hydrogeochemistry and geochemical simulations to assess water rock interactions in complex carbonate aquifers the case of aguadulce se spain abstract the hydrogeological unit of aguadulce campo de dalias aquifers se spain has a complex geometry this fact together with a continuous rise in water demand due to intensive agriculture and tourism create problems for groundwater quantity and quality in this paper classic geochemical tools managed by means of gis software and geochemical simulations are combined to delineate identify and locate the possible physicochemical processes acting in the aguadulce groundwater two main aquifers can be distinguished the carbonate or lower aquifer of triassic age and the calcodetritic or upper aquifer of plio quaternary age groundwaters from the latter are more saline and assuming all chlorinity originates from seawater intrusion the seawater contribution to their composition would be up to 7 nevertheless the carbonate aquifer appears not to be homogeneous it is compartmentalised into 4 zones where different processes explain the different groundwaters compositions zone 4 samples e margin of the carbonate aquifer resemble those of the plio quaternary aquifer where calcite precipitation dolomite and gypsum dissolution and some cation exchange water rock interaction together with seawater freshwater mixing occur in contrast water rock interaction predominates in zones 1 and 3 of the carbonate aquifer moreover zone 2 samples located between zones 1 and 3 are explained by water rock interaction in addition to mixing with plio quaternary aquifer waters the combination of geochemical simulations with gis and hydrogeochemical analyses has proven to be effective in identifying and locating the different physicochemical processes in the aquifer areas thus improving understanding of hydrogeochemistry in complex aquifers

origin of boron from a complex aquifer in southeast of spain a study of the boron content alongside cl s o 4 2 and no3 ions has enabled the factors that determine its origin to be distinguished in carbonate rocks with their higher saline content boron is associated with marine intrusion in the plioquaternary aquifer its origin is complex and is associated with three processes marine intrusion where there is a high cl content and the b cl ratio is close to that of seawater anthropogenic pollution at points with high b and no3 concentrations and where the b cl ratio is higher than that of seawater and the dissolution of evaporite deposits present in the plioquaternary strata at a series of sampling points where the so4 2 cl ratio is elevated and b

intensive agriculture wetlands quarries and water management a case study campo de dalias se spain the intensive agricultural activities that have developed over the last 50 years in the campo de dalias almeria region have required large quantities of gravel and clay as the basic materials for the substrate over which crops are raised with this motive numerous gravel pits have been opened that have extracted several million cubic metres of material in recent years similar quantities of clay have been extracted from the distal sectors of the alluvial fans that descend from the sierra de gador and from within a large endoreic basin in the latter quarries some wetlands have developed probably because of the rise in the water table level in the aquifer over which they lie the gravel pits are situated in the apical sectors of the alluvial fans overlying hydrogeological units that are widely overexploited for this reason the gravel pits could be used for artificial recharge in addition to increasing the availability of water in the aquifer the risk of catastrophic flooding would also be reduced

possibility of spatial variation of high frequency seismic motions due to random velocity fluctuation of sediments considering the possibility that random velocity fluctuation of sediments may affect spatial variation of high frequency seismic motions in small areas a few hundred meters in diameter we examine this possibility experimentally and numerically by comparing seismic array data obtained at three geologically different sites rock stiff sediment and soft sediment sites we make two observations related to the effect of random velocity fluctuation of sediments the first observation is that above 3 hz waveform spatial variation evaluated in terms of the cross correlation is larger at the stiff sediment site than at the rock site the second is that above 2 hz the amplitude spatial variation evaluated by the spectral ratio shows more observation station specific behavior at the soft sediment site than at the stiff sediment site we try to explain these two observations by modeling the sediments as random media two dimensional finite difference simulations for plane sh and sv wave incidences demonstrate that the sediments may affect the seismic waveform variation above 3 hz if the autocorrelation functions of the velocity fluctuations are in the range derived from well log velocity data the velocity structure at the soft sediment site is modeled as a two layered random media having a low velocity surface layer the finite difference simulations for this sediment model demonstrate that it is also possible that amplitude variation above 2 hz is caused by random velocity fluctuations in the low velocity surface layer

