modeling the hydromechanical responses of sandwich structure faults during underground fluid injection injection or withdrawal of fluid at depth may trigger felt seismicity at a site with natural faults or artificial fracturing cracks understanding how to avoid triggering felt earthquakes plays a crucial role in the success of underground anthropogenic activities such as subsurface energy storage and co2 geological sequestration with the application of a hydromechanical coupling finite element model we examine the potential of injection induced pore pressure change and the responding fault slippage along the fault surface in two injection scenarios multi layer injection mli and single layer injection sli the results indicate that fault slippage buildup is mainly located along the portion of the fault intersecting the reservoir mli leads to a relatively lower level of induced seismicity compared with sli in the fault zone the external zone and core of the fault exert a connection effect and barrier effect on the hydraulic connectivity respectively after 20 years of injection the pore pressure in the core presents a smaller change than that in the internal and external zones furthermore an uncertainty analysis was performed to evaluate the statistical significance of permeability in the caprock reservoir and fault core internal zone and external zone and only the permeability in the reservoir significantly affects the level of fault slippage based on the fault zone hydromechanics associated with subsurface energy storage and co2 geological sequestration

characterization of land subsidence induced by groundwater withdrawals in su xi chang area china su xi chang area is one of the typical regions in china which suffers from severe land subsidence various tools of field monitoring were integrated to study the characteristics and mechanisms of land subsidence in this region the occurrence and the development of the land subsidence in this region are strongly related to the groundwater pumping both in time and space the main consolidation layers are the soft mud layers however the compressibility of the confined sandy layers should not be ignored the second and third confined aquifers contributed more than 30 of total subsidence meanwhile irrecoverable deformations were also observed in the sandy layers different sandy layers deform diversely under different stress conditions some have the elastic feature but the soil strata including both sandy layers and clayey layers located in the center of the groundwater level depression cone exhibited obvious viscous mechanical behavior which caused the common lag phenomenon the sand composition mingled with small clay particles or interbeds and sand rheology are the two main reasons for the lag phenomena in sandy layers a series of laboratory tests for modeling the effective stress changes due to groundwater withdrawals were conducted to investigate the mechanism of the lag phenomenon based on the test results the relationship of stress strain time for saturated sands is obtained and it could be expressed as power functions the results also showed that the compression of the sandy layers was time dependent and its deformation could be remarkable when establishing land subsidence model the deformation for the similar soil formation could be elastic visco elastic and even visco elastic plastic because of the different groundwater level fluctuation experienced

engineering geological characteristics of expansive soils in china expansive soils are widely distributed in china six types and subtypes of expansive soils are classified based on their origins and geological times in this paper the soil samples from six representative areas in china were tested and analyzed including their clay content clay mineral composition chemical constitutes physico chemical indices swelling and shrinkage in light of the test results the engineering geological characteristics of each type of expansive soil are assessed

mechanical and petrophysical properties of north sea shales one of the problems when evaluating potential borehole stability problems in the drilling of hydrocarbon exploration and production wells is the lack of relevant data to describe the lithologies this relates in particular to the shales since these constitute most of the overburden and are also the most troublesome this paper presents a set of data from a variety of deeply cored shales from the north sea the shales have been extensively characterised and span a wide range of both petrophysical and mechanical properties depending on for example burial history and diagenesis special characteristics of shales have been tested and described including pore size distribution permeability anisotropy and temperature dependence appropriate procedures for sample handling testing and interpretation have been developed or modified from other related sciences

a note on induced stress changes in hydrocarbon and geothermal reservoirs abstract earthquakes have been induced by oil and gas production where pore pressures have decreased in some cases by several tens of mpa it has previously been suggested that such earthquakes are caused by poroelastic stressing of crust surrounding the reservoir induced earthquakes are also common in geothermal fields such as the geysers where strong correlations between both steam production and condensate injection and earthquake activity have been observed over the last several decades stress measurements within hydrocarbon reservoirs show that the least horizontal stress decreases with declining reservoir pressure as predicted by poroelasticity for circular disk shaped reservoirs isothermal reduction in pore pressure induces a relative horizontal tension within the reservoir production induced stressing may promote frictional sliding on pre existing faults within the reservoir itself normal faulting is promoted if the regional stress is extensional and the biot coefficient is sufficiently large 0 85 for reasonable coefficients of friction on the other hand dilatant fracturing and normal faulting are always promoted in extensional environments near the edge of the reservoir or in regions of high pore pressure gradient it is suggested that such fracturing could enhance fracture permeability in tight rocks adjacent to portions of the reservoir that experience large reductions in pore pressure due to production in regional compressional environments production modestly favors reverse faulting above and below the reservoir the ratio of thermal to poroelastic stress can be quite large in geothermal reservoirs such as the geysers reservoir wide energy balance considerations suggest that the average temperature has declined at the geysers by 6 c during the past 20 years reservoir average stress changes are thus on the order of 2 mpa and are certainly much larger near injection wells and steam producing fractures

