storage change in a flat lying fracture during well tests 1 the volume of water released from storage per unit head drop per volume of an rev is a basic quantity in groundwater hydrology but the details of the process of storage change in the vicinity of a well are commonly overlooked we characterize storage change in a flat lying fracture or thin sedimentary bed through the apparent hydraulic compliance cf the change in aperture of the fracture or thickness of the layer per unit change in pressure the results of theoretical analyses and field measurements show that cf increases with time near the well during pumping but it drops suddenly and may become negative at the beginning of recovery during a well test profiles of cfincrease with radial distance from a well but they are marked by a sharp increase and a sharp decrease at the edge of the region affected by the wellbore pressure transient the conventional view in groundwater hydrology is that storage change at a point is proportional to the local change in pressure which requires that the hydraulic compliance is uniform and constant it appears that this conventional view is a simplification of a process that varies in both space and time and can even take on negative values this simplification may be a source of uncertainty when interpreting well tests and extensometer records or predicting long term well performance

geodetic imaging of thermal deformation in geothermal reservoirs production depletion and fault reactivation abstract we investigate thermally induced surface deformation in geothermal systems to define source mechanisms at depth we assess the mechanical process of subsurface deformation by assuming a spherically cooled fractured reservoir in an infinite medium and derive relations that define magnitudes of thermal contraction stress change and permeability evolution the magnitude of thermal deformation in typical geothermal system is larger than anticipated and suggests two different modalities of surface subsidence thermal contraction and fault reactivation here surface deformation vertical displacement surface tilt and horizontal strain induced by the two different modalities are assessed with mogi contraction and okada slip models and compared with instrumental sensitivity of high precision surface geodetic tools we show that 1 year of geothermal operation at 10 mw with a power plant conversion efficiency of 12 can yield 3 0 104 m3 of subsurface volume change for a reservoir at 2000 m depth this induces 1 7 mm of vertical surface displacement 800 nano radians of surface tilt and 900 nano strains of surface strain this result implies that typically observed magnitudes of surface subsidence order of cm year are naturally expected in massive 100 mw scale geothermal operations and observed surface subsidence may largely be the result of thermal contraction conversely thermal unloading can trigger fault reactivation analysis with an okada slip model shows these shear offsets on pre existing faults can also result in surface deformations of considerable magnitude our analysis of field operational data from various geothermal projects suggests that both thermal contraction and slow fault reactivation may contribute to the observed large surface deformation comparison of predicted deformation with instrumental sensitivity of high precision surface tools confirms that geodetic signals especially tilt and strain are indeed sufficiently large to describe reservoir evolution and to potentially deconvolve reservoir parameters of interest such as permeability

numerical modeling of the productivity of vertical to shallowly dipping fractured zones in crystalline rocks groundwater resources in crystalline rock are typically associated with the weathered zone and regional sub vertical faults that are well connected to the surface however some sub horizontal and shallowly dipping fractured zones can also be highly productive aquifers in this paper numerical simulations of a conceptual hydrogeological model show that the flow to such strongly transmissive fractured zones is controlled by their transmissivity or by their deepening structure while leakage through the overlying rock units is generally the limiting factor recharge always occurs at least close to the outcrop of the fractured zone where the overlying rock is thinner and guarantees the availability of some groundwater at small dip angles recharge extends spatially and the flow within the fractured zone may even become the limiting factor when the hydraulic conductivity of the overlying rock is not less than two orders of magnitude smaller than the fractured zone transmissivity this is precisely the case of the ploemeur aquifer brittany france located in a crystalline rock geologic setting where groundwater in a shallowly dipping fractured zone is used as the source of water supply for a nearby city of 20 000 people simulation results show that the fractured zones may represent potential aquifers under a large variety of hydrogeological conditions aquifers in shallowly dipping structures differ strongly from those located in regional subvertical fault zones in terms of flow patterns and thus supposedly in terms of management of the groundwater resource they are more local than regional in scale and consequently do not require regional fracture connectivity the leakage through the overlying rock unit enhances water quality finally we argue that the potential widespread occurrence of these alternative and possibly less accessible resources should promote the development of appropriate identification methods

