a three dimensional stochastic rock mechanics model of engineered geothermal systems in fractured crystalline rock a three dimensional 3 d stochastic network model for simulating a hot dry rock hdr or hot wet rock hwr engineered geothermal system formed in fractured crystalline rock is presented the model addresses the problems of fracture network characterization from in situ field data such as fracture orientation size spacing and other mechanical properties the model can simulate the changes that occur within the rock mass during stimulation i e large volume fluid injection at pressures sufficient to allow shear slip on natural fractures it can also be used to simulate steady state circulation of the heat exchange system thus created and includes provision for predicting tracer response curves and heat extraction history the model has been applied to data gathered during the stimulation and circulation of a 2 2 km deep hdr reservoir at hijiori japan the predicted shape of the stimulated and shear propped fractures closely matched the distribution of seismic source distribution of acoustic emission ae regardless of realization of the fracture network suggesting that the geometry of the stimulated volume can be robustly predicted from knowledge of the fracture population and in situ stresses however hydraulic behavior and tracer tests during the circulation could only be satisfactorily simultaneously reproduced by a small subset of realizations these selected realizations obtained by matching initial circulation and tracer data are considered to give the best prospect of satisfactory long term thermal modeling the success in simultaneously modeling diverse data hydraulic microseismic and tracer lends confidence to the thermal predictions the results indicate that a large improvement in the long term thermal performance of the hijiori reservoir could result from increasing well spacing from 100 to 150 m without major degradation of the hydraulic performance

linking microearthquakes to fracture permeability change the role of surface roughness despite its importance the relation between microearthquakes meqs and changes in hydraulic properties during hydraulic stimulation of a fractured reservoir has rarely been explored and it is still not well understood to investigate this relation we first formulate a plausible scale dependence where fracture length and shear displacement are variables for channeling flow through heterogeneous aperture distributions for joints and faults by combining this formulation with the concept of the seismic moment we derive quantitative relations between the moment magnitude mw of meqs and the fracture permeability change in the directions orthogonal to kfault kjoint and parallel to kfault kjoint the shear displacement in the form kfault kjoint 116 4 100 46mw and kfault kjoint 13 1 100 46mw despite the simplicity of the derivation these relations have the potential to explain the results of field experiments on hydraulic stimulation such as the enhanced geothermal systems at soultz sous foret and basel

development of a shear flow test apparatus and determination of coupled properties for a single rock joint abstract a new laboratory technique for coupled shear flow tests of rock joints was developed and used to investigate the coupled effect of joint shear deformation and dilatancy on hydraulic conductivity of rock joints this technique was used to carry out coupled shear flow tests with an artificial created granite joint sample under constant normal loads and up to residual shear deformations of 20 mm the hydraulic conductivity was estimated by using a finite difference method and an approximate equation assuming the cubic law the shear flow testing results revealed that the change of hydraulic conductivity is approximately similar to that of the dilatancy of a joint the hydraulic conductivity increases rapidly by about 1 2 1 6 orders of magnitude for the first 5 mm of shear displacement after passing the residual shear stress the hydraulic conductivity becomes gradually a constant value with increasing shear displacement on the other hand the hydraulic conductivity after shearing is about one order of magnitude larger than that prior to shearing shear flow coupling characteristics obtained from these tests have a consistent trend with barton s model prediction during the initial shear process however increasing deviation between measured and predicted hydraulic conductivity of rock joint samples has been observed with increasing shear displacement

wet surface and dense atmosphere on early mars suggested by the bomb sag at home plate mars 1 we use the mars exploration rover spirit observation of a bomb sag produced by an explosive volcanic eruption to infer the atmospheric density at the time of eruption we performed analogue experiments to determine the relationship between the wetness of the substrate and the velocity and density of impacting clasts and 1 the formation or not of bomb sags 2 the morphology of the impact crater and 3 the penetration depth of the clast the downward deflection of beds seen on mars is consistent with water saturated sediment in the laboratory experiments collision angles 20 degrees from vertical are needed to produce bomb sags from the experiments we infer an impact velocity up to 4 101 m s lower than ejection velocities during phreatic and phreatomagmatic eruptions on earth if this velocity represents the terminal subaerial impact velocity atmospheric density exceeded 0 4 kg m3 at the time of eruption much higher than at present

hydromechanical behavior of a deformable rock fracture subject to normal stress lbl 12297 preprint to be published in the journal of geophysical research hydromechanical behavior of a deformable rock fracture subject to normal stress y w tsang and p a witherspoon january 1981 two week loan copy this is a library circulating copy which may be borrowed for two weeks for a personal retention copy call tech info diu is ion ext 6782 prepared for the u s department of energy under contract w 7405 eng 48