fully coupled poroelastic peridynamic formulation for fluid filled fractures a new fully coupled poroelastic peridynamic formulation is presented and its application to fluid filled fractures is demonstrated this approach is capable of predicting porous flow and deformation fields and their effects on each other moreover it captures the fracture initiation and propagation in a natural way without resorting to an external failure criterion the peridynamic predictions are verified by considering two benchmark problems including one and two dimensional consolidation problems moreover the growth of a pre existing hydraulically pressurized crack case is presented based on these results it is concluded that the current peridynamic formulation has a potential to be used for the analysis of more sophisticated poroelastic problems including fluid filled rock fractures as in hydraulic fracturing

geomechanical response to seasonal gas storage in depleted reservoirs a case study in the po river basin italy 1 underground gas storage ugs in depleted hydrocarbon reservoirs is a strategic practice to cope with the growing energy demand and occurs in many places in europe and north america in response to summer gas injection and winter gas withdrawal the reservoir expands and contracts essentially elastically as a major consequence of the fluid gas and water pore pressure fluctuations depending on a number of factors including the reservoir burial depth the difference between the largest and the smallest gas pore pressure and the geomechanical properties of the injected formation and the overburden the porous medium overlying the reservoir is subject to three dimensional deformation with the related cyclic motion of the land surface being both vertical and horizontal we present a methodology to evaluate the environmental impact of underground gas storage and sequestration from the geomechanical perspective particularly in relation to the ground surface displacements long term records of injected and removed gas volume and fluid pore pressure in the lombardia gas field northern italy are available together with multiyear detection of vertical and horizontal west east displacement of the land surface above the reservoir by an advanced permanent scatterer interferometric synthetic aperture radar psinsar analysis these data have been used to calibrate a 3 d fluid dynamic model and develop a 3 d transversally isotropic geomechanical model the latter has been successfully implemented and used to reproduce the vertical and horizontal cyclic displacements on the range of 8 10 mm and 6 8 mm respectively measured between 2003 and 2007 above the reservoir where a ugs program has been underway by stogit eni s p a since 1986 following a 5 year field production life because of the great economical interest to increase the working gas volume as much as possible the model addresses two ugs scenarios where the gas pore overpressure is pushed from the current 103 pi where pi is the gas pore pressure prior to the field development to 107 pi and 120 pi results of both scenarios show that there is a negligible impact on the ground surface with deformation gradients that remain well below the most restrictive admissible limits for the civil structures and infrastructures

joint sets that enhance production from middle and upper devonian gas shales of the appalachian basin the marine middle and upper devonian section of the appalachian basin includes several black shale units that carry two regional joint sets j1 and j2 sets as observed in outcrop core and borehole images these joints formed close to or at peak burial depth as natural hydraulic fractures induced by abnormal fluid pressures generated during thermal maturation of organic matter when present together earlier j1 joints are crosscut by later j2 joints in outcrops of black shale on the foreland northwest side of the appalachian basin the east northeast trending j1 set is more closely spaced than the northwest striking j2 set however j2 joints are far more pervasive throughout the exposed devonian marine clastic section on both sides of the basin by geological coincidence the j1 set is nearly parallel the maximum compressive normal stress of the contemporary tectonic stress field shmax because the contemporary tectonic stress field favors the propagation of hydraulic fracture completions to the east northeast fracture stimulation from vertical wells intersects and drains j2 joints horizontal drilling and subsequent stimulation benefit from both joint sets by drilling in the north northwest south southeast directions horizontal wells cross and drain j1 joints whenever present then staged hydraulic fracture stimulations if necessary run east northeast i e parallel to the j1 set under the influence of the contemporary tectonic stress field thereby crosscutting and draining j2 joints

