter by using modern global climatic data we here examine five selected previously proposed aridity indices ais in which the climatic variables involved including both precipitation and temperature are simple and likely available in studies of paleoclimatology and paleoecology although with different degrees of uncertainty they were first evaluated along the modern climatic zones of eastern china with the main metric of thornthwaite humidity index hi and with the supplementary reference of soil moisture index smi and near ground atmospheric relative humidity rh then ais and the mean annual precipitation map were further statistically compared with hi smi and rh respectively based on 1189 monitored data sets from meteorological stations over the world the results show that the koppen aridity index aikoppen expressed as mean annual precipitation divided by mean annual temperature plus a constant of 33 is the most accurate and precise index among all selected indices supported by the highest correlation coefficient respectively to hi smi and rh three widely employed major indicators sensitive to hydrological dynamics in climatology and meteorology specifically aikoppen does well mirror corresponding hi along four representative transects from north america south america africa and australia which cover the typical arid and humid climates and span the main terrestrial biome types moreover our results also distinctly reveal that as also shown by many studies on modern climate precipitation alone is inadequate to measure the hydrological condition because both temperature and evapotranspiration are two other critical factors that strongly influence water balance in the ecosystem meanwhile evapotranspiration is mainly affected by temperature based on the validated aikoppen we briefly discuss the aridity humidity condition in china during the middle miocene the results demonstrate that moisture did decrease westward but it is also clear that western china in the middle miocene appears not to have been as dry as previously thought indicated by the aikoppen values representing a sub humid to humid climate

nature of surface electrical conductivity in natural sands sandstones and clays the electrical conductivity of rocks results from conduction through the bulk solution occupying the pores and from surface conduction occurring at the fluid grain interface the nature of the surface electrical conductivity of shaly and clean sands and sandstones is examined surface conduction is characterized by the specific surface conductance which is the sum of three contributions i conduction within the electrical diffuse layer which makes a negligible contribution to the total specific surface conductance ii conduction in the stern layer which is shown to vary significantly with the salinity of the pore fluid at low salinities 10 6 to 10 3 mol 1 1 but becomes independent of salinity at higher salinities iii a mechanism operating directly on the mineral surface independent of salinity and perhaps associated with proton transfer at salinities higher than 10 3 mol 1 1 and at 25 c the specific surface conductance of quartz and clays is equal to 8 9 10 9 s and 2 5 10 9 s respectively equations describing the influence of surface conductivity and microstructure upon the macroscopic electrical conductivity of sands sandstones and shales are also developed

pore scale modeling of electrical and fluid transport in berea sandstone the purpose of this paper is to test how well numerical calculations can predict transport properties of porous permeable rock given its 3d digital microtomography ct image for this study a berea 500 sandstone sample is used whose ct images have been obtained with resolution of 2 8 m porosity electrical conductivity permeability and surface area are calculated from the ct image and compared with laboratory measured values for transport properties electrical conductivity permeability a finite difference scheme is adopted the calculated and measured properties compare quite well electrical transport in berea 500 sandstone is complicated by the presence of surface conduction in the electric double layer at the grain electrolyte boundary a three phase conductivity model is proposed to compute surface conduction on the rock ct image effects of image resolution and computation sample size on the accuracy of numerical predictions are also investigated reducing resolution i e increasi

geoelectrical mapping for improved performance of suds in clay tills many cities of the northern hemisphere are covered by low permeable clay tills posing a challenge for stormwater infiltration practices however clay tills range amongst the most heterogeneous types of sediments and infiltration rates can vary by several orders of magnitude this study evaluates if a 2d geoelectrical system can reveal such heterogeneity at field scale and thus be used to optimize the hydraulic performance of stormwater runoff infiltration systems the assessment is based on a field study where data from non invasive geoelectrical data are compared with data from invasive geological methods including borehole soil sample descriptions one excavation description and a near surface spear auger mapping project the experiments returned a significant correlation of geoelectrical and spear auger mapped surface sediments furthermore a highly permeable oxidized fracture zone in greater depths could be revealed on the 2d geoelectrical profiles the successful determination of highly permeable zones harbors potential for improved hydraulic performance of infiltration suds sustainable urban drainage systems