simulation of high frequency strong vertical motions using microtremor horizontal to vertical ratios we examined the possibility for simulation of vertical ground motions using microtremor horizontal to vertical spectral ratios comparing earthquake and microtremor horizontal to vertical spectral ratios we showed that although microtremor horizontal to vertical ratios are smaller than earthquake motion horizontal to vertical ratios their spectral shapes are similar also we showed that a correction factor to compensate for the difference between the two ratios is almost the same among geologically similar sites we then tried to reproduce strong vertical ground motions for the 1995 hyogo ken nanbu earthquake using corrected microtremor horizontal to vertical ratios vertical accelerations simulated were well reproduced in envelope and high frequency contents manuscript received 1 march 2002

vp vs ratio versus differential stress and rock consolidation a comparison between rock models and time lapse avo data the compressional to shear wave velocity ratio vp vs is an important parameter in seismic amplitude versus offset avo analysis and this parameter plays a key role especially for lithology and fluid prediction methods the p wave velocity is a key parameter in traditional pressure prediction methods because overpressure often results in a velocity reduction however for avo based pore pressure prediction methods one expects that the vp vs ratio also is a key parameter the hertz mindlin geomechanical model predicts a constant vp vs ratio as the differential stress changes in a dry package of identical spheres ultrasonic core measurements show increased vp vs ratios as the differential stress decreases especially for unconsolidated wet sands thus one is likely to assume that the vp vs ratio is dependent on rock consolidation by combining the hertz mindlin model with the gassmann model we show how to obtain a sim ple rock physics framework including both the differential stress and

hydrodynamic aquifer or reservoir compartmentalization changes in oil water contact owc depth across a field are often a signature of reservoir compartmentalization as a result of faulting or stratigraphic barriers such as shales but may equally well be caused by an underlying hydrodynamic aquifer in particular the pressure depth data obtained from an aquifer whose flow is changing over time can look very similar to that obtained from a compartmentalized reservoir misunderstanding which of these mechanisms causes the observed changes in owc across the field may result in poor estimates of oil in place and reduced recovery to address this problem an analytic expression is presented to estimate the time taken for a steady state tilted owc to be established once an aquifer starts flowing a comparison with simulations of hydrodynamic aquifers in homogeneous compartmentalized and heterogeneous reservoir models shows that this expression can be used in combination with the one derived by m k hubbert for the steady state tilt of the owc to clarify whether a reservoir contains barriers or baffles to flow or may simply have not yet reached equilibrium

carbonate rocks and petroleum reservoirs a geological perspective from the industry abstract carbonate oil reservoirs are sometimes regarded with apprehension in the petroleum industry since it can be difficult to predict the quality of and ensure high recovery factors from this rock family particular problems are the complex and heterogeneous nature of porosity in carbonate rocks often leading to large ranges in permeability for any given porosity and the organization of carbonate successions most commonly as vertically heterogeneous but laterally persistent layers important issues that arise time and again in carbonate reservoir description include a predicting reservoir quality at inter well scales and in uncored wells b recognizing problematic high permeability layers c determining the permeability component to allocate to fractures and connected vug systems and d populating reservoir models with representative physical parameters because porosity in carbonate rocks generally presents as diverse and heterogeneous conventional core plugs are seldom representative of large rock volumes and significant issues remain in terms of the scale compatibility of the various datasets for measured physical parameters that are used in carbonate reservoir description many of the world9s largest carbonate reservoirs were discovered and developed shortly after the second world war and are now showing signs of maturity expressed variously as poor pressure support water or gas breakthrough and stranded resources the proportion of the world9s conventional petroleum that is reservoired in carbonate rocks is commonly estimated at around 50 60 and many large carbonate reservoirs are likely to have a production lifetime beyond 50 years it is no coincidence then that the petroleum industry has been the primary source of funding of and promotion of research into carbonate rocks and depositional systems often with impacts extending well beyond oil and gas exploitation

