experimental studies of electrokinetic conversions in fluid saturated borehole models experimental and theoretical studies show that there are electromagnetic em fields generated by seismic waves with two kinds of conversion mechanisms in a fluid saturated porous medium within a homogeneous formation the seismic wave generates a seismoelectric field that exists only in the area disturbed by the seismic wave and whose apparent velocity is that of the seismic wave at an interface between differing formation properties the generated seismoelectric wave is a propagating em wave that can be detected everywhere an electrode used as a receiver on the ground surface can detect the propagating em wave generated at an interface but cannot detect the seismoelectric field generated in a homogeneous formation when the electrode is in a borehole and close to a porous formation it can detect both the em waves and the seismoelectric field in this paper electrokinetic measurements are performed with borehole models made of natural rocks or artificial materials experimental results show that

vertical seismoelectric profiling in a borehole penetrating glaciofluvial sediments 1 seismoelectric signals have been measured as a function of depth in a borehole penetrating glaciofluvial sands silts and glacial till using a broadband surface seismic source and a downhole electrode array transient electric field pulses with amplitudes of 1 to 4 v m accompanied the arrival of seismic p waves at the electrodes but no simultaneous interfacial signals were observed above the noise floor of approximately 0 2 v m the co seismic effect was strongest in a sand and gravel layer where its amplitude is consistent with the predictions of a simplified theoretical model normalization of the amplitude logs by measurements of seismic particle velocity and electrical conductivity enhanced their sensitivity to changes in lithology and porosity the results of this experiment suggest that co seismic seismoelectric effects show potential as a porosity permeability logging tool in the borehole environment

subtraction of powerline harmonics from geophysical records harmonic noise generated by power lines and electric railways has plagued geophysicists for decades the noise occurs as electric and magnetic fields at the fundamental frequency of power transmission typically 60 hz in north america and its harmonics it may be recorded directly during time domain measurements of electric and magnetic felds or indirectly by geophone cables during the acquisition of seismic data

active seismoelectric exploration of glaciers 1 repeatable and strong seismoelectric signals were recorded on glacier de tsanfleuron switzerland using a vertical sounding geometry electromagnetic waves are inferred to be generated by electrokinetic conversion of seismic energy within the snow pack and near the dry wet ice and ice bed interfaces a simple gradient based scheme allows such electrokinetic interface responses eirs to be isolated from noise eirs depend sensitively on the azimuthal orientation of the receiving array of electrical dipoles seismoelectric techniques promise to allow mapping even of thin water bearing strata within or beneath glaciers or frozen ground estimation of hydraulic or fluid properties of such strata as well as monitoring of ice fracturing or basal properties and processes at improved spatial resolution

electroseismic and seismoelectric measurements of rock samples in a water tank an electromagnetic em or seismic wave can induce seismic or em waves because of the electrokinetic conversion based on the electric double layer in a fluid saturated porous medium we tested a new method for observing electroseismic and seismoelectric conversions in rock samples our method is designed to overcome the shortcoming of previous attempts to separate signals generated by a continuous electric or seismic source in a small container we first observed acoustic fields around electrodes excited by an electric pulse in a water tank or in a water saturated porous sample in our approach we immersed rock samples in a water tank and measure the seismic or electric responses using electric or acoustic pulses conveyed through the immersed electrodes or hydrophone we measured electroseismic and seismoelectric frequency responses in berea sandstone and westerly granite samples at a frequency range of 15 150 khz the measurements clearly separate the effects of the electric source background noises

seismoelectric imaging of the vadose zone of a sand aquifer we have acquired a 300 m seismoelectric section over an unconfined aquifer to demonstrate the effectiveness of interfacial signals at imaging interfaces in shallow sedimentary environments the seismoelectric data were acquired by using a 40 kg accelerated weight drop source and a 24 channel seismoelectric recording system composed of grounded dipoles preamplifiers and seismographs in the shot records interfacial signals were remarkably clear they arrived simultaneously at offsets as far as 40 m from the seismic source the most prominent signal was generated at the water table at a depth of approximately 14 m and had peak amplitudes on the order of 1 v m a weaker response was generated at a shallower interface that is interpreted to be a water retentive layer the validity of these two laterally continuous events and of other discontinuous events indicative of vadose zone heterogeneity is corroborated by the presence of reflections exhibiting similar characteristics in a ground penetrating rada

