transport in fractured porous solids laboratory measurements are made of the permeability and the resistivity of sintered porous media with disordered fractures over a wide range of matrix porosity we discuss the preparation and characterisation of the samples approximating the topology of a rough fracture by a single discrete fracture can introduce large errors in the prediction of the permeability we test the validity of empirical expressions relating permeability resistivity and porosity for fractured samples resistivity correlations with porosity are independent of the presence of fractures in contrast permeability correlations show a strong dependence attempts to decouple the permeability of the fractured sample as a parallel sum of matrix and fracture permeability leads to large errors the results indicate that transport in a medium with two distinct families of pathways cannot be described by a single valued transport coefficient

stable chlorine isotopes in the palo duro basin texas evidence for preservation of permian evaporite brines experimental evaporation of seawater yields brines with 37cl from 0 0 initial to 0 9 in the palo duro basin brines with 37cl values overlapping the 0 1 to 0 4 range of halite evaporite can be generated by a set of processes including dissolution of halite in meteoric water such brines occur above and below an evaporite aquitard brines with 37cl values of 0 4 to 1 0 in the evaporite aquitard and in a deep brine aquifer cannot be generated by dissolution of halite considered with br and cl content d and noble gas content the 37cl data indicate that such brines originated as evapoconcentrated seawater high br evaporite brine formed directly from seawater on the eastern side of the basin whereas low br evaporite brines on the western side formed after an influx of meteoric water at the time of evaporite formation there has not been detectable vertical flow of meteoric water across the evaporite aquitard strata beneath the evaporite contain compartments that have been isolated geochemically since the permian

analytic crack solutions for tilt fields around hydraulic fractures the recent development of downhole tiltmeter arrays for monitoring hydraulic fractures has provided new information on fracture growth and geometry these downhole arrays offer the significant advantages of being close to the fracture large signal and being unaffected by the free surface as with surface tiltmeter data analysis of these measurements requires the inversion of a crack or dislocation model to supplement the dislocation models of davis 1983 okada 1992 and others this work has extended several elastic crack solutions to provide tilt calculations the solutions include constant pressure 2d penny shaped and 3d elliptic cracks and a 2d variable pressure crack equations are developed for an arbitrary inclined fracture in an infinite elastic space effects of fracture height fracture length fracture dip fracture azimuth fracture width and monitoring distance on the tilt distribution are given as well as comparisons with the dislocation model the results show that the tilt measurements are very sensitive to the fracture dimensions but also that it is difficult to separate the competing effects of the various parameters

surface deformation associated with a dipping hydrofracture crustal deformation associated with hydrofracture is modeled by a dipping rectangular dislocation beneath the surface of an elastic half space the burger s vector is taken normal to the rectangular surface analytical expressions for vertical displacements are obtained from integration of volterra s equation by using mindlin s point force solutions for the elastic halfspace in the limits of 0 and 90 dip the results agree with those obtained by maruyama 1964 for poisson s ratio 0 25 expressions for arbitrary poisson s ratio are given for elongate dislocations the displacement field agrees with curves given by pollard and holzhausen 1979 for two dimensional near surface fractures at various dips at dip 0 a deep square dislocation gives displacements indistinguishable from those of sun s 1969 model of a horizontal penny shaped crack beneath the surface of an elastic half space modifying his result for shallow depths shows that they correspond to a dislocation of semi elliptical cross section with the surface displacement field asymptotically approaching a semi elliptical shape as depth decreases to zero similarly the surface displacement field of the square dislocation approaches that of its rectangular cross section nonlinear inversion of surface tilt fields associated with hydrofracture of deep boreholes gives estimates of fracture geometry position and orientation along with their uncertainties two examples are presented one of a near horizontal and one of a near vertical fracture