coupled hydrogeophysical inversion to identify non gaussian hydraulic conductivity field by jointly assimilating geochemical and time lapse geophysical data abstract reliable inversion of spatial heterogeneity of hydraulic conductivity is crucial to understand subsurface fluids migration the ensemble smoother direct sampling method es ds has proven to be an effective method to identify non gaussian hydraulic conductivity distributions by incorporating a variety of traditional hydrodynamic measurements e g piezometric head however inversion problems for non gaussian parameters often suffer from a sparsity of the available data from direct sampling in boreholes as a non intrusive cost effective and high sampling density method time lapse geophysical technique has not yet drawn much attention as a useful source of information for delineating the underlying non gaussian heterogeneity in this study we integrated coupled hydrogeophysical modeling and the es ds algorithm to estimate non gaussian hydraulic conductivity field by assimilating both geochemical and time lapse geophysical datasets four synthetic cases for a salt injection experiment monitored by both sampling analysis and electrical resistivity tomography are conducted to assess the ability of the proposed approach to characterize hydraulic properties by assimilating different types of data results show that using geochemical or geophysical data alone only allow a rough reconstruction of subsurface heterogeneity of aquifers but might lose the fine structure by incorporating multi source datasets the main patterns of the non gaussian reference fields can be reflected with an improved resolution the time lapse geophysical methods open up new opportunities to accurately characterize non gaussian aquifers and monitor the dynamic processes of subsurface fluids

the cardston earthquake swarm and hydraulic fracturing of the exshaw formation alberta bakken play more than 60 small earthquakes m l 0 7 3 0 were detected from december 2011 to march 2012 north of cardston alberta an area with little evidence for previous seismic activity the timing of these events closely correlates 99 7 confidence with hydraulic fracturing completions of the devonian mississippian age exshaw formation at a nearby horizontal well unanimous waveform multiplicity within the swarm suggests that the events share a similar origin and source mechanism this observation is corroborated by the point like collocation of hypocenters within the crystalline basement during robust double difference relocations furthermore the presence of a pre existing fault is confirmed via formation top offset mapping and interpreted to be a late cretaceous extensional fault the confirmation of this fault at depth provides a plausible pathway for rapid hydraulic communication from the fracturing interval into the crystalline basement consistent with structural interpretations and available stress information moment tensor inversion of the largest magnitude event m w 3 0 indicates reactivation of a basement fault with normal slip we conclude that the genesis of this earthquake swarm was likely caused by increased pore pressure within the basement fault as a result of fracturing stimulation online material figure showing frequency magnitude distribution of earthquakes and table of the velocity models used in the study

estimation of hydraulic parameters of shaly sandstone aquifers from geoelectrical measurements electrical and hydraulic conductivities of shaly sandstones are described using a capillary approach for a granular clay bearing material the clays are assumed to occur as shale shells uniformly coating the insulated sand grains the real and imaginary components of the complex electrical conductivity for this material model are written in terms of a unique solid matrix conductivity treated as a volumetric property above a critical salt concentration the conductive contribution of the shells is independent of the electrolyte salinity under this condition the equation for the bulk conductivity of the sandstone can be expressed in a simplified form however below the critical concentration the matrix conductivity is dependent on the conductivity of the water saturating the shaly component and can be expressed only by the complete equation the hydraulic conductivity for this model is expressed by a modified kozeny carman equation a new semi empirical equation relates the hydraulic conductivity for such rocks to their porosity formation resistivity factor and the electrical conductivity of its solid matrix these combined properties are described as the lithoporosity factor in this new formulation the petrophysical parameters involved are easily determined from the electrical geophysical measurements the performance of this equation is firmly tested with experimental laboratory data available in the literature its application is then extended to estimate the hydraulic parameters of a shaly sandstone aquifer in bahia brazil using either the borehole or the surface geoelectrical data examples are given to emphasize the combined use of electrical resistivity and induced polarization measurements in computing hydraulic properties

water saturations in a wilcox shaly reservoir sandstone fordoche field point coupee parish louisiana abstract a new model has been derived for calculation of water saturation in shaly reservoir sandstones the model is based on effective medium theory emt and has been used successfully on a wide range of clayey low resistivity reservoirs a further independent test of saturations calculated by the model was made for a deep wilcox shaly reservoir at a depth of 13 176 ft 4016 m in fordoche field the reservoir w8 has a low average resistivity of about 2 5 ohm m and an estimated 18 clay as compared to an average resistivity of 1 5 ohm m in an underlying wet sandstone w 10 of similar clay content for the reservoir calculated water saturations are in the range of 35 to 50 increasing downward and suggest that the shaly sandstone should produce water free oil other shaly sand models generally give water saturations in excess of 50 for the reservoir water saturations calculated by the emt model agree well with other parameters for sandstones reported production core analysis and synthetic capillary pressures the reservoir w8 had an initial potential of 213 bbl of oil per day confirming water free oil production which could have been predicted by the emt model

