the influence of pore pressure and confining pressure on dynamic elastic properties of berea sandstone compressional and shear wave velocities of watersaturated berea sandstone have been measured as functions of confining and pore pressures to 2 kbar the velocities measured by the pulse transmission technique were obtained at selected pressures for the purpose of evaluating the relative importance of confining pressure and pore pressure on elastic wave velocities and derived dynamic elastic constants changes in berea sandstone velocities resulting from changes in confining pressure are not exactly canceled by equivalent changes in pore pressure for properties that involve significant bulk compression compressional wave velocities and bulk modulus an incremental change in pore pressure does not entirely cancel a similar change in confining pressure on the other hand it is shown that a pore pressure increment more than cancels an equivalent change in confining pressure for properties that depend significantly on rigidity shear wave velocity and poisson s ratio this behavior as well as observed

dynamics of carbon dioxide emission at mammoth mountain california mammoth mountain a dormant volcano in the eastern sierra nevada california has been passively degassing large quantities of cold magmatic co2 since 1990 following a 6 month long earthquake swarm associated with a shallow magmatic intrusion in 1989 a search for any link between gas discharge and volcanic hazard at this popular recreation area led us to initiate a detailed study of the degassing process in 1997 our continuous monitoring results elucidate some of the physical controls that influence dynamics in flank co2 degassing at this volcano high coherence between variations in co2 efflux and variations in atmospheric pressure and wind speed imply that meteorological parameters account for much if not all of the variability in co2 efflux rates our results help explain differences among previously published estimates of co2 efflux at mammoth mountain and indicate that the long term annual co2 degassing rate has in fact remained constant since 1997 discounting the possibility of large meteorologically driven temporal variations in gas efflux at other volcanoes may result in spurious interpretations of transients that do not reflect actual geologic processes

scale dependence of soil permeability to air measurement method and field investigation this work investigates the dependence of soil permeability to air on sampling scale in near surface unsaturated soils a new dual probe dynamic pressure technique was developed to measure permeability in situ over different length scales and different spatial orientations in the soil soils at three sites were studied using the new technique each soil was found to have higher horizontal than vertical permeability significant scale dependence of permeability was also observed at each site permeability increased by a factor of 20 as sampling scale increased from 0 1 to 2 m in a sand soil vegetated with dry grass and by a factor of 15 as sampling scale increased from 0 1 to 3 5 m in a sandy loam with mature coast live oak trees quercus agrifolia the results indicate that standard methods of permeability assessment can grossly underestimate advective transport of gas phase contaminants through soils

constraints on hydraulic parameters and implications for groundwater flux across the upland estuary interface abstract analyses of independent laboratory and field scale measurements from two sites on sapelo island georgia reveal heterogeneity in hydraulic parameters across the upland estuary interface regardless of the method used short duration pumping tests amplitude attenuation of tidal pumping data sediment grain size distributions and falling head permeameter tests we obtain hydraulic conductivity of 10 4 m s 1 for the fine grained well sorted clean sands that make up the upland areas proximal to the upland estuary boundary the tidal pumping analyses and permeameter tests suggest that hydraulic conductivities decrease by more than two orders of magnitude a result consistent with the presence of a clogging layer such a clogging layer may arise due to a variety of physical chemical or biological processes the extent and orientation of the layers of reduced hydraulic conductivity near the upland estuary boundary influence the nature of the aquifer s response to tidal forcing where the lower conductivity layer forms a relatively flat creek bank tidal pumping produces a primarily mechanical response in the adjacent aquifer where the creek bank is nearly vertical there is a more direct hydraulic connection between the tidal creek and the adjacent aquifer the clogging layer likely contributes to the development of complicated flow pathways across the upland estuary boundary effective flow paths calculated from tidal pumping data terminate within the marsh beyond the boundary of the upland aquifer suggesting a diffuse regime of groundwater discharge in the marsh we postulate that in many settings submarsh flow may be as important as seepage faces for groundwater discharge into the marsh estuary complex

mesoscale analysis of the activation of a cold front during cyclogenesis summary the archetypal mesoscale structure of an ana cold front comprises a narrow cold frontal rainband ncfr associated with line convection embedded within a wide cold frontal rainband wcfr due to the slantwise ascent associated with a strong transverse front mesoscale circulation whereas most mesoscale observational studies have concentrated on this mature stage the present paper explores by means of a detailed case study how such a mature frontal system develops from pre existing features the study is based upon the synthesis of data spanning many scales in the form of satellite imagery observations from conventional and multi parameter doppler radar and surface reports together with diagnostics from an operational mesoscale forecast model the cold frontal zone in this case is characterized by multiple cold fronts the dominant second cold front is studied in detail from the point of view of its evolution and its relationship to neighbouring fronts especially the leading front associated with the initial polar front cloud band the dominant cold front started as a shallow rope cloud in the cold sector and at a fairly early stage it produced a ncfr due to line convection then over a period of only a few hours a dry intrusion and an associated strong direct transverse front circulation led to the formation of a canopy of mid level cloud and a wcfr the wcfr was attributable not only to the rearward ascending outflow from the line convection but also to the re invigoration of ascent within the initial polar front cloud band that the line convection was undercutting although the transverse circulation was probably intensified by precipitation processes it is inferred that it was mainly a manifestation of the larger scale environmental flow that existed independently of the major precipitation features

retention of high permeability during shallow burial 300 to 500 m of carbonate grainstones abstract a progressive decrease in matrix permeability occurs with burial in the paleogene limestones of west central florida yet grainstones with permeabilities 400 md persist below burial depths of 300 m why some grainstones retain high permeability during passage through the shallow burial realm was investigated using 85 dominantly foraminifera and micritized grain grainstones from the eocene avon park formation twenty seven variables representing diagenesis stratigraphic packaging depositional energy grain types and pore network attributes were quantified permeabilities range from 23 to 7 160 md and thin section porosities range from 14 to 36 grain size lower coarse to upper fine sand covaries positively with sorting poor to very good the samples are from three different systems tracts within the avon park and sampled grainstone bodies ranged in thickness from 0 5 to 3 5 m evidence of diagenesis include mechanical and chemical burial compaction pre compaction cements and dissolution original interparticle porosity loss due to compaction copl and cementation cepl range from 0 to 35 3 and 1 6 to 26 2 respectively most original intraparticle porosity is occluded but most moldic porosity which ranges from 1 2 to 12 remains open multivariate regression reveals that 61 of the variance in permeability is attributed to grain size cepl copl and systems tract a proxy for relative abundance of compactable foraminifera versus robust micritized grains large grain size means a large initial permeability all other regression components reflect diagenetic reductions in permeability observed ranges in cepl and copl values mean they can reduce permeability by more than three orders of magnitude whereas the other regression parameters reduce it by only one order of magnitude retention of high 400 md permeability can occur by 1 cementation of 40 of the original interparticle pore space which inhibits subsequent compaction yet preserves high permeability or 2 a combination of cementation and compaction that destroys less than two thirds of the original interparticle pore space these relations derived from originally calcite rich sediments provide a quantitative reference by which to evaluate permeability preservation during shallow burial in numerical simulation of diagenesis and reservoir development capillary pressure data also support the hypothesis that pore geometries and hence permeability respond differently to compaction versus cementation cement dominated samples exhibit a dominance of porosity behind intermediate sized pores at higher permeabilities than compaction dominated samples compaction also does not yield a large change in the amount of porosity behind pore throats smaller than 1 at any permeability above 20 md whereas cementation dominated diagenesis generates significant amounts of pore space behind those small throats once permeability goes below 100 md these differences arise because cementation converts the original interparticle pores to a system of interparticle polyhedral and sheet like pores connected by progressively smaller pore throats between cement crystals whereas compaction merely constricts the original interparticle porosity behind smaller intergranular pore throats

predicting porosity from acoustic velocities in siliciclastics a new look two principally different mechanisms of porosity reduction induced elastic stiffening of siliciclastic rocks are recognized which in the domain of grain supported siliciclastics with less than 15 volume clay result in two linear trends with different slopes in the acoustic velocity porosity plane transition between the two mechanisms occurs at about 30 porosity and roughly coincides with the transition from 1 early diagenesis characterized by mechanical compaction and initial intergranular bonding to 2 advanced chemical diagenesis caused by pressure solution and cementation peculiarities of velocity stress relations in each of these diagenetic domains suggest that while the stress factor is important in loose sandstones it has practically very little effect on the frame moduli of consolidated less than about 30 porosity sandstones at stress magnitudes beyond the closure stress of microcracks introduced by natural or coring related processes appropriate grain contact and effective medium

land subsidence due to groundwater withdrawal potential damage of subsidence and sea level rise in southern new jersey usa land subsidence due to groundwater withdrawal combined with a global sea level rise creates a serious environmental problem in the coastal region groundwater withdrawal results in fluid pressure change in the layers the pressure change in the layers induces both elastic and inelastic land compaction the elastic compaction can be recovered if the water level rises again and inelastic compaction becomes permanent groundwater response to barometric pressure change is used to estimate the elastic compaction in this study the storativity specific storage and other layer and hydrological information are used to estimate the inelastic compaction of the layers due to fluid withdrawal the discussed methods are applied to estimate and predict the subsidence potentials resulting from overdrafting of the groundwater in the southern new jersey the estimated subsidence is about 2 3 cm near the location of monitoring wells in atlantic camden cumberland and cape may counties over the past 20 years if the current trend of water level drop continues the average subsidence in southern new jersey in the vicinity of some monitoring wells will be about 3 cm in the next 20 years the rise of global sea level is about 2 mm year on average because of the very gentle slope in southern nj the combination of subsidence and sea level rise will translate into a potentially substantial amount of land loss in the coastal region in each 20 year period this combination will also accelerate the coastal flooding frequency and the erosion rate of the new jersey coastal plain and pose a serious threat to the coastal economy