synthetic rough fractures in rocks natural fractures serve a very important function in the transport of fluid through rocks as well as in the flow of electrical charge and heat the creation of numerically synthesized fractures can aid the study of the physical processes connected with fractures synthetic fracture is the term used to describe fractures that are created numerically in such a way that they share the same mean geometrical characteristics as specific natural fractures measured by profiling by a process known as tuning we have modified methods for producing synthetic rough surfaces whose geometric properties are tuned to mimic natural fracture surfaces in rocks in order to create synthetic fractures that are statistically identical to those found in rocks one important such modification has been the incorporation of a method that allows the surfaces to be matched at long wavelengths and unmatched at short wavelengths with the degree of matching varying smoothly in between as it does for real fractures we have compared numerically synthetic fractures created using the new method with fractures created using an existing technique that uses a mismatch wavelength as a sudden discontinuity between matched and unmatched behavior as well as data from fractures in real rocks this comparison has shown that the new technique provides much more realistic numerically synthesized fractures than previous methods synthetic fractures created with the new method have been used in normal closure and fluid flow modeling and the results are reported in a companion paper

roughness of fault surfaces over nine decades of length scales 1 we report on the topographic roughness measurements of five exhumed faults and thirteen surface earthquake ruptures over a large range of scales from 50 m to 50 km we used three scanner devices lidar laser profilometer white light interferometer spanning complementary scale ranges from 50 m to 10 m to measure the 3 d topography of the same objects i e five exhumed slip surfaces vuache sillingy bolu corona heights dixie valley magnola a consistent geometrical property i e self affinity emerges as the morphology of the slip surfaces shows at first order a linear behavior on a log log plot where axes are fault roughness and spatial length scale covering five decades of length scales the observed fault roughness is scale dependent with an anisotropic self affine behavior described by four parameters two power law exponents h constant among all the faults studied but slightly anisotropic h 0 58 0 07 in the slip direction and h 0 81 0 04 perpendicular to it and two pre factors showing variability over the faults studied for larger scales between 200 m and 50 km we have analyzed the 2 d roughness of the surface rupture of thirteen major continental earthquakes these ruptures show geometrical properties consistent with the slip perpendicular behavior of the smaller scale measurements our analysis suggests that the inherent non alignment between the exposed traces and the along or normal slip direction results in sampling the slip perpendicular geometry although a data gap exists between the scanned fault scarps and rupture traces the measurements are consistent within the error bars with a single geometrical description i e consistent dimensionality over nine decades of length scales

field measurement of radial solute transport in fractured rock the results of a tracer experiment conducted in a single fracture are interpreted using a semianalytical model which accounts for advective dispersion matrix diffusion mixing in the test zones and for tortuosity the experiment was conducted using a conservative tracer which was injected into a steady divergent flow field arrival of tracer was monitored in an array of 13 boreholes intersecting the fracture over a square area of approximately 30 m on a side the arrival of tracer was detected in 11 of the 13 boreholes simulation of the transport process suggests that matrix diffusion may play a significant role in the migration of solutes contrary to previously published results the relative influence of advective dispersion was found to be increasingly diminished with increasing scale fracture apertures determined from the results of the tracer experiment were found to be in general agreement with apertures calculated from independent hydraulic tests the individual advective processes that contribute to advective dispersion remain unresolved on the basis of this experiment

self propping and fluid flow in slightly offset joints at high effective pressures we have made laboratory measurements of joint closure and permeability of both well and poorly mated laboratory produced joints in westerly granite under joint normal stresses to 160 mpa appropriate to midcrustal depths we have also made detailed topographic measurements of the joint surfaces both before and after pressure testing the purpose of the study was to characterize and understand the hydraulic behavior of joints under conditions where fluid migration under natural settings is known to occur but where physical conditions namely high lithostatic load suggest that the presence of open fluid conducting joints might be improbable normal stress was applied by hydrostatic confinement of cylindrical samples each containing a single axial tensile fracture experiments were performed at room temperature under conditions designed to minimize chemical effects of dissolution or precipitation we found that while a mated joint can be completely closed by the application of high normal stresses the same joint laterally offset by 0 53 mm remains open and many orders of magnitude more hydraulically conductive than the mated joint even at highest stresses detailed topographic observations are consistent with self propping of the offset joint permanent damage to the surfaces of the offset joint is not widespread but occurs at isolated locales covering about 10 of the surface damage is confined to regions of negative convex upward curvature such as summits and the edges of plateaus approximately 20 of the joint surface is in wall to wall contact at 160 mpa and the flow tortuosity thus induced is probably the cause of the breakdown of the parallel plate approximation for fluid flow in the offset joint