estimation of aquifer hydraulic parameters from surficial geophysical methods a case study of keritis basin in chania crete greece summary knowledge of aquifer parameters is essential for the management of groundwater resources conventionally these parameters are estimated through pumping tests carried out on water wells few boreholes may be available and carrying out pumping tests at a number of sites may be costly and time consuming the application of geophysical methods in combination with pumping tests provides a cost effective and efficient alternative to estimate aquifer parameters a geophysical method is used to obtain aquifer characteristics that are estimated through the pumping tests a correlation is established between these parameters at other sites where pumping has not been carried out in this way the entire investigation area could be covered to characterize an aquifer system this study has been carried out in the keritis basin in chania crete greece where the aquifer characteristics are required for the management of groundwater in the region

geophysical evaluation of sandstone aquifers in the reconcavo tucano basin bahia brazil the upper clastic sediments in the reconcavo tucano basin comprise a multilayer aquifer system of jurassic age its groundwater is normally fresh down to depths of more than 1000 m locally however there are zones producing high salinity or sulfur geothermal waters in other areas the system is being exploited heavily to support a petrochemical center and related industries analysis of electrical logs of more than 150 wells enabled the identification of the most typical sedimentary structures and the gross geometries for the sandstone units in selected areas of the basin based on this information the thick sands are interpreted as coalescent point bars and the shales as flood plain deposits of a large fluvial environment the resistivity logs and core laboratory data are combined to develop empirical equations relating aquifer porosity and permeability to log derived parameters such as formation factor and cementation exponent temperature logs of 15 wells were useful to quantify the water leakage t

the occurrence of burretiodendron from the oligocene of south china and its geographic analysis the fossil records of burretiodendron rehder are reviewed based on diagnostic winged fruits from the oligocene ningming formation guangxi south china today this genus is endemic to southeast asia with six extant species that are well distributed in limestone mountain forests under a monsoonal climate the fossil records of this genus were represented only in yunnan of southwestern china the fossil fruits are assigned to a new species burretiodendron guangxiensis j l dong et b n sun sp nov are smaller than those of living species burretiodendron is a good indicator of paleoclimate and karstification due to its restricted distribution which is determined by specific temperature precipitation and the topographic condition we investigated the climate requirements of burretiodendron it is possible to accurately infer that the ningming paleoflora represented a warm and humid climate with seasonal precipitation during the oligocene edaphic preferences of the nearest living relative identified for the fossil species may point to the existence of a karstic system in the ningming region during the oligocene

a grain conductivity approach to shaly sandstones the effects of clay conduction on the electrical behavior of shaly sandstones at low frequencies are analyzed by considering self similar mixtures of conductive grains as representative of these porous rocks an essential step in this model is the representation of the surface conductivities of the clay platelets by an equivalent volume conductivity based on their pattern of occurrence the clays are treated either as a continuous coating over the sand grains or as individual detrital grains mixed with a nonconductive mineral matrix in the first case the solids are modeled as layered conductive particles taken as spheres to a first approximation in the second case we generalize from the results of a three component self similar mixture of spherical particles for linear approximations the models are described by expressions quite similar to the frequently used waxman smits and dual water equations but dependent upon the clay type concentration and its distribution in the rock the models are written in terms of geometric parameters readily available from well log measurements the derived analytical expressions are successfully applied to describe a set of available experimental core and geophysical log data the results clearly demonstrate the applicability of the equations to well log interpretation as a practical procedure for computing formation factors and shaliness of argillaceous sandstones