optically continuous silcrete quartz cements of the st peter sandstone high precision oxygen isotope analysis by ion microprobe a detailed oxygen isotope study of detrital quartz and authigenic quartz overgrowths from shallowly buried 1 km quartz arenites of the st peter sandstone in sw wisconsin constrains temperature and fluid sources during diagenesis quartz overgrowths are syntaxial optically continuous and show complex luminescent zonation by cathodoluminescence detrital quartz grains were separated from 53 rocks and analyzed for oxygen isotope ratio by laser fluorination resulting

short period strain 0 1 105 s near source strain field for an earthquake m l 3 2 near san juan bautista california measurements of dilational earth strain in the frequency band 25 10 5 hz have been made on a deep borehole strainmeter installed near the san andreas fault these data are used to determine seismic radiation fields during nuclear explosions teleseisms local earthquakes and ground noise during seismically quiet times strains of less than 10 10 on these instruments can be clearly resolved at short periods 10 s and are recorded with wide dynamic range digital recorders this permits measurement of the static and dynamic strain variations in the near field of local earthquakes noise spectra for earth strain referenced to 1 strain 2 hz show that strain resolution decreases at about 10 db per decade of frequency from 150 db at 10 4 hz to 223 db at 10 hz exact expressions are derived to relate the volumetric strain and displacement field for a homogeneous p wave in a general viscoelastic solid as observed on colocated dilatometers and seismometers a rare near field recording of strain and seismic velocity was obtained on may 26 1984 from an earthquake ml 3 2 at a hypocentral distance of 3 2 km near the san andreas fault at san juan bautista california while the data indicate no precursory strain release at the 5 10 11 strain level a coseismic strain release of 1 86 nanostrain was observed this change in strain is consistent with that calculated from a simple dislocation model of the event ground displacement spectra determined from the downhole strain data and instrument corrected surface seismic data suggest that source parameters estimated from surface recordings may be contaminated by amplification effects in near surface low velocity materials

convective mixing in a tropopause fold we present a case study of the passage of a tropopause fold over the uk behind a cold front with emphasis on the mixing caused by convection extending into the fold the event took place on 15 16 january 1999 and was the subject of intensive observations using the met office c130 aircraft and the mesosphere stratosphere troposphere mst radar at aberystwyth here we concentrate on radar and satellite observations during the afternoon of 16 january when the surface cold front had passed over the uk a tongue of moist air moved north eastwards over wales at 700 hpa at this time which because of the very dry air in the fold above resulted in potential instability the resulting convection was clearly observed in noaa satellite images the mst radar depicted the passage of the cold front and tropopause fold as a layer of high echo power and vertical wind shear ascending with time spectral widths showed the fold to be free of turbulence until 1200 utc on 16 january when convection was observed reaching into the frontal zone and generating turbulence eddy dissipation and diffusivity rates of 8 6 mw kg 1 and 8 5 m2s 1 respectively were derived for this event to place these figures in context they are compared with corresponding rates derived for sixteen other passages of tropopause folds over the radar each resulting from shear rather than convective instability the convective event is found to be comparable to the strongest shear events and to correspond to moderate turbulence as experienced by an aircraft this process is of potential importance for atmospheric chemistry because it mixes boundary layer air directly with stratospheric air over a timescale of 1 2 hours copyright 2004 royal meteorological society

spectrum response of lj well to various stresses during non seismic and seismic periods the well water level in a deep well has significant frequency dependence on various crustal stresses which can provide an effective pathway for determining the well aquifer properties and investigating the response mechanism of groundwater however due to the limitations and complexity of the field conditions there is a lack of on site stress strain data for rocks therefore it is difficult to directly and quantitatively interpret the transfer response between the strain stress and the well water level the observation item data for the lj well in china are relatively complete including rainfall barometric pressure volumetric strain and deep water level data by calculating the spectral period spectral density coherence function and transfer function of various physical variables the spectrum response characteristics of the well aquifer system to various stresses can be effectively obtained when the crust is in a relatively stable state the semidiurnal and diurnal waves are dominant moreover the transfer functions of the well water level s response to the theoretical semidiurnal and diurnal earth tides and the barometric pressure are basically consistent with the correlation analysis results in addition when earthquakes occur the signals of the volumetric strain and the well water level can more effectively highlight the relatively intermediate and high frequency information the transfer function between the well water level and the volumetric strain is nearly an order of magnitude smaller than that in the stable state indicating that the hydrogeological conditions of the lj well aquifer change instantaneously when subjected to seismic waves all the above conclusions show that the correlation and transfer function based on spectral analysis is a feasible and advantageous method of determining the correlation of various physical variables these results provide a foundation for further research on the hydrogeological characteristics of aquifers

estimates of velocity dispersion between seismic and ultrasonic frequencies it is generally accepted that acoustic velocities in fluid saturated rocks vary with frequency evidence comes from experimental measurements and from theoretical causality arguments we have developed a simple analysis technique that gives estimates of total velocity dispersion between zero frequency and any measurement frequency the technique requires compressional p and shear s wave velocity measurements on dry and fully saturated rock assuming that the dry velocities are independent of frequency the biot gassmann equations are used to calculate the zero frequency velocities in the fully saturated rock any difference between the measured velocities and the calculated zero frequency velocities is interpreted as evidence of dispersion application of this analysis technique to a variety c ultrasonic data sets gives consistent results in many rocks dispersion between zero frequency and ultrasonic frequencies is on the order of 10 percent at low effective stress and it decreases to only a few pe

sandstone reservoir quality prediction the state of the art joanna ajdukiewicz joined exxon production research company in 1980 she was reservoir quality assessment and prediction team lead there from 1991 to 1995 and at imperial oil research centre in calgary from 1995 to 1997 subsequently she has worked a variety of exploration company assignments in the north sea gulf of mexico and middle east her current interests are in predicting the distribution of early diagenetic controls on deep reservoir quality rob lander develops diagenetic models for geocosm llc he obtained his ph d in geology from the university of illinois in 1991 was a research geologist at exxon production research from 1991 to 1993 and worked for rogaland research and geologica as from 1993 to 2000 he is also a research fellow at the bureau of economic geology to guess is cheap to guess wrongly is expensive chinese proverb reservoir quality predictive models will be a useful element of risk analysis until remote sensing tools are invented that accurately measure effective porosity and permeability ahead of the bit this issue of the aapg bulletin highlights recent advances in a new generation of reservoir quality models that have successfully predicted porosity and permeability in diverse siliclastic reservoirs under many different burial conditions most previous attempts at predrill reservoir quality prediction have relied on empirical correlations or on first principle geochemical simulations that incorporate laboratory derived input parameters wood and byrnes 1994 the new reservoir quality models differ from previous approaches in that although incorporating theory inspired algorithms they include terms with values that are explicitly designed to be calibrated by and tested against data sets of high quality petrographic analyses that are linked to thermal and effective stress histories petrographic observations therefore provide essential constraints in these models on the types timing and rates of key geologic processes affecting sandstone pore systems this approach avoids the pitfalls inherent

aquifer heterogeneity characterization with oscillatory pumping sensitivity analysis and imaging potential 1 periodic pumping tests in which a fluid is extracted during half a period then reinjected have been used historically to estimate effective aquifer properties in this work we suggest a modified approach to periodic pumping test analysis in which one uses several periodic pumping signals of different frequencies as stimulation and responses are analyzed through inverse modeling using a steady periodic model formulation we refer to this strategy as multifrequency oscillatory hydraulic imaging oscillating pumping tests have several advantages that have been noted including no net water extraction during testing and robust signal measurement through signal processing through numerical experiments we demonstrate additional distinct advantages that multifrequency stimulations have including 1 drastically reduced computational cost through use of a steady periodic numerical model and 2 full utilization of the aquifer heterogeneity information provided by responses at different frequencies we first perform fully transient numerical modeling for heterogeneous aquifers and show that equivalent results are obtained using a faster steady periodic heterogeneous numerical model of the wave phasor the sensitivities of observed signal response to aquifer heterogeneities are derived using an adjoint state based approach which shows that different frequency stimulations provide complementary information finally we present an example 2 d application in which sinusoidal signals at multiple frequencies are used as a data source and are inverted to obtain estimates of aquifer heterogeneity these analyses show the different heterogeneity information that can be obtained from different stimulation frequencies and that data from several sinusoidal pumping tests can be rapidly inverted using the steady periodic framework

borehole water level response to barometric pressure as an indicator of aquifer vulnerability the response of borehole water levels to barometric pressure is a function of the confining layer and aquifer properties this study aims to use this response as an aid towards quantitative assessment of groundwater vulnerability applying the techniques to the confined semi confined part of the chalk aquifer in east yorkshire uk time series analysis techniques are applied to data collected from twelve monitoring boreholes to characterize and remove components contributing to the borehole water level signal other than barometric pressure such as recharge and earth tides barometric response functions are estimated using the cross spectral deconvolutionaveraging technique performed with up to five overlapping frequency bands a theoretical model was then fitted to the observed barometric response functions in order to obtain estimates of aquifer and confining layer properties derived ranges for pneumatic and hydraulic diffusivities of the confining layer vary over four orders of magnitudes 0 9 to 128 0 m2 day and 10 0 to 5 0 104 m2 day respectively indicating that the aquifer is nowhere purely confined discrepancies between estimates of aquifer transmissivity derived from the barometric response function and pumping tests have been explored using slug tests and results suggest that aquifer model transmissivity are highly sensitive to borehole construction a simple flow model constructed to test the potential impact of confining layer heterogeneity on the barometric response function shows that while high frequencies reflect the immediate vicinity of the borehole low frequencies detect confining layer properties up to some 500 meters distant from the borehole a characteristic time scale is introduced as a function of derived properties of the confining layer and is used as a quantitative measure of the degree of aquifer confinement it is concluded that barometric response functions are sensitive to confining layer properties and thus can provide a useful tool for the assessment of aquifer vulnerability