permeability of illite bearing shale 2 influence of fluid chemistry on flow and functionally connected pores 1 bedding parallel permeability of illite rich shale of the wilcox formation has been investigated using distilled water and 1 m solutions of nacl kcl and cacl2 as pore fluids despite low modal concentrations of swelling clays specimens expand upon fluid saturation and permeabilities depend on fluid composition permeabilities to flow of 1 m cacl2 are 3 5 times greater than values measured for the other pore fluids suggesting sensitivity to exchange of divalent cations for monovalent cations at clay mineral surfaces permeabilities of individual samples exhibit nonrecoverable changes with sequential changes in composition of incoming fluid permeabilities k at varying effective pressure pe fit a cubic law k k0 1 pe p1 m 3 where m and p1 are independent of fluid composition and k0 is greater for transport of 1 m cacl2 than that for transport of the other pore fluids assuming that fluid conduits have crack like dimensions the lack of sensitivity of m and p1 to fluid composition suggests that surface roughness and asperity stiffness of conduits are unaffected by cation exchange while changes in k0 reflect changes in the clay fluid interfaces of the connected pore space index terms 5114 physical properties of rocks permeability and porosity 5139 physical properties of rocks transport properties 1832 hydrology groundwater transport 3947 mineral physics surfaces and interfaces 1045 geochemistry low temperature geochemistry keywords permeability shale fluid chemistry citation kwon o b e herbert and a k kronenberg 2004 permeability of illite bearing shale 2 influence of fluid chemistry on flow and functionally connected pores j geophys res 109 b10206 doi 10 1029 2004jb003055

three dimensional baroclinic eddies in the ocean evolution propagation overall structures and angular models abstractthe evolution and dynamics of an initially gaussian baroclinic vortex embedded in a resting stratification environment are investigated with a three dimensional primitive equation model th

characteristics of the london clay from the terminal 5 site at heathrow airport the innovative engineering approach adopted for the new terminal 5 at heathrow airport called for an advanced investigation of the london clay strata including detailed in situ profiling and stress path laboratory testing on high quality rotary cored samples although the scope of the investigations exceeded that normally specified for conventional design questions relating to the structure and anisotropy of stiffness and strength of the clay remained that could not be answered further research was required and the deep excavations at the site provided the opportunity for a team from imperial college to take multiple block samples from three depths supplemented by two additional dedicated rotary cored boreholes intensive research was performed at imperial college on these samples as described in three companion papers by gasparre et al and nishimura et al this overview paper integrates the findings from the recent research with those from the commercial investigation and with earlier studies to e

estimation of flow properties using surface deformation and head data a trajectory based approach 1 a trajectory based algorithm provides an efficient and robust means to infer flow properties from surface deformation and head data the algorithm is based upon the concept of an arrival time of a drawdown front which is defined as the time corresponding to the maximum slope of the drawdown curve the technique involves three steps the inference of head changes as a function of position and time the use of the estimated head changes to define arrival times and the inversion of the arrival times for flow properties trajectories computed from the output of a numerical simulator are used to relate the drawdown arrival times to flow properties the inversion algorithm is iterative requiring one reservoir simulation for each iteration the method is applied to data from a set of 14 tiltmeters located at the raymond quarry field site in california using the technique i am able to image a high conductivity channel which extends to the south of the pumping well the presence of this permeable pathway is supported by an analysis of earlier cross well transient pressure test data

horizontal aquifer movement in a theis thiem confined system the skeletal matrix of an aquifer is known to move laterally toward a discharging well the mechanisms by which it moves relative to the well have been only partially studied in the past examining the relation of drawdown to volume strain for an assumed poroelastic solid has been a common approach by way of contrast the present study examines the relation of the velocity of solids aquifer matrix to their hydraulic driving forces the present approach can be considered darcian and allows the displacement field of the aquifer matrix to be calculated directly a new formulation of the darcy gersevanov law of water flowing relative to moving solids is applied to a theis thiem confined aquifer the aquifer is found to start with a maximum velocity when the pump is turned on and then to decelerate as time progresses dimensionless type curves of horizontal movement of the skeletal matrix are calculated the resulting equation of aquifer deformation is checked against 1 results from alternatively using the standard poroelastic stress strain approach and 2 the fundamental storage equation for transient groundwater flow