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

cenozoic climate change in eastern asia part i abstract this special issue provides new studies in the field of cenozoic climate change in eastern asia the papers in this volume are multidisciplinary in nature and examine a range of topics including paleovegetation sedimentology clay mineralogy geochemistry magnetostratigraphy and climate modelling the findings of these studies demonstrate that analysis of terrestrial paleoclimate changes in eastern asia may offer insights into the effects of tibetan plateau uplift and ultimately the dynamic processes of global change that took hold throughout the cenozoic the second part of this special issue to be published later will add a paleoecology component examining how cenozoic climate change has impacted floras and faunas in eastern asia

simultaneous core sample measurements of elastic properties and resistivity at reservoir conditions employing a modified triaxial cell a feasibility study adaptations of existing triaxial cells for ultrasonic p and s wave measurements are well documented this paper proposes further modification of such a cell so that also resistivity measurements can be carried out simultaneously at reservoir conditions by employing the top cap and the pedestal of the cell as electrodes axial resistivity measurements are now feasible in order to minimize the polarization effect of this two electrode arrangement careful analyses have been carried out to optimize the choice of electrode coating and measurement frequency band radial resistivity measurements are also included in the system by introducing a strap electrode system in a reservoir under production changes in both saturations temperature if steam injection and stresses can take place therefore the modified triaxial system should be able to measure the integrated effects on the acoustic parameters and electric responses caused by variations in each of these parameters the feasibility of the system to obtain such reliable information is demonstrated employing a small selection of core samples in the future such combined measurements on reservoir core samples can be used to link both seismic and electromagnetic observations to the actual earth model and constrain both modelling and inversion

determination of effective grain geometry for electrical modeling of sedimentary rocks accurate electrical modeling of sedimentary rocks is crucial for the interpretation of electrical survey data and must take into account the geometric information of the rock grains we have developed an incremental model for the multiphase electrical conductivity of sedimentary rocks on the theoretical basis of differential effective medium models the developed incremental model was first validated on clean and clay rich sandstones and then applied to simulate the conductivity offive digitally created rock samples with different spectra of grain aspect ratios the conductivity is calculated as a function of water conductivity at full water saturation and an effective grain aspect ratio for a two phase medium is determined to reproduce the electrical behavior of the digital rocks it was found that the effectivegrain aspect ratio can either be determined analytically or estimated from the aspect ratio spectrum a link between the obtained effective grain aspect ratio and the cementation coefficient widely used in petrophysics has been established the cementation coefficient increases with the decrease of the grain aspect ratio increasing the z axis depolarization factor and grain conductivity and the increase of sample porosity it showed that the cementation coefficient can be interpreted as a measure of the connectivity of pores as well as the conductivity of the grains our results gave us new insights into the physical meanings of the grain aspect ratio and cementation coefficient which could be used to facilitate the electrical modeling or interpretation of reservoir rocks

electrical properties of partially saturated sandstones novel computational approach with hydrogeophysical applications 1 electric and electromagnetic geophysical tools are suitable methods for investigating moisture content transport and storage properties of the subsoil with noninvasive surveys interpretation of field data is still based on empirical or semiempirical equations which must be calibrated with complex time consuming laboratory measurements in this paper we develop pore scale models suitable for computing the effective electric conductivity and the effective permittivity of partially saturated porous media on the basis of simple structural parameters grain size distribution and porosity we compute the electrical conductivity with three approaches that model the conductivity of the shell of coating clay around solid grains of shaly sandstones using different assumptions we compare the simulated results with experimental data from sherwood sandstone uk and discuss the effect of these assumptions on the effective conductivity simulations performed using a modeling approach that accounts for interaction between volume and surface conduction show an excellent agreement with experimental data we also model the effective permittivity of the same porous medium at several saturation values and obtain a good match with laboratory measurements

an effective medium algorithm for calculating water saturations at any salinity or frequency an algorithmic approach is used to mix the conductivities and geometric factors of the disperse components the rock and hydrocarbon particles with the host conductivity formation water the theoretical basis for the algorithm is the hanai bruggeman hb equation which itself incorporates only one disperse component the new approach the incremental model accommodates geometric factors such as sand and shale porosity exponents saturation exponent and also accommodates the associated grain conductivities its advantage over previous methods is that it works at any water salinity or tool frequency while allowing saturation and porosity exponents to have values other than 1 5 the algorithm is general and is written to accommodate simultaneous mixing of up to three disperse components and the formation water but it can be extended to accommodate any number of disperse components in its application to shaley sands hydrocarbon and sand elements are set to zero conductivity at low frequency but they can be nonzero for calculating saturations at higher frequencies the reason for this is that hydrocarbon and sand conductivities are real and very close to zero at low frequencies but at high frequencies the dielectric constants become significant making the complex conductivities nonzero the incremental model compared well with the waxman smits model on multiple water conductivity saturation data from two published experimental data sets the model is adaptable to other rock conductivity problems such as vuggy porosity vuggy water saturation and clay coated sand grains the potential exists for the algorithm to be part of a comprehensive computer program for calculating rock conductivities and saturations using many different combinations of rock fabrics and compositions