origin of quartz cements in some sandstones from the jurassic of the inner moray firth uk the extent of quartz cementation in shallow marine sandstones of the brora arenaceous formation oxfordian is closely related to the occurrence and abundance of rhaxella perforata sponge spicules three cement morphologies are identified chalcedonic quartz microquartz and mesoquartz chalcedonic quartz forms matrix supported cements which preserve moulds of rhaxella spicules chalcedonic quartz crystals have inequant development of crystal faces on average 0 1 m in diameter and are the first formed cement and reveal homogeneous dark grey tones on the sem cl bei microquartz forms 5 10 m diameter crystals which commonly grow on chalcedonic quartz substrates and show various grey tones under sem cl bei mesoquartz crystals grow in optical continuity with their host grains have 20 m a axial diameter crystals and exhibit distinctly zoned luminescence although no opaline silica is preserved the quartz cement is interpreted to have formed from an opaline precursor detrital quartz has an average 18o composition of 12 2 and mesoquartz syntaxial overgrowth has an average 18o composition of 20 0 estimates of the 18o compositions of microquartz and chalcedonic quartz are complicated by the problem of isolating the two textural types mixtures of the two give consistently higher 18o compositions than mesoquartz the higher estimate being 39 2 from oxygen isotope data the formation of quartz microquartz and chalcedonic quartz is interpreted to have taken place between 35 and 71 c in marine derived pore waters organic and inorganic maturation data constrain the upper temperature limit to less than 60 c

detecting the vulnerability of groundwater in semi confined aquifers using barometric response functions summary the use of barometric response functions brfs for detecting the presence of fully penetrating highly conductive bodies within aquifer confining layers that present potential pathways for contaminants is explored brfs are determined from borehole water level wl and barometric pressure bp records past studies have shown that confining layer properties can be estimated from brfs providing a potential link between brfs and the concept of groundwater vulnerability existing analytical models that predict the brf from system properties assume homogeneity within the aquifer and its confining layer conditions which are seldom satisfied in nature the impact of partially and fully penetrating high diffusivity heterogeneities within a confining layer representing potential high flow pathways for contaminants on the brf is investigated through a suite of three dimensional transient numerical simulations of the confining layer aquifer system the results are interpreted through comparison with a modified pre existing analytical model for the brf comparison of numerically and analytically calculated brfs reveals that the key effect of a localised fully penetrating high diffusivity heterogeneity within a low diffusivity confining layer is to reduce the brf gain with only minor changes to the phase this impact on the brf decreases with increasing distance from the heterogeneity the importance of heterogeneity size is secondary to distance from the borehole and partially penetrating heterogeneities affect the brf to only a minor extent data from a study of the chalk aquifer e yorkshire england which is semi confined by heterogeneous glacial sediments display variations in brfs which are qualitatively similar to those shown by the numerical results it is suggested that the variation in brfs estimated from borehole records across a semi confined aquifer could be used to assess the degree of spatial continuity of low diffusivity lithologies within the confining layer which protect the aquifer against surface sourced contamination and thus provide a tool to improve groundwater vulnerability assessment

earth tide analysis specifics in case of unstable aquifer regime we consider the main factors that affect underground water flow including aquifer supply collector state and distant earthquakes seismic waves passage in geodynamically stable conditions underground inflow change can significantly distort hydrogeological response to earth tides which leads to the incorrect estimation of phase shift between tidal harmonics of ground displacement and water level variations in a wellbore besides an original approach to phase shift estimation that allows us to get one value per day for the semidiurnal m2 wave we offer the empirical method of excluding periods of time that are strongly affected by high inflow in spite of rather strong ground motion during earthquake waves passage we did not observe corresponding phase shift change against the background on significant recurrent variations due to fluctuating inflow influence though inflow variations do not look like the only important parameter that must be taken into consideration while performing phase shift analysis permeability estimation is not adequate without correction based on background alternations of aquifer parameters due to natural and anthropogenic reasons

aquifer imaging with pressure waves evaluation of low impact characterization through sandbox experiments understanding the detailed spatial variation of hydraulic properties in the subsurface has been the subject of intensive research over the past three decades a recently developed approach to characterize subsurface properties is hydraulic tomography in which a series of pumping tests are jointly inverted using a heterogeneous numerical model recently cardiff et al 2013 proposed a modified tomography approach named oscillatory hydraulic tomography oht in which periodic pumping signals of different frequencies serve as the aquifer stimulation and pressure responses are recorded at observation locations for tomographic analysis its key advantages over traditional hydraulic tomography are that 1 there is no net injection or extraction of water and 2 the impulse an oscillatory signal of known frequency is easily extracted from noisy data however oht has only been evaluated through numerical experiments to date in this work we evaluate oht performance by attempting to image known heterogeneities in a synthetic aquifer an instrumented laboratory sandbox is filled with material of known hydraulic properties and we measure aquifer responses due to oscillatory pumping stimulations at periods of 2 5 10 and 20 s pressure oscillation time series are processed through fourier transforms and inverted tomographically to obtain estimates of aquifer heterogeneity using a fast steady periodic groundwater flow model we show that oht is able to provide robust estimates of aquifer hydraulic conductivity even in cases where relatively few pumping tests and observation locations are available the use of multiple stimulation frequencies is also shown to improve imaging results

determination of aquifer transmissivity from earth tide analysis the water level in an open well tapping an artesian aquifer responds to pressure head disturbance caused by earth tide dilatation of the aquifer because a finite amount of time is needed for water to flow into and out of the well there exists a phase shift or time lag between the tidal dilatation of the aquifer and the water level response in the well we derive an analytical solution that expresses the phase shift as a function of the aquifer transmissivity storage coefficient well radius and the period of the harmonic disturbance this solution is rather insensitive to the storage coefficient thus if the phase shift is known for a harmonic disturbance the transmissivity can be calculated given a rough estimate of the storage coefficient theoretical analysis shows that a significant phase shift may be present even if the disturbance is slowly varying as in the case of earth tides this opens the possibility of estimating aquifer transmissivity from water level records that show earth tide fluctuations a case study using data from a site near parkfield california is presented to illustrate application of the theory phase shifts of the o1 25 82 hour period and m2 12 42 hour period tidal constituents are chosen for analysis because they are free of systematic contamination by fluctuations in barometric pressure a brief error analysis suggests that the computed o1 phase shift is subject to large uncertainty while the computed m2 phase shift is substantially more accurate based on an assumed storage coefficient range of 10 4 to 10 6 the estimated transmissivity range is 8 10 6 to 2 10 5 m2 s while hydraulic tests have not been performed to validate these estimates the range is consistent with the transmissivity value determined by other investigators from analysis of the water level response to an earthquake

interpretation of earth tide response of three deep confined aquifers the response of a confined areally infinite aquifer to external loads imposed by earth tides is examined because the gravitational influence of celestial objects occurs over large areas of the earth the confined aquifer is assumed to respond in an undrained fashion since undrained response is controlled by water compressibility earth tide response can be directly used only to evaluate porous medium compressibility if porosity is known moreover since specific storage ss quantifies a drained behavior of the porous medium one cannot directly estimate ss from earth tide response except for the fact that barometric changes act both on the water surface in the well and on the aquifer as a whole while stress changes associated with earth tides act only in the aquifer the two phenomena influence the confined aquifer in much the same way in other words barometric response contains only as much information on the elastic properties of the aquifer as the earth tide response does factors such as well bore storage aquifer transmissivity and storage coefficient contribute to time lag and damping of the aquifer response as observed in the well analysis shows that the observation of fluid pressure changes alone without concurrent measurement of external stress changes is insufficient to interpret uniquely earth tide response in the present work change in external stress is estimated from dilatation by assuming a reasonable value for bulk modulus earth tide response of geothermal aquifers from marysville montana east mesa california and raft river valley idaho were analyzed and the ratio of ss to porosity was estimated comparison of these estimates with independent pumping tests shows reasonable agreement

determination of hydrogeological parameters using sinusoidal pressure tests a theoretical appraisal a method for determining the hydrogeologic parameters of formations of interest based on a sinusoidal pressure fluctuation in an excitation borehole is proposed equations are derived which describe the dependence of pressures and phase lags outside the excitation borehole on distance signal frequency specific storage hydraulic conductivity and flow rates these cover 2 distinct configurations that of a point source deep within a water saturated elastic formation and that of a line source totally penetrating a confined aquifer the ranges of application of these 2 arrangements are appraised using existing data on hydraulic diffusivities to derive likely excitation and response pressures for various flow rates and signal frequencies the 2 configurations require the accurate measurement of phase shifts in the case of the point source and of amplitude in the line source case and it is concluded that the ranges of applications are useful but limited 20 references

effects of diagenesis and clays on compressional velocities in rocks experimental results at ultrasonic frequencies in brine or water saturated samples cut perpendicular to bedding demonstrate that compressional velocities vary linearly with porosity and volume fraction clay in detrital silicate rocks characterized by pores with low aspect ratios p wave velocity is more sensitive to porosity than clay content obeying the empirically derived expression vp 2 4c 8 6 5 8 at 800 bars confining pressure and 400 bars pore pressure where the units of vp are kilometers per second is the volume fraction pores and c is the volume fraction clay deviations from this equation are less than 2 with the exception of the high pore aspect ratio st peter sandstone which has a compressional velocity that is 17 higher than the predicted value the equation is insensitive to the chemical compostion of the dominant clay mineral and apparently insensitive to the location of the clay grains with respect to the mineral framework e g in free pore space or in contact zones between mineral grains of lower compressibilities

diagnosing high porosity sandstones strength and permeability from porosity and velocity nonuniqueness in relating velocity to porosity in core and well log data complicates interpretation of sonic and seismic measurements one reason for this nonuniqueness in sandstones is clay e g han 1986 another reason is textural variability among samples dvorkin and nur 1996 examine two relatively clay free sandstone groups in the same porosity range but whose velocities significantly differed figure 1a by comparing the data with effective medium theories they interpret this velocity difference as resulting from the difference in the position of diagenetic cement the explanation is that in the fast oseberg rocks contact cement is located predominantly at the grain contacts whereas in the slow troll rocks noncontact cement is located predominantly away from these contacts