flow bearing structures of fractured rocks insights from hydraulic property scalings revealed by a pumping test abstract a long duration pumping test conducted over 151 days in a fractured sandstone and shale formation displays a nonstandard drawdown response and anomalous pressure diffusion which cannot be properly interpreted using existing frameworks e g homogeneous double porosity boundary conditions and fractal models an alternative framework with simple geometry and more complex hydraulic properties is thus proposed to interpret such kind of drawdown responses the analytical development allows first to demonstrate all scaling relations in this interpretation framework then and most importantly the multi scale hydraulic test provides consistent scalings of transmissivity t to storativity s over distances ranging from 83 to 383 m in a faulted area drawdown analysis in several monitoring wells shows persistent decrease of transmissivity in highly channelized fracture flow structures in one structure the cubic dependency of transmissivity to storativity identifies a well defined fault and also demonstrates the validity of poiseuille flow at a scale rarely investigated in the other structure the linear dependency of transmissivity to storativity indicates that the flow bearing structure is the surrounding fracture network well designed pumping tests combined with scaling analysis driven by geological evidence thus provide essential information on flow bearing structures for site characterization and modeling tasks at least for moderate to low permeable fractured rocks the scaling of transmissivity to storativity appears to be more informative than any separate interpretation of hydraulic property scaling exponents

precambrian tectonics and the physicochemical evolution of the continental crust i the gabbro eclogite transition revisited abstract we report the first occurrence of retrograde eclogite shear zones cutting proterozoic granulites from australia the musgrave range granulites were metamorphosed at about 12 kbar pressure and 850 900 c the granulites then cooled isobarically and developed a variety of lower temperature mineral reaction coronas typical of garnet granulites these rocks are cut by a major shear zone the davenport shear in which lower temperature fine grained eclogite developed this demonstrates that mafic rocks in the deep crust can cool down into the thermodynamic stability field of eclogite without undergoing transformation to eclogite we agree with harte et al 1981 that rocks lacking a fluid phase in stable tectonic regions are unlikely to maintain local equilibrium at ambient geotherm conditions until depths well within the upper mantle are reached it is proposed that many isobaric high pressure granulites could have cooled down into the eclogite field before their later excavation to the surface and did not transform to an eclogite mineralogy the inability of the lower crust to transform into eclogite by retrograde reaction has important implications for the seismic petrologic and geochemical character of the lower crust the continental moho cannot be caused by the gabbro eclogite transition preservation of relatively low density high temperature granulite and gabbroic mineral assemblages in the lower continental crust prohibits major recycling of lower crust back into the mantle once it is removed from active plate boundaries however in island arcs with magmatically thickened crust mafic rocks at a depth of 60 to 70 km will be in the eclogite stability field at high enough temperatures 800 900 c for eclogite to rapidly form and sink back into the mantle this could result in a net accreted crust of broadly andesitic composition in contrast later growth of continental crust by basalt underplating in stabilised shield regions will not result in subsequent eclogite formation and lower crustal recycling back into the mantle will not occur thus estimates of the average composition of the continental crust which are based on a mass balance of plate margin basaltic input from the mantle will not be adequate

roughness of natural fault surfaces the roughness of fault surfaces is important in the mechanics of fault slip and could play a role in determining whether sliding occurs via earthquakes or fault creep we have made preliminary measurements of the power spectral density of several fault surfaces over the wavelength range from 10 5 to 1 m using field and laboratory scale profilimeters the fault surfaces are strongly anisotropic profiles parallel to the slip direction have amplitudes about one order of magnitude lower than those perpendicular to the slip direction over most of the wavelength interval measured fault roughness perpendicular to the slip direction is similar to the roughness of natural joints the greater smoothness in the slip direction presumably represents wear resulting from slip combining our data with previous measurements of the roughness spectrum of the san andreas fault shows that fault surfaces are fractal over nearly eleven orders of magnitude in wavelength

numerical simulation of shear induced flow anisotropy and scale dependent aperture and transmissivity evolution of rock fracture replicas fluid flow anisotropy in a single rock fracture during a shear process is an important issue in rock mechanics and is investigated in this paper using fem modelling considering evolutions of apert

