p wave velocity anisotropy related to sealed fractures reactivation tracing the structural diagenesis in carbonates abstract fracture properties are important in carbonate reservoir characterization as they are responsible for a large part of the fluid transfer properties at all scales it is especially true in tight rocks where the matrix transfer properties only slightly contribute to the fluid flow open fractures are known to strongly affect seismic velocities amplitudes and anisotropy here we explore the impact of fracture evolution on the geophysical signature and directional v p anisotropy of fractured carbonates through diagenesis for that purpose we studied a meter scale parallelepiped quarry block of limestone using a detailed structural and diagenetic characterization and numerous v p measurements the block is affected by two en echelon fracture clusters both being formed in opening mode mode 1 and cemented but only one being reactivated in shear we compared the diagenetic evolution of the fractures which are almost all 100 filled with successive calcite cements with the p wave velocities measured across this meter scale block of carbonate which recorded the tectonic and diagenetic changes of a south provence sedimentary basin we found that a directional v p anisotropy magnitude as high as 8 16 correlates with the reactivated fractures cluster dip angle which is explained by the complex filling sequence and softer material present inside the fractures that have been reactivated during the basin s tectonic inversion we show that although a late karstification phase preferentially affected these reactivated fractures it only amplified the pre existing anisotropy due to tectonic shear we conclude that v p anisotropy measurements may help to identify the fracture sealing opening processes associated with polyphased tectonic history the anisotropy being independent of the current stress state this case shows that velocity anisotropies induced by fractures resulted here from a cause that is different from how these features have often been interpreted selective reactivation of sealed fractures clusters rather than direction of currently open ones

a model for flow in the chalk unsaturated zone incorporating progressive weathering summary groundwater from unconfined chalk aquifers constitutes a major water resource in the uk the unsaturated zone in such systems plays a crucial role in the hydrological cycle determining the timing and magnitude of recharge and the transport and fate of nutrients however despite more than three decades of study our physical understanding of this system is incomplete in this research state of the art instrumentation provided high temporal resolution readings of soil moisture status rainfall and actual evaporation from two sites in the pang and lambourn catchments berkshire uk for a continuous two year period 2004 5 a parsimonious physically based model for the flow of water through the chalk unsaturated zone including a novel representation of the soil and weathered chalk layers was developed the parameters were identified by inverse modelling using field measurements of water content and matric potential the model was driven by rainfall and evaporation data and simulated fluxes throughout the profile including the discrete matrix and fracture components down to the water table but not the water table response results showed that the model was able to reproduce closely the observed changes in soil moisture status recharge was predominantly through the matrix and the recharge response was strongly attenuated with depth however the activation of fast recharge pathways through fractures in the chalk unsaturated zone was highly sensitive to rainfall intensity relatively modest increases in rainfall led to dramatically different recharge patterns with potentially important implications for groundwater flooding the development and migration of zero flux planes with time and depth were simulated the simulations also provided strong evidence that for water table depths greater than 5 m recharge fluxes persist throughout the entire year even during drought conditions with important implications for the calculation of specific yield from baseflow estimates and the representation of recharge in groundwater models

a statistical analysis of bottom hole temperature data in the hinton area of west central alberta abstract considerable differences in the spread of bottom hole temperature values from petroleum exploration well logs plotted as a function of depth are observed over a region of west central alberta the spatial variation of the spread is investigated and it is found to be greater toward the rocky mountain disturbed belt in the west the spatial variation there does not seem to correspond directly to local topography and may be partly due to faults or fractures and related water movement or other causes it also seems to coincide with the geothermal gradient anomaly reported by lam et al 1982 the variation of the spread is considered in terms of the extent to which subsurface isothermal surfaces follow variations in local topography

impact of sedimentology and diagenesis on the petrophysical properties of a tight oolitic carbonate reservoir the case of the oolithe blanche formation bathonian paris basin france the oolithe blanche formation was studied in three quarries located at the south eastern edge of the paris basin france heterogeneities in reservoir properties were assessed through a sedimentological diagenetic and petrophysical study the relationships between depositional settings diagenesis and petrophysical properties were analysed using detailed petrographic studies image analysis nano ctscans and petrophysical measurements the carbonate reservoir pore network is mainly controlled by intraparticle microporosity which ensures the connectivity with interparticle meso and macroporosity early cementation vs early compaction processes mainly grain interpenetration may have considerable influence on fluid flow properties and parameters such as permeability acoustic velocities and tortuosity better reservoir properties are found when compaction processes begin before cementation from statistical analyses e g principal component analysis and linear discriminant analysis a sedimentological diagenetic and petrophysical model is proposed that is in a good agreement with the geological model developed from field work

a review of the nature and origin of limestone microporosity abstract limestone microporosity is ubiquitous and extensively developed in most phanerozoic limestones from an economic perspective microporosity is important because it contributes substantially to the carbonate pore system which can host significant volumes of water and hydrocarbons therefore determining the presence and distribution of limestone micropores is necessary for accurate hydrocarbon estimations reservoir characterization and fluid flow simulations from an academic standpoint microporosity is important because its genesis is intimately linked with the mineralogical stabilization of metastable sediments a fundamental process in carbonate diagenesis many types of micropores contribute to what has been referred to as microporosity but the vast majority is hosted among low magnesium calcite lmc microcrystals that are present in limestone matrix and allochems geochemical textural and mineralogical data from natural settings and laboratory experiments indicate that lmc microcrystals are diagenetic in origin more specifically these data support a diagenetic model of mineralogical stabilization that involves dissolution of precursor sediments dominated by aragonite and high magnesium calcite hmc minerals and precipitation of lmc microcrystal cements the stabilization process is inferred to take place in the meteoric marine and burial diagenetic realms although it has not been directly observed carbon and oxygen isotopes as well as trace element data suggest that lmc microcrystals form during burial diagenesis in marine like fluids evidence suggests that porosity is not generated during this dissolution precipitation process but rather inherited from the precursor sediments the final arrangement of the micropores in a limestone however depends on the precise diagenetic pathway lmc microcrystals exhibit a range of microcrystalline textures that are classified on the basis of crystal morphology and size the three main textural classes granular framework fitted mosaic and clustered have been recognized across a wide range of ages depositional settings burial depths and precursor types and are characterized by distinct petrophysical properties such as porosity permeability and pore throat size observations from modern sediments also support the hypothesis that lmc microcrystals develop from aragonite and hmc dominated lime mud the origin of lime mud has been extensively studied but still highly debated of particular interest to the discussion of microporosity are proposed secular variations in the dominant mineralogy of carbonate sediments through the phanerozoic microporous limestones comprised of lmc microcrystals are equally abundant during times of aragonite seas and calcite seas which suggests that no special mineral precursor is required microporous textures are also observed in deep marine chalks where micropores are hosted between chalk constituents unlike shallow marine limestones deep marine sediments start out as mostly lmc therefore mineralogical stabilization is not a significant process in chalk diagenesis

recharge of the upper chalk aquifer at a site in hampshire england 2 solute movement abstract this paper describes a field experiment to study the movement of solutes through the unsaturated zone of the chalk using soil physical techniques to calculate water fluxes and sequential soil coring to measure solute concentrations with depth and time deuterium oxide was used as a tracer to follow water movement nitrate leaching beneath spring barley was calculated below the root zone approximately 40 kg ha 1 yr 1 of nitrate nitrogen were leached beyond root depth 1 m in the two study years at concentrations of between 20 and 75 mg l 1 and at a downward velocity of 0 85 m yr 1

timing and chemistry of igneous events associated with the southern oklahoma aulacogen abstract igneous activity in the southern oklahoma aulacogen of north america was concentrated in the early rifting stages of aulacogen development the time span over which liquids rose may not have exceeded 50 m y and certainly terminated before the upper cambrian igneous activity began with three basaltic liquids stratigraphically identifiable but perhaps not all distinct genetically this was followed by one large rhyolitic granitic episode of a type character one final basaltic event ended the activity all the basaltic types seem to be tholeiitic showing more kinship with either the older proterozoic north american midcontinental rift or the northern part of the cenozoic rio grande rift than the cenozoic east african rift two major uplifts occurred one between the earlier basalts and the rhyolite and one much later after all igneous activity was over in the pennsylvanian