early quartz cements and evolution of paleohydraulic properties of basal sandstones in three paleoproterozoic continental basins evidence from in situ δ18o analysis of quartz cements quartz cement microstratigraphy and high precision in situ 18 o values obtained by secondary ion mass spectrometry sims from m size quartz cement zones have been used here to determine the timing of cementation and to evaluate precipitation mechanisms within the basal sandstones of three economically significant paleoproterozoic basins the athabasca and thelon basins canada and the mcarthur basin australia in these examples the earliest quartz cements have the highest 18 o values up to 33 mean 26 0 v smow indicative of low temperature precipitation at depths of 0 to 1 1 km some paragenetically early cement phases however have lighter isotopic values that suggest either precipitation from isotopically depleted water or precipitation at higher temperatures subsequent generations of quartz cements have progressively lower 18 o values mean 16 1 3 consistent with precipitation at higher temperatures these data combined with petrographic observations indicate quartz cementation began in near surface vadose and phreatic zones the next stage of cementation is characterized by syntaxial burial cement overgrowths regionally and stratigraphically well sorted sandstone facies that were initially aquifers preferentially experienced early quartz cementation which resulted in cement bridged pore throats at relatively shallow depths of 0 2 km and very early in their burial history transforming these units into diagenetic aquitards as a result these units did not experience mineralization compositionally and texturally immature braided fluvial facies did not experience early addition of quartz cement but are instead marked by minor syntaxial overgrowth cement that make upb5 of the intergranular volume formed at depths of 3 5 km and were variably replaced by illite and chlorite during burial these lithologies were still open to fluid movement at critical times in the basin when u and

structural characterization of an island aquifer via tidal methods 1 a set of water level time series collected along a transect through a sedimentary island aquifer was used to test the utility of various simple models of ocean tidal propagation in bounded one dimensional aquifers fourier spectra were calculated for the ocean tidal modes and compared with spectra measured in wells along the island transect other sources of fluctuation could be neglected an observed spatial bias in the well responses attenuations and lags could not be modeled by a homogeneous aquifer theory a theory involving composite heterogeneity accounted well for the spatial bias yielding estimates of aquifer transmissivities and storage coefficients indicating a fivefold difference in hydraulic diffusivity along the transect a lack of well locations toward one end of the transect reduced the statistical significance of this result with correlations between regression parameters evident at the same time a second bias was seen involving the ratio of signal amplitude and lag with penetration distance into the aquifer as observed in prior tidal studies a brief set of numerical experiments showed that horizontal layering in aquifer properties was the most probable cause of this propagation bias application of these results to the island data set supported a conceptual stratigraphic model of a highly conductive sloping stratum underlying a less conductive superficial sand layer this model is inconsistent with well logs along the island transect but is supported by additional off transect well logs it was concluded that one dimensional tidal propagation models may be useful in inverse characterization of aquifers with macroscale hydrogeological structures and that the analysis of measured propagation bias has the potential to yield extra information on aquifer properties in the vertical direction

the response of water level in a well to a time series of atmospheric loading under confined conditions the water level in a well that penetrates a confined aquifer can fluctuate in response to changes in atmospheric pressure the response varies with the well casing and screen dimensions the transmissivity and compressibility of the aquifer and to a small extent its storativity recently this loading response problem has been solved in terms of a frequency response function that characterizes how attenuation and phase shifts in the response signal vary with frequency the counterpart of this solution in the time domain is an impulse response function this solution has the immediate appeal that it can be used directly to filter raw loading and water level records via serial convolution where the response at any time is a weighted aggregate of the previous loading signal the impulse response function derives from well known solutions to the slug test problem when based on the cooper bredehoeft papadopulos solution the response function is precise but computationally intensive based on the hvorslev solution the response function is computationally simple but applicable only to aquifers with small storativity simulations and a field example clearly illustrate the dominating influence of transmissivity in dampening and lagging the response of a confined aquifer to a loading signal and how both effects increase with higher frequency the results also illustrate the weak influence of storativity in modulating the response signal

tectonic signatures in centimeter scale velocity porosity relationships of costa rica convergent margin sediments 1 the costa rica convergent margin investigated during ocean drilling program leg 170 offers a unique opportunity to compare the tectonic effects of rapid subduction on incoming oceanic sediments to their laterally equivalent underthrust counterparts and to terrestrially derived wedge materials elevated pressure laboratory measurements of ultrasonic compressional and shear wave velocity and porosity are used to examine the importance of tectonic lithologic and diagenetic controls on physical and elastic properties of sediments in these three key tectonic domains depositional and stress path histories of the three domains for example can be distinguished by 1 trends of in situ velocity porosity and derived measurements correspondence and 2 the mechanical response of representative materials to isotropic consolidation a compressional wave velocity porosity model critical for the application of seismic imaging to margin wide physical property and mass balance estimates is developed from the laboratory measurements and shown to be consistent with the information derived from lwd bulk density and migrated seismic reflection data this consistency of the velocity porosity model over the large range of both frequency and length measurement scales is a key result supporting the assertion that core and borehole physical property measurements can be extrapolated to larger domains finally dewatering and overpressure effects critical factors in subduction zone and fault process dynamics and increasingly common multiphase converted wave imaging targets are discussed in terms of laboratory estimated in situ compressional and shear wave velocity relationships

ocean tide induced head fluctuations in wells wells in coastal aquifers can attenuate and delay aquifer hydraulic head fluctuations induced by ocean tides to infer how the attenuation delay depend on system dimensions and hydraulic properties i solved a boundary value problem in which a well with storage fully penetrates a confined coastal aquifer the well induced attenuation and delay are 1 maximum at the well and decrease to zero at the aquifer s horizontal periphery 2 generally increasing functions of well radius distance from seaward boundary and tidal frequency 3 decreasing functions of transmissivity and 4 nearly independent of storativity for lesser radii and generally decreasing functions of storativity for greater radii approximations were developed for 1 a point in the aquifer valid when the distance from the point to the well greatly exceeds the well radius and 2 at the well valid when the distance from the well to the seaward boundary greatly exceeds the radius

estimating aquifer parameters from analysis of forced fluctuations in well level an example from the nubian formation near aswan egypt 2 poroelastic properties we discuss the in situ estimation of aquifer poroelastic properties from observed water level fluctuations in five wells sampling the 0 30 porosity nubian sandstone near aswan reservoir egypt the study area is close to ideal for the application of poroelastic theory because of the relatively simple stratigraphy and the absence of cultural and climatological noise in this paper we use approximately 2 years data sampled at 0 2 hour intervals to calculate frequency dependent admittances between the well levels and the recognized forcing functions of the earth tides and barometric fluctuations the effect of variations in lake level is treated in a companion paper the time series analysis techniques that we employ are described in detail three of the wells show equilibrium confined response at tidal frequencies which allows various in situ poroelastic parameters of the aquifer to be derived from the tidal and barometric admittance values we make extensions to earlier treatments of poroelastic theory in order to include the effect of horizontal strain resulting from barometric loading the modifications proved of minor importance for our data set because of the high compliance of the aquifer material and the shallow depth to basement in situ shear modulus is determined as 5 4 6 4 109 pa and uniaxial strain loading efficiency as 0 33 each of these parameters depends on the field measurements of well level and air pressure and also depends strongly on a theoretical estimate of the solid earth areal strain tides the principal source of error in lies in these areal strain estimates we measured poisson s ratio in the laboratory and found that it lies in the range 0 13 0 18 this together with the admittance values allows estimates of uniaxial strain modulus 13 19 109 pa with the smaller values at shallower depth specific storage 1 5 1 9 10 6 m 1 with the larger values at shallower depth porosity 0 2 0 3 skempton s constant 0 54 0 58 and biot s constant 0 78 0 85 laboratory measurements of uniaxial strain modulus are about 50 higher than the in situ estimates probably reflecting scale effects despite the high porosity use of a theory of aquifer response in which the solid constituent is considered incompressible produces significant errors in these estimates

differences between static and dynamic elastic moduli of a typical seismogenic rock summary static and dynamic elastic moduli of calcare massiccio mudstone limestone the typical seismogenic rock in the italian apennines are measured using a standard uniaxial static compression test a dual cantilever forced oscillation test and ultrasonic measurement of elastic wave velocities these measurements cover nine decades in frequency including the seismic domain neither a significant frequency dependence nor a pronounced strain amplitude dependence was observed providing a young s modulus of 75 7 gpa and a poisson s ratio of 0 28 0 02 these values are characteristic of calcare massiccio in undamaged condition

an analysis of earth tide induced groundwater flow in eastern botswana abstract earth tide induced groundwater level fluctuations with a maximum amplitude of 12 cm have been observed in a fractured shale aquifer in eastern botswana comparison of the oscillations with the tidal variations in the gravity field of the earth revealed a remarkable phase advance of the groundwater tides relative to the earth tides the phase shift ranges from 28 1 h for the semi diurnal frequency group to about 47 4 h for the diurnal group of the tidal spectrum a theoretical model is presented that attributes the marked amplitude to a high compressibility of the aquifer and explains the positive phase shift through a periodic groundwater flow between the shale basin and the surrounding aquifers the horizontal hydraulic gradient causing this groundwater movement is assumed to be induced by the tidal strain differentiation between the compressible shale and the more rigid arenitic and dolomitic adjoining rocks the magnitude of the generated groundwater flow is of the order of 14 m 3 h 1 at the outer fringe of the area involved the tidal dilatation in the centre of the shale basin is about 30 times the theoretical value for homogeneous conditions

general solution for tidal behavior in confined and semiconfined aquifers considering skin and wellbore storage effects tidal analysis provides a cost effective way of estimating aquifer properties tidal response models that link aquifer properties with tidal signal characteristics such as phase and amplitude hav

frequency characteristics of the response of water pressure in a closed well to volumetric strain in the high frequency domain 1 oscillations of water pressures and crustal strains due to the seismic waves of the 2010 chile earthquake were observed in japan the oscillations of water pressures observed over the frequency range of 0 002 to 0 1 hz were negative proportional to the oscillations of volumetric strains the responses of water pressures in closed wells are frequency dependent the expression for the response of water pressure in a closed well to crustal strain is developed based on the poroelastic theory the expression developed in the present paper describes the frequency characteristics of the responses the response is useful for the estimation of rock properties in addition the responses of water pressure due to tidal volumetric strain are estimated and compared with the responses due to the seismic waves