an experimental investigation of hydraulic behaviour of fractures and joints in granitic rock a method of measuring mean mechanical aperture of fractures based on gas volume balance is introduced the effects of shear displacement and normal stress on mechanical and hydraulic behaviour of fractures are also investigated the results obtained from tests conducted on granite samples from olympic dam central australia are compared with those calculated from existing shear dilation theories it is found that hydraulic aperture is considerably narrower than the measured mean mechanical aperture this highlights the need to consider tortuosity and surface roughness of fractures in the calculation of hydraulic aperture it is also found that shear dilation angle decreases linearly with increases in confining pressure as opposed to more rapid decreases predicted by existing empirical models from the results of this study a range of data describing the relationships between confining pressure shear displacements hydraulic aperture and permeability are presented which could help to develop stimulation programs for geothermal reservoirs

hydrologic issues associated with nuclear waste repositories significant progress in hydrology especially in subsurface flow and solute transport has been made over the last 35 years because of sustained interest in underground nuclear waste repositories the present paper provides an overview of the key hydrologic issues involved and to highlight advances in their understanding and treatment because of these efforts the focus is not on the development of radioactive waste repositories and their safety assessment but instead on the advances in hydrologic science that have emerged from such studies work and results associated with three rock types which are being considered to host the repositories are reviewed with a different emphasis for each rock type the first rock type is fractured crystalline rock for which the discussion will be mainly on flow and transport in saturated fractured rock the second rock type is unsaturated tuff for which the emphasis will be on flow from the shallow subsurface through the unsaturated zone to the repository the third rock type is clay rich formations whose permeability is very low in an undisturbed state in this case the emphasis will be on hydrologic issues that arise from mechanical and thermal disturbances i e on the relevant coupled thermo hydro mechanical processes the extensive research results especially those from multiyear large scale underground research laboratory investigations represent a rich body of information and data that can form the basis for further development in the related areas of hydrologic research

diversity of channeling flow in heterogeneous aperture distribution inferred from integrated experimental numerical analysis on flow through shear fracture in granite 1 shear mode ii fractures with shear displacements of 1 and 5 mm were generated by direct shear on granite under normal stresses of 1 20 and 60 mpa fracture surface mapping showed that the surface roughnesses of the shear fractures decreased with increasing shear displacement and normal stress and were smaller than those of tensile fractures reported in our previous study fluid flow experiments on the shear fractures provided fracture permeabilities at a wide range of confining pressures of 10 100 mpa nonmonotonic permeability was usually observed to decrease with increasing confining pressure however the permeability changes were different between the shear fractures generated at the normal stress of 20 and 60 mpa in addition obvious permeability changes with shear displacement were observed for 60 mpa whereas no significant difference was observed for 20 mpa comparing the shear fractures with the tensile fractures having shear displacements revealed clear differences even for equivalent shear displacements numerical models that were constructed using the data of the fracture surface mapping by matching their permeabilities with the experimentally evaluated fracture permeabilities revealed the development of preferential flow paths i e channeling flows for the shear fractures providing a diversity of channeling flow in heterogeneous aperture distributions of rock fractures in the earth s crust

constant dimensionality of fault roughness from the scale of micro fractures to the scale of continents 1 many faults and fractures in various natural and man made materials share a remarkable common fractal property in their morphology we report on the roughness of faults in rocks by analyzing the out of plane fluctuations of slip surfaces they display a statistical power law relationship with a nearly constant fractal exponent from millimeter scale micro fractures in fault zones to coastlines measuring thousands of kilometers that have recorded continental breakup a possible origin of this striking fractal relationship over 11 orders of magnitude of length scales is that all faulting processes in rocks share common characteristics that play a crucial role in the shaping of fault surfaces such as the effects of elastic long range stress interactions and stress screening by mechanical heterogeneities during quasi static fracture growth

fluid flow in fractally rough synthetic fractures fluid flow through fractures in rocks depends upon the roughness of the fracture surfaces in this work the height of both surfaces of a fracture in a core from the higashi hachimantai geothermal test field in northern japan have been measured and analyzed to determine the monofractal behavior of the surfaces and resulting aperture and the extent of surface matching we have used these parameters to create synthetic fractures that are extremely good imitations of the measured fracture by using a new technique for controlling surface mismatching these numerically synthesized fractures have been used in flow modeling by solving reynolds equation in the three dimensions and for calculating the transmissivity of the field fracture the modeled transmissivity showed good agreement with the fracture transmissivity obtained from field pressure tests and indicates that such an approach is able to estimate larger scale flow through real sub surface fractures