thermal structure of the anadarko basin the anadarko basin of oklahoma is a two stage paleozoic cratonic basin with as much as 12 km 7 5 mi or more of sedimentary fill we present a present day thermal model of the basin based on lithologic analysis at 3 m 10 ft intervals in 63 wells heat flow measurements at seven sites and in situ thermal conductivity calibration of the sediment section at two sites we do not use bht bottom hole temperature information in the process but we do at the end of the process compare the independently predicted temperatures to bht information the in situ calibration of thermal conductivity was accomplished using detailed temperature logs and represents a new practical application for evaluating basin thermal characteristics shale exerts the most control on the temperature distribution because it is the most abundant lithology and has the lowest thermal conductivity shale comprises 47 by volume of rock in the basin and represents 75 of total thermal resistance directly related to temperature gradient therefore shale dominates the thermal structure of the basin thus the problems in sampling and in characterizing the in situ thermal conductivity of shale from laboratory measurements represent a major limitation in basin thermal analysis we use the in situ calibration approach as a way to address the difficulty the temperatures calculated do not mimic the structure of the sediments i e the hottest area on a given age horizon in the lower paleozoic is not in the most deeply buried part of the anadarko basin the combination of decreasing heat flow toward the wichita mountains and the facies changes in the pennsylvanian units from marine shale low thermal conductivity in the basin to the granite wash high thermal conductivity toward the uplift results in the highest temperatures being displaced about 50 km 31 mi northward into the basin the pattern of vitrinite reflectance in the woodford shale is virtually identical to the present day reconstructed temperature pattern therefore we conclude that the thermal pattern is and has been dominated by conductive heat transport

the geothermal regime of the northern yukon and mackenzie delta regions of northwest canada studies of two regional profiles temperature data from deep petroleum exploration wells and thermal conductivity estimates based on net rock analysis data have been used to make terrestrial heat flow estimates along two profiles across the sedimentary strata of the mackenzie delta northern yukon and offshore beaufort sea regions

coal rank and burial history of cretaceous tertiary strata in the grande cache and hinton areas alberta canada implications for fossil fuel exploration the present study discusses coal rank and burial histories for cretaceous tertiary coal measures and thermal maturity of associated source rocks coal rank ranges from subbituminous to semianthracite coalification maps for selected coal zones indicate a broad coalification maximum east of the deformed belt in the pocahontas brule and hinton areas rank levels appear to be elevated locally due to geothermal anomalies thermal modelling indicates that the westward decrease of coal rank in lower cretaceous strata is related to a westward decrease in the duration of burial beneath maastrichtian eocene foreland basin deposits upper cretaceous tertiary strata were subjected to relatively low geothermal gradients 20 c km whereas lower cretaceous strata were exposed to much higher gradients up to 46 c km tectonic loading in the foothills had only a minor impact on coalification at obed marsh alberta syncline thermal modelling suggests that deformation in the thrust belt continued for at least

pore space evolution and elastic properties of platform carbonates urgonian limestone barremian aptian se france abstract a dataset of 214 ultrasonic velocity and porosity measurements on barremian aptian carbonates from provence se france provides well constrained velocity porosity transforms and allows the quantification of the impact of pore type and diagenetic history on these velocities a numerical approach epar equivalent pore aspect ratio was used to link diagenetic transformations pore network evolution and elastic properties three categories of samples characterized by their dominant pore type were discriminated from the velocity and porosity database by means of the epar values derived from bulk k epar and shear epar moduli 1 purely microporous limestones low k and epar 0 3 three velocity porosity trajectories related to three diagenetic paths were defined and quantified from the urgonian database 1 epar preserving micro scale cementation of micrite 2 non epar preserving dissolution with moldic pore development and 3 epar preserving sparry calcite cementation of molds equivalent pore aspect ratio can therefore be regarded as a robust tool to decipher diagenetic trends in velocity porosity transforms and may help predicting pore architecture from subsurface data

effect of supercritical co2 on carbonates savonnieres sample case study co2 geosequestration is an efficient way to reduce greenhouse gas emissions into the atmosphere carbonate rock formations are one of the possible targets for co2 sequestration due to their relative abundance and ability to serve as a natural trapping reservoir the injected supercritical co2 can change properties of the reservoir rocks such as porosity permeability tortuosity and specific surface area due to dissolution and precipitation processes this in turn affects the reservoir characteristics i e their elastic properties storage capacity stability etc the tremendous progresses made recently in both microcomputed x ray tomography and high performance computing make numerical simulation of physical processes on actual rock microstructures feasible however carbonate rocks with their extremely complex microstructure and the presence of microporosity that is below the resolution of microcomputed x ray tomography scanners require novel quite specific image processing and numerical simulation approaches in the current work we studied the effects of supercritical co2 injection on microstructure and elastic properties of a savonni eres limestone we used microtomographic images of two savonni eres samples i e one in its natural state and one after injection and residence of supercritical co2 a statistical analysis of the microtomographic images showed that the injection of supercritical co2 led to an increase in porosity and changes of the microstructure i e increase of the average volume of individual pores and decrease in the total number of pores the co2 injection residence also led to an increase in the mean radii of pore throats an increase in the length of pore network segments and made the orientation distribution of mesopores more isotropic numerical simulations showed that elastic moduli for the sample subjected to supercritical co2 injection residence are lower than those for the intact sample

a simple model of variable residence time flow and nutrient transport in the chalk summary a basic problem of modelling flow and transport in chalk catchments arises from the existence of a deep unsaturated zone with complex interactions between flow in fractures and water held in the fine pores of the rock matrix the response of the water table to major infiltration episodes is rapid of the order of days however chemical signals are strongly damped suggesting that this water is of varying age with a corresponding mixed history of nutrient loading clearly this effect should be represented in any model of nutrients in chalk systems the applicability of simplified physically based model formulations to represent the dual response in an integrated way has been investigated by a variety of researchers but it has been shown that these approximations break down in application to the chalk mathias et al mathias s butler a p jackson b m wheater h s this issue characterising flow in the chalk unsaturated zone in wheater h s peach d neal c editors hydrology on locar in the pang lambourn special issue of j hydrol doi 10 1016 j jhydrol 2006 04 010 present a dual permeability model that explains the observed response but such complex formulations are not readily incorporated in catchment scale nutrient models this paper reviews previous approaches to modelling the chalk and then presents a pragmatic approach with transport of solute and water through the unsaturated zone treated separately and combined at the water table varying residence times are included through considering the distance between the water table and the soil surface and the history of nutrient application at the surface if an average rate of downwards migration of the nutrients is assumed it is possible to derive a travel time distribution of nitrate transport to the water table using a dtm digital terrain model map of elevation and information on groundwater levels this distribution can then be implemented through difference equations the rationale behind the model and the resulting algorithm is described and the algorithm then applied to a hypothetical case study of nutrient loading located in the lambourn a groundwater dominated chalk catchment in southern england simulated groundwater concentrations are very similar in magnitude and variability to observed chalk groundwater series suggesting that this simple conceptual model may well be able to capture the dominant responses of nutrient transport through the chalk

thermal state in the north viking graben north sea determined from oil exploration well data we can deduce thermal conductivities and thermal gradients from extensively available oil exploration data geophysical well logs cores cuttings formation thicknesses and temperatures thermal conductivity is predicted at three significant scales first it is computed at the scale of well log electrofacies thicknesses from 1 to 10 m using a geometric mean model calibrated on laboratory measurements made on the main sedimentary rocks the electrofacies conductivity is calculated as a function of the mineralogy the porosity and the saturating fluids second it is estimated at formation scale at each well site thicknesses from 100 to a few thousand meters using a serial model that accounts for the anisotropy due to sediment stacking and for temperature effects finally for each formation thicknesses on the order of 1 km the average conductivity field is mapped at basin scale extent on the order of 100 km using a geostatistical treatment accounting for lateral facies and or porosity changes fo

geothermal gradients in the steen river area of northwestern alberta abstract a total of 6540 bottom hole temperature values from 1879 petroleum exploration wells in northwestern alberta in the region 57 n 60 n and 114 w 120 w have been used to estimate temperature gradients there a thermal gradient contour map constructed for the region shows a number of local high geothermal gradient areas comparison with available aeromagnetic and gravity maps indicates that a high geothermal gradient near steen river is probably associated with an igneous intrusion and that nearby high geothermal gradient areas may be due to the transport of heat away from the basement by upward and lateral water motion also it is noted that in this region of alberta oil field locations appear to coincide with areas of low geothermal gradient whereas gas fields appear to coincide with high geothermal gradients

four year comparison of water contents beneath a grass ley and a deciduous oak wood overlying triassic sandstone in lowland england summary differences in the seasonal water dynamics of a sand soil overlying triassic sandstone have been investigated to a depth of 9 m beneath both a grass ley and a pendunculate oak woodland within clipstone forest nottinghamshire england fortnightly measurements with a neutron probe over a four year period allowed a comparison of the soil rock water content to depths rarely reported in spring the rate of decrease of water content of the uppermost 2 m of soil was much greater under grass than oak woodland in contrast the rate of decrease under oak was greater after leafing out in may while the rate of rewetting in early autumn was lower for this land use until senescence and leaf fall in late autumn in the uppermost 2 m of soil a depth that includes all plant roots the soil moisture minima were between 47 and 58 mm lower under oak than grass in each year of monitoring as a result of both these drier conditions and the comparatively late leaf fall of this species penetration of the winter season wetting front to 2 m was delayed by between one and three months at the oak site relative to grass in years of near average rainfall rewetting at 9 m lags by 10 12 months compared to the surface giving an average penetration rate for the wetting front to this depth of 25 30 mm day 1 with little observable differences between the land uses preferential flow is evident under both sites affecting the profile to 3 m in all years and to at least 6 m following winters experiencing exceptional rainfall