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

numerical study on the responses of groundwater and strata to pumping and recharge in a deep confined aquifer abstract groundwater drawdown and strata settlements induced by dewatering in confined aquifers can be relieved by artificial recharge in this study numerical simulations of a field multi well pumping recharge test in a deep confined aquifer are conducted to analyze the responses of groundwater and strata to pumping and recharge a three dimensional numerical model is developed in a finite difference software which considers the fluid mechanical interaction using the biot consolidation theory the predicted groundwater drawdown and ground settlements are compared to the measured data to confirm the validation of the numerical analysis of the pumping and recharge both numerical results and measured data indicate that the effect of recharge on controlling the groundwater drawdown and strata settlements correlates with the injection rate and well arrangements since the groundwater drawdown induced by pumping can be controlled by artificial recharge soil compression can be relieved by reducing the changes of effective stress of the soils consequently strata settlement induced by pumping can be relieved by artificial recharge and ground settlements can be eliminated if an appropriate injection rate and well arrangement are being determined moreover the changes of the pore pressure and seepage force induced by pumping and recharge will also result in significant horizontal deformations in the strata near the recharge wells

compaction driven evolution of porosity and permeability in natural mudstones an experimental study this paper describes a series of experiments designed to investigate the influence of lithology on the compactional loss of porosity and permeability in mudstones two intact samples of london clay with clay fractions of 40 and 67 were compacted to 33 mpa effective stress clay fraction permeability porosity pore size distribution and specific surface area were measured and their evolution was monitored throughout the compaction process electron microscopy was combined with mercury porosimetry to trace the collapse of the pore structure with increasing effective stress in both cases porosity loss occurred primarily by the collapse of large pores this process is more obvious in the coarser grained sample because throughout the compaction process it has a much broader range of pore radii and a much greater mean pore radius consistent with the pore size distributions the permeability of the coarser sample ranges from 10 10 m s 1 to 10 12 m s 1 while that of the finer grained sample ranges from 4 10 12 m s 1 to 5 10 14 m s 1 during progressive compaction from 2 to 33 mpa the compressibility of the finer grained sample is greater than that of the coarser grained sample 0 15 as opposed to 0 07 however in both cases the compressibility is much lower than that inferred for lithologically similar samples compacted over geological timescales the demonstration that both porosity and lithology clay fraction influence the permeability of mudstones should allow the development of more realistic porosity permeability relationships which take into account lithological variations exhibited by mudstones

natural fractures in the barnett shale and their importance for hydraulic fracture treatments gas production from the barnett shale relies on hydraulic fracture stimulation natural opening mode fractures reactivate during stimulation and enhance efficiency by widening the treatment zone knowledge of both the present day maximum horizontal stress which controls the direction of hydraulic fracture propagation and the geometry of the natural fracture system which we discuss here is therefore necessary for effective hydraulic fracture treatment design we characterized natural fractures in four barnett shale cores in terms of orientation size and sealing properties we measured a mechanical rock property the subcritical crack index which governs fracture pattern development natural fractures are common narrow 0 05 mm 0 002 in sealed with calcite and present in en echelon arrays individual fractures have high length width aspect ratios 1000 1 they are steep 75 and the dominant trend is west northwest other sets trend north south the narrow fractures are sealed and cannot contribute to reservoir storage or enhance permeability but the population may follow a power law size distribution where the largest fractures are open the subcritical crack index for the barnett shale is high indicating fracture clustering and we suggest that large open fractures exist in clusters spaced several hundred feet apart these fracture clusters may enhance permeability locally but they may be problematic for hydraulic fracture treatments the smaller sealed fractures act as planes of weakness and reactivate during hydraulic fracture treatments because the maximum horizontal stress trends northeast southwest and is nearly normal to the dominant natural fractures reactivation widens the treatment zone along multiple strands

the stiffness of natural london clay an investigation of natural london clay is reported involving advanced triaxial hollow cylinder apparatus hca and dynamic testing techniques significant anisotropy was revealed at all scales of deformation and the framework of cross anisotropic elasticity was found to apply broadly to the initial elastic behaviour the stiffness parameters obtained by independent techniques generally exhibited good agreement with the greatest deviation being seen in the poisson s ratios which fell far from the values usually assumed in conventional foundation analysis probing tests established the limits to the elastic domain over a range of depths showing that these scaled in proportion to the mean effective stress level as did those of a second kinematic surface that surrounded the elastic domain once engaged this second surface signified a new pattern of strain increment directions faster elastic plastic stiffness decay with strain and also a greater dependence of behaviour on recent stress history howev