detection of subtle basement faults with gravity and magnetic data in the alberta basin canada editor s note this paper is based on a presentation at the 2003 canadian society of petroleum geologists canadian society of exploration geophysicists joint convention in calgary exploration for a wide range of mineral deposits is critically dependent on knowledge of the location and age of fractures and faults oil and gas fields in many sedimentary basins are distributed along fault controlled linear trends and fault identification is often used effectively for target area selection in hydrocarbon exploration similarly mineral deposits in various geologic settings are commonly associated with fluid conducting faults in the platformal phanerozoic alberta sedimentary basin in western canada figure 1 two fundamentally different types of crystalline basement structure formed in different tectonic conditions are recognized lyatsky et al 1999 figure 1 location of the northern alberta study area in relation to main regional geologic features 1 archean and early proterozoic hudsonian and older ductile orogenic structures and 2 middle proterozoic to recent cratonic ones the influence of ancient ductile structures on the alberta basin seems largely confined to the control on early paleozoic depositional and drape patterns by the precambrian erosional basement relief which may to some extent be related to the basement lithology distribution controlled by ductile ancient structures these structures were mostly healed and innactive during the phanerozoic development and evolution of the alberta basin and thus of limited significance to fluid migration their geophysical expression typically consists of large magnetic and gravity anomalies which often obscure the potential field signatures of the desirable brittle faults the steep brittle basement faults in the western canadian platforms and cordilleran foreland although much more subtle than their spectacular counterparts in western united states exerted considerable syn and postdepositional influence on the phanerozoic sedimentary cover occasionally brittle faults and fractures follow the older orogenic basement structures but commonly cut across them even when subresolution seismically many

reconstruction of atmospheric co2 during the oligocene based on leaf fossils from the ningming formation in guangxi china abstract recently several leaf fossils with good cuticles were discovered from the oligocene deposits in guangxi china the high fossilization potential of these leaves and easily identifiable stomata and epidermal cells make them an excellent source for co2 reconstruction in this study atmospheric co2 of the oligocene is reconstructed using the mechanistic theoretical model based on stomatal data photosynthesis and gas exchange control and using an alternative method based only on stomatal ratio fossil leaves of buxus ningmingensis chuniophoenix slenderifolius and cephalotaxus ningmingensis two angiosperms and one gymnosperm were considered it was found that some differences were present between the results obtained by the two methods the sr based method yields a somewhat narrower co2 range from 355 to 578 ppmv than the model approach from 255 to 972 ppmv which encloses the former range the co2 results derived from the three species using the two approaches are overlapped to a high degree with co2 data from other terrestrial plants and phytoplankton material more data provided by different proxies are desirable to unravel the interactions between atmospheric co2 and climate change for the oligocene

estimation of porosity and specific yield by application of geoelectrical method a case study in western iran summary vertical electric soundings vess with a schlumberger electrode configuration were recorded in the mahidashat plain kermanshah province located in the western part of iran in order to estimate the hydraulic parameters of the aquifer system the geological formations surrounding the plain are mainly cretaceous limestones and plagioclases with regular layering of miocene age the northwestern part of plain is composed of red marls of eocene age in order to ascertain the subsurface geological framework the general distribution of resistivity response of the geological formations was obtained geoelectrical sections along a number of lines have been prepared probable lithological patterns from these sections have been identified in the present study an attempt to estimate porosity and specific yield from resistivity data has been made for alluvial aquifers in mahidashat plain the results indicated that the porosity varies from 0 18 to 0 66 and the average specific yield is 0 15 the estimated data are compared with field real data and their credibility was calculated by using the paired t test method