terrestrial heat flow density estimates for the jeanne d arc basin offshore eastern canada corrected bottom hole temperatures from 35 wells together with measured and assumed rock thermal conductivities are used to estimate linear geothermal gradients and effective thermal conductivities in the jeanne d arc basin in offshore eastern canada heat flow density values calculated for each well location indicate that heat flow density is slightly higher in the deeper northern part of the basin than in the southern part it appears that the heat flow density distribution is affected by fluid motion within the sediments and not by heat generation or basement topography dehydration is suggested as the mechanism that produces the fluid flow pattern that influences the heat flow density distribution in the basin and a simple fluid flow model of the jeanne d arc basin is presented

effects of microporosity on sonic velocity in carbonate rocks the elastic moduli of a rock are affected by three main factors pore fluid rock framework and pore space in carbonate rocks the latter two factors are a function of the depositional environment and the diagenetic history cementation recrystallization and dissolution processes can change the mineralogy and texture of the original framework and thereby alter the original grain to grain contacts and or occlude pore space dissolution processes can enlarge interparticle pore space or dissolve grains entirely thereby increasing porosity these diagenetic alterations and associated changes in the rock frame and pore structure result in a wide velocity range at a given porosity

relating background fractures to diagenesis and rock physical properties in a platform slope transect example of the maiella mountain central italy abstract fractured reservoirs are of prime interest as fracture networks control most of the fluid flow and or accumulation however characterizing 3d fracture patterns from subsurface data remains challenging studying fractures on outcrops is a good substitution to 1d data from subsurface exploration tools in addition outcrops allow deciphering the nature origin and conditions for fracture formation through the geodynamic history in this paper we aim at characterizing the true 3d fracture patterns and determining the genetic role of facies diagenesis and rock physical properties we targeted a platform slope transect within a carbonate reservoir analog the maiella mountain in central italy where implications for analog hydrocarbon reservoir can be discussed fracture patterns are sorted based on geometric and kinematic criteria from field measurements and petrographic analyzes on thin sections sedimentary facies pore types and rock physical properties have been characterized in order to establish the impact of early diagenesis on rock evolution diagenetic sequences have been unraveled and correlated to the fractures fracture sequences have been determined considering the cross cutting relationships and compared with burial uplift history in the two studied formations platform and slope carbonates we interpret a stage of fracturing perpendicular to bedding formed at shallow depth and occurring prior to major regional tectonic events the studied carbonates have undergone early diagenesis during fast and shallow burial conferring early brittle behavior the amount of stylolites is not correlated to burial depth but to fracture density porosity and free air p wave velocity it means that fracture development mechanical and petrophysical properties are acquired during early diagenesis both studied formations have undergone the same geodynamic history and their brittle response is different and not related to folding but to burial and early cementation deciphering the close relationship between sedimentary facies diagenetic and geodynamic history has allowed unraveling the controling factors on rock properties and therefore on fracture pattern

estimation of natural groundwater recharge in the karoo aquifers of south africa abstract a 3 year project to study the natural groundwater recharge of aquifers in the semi arid karoo formations of south africa was undertaken two typical karoo aquifers at dewetsdorp and de aar were selected for study purposes data were collected from both the saturated and unsaturated zone neutron probe measurements showed that there was no increase in the water content beneath a depth of 1m below the surface even with the exceptionally high rainfall in february 1988 neutron measurements indicated that very little soil matrix flow occurred which implied that most of the recharge occurred along preferred pathways a triangular finite element network was used to determine the relative saturated volume fluctuations svf of the aquifers from the observed water level changes over a period of time which allowed determination of the storativity s and the recharge the main advantage of the method lies in determining recharge and storativity which are both unknowns in the water balance equation and which both contribute to the water level response the svf method showed that the recharge in the karoo formations of south africa varies between 2 and 5 of the annual rainfall in areas which are overlain by a thick soil cover the recharge is less than 3 while recharge in hilly areas with a thin soil cover may be of the order of 5

advances in modelling groundwater behaviour in chalk catchments groundwater in chalk catchments is a major resource that also helps support internationally important habitats and ecosystems its dual porosity and dual permeability properties coupled with large scale structural features such as hard rock layers and marls produce a highly complex hydrogeological system recent impacts from groundwater flooding as well as vulnerability to drought have raised questions over the ability of traditional approaches to model these aquifers current work on near surface hydrological processes has highlighted the importance of the soil and weathered zone for controlling recharge rates in addition karst like features sedimentary deposits and valley bottom processes govern stream aquifer interaction and present a challenge in their representation in any modelling system methods that have and are being developed to incorporate these features and their use in modelling chalk catchments are described these are required in order to address major challenges such as groundwater flooding and drought impacts both of which could become more frequent and intense as a result of climate change

spatial heterogeneity of high resolution chalk groundwater geochemistry underground quarry at saint martin le noeud france chalk groundwater is an important aquifer resource in france because it accounts for a production of 12 million m3 y 1 with a large proportion reserved for drinking water processes occurring in the unsaturated zone uz and the overlying superficial formations have a high impact on chalk groundwater geochemistry and require better understanding the study site is a former underground chalk quarry located near beauvais france that extends over 1200 m in length at a depth ranging from 20 to 30 m the water table intersects the cavity creating 15 underground lake that give access to the chalk groundwater lakes geochemistry has been studied water samples were collected in july 2013 and major ion concentrations were analyzed uz and clay with flints thickness above each lake were estimated qualitatively using an electromagnetic sensor em31 and underground gps the results unexpectedly showed that groundwater quality varied widely in spatial terms for both allochthonous and autochthonous ions e g hco3 ranged from 2 03 to 4 43 meq l 1 no3 ranged from 0 21 to 1 33 meq l 1 principal component analysis indicated the impact of agricultural land use on water quality with the intake of no3 as well as so42 cl and ca2 chalk groundwater geochemistry is compared with the nature and structure of the uz we highlight correlations 1 between thick clay with flints layers and the ions mg2 and k and 2 between uz thickness and na in conclusion this paper identifies various ion sources agriculture clay with flints and chalk and demonstrates different processes in the uz dissolution ionic exchange and solute storage

experimental investigation of solute transport in unsaturated fractured rock an experiment is designed to perform tracer tests in an unsaturated fractured rock with a horizontal fracture data from an intact and an artificial sandstone sample was collected and used to discuss the effect of the fracture on tracer migration the delay time of the tracer in the fracture was further determined in terms of the fracture aperture involved an alternative electrical conductivity or electrical resistance method was developed to measure the change in the tracer concentration with time and space the method causes no disturbance to the flow and concentration fields and is convenient to use the test results show the fluctuations in the tracer concentrations and there were 2 3 peak values of concentration in the monitored sections related to the heterogeneity of the water content and pore distribution also the fracture was found to delay migration of the tracer before it is filled with the tracer solution and quicken the velocity of migration afterwards this results in accumulation of the tracer near the fracture furthermore the delay time of the tracer increases with fracture aperture in a nonlinear manner

estimation of groundwater recharge to chalk and sandstone aquifers using simple soil models abstract on the assumption that the water draining below the root zone is potentially available for groundwater recharge two current uk methods for estimating annual groundwater recharge have been compared with a new soil model using data from four sites under permanent grass in the uk two sites representative of the chalk aquifer at bridgest farm hampshire and fleam dyke cambridgeshire and two sites on the triassic sandstone at bicton college devon and bacon hall shropshire a four root layers model frlm the penman grindley model and the uk meteorological office rainfall and evaporation calculation system morecs were used the new soil model was run with potential evaporation as input both from the morecs and from the penman monteith equation the models were run for the chalk sites both with and without a bypass flow of 15 of rainfall bypass was not considered for the sandstone sites the performance of the models was tested against neutron probes measurements of soil moisture deficits in addition the annual groundwater recharge estimated from the models was compared with the published values obtained from the zero flux plane method generally the penman grindley model was more successful in predicting the time for soil to return to its field capacity than in predicting the magnitude of the soil moisture deficit the annual groundwater recharge was predicted with reasonable accuracy the morecs relatively tended to overestimate the soil moisture deficits and to delay the time at which the soil returns to its field capacity the consequences were underestimates of annual groundwater recharge owing either to the higher values of potential evaporation calculated from the morecs or tothe high available water capacity values associated with the soils under consideration the new soil model frlm predicts the soil moisture deficits successfully and hence is reliable in estimating the annual groundwater recharge the model is capable of doing this with potential evaporation input calculated either from the morecs or from the penman monteith equation the model also demonstrated that the inclusion of 15 of rainfall as bypass flow is viable for chalk sites