the mechanical behaviour of synthetic poorly consolidated granular rock under uniaxial compression abstract in order to isolate the effect of grain size and cementation on the mechanical behaviour of poorly consolidated granular rock we prepared synthetic rock samples in which these two parameters were varied independently various proportions of sand portland cement and water were mixed and cast in a mold the mixture was left pressure free during curing thus ensuring that the final material was poorly consolidated we used two natural well sorted sands with grain sizes of 0 22 and 0 8 mm the samples were mechanically tested in a uniaxial press static young s modulus was measured during the tests by performing small stress excursions at discrete intervals along the stress strain curves all the samples exhibited nonlinear elasticity i e young s modulus increased with stress as expected we found that the uniaxial compressive strength increased with increasing cement content furthermore we observed a transition from grain size sensitivity of strength at cement content less than 20 30 to grain size independence above this value the measured values of young s modulus are well explained by models based on rigid inclusions embedded in a soft matrix at high cement content and on cemented grain to grain contacts at low cement content both models predict grain size independence in well sorted cemented sands the observed grain size sensitivity at low cement content is probably due to microstructural differences between fine and coarse grained materials caused by small differences in grain sorting quality

measurements of dissipation rate in frontal zones summary this paper demonstrates that it is possible to use measurements of the doppler spectrum width from a highresolution radar to obtain quantitative estimates of dissipation rate during the passage of precipitating frontal zones using the high resolution chilbolton radar this method has been applied for the first time to infer the rate at which kinetic energy is dissipated by turbulence within mid and lower tropospheric frontal zones analysis of detailed measurements for one cold frontal region showed multiple shallow sheets of high dissipation rate with spatially averaged values around i x m2s 3 comparable values were also observed in a warm frontal zone the magnitude of the observed dissipation rate supports the hypothesis that mixing played a major role in determining the mean properties of the fronts in that the turbulence acted to destroy the frontal shear layer on a tirne scale of several hours these issues have particular relevance to the representation of fronts within future very high resolution numerical weather prediction models

critical porosity a key to relating physical properties to porosity in rocks discovering accurate relations between porosity and seismic wave velocities in porous rocks has been an important topic of rock physics for decades such relations if they actually exist are critical when seismic and or sonic data are to be used to infer porosity and porosity related properties e g permeability strength saturation in situ these inferences became especially important in recent years with the rapid development of seismic and sonic methods which are applied to the characterization of heterogeneous reservoirs and recovery monitoring

depth discrete specific storage in fractured sedimentary rock using steady state and transient single hole hydraulic tests abstract a method is presented for obtaining depth discrete values of specific storage ss from single hole hydraulic tests in fractured rock boreholes using straddle packers 1 5 17 m test intervals low flow constant head ch step tests analyzed using the thiem method provide transmissivity t values free from non darcian error short term constant rate pumping tests 0 5 2 h analyzed using the cooper jacob approximation of the theis method provide s from the hydraulic diffusivity using the darcian t value from the ch step test this synergistic use of two types of hydraulic tests avoids the common source of error when pumping tests injection or withdrawal are conducted at higher flow rates and thereby induce non darcian flow resulting in the underestimation of t other errors such as well bore storage and leakage can also substantially influence s by causing a shift in the time axis of the cooper jacob semi log plot in this approach the darcian t values from the ch step tests are used in the analysis of the transient pumping test data for calculating s throughout the pumping test using the cooper jacob approximation to minimize all of the aforementioned errors resulting in more representative s values the effect of these non idealities on the measured drawdown is illustrated using the theis equation with the darcian t and s values to calculate drawdown for comparison to measured data the ss values for tests in sandstone obtained from this approach are more consistent with confined aquifer conditions than values derived from the traditional cooper jacob method and are within the range of field and lab values presented from a compilation of literature values for fractured sandstone 10 7 10 5 m 1 this method for obtaining ss values from short interval straddle packer tests improves the estimation of both k and ss and provides opportunity to study their spatial distribution in fractured rock

radar observations of wind shear splitting within evolving atmospheric kelvin helmholtz billows summary the high resolution radar at chilbolton was used to measure the velocity structure of large amplitude kelvinhelmholtz billows within a precipitating warm frontal zone a deep layer of frontal shear was observed to split into thin layers of more concentrated shear displaying the characteristic braided structure previously reported within clear air radar reflectivity patterns and attributed to a splitting of the thermal stratification the billows were situated within a region of strong wind veer with height and they were orientated at right angles to the mean flow such that air parcels within them were tending to follow helical trajectories up the inclined frontal zone radar scans normal to the axes of the billows at different distances from their origin close to the position of the surface warm front provided an indication of the evolution of the split shear structure

application of multiple approaches to investigate hydraulic connection in multiple aquifers system in coalfield abstract understanding the hydraulic connections between overburden aquifers is key to safe coal mining however accurately identifying such connections remains challenging conventional investigation methods include geophysical investigation pumping test and hydrochemical analysis which are time consuming expensive and cannot determine continuous variations in hydraulic connection in this paper we performed time series analysis for analyzing water level time series data to identify the hydraulic connections between overburden aquifers in a coalfield the proposed method can identify such connections more clearly than hydrochemical methods it is especially useful in areas where an aquifer system is subject to strong perturbations

seven year history of vertical hydraulic diffusivity related to excavation around an underground facility abstract significant amounts of groundwater drain induced by the excavation of an underground facility will influence various site formation parameters such as permeability in this study a spectral analysis was applied to long term records of pore pressure responses to atmospheric loading in order to clarify the history of rock permeability changes at the horonobe underground research laboratory url in japan this study revealed that excavation of the url influenced nearby aquifers and reduced their vertical hydraulic diffusivity at a point approximately 130 m distant from the url it was found that hydraulic diffusivity has decreased by approximately 7 to 55 in the five years since the excavation started at a point approximately 860 m distant from the url the vertical hydraulic diffusivity was found to have decreased by approximately 26 even though pore pressure had not changed significantly this study confirmed that long term permeability changes could be monitored via pore and atmospheric pressure records more specifically during the development of a geological disposal system which can take several tens of years the vertical permeability of the site can be continuously monitored from the period before the start of the excavation through to the repository s post closure period

characteristics of tropopause folds over arctic latitudes 1 characteristics of tropopause folds over arctic latitudes have been studied using vhf radar measurements supplemented by balloon measurements the variation of the radar parameters during the passage of tropopause folds is discussed in detail to our knowledge these observations constitute the first spaced antenna sa radar measurements during the passage of tropopause folds this allows us to compare the parameters detectable using this mode with those observed using other configurations such as the doppler beam swinging dbs technique in general the structural characteristics such as the slope of folds seem to be similar at arctic latitudes to that at midlatitudes however the height of the tropopause and the axis of the jet stream and hence the folding are found to be lower by 1 2 km than their counterparts in midlatitudes in the case studies the radar derived parameters such as the signal to noise ratio snr and vertical shear of horizontal wind clearly show the upper air frontal zone the frontal circulation conceived from vertical velocity including the warm conveyer belt flow and the dry intrusion is clearly visible in the first case whereas it is masked by high amplitude mountain lee waves in the second case further the frontal zone seems to be acting as a critical layer to mountain lee wave activity by absorbing filtering the wave activity the aspect angles derived from the present analysis agree well with those estimated by vertical beam spectral width but are small in comparison with those estimated by the power ratio method the mean full correlation analysis fca turbulent velocity is estimated using the esrad data obtained during the passage of 15 tropopause folds the mean eddy diffusion coefficients kz near the tropopause and in the upper portion of the fold where strong turbulence is seen in case studies are found to be 3 54 and 6 4 m2 s 1 respectively utilizing the mean kz and the mean ozone gradient obtained from ozonesondes values the ozone fluxes across the tropopause and topside of the fold due to turbulence are estimated as 0 71 m s 1 ppbv and 0 32 m s 1 ppbv respectively although the flux across the tropopause is more than that occurring near the fold the exchange occurring through folds could be more significant to the tropospheric chemical budget

hydraulic and acoustic properties as a function of porosity in fontainebleau sandstone laboratory measurements have been made of the permeability k free porosity l compressional velocities vp or ve and compressional attenuations qp or qe in fontainebleau sandstone over a continuous range of porosities from 3 to 28 this large variation was achieved without any composition change fontainebleau sandstone is made of fine quartz grains with regular grain size 250 m permeability was measured with a falling head permeameter velocities and attenuations were obtained either through an ultrasonic experiment for frequencies around 500 khz or through a resonant bar technique experiment for frequencies around 5 khz and in both cases with varying water saturation the results show an excellent correlation between permeability k and total porosity for all our samples for low porosities 3 to 9 permeability in millidarcies is 2 75 10 5 7 33 while for high porosities 9 to 28 permeability k in millidarcies is given by 0 303 3 05 the correlation is also excellent between free porosity and total porosity on the other hand the correlation between acoustic properties and total porosity is not as clear as for hydraulic properties whatever the frequency 500 khz or 5 khz or the water saturation on the average velocity decreases and attenuation roughly increases with increasing total porosity velocity and attenuation values are related to the variation of grain contact structure and two samples with the same porosity and permeability may exhibit different velocities and attenuations the clear correlation between hydraulic properties and porosity is related to constant grain size while the lack of correlation for acoustic properties emphasizes the importance of the microstructure

effects of porosity and clay content on wave velocities in sandstones the ultrasonic compressional vp and shear vs velocities and first arrival peak amplitude ap were measured as functions of differential pressure to 50 mpa and to a state of saturation on 75 different sandstone samples with porosities ranging from 2 to 30 percent and volume clay content c ranging from 0 to 50 percent respectively both vp and vs were found to correlate linearly with porosity and clay content in shaly sandstones at confining pressure of 40 mpa and pore pressure of 1 0 mpa the best least squares fits to the velocity data are vp km s 5 59 6 93 2 18c and vs km s 3 52 4 91 1 89c deviations from these equations are less than 3 percent and 5 percent for vp and vs respectively the velocities of clean sandstones are significantly higher than those predicted by the above linear fits about 7 percent for vp and 11 percent for vs which indicates that a very small amount of clay 1 or a few percent of volume fraction significantly reduces the elastic moduli of sandstones for shaly