permeability of illite bearing shale 1 anisotropy and effects of clay content and loading direction relative to bedding clay content 40 65 and effective pressure pe 2 12 mpa permeability k is anisotropic at low pe measured k values for flow parallel to bedding at pe 3 mpa exceed those for flow perpendicular to bedding by a factor of 10 both for low clay content lc and high clay content hc samples with increasing pe k becomes increasingly isotropic showing little directional dependence at 10 12 mpa permeability depends on clay content k measured for lc samples exceed those of hc samples by a factor of 5 permeability decreases irreversibly with the application of pe following a cubic law of the form k k0 1 pe p1 m 3 where k0 varies over 3 orders of magnitude depending on orientation and clay content m is dependent only on orientation equal to 0 166 for bedding parallel flow and 0 52 for flow across bedding and p1 18 27 mpa appears to be similar for all orientations and clay contents anisotropy and reductions in permeability with pe are attributed to the presence of crack like voids parallel to bedding and their closure upon loading respectively index terms 5114 physical properties of rocks permeability and porosity 5139 physical properties of rocks transport properties 5112 physical properties of rocks microstructure 1832 hydrology groundwater transport keywords permeability shale connected pore space

interbed storage changes and compaction in models of regional groundwater flow water released from permanent compaction of compressible fine grained interbeds within confined aquifers may be a significant source of pumped water permanent or inelastic compaction of the interbeds occurs when head declines from pumping cause the effective stress or grain to grain load to exceed the elastic limits of the interbeds as a result the grains in the interbeds rearrange and excess water is expelled the amount of inelastic compaction generally is proportional to the increase in effective stress and the decrease in head a common approach for the simulation of elastic and inelastic compaction in groundwater flow models is to assume that head changes in the aquifer result in instantaneous storage changes in the compressible interbeds a term is added to the groundwater flow equation to account for the storage changes changes in specific storage may be computed explicitly from the results at the previous time step in the finite difference formulation of the groundwater flow equation a better approach is to implicitly apportion storage changes between elastic and inelastic components within a time step if storage changes cannot be considered to occur instantaneously with change in head in the aquifer another approach is taken equations for horizontal flow in the aquifer are coupled with equations for vertical flow in the compressible interbeds to simulate flow in half a representative doubly draining interbed storage changes and compaction are calculated for the representative half thickness and are extrapolated to the entire thickness of all interbeds within each cell this approach was applied to an existing model of groundwater flow in the central valley of california the simulation demonstrates that solving coupled systems of equations is feasible for a regional flow model

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

a numerical model to calculate land subsidence applied at hangu in china abstract the deep unconsolidated sedimentary aquifers of eastern china are heavily over exploited and this causes aquifer compaction 1 which results in land subsidence the geological formation contains significant thicknesses of clay which introduces time delays between the extraction of the groundwater and the resulting subsidence a new computer code called the interbed drainage package has been developed for the popular modflow model to address this behaviour it has been applied in a simulation of the port of hangu and the results are being used to manage the land subsidence problem

ocean loading station displacements observed by vlbi ocean tidal loading causes small displacements of vlbi observing stations that should be taken into account in vlbi data analysis the a posteriori delay and delay rate errors of least squares fits of those vlbi experiments with stations near ocean coasts and on islands are shown to decrease significantly after correcting the vlbi observables for the ocean loading effect in extreme cases station coordinates and baseline lengths may change by a few centimeters after applying the ocean loading corrections conversely these results demonstrate that ocean tidal loading can be monitored using high precision vlbi however the present global ocean tidal loading model is still inadequate for some stations and should be expanded for future applications