acoustic properties of ancient shallow marine carbonates effects of depositional environments and diagenetic processes middle jurassic paris basin france abstract examination of petrophysical properties acoustic velocity porosity permeability and density and petrographical characteristics texture facies composition and diagenesis of more than 250 core plugs from the middle jurassic carbonates of the eastern paris basin provides insights into the parameters controlling acoustic velocities in relatively low porosity carbonate rocks 20 the pore type observations reveal distinct acoustic velocities in samples with intergranular macropores and samples with micropores in subhedral micrite such that velocities in microporous mudstone wackestone lagoonal deposits are greater than in macroporous grainstone shoal samples at a given porosity range 15 20 the standard wyllie and raymer transforms fit very well with the linear regression between acoustic velocity and porosity from mudstone or lagoonal facies marls and fine grained deposits interpreted as lagoonal facies include statistically significant correlation r 0 9 between velocity and porosity however the data suggest that the wide scatter in velocity porosity relationship from grainstones are not the result of different sorting grain size pore type dolomite content or clay content instead early cementation greatly influences acoustic properties during diagenesis and are interpreted to account for the high variability of velocities over a given porosity range specifically at a given porosity acoustic velocities in compacted grainstone that did not undergo early cementation are higher than in early cemented grainstone petrographic observations suggest that early cementation limits mechanical compaction creating a heterogeneous medium from the earliest stages of diagenesis non touching grains preservation of intergranular macropores that are partially to totally filled by later blocky calcite cement the abundant interfaces between micritized ooids early cement fringes and blocky calcites in grainstones may induce significant wave attenuation as a result the standard time average equations fail to predict the effect of diagenetic features such as early cementation on sonic velocity conversely an absence of early cementation favors mechanical compaction grain to grain contact and suturing the result is a homogeneous micritized grain supported network that may facilitate wave propagation through demonstration of the key role of early cementation in the explanation of variability in acoustic properties the results of this study illustrate the complicated factors influencing velocity transforms in carbonates wyllie and raymer i e classical tools for predicting reservoir properties these insights on the interpretation of vp and the refinement of velocity porosity transforms in grainstone units may be broadly applicable to enhancing seismic based exploration in carbonate successions

geothermics of the williston basin in canada in relation to hydrodynamics and hydrocarbon occurrences over 8 400 bottom hole temperature bht values from the canadian part of the williston basin were analyzed and a temperature high was discovered in the weyburn area of southeastern saskatchewan geothermal gradients thermal conductivities and heat flow have been investigated for most of the mesozoic cenozoic clastic unit as well as the upper paleozoic carbonate evaporite unit regional heat flow variations with depth occur which are closely related to the hydrodynamics governed by the topography and geology the blanketing effect of low conductivity shaly formations may cause a temperature anomaly in the south where the thickest phanerozoic cover exists however the weyburn high can be explained only partially in this way hydrodynamics has also contributed to formation of the temperature anomaly there the process of forming the anomaly by the blanketing effect and hydrodynamics also contributed to oil deposition there is a correlation between mississippian oil occurrences in the southeastern part o

north american central plains conductivity anomaly goes east the north american central plains electrical conductivity nacp anomaly has been known for almost two decades and its influence on palaeotectonic models of the north american continent has been significant magnetometer array studies have located the structure in a gross sense but there has not been until now a comprehensive magnetotelluric mt survey of it in this letter we report on the preliminary interpretation of data from thirty five mt sites recorded along a 400 km east west profile just north of the us canadian border we show that the anomaly at this latitude is 75 km farther east of the location previously mapped by the array studies modelling indicates that the conductive body has its top surface at about 10 km depth and appears to be anticlinal in shape the profile also extends sufficiently east that it traverses another previously known electrical structure referred to herein as the tobe anomaly we consider briefly other geophysical and geological data for the region and tentatively infer that the nacp structure is terminated to the east by the interpreted southern extension of the tabbernor fault fold system and that the tobe anomaly is an expression of the known southern extension of the thompson nickel belt both beneath phanerozoic sediments of the williston basin

laboratory measurements of the acoustic and transport properties of carbonate rocks and their link with the amount of microcrystalline matrix laboratory data and computer tomography ct scan image analysis of carbonate rocks were combined demonstrating a quantitative link between acoustic and transport properties the fraction of microcrystalline calcite micrite in the matrix and the grain to micrite matrix ratio samples from the monte acuto formation gargano italy a transgressive system tract tst whose microstructure ranges from basal pelagic mudstones to coarse calciturbidites were analyzed results indicate that high micrite rocks with low grain to micrite matrix ratios typical of low energy depositional settings are relatively stiffer and more impermeable in contrast lower amounts of micrite due to high energy depositional settings or its removal from intergranular macropores by progressive leaching of the matrix leads to high grain to micrite matrix ratios this process will increase porosity and reduce rock stiffness both of which reduce velocity decreasing micrite content correlates well with increasing macroporosity

mechanisms of groundwater recharge and pesticide penetration to a chalk aquifer in southern england abstract in order to assess the potential for enhanced agrochemical contamination of shallow groundwaters a field study was established on the upper chalk in hampshire uk two instrumented sites 380 m apart were established on a hillslope one on the interfluve with a deep water table 18 m depth the other on the dry valley bottom where the groundwater was close to the surface 4 m depth hourly measurements of water potentials in the unsaturated zone to 3 0 m depth identified very different groundwater recharge processes between the two sites in response to the same storm event on the interfluve site with the deep water table only matrix flow through the chalk unsaturated zone at 3 m depth was identified in contrast at the dry valley bottom with a shallow water table both rapid preferential flow and matrix flow processes were observed at a 3 m depth the correlation between groundwater depth measurements and unsaturated profile moisture content measurements demonstrated the importance of the capillary fringe in sustaining a higher moisture content in the unsaturated zone at the shallow groundwater site the resulting reduced water storage capacity for vertical drainage fluxes meant that little water was required to wet the shallow profile before rapid preferential flow events demonstrated by rapid water potential responses occurred however where the groundwater was deeper intermediate storage sites located on chalk surfaces and at chalk ped block contact points remained empty and unsaturated water potential profiles showed that rainfall pulses were attenuated as these sites absorbed the downward water fluxes consequently preferential events at these deep groundwater sites are rare the importance of these intermediate storage sites in controlling recharge processes is highlighted the potential mass load of pesticide transported to the shallow groundwater in preferential events during 1996 7 was determined using bromide tracer studies water balance calculations and measured groundwater pesticide concentrations an estimated 0 1 of the applied pesticide reached the shallow groundwater along preferential pathways in 1996 7 calculations under a worst case scenario showed that this value did not increase beyond 0 2 of pesticide applied

modeling dynamic elastic properties of compacting chalk reservoirs using an integrated rock physics workflow a case study in the ekofisk field norway an integrated rock physics modeling workflow is discussed that aims at predicting the effective elastic moduli and density of a producing reservoir in response to pressure porosity and fluid saturation changes and that is suitable for application to compacting chalk reservoirs a simple extended form of nur s modified voigt model is used to build the dry rock elastic modulus and porosity relationship granular medium contact theory is used to model pressure change and gassmann s equation is used to model the fluid effect a dynamic compaction model from reservoir simulation is used to model porosity change due to compaction the rock physics model is calibrated at well locations from the ekofisk field in the north sea however the absence of time lapse logging makes the 4d calibration challenging effective fluid properties are calculated dynamically with the fluid acoustics for geophysics flag software program using inputs from the reservoir simulator and pvt measurements for low water saturatio

a comment on a magnetovariational study of a geothermal anomaly by m r ingham d k bingham and d i gough in a recent paper ingham bingham cough 1983 report a geomagnetic induction anomaly which is coincident with a geothermal gradient anomaly discovered by lam jones lambert 1982 in the hinton edson region of alberta canada the position of the threecomponent magnetometer array was over a geothermal gradient anomaly whose axis according to lam et al 1982 strikes in a ne sw direction lngham et af 1983 find that their measurements are consistent with an electrical conductivity anomaly whose top is perhaps 10 km deep and which extends to great depth they suggest that the correlation between the geomagnetic induction anomaly and the geothermal gradient anomaly supports the inference that both are due to the presence of partial melt in the crust this interpretation is alternative to the suggestion given by lam er a 1982 that the thermal anomaly may be the result of the migration of heated water from west of the miette region along the south westward dipping fault planes at great depths of 3 4 km the area of elevated geothermal gradient between hinton and edson was found by lam el a 1982 on the basis of a study of bottom hole temperatures bhts from exploration well logs the average geothermal gradient values were determined from the slope of the least squares fitted straight line from each temperature depth plot in 3 x 3 township range areas and assigned to the centre of that area each area is equal to 28 8 x 28 8 km2 the dominion land survey system used in alberta the temperature depth plots were constructed from bht data which came from large depth intervals characterized by the sedimentary rocks of different thermal conductivities and under different hydrodynamic conditions most probably this is why the standard error of estimate of a theoretical regression of temperature against depth is large and equals 10 c in the study area also in most cases the average geothermal gradients in the study area were determined on the basis of bht values from depths greater than 1 km although lam et a 1982 treated the hinton edson thermal gradient high as a local anomaly from fig 1 it can be seen that it is part of a much larger high geothermal heat flow zone which strikes nw se east of the eastern limit of the disturbed belt a recent broad regional heat flow study of southern and central alberta by majorowicz jones lam 1984 shows that the nw se direction of the axis of the elevated heat flow