understanding the hydromechanical behavior of a fault zone from transient surface tilt and fluid pressure observations at hourly time scales flow through reservoirs such as fractured media is powered by head gradients which also generate measurable poroelastic deformation of the rock body the combined analysis of surface deformation and subsurface pressure provides valuable insights of a reservoir s structure and hydromechan ical properties which are of interest for deep seated co 2 or nuclear waste storage for instance among all surveying tools surface tiltmeters offer the possibility to grasp hydraulically induced deformations over a broad range of time scales with a remarkable precision here we investigate the information content of transient surface tilt generated by the pressurization a kilometer scale subvertical fault zone our approach involves the combination of field data and results of a fully coupled poromechanical model the signature of pressure changes in the fault zone due to pumping cycles is clearly recognizable in field tilt data and we aim to explain the peculiar features that appear in 1 tilt time series alone from a set of four instruments and 2 the ratio of tilt over pressure we evidence that the shape of tilt measurements on both sides of a fault zone is sensitive to its diffusivity and its elastic modulus the ratio of tilt over pressure predominantly encompasses information about the system s dynamic behavior and extent of the fault zone and allows separating contributions of flow in the different compartments hence tiltmeters are well suited to characterize hydromechanical processes associated with fault zone hydrogeology at short time scales where spaceborne surveying methods fail to recognize any deformation signal

systematic change of foraminiferal mg ca ratios across a strong salinity gradient abstract the mg ca ratio of foraminiferal calcite is an important proxy for estimating past ocean temperatures used in conjunction with 18 o of foraminiferal calcite it allows deconvolution of temperature and ice volume signals to infer past ocean temperatures and salinities assuming the relationship between seawater 18 o and salinity is known such work assumes that temperature is the only or at least the dominant environmental controller of foraminiferal mg ca the semi enclosed mediterranean sea where salinity varies from 36 to 40 psu over a seasonal temperature range of between only 5 c to 8 c provides a relevant setting to test this assumption outside the laboratory in this study planktonic foraminifera o universa g siphonifera g bulloides and g ruber white and pink were picked from 11 box core tops spanning the mediterranean salinity gradient and analysed for their trace element concentrations mg ca ratios are higher for the associated calcification temperatures than in other regions where calibrations have been conducted and correlate poorly with calcification temperature mg ca ratios are particularly high for samples from the eastern mediterranean where salinity is unusually high correlations of mg ca with the calcification salinity are statistically significant with mg ca changing by 15 59 per psu suggesting that salinity may act as a control on mg ca ratios in addition to the dominant temperature control we show that contamination by non carbonate material and diagenetic high mg carbonate overgrowths cannot account for the observed trend of increasing mg ca with salinity a relationship between mg ca and salinity is also suggested by re analysis of calibrations from open ocean settings these new mediterranean results are from a region with unusually high salinity but suggest that the effects of salinity on the mg ca palaeothermometer should be considered even in open ocean settings particularly where large salinity changes occurred in the past

a multidisciplinary fractured rock characterization study at raymond field site raymond ca abstract a dedicated field site was developed and a suite of experiments were conducted in the sierra nevada foothills near the town of raymond ca to develop and test a multi disciplinary approach to the characterization of groundwater flow and transport in fractured rocks a wealth of geologic hydrologic and geophysical data was collected at the site using a variety of unique tools a cluster of nine approximately 90 m deep boreholes were drilled at the site in a v shaped pattern with an angle of 60 the boreholes are spaced 7 5 15 30 and 60 m from the central borehole various geophysical and hydrologic tests were conducted in and between these boreholes integration of cross hole radar and seismic tomography borehole flow surveys and images from a new digital borehole scanner indicated that groundwater flow is mainly confined to a few sub horizontal fracture zones a unique suite of hydraulic tests were conducted in which three to four intervals in each of the nine boreholes were isolated using pneumatic packers some 130 injection tests were conducted and more than 4100 cross hole transient pressure measurements were obtained a computer algorithm was developed to analyze such massive interference data systematically as a result of the analysis an image of the fracture connections emerged which is consistent with the geophysical data high precision tiltmeters were effective in remotely characterizing the preferential flow path several radial convergent tracer tests were conducted by injecting a mixture of several conservative tracers and one sorbing tracer deuterium fluorescein lithium bromide and polystyrene micro spheres some differences between the breakthrough curves are observed which may be due to possible differences among so called conservative tracers some characterization tools were found to be more effective than others in locating flowing fractures however no single tool was almighty characterization of fractured rock is extremely challenging and requires a stepwise and well thought approach which is basically a good old scientific approach prediction of transport based on the characterization results is even more challenging and one should always bear in mind that it is virtually impossible to uniquely characterize a fractured rock