in situ stress dependence of wave velocities in reservoir and overburden rocks seismic waves propagate through a stressed earth sonic waves recorded by a borehole sonic logging tool propagate in the near well environment which is also stressed albeit under different stress conditions than the untouched formation far away cores excavated from within the earth undergo stress release and are then reloaded in the laboratory but hardly ever to the complete fully anisotropic in situ state of stress and pore pressure based on this we easily recognize that stress sensitivity affects our ability to compare and correlate geophysical and petrophysical measurements of wave velocities on the other hand it also provides an avenue to extract information about rock stresses as an example the presence of abnormally low velocities in seismic or log data is evidence of high pore pressure

frequency dependent hydraulic properties estimated from oscillatory pumping tests in an unconfined aquifer summary oscillatory pumping tests were conducted at the boise hydrogeophysical research site a periodic pressure signal is generated by pumping and injecting water into the aquifer consecutively and the pressure response is recorded at many points around the source we present and analyze the data from the field test after applying fourier analysis we then match the data with a recently derived analytical solution for homogeneous formations to estimate the equivalent aquifer properties conductivity k specific storage s s and specific yield s y the estimated values are shown to be in agreement with previous estimates conducted at this site we observe variations in the estimated parameters with different oscillation periods of pumping the trend of the parameters with changing period is discussed and compared to predictions by existing theory and laboratory experiments dealing with dynamic effective properties it is shown that the results are qualitatively consistent with recent works on effective properties of formations of spatially variable properties in oscillatory flow to grasp the impact of heterogeneity a simple configuration is proposed helping explain the observed increase in effective conductivity with decreasing period

estimating aquifer parameters from analysis of forced fluctuations in well level an example from the nubian formation near aswan egypt 3 diffusivity estimates for saturated and unsaturated zones atmospheric pressure variations provide a broadband signal that may force a sympathetic response in well water levels in this paper time series analysis techniques are used to estimate the response as a frequency dependent admittance function which is then modeled to provide estimates of the fluid transport properties of strata the data derive from five cased piezometer wells sampling aquifers in the nubian formation southwest of aswan egypt three shallow wells 100 140 m deep sample a water table aquifer a fourth w3 400 m deep samples a basal aquifer in the same area that behaves in a confined manner up to a period of several years the fifth well samples another basal aquifer and shows evidence of partial blockage nontidal water level variations in the shallow wells are due almost entirely to barometrically driven flow of air and water using a simple model to fit the observed barometric admittance spectra we obtain estimates of horizontal and vertical permeabilities for water in the saturated zone local horizontal permeability is constrained by modeling the effects of flow induced pressure gradients near the screen for the w3 deep well sampling the basal aquifer the resulting values 0 15 0 3 2 are marginally lower than the large scale 5 km estimates 0 32 0 43 2 derived in a previous paper however the values for the three wells sampling the water table aquifer although consistent among themselves 0 2 0 5 2 are significantly lower than the large scale estimate 1 0 1 5 2 this is contrary to what might be expected given that the wells are preferentially screened in clean sandstones vertical permeability estimated by modeling partial confinement effects is constrained for only one well a low value was obtained because of the presence of claystone beds in the diffusion path between screen and water table at this well the effects of air wave diffusion are clearly manifest in the spectra of one well where the water table lay at a depth of about 40 m the form of the spectra was well fit by ascribing a uniform pneumatic diffusivity of 1 75 10 m 3m2 s to the unsaturated zone however it was also necessary to include an apparent attenuation of the air wave at the capillary fringe of about 0 5 we propose that the effect is due not to attenuation but that it reflects compression of the phreatic surface arising from the presence of trapped air pockets in the underlying saturated zone a 40 m rise in the water table at the site during the decade prior to the measurements might explain the presence of significant quantities of trapped air this rise in water table together with the arid climate might be taken to suggest that the moisture content of the unsaturated zone is negligible except within a meter or so of the water table however calculation of the intrinsic rock permeability from pneumatic diffusivity assuming zero moisture content yields an estimate which is considered to be too low the likely explanation is that the assumption of zero moisture content is in error despite conditions which are as favorable as are ever likely to be realized under field conditions

oscillatory pumping wells in phreatic compressible and homogeneous aquifers oscillatory well pumping was proposed recently as a tool for hydraulic tomography periodic pumping at a few frequencies is carried out through vertical intervals along the pumping well and the periodic head is measured along a few piezometers the paper presents an analytical solution for the head field in an unconfined aquifer of finite depth under the common assumptions of a linearized water table condition different horizontal and vertical constant permeabilities constant specific storativity and water table drainable porosity and small well radius to length ratio the solution provides the expressions of the amplitude and phase of the head as a function of coordinates frequency and the problem parameters the solution simplifies to one pertaining to an upper constant head condition and a rigid aquifer for a wide range of the dimensionless frequency values

earth tide forcing of glacier drainage 1 fourier analysis reveals that winter electrical self potential sp water pressure pw and electrical conductivity ec time series collected beneath haut glacier d arolla switzerland are forced by earth and atmospheric tides forcing is dominant during periods of expanding bedrock consistent with glacier substrate deformation periodically driving water from the ice body into the bed this may modify the strength of subglacial sediments and could therefore influence glacier drainage and motion on a global scale

applicability of method to estimate transmissivity based on yield drawdown analysis in mountainous fractured rock aquifers a case study in taiwan abstract the observation of yield drawdown response in the course of pumping test as well as its derived application for aquifer characterization is an essential practice in a geotechnical investigation on the basis of that for providing a reasonable estimate of aquifer transmissivity on site a number of empirical models have therefore been proposed yet the majority of previous studies are conducted based on investigations at homogeneous alluvial plain very few particularly in the case of taiwan are carried out focusing on mountainous fractured rock aquifers aiming to address this problem the observation data of 53 pumping tests obtained from a multi years in situ geological investigation program are analyzed and the applicability of empirical log log linear relationship between t and q s is examined our analysis reveals that the yield drawdown responses derived from different geologic formations are quantitatively distinct and those empirical rules derived from the alluvial landform should be used with care when applying in mountainous fractured rock aquifers based on the analysis of statistical results in our study with a systematic investigation and clarification of the q s relationship in advance a satisfactory and cost effective solution is obtained

measuring well hydraulic connectivity in fractured bedrock using periodic slug tests summary periodic hydraulic experiments were conducted in a five spot well cluster completed in a single bedding plane fracture tests were performed by using a winch operated slug submerged solid cylinder to create a periodic head disturbance in one well and observing the phase shift and attenuation of the head response in the remaining wells transmissivity t and storativity s were inverted independently from head response inverted t decreased and s increased with oscillation period estimated s was more variable among well pairs than t suggesting s may be a better estimator of hydraulic connectivity among closely spaced wells these estimates highlighted a zone of poor hydraulic connection that was not identified by a constant rate test conducted in the same wells periodic slug tests appear to be a practical and effective technique for establishing local scale spatial variability in hydraulic parameters

a view toward the future of subsurface characterization cat scanning groundwater basins 1 in this opinion paper we contend that high resolution characterization monitoring and prediction are the key elements to advancing and reducing uncertainty in our understanding and prediction of subsurface processes at basin scales first we advocate that recently developed tomographic surveying is an effective and high resolution approach for characterizing the field scale subsurface fusion of different types of tomographic surveys further enhances the characterization a basin is an appropriate scale for many water resources management purposes we thereby propose the expansion of the tomographic surveying and data fusion concept to basin scale characterization in order to facilitate basin scale tomographic surveys different types of passive basin scale cat scan technologies are suggested that exploit recurrent natural stimuli e g lightning earthquakes storm events barometric variations river stage variations etc as sources of excitations along with implementation of sensor networks that provide long term and spatially distributed monitoring of excitation as well as response signals on the land surface and in the subsurface this vision for basin scale subsurface characterization faces many significant technological challenges and requires interdisciplinary collaborations e g surface and subsurface hydrology geophysics geology geochemistry information and sensor technology applied mathematics atmospheric science etc we nevertheless contend that this should be a future direction for subsurface science research

bedrock fracture parameters from the interpretation of well tides this paper presents a theory to account for the main features of the tidal response of an isolated plane fracture as revealed by the water level in an intersecting open borehole according to the theory the diurnal and semidiurnal tidal constituents both amplitude and phase of water level variations depend on the fracture aperture the orientation dip and strike and the radial extent of the fracture and the compressibility of the asperites the theory is applied to water level observations made in six open boreholes located in crystalline rock at a test site at the chalk river nuclear laboratories atomic energy of canada limited in chalk river ontario canada the boreholes were uncased and intersected many open fractures so that a definitive test of the theory could not be made however in four cases a fracture model could be found which fitted the observations within the experimental error

predicting lithology and transport properties from acoustic velocities based on petrophysical classification of siliciclastics based on the recently developed petrophysical classification of siliciclastics which takes into account the amount of the volumetric clay content c and textural position of clay it is shown that acoustic velocities can be fairly accurate tools in predicting lithology porosity and ultimately transport properties of these rocks four major petrophysical groups of carbonate and organic poor siliciclastics are distinguished 1 clean arenites c 35 percent the compressional velocity versus porosity relation for consolidated rocks in each of these groups is found to be linear with very high correlation coefficients this allows for remarkably accurate porosity estimates or lithology prediction in consolidated siliciclastics from acoustic velocities compared to the widely used time average wyllie equation or its improved modification raymer equations both of which neglect textural factors