beyond laboratory scale prediction for channeling flows through subsurface rock fractures with heterogeneous aperture distributions revealed by laboratory evaluation the present study evaluates aperture distributions and fluid flow characteristics for variously sized laboratory scale granite fractures under confining stress as a significant result of the laboratory investigation the contact area in fracture plane was found to be virtually independent of scale by combining this characteristic with the self affine fractal nature of fracture surfaces a novel method for predicting fracture aperture distributions beyond laboratory scale is developed validity of this method is revealed through reproduction of the results of laboratory investigation and the maximum aperture fracture length relations which are reported in the literature for natural fractures the present study finally predicts conceivable scale dependencies of fluid flows through joints fractures without shear displacement and faults fractures with shear displacement both joint and fault aperture distributions are characterized by a scale independent contact area a scale dependent geometric mean and a scale independent geometric standard deviation of aperture the contact areas for joints and faults are approximately 60 and 40 changes in the geometric means of joint and fault apertures m em joint and em fault with fracture length m l are approximated by em joint 1 102 l0 1 and em fault 1 103 l0 7 whereas the geometric standard deviations of both joint and fault apertures are approximately 3 fluid flows through both joints and faults are characterized by formations of preferential flow paths i e channeling flows with scale independent flow areas of approximately 10 whereas the joint and fault permeabilities m2 kjoint and kfault are scale dependent and are approximated as kjoint 1 10 12 l0 2 and kfault 1 10 8 l1 1

topography of natural and artificial fractures in granitic rocks implications for studies of rock friction and fluid migration abstract the topography of fractures and joints has a strong influence on their frictional strength and fracture permeability important aspects of the surfaces are the size distribution and density of contact spots between the surfaces which can be calculated using topographic data for a variety of tensile fracture surfaces in granite including both natural joints and man made fractures spectral and statistical properties are similar suggesting that man made fractures in granites can be acceptable substitutes for natural fractures in some experimental situations the topographic data indicate that fracture surfaces at scales from 0 1 to 200 mm are approximately fractal and statistically self affine a log log plot of power spectral density vs spatial frequency calculated from the fracture surfaces indicates a spectral slope of 2 3 0 2 yielding a fractal dimension d between 2 25 and 2 45 shear fracture surfaces are also fractal but have anisotropic roughness which develops during the fracture initiation process the amount of anisotropy that develops on the shear fracture surfaces is small in comparison to that exhibited by natural fault surfaces which include anisotropy that results from post failure wear and from surface evolution for fractures like those measured in this study simple simulations indicate that the aperture size and number density of wall to wall contacts between the surfaces change non linearly with relative shear displacement of the surfaces it is possible to make preliminary estimates of how the permeability and frictional properties of fractures and joints depend on the size distribution and character of the contact spots furthermore given that artificial fractures can be generated numerically with statistical properties similar to those of natural or man made fractures it is reasonable for systematic studies of the effects of roughness on friction and fluid flow to use computer designed surfaces to provide a range of variability that is not easily accessible in the laboratory

shear deformation and eclogite formation within granulite facies anorthosites of the bergen arcs western norway the anorthosites of the bergen arcs contain two distinct metamorphic mineral assemblages which are stable under different p t conditions a granulite facies assemblage which equilibrated at t 800 900 c p 10 kbar is defined by the minerals plagioclase al rich diopside cpx i garnet gnt i scapolite orthopyroxene dark brown hornblende this assemblage is linked by corona structures to a primary magmatic mineralogy where coexistence of olivine and plagioclase limits the maximum crystallization pressure of the anorthosites to 8 kbar at 1200 c the anorthosites are transected by a series of fine grained shear zones in which the granulite facies assemblage is replaced by an eclogite mineralogy defined by omphacite cpx ii jd40 50 garnet kyanite epidote clinozoisite phengite quartz amphibole with plagioclase sometimes remaining in the marginal parts mineral compositions indicate equilibration conditions for the eclogite paragenesis of t 700 800 c p 16 19 kbar a series of textural and mineralogical changes which can be observed as the strain increases into the shear zones demonstrates that the eclogite mineralogy is formed at the expense of the granulite facies minerals during the early stages of shear zone development the eclogite mineralogy defines a strong mylonitic fabric which again is truncated by centimetres thick secondary shear zones containing clasts of both granulite and eclogite minerals these latter fine grained ultramylonites may be connected to uplift of this deep seated complex the eclogite shear zones are highly oblique to the granulite structures indicating that the eclogite shear zones formed under a new stress regime rb sr dating shows that the granulite facies assemblage formed in sveconorwegian time or earlier while minerals from shear zones define ages around 400 ma indicating a caledonian formation of the eclogites this work demonstrates the critical role of deformation in triggering metamorphic reactions whether the shear stress also was important in stabilizing the eclogite assemblages is not clear from the available data