wave propagation in heterogeneous porous media a velocity stress finite difference method a particle velocity stress finite difference method is developed for the simulation of wave propagation in 2 d heterogeneous poroelastic media instead of the prevailing second order differential equations we consider a first order hyperbolic system that is equivalent to biot s equations the vector of unknowns in this system consists of the solid and fluid particle velocity components the solid stress components and the fluid pressure a maccormack finite difference scheme that is fourth order accurate in space and second order accurate in time forms the basis of the numerical solutions for biot s hyperbolic system an original analytic solution for a p wave line source in a uniform poroelastic medium is derived for the purposes of source implementation and algorithm testing in simulations with a two layer model additional slow compressional incident transmitted and reflected phases are recorded when the damping coefficient is small this slow compressional wave is highly attenuated in porous media saturated by a viscous fluid from the simulation we also verified that the attenuation mechanism introduced in biot s theory is of secondary importance for fast compressional and rotational waves the existence of seismically observable differences caused by the presence of pores has been examined through synthetic experiments that indicate that amplitude variation with offset may be observed on receivers and could be diagnostic of the matrix and fluid parameters this method was applied in simulating seismic wave propagation over an expanded steam heated zone in cold lake alberta in an area of enhanced oil recovery eor processing the results indicate that a seismic surface survey can be used to monitor thermal fronts

artificial neural network forward modelling and inversion of electrokinetic logging data an artificial neural network method is proposed as a computationally economic alternative to numerical simulation by the biot theory for predicting borehole seismoelectric measurements given a set of formation properties borehole seismoelectric measurements are simulated using a finite element forward model which solves the biot equations together with an equation for the streaming potential the results show that the neural network method successfully predicts the streaming potentials at each detector even when the input pressures are contaminated with 10 gaussian noise a fast inversion methodology is subsequently developed in order to predict subsurface material properties such as porosity and permeability from streaming potential measurements the predicted permeability and porosity results indicate that the method predictions are more accurate for the permeability predictions with the inverted permeabilities being in excellent agreement with the actual permeabilities this approach was finally verified by using data from a field experiment the predicted permeability results seem to predict the basic trends in permeabilities from a packer test as expected from synthetic results the predicted porosity is less accurate investigations are also carried out to predict the zeta potential the predicted zeta potentials are in agreement with values obtained through experimental self potential measurements

borehole electrokinetic responses in fracture dominated hydraulically conductive zones electrokinetic borehole logging experiments conducted in fracture dominated devonian metasediments and carboniferous limestone boreholes containing dissolu tion discontinuities indicate a strong relative amplitude correlation between a downhole electrokinetic response and previously obtained hydrogeological data for the respective boreholes voltages in the range 0 2 1 5 volt were recorded per mpa of gauge pressure induced in the borehole fluid a relationship between fracture aperture and the frequency content of the electrical data has also been observed

numerical analysis of seismoelectric wave propagation in spatially confined geological units using numerical modelling we investigate the evolution of seismoelectric effects induced by seismic excitation in spatially confined lithological units typical geometries represent clay lenses embedded in an aquifer or petroleum deposits in a host rock in fluid saturated rocks seismic waves can generate electromagnetic fields due to electrokinetic coupling mechanisms associated with such processes in the vicinity of the fluid mineral interface two seismoelectric phenomena are investigated 1 the co seismic field associated with the seismic displacement at each point in a subsurface and 2 the interface response generated at layer boundaries our modelling uses a simplified time domain formulation of the coupled problem and an efficient 2d finite element implementation to gain insight into the morphogenetic field behaviour of the seismoelectric effects several numerical simulations for various target geometries were treated accordingly we varied both the thickness of the confined units and the value of the electrical bulk conductivity in porous media analysis of these effects shows differences between interface responses for electrically conductive versus resistive units so the pertinent contrast in electrical bulk conductivity controls the shape and structure of these seismoelectric conversion patterns moreover the seismoelectric interface response captures both the petrophysical and geometrical characteristics of the geological unit these models demonstrate the value of using seismoelectric interface response for reservoir characterization in either hydrogeological or hydrocarbon exploration studies

