impact of poroelastic response of sandstones on geothermal power production during geothermal power production using a borehole doublet consisting of a production and injection well the reservoir conditions such as permeability k porosity and skempton coefficient b at the geothermal research site gross schoenebeck germany will change besides a temperature decrease at the injection well and a change of the chemical equilibrium also the pore pressure pp will vary in a range of approximately 44 mpa 10 mpa in our reservoir at 3850 to 4258 m depth this leads to a poroelastic response of the reservoir rocks depending on effective pressure p eff difference between mean stress and pore pressure resulting in a change in permeability k porosity and the poroelastic parameter skempton coefficient b hence we investigated the effective pressure dependency of flechtinger sandstone an outcropping equivalent of the reservoir rock via laboratory experiments the permeability decreased by 21 at an effective pressure range from 3 to 30 mpa the porosity decreased by 11 p eff 6 to 65 mpa and the skempton coefficient decreased by 24 p eff 4 to 25 mpa we will show which mechanisms lead to the change of the mentioned hydraulic and poroelastic parameters and the influence of these changes on the productivity of the reservoir the most significant changes occur at low effective pressures until 15 to 20 mpa for our in situ reservoir conditions p eff 43 mpa a change of 10 mpa effective pressure will result in a change in matrix permeability of less than 4 and in matrix porosity of less than 2 besides natural fracture systems fault zones and induced hydraulic fractures the rock matrix its only one part of geothermal systems all components can be influenced by pressure temperature and chemical reactions therefore the determined small poroelastic response of rock matrix does not significantly influence the sustainability of the geothermal reservoir

a novel dynamic impact pressure model of debris flows and its application on reliability analysis of the rock mass surrounding tunnels abstract assessing the influence of the impact pressure exerted on surrounding rock mass by potential debris flows is one of the challenges in a mountain tunnel construction project this paper proposes an effective mathematical model for the assessment of impact pressure exerted by debris flows on obstacles the characteristics of the new model are analyzed and the parameters determination method for the new model are deduced also a new method for dynamic reliability analysis of the rock mass surrounding tunnels is proposed and is constituted into three key steps first by inputting impact pressure of debris flows generated by the aforementioned new model the flac3d is used as the dynamic analysis engine to obtain the time varying stress distribution of surrounding rock mass during the impact of debris flow second the factor of safety fos contours of surrounding rock mass are generated based on element states using the maximum tensile stress criterion and the mohr coulomb yield criterion third by using the time varying contours of the fos a failure probability and a reliability index are obtained from a reliability perspective a case study shows the complete analysis process and confirms the effectiveness of the above methodology in sum this paper provides new ideas new methods and a reference example for evaluating the influence of dynamic impact exerted by debris flows on the rock mass surrounding tunnels

the impact of gas slippage on permeability effective stress laws implications for predicting permeability of fine grained lithologies abstract the impact of gas slippage on experimentally derived permeability effective stress laws has been investigated using gas shale from the montney formation canada and previously published data for gas shales from the eagle ford and marcellus formations usa in these low permeability reservoirs gas slippage results in apparent permeability effect stress law coefficients less than one and drives coefficients towards lower values at higher confining pressures and lower pore pressures the results show that in low permeability rocks such as shale gas and shale oil reservoirs gas slippage is significant at pore pressures in excess of 7 mpa and if not considered results in significant errors in calculated effective stress law coefficients permeability effective stress laws reported in the literature for fine grained lithologies under the assumption that gas slippage was negligible at and above pore pressures of 7 mpa are likely in error such studies need to be thoroughly re examined and future studies of fine grained lithologies need to be conscious of significant apparent permeability variation due to gas slippage at pore pressures at and above 7 mpa

closure of the mongol okhotsk ocean insights from seismic tomography and numerical modelling abstract the existence of the palaeozoic and mesozoic mongol okhotsk ocean is evident from the mongol okhotsk suture which stretches from central mongolia to the sea of okhotsk a lack of sufficient palaeomagnetic data and an otherwise diffuse suture with an abrupt termination to the west has led to difficulties in reconstructing the history geometry and closure of this ocean both the timing and style of the ocean s closure are unclear and have led to several alternative reconstructions closure timing ranges between the late jurassic 155 ma and beginning of the early cretaceous 120 ma and the proposed kinematics include contemporaneous subduction along two opposite margins subduction along only one margin or with a component of left lateral shear in the present study numerical models of mantle convection are coupled with global plate reconstructions to investigate ambiguities regarding the closure of the mongol okhotsk ocean in order to decipher the tectonic history of this enigmatic region two end member scenarios of subduction location either along the present day northern or the southern margins of the mongol okhotsk ocean are imposed as kinematic surface boundary conditions for the past 230 myrs through a comparison to seismic tomography the results indicate a preferred subduction history along the siberian margin relative northern margin of the mongol okhotsk ocean at present day the slab remnant is predicted to be located farther west than previously proposed furthermore we find that the subducting slabs in this region generate a hot dense pile at the same location and with a similar shape as the perm anomaly