use of in situ fiber optic sensors to characterize highly heterogeneous elastic displacement fields in fractured rocks fractured and porous rock masses undergo complex deformations relating to geological mechanical and hydrological processes such as plate tectonics earthquakes earth tides and the engineering design of structures in and on rock masses the distribution of stresses in the earth s crust governs the deformation field within and on the surface of geological systems in turn the rock stiffness the presence of faults and others discontinuities the topographical variations the pore pressures body forces and tectonic forces affect the stresses distribution in the earth 1 under basic loading or unloading such as overburden loads tectonics forces underground excavation fractured rock masses generally deform according to a complex mechanical or hydromechanical behavior 1 2 displacements are first localized along pre existing discontinuities and then propagate within the porous rock matrix 2 3 along discontinuity planes the displacements are generally of high magnitude and instantaneous while displacements of the rock matrix are generally of lesser magnitude and slower thus in active zones deformation changes within fractured rocks present a large frequency range and can be both static and dynamic static changes involve static deformations that can be produced by volcanoes tectonic sources hydrologic effects while dynamic changes are best represented by seismic waves produced by earthquake sources 4 geodesy has been the classical field measurements method for static changes and seismology for

a coupled inversion of pressure and surface displacement a coupled inversion of transient pressure observations and surface displacement measurements provides an efficient technique for estimating subsurface permeability variations the methodology has the advantage of utilizing surface observations which are typically much less expensive than measurements requiring boreholes furthermore unlike many other geophysical observables the relationship between surface deformation and reservoir pore fluid volume changes is relatively well understood our treatment enables us to partition the estimation problem into a sequence of three linear subproblems an application of the approach to a set of tilt and borehole pressure data from the raymond field site in california illustrates its efficiency and utility the observations are associated with a well test in which fluid is withdrawn from a shallow fracture zone during the test 13 tiltmeters recorded the movement of the ground surface simultaneously nine transducers measured pressure changes in boreholes intersecting the fracture system we are able to image a high permeability north trending channel located within the fracture zone the existence and orientation of this high permeability feature is substantiated by a semiquantitative analysis of some 4000 transient pressure curves

tilt and strain deformation induced by hydrologically active natural fractures application to the tiltmeters installed in sainte croix aux mines observatory france we investigate the deformation induced by water pressure variations in hydrologically active natural fractures and recorded by tiltmeters and strainmeters the deformation associated with a single fracture is derived using finite element modelling fem a range in fracture geometries is explored first to highlight the sensitivity of each geometrical parameter to the deformation and secondly to allow transfer to observation sites water level variations in the fracture are then derived from a hydrological model driven by observed rainfall and calibrated on fracture water flow measurements the modelling results are explicitly applied to constrain the local hydrological contribution to observations with the 100 m long hydrostatic tiltmeter installed at sainte croix aux mines france our study shows that well founded physical modelling of local hydrological effect allows a substantial correction of records in observatories

inferring field scale properties of a fractured aquifer from ground surface deformation during a well test fractured aquifers which bear valuable water resources are often difficult to characterize with classical hydrogeological tools due to their intrinsic heterogeneities here we implement ground surface deformation tools tiltmetry and optical leveling to monitor groundwater pressure changes induced by a classical hydraulic test at the ploemeur observatory by jointly analyzing complementary time constraining data tilt and spatially constraining data vertical displacement our results strongly suggest that the use of these surface deformation observations allows for estimating storativity and structural properties dip root depth lateral extension of a large hydraulically active fracture in good agreement with previous studies hence we demonstrate that ground surface deformation is a useful addition to traditional hydrogeological techniques and opens possibilities for characterizing important large scale properties of fractured aquifers with short term well tests as a controlled forcing