gravity characterization of the la rioja valley basin argentina thelariojavalleyisasedimentarybasininthepampean ranges a region of basement uplifts and broad valleys in the andean foreland the present study advances understanding ofthegenesisofthebasinbyprovidingsubsurfacedataonits geometry and characteristics gravity and topographic data including a newly completed gravity survey were integrated tocreateacompletebougueranomalymap eulerandwerner deconvolution techniques sum with traditional potentialfieldsmethodsandsparseindependentdatafromseismicand magnetotelluric methods to test and constrain the subsurface geophysical characterization of the la rioja valley basin the residual anomaly obtained through upward continuation was inverted to obtain the best 3d gravity model of the la riojavalley basin which shows the first order geometry ofthebasin thisrevealsthatthebasinisasymmetric withup to 6000 m of low density basinfill in a depocenter located in thewest centralsectorofthevalley second orderfeaturesof thebasinincludeasoutheast trendingbasementhigh likelya fault zone that subdivides the basin which has been revealed by a suite of analytical methods 3d model of depth to basement a 2d inverse model and werner deconvolution solutions

evaluation of groundwater potential in kabirwala area pakistan a case study by using geophysical geochemical and pump data knowledge of hydraulic parameters hydraulic conductivity and transmissivity is essential for the delineation of groundwater potential zones conventionally these parameters are measured using pumping tests carried out on boreholes however pumping tests are costly labour intensive and require a considerable amount of equipment the integration of geophysical methods with pumping tests provides efficient and cost effective alternative to calculate hydraulic parameters fifty electrical resistivity soundings were carried out in the study area using schlumberger interelectrode configuration to obtain hydraulic characteristics that are estimated through the pumping tests to apply this approach successfully sufficient number of boreholes are used part of the boreholes in which pumping tests were carried out is used for both to constrain resistivity inversions and to establish the empirical relationship between the interpreted geophysical and hydraulic parameters the rest of the boreholes without pumping tests are still used for constraining the inversions initially aquifer parameters were measured using pumping tests at 12 water wells afterwards transmissivity t and hydraulic conductivity k were correlated with transverse resistance tr and the bulk resistivity o of the aquifer at other sites where pumping tests had not been conducted in this way the entire study area was covered to assess the groundwater reserves the hydraulic properties obtained by the geophysical method fit pretty well to both the pumping and physicochemical data of the investigated area the integrated study reveals five layers i e topsoil clay clay sand sand and gravel sand and three potential zones i e high medium and low potential aquifer zones with specific ranges of t k tr and o the results suggest that in case of sparse well data the aquifer parameters can be estimated using the relations depending on the specifications of the area

a simple way to model the pressure dependency of rock velocity abstract modeling the pressure dependency of rock velocity is important for interpreting and comparing the seismic and earthquake data from different depths this study develops a multicomponent differential effective medium model for the elastic properties of porous rocks with two types of pores in the grain background without mixing order the developed model is applied to modeling the pressure dependent elastic velocity of porous rocks by incorporating the variation of stiff and compliant porosity as a function of pressure the pressure dependent stiff and compliant porosity were inverted from the measured total porosity under pressure using a dual porosity model and the unknown constant stiff and compliant pore aspect ratios were inverted by best fitting the modeled velocity to the measured data application of the approach to a low porosity granite and a medium porosity sandstone sample showed that the pressure dependency of rock velocity can be satisfactorily modeled by the developed model using the pressure dependent stiff and compliant porosity and carefully estimated stiff and compliant pore aspect ratio values

contaminations at the derma of gaia a case study in environmental geology crucial problems of natural resource conservation in gaia are related to industrial agricultural and urban pollutions of its atmosphere water bodies and upper crust today one of the main human concerns is how to survive and to manage the environmental changes caused by widespread disasters related to improper disposal of large industrial and urban waste during the last decade we have developed hydro bio geological methods to quantitatively describe the soil and water contamination within a 4 0 km2 area including two landfill deposits and a tannery industry of alagoinhas city bahia state brazil geological reconnaissance works and a detailed geophysical survey consisting of 59 schlumberger resistivity and time domain induced polarization soundings were conducted around this urban industrial disposal area to detect and delineate the 3 d extent of an underground contamination plume these indirect results pointed out the presence of a strong electrical conductive anomaly within the aquifer resulting from invasive fluids from the landfills and from the surface disposal lagoons from the tannery complimentarily permanent multi electrode logging arrays were installed on three monitoring wells constructed with thin rings copper electrodes of 1 0 cm width externally mounted at 0 5 m distance interval on the entire length of the rigid pvc well casings and filter sections of such wells in each well the ring electrodes are accessed in different electrode combinations at the ground surface through electrical insulated multi cables repeated apparent resistivity and chargeability logs were obtained for these wells using normal electrode arrays such measurements were also used to characterize the plume extent and to estimate changes in water chemistry below the water table and throughout the upper vadose section of the marizal sao sebastiao aquifer system chemical analyses of water samples collected at available wells and along the neighboring sauipe river have shown drastic changes in the total dissolved solids major cations and anions contents total chromium and other heavy metals inorganic macro components biochemical oxygen demand chemical oxygen demand nutrients and bacterial content this work has conclusively shown that the subsurface is severely contaminated by liquids generated from these three surface sources in addition the monitoring technique using jointly electrical soundings and multi electrode wells is an efficient and low cost complement for an environmental evaluation of extensive aquifers