crosshole seismoelectric measurements in borehole models with fractures laboratory experiments are performed in crossborehole models with fractures to investigate seismoelectric conversions in the fractures using an electrode in a borehole we measure the electric field induced by an acoustic wave and we investigate the relationship between the electric signal and the fracture aperture using ultrasonic fracture borehole models the experimental results confirm that a radiating electromagnetic em wave is induced by a guide wave at a fracture between an acoustic source and electric receiver boreholes the position of a vertical or inclined fracture between two boreholes can be determined using the arrival times of the em wave and the formation velocity by placing the acoustic source at a different depth and recording electric signals with real or synthetic arrays of acoustic and electric receivers in the second borehole crosshole seismoelectric measurements might be a technique for investigating fractures between boreholes more directly than traditional acoustic measurements

constitutive equations for ionic transport in porous shales 1 the constitutive coupled equations describing ionic transport in a porous shale are obtained at the scale of a representative elementary volume by volume averaging the local nernst planck and stokes equations the final relationships check the onsager reciprocity to the first order of perturbation of the state variables with respect to the thermostatic state this state is characterized by a modified version of the donnan equilibrium model which accounts for the partition of the counterions between the stern and diffuse gouy chapman layers after upscaling the local equations the material properties entering the macroscopic constitutive equations are explicitly related to the porosity of the shale its cation exchange capacity and some textural properties such as the electrical cementation exponent entering archie s law this new model is then applied to predict the salt filtering and electrodiffusion efficiencies of a shale layer

anatomy of a seismoelectric conversion measurements and conceptual modeling in boreholes penetrating a sandy aquifer 1 conversions of compressional seismic waves to electric fields have been measured in two boreholes drilled in an unconfined sandy aquifer on the gnangara mound near perth australia the seismoelectric conversions at both field sites occurred in the vicinity of the water table at 13 m depth and yielded maximum amplitudes of 1 v m using a sledgehammer source on surface partially cemented layers inferred from geological and geophysical logs straddle the water table and may play a role in generating the conversion and influencing its amplitude distribution the dense vertical sampling used in these borehole experiments reveals spatial and temporal polarity reversals of the interfacial signal which provide new evidence in support of the conceptual model for seismoelectric conversions at interfaces we demonstrate that the growth rate of the source zone and its maximum vertical extent below the water table are encoded in the polarity of the interfacial signal these experiments confirm that vertical seismoelectric profiling can be used to gain further insight into seismoelectric conversions and characteristics of interfaces that makes them amenable to detection

characterization of transport properties of argillaceous sediments application to the callovo oxfordian argillite 1 we consider the case of a cylindrical cored specimen of a saturated argillaceous sediment located between two reservoirs filled with an electrolyte one of the boundaries of the sample is submitted to a sharp pressure or salinity change the migration of the resulting pressure or saline front through the core specimen is responsible for the apparition of an electrical field which is called the streaming potential the diffusion potential for a salinity gradient respectively the temporal variation of this electrical field is recorded with ag agcl nonpolarizable electrodes and used to monitor the evolution of the pressure or saline front between the two reservoirs there is a finite interval of time before which the steady state condition holds through the core in both cases the electrical potentials exhibit a relaxation with a relaxation time constant depending on the square of the length of the cylindrical core specimen and on its hydraulic or ionic diffusivity the experiments described here provide new methodologies to determine the hydraulic and ionic diffusivities of clay rich materials these experiments confirm also the predictions of a transport model developed recently for such materials and illustrate a powerful geophysical method to obtain transport properties not only in the laboratory but also in the field using a network of nonpolarizable electrodes to remotely monitor dissipation processes occurring inside the investigated system

stochastic inversion of permeability and dispersivities from time lapse self potential measurements a controlled sandbox study 1 we test the ability of the self potential method to provide information that can be used to invert the permeability and the dispersivities of a porous material we first formulate the semi coupled system of equations describing the occurrence of self potential signals associated with the transport of salt in a porous material like sand two contributions in the source current density arise from the electrokinetic coupling associated with the flow of the pore water and the diffusion potential due to the gradient in the activity of the salt a controlled laboratory sandbox experiment is performed to show that time lapse self potential measurements can be used to invert in a bayesian framework the permeability and dispersivities