chlorine isotope chemistry of serpentinites from elba italy as an indicator of fluid source and subsequent tectonic history chlorine concentrations and 37cl and d values are reported for serpentinites in different tectonic positions on elba italy serpentinites from high in the nappe sequence contain 0 01 0 1wt cl with 37cl values from 0 9 to 1 4 samples with positive 37cl values occur beneath gabbro and basalt and are interpreted as having been serpentinized by interaction with seawater samples with negative 37cl values are in direct contact with sedimentary rocks these samples were juxtaposed against and or buried by sediments in response to low angle normal faulting on the seafloor and serpentinization probably occurred by subsequent interaction with sedimentary pore fluids most samples from a structurally lower nappe and from areas affected by contact metamorphism lost their original cl during heating low d values for all samples suggest postserpentinization interaction with meteoric water but neither cl nor o isotope ratios were affected by this interaction our results demonstrate that chlorine can be retained in obducted serpentinites up to low greenschist conditions and that the cl isotope composition of such serpentinites preserves a record of seafloor tectonic processes

chlorine isotope evidence for multicomponent mantle metasomatism in the ivrea zone abstract metasomatism of the finero peridotite ivrea zone italy has previously been ascribed to mantle melts generated in a rift or plume setting and or to subduction fluids we combine cl h and o stable isotope geochemistry with petrologic and major and trace element data to further constrain sources and setting of the metasomatic agents and to assess fluid infiltration mechanisms relatively unmetasomatized samples from the balmuccia peridotite serve as our control population 37cl 0 7 to 0 4 n 13 we analyzed 47 samples from four finero rock types 1 spinel harzburgite with minor amphibole phlogopite 2 harzburgite with several percent phlogopite amphibole 3 amphibole rich segregations and 4 phlogopite segregations 37cl values range from 2 0 to 2 1 and cannot be reconciled with metasomatism by a single homogeneous fluid three components describe most of the sample variability a endmember spinel peridotite as represented by the balmuccia samples b a hydrated clinopyroxenite component with low 37cl and high si al ca and d responsible for formation of type 3 amphibole segregations and c a component with high 37cl d cl cr lile and hfse that formed type 4 phlogopite segregations type 1 and 2 peridotite compositions are consistent with different degrees of mixing between these three components centimeter scale isotopic gradients indicate that much of the fluid infiltration was channelized rather than pervasive the data support metasomatism in a forearc wedge with fluids sourced from at least two subducted components with distinct chemical and isotopic compositions e g 37cl 2 overall our results show that relatively shallow and heterogeneous fluid release events from the downgoing slab can profoundly modify the mantle wedge

chlorine isotopic composition in seafloor serpentinites and high pressure metaperidotites insights into oceanic serpentinization and subduction processes bulk rock chlorine content and isotopic composition 37 cl were determined in oceanic serpentinites high pressure metaperidotites and metasediments in order to gain constraints on the global chlorine cycle associated with hydrothermal alteration and subduction of oceanic lithosphere the distribution of insoluble chlorine in oceanic serpentinites was also investigated by electron microprobe the hydrothermally altered ultramafic samples were dredged along the south west indian ridge and the mid atlantic ridge the high pressure metamorphic samples were collected in the western alps metaperidotites in the erro tobbio unit and metasediments in the schistes lustres nappe oceanic serpentinites show relatively large variations of bulk rock cl contents and 37 cl values with mean values of 1105 596 ppm and 0 7 0 4 o respectively n 8 1 serpentines formed after olivine meshes show lower cl content than those formed after orthopyroxene bastites in bastites of two different samples cl is positively correlated with al 2 o 3 and negatively correlated with sio 2 these relationships are interpreted as reflecting preferential cl incorporation into the bastite structure distorted by al substituted for si rather than different alteration conditions between olivine and orthopyroxene minerals high pressure metaperidotites display relatively homogeneous cl contents and 37 cl values with mean values of 467 88 ppm and 1 4 0 1 respectively n 7 1 a macroscopic high pressure olivine bearing vein formed from partial devolatilization of serpentinites at 2 5 gpa and 500 600 c shows a cl content and a 37 cl value of 603 ppm and 1 6 o respectively metasediments n 2 show low whole rock cl contents 15 ppm cl that did not allow cl isotope analyses to be obtained the range of negative 37 cl values observed in oceanic serpentinites is likely to result from water rock interaction with fluids that have negative 37 cl values the homogeneity of 37 cl values from the high pressure olivine bearing vein and the metaperidotite samples implies that progressive loss of cl inherited from oceanic alteration throughout subduction did not significantly fractionate cl isotopes chlorine recycled in subduction zones via metaperidotites should thus show a range of 37 cl values similar to the range found in oceanic serpentinized peridotites