temporal change in permeability of the rock estimated from repeated water injection experiments near the nojima fault in awaji island japan 1 three boreholes with depths of 500 800 and 1800 m were drilled near the nojima fault which is one of the 1995 hyogoken nanbu earthquake faults in order to research the structure and its temporal change of the active fault the water injection experiments were conducted from the 1800 m borehole in 1997 and 2000 then the discharge changes at the 800 m borehole were observed during the water injections considering the permeable zone near the fault as simple two dimensional layer with an uniform thickness we estimated the permeability of the permeable zone near the nojima fault from the discharge changes associated with the water injections it is found that the permeability of the permeable zone in 2000 became lower than that in 1997

geodetic tools for hydrogeological surveys 3d displacements above a fractured aquifer from gps time series deep porous reservoirs are subject to charge and discharge of fluids oil gas or water either naturally or induced by human exploitation this leads to a variation in pressure inside the reservoir and consequently to a deformation of the overlying material the knowledge of the ground surface displacements allows inferring the fluid migrations and the hydromechanical properties in the porous reservoir different kinds of geodetic tools are able to measure this ground deformation gps radar interferometry insar tiltmeters or leveling each of them has its own spatial and time characteristics and accuracies that conduct to different kind of applications after a review of the geodetic studies applied to hydrogeological processes we describe two examples of gps time series measurements above the granitic fractured aquifer of ploemeur located in french brittany these time series records the 3d displacements induced by the sum of different processes in this site the involved processes are mainly the ground deformation related to piezometric level variations in the aquifer that we are looking for and the ocean tide loading that can reach several centimeters in the study area we present the protocol of the gps data survey and the processing strategy applied to extract the effect of hydrogeological process with sufficient accuracy two different experiments were studied the long term deformation corresponding to seasonal hydrological cycle and the short term deformation associated to a pumping test for a same variation in piezometric levels the vertical ground displacements show larger amplitude for long term signal than for short one indicating a behavior depending on the duration of the hydrogeological load this difference of reactivity in time can be related to the heterogeneity of the studied aquifer finally this work shows that geodetic measurements provide important constraints for characterizing aquifer system response

a portable borehole extensometer and tiltmeter for characterizing aquifers 1 the solid skeleton of an aquifer moves in response to changes in water pressure barometric pressure earth tides and other factors and measuring these movements can help characterize aquifers a device for measuring the vertical displacement and horizontal shear or tilt at the same time and place has been developed by combining a tiltmeter and extensometer on a frame that can be temporarily anchored to borehole walls the device can resolve displacements on the order of 10 8 m and tilts on the order of 10 8 rad during a 4 h long pumping test in fractured gneiss the rock contracted by 3 m in response to 2 m of drawdown a compliance of roughly 1 5 m of displacement meter of head change 1 5 10 10 m pa tilt of 10 s of rad to the southwest occurred during pumping and both the displacement and the tilt returned during recovery the tilt signal is repeatable during sequential tests and it changes in magnitude with depth it can be explained by a fracture zone that strikes roughly ew and dips to the south semidiurnal tilts of roughly 0 1 rad occur during ambient conditions at periods of the o1 and m2 earth tides diurnal displacements of several tens of nanometers are associated with ambient fluctuations in water level when barometric pressure changed by several 100 pa increasing barometric pressure causes water level to fall but elevates the total pressure in the well this correlates with dilational displacement while falling total pressure correlates with contraction during ambient conditions

field evaluation of the hydromechanical behavior of flat lying fractures during slug tests summary slug tests were conducted at depths of 20 50 m in a fractured gneiss and axial displacements were measured along the borehole with a portable extensometer in order to evaluate the feasibility of combining pressure and displacement measurements to improve the characterization of fractured rock displacements on the order of microns occurred during slug tests when maximum head changes were on the order of meters maximum displacement lagged behind the maximum head and the signals at a given location were repeatable to within reasonable tolerances tests were conducted at 12 packed off depth intervals in a borehole and the signals from each interval were distinctly different from those at other depths parameter estimation techniques were used with a hydromechanical model to interpret the field results and the findings show that there are three transmissive zones in the borehole and the compliance of the fractures generally decreases with depth the inversion also highlights the importance of considering heterogeneities in the vicinity of the well bore when interpreting hydromechanical tests zones of leakage and blockage in the fractures were predicted in the vicinity of the well bore and their presence had a significant effect on the displacement signals