the effect of methodology on volumetric uncertainty estimation in static reservoir models the importance of reservoir uncertainties for the prediction of petroleum recovered volumes and fluid flow performance is well known large uncertainties in reservoir gross volume estimation derive not only from the measurement errors but also from the way that the static reservoir model is constructed the aim of this article is to explore the uncertainty induced by the combination of the different steps in construction of the reservoir model these steps can be split into three main areas geometry internal heterogeneities and petrophysical properties the first task consists of building the architecture through the delineation of units it must deal with the sparseness of control data layer intercepts measured at few wells sometimes deviated and the complexity of the stratigraphic description several heterogeneous layers presence of faults and account for the seismic horizons observed each layer is then populated with lithofacies reflecting the geological environment this environment is characterized by the depositional sequence as well as the number of lithotypes facies with similar properties their proportions spatial trends and arrangement transition between facies interpreted seismic attributes can bring additional constraints on the lithotype proportions each lithotype is then assigned petrophysical properties finally the hydrocarbon volumes in place are calculated above an oil water contact uncertainties are evaluated within a realistic layering model using relevant stochastic techniques categorical and multigaussian simulations and choosing the adequate parameters the quantification is performed on global volumes as well as on more local criteria the results show that the choice of modeling workflow has an impact on the hydrocarbon volumetric assessment affecting both the estimate of mean volume and the range of uncertainty about the mean this needs to be taken into account when undertaking reservoir volumetric assessments

uncertainties in reservoir production forecasts being aware of uncertainties in forecasts of production characteristics is important for reservoir management decisions concerning further appraisal drilling flexibility in development plans and selection among reservoir prospects all require that uncertainties are taken into account this study addresses the problem of quantifying uncertainties due to incomplete knowledge of the initial reservoir characteristics with emphasis on the difference between heterogeneity modeling and assessment of uncertainty in this study we outline a formalism for uncertainty modeling in a bayesian framework and present an extensive case study of a north sea brent group reservoir the results are obtained by computer software implemented such that no human interference is required once the stochastic reservoir model is established once the stochastic reservoir model is established multiple realizations can be generated rescaled and fed into a fluid flow simulator to forecast production characteristics and quantify uncertainty associated with response parameters such as cumulative oil production recovery factors and water cuts the results demonstrate that uncertainty in model parameters contributes significantly to the overall uncertainty the most influential parameters in our case study include the sealing capacity of major faults seismic velocities used in depth conversion and average porosities and shale continuity within the main reservoir sandstone

seismic inversion for reservoir properties combining statistical rock physics and geostatistics a review there are various approaches for quantitative estimation of reservoir properties from seismic inversion a general bayesian formulation for the inverse problem can be implemented in two different work flows in the sequential approach first seismic data are inverted deterministically or stochastically into elastic properties then rock physics models transform those elastic properties to the reservoir property of interest the joint or simultaneous work flow accounts for the elastic parameters and the reservoir properties often in a bayesian formulation guaranteeing consistency between the elastic and reservoir properties rock physics plays the important role of linking elastic parameters such as impedances and velocities to reservoir properties of interest such as lithologies porosity and pore fluids geostatistical methods help add constraints of spatial correlation conditioning to different kinds of data and incorporating subseismic scales of heterogeneities

hydrogeochemical characterization and isotope investigations of a carbonate aquifer of the northern part of the united arab emirates abstract this paper assesses a carbonate aquifer of the wadi al bih area in the northeastern part of uae using hydrogeochemical and isotope approaches analyses of groundwater samples showed that the tds and high concentrations of major cations and anions were encountered in the lower segment of the wadi al bih area most of the groundwater salinity was noticed downstream of the wadi and this may be attributed to the brines that underlie the groundwater and also to the over pumping of groundwater with mostly very low recharge nitrate concentrations observed in the groundwater of the study area may be ascribed to the nature of the karastic aquifer which could lead to the dominance of dissolved oxygen that makes no 3 the dominant form of nitrogen the presence of sulfate in collected groundwater samples is due to the gypsum bearing mudstone in the lower segment of the wadi al bih carbonate aquifer majority of the groundwater samples showed the presence of nacl which indicates the possible influence of the underlying brine the mixing process of brine water and freshwater was noted in the shift from cahco 3 facies to ca cl facies the piper plot showed a ca rich to na rich water type shift which could be explained by a cation exchange process the oxygen and hydrogen isotope compositions in the groundwater samples suggest that the main source of precipitation is the mediterranean sea with some possible effects of the arabian sea a trend of increasing chloride concentration with enrichment of hydrogen isotope compositions suggests that groundwater originated from evaporated raindrops or evaporated surface water the similarity of oxygen and hydrogen isotope compositions between the eastern gravel plain ophiolite and the northern carbonate aquifers indicates the presence of a common source of recharge