a new concept in modeling the dielectric response of sandstones defining a wetted rock and bulk water system experimental data for the real part of the dielectric constant k of three sandstone samples are considered as a function of the level of water saturation sw in the frequency range 60 khz to 4 mhz existing theoretical models have previously shown poor agreement with k versus sw data for rock samples undoubtedly due to the complexity involved in adequately accounting for geometrical and electrochemical effects in analyzing the data presented here we find a pronounced increase in k in the low saturation region which in all cases can be attributed to the establishment of geometrical and surface effects associated with the rock water interface when this increase in k is accounted for by defining wetted matrix parameters the data show excellent agreement with existing theoretical models

correlation of geoelectric data with aquifer parameters to delineate the groundwater potential of hard rock terrain in central uganda knowledge of aquifer parameters is essential for management of groundwater resources conventionally these parameters are estimated through pumping tests carried out on water wells this paper presents a study that was conducted in three villages tumba kabazi and ndaiga of nakasongola district central uganda to investigate the hydrogeological characteristics of the basement aquifers our objective was to correlate surface resistivity data with aquifer properties in order to reveal the groundwater potential in the district existing electrical resistivity and borehole data from 20 villages in nakasongola district were used to correlate the aquifer apparent resistivity e with its hydraulic conductivity ke and aquifer transverse resistance tr with its transmissivity te ke was found to be related to e by text log k text e 0 002 rho text e 2 692 similarly tr was found to be related to t by text tr 0 07t text e 2260 using these expressions aquifer parameters tc and kc were extrapolated from measurements obtained from surface resistivity surveys our results show very low resistivities for the presumed water bearing aquifer zones possibly because of deteriorating quality of the groundwater and their packing and grain size drilling at the preferred ves spots was conducted before the pumping tests to reveal the aquifer characteristics aquifer parameters to and ko as obtained from pumping tests gave values 29 424 7 m2 day 374 3 m day 9 801 1 m2 day 437 0 m day 31 852 4 m2 day 392 9 m day the estimated aquifer parameter tc and kc when extrapolated from surface geoelectrical data gave 7 142 9 m2 day 381 9 m day 28 200 0 m2 day 463 4 m day 19 428 6 m2 day 459 2 m day for tumba kabazi and ndaiga villages respectively interestingly the similarity between the kc and ko pairs was not significantly different we observed no significant relationships between the tc and to pairs the root mean square errors were estimated to be 18 159 m2 day and 41 4 m day

relating electrical conduction of alluvial sediments to textural properties and pore fluid conductivity electrical conductivity of alluvial sediments depends on litho textural properties fluid saturation and porewater conductivity therefore for hydrostratigraphic applications of direct current resistivity methods in porous sedimentary aquifers it can be useful to characterize the prevailing mechanisms of electrical conduction electrolytic or shale conduction according to the litho textural properties and to the porewater characteristics an experimental device and a measurement protocol were developed and applied to collect data on eight samples of alluvial sediments from the po plain northern italy characterized by different grain size distribution and fully saturated with porewater of variable conductivity the bulk electrical conductivities obtained with the laboratory tests were interpreted with a classical two component model which requires the identification of the intrinsic conductivity of clay particles and the effective porosity for each sample and with a three component model the latter is based on the two endmember mechanisms surface and electrolytic conduction but takes into account also the interaction between dissolved ions in the pores and the fluid grain interface the experimental data and their interpretation with the phenomenological models show that the volumetric ratio between coarse and fine grains is a simple but effective parameter to determine the electrical behaviour of clastic hydrofacies at the scale of the representative elementary volume