satellite based measurements of surface deformation reveal fluid flow associated with the geological storage of carbon dioxide interferometric synthetic aperture radar insar gathered over the in salah co sub 2 storage project in algeria provides an early indication that satellite based geodetic methods can be effective in monitoring the geological storage of carbon dioxide an injected volume of 3 million tons of carbon dioxide from one of the first large scale carbon sequestration efforts produces a measurable surface displacement of approximately 5 mm year using geophysical inverse techniques we are able to infer flow within the reservoir layer and within a seismically detected fracture fault zone intersecting the reservoir we find that if we use the best available elastic earth model the fluid flow need only occur in the vicinity of the reservoir layer however flow associated with the injection of the carbon dioxide does appear to extend several kilometers laterally within the reservoir following the fracture fault zone

poroelasticity observations of anomalous near surface tilt induced by ground water pumping abstract ground tilt signals observed at three different test sites in germany confirm earlier observations of surface deformation occurences caused by the withdrawal of ground water from nearby wells the strength of the signals presented here ranges from a few rad to 230 rad whereby ground tilt was measured in shallow boreholes at depths between 2 and 4 m analysis of the tilt signals suggests that local inhomogeneities in the subsoil can have significant impact on several signal parameters namely its maximum amplitude its variation in time and its strike with respect to the direction of the productive well the observed data emphasize the likelihood of various causes for deviations from the normal tilt response that holds for an isotropic poroelastic half space in particular at one site a reverse well level change also known as noordbergum effect in hydrogeology is seen together with a respective response in the tilt signal the study concludes that near surface deformation in the vicinity of pumped wells bears a wealth of information that may be useful to constrain the conditions of fluid flow at depth and that there is a need for model calculations to fully understand the involved phenomena

quantifying fractured crystalline rock properties using well tests earth tides and barometric effects summary characterization of fractured rock aquifers often requires the acquisition and analysis of diverse datasets obtained from various instrumentation configurations in this investigation at the fractured rock research site in floyd county virginia a high precision borehole extensometer and tiltmeter were used during pumping to monitor deformation in the vicinity of fractures identified from borehole logging strain data obtained from earth tide analyses were used with the extensometer and tiltmeter data to quantify hydromechanical properties including fracture volumetric specific storage porosity poisson s ratio the drained formation elastic modulus and the effective dip direction of the fracture borehole tiltmeter data were used to estimate deformation caused by an aquifer test consisting of three pumping and recovery periods performed in well ex 1 during each period of the aquifer test the extensometer located in w 03 and 27 7 m from the pumping well was anchored over 2 m long sections of 1 a fracture in hydraulic communication with ex 1 2 a fracture that is not hydraulically connected with ex 1 and 3 an unfractured portion of bedrock directly above the hydraulically connected fracture results from the pumping tests yielded compressibilities of 1 3 10 11 pa 1 and 1 7 10 11 pa 1 for the lower and upper fractures respectively when coupled with areal strain calculated from earth tide analyses the volumetric specific storage values are 3 2 10 11 pa 1 and 2 8 10 11 pa 1 and the poisson s ratios are 0 26 and 0 31 respectively using this with a calculated barometric efficiency of 0 45 allows for porosity calculations of 0 02 and 0 03 respectively for the vicinity of fractures in well w 03

microseismicity constrained discrete fracture network models for stimulated reservoir simulation abstractthe effectiveness of hydraulic fracture stimulation in low permeability reservoirs was evaluated by mapping microseismic events related to rock fracturing the geometry of stage by stage event point sets were used to infer fracture orientation particularly in the case where events line up along an azimuth or have a planar distribution in three dimensions locations of microseismic events may have a higher degree of uncertainty when there is a low signal to noise ratio either due to low magnitude or to propagation effects low signal to noise events are not as accurately located in the reservoir or may fall below the detectability limit so that the extent of fracture stimulated reservoir may be underestimated in the bakken formation of the williston basin we combined geologic analysis with process based and stochastic fracture modeling to build multiple possible discrete fracture network dfn model realizations we then integrated the geologic model with production data and numerical simul