geothermal gradients in the hinton area of west central alberta temperature data from petroleum exploration well logs of 3360 wells in a region of west central alberta are used to estimate thermal gradients a relatively high geothermal gradient 36 c km of oblong shape located near hinton is observed the axis of the anomaly strikes approximately southwest northeast and passes through the miette hot springs area it appears that water is heated at depth in the rocky mountain disturbed region and travels eastward and toward the surface along fault planes

coalification shale diagenesis and thermal modelling in the alpine foreland basin the western molasse basin switzerland france abstract the analysis of coalification and shale diagenesis in oligocene and lower miocene sediments in the western part of the molasse basin western switzerland and haute savoie france shows a close relationship between the very low temperature metamorphism in the foreland and the tectonic history in the orogenic belt the degree of thermal maturation generally increases towards the alpine front isomaturity lines however run slightly oblique to today s alpine front this is probably due to the tectonic burying under the alpine nappes in early miocene time second order variations of the coalification pattern are explained as resulting from a regional discharge of warm fluids controlled by tectonic structures

modelling flow and heat transfer through unsaturated chalk validation with experimental data from the ground surface to the aquifer abstract during the winter and spring of 2000 2001 large floods occurred in northern france somme river basin and southern england patcham area of brighton in valleys that are developed on chalk outcrops the floods durations were particularly long more than 3 months in the somme basin and caused significant damage in both countries to improve the understanding of groundwater flooding in chalk catchments an experimental site was set up in the hallue basin which is located in the somme river basin france unsaturated fractured chalk formation overlying the chalk aquifer was monitored to understand its reaction to long and heavy rainfall events when it reaches a near saturation state the water content and soil temperature were monitored to a depth of 8 m and the matrix pressure was monitored down to the water table 26 5 m below ground level the monitoring extended over a 2 5 year period 2006 2008 under natural conditions and during two periods when heavy artificial infiltration was induced the objective of the paper is to describe a vertical numerical flow model based on richards equation using these data that was developed to simulate infiltrating rainwater flow from the ground surface to the saturated aquifer the marthe computer code which models the unsaturated saturated continuum was adapted to reproduce the monitored high saturation periods composite constitutive functions hydraulic conductivity saturation and pressure saturation that integrate the increase in hydraulic conductivity near saturation and extra available porosity resulting from fractures were introduced into the code using these composite constitutive functions the model was able to accurately simulate the water contents and pressures at all depths over the entire monitored period including the infiltration tests the soil temperature was also accurately simulated at all depths except during the infiltrations tests which contributes to the model validation the model was used to calculate the aquifer recharge over a long period that included droughts and floods the calculated recharge is realistic as it makes it possible to simulate the corresponding monitored groundwater level data which increases confidence in the modelling approach

analysis of water level response to rainfall and implications for recharge pathways in the chalk aquifer se england summary water table response to rainfall was investigated at six sites in the upper middle and lower chalk of southern england daily time series of rainfall and borehole water level were cross correlated to investigate seasonal variations in groundwater level response times based on periods of 3 month duration the time lags in days yielding significant correlations were compared with the average unsaturated zone thickness during each 3 month period in general for cases when the unsaturated zone was greater than 18 m thick the time lag for a significant water level response increased rapidly once the depth to the water table exceeded a critical value which varied from site to site for shallower water tables a linear relationship between the depth to the water table and the water level response time was evident the observed variations in response time can only be partially accounted for using a diffusive model for propagation through the unsaturated matrix suggesting that some fissure flow was occurring the majority of rapid responses were observed during the winter spring recharge period when the unsaturated zone is thinnest and the unsaturated zone moisture content is highest and were more likely to occur when the rainfall intensity exceeded 5 mm day at some sites a very rapid response within 24 h of rainfall was observed in addition to the longer term responses even when the unsaturated zone was up to 64 m thick this response was generally associated with the autumn period the results of the cross correlation analysis provide statistical support for the presence of fissure flow and for the contribution of multiple pathways through the unsaturated zone to groundwater recharge

recharge of the upper chalk aquifer at a site in hampshire england 1 water balance and unsaturated flow abstract measurements of the annual cycle of changes in water content and potential in the 40 m thick unsaturated zone of upper chalk at a site in southern england are described measured evaporation continued at the penman potential rate until the soil moisture deficit reached 175 mm this suggested that a root constant of 200 mm would be more appropriate than the much lower values generally used the field capacity concept could not be reconciled with the timing of renewed water recharge and the reasons for this are discussed the mechanisms of water flow through the unsaturated zone of the chalk are examined and it is shown that at this upper chalk site matrix flow is the dominant recharge mechanism

an integrated study of the petrophysical properties of carbonate rocks from the oolithe blanche formation in the paris basin abstract petrophysical properties were measured on oolitic limestone from the oolithe blanche formation middle jurassic in the paris basin eighteen oriented blocks were collected from three outcrops regarding of the three main facies oolitic shoal facies tide dominated facies and prograding oolitic facies we investigated the relationship between both compressional wave and electrical conductivity with different petrophysical properties such as porosity water porosity and mercury porosity permeability and capillarity imbibition these have led us to relate the variations of petrophysical properties to several microstructural parameters among them the microporous structure is the most important concerning p wave velocities the general trend observed is as expected a decrease of velocities as the porosity increases but with a significant fluctuation of velocities for a given value of porosity we have used two distinct effective medium approximations to describe the velocity variations the self consistent sc approximation and the cemented contact theory cct but no unique model can simply explain our velocity behaviours the main parameter that controls the p wave velocities is the distribution of microporosity inside oolites for samples with velocities higher than 4 km s the microporosity is mainly located in the rim of the ooids while for samples with velocity lower than 4 km s the microporosity is homogeneous across the ooids acoustical fabrics which are controlled by the facies indicate that sedimentary textural components such as the amount of cement and arrangement of elements within the oolitic limestones bioclasts pellets and ooids and their degree of connectivity may have some influences on the acoustic velocities in contrast with acoustic properties the electrical conductivity data are not so clustered by facies indicating that transport properties are more influenced by microstructural heterogeneities one single archie s law can well account for all the data sets but these sets also show a large range of tortuosity factor related to the microporosity arrangement inside oolites some good predictive permeability modeling were found using mercury injection spectra our investigations reveal that the best way for fluids to flow is to pass through the microporosity in the oolites and that permeability depends mainly of the connectivity of the ooids which is certainly related to the facies

variations in petrophysical properties along a mixed siliciclastic carbonate ramp upper jurassic ricla ne spain abstract a multi scale petrophysical study was performed on an upper jurassic siliciclastic carbonate ramp system near the village of ricla spain a combination of textural field observations thin section and grain size analysis chemical mineralogical thermo gravimetric analysis and physical porosity gamma ray and velocity measurements properties was used to capture the heterogeneity of this mixed sedimentary system subsequently synthetic seismic sections with varying resolution were created to show the characteristics of the internal ramp structures the translation from the measured petrophysical properties to a synthetic seismic section helps to better understand subsurface seismic although upscaling problems are a recurring issue the homogeneity of the samples and the continuity of the outcrop and facies reduce the number of uncertainties acoustic properties are generally controlled by the amount and type of pore spaces due to the low porosities the ramp geometry is characterized by an overall lateral homogeneity and vertical heterogeneity textural sedimentological and stratigraphic transitions in the outcrop are related to the defined facies each has its own unique mineralogical signature amplitude variations in the synthetic seismic profile are primarily caused by changes in mineral composition thus facies transitions

a statistical analysis of bottom hole temperature data in southern alberta when bottom hole temperatures bht are plotted as functions of depth for different areas the plots exhibit differences in the spread of the data the regional variations in spread in southern alberta were mapped in detail on the basis of 33 653 bht data from 18 711 wells there are local areas with anomalously high spread values and the spread generally increases westward toward the disturbed belt also the spread values for data below the paleozoic erosional surface are greater than those above greater spread in the data appears to be associated with the occurrence of faults steeply dipping strata of different thermal conductivity and rough topography the increased spread associated with faults and steeply dipping strata is probably due to water movement this suggests that bottom hole temperatures may provide information about subsurface structure and phenomena as well as information on temperature