modelling production caused changes in conductivity for a siliciclastic reservoir a differential effective medium approach marine controlled source electromagnetic sounding is a rapidly growing exploration technique that complements the seismic method in case of pore fluid discrimination between water and oil further development of the method is foreseen to be within reservoir monitoring involving permanent instrumentation on both seafloor and within wells such advanced applications demand a good understanding and description of the electric earth model to ensure accurate modelling of possible earth responses as well as successful inversion of measurement data based on earlier works carried out within petrophysics and resistivity logging an extended effective medium scheme is derived that can be applied to model reservoir production effects this rock physics model has the potential of taking into account the effect of important parameters like grain shape distribution grain alignment shaliness salinity saturation temperature and stress based on a uniform formulation it has been calibrated by employing various core sample measurements the effective medium scheme can easily be interfaced with an existing standard electromagnetic modelling program and several such examples are presented

evidence of pore and fracture filling gas hydrates from geophysical logs in consolidated rocks of the muli area qinghai tibetan plateau permafrost china

conductivity models for archie rocks abstractthe petroleum industry s standard porosity resistivity model i e archie s law although it is fit for its purpose remains poorly understood after seven decades of use this results from the choice of the graphical display and trend formula used to analyze archie s seminal porosity resistivity data taken in the nacatoch sandstone a petroliferous clastic formation in the gulf of mexico coastal area archie s model accurately predicts the conductivity brine volume trend for this sandstone not all rocks follow the same porosity resistivity trends observed in the nacatoch sandstone but those that do are defined as archie rocks archie s nacatoch sandstone data set has significant irreducible scatter or noise data with significant scatter cannot be used to uniquely define a trend alternative graphical analyses of archie s nacatoch sandstone data indicates that archie could have analyzed these data differently had it occurred to him to do so a physics based porosity conductivity model a ge

faults and associated karst collapse suggest conduits for fluid flow that influence hydraulic fracturing induced seismicity during december 2011 a swarm of moderate magnitude earthquakes was induced by hydraulic fracturing hf near cardston alberta despite seismological associations linking these two processes the hydrological and tectonic mechanisms involved remain unclear in this study we interpret a 3d reflection seismic survey to delve into the geological factors related to these earthquakes first we document a basement rooted fault on which the earthquake rupture occurred that extends above the targeted reservoir second at the reservoir s stratigraphic level anomalous subcircular features are recognized along the fault and are interpreted as resulting from fault associated karst processes these observations have implications for hf induced seismicity as they suggest hydraulic communication over a large vertical distance reconciling the discrepancy between the culprit well trajectory and earthquake hypocenters we speculate on how these newly identified geological factors could drive the sporadic appearance of induced seismicity and thus be utilized to avoid earthquake hazards

electromagnetic properties of dry and water saturated basalt rock 1 110 ghz this paper reports on the measured electromagnetic properties of dry and water saturated basalt rock over a frequency range of 1 110 ghz tests were conducted in standard waveguides below 12 ghz and with free space systems above 12 ghz the basalt used in this investigation was found to be nonmagnetic measured relative permittivities for the dry basalt varied from approximately 8 19 0 71 at 1 12 ghz to 6 80 0 49 at 110 ghz the porosity of the basalt was determined to be roughly 10 properties of water saturated basalt were also measured at several frequencies and compared to theoretical predictions based on a simple maxwell garnett mixing theory finally the potential of using microwave tomography on basalt rock was examined based on the resulting properties

modelling the low frequency electrical properties of pyrite bearing reservoir sandstones abstract marine controlled source electromagnetic sounding has developed rapidly in recent years to complement conventional seismic method for better discrimination of pore fluid to obtain quantitative and reliable interpretation of the csem data a robust rock physics model is vital to link the bulk rock electrical conductivity to the electrical properties and microstructure of the rock constituents especially when some of the constituents exhibit extreme electrical behaviours e g pyrite a common mineral associated with reservoir rocks based on the multi phase incremental model validated on published experimentally measured electrical conductivity of pyrite bearing sandstones the effects of key parameters i e pyrite content porosity pyrite conductivity grain aspect ratio and water saturation on the electrical conductivity of pyrite bearing sandstones and their corresponding csem responses were comprehensively studied the results are expected to assist in the csem data interpretation when a pyrite bearing sandstone reservoir is encountered in the future

electrical properties of artificial clay bearing sandstone rocks which contain clay minerals often display electrical properties which cannot be predicted by bulk electrical properties of the constituents cohen 1981 interactions between clay minerals and groundwater can produce polarization phenomena decreases in resistivity and supposed nonlinear behavior