porosity and permeability characterization of coal a micro computed tomography study abstract a unique contrast agent technique using x ray micro computed tomography micro ct was developed for studying micrometer sized features in coal the technique allows for the visualization of coal fractures not visible with conventional imaging methods a late permian medium volatile bituminous coal from moura coal mine was imaged and the resulting three dimensional coal cleat system was extracted for fluid flow simulations the results demonstrate a direct relationship between coal lithotype and permeability i e bright coals offer more permeability than dull coals however there was no direct relationship between porosity and permeability for any given lithotype scanning electron microscope and energy dispersive spectrometry sem eds together with x ray diffraction xrd methods were used for identifying mineral matter at high resolution after segmentation of the micro ct image mineral phase was removed from the segmented data and it was found that permeability was significantly improved by increasing cleat void space and connectivity suggesting that enhanced recovery methods could target de mineralization techniques overall only the epigenetic mineral phases in the bright band influenced permeability while lithotype had a stronger impact on permeability than porosity coal lithotype and mineralization are important evaluation criteria when considering coal seam gas development sites

evaluation of a downhole tiltmeter array for monitoring hydraulic fractures a series of hydraulic fracture experiments using a downhole tiltmeter array called an inclinometer array was conducted at the department of energy doe gas research institute gri multi site facility in colorado the inclinometer array was used to measure the deformation of the reservoir rock in response to hydraulic fracture opening and confirm microseismically measured results in addition the inclinometer array was found to be a useful tool for accurately measuring closure stress measuring residual widths of both propped and unpropped fractures estimating proppant distribution and evaluating values of in situ moduli

feasibility of monitoring hydraulic fracturing using time lapse audio magnetotellurics abstracthydraulic fracturing is widely used for initiating and subsequently propagating fractures in reservoir strata by means of a pressurized fluid to release oil and gas or to store industry waste downhole or surface microseismic monitoring is commonly used to characterize the hydraulically induced fractures however in some cases downhole microseismic monitoring can be difficult due to the limitation imposed by boreholes surface microseismic monitoring often faces difficulties acquiring high signal to noise ratio data because of the on site noise from hydraulic fracturing process research and field observations indicate that injecting conductive slurry or water into a strata may generate distinct time lapse electromagnetic anomalies between pre and posthydraulic fracturing these anomalies provide a means for characterizing the hydraulic fracturing using time lapse electromagnetic methods we examined the time lapse variation over an hour one day one month and two years of observed audio magn

digital rock analysis for accurate prediction of fractured media permeability abstract determining the permeability of fractured rocks depends significantly on fracture geometry and topology to date no practical approach has been proposed to produce realistic binary images of fractured rocks from micro computed tomography micro ct images for fluid flow simulation in this paper a novel method is developed for generating a binary image that contains the true characteristics of fractured rocks for accurate computation of permeability the method employs high resolution scanning electron microscope sem data for calibration of micro ct images micro ct is used to obtain 3d images of a highly fractured rock sample with a resolution of 16 5 m and sem is applied to obtain images with nanometer resolution from polished surfaces of the sample the sem images are then registered to the micro ct images to facilitate image segmentation and generate a calibration curve the calibration curve correlates the grayscale values at the midpoint of each fracture to the true aperture size measured from sem data thinned fractures of two subsets are extracted and used to obtain the gray scale values at the midpoint of fractures these are converted to the true aperture value using the calibration curve and subsequently grown by an adjustment algorithm to produce 3d calibrated binary images that are representative of the true fracture system the connectivity and aperture size distribution of the subsets before and after calibration are quantified the permeability of the subsets before and after calibration are computed using a direct numerical simulator and compared with experimental measurements the computed permeabilities demonstrate that using non calibrated images generates massive permeability errors whereas calibrated images produce accurate permeability results that nearly coincide with experimental measurments the method can be applied to fractured rocks for better prediction of permeability and other petrophysical properties