matrix microcrystalline structure and acoustic properties of oomoldic dolograinstone previous studies have shown that carbonate rock with rounded moldic macropores has a higher compressional velocity at a given porosity than rock with interparticle or intercrystalline porosity and high aspect ratio macropores our study of permian dolograinstone challenge this comonlny accepted results petrophysical and acoustic velocities were measured on 55 mini core plugs collected along an approximately 1 kilometer km long horizontal transect within a single grainstone unit having lateral changes from grainstone with dominantly interparticle porosity to grainstone with mostly moldic porosity the studied dolograinstone samples have a large scattering of acoustic velocity up to 1 500 meters per second m s at equal porosity one some oomoldic grainstone samples have either higher velocity or significantly lower velocity than that of the intercrystalline grainstone samples petrographic analysis under plain light and uv light combined with mercury injection capillary pressure micp data and scann

the significance of flow in the matrix of the chalk unsaturated zone the significance of flow in the matrix of the chalk unsaturated zone in comparison with flow in fractures has been the subject of much debate in this article important elements of the literature are discussed in detail and several simple modelling analyses based on steady state flow are presented a study of the sensitivity of solute spreading to fracture spacing in models that ignore matrix flow shows that this latter assumption is generally incompatible with observed solute profiles unless unrealistically small fracture spacings are assumed the effect of air phase continuities e g bedding planes on matrix flow has also been examined these discontinuities are frequently interrupted by points of connectivity between matrix blocks an issue therefore is the relationship between connectivity and its effect on inter block conductance a simple analysis of the laplace equation shows that just 1 connectivity represents an effective pathway equivalent to 18 of the local rock hydraulic conductivity obviously when there is no fracture flow solute spreading is significantly reduced however dual permeability model simulations show that matrix flow reduces solute spreading in the presence of persistent fracture flow all of the above studies suggest that flow in the matrix of the chalk unsaturated zone is significant and that ignoring it may result in a serious misunderstanding of the system

timing of organic maturation coalification relative to thrust faulting in the southeastern canadian cordillera abstract in order to access the effects if any of overthrusting tectonic burial on levels of organic maturation coalification detailed vitrinite reflectance profiles were constructed for 11 deep boreholes that penetrated stacked thrust sheets of mesozoic and paleozoic strata in the southeastern canadian cordillera recognition of the timing and degree of maturation resulting from emplacement of thrust sheets is largely dependent on the accuracy with which the preorogenic level of maturation of the strata is known the vitrinite reflectance profiles of several boreholes suggest that a significant component of organic maturation coalification postdates emplacement of overthrust sheets and have resulted from tectonic burial for other boreholes however the maturation profiles are ambiguous and suggest that postorogenic maturation if any was insufficient to overprint preorogenic levels of maturity maturity levels and reflectance gradients of mesozoic strata in general are lower in the southern part of the southeastern cordillera than in the northern part which imply higher paleoheat flow in the north

thermal maturity and hydrocarbon potential of the sedimentary succession from the hecla field in sverdrup basin arctic canada abstract the thermal maturity and source rock potential of the upper palaeozoic and mesozoic sediments in the hecla field melville island arctic canada have been studied using reflected light microscopy and rock eval pyrolysis approximately 250 polished whole rock samples were examined and their reflectance r 0 random measured in addition approximately 100 samples were subjected to rock eval toc analyses hydrogen rich organic matter in the schei point group sediments is dominated by alginite tasmanales dinoflagellate cysts with minor amounts of sporinite cutinite resinite and liptodetrinite in an amorphous fluorescing matrix vitrinite reflectance in cretaceous sediments ranges from 0 41 to 0 54 in jurassic sediments it ranges from 0 43 to 0 64 and in triassic sediments from 0 50 to 0 65 the triassic schei point group calcareous shales and marlstones contain organic matter mainly of marine origin whereas the predominantly terrestially derived organic matter present in the jameson bay lower jurassic and in the upper jurassic to lower cretaceous deer bay formations have ower toc only the ringnes formation has a toc content of equivalent to or greater than schei point source rocks within the schei point group the cape richards and eden bay members of the hoyle bay formation are slightly richer in toc than the murray harbour formation cape caledonia member higher average toc contents 3 0 have been reported in the cape richards and eden bay members in almost all hecla drillholes variations in the level of thermal maturity of mesozoic sediments in the hecla field are a function of burial depth the stratigraphic succession thickens towards the main sverdrup basin depocentre located in a n ne direction the pattern of the isoreflectance contours at the top of the triassic barrow formation is similar to that of formation boundary lines of the same formations an indication that present day maturation levels are largely controlled by basin subsidence

estimating infiltration recharge using a response function model abstract rainfall infiltration influences both the quantity and quality of groundwater systems the knowledge of the process of infiltration recharge is of great importance to the management of groundwater systems and the hydraulically connected streams in this study a response function model is developed to estimate soil water flux at the water table or the process of infiltration recharge from rainfall and evaporation data the gamma probability density function is modified to represent the travel time distribution of infiltrating water by rainfall events the travel time distribution is used to determine the recharge process according to the effective infiltration of a rainfall event the effective infiltration is the amount of soil water pushed down into groundwater by infiltrating water of a rainfall event and is evaluated based on the vadose zone soil water balance superposition is employed to compute the recharge rate produced by a sequence of rainfall events estimations of soil water flux at different groundwater depths are compared with lysimetric observations in the field good agreements between the estimated and observed results confirm the reliability of the response function model for predicting infiltration recharge processes

heterogeneities and diagenetic control on the spatial distribution of carbonate rocks acoustic properties at the outcrop scale abstract carbonate rocks are characterized by a high heterogeneity of their properties at the outcrop scale that results from complex interactions between sedimentary diagenetic and fracturing processes here we show acoustic p wave velocity measurements conducted step by step on three decameter scale outcrop surfaces in cretaceous carbonate rocks with contrasted heterogeneities two shallow water highly fractured cassis and low fractured calissanne carbonates and one basin highly compacted grignantes p wave measurements were compared to outcrop geology and with plug porosity p wave velocity laboratory measurements and a thin section study results show a strong scale dependence of p wave velocities which always are lower at the decimeter scale than at the plug scale vp in situ versus vp plug large discrepancies 2000 m s highlight the signature of large heterogeneities open fractures stylolithes and lower discrepancies in situ distribution follows the dip of the ripple foresets which are controlling grain sorting and porosity in calissanne outcrop the near isotropic vp are explained by an early intense fracturing and cementation in cassis outcrop and the strong horizontal anisotropy with a hole effect behavior on variograms highlights the late re opening of multiple intervals of compaction bands in grignantes these results illustrate that the early diagenesis coupled to fracture or stylolithe reactivation opening are two key processes that explain the outcrop scale p wave velocity distribution anisotropy in carbonates

mechanisms of water storage and flow in the unsaturated zone of the chalk aquifer abstract it is known that the volumes of water draining from some chalk catchments in recessions are significantly greater than can be explained by gravity drainage from fissure porosity the most likely source of this water is slow drainage from the matric porosity above the water table this paper suggests that the location of this storage is in the irregularities on the fissure surfaces studies of resin impregnated blocks of chalk failed to reveal the presence of hydrologically significant microfissures or macropores that could be the source of additional drainage ultrasonic measurements at varying values of effective stress show no indication of changes in the acoustic transmission properties that could be attributed to closure of microfissures drainage and mercury intrusion measurements indicate that there is significant storage on block surfaces the drainage measurements confirm that the storage is of the order of magnitude about 0 3 needed to explain the slow drainage this additional storage explains why the water table is slow to respond after recharge events and why the chalk is resilient to drought the presence of storage in the unsaturated zone implies that the position of the water table may not be an accurate indicator of groundwater resources the concept of filling and draining of irregularities on fissure surfaces also leads to a new model for the generation of fissure flow in the unsaturated zone of the chalk this suggests that fissure flow can be generated at any depth in the profile and in a sequence of uniform vertical permeability is likely to originate near the water table rather than high in the unsaturated zone

a magnetovariational study of a geothermal anomaly summary during 1980 september and october an array of 31 threecomponent magnetometers was operated over a known geothermal anomaly in the rocky mountains foothills of alberta the purpose of the array was to investigate the possibility of the existence of a geomagnetic induction anomaly coincident with the geothermal anomaly examples of magnetograms and fourier transform anomaly maps are presented and show that although there is some indication of an anomaly this is to a great extent masked by the presence of large external source field gradients a detailed transfer function analysis of the data is presented both single station transfer functions and a solution of the induction matrix are calculated the latter involves the representation of the normal fields by least squares fitted planes and a justification of the validity of this method is given contour plots of the response of the anomalous vertical field to horizontal hypothetical events and pseudosections of iza hni for traverses across the array are shown these indicate the existence beneath the geothermal anomaly of a body of anomalously high electrical conductivity by treating the observed values of the in phase part of iza ha i along a traverse across the anomaly as due to vertical dipoles it is shown that the top of the conductive body probably lies at 10 20km depth the pseudosections suggest that the body extends at least to lower crustal depths the correlation of the conductivity and geothermal anomalies supports the inference that both are due to the presence of partial melt in the crust