hydromechanical properties and alteration of natural fracture surfaces in the soultz granite bas rhin france natural fractures are characterized by rough surfaces and complex fluid flows a large distribution of apertures residual voids within their walls and the presence of contact points in situ normal loads produce heterogeneous flows channeling the resulting permeabilities porosities or fluid rock exchange surfaces cannot be realistically modeled by parallel and smooth plate models four natural fractures are sampled at different depths and degrees of alteration in the soultz sandstone and granite eps1 drillhole soultz sous forets bas rhin france the fracture surfaces are measured with mechanical profilometry and maps of asperity heights xyz resulting local apertures xye are then calculated a statistical study of the surface profiles xz show that the fractures are more or less rough and tortuous according to the types of alteration altered samples are characterized by smoother surfaces of fractures such differences imply that i the average fracture aperture is not representative for the whole fracture and that ii the different local apertures should be integrated in hydraulic and mechanical models a hydraulic model finite difference calculations of fluid flow taking into account the elastic closure hertz contact theory of fractures with depth is used maps of contact points and relative local loads within the fracture planes are compared to flow maps they show different channeling of fluid flows strongly altered fractures are characterized by homogeneous fluxes despite the presence of numerous contact zones during the closure of fracture by contrast fresh fractures develop increasing fluid flow channels with depth fracture closure increasing normal stress does not systematically increase the channeling of fluid flow there is evidence for a general smoothing out of the irregularities of the fracture walls due to precipitation of secondary minerals indicating that the cubic law can be commonly valid also at great crustal depth but this validity depends on the degree of fracture alteration mineralogical and geochemical observations thus should be taken into account to perform more accurate permeability calculations and models of fluid circulation in fracture networks d 2002 elsevier science b v all rights reserved

single fractures under normal stress the relation between fracture specific stiffness and fluid flow abstract fracture specific stiffness and fluid flow through a single fracture under normal stress are implicitly related through the geometry of the void space and contact area that comprise the fracture data from thirteen different rock samples each containing a single fracture show that relationships between fracture specific stiffness and fluid flow through a fracture fall into two general classes of behavior fractures either fall on a loosely defined universal curve relating fluid flow to fracture specific stiffness or else the flow is weakly dependent on fracture specific stiffness the second relationship shows that flow decreases slowly with increasing fracture specific stiffness the first relationship shows that flow decreases rapidly for increases in fracture specific stiffness to understand this behavior computer simulations on simulated single fractures were performed to calculate fluid flow fracture displacement and fracture specific stiffness as a function of normal stress simulated fractures with spatially correlated and uncorrelated aperture distributions were studied fractures with spatially uncorrelated aperture distributions tend to exhibit a weak dependence of fluid flow on fracture specific stiffness because these fractures tend to have multiple connected paths across the sample which can support flow with uniformly distributed contact area thus an increment in stress will increase the stiffness of the fracture without greatly reducing the amount of fluid flow on the other hand fractures with spatially correlated aperture distributions tend to belong to the universal relationship because correlated fractures tend to have only one or two dominant flow paths and the contact area is limited to a few regions resulting in a compliant fracture thus an increment in stress on a spatially correlated fracture will result in an increase in stiffness and rapid decrease in fluid flow these spatial correlations in fracture void geometry can be differentiated in the laboratory based on the observed fracture specific stiffness fluid flow relationship for a single fracture under normal loading

emergence of anomalous transport in stressed rough fractures abstract we report the emergence of anomalous non fickian transport through a rough walled fracture as a result of increasing normal stress on the fracture we show that the origin of this anomalous transport behavior can be traced to the emergence of a heterogeneous flow field dominated by preferential channels and stagnation zones as a result of the larger number of contacts in a highly stressed fracture we show that the velocity distribution determines the late time scaling of particle spreading and velocity correlation determines the magnitude of spreading and the transition time from the initial ballistic regime to the asymptotic anomalous behavior we also propose a spatial markov model that reproduces the transport behavior at the scale of the entire fracture with only three physical parameters our results point to a heretofore unrecognized link between geomechanics and particle transport in fractured media