the anthropogenic impact on mediterranean karst aquifers cases of some spanish aquifers mediterranean karstic aquifers are a major source of water supply for drinking water and agricultural use in semiarid areas the risk of causing an intensive exploitation is high leading to degradation processes of water quality not only due to limited agricultural activities developed on the karstic rocks being generally poorly developed soils but to the presence of deep evaporates which can be mobilised or because of being coastal aquifers where seawater intrusion can progress rapidly moreover karstic massifs constitute often positive reliefs that can generate barriers for civil works more and more saved by building sophisticated tunnels such works can affect the quantity and quality of the waters from the karst five examples of human impacts on some karst aquifers in se of spain are shown in this paper three of them with impacts on water quality and the other two correspond to the impact of tunnels in high speed trains drilling below the water table

impacts of human activities on recharge in a multilayered semiarid aquifer campo de cartagena se spain the development of intense agriculture in semiarid areas modifies intensity and spatial distribution of groundwater recharge by summing irrigation return flow to limited rainfall infiltration environmental tracers provide key information but their interpretation is complicated by more complex groundwater flow patterns in multilayered aquifers the real origin of the groundwater samples is hard to assess because of local mixing processes occurring inside long screened boreholes we use environmental tracers 14c 13c 2h 18o 3h to investigate the long term evolution of recharge in the five layer campo de cartagena aquifer in south eastern spain in addition to high resolution temperature loggings to identify the depth of origin of groundwater despite the complex background this methodology allowed a reliable interpretation of the geochemistry and provided a better understanding of the groundwater flow patterns the tritium method did not give good quantitative results because of the high variability of the recharge signal but remained an excellent indicator of recent recharge nonetheless both pre anthropization and post anthropization recharge regime could be identified and quantified by radiocarbon before the development of agriculture recharge varied from 17 mm year 1 at the mountain ranges to 6 mm year 1 in the plain whereas the mean annual rainfall is about 300 mm in response to the increase of agricultural activity recharge fluxes to the plain were amplified and nowadays reach up to 210 mm year 1 in irrigated areas these values are strengthened by global water budget and local unsaturated zone studies copyright 2013 john wiley sons ltd

source model of the 1995 hyogo ken nanbu earthquake and simulation of near source ground motion the 1995 hyogo ken nanbu earthquake struck the heavily populated kobe and adjacent cities in western japan more than 6400 people were killed and more than 150 000 buildings were destroyed the characteristics of mainshock ground motions in the heavily damaged area are needed to understand how buildings and bridges performed and why they reached failure unfortunately very few strong ground motions were recorded in the heavily damaged area during the mainshock in this study we attempt to estimate mainshock ground motions by using the em pirical green s function method egf method first we assume an initial source model with the asperities based on the rupture process obtained by inversion of strong ground motion records for simplicity we consider each asperity as a sub event with uniform stress drop in a finite extent then the initial model was improved by matching the synthetic and observed ground motions using a trial and error pro cedure the final model consists of three subevents subevent 1 with stress drop of 163 bars under the akashi strait around the rupture starting point subevent 2 with stress drop of 86 bars under the nojima fault in awaji island and subevent 3 with stress drop of 86 bars under kobe finally we estimate strong ground motions using aftershock records at sites where the mainshock was not recorded the near source motions in kobe synthesized with the best fit model are characterized by two large pulses with a duration of 1 to 3 sec the pulses are caused by forward rupture directivity effects from subevents 1 and 3 peak horizontal acceleration and velocity of the synthesized motions at the heavily damaged sites are about 1000 cm sec 2 and 130 crrdsec respectively while those at a rock site in the near source region are about 300 crrdsec 2 and 60 cm sec

stochastic modeling of incised valley geometries a stochastic modeling procedure designed to capture sequence stratigraphic principles has been developed for modeling fluvial reservoirs where high frequency base level fluctuations have exerted a strong influence on reservoir architecture reservoir stratigraphy and architecture are defined by the successive simulation of two types of surfaces base level rise flooding surfaces and base level fall surfaces sequence boundaries the flooding surfaces are modeled as standard two dimensional gaussian fields modeling sequence boundaries with incised valleys is more complex and required the development of a novel object modeling technique this new model can be used to generate realistic valley geometries and is flexible enough to allow for complex multiwell conditioning the modeling procedure is illustrated using a test data set based on well interpretations from the fluvial statfjord formation in the statfjord field of the norwegian north sea the main reservoir sandstones were deposited in valleys defined by a sequence boundary at the base and a flooding surface at the top whereas the main barriers to flow are mudstone rich intervals deposited on unconfined alluvial plains five sequence boundaries and four flooding surfaces have been interpreted within an approximately 60 m thick reservoir interval simulation of these surfaces using the new modeling procedure defines the three dimensional distribution of reservoir units and barriers the modeling procedure allows the simulation of realistic geometries that are in accordance with the geologist s conceptual model for the reservoir the models also provide an enhanced description of reservoir distribution and connectivity and can serve as an improved basis for reservoir management well placement and predictions of reservoir performance in complex fluvial reservoirs