silica diagenesis porosity evolution and mechanical behavior in siliceous mudstones mowry shale cretaceous rocky mountains u s a quartz in mudstones of the mowry shale cretaceous rocky mountain region takes several forms extrabasinal detrital silt some with transported overgrowths replacement of skeletal debris minor overgrowth on detrital quartz and replaced radiolaria pore filling in the intragranular pores of allochems and authigenic microquartz that is dispersed through the clay size matrix the matrix dispersed microquartz has cl character similar to the overgrowths with which it is intergrown supporting the interpretation that it is authigenic and pore filling radiolaria are widely observed in these mudrocks but are poorly preserved by partial mineral replacement quartz dolomite calcite pyrite we interpret dissolved radiolaria and possibly now cryptic diatoms as the likely source of silica for the overgrowths and microquartz through a reaction pathway that entailed the formation of opal ct lepispheres that subsequently recrystallized to microquartz a newly devised variation of the igv intergranular volume concept a parameter igvm is applied for partitioning the causes of porosity decline in mudstones all of the samples examined contain authigenic microquartz which averages around 40 of the rock volume the large volume of microquartz together with the volumes of surviving intergranular pores and pore filling solid hydrocarbon constrain the porosity to around 50 at the time of initial lepisphere formation despite the exceptional abundance of cement overall porosity decline is compaction dominated the presence of significant volumes of cement has implications for mechanical rock properties in the mowry shale which is expected to manifest brittle behavior where cements are most prominently developed

response of the water level in a well to earth tides and atmospheric loading under unconfined conditions the response of the water level in a well to earth tides and atmospheric loading under unconfined conditions can be explained if the water level is controlled by the aquifer response averaged over the saturated depth of the well because vertical averaging tends to diminish the influence of the water table the response is qualitatively similar to the response of a well under partially confined conditions when the influence of well bore storage can be ignored the response to earth tides is strongly governed by a dimensionless aquifer frequency q u the response to atmospheric loading is strongly governed by two dimensionless vertical fluid flow parameters a dimensionless unsaturated zone frequency r and a dimensionless aquifer frequency qu the differences between q u and qu are generally small for aquifers which are highly sensitive to earth tides when q u and qu are large the response of the well to earth tides and atmospheric loading approaches the static response of the aquifer under confined conditions at small values of q u and qu well response to earth tides and atmospheric loading is strongly influenced by water table drainage when r is large relative to qu the response to atmospheric loading is strongly influenced by attenuation and phase shift of the pneumatic pressure signal in the unsaturated zone the presence of partial penetration retards phase advance in well response to earth tides and atmospheric loading when the theoretical response of a phreatic well to earth tides and atmospheric loading is fit to the well response inferred from cross spectral estimation it is possible to obtain estimates of the pneumatic diffusivity of the unsaturated zone and the vertical hydraulic conductivity of the aquifer

determination of fluid flow properties from the response of water levels in wells to atmospheric loading the water level in a well that taps a partially confined aquifer is often sensitive to atmospheric loading the magnitude and character of this response is partly governed by the well radius the lateral hydraulic diffusivity of the aquifer the thickness and vertical pneumatic diffusivity of the unsaturated zone and the thickness and vertical hydraulic diffusivity of the saturated zone overlying the aquifer these key elements can be combined into five dimensionless parameters that partly govern the phase and attenuation of the response in many cases the response of a well to atmospheric loading can be broken up into a high intermediate and low frequency response the high frequency response is governed largely by the well radius and lateral diffusivity of the aquifer the intermediate frequency response is governed by the loading efficiency of the aquifer the low frequency response is governed by the vertical pneumatic diffusivity and thickness of the unsaturated zone and the vertical hydraulic diffusivity and thickness of the saturated material above the aquifer cross spectral estimation is used to fit the response to atmospheric loading of three water wells to the theoretical curves in order to yield estimates of three of the key dimensionless parameters these estimates then are used to make estimates or place bounds on the vertical pneumatic diffusivity of the unsaturated zone the lateral permeability of the aquifer and the composite vertical hydraulic diffusivity of the overlying saturated materials

hydraulic head in a clayey sand till over multiple timescales this paper presents an analysis of hydraulic head data measured every 2 h for 2 years in the leading edge of a drumlin that consists of weathered brown clayey sand till and underlying unweathered

dynamic and static moduli static and dynamic bulk moduli ks and kd are measured as continuous functions of pressure from zero to 2 3 kilobars for two sandstones a tuff limestone granite and oil shale results for the sandstones and granite are in good agreement with previously reported data with ks kd varying from about 0 5 at atmospheric pressure to close to unity at pressures 2 kilobars and above for rocks behaving elastically under static loading the ks kd ratio is inversely related to the microcrack density for the limestone time dependent deformation associated with pore collapse results in ks kd ratios approaching 0 1 at high pressure upon unloading while initially high 1 0 at high pressures ks kd becomes lower than values obtained during loading at low pressures 1 kilobar due to opening of microcracks generated during pore collapse for the oil shale in which few microcracks exist ks kd remains relatively constant with pressure at a value of about 0 7

some problems on detection of earthquake precursors by means of continuous monitoring of crustal strains and tilts previous work carried out in japan to search for earthquake precursors by means of continuous monitoring of crustal strains and tilts was reexamined we find no evidence of reliable precursors observed simultaneously with more than two instruments or at more than two observation sites there is a fair chance to detect earthquake precursors if strain meters and tiltmeters are distributed at many closely spaced sites in and around the source region but observations with strain meters and tiltmeters have not been executed at distances less than twice the source dimension we thus propose the following relation as a criterion of earthquake prediction at the present stage m 1 96 log r 3 84 where m is the magnitude of an earthquake and r kilometers corresponds to 2 times the radius of the source dimension precursory strain and tilt changes may be detected within the distance of r as revealed by data of geodetic surveys then we examined whether this criterion can be revised by employing reliable data obtained from laser strain meters installed in a deep tunnel at the amagase station kyoto japan during the period of 32 months from january 1 1987 to august 31 1989 there occurred three moderate earthquakes exceeding magnitude 4 within 30 km of the strain meter but we could not detect anomalous strain changes associated with earthquakes strain data obtained from laser strain meters at amagase do not correlate with surface meteorological changes such as atmospheric and temperature changes and rainfalls but are affected by the changes in the groundwater table around the observation tunnel a search of tidal strain data from the laser strain meters at amagase reveals no evidence of anomalous changes in tidal signals during the 32 months of observation the limit of detection for changes in the tidal strain amplitudes are 5 for the m2 constituent during the 32 month averaging period judging from these facts it would be difficult to detect earthquake precursors by employing strain meters and tiltmeters at distances of more than twice the earthquake source dimension in searching for precursory changes one must take into account the effect of groundwater flow even when strain meters and tiltmeters are installed in a deep tunnel to avoid the surface meteorological effects

an analysis of the roles of stress temperature and ph in chemical compaction of sandstones abstract chemical compaction also known as pressure solution involves dissolution along grain contacts and transport of solute to the adjacent pore space by diffusion the driving force for diffusion is a gradient in chemical potential therefore chemical compaction requires persistent gradients in chemical potential along grain contacts in order to drive diffusion continuously such gradients exist in porous rocks because of the heterogeneous distribution of stress over the grain surfaces the rate of chemical compaction depends on stress fluid pressure temperature and the composition of the pore fluid which itself depends on various processes that add or remove solute an alternative model of chemical compaction invokes the effect of sheet silicates on ph to account for localized dissolution of grains adjacent to stylolites or where sheet silicates are present along grain contacts in this model the rate of chemical compaction is independent of stress and fluid pressure depending only on temperature this model is untenable because the proposed mechanism cannot give rise to the persistent gradient in chemical potential required to drive diffusion however sheet silicates may increase the rate of chemical compaction because of their influence on dissolution and diffusion rates the development of anisotropic fabrics as a result of chemical compaction and the widespread occurrence of stylolites in carbonates as well as sandstones are inconsistent with the ph model and provide strong support for the role of stress in chemical compaction

laboratory measurements of porosity permeability resistivity and velocity on fontainebleau sandstones the relations among the resistivity elastic wave velocity porosity and permeability in fontainebleau sandstone samples from the ile de france region around paris france were experimentally revisited these samples followed a permeability porosity relation given by kozeny carman s equation for the resistivity measurements the samples were partially saturated with brine archie s equation was used to estimate resistivity at 100 water saturation assuming a saturation exponent n 2 using self consistent sc approximations modeling with grain aspect ratio 1 and pore aspect ratio between 0 02 and 0 10 the experimental data fall into this theoretical range the sc curve with the pore aspect ratio 0 05 appears to be close to the values measured in the entire porosity range the elastic wave velocity was measured on these dry samples for confining pressure between 0 and 40 mpa aloading and unloading cycle was used and did not produce any significant hysteresis in the velocity pressure behavior for the velocity data using the sc model with a grain aspect ratio 1 and pore aspect ratios 0 2 0 1 and 0 05 fit the data at 40 mpa pore aspect ratios ranging between 0 1 0 05 and 0 02 were a better fit for the data at 0 mpa both velocity and resistivity in clean sandstones can be modeled using the sc approximation in addition a linear fit was found between the p wave velocity and the decimal logarithm of the normalized resistivity with deviations that correlate with differences in permeability combining the stiff sand model and archie for cementation exponents between 1 6 and 2 1 resistivity was modeled as a function of p wave velocity for these clean sandstones

sandstone porosity loss a big picture view of the importance of compaction proper assessment of the relative importance of porosity loss by compaction and cementation is important to the prediction of porosity in sandstones studies of mass transport during diagenesis and the modeling of basin fluid flow quantitative estimation of the amounts of porosity loss by compaction and cementation can be made from standard point count data on cement and pore space abundance this method is discussed and its sources of error are evaluated error in the method arises mainly from uncertainty in initial sandstone porosities and the amount of local grain dissolution during burial data on the porosity of modern sands indicate that assumed initial porosities of 40 to 45 will produce small average errors in the calculation of compactional porosity loss for clean sandstones grain dissolution whether resulting in local porosity enhancement by export in solution of former grain mass or local precipitation of authigenic cement will cause an underestimation of the significance of compaction a large database of point count data from diverse sandstones is used to provide a broad perspective on the importance of compaction and cementation to sandstone porosity loss it is shown that the global importance of compactional porosity loss has generally been under appreciated in fact compaction mechanical and chemical is probably the dominant mechanism of porosity loss in most sandstones the extent of compactional porosity loss is related to sand grain composition and basin thermal structure