seasonal subsidence and rebound in las vegas valley nevada observed by synthetic aperture radar interferometry analyses of areal variations in the subsidence and rebound occurring over stressed aquifer systems in conjunction with measurements of the hydraulic head fluctuations causing these displacements can yield valuable information about the compressibility and storage properties of the aquifer system historically stress strain relationships have been derived from paired extensometer piezometer installations which provide only point source data because of the general unavailability of spatially detailed deformation data areal stress strain relations and their variability are not commonly considered in constraining conceptual and numerical models of aquifer systems interferometric synthetic aperture radar insar techniques can map ground displacements at a spatial scale of tens of meters over 100 km wide swaths insar has been used previously to characterize larger magnitude generally permanent aquifer system compaction and land subsidence at yearly and longer timescales caused by sustained drawdown of groundwater levels that produces intergranular stresses consistently greater than the maximum historical stress we present insar measurements of the typically small magnitude generally recoverable deformations of the las vegas valley aquifer system occurring at seasonal timescales from these we derive estimates of the elastic storage coefficient for the aquifer system at several locations in las vegas valley these high resolution measurements offer great potential for future investigations into the mechanics of aquifer systems and the spatial heterogeneity of aquifer system structure and material properties as well as for monitoring ongoing aquifer system compaction and land subsidence

deformation characteristics of a clayey interbed during fluid injection surface deformation due to fluid withdrawal has long been observed at the surface above aquifers and oil reservoirs uplift associated with fluid injection has also been observed although the processes of subsidence and uplift are reversible in a poroelastic setting the presence of clayey interbeds can result in ground deformation behavior non reversible because of their low permeability and nonlinear behavior in this investigation a cam clay model is used in conjunction with a poroelastic model to simulate the presence of a laterally extensive lens shaped clayey interbed in a sandstone aquifer during fluid injection spatial and temporal changes associated with this interbed during aquifer pressurization are captured and can be clearly differentiated from the deformation of the surrounding poroelastic aquifer formation results for pore pressures and ground surface deformation patterns can be categorized into three distinct time intervals an early time interval where the aquifer is pressurized but not the interbed leading to a lower region above the interbed an intermediate time interval in which the interbed pressures slowly increase approaching the pressure of the adjacent aquifer leading to a potentially large surface uplift above the interbed and a late time interval in which pressure equilibration is achieved between the interbed and aquifer and a highly non symmetrical irregular surface deformation pattern results which may be higher or lower than the background depending on the interbed characteristics reservoir configuration is found to be an important factor influencing ground deformation behavior with more obvious deformation always occurring in a laterally confined aquifer as opposed to a laterally infinite aquifer

three dimensional deformation and strain induced by municipal pumping part 2 numerical analysis summary field measurements consisting of water levels from a municipal well and three dimensional surface deformations and strains from high precision gps measurements at various radial distances from the well were collected as part of a 62 day controlled aquifer test at mesquite nv these measurements were used as observations in several numerical models and a parameter estimation code to characterize and constrain hydraulic and mechanical properties of a 400 m thick basin fill aquifer a parsimonious approach was used in conceptualizing the aquifer system nonetheless results from the calibrated deformation and flow models accurately reproduced the observed head and deformations during the first 20 days of pumping the time at which a new equilibrium was achieved surface deformations were shown to reflect hydraulic anisotropy and direction of principal conductivity in addition the radius of influence and cone of depression from pumping was approximated in spite of the fact that no monitoring well data existed at the site sensitivity analysis indicates that cyclical head values are most sensitive to changes in horizontal hydraulic conductivity while time dependent vertical deformations are most sensitive to changes in skeletal specific storage this investigation shows that gps monitoring can be used in place of costly monitoring wells to characterize aquifers for water management purposes where skeletal deformation tends to be elastic

rapid subsidence over oil fields measured by sar interferometry the lost hills and belridge oilfields are in the san joaquin valley california the major oil reservoir is high porosity and low permeability diatomite extraction of large volumes from shallow depths causes reduction in pore pressure and subsequent compaction forming a surface subsidence bowl we measure this subsidence from space using interferometric analysis of sar synthetic aperture radar data collected by the european space agency remote sensing satellites ers 1 and ers 2 maximum subsidence rates are as high as 40 mm in 35 days or 400 mm yr measured from interferograms with time separations ranging from one day to 26 months the 8 and 26 month interferograms contain areas where the subsidence gradient exceeds the measurement possible with ers sar but shows increased detail in areas of less rapid subsidence synoptic mapping of subsidence distribution from satellite data powerfully complements ground based techniques permits measurements where access is difficult and aids identification of underlying causes