temporal and spatial scaling of hydraulic response to recharge in fractured aquifers insights from a frequency domain analysis quantification of the recharge in fractured aquifers is particularly challenging because of the multiscale heterogeneity and the range of temporal scales involved here we investigate the hydraulic response to recharge of a fractured aquifer using a frequency domain approach transfer functions are calculated in a range of temporal scales from 1 day up to a few years for a fractured crystalline rock aquifer located in ploemeur s brittany france using recharge and groundwater level fluctuations as input and output respectively the spatial variability of the response to recharge characteristic response time amplitude temporal scaling is analyzed for 10 wells sampling the different compartments of the aquifer some of the transfer functions follow the linear reservoir model behavior on the contrary others display a temporal scaling at high frequency that cannot be represented by classic models large scale hydraulic parameters estimated from the low frequency response are compared with those estimated from hydraulic tests at different scales the variability of transmissivity and storage coefficient tends to decrease with scale and the average estimates converge toward the highest values at large scale the small scale variability of diffusivities which implies the existence of a range of characteristic temporal scales associated with different pathways is suggested to be at the origin of the unconventional temporal scaling of the hydraulic response to recharge at high frequency

resolving the geometry of hydraulic fractures from tilt measurements this paper discusses the resolution of geometrical characteristics of pressurized fractures from tiltmeter data the quasi static deformation and tilt field induced by such fractures can be modeled by superposition of displacement discontinuity dd singularities despite the relatively common use of such measurements to infer fracture characteristics there is a widespread misunderstanding of what can be accurately determined depending on the relative distance between the tiltmeter array and the fracture we investigate in detail the resolution of the dimensions and orientation of hydraulic fractures or faults from tilt measurements in particular we formally prove that at a distance larger than about twice the characteristic length of the fracture elastostatic measurements such as those measured by tiltmeters are not able to resolve independently all the dimensions of the fracture although the fracture volume can be robustly inverted from the data the resolution of fracture orientation is also discussed using an analysis based on a spatial fourier transform of the tilt field the relative angle between the plane where the measurements are located and the fracture plane plays a major role in the accuracy of this estimation in an illustrative field example where the measurements are located in the far field of the fracture deformation field we show how a single dd singularity can be used to model tiltmeter data and efficiently obtain the fracture orientation and volume

strainmeters and tiltmeters despite steady effort over the last century continuously recording tiltmeters and strainmeters have not yet been successful except for earth tide measurements this article reviews the techniques and instrument designs that have been developed in this field the continuous measurement of true tectonic motions which have rates of 10 14 s 1 requires extremely high instrument stability but more rapid motions tides and seismic waves apart are even smaller and not much more easily detectable much past effort has been spent improving the transducers used in these instruments which usually measure small displacements the commonest choices are optical the most accurate capacitive the most sensitive and inductive the most rugged nowadays building a transducer is the easiest part a much harder task equally important to a good design is attaching the instrument to the ground so that it can detect the signal wanted this part of the design includes choosing a location a large underground opening is thermally stable but distorting a surface installation is easy to build but noisy because of soil weathering and a borehole is inaccessible to weather but also to the operator all such installations and indeed the whole field of strain and tilt measurement of course rely on the assumption that the deformations of interest can be measured over baselengths of a few hundred meters or less this is true for tides and seismic waves but unproven for tectonic motions appropriate attachment techniques differ for each location and many mundane details such as cementing techniques for borehole instruments remain to be worked out the goal of measuring tectonic and tidal tilt has created many tiltmeter designs most are relatively small instruments that use some form of pendulum or bubble level a few use a liquid surface to measure tilts over a long baseline repeated experience has shown the latter type when well built to be superior to the former proving end monument motions to be a dominant source of noise the same appears to hold true for strainmeters the best results coming from long base laser instruments though strainmeters using rigid or flexible material length standards are useful for special purposes and borehole instruments show promise because achieving a good design has been so difficult it is important to select the goals an instrument must meet and be prepared to compromise on others the difficulty of validating results from this type of instrument makes comparison tests essential such tests as have been made so far show that good results cannot be gotten at low cost or without careful attention to details