modelling permeability for coal reservoirs a review of analytical models and testing data abstract as with other reservoir types permeability is a key controlling factor for gas migration in coalbed methane reservoirs the absolute permeability of coal reservoirs changes significantly during gas production often initially decreasing but then increasing as the reservoir pressure and gas content is drawn down it has also been observed to decrease markedly during co2 injection to enhance coalbed methane recovery in order to predict gas migration models for coal permeability must represent the mechanisms leading to these observed behaviours the permeability of coal reservoirs behaves in a similar fashion to other fractured reservoirs with respect to effective stress decreasing exponentially as the effective stress increases however a unique effect of coal is that it shrinks with gas desorption and swells with adsorption within the reservoir this swelling shrinkage strain leads to a geomechanical response changing the effective stress and thus the permeability modelling coal permeability incorporating the impacts from both effective stress and coal swelling shrinkage dates back about 25 years since then a number of permeability models have been developed in recent years this topic has seen a great deal of activity with a growing body of research on coal permeability behaviour and model development this article presents a review of coal permeability and the approaches to modelling its behaviour as an important part of this the field and laboratory data used to test the models are reviewed in detail this article also aims to identify some potential areas for future work

chlorine transport processes through a 2000 m aquifer aquitard system abstract in the paris basin in france the callovo oxfordian cox is currently studied over a 250 km2 surface area by the french national radioactive waste management agency in order to assess the feasibility of long term underground nuclear waste repository the cox is a 140 m thick clay rich layer which is part of the 2000 m aquitard aquifer system constituting the sedimentary cover in such sedimentary context the transport processes of potential contaminants can be represented by both vertical diffusion and horizontal advection through the most permeable layers chloride is used as a natural conservative tracer and is monitored in term of concentrations and isotopic composition 37cl for both pore and groundwater during this study the samples were collected from three boreholes located in the center of the studied zone one of them est433 going down to 2000 m depth the main solute transport process is shown to be vertical diffusion from the massive keuper halite level to the rest of the sedimentary pile this global diffusive system can be occasionally disturbed by horizontal circulation of groundwater occurring in the oxfordian and dogger limestone formations therefore these circulations cut the global diffusive system in a succession of independent diffusive systems in this study the data set was implemented in a simplified 2d solute transport model and scenarii reproducing known history in term of paleo circulations inside the system were applied and allowed to obtained a good fit of the data model results showed that paleo circulations occurring between 145 ma and 110 ma still have an impact on current distribution of chloride in the system especially for 37cl the model highlights the need of the presence of a circulation spatially limited at the base of the liassic formation to fit the data the best fit obtained indicated current residence time of 500 ka in the dogger and oxfordian with respective onset of the circulations at 20 ma and 5 ma

chlorine isotope variations along the central american volcanic front and back arc volcanic outputs ash tephra and lava samples of 23 volcanic centers from the volcanic front secondary front and back arc in central america were analyzed for their 37cl values with the goal of using chlorine isotopes as a tracer of fluids sourced from the subducting cocos slab 37cl values range from 2 6 to 3 0 with systematic variations along the length of the front values from the northernmost guatemala and el salvador and southernmost costa rica ends of the front have mantle like signatures in contrast 37cl values are both positive and negative in the center of the front nicaragua implying a sediment and or serpentinite derived component geophysical observations are consistent with extensive hydration of the cocos plate offshore of nicaragua in support of a serpentinite derived fluid source fluids from dehydrating serpentinites may also incorporate cl from overlying sediments resulting in a multiple source chlorine signature