analysis of rainfall recharge relationships abstract understanding the recharge process and its relationship with rainfall is of critical importance to the management of groundwater systems and enormous effort has been made to estimate the amount and process of recharge by infiltration using precipitation data in the present research in situ lysimeter experiments and numerical simulations were used to study the relationships between rainfall and recharge by infiltration at different groundwater depths four lysimeters 1 5 3 4 5 and 5 m deep were installed in the field to measure the infiltration recharge rates under conditions of fixed water tables at the bottoms of the soil columns annual infiltration recharges at different groundwater depths were obtained through the lysimeter measurements the effect of rainfall pattern and annual rainfall distribution on infiltration recharge was simulated at various groundwater depths using a numerical model based on soil water dynamics and comparisons of the simulated and observed recharges showed very good agreement relationships between rainfall and infiltration recharge at different groundwater depths were investigated using the lysimeter measurements and computer simulations groundwater systems were classified into three categories i e shallow water table intermediate water table and deep water table based on the relationship between rainfall and infiltration recharge at different groundwater depths

interrelations of the petrophysical sedimentological and microstructural properties of the oolithe blanche formation bathonian saline aquifer of the paris basin abstract the paris basin seems a suitable location for co2 capture and storage given both the amount of co2 produced and the availability of depleted fields and deep saline aquifers this study investigates the petrophysical properties in relation to the sedimentary and diagenetic environment of the oolithe blanche formation middle jurassic a deep saline aquifer considered a potential candidate for co2 storage because of the scarcity of core data in the paris basin our investigation was based on the study of field analogues in the south east part of the paris basin the oolithe blanche formation bathonian is 70 80 m thick eighteen oriented blocks were collected from three outcrops selected for the different sedimentological facies identified in the formation their petrophysical properties were measured porosity pore size distribution derived from mercury injection tests permeability and capillary imbibition parameters the sedimentary and diagenetic facies were defined by using optical microscopy coupled with image analysis on thin sections and sem the oolithe blanche formation is composed of oolitic and bioclastic limestones deposited in a shallow marine setting three main sedimentological facies were defined the oolitic shoal facies the tide dominated facies and the prograding oolitic facies they exhibit subtle variations in composition and in the distribution of carbonate textures porosity measured using the water saturation triple weight method ranges from 6 to 34 permeability values are low between 0 1 md and 9 md the data from mercury intrusion porosimetry show that the distribution of the pore throat diameter is either unimodal microporosity only or bimodal macro and microporosity microporosity is intraparticle intraooid and macroporosity is interparticle and is related to dolo dedolomitization variations of petrophysical parameters can be explained by the microstructure now these latter results calibrated by studying field analogues must be extended to borehole data and core data to optimize our knowledge of the deep saline aquifer of the oolithe blanche formation without such investigations it will be impossible to estimate the suitability of this deep saline aquifer for co2 storage

processes of water movement through a chalk coombe deposit in southeast england the processes of water movement through the coombe deposit in a chalk dry valley near eastbourne in southeast england were investigated using simple methods based on regular weekly measurements of rainfall soil water content and soil water potential the drainage flux recharge through the soil was determined using the water balance method during the winter and the zero flux plane zfp method after the appearance of the zfp in the spring the unsaturated hydraulic conductivity was derived applying darcy s law in a novel way using the measured potential gradients and weekly drainage fluxes the derived conductivity characteristics were adequate to identify the flow mechanisms to illustrate the difference in behaviour between the horizons of the soil profile and to give some indication of pore water velocities the mean daily drainage flux at 2 85 m depth during the recharge period from 10 october 1980 to 29 may 1981 was 1 6 mm d 1 weekly mean rates of up to 3 7 mm d 1 were observed but peak short term rates must have considerably exceeded this figure it was shown that in the lower part of the coombe deposit when drainage fluxes are large much of the flux passes through a very small proportion of the wetted cross sectional area of the soil this gives rise to pore water velocities of at least 3 m d 1 at a depth of 2 85 m and 0 5 m d 1 between 0 5 m and 2 5 m depth these results show that pollutants may be moved very rapidly through the profile in this and similar material the core sampling techniques normally used to monitor pollutant movement in the chalk are unlikely to succeed in detecting this movement not only because it is transient but also because it occupies only a very small proportion of the water filled pores

geothermal energy potential in the hinton edson area of west central alberta the hinton edson area located about 200 km west of edmonton in alberta coincides with a geothermal anomaly of relatively high average geothermal gradient 36 c km the anomaly was discovered b

evidence for a shallow highly permeable zone in the chalk of hampshire u k abstract studies of the chalk in the u k in the last 10 15 years have shown that it is generally the top 20 50 m below the water table which provides most of the aquifer yield an investigation in hampshire in connection with a river augmentation scheme using seasonal groundwater abstraction shows the chalk in the area to have a particularly thin and well developed 6 m thick zone possessing both high transmissivity and storativity evidence is put forward to support its existence

self potential as a predictor of seawater intrusion in coastal groundwater boreholes abstract monitoring of self potentials sps in the chalk of england has shown that a consistent electrical potential gradient exists within a coastal groundwater borehole previously affected by seawater intrusion si and that this gradient is absent in boreholes further inland furthermore a small but characteristic reduction in this gradient was observed several days prior to si occurring we present results from a combined hydrodynamic and electrodynamic model which matches the observed phenomena for the first time and sheds light on the source mechanisms for the spatial and temporal distribution of sp the model predictions are highly sensitive to the relative contribution of electrochemical exclusion and diffusion potentials the exclusion efficiency in different rock strata geoelectric heterogeneity largely due to marls and hardgrounds with a relatively high exclusion efficiency was the key factor in controlling the magnitude of the modeled sp gradient ahead of the saline front and its evolution prior to breakthrough the model results suggest that where sufficient geoelectric heterogeneity exists borehole sp may be used as an early warning mechanism for si

unsaturated flow and solute transport through the chalk tracer test and dual permeability modelling a tracer test was carried out in the unsaturated chalk at the fleam dyke research site in cambridgeshire uk to investigate the role of the chalk fractures and matrix in unsaturated flow and solute transport the experiment under natural rainfall conditions involved distributing deuterated water on a grass covered lysimeter a cube of volume 125 m3 and on an adjacent 4 m 4 m field plot tracer migration was monitored through regular core sampling and collection of lysimeter drainage water the presence of occasional secondary peaks in sampling of the vertical tracer profile suggested the occurrence of fracture flow allowing some tracer to bypass the chalk matrix however in the 15 months following application none of the tracer was detected in the lysimeter drainage at 5 m depth modelling of the tracer results was undertaken with the 1 d numerical transient dual permeability model macro 5 0 initially developed for macroporous soils modelling results showed that macro 5 0 could reliably simulate transient recharge through the chalk the simulations suggested that fracture flow is important at the site but that it is only initiated at 1 m depth or deeper the extent of fracture flow appeared to be highly variable in different layers of the profile varying between 40 and 85 of the cumulative flux mainly depending on the saturated hydraulic conductivity of the matrix diffusion between the fractures and the matrix tended to equalize solute concentrations in both flow domains although solute bypass through the fractures occurred in some chalk strata besides diffusive exchange the modelling stressed the importance of advective exchange of solutes the results suggest that the chalk aquifer at the fleam dyke site is only moderately vulnerable to pollution even though for moderate rainfall conditions some bypass flow was possible

temperature distributions at the paleozoic and precambrian surfaces and their implications for geothermal energy recovery in alberta a large number of bottom hole temperature bht data from alberta 55 246 bht from 28 260 wells have been used to construct paleozoic and precambrian surface temperature maps a northward increase of average heat flow in alberta results in higher subsurface temperatures at the precambrian basement and at the top of the paleozoic toward the north and northeast than at the same depths in the south and southeast however the temperature distribution at these surfaces is more depth dependent than gradient dependent and so higher temperature values occur in the western part of the basin as a result good geothermal energy potential exists throughout the western half of the province especially for regions west of the calgary swan hills grande prairie rainbow lake line through the central part of the basin zones occur where the isotherms and the isopach lines of the phanerozoic are parallel these zones probably represent regions where little disturbance to heat transport by vertical water motion oc

transient simulations of flow and transport in the chalk unsaturated zone chalk is a fractured porous medium composed of matrix blocks bounded by interconnected fractures furthermore there are a number of commonly observed and apparently contradictory phenomena these include a fast water table response slow solute migration and very little solute dispersion to the authors knowledge no unified physically based numerical model has been able to reconcile all of these points in this paper these issues were addressed through the development of a transient dual permeability model of flow and transport the behaviour of the model was explored through a hypothetical scenario the one dimensional model featured a fixed water table at 10 m depth a recharge time series derived using the penman grindley model in conjunction with daily precipitation and monthly potential evaporation data from the kennet valley berkshire was applied at the top of the model a conservative solute that could be tritium chloride or nitrate was applied to the recharge for 1 year subsequent years involved the input of clean water the simulations suggested that although transient effects have been previously neglected overlying soil and gravelly chalk layers are likely to cause significant attenuating effects on flow such that most flow occurs through the matrix fracture flow was found to be episodic and infrequent and represented between 17 and 30 of the annual recharge