direct measurement of contact area and stress dependence of anisotropic flow through rock fracture with heterogeneous aperture distribution abstract direct measurement of a contact area using pressure sensitive film was performed for artificially generated granite tensile fractures with different shear displacements of 2 3 and 5 mm and at various normal stresses of up to approximately 100 mpa to clarify the relationship between anisotropic flow and normal stress in a rock fracture with shear displacement aperture distributions with contact areas were then numerically generated using fracture surface geometry data and anisotropic flow was evaluated through a bi directional flow simulation the directional distributions of contacting asperities in the fracture plane were clearly observed for every given condition and the contacting asperities tended to align in the direction perpendicular to shear displacement generally the contact area increased and the anisotropic distribution was enhanced with increasing normal stress however the contact areas for 3 mm shear displacement were less stress dependent anisotropic flow with higher permeability in the perpendicular direction was always observed for aperture distributions with an anisotropic distribution of the contacting asperities flow paths created in the aperture distributions seemed less tortuous in the perpendicular direction due to the distribution of the contacting asperities the anisotropic flow was enhanced with increasing normal stress to the fracture and was more evident for the smaller shear displacements of 2 mm due to the high sensitivity of the contact area to the normal stress the results suggested that the anisotropic flow was likely for a wide range of normal stresses and correspondingly at varying depths in the earth s crust at which anisotropic flow was enhanced with increasing normal stress based on the stress dependence of the contact area in addition the stress dependent anisotropic flow is expected for much higher normal stresses because complete fracture closure with 100 contact area may be unexpected under the crustal stress conditions at depths of several to ten thousand meters

permeability anisotropy induced by the shear displacement of rough fracture walls 1 the permeability anisotropy that results from a shear displacement between the complementary self affine walls of a rough fracture is investigated experiments in which a dyed fluid radially injected into a transparent fracture displaces a transparent one are presented a clear anisotropy is observed in the presence of shear displacements and allows us to estimate the ratio of the permeabilities for flows parallel and perpendicular to a simple model which accounts for the development of channels perpendicular to qualitatively explains these results and predicts a permeability decreasing increasing linearly with the variance of the aperture field for flow parallel perpendicular to the shear displacement these predictions are then compared to the results of numerical simulations performed using a lattice boltzmann technique and to the anisotropies measured in displacement experiments

fluid pocket generation in response to heterogeneous reactivity of a rock fracture under hydrothermal conditions fractures are the location of various water rock interactions within the earth s crust however the impact of the chemical heterogeneity of fractures on hydraulic properties is poorly understood we conducted flow through experiments on the dissolution of granite with a tensile fracture at 350 c and fluid pressure of 20 mpa with confining pressure of 40 mpa the aperture structures were evaluated by x ray computed tomography ct before and after the experiments under the experimental conditions quartz grains dissolve rapidly to produce grain scale pockets on the fracture surface whereas altered feldspar grains act as asperities to sustain the open cavities the fracture contained gouge with large surface area the feedback between fluid flow and the rapid dissolution of gouge material produced large fluid pockets whereas permeability did not always increase significantly such intense hydrological chemical interactions could strongly influence the porosity permeability relationship of fractured reservoirs in the crust

geoflow a novel model simulator for prediction of the 3 d channeling flow in a rock fracture network 1 a fluid flow experiment was conducted on a granite sample containing two intersecting fractures at constant confining pressure water was supplied to the sample via a single inlet port and the effluent was collected using four isolated outlet ports the flow rate varied widely among these ports indicating the formation of 3 d preferential flow paths channeling flow which likely occur in fractured rocks but have been considerably difficult to identify by existing methods the novel concept of geoflow a discrete fracture network model simulator in which fractures have a heterogeneous aperture distribution has been developed to analyze such complex fluid flow a fluid flow simulation was conducted using geoflow with aperture distributions within the two fractures as determined using fracture surface topography data despite the simplicity of the simulation geoflow revealed a 3 d channeling flow within the sample which explains the general trend of the uneven outflows in the experiment

influence of fracture scale heterogeneity on the flow properties of three dimensional discrete fracture networks dfn while permeability scaling of fractured media has been so far studied independently at the fracture and network scales we propose a numerical analysis of the combined effect of fracture scale heterogeneities and the network scale topology the analysis is based on 2 106 discrete fracture network dfns simulations performed with highly robust numerical methods fracture local apertures are distributed according to a truncated gaussian law and exhibit self affine spatial correlations up to a cutoff scale lc network structures range widely over sparse and dense systems of short long or widely distributed fracture sizes and display a large variety of fracture interconnections flow bottlenecks and dead ends at the fracture scale accounting for aperture heterogeneities leads to a reduction of the equivalent fracture transmissivity of up to a factor of 6 as compared to the parallel plate of identical mean aperture at the network scale a significant coupling is observed in most cases between flow heterogeneities at the fracture and at the network scale the upscaling from the fracture to the network scale modifies the impact of fracture roughness on the measured permeability this change can be quantified by the measure a2 which is analogous to the more classical power averaging exponent used with heterogeneous porous media and whose magnitude results from the competition of two effects i the permeability is enhanced by the highly transmissive zones within the fractures that can bridge fracture intersections within a fracture plane ii it is reduced by the closed and low transmissive areas that break up connectivity and flow paths citation de dreuzy j r y meheust and g pichot 2012 influence of fracture scale heterogeneity