relationships among compressional wave attenuation porosity clay content and permeability in sandstones anelastic attenuation is the process by which rocks convert compressional waves into heat and thereby modify the amplitude and phase of the waves understanding the causes of compressional wave attenuation is important in the acquisition processing and interpretation of high resolution seismic data and in deducing the physical properties of rocks from seismic data we have measured the attenuation coefficients of compressional waves in 42 sandstones at a confining pressure of 40 mpa equivalent to a depth of burial of about 1 5 km in a frequency range from 0 5 to 1 5 mhz the compressional wave measurements were made using a pulse echo method in which the sample 5 cm diameter 1 8 cm to 3 5 cm long was sandwiched between perspex lucite buffer rods inside the high pressure rig the attenuation of the sample was estimated from the logarithmic spectral ratio of the signals corrected for beam spreading reflected from the top and base of the sample the results show that for these samples compressio

geotechnical properties of weak sandstones weak sandstones are here defined as having a saturated uniaxial compression strength of 0 5 20 mpa the mineralogy texture density porosity and saturated moisture content of these materials have

ultrasonic velocities in sands revisited ultrasonic compressional and shear wave velocities of isotropic sands are shown to be dependent on their mineralogy their porosity their fluid content and their state of consolidation under fixed temperature and pressure conditions this leads to a distinction between two broad classes of sands those that are well consolidated and those that are loosely consolidated changes in elastic velocities reflect changes in the ratio of bulk and shear moduli to density in response to lithologic variations we decouple the two effects by examining changes in elastic moduli with respect to changes in lithology and we observe three main points 1 for consolidated sandstones the effects of mineralogy and porosity can be approximated both empirically and theoretically by a modified isostrain theory the dry bulk and shear moduli of the rock aggregate follow a mixing law being linear combinations of the respective moduli of the individual constituents the dry elastic moduli of families of clean sands and s

using earth tide induced water pressure changes to measure in situ permeability a comparison with long term pumping tests good constraints on hydrogeological properties are an important first step in any quantitative model of groundwater flow field estimation of permeability is difficult as it varies over orders of magnitude in natural systems and is scale dependent here we directly compare permeabilities inferred from tidal responses with conventional large scale long term pumping tests at the same site tidally induced water pressure changes recorded in wells are used to infer permeability at ten locations in a densely fractured sandstone unit each location is either an open hole well or a port in a multilevel monitoring well tidal response is compared at each location to the results of two conventional long term and large scale pumping tests performed at the same site we obtained consistent values between the methods for a range of site specific permeabilities varying from 10 15 m2 to 10 13 m2 for both open wells with large open intervals and multilevel monitoring well we conclude that the tidal analysis is able to capture passive and accurate estimates of permeability

the effect of systematic diagenetic changes on the mechanical behavior of a quartz cemented sandstone abstracta key goal of petrophysical studies of sandstones is to relate common field measurements particularly seismic or sonic velocities to parameters defining the rock s mechanical and hydrologic characteristics these include elastic and inelastic mechanical properties porosity and permeability we explored relationships among these properties in variably quartz cemented mature arenites of the st peter sandstone with porosities ranging from 9 to 25 in a previous paper we described microstructural changes accompanying progressive quartz cementation and related porosity and permeability reduction in this sample suite here we report ultrasonic velocities ultrasonic velocities dynamic and static elastic properties confined compressive strength and tensile strength analyses of these data demonstrated that factors controlling permeability also fundamentally determined the elastic and inelastic mechanical properties we found that the number of grain contacts or bonds per number of grains vi

temporal changes of hydraulic properties of overburden aquifer induced by longwall mining in ningtiaota coalfield northwest china abstract characterizing the mining induced temporal changes of hydraulic properties of the overburden aquifer is significant for groundwater resource protection conventional hydrogeological methods e g hydraulic test physical model test and numerical simulation of determining hydraulic properties of the overburden aquifer cannot quantitatively analyze the temporal changes of the hydraulic properties induced by mining disturbances this paper demonstrates a quantitative determination for the temporal changes of parameters compressibility porosity and specific storage in the overburden aquifer influenced by the mining processes based on in situ continuous measurements of groundwater level that was affected by earth tide atmospheric loading and mining disturbances the results showed that when working face reached a certain distance 127 m from borehole j6 in this study those parameters compressibility porosity and specific storage of overburden aquifer began to show gradual decrease with approximately up to two order of magnitudes after the working face passed by the observation borehole j6 those properties of overburden aquifer recovered in about 80 days which might reflect the characteristic of elastic deformation of the aquifer those findings of the mining induced parameters temporal changes could improve our understanding of the mining effects on aquifer system and could be meaningful in groundwater resource protection

systematic diagenetic changes in the grain scale morphology and permeability of a quartz cemented quartz arenite the material properties of sedimentary rocks are controlled by a range of parameters including grain size sorting and modification of the original sediment through the diagenetic processes of compaction and cementation to isolate the effects of diagenesis and explore how they modify permeability we quantified changes in grain and pore morphology accompanying progressive diagenesis of a simple system a well sorted variably quartz cemented quartz arenite of relatively uniform grain size the most common type of authigenic cement in sandstones quartz overgrowths is responsible for significant porosity and permeability reduction the distribution of overgrowths is controlled by available pore space and the crystallographic orientations of individual quartz grains we show that progressive quartz cementation modifies the grain framework in consistent predictable ways detailed microstructural characterization and multiple regression analyses demonstrate that both the number and length of grain contacts increase as the number of pores increases and the number of large well connected pores decreases with progressive diagenesis the aforementioned changes progressively alter pore shape and reduce pore size variability and bulk permeability these systematic variations in the pore network correlate with changes in permeability such that we can use our data to calibrate the kozeny carmen relation demonstrating that it is possible to refine predictions of permeability based on knowledge of the sedimentary system

flow to a partially penetrating well with variable discharge in an anisotropic two layer aquifer system abstract a general analytical model for the problem of variable discharge of groundwater from a well in an anisotropic two layered aquifer system is developed by taking account of the interface flow between the two layers the well of infinitesimal radius partially penetrates the lower layer and is pumped at a variable discharge the horizontal as well as vertical flows in both layers are included and importantly the effects of constant head case 1 and no flux case 2 boundaries at the top of the upper layer are considered laplace domain solutions for drawdown in dimensionless form are derived with the help of hankel transform and are inverted to the time domain numerically the drawdown characteristics induced by an exponentially decayed rate of pumping are discussed and sensitivity analysis is also performed to explore the influence of different parameters on drawdown characteristics the results show that the drawdown around a partially penetrating well in the lower pumped layer induced by an exponential decreasing pumping rate usually contains three stages the effect of anisotropy and well configuration have great influences on the drawdown distribution near the pumping well and the horizontal flow and storativity of the upper unpumped layer cannot be ignored in determining the upper aquifer drawdown the sensitivity analysis also illustrates that the dimensionless drawdown in the lower pumped layer is very sensitive to well configuration parameters all the time it is only sensitive to the hydraulic parameters of the lower aquifer for case 1 and to the hydraulic parameters of the lower layer and the specific storage of the upper layer at late times the dimensionless drawdown of the upper layer is not sensitive to the variable well discharge parameters over the whole pumping period and is not sensitive to the storage parameters of both layers for case 1 however the drawdown in the upper layer is sensitive to all the hydraulic parameters and well configuration parameters for case 2 at late times

the estimation of fluid flow properties from the response of water levels in wells to the combined atmospheric and earth tide forces the water level in an open well tapping a confined formation is influenced by natural forces including the solid earth tide set and atmospheric pressure variation apv the spectral method is used to analytically derive a model for well response to both random and periodic components of the combined set and apv forcings csa an inverse theory and algorithm are developed in order to provide improved results when using the model to estimate the hydraulic parameters associated with a given formation an examination of the response surface of the estimation criterion reveals a uniqueness problem in estimating storativity s since there is little correlation between the transmissivity t and s estimators a good estimate for t is still possible independent of having accurate knowledge of s an estimate of t is possible only if the data contain sufficient information so that the analysis occurs within an identifiability window the csa estimation methodology is compared to individual set and apv schemes the csa scheme gives the greatest probability that sufficient information is contained in a data record so that t is indeed identifiable the results of applications to synthetic data indicate that the csa scheme gives a t estimate with the most precision and also that it requires collecting fewer observations these results are discussed in light of practical considerations when designing data collection procedures

release of potential shearing instability in warm frontal zones potential shearing instability pshi exists in the atmosphere when the richardson number in a stably stratified shear layer would be less than 1 4 if the layer were lifted to saturation sometimes the air entering a warm frontal zone near the position of the surface warm front is initially unsaturated its richardson number is greater than 1 4 but pshi exists over a deep layer this paper presents a study of a warm frontal zone using observations from the high resolution doppler radar at chilbolton supported by radiosondes and output from the mesoscale version of the operational united kingdom meteorological office unified model very large amplitude kelvin helmholtz billows were observed to form where the pshi was realised following the onset of saturation the billows were probably intense enough to be a hazard for air traffic and an important source of momentum transfer rough estimates from the radar of vertical momentum fluxes due to the billows are shown to be broadly consistent with measurements by the same radar of the change in velocity profile across the frontal zone from start to end of the billow train the present version of the unified model does not parametrize vertical mixing due to shearing instability in the free atmosphere this may be an important omission

compressional velocity and porosity in sand clay mixtures laboratory measurements of porosity and compressional velocity were conducted on unconsolidated brine saturated clean ottawa sand pure kaolinite and their mixtures at various confining pressures a peak in p velocity versus clay content in unconsolidated sand clay mixtures at 40 percent clay by weight was found the peak in velocity is 20 30 percent higher than for either pure clay or clean sand a minimum in porosity versus clay content at 20 40 percent clay by weight is also observed such behavior is explained using a micro geometrical model for mixtures of sand and clay in which two classes of sediments are considered 1 sands and shaley sands in which clay is dispersed in the pore space of load bearing sand and thus reduces porosity and increases the elastic moduli of the pore filling material and 2 shales and sandy shales in which sand grains are dispersed in a clay matrix for these sediments the model reproduces the extrema in velocity and porosity and accounts for much of the scatter in