late pleistocene glaciation of the kleiner arbersee area in the bavarian forest south germany abstract during pleistocene mountain glaciation of the bavarian forest south germany the wurmian kleiner arbersee glacier left behind glacial landforms and sediments which are described classified and interpreted using a combination of geomorphological sedimentological pedological surveying and absolute dating methods the latest kleiner arbersee glacier with a maximum length of 2600 m a minimum width of 800 m and a thickness of 115 m formed an elongated cirque four lateral moraines one divided end moraine one recessional moraine a proglacial lake and a basin in which lake kleiner arbersee was established after deglaciation beyond the glacial limit the landscape is denuded by periglacial slope deposits which are differentiated from the glacigenic sediments based upon clast fabrics clast shapes and sediment consolidation within the glacial limit sandy gravelly to silty gravelly tills are widely distributed whereas glaciolacustrine sediments are restricted to a small area north of the lake small variations in the sand and silt fraction of the tills are explained by melt out processes quartz mica and chlorite derived from gneiss bedrock are dominant in the clay mineral spectrum of tills but also gibbsite as a product of pre pleistocene weathering is present giving evidence of glacially entrained saprolites an irsl date of glaciolacustrine sediments 32 4 9 4 ka bp confirms the wurmian age for the glaciation and radiocarbon ages of the basal sediments 12 3 0 4 and 12 5 0 2 ka bp uncalibrated in the lake kleiner arbersee prove that the basin was ice free before the younger dryas

using borehole electroseismic measurements to detect and characterize fractured permeable zones in 1996 we measured stoneley wave induced electrical fields in an uncased water well drilled in fractured granite and diorite near hamilton massachusetts stoneley waves generated by sledgehammer blows to the surface casing produced a flow of pore fluid in permeable zones intersected by the borehole in turn this flow induced a streaming electrical field even though these electrical signals were very small tens of microvolts we were able to detect them using electrodes placed in the borehole after power line and telluric signals were canceled by remote referencing and notch filtering amplitude analysis of the electrical fields confirmed that they were induced by fluid flow in the fractured formation the normalized amplitudes of these electrical fields correlate with the fracture density log and agree with the theoretical model for this electroseismic phenomenon our biot theory based model predicts that borehole electroseismic measurements can be used to characterize permeable zones according t

three dimensional inversion of self potential data used to constrain the pattern of groundwater flow in geothermal fields 1 we propose an algorithm to invert self potential signals measured at the ground surface of the earth to localize hydromechanical disturbances or to the pattern of groundwater flow in geothermal systems the self potential signals result from the divergence of the streaming current density groundwater flow can be either driven by topography of the water table free convection or deformation of the medium the algorithm includes the electrical resistivity distribution of the medium obtained independently by dc resistance tomography or electromagnetic methods or by coding the assumed geology in terms of distribution of the electrical resistivity accounting for the effect of the temperature and salinity distributions and possibly constraints from borehole measurements inversion of the distribution of the source current density from ground surface and borehole self potential measurements is achieved by solving the inverse problem using tikhonov regularization solutions that are compatible with the physics of the primary flow problem by introducing assumptions regarding the smoothness or the compactness of the source and the three dimensional distribution of the electrical resistivity of the system the inverse problem can be solved in obtaining the three dimensional distribution of the current source density in the ground however an annihilator can be added to the inverted source geometry without affecting the measured self potential field annihilators can be obtained from boundary conditions synthetic models and a sandbox experiment are discussed to demonstrate the validity of the algorithm an application is presented to the geothermal field of cerro prieto baja california mexico using literature data inversion of the self potential and resistivity data allows observing a plume of hot groundwater rising to the ground surface in the central part of the investigated area and discharging to the ground surface in the southwest part the temperature anomaly associated with the existence of this plume is independently observed by interpolating borehole temperature measurements we found a good agreement between the distribution of the temperature and the inverted source current density the proposed method appears therefore as a noninvasive method for remote detection and three dimensional mapping of subsurface groundwater flow

field trials of a seismoelectric method for detecting massive sulfides an underground test of a seismoelectric prospecting method for massive sulfides was performed at the mobrun mine rouyn noranda quebec in june 1991 the method is based upon the conversion of seismic energy to high frequency pulses of electromagnetic radiation by sulfide minerals the delay between shot detonation and detection of the electromagnetic radiation gives a one way traveltime for the acoustic wave to reach the zone of seismoelectric conversion which when combined with p wave velocity allows the shot to ore zone distance to be calculated a 0 22 kg explosive charge located within 50 m of the orebody provided the seismic excitation and the resulting electromagnetic emissions were received by electric dipole and induction coil antennas first arrival information from a 35 shot survey above an orebody the 1100 lens provides firm evidence that short duration pulses of electromagnetic radiation are produced by the passage of acoustic waves through the orebody the survey also demonstrated that