simple mathematical model of a rough fracture a simple mathematical model of rough walled fractures in rock is described which requires the specification of only three main parameters the fractal dimension the rms roughness at a reference length scale and a length scale describing the degree of mismatch between the two fracture surfaces fractured samples collected from natural joints and laboratory specimens have been profiled to determine the range of these three parameters in nature it is shown how this surface roughness model can be implemented on a computer allowing future detailed study of the mechanical and transport properties of single fractures and the scale dependence of these properties

the role of deformation in aiding recrystallization an example from a high pressure shear zone central australia a dolerite body in the western musgrave block was variably approached the dolerite shows no evidence of any metamorphism and or deformation that predates the recrystallized in a 0 5 1 m wide sharply defined high grade shear zone at p 12 14 kbar and t 750 c all samples within and shear zone recrystallization that took place under highand low strain conditions resulted in markedly different adjacent to the shear zone have a common protolith they are divided into unfoliated group 1 samples outside the shear zone and foliated metamorphic textures and mineral compositions the occurrence is particularly useful for understanding the group 2 samples within the shear zone group 1 samples show a progressive increase in the degree of recrystallization as the shear role of deformation and reaction kinetics in transforming the igneous textures and minerals into metamorphic zone is approached systematic changes in modal proportions and mineral composition reflect increased reaction rates as a result of assemblages high pressure high temperature reaction coronas are increasing strain and variations in ah2o group 1 samples are dominated by garnet bearing coronas that separate orthopyroxene well documented in partially recrystallized metabasites from several terranes e g griffin 1972 griffin heier clinopyroxene and ilmenite from plagioclase low strain in the group 1 samples allowed the preservation of comparatively al rich 1973 mclelland whitney 1977 austrheim griffin 1985 pognante 1985 koons et al 1987 rubie 1990 fe mg poor compositional domains replacing igneous plagioclase and fe mg rich al poor domains replacing igneous pyroxene indares 1993 many examples preserve an incomplete group 2 samples are more thoroughly recrystallized do not contain transition from gabbro or dolerite protoliths to garnet coronas and have more constant mineral compositions reflecting granulite or eclogite facies assemblages e g griffin higher diffusion rates the wide range in mineral composition and heier 1973 mork 1985a b indares 1993 where textures and their relationship to strain intensity within the gabbro metamorphism was accompanied by high strain the body emphasize the important role that deformation and fluids on recrystallization of protoliths is commonly more complete all scales play in the development of metamorphic textures austrheim griffin 1985 mork 1985a pognante 1985 koons et al 1987 rubie 1990 the presence of h2o may also further aid reaction progress by enhancing intergranular diffusion and deformation brodie rutter

local non vuggy modeling and relations among porosity permeability and preferential flow for vuggy carbonates abstract it is challenging to predict the permeability of a vuggy carbonate based on a bulk porosity indicator such as the effective porosity obtained by helium porosimetry the primary reason is that heterogeneity in the local porosity distribution within the rock may cause nonuniform fluid flow or preferential flow due to the large amount of hydraulically ineffective pore spaces here we present the results of a new x ray computed tomography ct based numerical fluid flow analysis for various types of vuggy carbonate samples together with experimental visualization of the flow paths within some samples to numerically analyze the preferential flow the samples are modeled as aggregates of submillimeter scale non vuggy carbonates with different porosities for which the widely used lucia bulk porosity permeability relations of non vuggy carbonate rock are applied local non vuggy modeling the local porosity distribution is estimated using x ray computed tomography of the samples the local permeability distribution is then estimated based on the local porosity distribution and a single phase darcy flow simulation is performed this provides the bulk porosity and permeability and the preferential flow within the samples which are consistent with experimentally measured values and visualized flow paths both lognormal and normal distributions of local porosity are identified preferential flow is associated with a lognormal distribution and the geometric standard deviation is related to the degree of preferential flow we show that in the case of a normal local porosity distribution the bulk permeability can be predicted based on a bulk porosity indicator such as the effective porosity measured using helium porosimetry additionally we show that in the case of a lognormal local porosity distribution the permeability is a function of the geometric mean and the geometric standard deviation of the distribution this new method will contribute to better evaluation and modeling of vuggy carbonate reservoirs aquifers for hydrocarbon production carbon storage and water resource conservation