comparison of site response characteristics inferred from microtremors and earthquake shear waves we investigated the validity of seismic site response characteristics es timated from microtremors by comparing them with those of earthquake motions for this purpose we observed microtremors as well as earthquake motions using large 5 km diameter and small 0 5 km diameter arrays deployed on soft sedi ments specifically we examined four estimates from microtremors relative site amplification factors to incident shear waves site amplification factors by the naka mura method resonance frequency in horizontal to vertical spectral ratios and horizontal to vertical spectral ratios as a result of the comparisons we obtained the following conclusions the relative amplification factors can be inferred from horizontal component ratios of microtremors to a reference site within a small area of several hundred meters the horizontal to vertical spectral ratios inferred by the nakamura method partly reflect site amplification factors but do not agree with site amplification factors a sharp peak frequency in the horizontal to vertical spectral ratios is possibly the resonance frequency the horizontal to vertical spectral ratios of microtremors either agree with those of earthquake motions at some array sites or are slightly smaller at the other sites

nitrates as indicators of aquifer interconnection application to the campo de dalias se spain relatively high concentrations of no3 usually have their origin in processes of organic pollution and excessive use of inorganic fertilizers in the case of agricultural areas these activities may generate great quantities of nitrates this fact has enabled us to use the nitrate ion to characterize an exploited aquifer unit of a very complex aquifer system as is the case for the campo de dalias aquifer system se spain the shallow boreholes which draw water from intensively cultivated superficial formations yield waters with a high no3 content when the boreholes are deeper and penetrate low permeability formations in the superficial layers the waters contain little no3 similar to what happens in areas of recharge where agricultural activities are absent in addition using longitudinal sections it is possible to demonstrate the possible existence of connections between superficial and deep aquifers using no3 as a tracer similarly one can locate those sectors responsible for contamination caused by the poorly lined boreholes themselves when they perforate more than one aquifer in a multiple aquifer formation

seawater intrusion and associated processes in a small coastal complex aquifer castell de ferro spain an attempt to identify the hydrogeochemical processes that accompany current or past intrusion of seawater in the castell de ferro coastal aquifer se spain was made using ionic deltas ionic ratios and saturation indices alluvial and coastal quaternary sediments and triassic marbles constitute this complex aquifer cation exchange dolomitization and calcite dissolution were identified as operating in the aquifer the cation exchange processes in the detrital materials are different from those in the marbles in addition it was determined that while the processes of marine intrusion associated with periods of low groundwater levels still persist in the detrital aquifer in the carbonate sector the flushing process characteristic of wetter conditions has begun

hydrogeochemical processes in the groundwater environment of muktsar punjab conventional graphical and multivariate statistical approach understanding the hydrogeochemical processes that govern groundwater quality is important for sustainable management of the water resource a study with the objective of identifying the hydro geochemical processes and their relation with existing quality of groundwater was carried out in an intensively cultivated district of punjab india the study approach includes conventional graphical plots and multivariate analysis of the hydrochemical data to define the geochemical evaluation of aquifer system based on the ionic constituents water types hydrochemical facies and factors controlling groundwater quality the results suggest that different natural hydrogeochemical processes like simple dissolution mixing weathering of carbonate minerals locally known as kankar silicate weathering and ion exchange are the key factors in the pre monsoon which was superseded by leaching processes loaded with anthropogenic inputs in the post monsoon limited reverse ion exchange has been noticed at few locations of the study area especially in pre monsoon periods there was a significant effect of monsoon observed in terms of hardness and the significant amount of area with temporary hardness ca2 mg2 hco 3 type in the pre monsoon switched to permanent hardness domain i e ca2 mg2 cl type by the post monsoon at most factor analyses substantiate the findings of conventional graphical plots and provide greater confidence in data interpretation thus the study highlights the descriptive capabilities of conventional and multivariate techniques as effective tools in groundwater evaluation