chlorine isotope behavior during prograde metamorphism of sedimentary rocks abstract chlorine stable isotope compositions of two sedimentary sequences and their metamorphic equivalents were measured in order to study fractionation effects during prograde metamorphism and devolatilization protoliths n 25 were collected from a 50 m section of triassic fluvial and playa lake strata and jurassic liassic marine black shales in a well characterized quarry low greenschist to middle amphibolite facies equivalents n 80 were collected from the glarus alps urseren zone and lucomagno region bulk 37 cl values are constant within individual sedimentary layers but vary from 2 0 to 2 4 in triassic rocks and from 3 0 to 0 in the black shales dolomitic and gypsiferous samples have positive 37 cl values but marls and shales are isotopically negative bulk cl contents show only small declines during the earliest stages of metamorphism metamorphic equivalents of the triassic and liassic protoliths record the same overall ranges in 37 cl as their protoliths samples with highly correlated bulk compositions but different metamorphic grade show no statistically significant difference in 37 cl these data lead to the following conclusions 1 terrestrial and marine sedimentary rocks display large primary heterogeneities in chlorine isotope composition as a result an unambiguous sedimentary signature does not exist in the chlorine stable isotope system 2 no isotopic fractionation is discernable during metamorphic devolatilization even at low temperatures alpine style metamorphism thus has little to no effect on bulk chlorine isotopic compositions despite significant devolatilization 3 cl is largely retained in the rocks during devolatilization contrary to the normally assumed hydrophilic behavior of chlorine continuous release of mixed volatile c o h fluids likely affected cl partitioning between fluid and minerals and allowed chlorine to remain in the rocks 4 there is no evidence for fluid communication across meta sedimentary layers except within the urseren shear zone these data contribute to a relatively closed system view of metamorphic devolatilization from anchizone through mid amphibolite facies conditions

chlorine isotope constraints on fluid rock interactions during subduction and exhumation of the zermatt saas ophiolite 1 chlorine isotope compositions of high pressure 2 3 gpa serpentinite rodingite and hydrothermally altered oceanic crust aoc differ significantly from high and ultrahigh pressure 3 2 gpa metasedimentary rocks in the aosta region italy texturally early serpentinites rodingites and aoc have bulk 37cl values indistinguishable from those of modern seafloor analogues 37cl 1 0 to 1 0 in contrast serpentinites and aoc samples that recrystallized during exhumation have low 37cl values 2 7 to 0 5 37cl depletion correlates with progressive changes in bulk chemistry hp uhp metasediments have low 37cl values median 2 5 that differ statistically from modern marine sediments median 0 6 cl in metasedimentary rocks is concentrated in texturally early minerals indicating modification of seafloor compositions early in the subduction history the data constrain fluid sources during both subduction and exhumation related phases of fluid rock interaction 1 marine sediments at the top of the downgoing plate likely interacted with isotopically light pore fluids from the accretionary wedge in the early stages of subduction 2 no pervasive interaction with externally derived fluid occurred during subsequent subduction to the maximum depths of burial 3 localized mixing between serpentinites and fluids released by previously isotopically modified metasediments occurred during exhumation in the subduction channel most samples however preserved protolith signatures during subduction to near arc depths

chemical and carbon isotopic evolution of hydrocarbons during prograde metamorphism from 100 c to 550 c case study in the liassic black shale formation of central swiss alps abstract hydrocarbon distributions and stable isotope ratios of carbonates 13ccar 18ocar kerogen 13cker extractable organic matter 13ceom and individual hydrocarbons of liassic black shale samples from a prograde metamorphic sequence in the swiss alps were used to identify the major organic reactions with increasing metamorphic grade the studied samples range from the diagenetic zone 17 n alkanes suggests the occurrence of cracking reactions of high molecular weight compounds the isotopically heavier up to 5 6 c 13 n alkanes with metamorphism suggests progressive thermal release of kerogen linked fatty acid precursors and degradation of n alkanes changes of the steroid and terpenoid distributions are clearly related to increasing metamorphic temperatures the absence of 18 h 22 29 30 trisnorneohopane ts the occurrence of 17 h trisnorhopane 17 h 21 h hopanes in the c29 to c31 range and 5 h 14 h 17 h 20r c27 c29 steranes in the low diagenetic samples the occurrence of specific hydrocarbons e g n alkylcyclopentanes cadalene hydrogenated aromatic compounds in metamorphic samples points to kerogen degradation reactions most probably occurring in the presence of water and under reducing conditions the changes of hydrocarbon distributions and carbon isotopic compositions of n alkanes related to metamorphism suggest that the organic geochemistry may help to evaluate the lowest grades of prograde metamorphism