upscaling of elastic properties in carbonates a modeling approach based on a multiscale geophysical data set linking ultrasonic measurements made on samples with sonic logs and seismic subsurface data is a key challenge for the understanding of carbonate reservoirs to deal with this problem we investigate the elastic properties of dry lacustrine carbonates at one study site we perform a seismic refraction survey 100 hz as well as sonic 54 khz and ultrasonic 250 khz measurements directly on outcrop and ultrasonic measurements on samples 500 khz by comparing the median of each data set we show that the p wave velocity decreases from laboratory to seismic scale nevertheless the median of the sonic measurements acquired on outcrop surfaces seems to fit with the seismic data meaning that sonic acquisition may be representative of seismic scale to explain the variations due to upscaling we relate the concept of representative elementary volume with the wavelength of each scale of study indeed with upscaling the wavelength varies from millimetric to pluri metric this change of scale allows us to conclude that the behavior of p wave velocity is due to different geological features matrix porosity cracks and fractures related to the different wavelengths used based on effective medium theory we quantify the pore aspect ratio at sample scale and the crack fracture density at outcrop and seismic scales using a multiscale representative elementary volume concept results show that the matrix porosity that controls the ultrasonic p wave velocities is progressively lost with upscaling implying that crack and fracture porosity impacts sonic and seismic p wave velocities a result of paramount importance for seismic interpretation based on deterministic approaches

quantification of pore structure and its effect on sonic velocity and permeability in carbonates carbonate rocks commonly contain a variety of pore types that can vary in size over several orders of magnitude traditional pore type classifications describe these pore structures but are inadequate for correlations to the rock s physical properties we introduce a digital image analysis dia method that produces quantitative pore space parameters which can be linked to physical properties in carbonates in particular sonic velocity and permeability the dia parameters derived from thin sections capture two dimensional pore size domsize roundness aspect ratio ar and pore network complexity poa comparing these dia parameters to porosity permeability and p wave velocity shows that in addition to porosity the combined effect of microporosity the pore network complexity and pore size of the macropores is most influential for the acoustic behavior combining these parameters with porosity improves the coefficient of determination r2 velocity estimates from 0 542 to 0 840 the analysis shows that samples with large simple pores and a small amount of microporosity display higher acoustic velocity at a given porosity than samples with small complicated pores estimates of permeability from porosity alone are very ineffective r2 0 143 but can be improved when pore geometry information poa r2 0 415 and domsize r2 0 383 are incorporated furthermore results from the correlation of dia parameters to acoustic data reveal that 1 intergrain and or intercrystalline and separate vug porosity cannot always be separated using sonic logs 2 p wave velocity is not solely controlled by the percentage of spherical porosity and 3 quantitative pore geometry characteristics can be estimated from acoustic data and used to improve permeability estimates

maturity studies and source rock potential in the southern sverdrup basin arctic canada abstract the purpose of the study is to better understand the relationship between organic matter optical properties and the presence of potentially large oil and gas accumulations in arctic canada the type and thermal maturity of the dispersed organic matter of the mesozoic formations in the southern sverdrup basin melville island have been studied using organic petrology and rock eval pyrolysis all types of organic matter are present in the strata of mesozoic age hydrogen rich liptinite is dominated by alginite botryococcus and tasmanites dinoflagellate cysts and amorphous fluorescing matrix sporinite cutinite resinite and liptodetrinite made up the lesser hydrogen rich exinite vitrinite reflectance in cretaceous sediments ranges from 0 36 to 0 65 ro in jurassic sediments it ranges from 0 40 to 1 0 ro and in the triassic from 0 45 to 1 30 ro showing an overall increase with depth of burial cretaceous sediments of the deer bay formation are thermally immature and contain organic matter of terrestrial origin the upper jurassic shales of the ringnes formation contain predominantly organic matter of liptinitic and exinitic origin with a considerable vitrinitic input at optimum maturation levels potential source beds of this formation would have a good hydrocarbon generating potential the hydrocarbon potential however would be limited to the generation of gases due to the leanness of the source rocks parts of the lower jurassic jameson bay formation are organic rich and contain a mixed exinitic vitrinitic organic matter botryococcus colonial algae but visible organic matter is dominated by high plant remains mainly spores the schei point group shales and siltstones contain organic matter of almost purely marine origin whereas the predominantly higher plant derived organic matter found in the deer bay jameson bay and partly in the ringnes formations have higher toc among the schei point group samples the cape richards and eden bay members of the hoyle bay formation are richer in toc 2 0 than the murray harbour formation cape caledonia member this may reflect differences in the level of maturity or in the depositional environment more anoxic conditions for the former regional variations in the level of thermal maturity of mesozoic sediments in sverdrup basin appear to be a function of burial depth the mesozoic formations thicken towards the basin centre nne direction reflecting the general pattern of increasing thermal maturity north of sabine peninsula however the regional thermal maturation pattern of the mesozoic is not solely a reflection of the present day geothermal gradient which indicates that anomalous zones of high geothermal gradient may have existed in the past at least since when the mesozoic sediments attained maximum burial depth the contour pattern of the regional variation of maturity at the base of numerous triassic formations is similar to that of the structural contours of the sverdrup basin indicating that present day maturation levels are largely controlled by basin subsidence

hydrological processes in the chalk unsaturated zone insights from an intensive field monitoring programme as part of the nerc lowland catchment research programme locar the pang lambourn catchments berkshire uk have been extensively instrumented to provide an improved understanding of the hydrological processes in the unsaturated zone of the chalk a subject of much debate over the past 30 years to quantify the movement of water through the unsaturated zone it is necessary to measure matric potential and water content as well as input and output fluxes from precipitation evapotranspiration and groundwater recharge previous studies have indicated the need for fine temporal resolution data to monitor this system effectively due to the challenges faced in meeting this objective a monitoring scheme was designed that combines a variety of instrumentation to provide the required range accuracy and spatial and temporal resolution of data this paper firstly presents an overview of the monitoring programme and a critical discussion of the instrumentation used subsequently the field data are used to characterise the hydrological properties of the unsaturated zone and to gain insight into recharge processes the interpretation of the data presented in this paper indicate that in the chalk unsaturated zone at west ilsley matrix flow is the dominant recharge mechanism

estimates of terrestrial thermal gradients and heat flow variations with depth in the hinton edson area of the alberta basin derived from petroleum bottom hole temperature data there is a significant increase in terrestrial heat flow with depth in the hinton edson area of the deep part of the western canadian sedimentary basin in alberta this is especially true near the rocky mountain foothills which is an area of high relief high hydraulic head and regional water recharge gravity imposed downward movement of meteoric water through the thick sedimentary strata with velocities as low as 10 sup 10 m s to 0 5 x 10 sup 9 m s may cause an increase of heat flow with depth such disturbance of heat flow with depth on a regional scale in the sedimentary strata means that it is not possible to determine the background conductive steady state heat flow associated with crustal or upper mantle heat sources in such an area from measurement of conductive heat flow in the part of the sedimentary column where water movement occurs this is because the convective portion cannot be determined particularly when measurements are made in only part of the regional hydrodynamic system of the basin

micro and nano pores in intrasalt microbialite dominated carbonate reservoirs ara group south oman salt basin abstract dolomitic microbialites form important exploration targets for the oil and gas industry in many parts of the world it is known that a significant portion of their total porosity and potential storage capacity is formed by micropores despite their economic importance few studies attempted to characterize the micro to nanoporosity in dolomitic microbialites recent advances in the field of microscopy now allow to image and analyze their pore systems on a hitherto unprecedented scale this study evaluates pore systems in neoproterozoic ara group carbonates forming part of the deeply buried intra salt a2c hydrocarbon play of the south oman salt basin sosb micro and nanoporosity there is hosted by aphanocrystalline and to a minor extent microcrystalline dolomite image analysis derived from broad ion beam milling and scanning electron microscopy bib sem of representative samples display a contribution between 50 and 100 from micro and nanopores to total porosities which are up to 17 the main diagenetic controls on microporosity in the a2c are the formation and preservation of primary or early diagenetic aphanocrystalline dolomite and the presence of evaporites calcite and solid bitumen petrographic and petrophysical observations show good preservation of the original textural and geochemical attributes in most dolomite samples even after burial to 5 km depth for the past 500 million years this suggests a structurally and hydrodynamically isolated rockbuffered system with a limited extent of cementation confocal laser scanning microscopy clsm reveals significant amounts of hydrocarbons which manifest as degenerated organic material in the carbonates they originated from precursor bacterial organic matter in microbial laminite thrombolite and peloidal source rocks and might have prevented extensive recrystallization of the aphanocrystalline dolomite matrix and further cementation of the porespace primary dolomite might still be preserved in the a2c microbialites as petrographic observations reveal similarities in crystal sizes and the texture of euhedral aphanocrystalline dolomite as observed in comparable sedimentary systems