stable cl isotopes in subduction zone pore waters implications for fluid rock reactions and the cycling of chlorine stable cl isotope ratios measured in marine pore waters associated with the barbados and nankai subduction zones extend significantly to 8 the range of 37 cl values reported for natural waters these relatively large negative values together with geologic and chemical evidence from barbados and nankai and recent laboratory data showing that hydrous silicate minerals i e those with structural oh sites are enriched up to 7 5 in 37 cl relative to seawater strongly suggest that the isotopic composition of cl in pore waters from subduction zones reflects diagenetic and metamorphic dehydration and transformation reactions these reactions involve clays and or other hydrous silicate phases at depth in the fluid source regions chlorine therefore cannot be considered geochemically conservative in these systems the uptake of cl by hydrous phases provides a mechanism by which cl can be cycled into the mantle through subduction zones thus stable cl isotopes should help in determining the extent to which cl and companion excess volatiles like h 2 o and co 2 cycle between the crust and mantle

37cl 35cl variations in a diffusion controlled groundwater system abstract groundwaters in the low permeability quaternary glacial deposits of southwestern ontario commonly exhibit increasing cl concentrations with depth because these deposits were formed in a freshwater glacial environment and because cl is not derived from weathering of these deposits previous investigations hypothesized that upward diffusion of saline formation waters from the shallow bedrock caused this cl trend this hypothesis was tested by measuring 37 cl 35 cl ratios in the groundwaters from two typical sites and comparing the results with theoretically derived isotopic distributions produced by diffusion 37cl measurements expressed relative to standard mean ocean chloride smoc ranged from 0 8 to 2 2 and vertical profiles showed a gradual enrichment in 35cl relative to 37cl with increasing distance upward from the bedrock till interface 537cl distributions were simulated with a mathematical solute transport model incorporating the effects of kinetic isotopic partitioning a sensitivity analysis indicated that the model results were affected by the groundwater velocity the isotope enrichment factor and diffusion times agreement between the simulated and observed cl isotope profiles was obtained using a groundwater velocity of 0 an isotopic enrichment factor of 1 0012 and diffusion times ranging from 14 000 to 16 000 years based on these results we conclude that the isotopic enrichment in 35cl was caused by upward diffusion over a period of about 15 000 years this diffusion period is consistent with what is known about the quaternary history of the area

chlorine isotope variations across the izu bonin mariana arc chlorine isotope ratios were determined for volcanic gas geothermal well ash and lava samples along the izu bonin mariana volcanic front serpentinite clasts and muds from serpentine seamounts conical south chamorro torishima basalts from the guguan cross chain and sediments from ocean drilling program odp sites 800 801 802 and 1149 there is no systematic variation in 37 cl values along the volcanic front in either gas or ash samples in contrast distinct variations occur across the arc implying variations in the fluid source at different depths within the subduction zone serpentinite clasts and serpentine muds from the seamounts tap a source of 30 km depth and have 37 cl values of structurally bound chloride of 0 4 0 4 n 24 identical to most seafloor serpentinites suggesting a serpentinite chrysotile and or lizardite to antigorite transition fluid source tapping deeper levels of the subduction zone 115 130 km depth volcanic gases and ashes have 37 cl values averaging 1 1 1 0 n 29 precisely overlapping the range measured in sediments from odp cores 1 1 0 7 n 11 and limited altered oceanic crust aoc both sediments and aoc are possible cl sources in the volcanic front the guguan cross chain basalts come from the greatest depths and have an average 37 cl value of 0 2 0 2 n 3 suggesting a second serpentine derived source in this case from antigorite breakdown at 200 km depth