structural development of the snow lake allochthon and its role in the evolution of the southeastern trans hudson orogen in manitoba central canada the snow lake allochthon is a zone of tectonic interleaving of sedimentary rocks of an inverted marginal basin kisseynew domain with island arc and oceanic rocks it is located in the southeaster

effective stress law for the permeability of clay rich sandstones 1 two models of clay rich sandstones are analyzed to explain the relative sensitivity of permeability to pore pressure and confining pressure in one model the clay lines the entire pore wall in a layer of uniform thickness and in the second model the clay is distributed in the form of particles that are only weakly coupled to the pore walls equations of elasticity and fluid flow are solved for both models giving expressions for the effective stress coefficients in terms of clay content and the elastic moduli of the rock and clay both models predict that the permeability will be much more sensitive to changes in pore pressure than to changes in confining pressure the clay particle model gives somewhat better agreement with data from the literature and with new data on a stainton sandstone having a solid volume fraction of 8 clay

mapping the 3d lithofacies architecture of a vms ore system on a curvilinear faulted grid a case study from the flin flon mining camp canada abstract the 3d lithofacies architecture of the thrust imbricated paleoproterozoic 85 5 mt flin flon volcanogenic massive sulfide vms ore system trans hudson orogen canada has been mapped in 3d using a numerical grid modeling methodology this methodology is based on the structural knowledge universal approach skua modeling work flow developed for modeling hydrocarbon reservoirs one of the major advantages of applying this methodology to mineral exploration is that it allows exploiting knowledge on the structural setting of the ore deposit without the need to determine all kinematic constraints that would be required for a full 3d balanced restoration the work flow proceeds by modeling the volume of the thrust repeated mine horizon on a curvilinear faulted grid that is conformable to the enveloping geological structure and that includes discontinuities to model fault offsets it then uses a coordinate transformation to partly remove the influence of geological structure on euclidean distance based geostatistical estimations it subsequently applies the inverse of this coordinate transformation to represent the interpolated or simulated lithofacies distribution in the finite deformed state randomized validation experiments show that the geostatistical analysis resulted in an estimated overall 74 accuracy of the predicted lithofacies classes over the grid the lithofacies grid models provide insight into the post depositional deformation history of the ore system and the rifted volcanic arc setting in which the flin flon massive sulfide ore was deposited the lithofacies grid models also serve as stratified containers for generating lithochemical property models that can be used for spatially characterizing ore forming processes such as hydrothermal alteration and ore metal zoning

experimental investigation of matrix permeability of gas shales predicting long term production from gas shale reservoirs has been a major challenge for the petroleum industry to better understand how production profiles are likely to evolve with time we have conducted laboratory experiments examining the effects of confining stress and pore pressure on permeability experiments were conducted on intact core samples from the barnett eagle ford marcellus and montney shale reservoirs the methodology used to measure permeability allows us to separate the reduction of permeability with depletion because of the resultant increase in effective confining stress and the increase in permeability associated with knudsen diffusion and molecular slippage also known as klinkenberg effects at very low pore pressure by separating these effects we are able to estimate the relative contribution of both darcy and diffusive fluxes to total flow in depleted reservoirs our data show that the effective permeability of the rock is significantly enhanced at very low pore pressures because of the slippage effects we use the magnitude of the klinkenberg effect to estimate the effective aperture of the flow paths within the samples and compare these estimates to scanning electron microscopy image observations our results suggest effective flow paths to be on the order from tens of nanometers in most samples to 100 200 nm in a relatively high permeability eagle ford sample finally to gain insight on the scale dependence of permeability measurements the same core plugs were crushed and permeability was again measured at the particle scale using the so called gas research institute method the results show much lower permeability than the intact core samples with very little correlation to the measurements on the larger scale cores

numerical analysis of dynamics of debris flow over erodible beds in wenchuan earthquake induced area the basal entrainment of debris flows play a significant role in its amplification and the final volume of deposition could be several to hundred times of its initial volume in this paper the shallow water equations coupled with basal material entrainment applied in debris flows have been given to demonstrate the amplification a new basal entrainment model taking advantage of both coulomb and voellmy frictional laws are proposed providing a unified formula to simulate the stop and go process of debris flows both time and space second order maccormack tvd finite difference method is suggested to solve the coupled equations numerical comparisons with usgs flume experiment and hongchun gully debris flow in wenchuan earthquake induced area are carried out to prove its effectiveness it is established that the momentum exchange term between the flows and the basal materials has a significant influence on the dynamic characteristics and the entrainment effects are essential to model the dynamic process of debris flows in an earthquake induced area c 2014 elsevier b v all rights reserved

influence of microheterogeneity on effective stress law for elastic properties of rocks understanding the effective stress coefficient for seismic velocity is important for geophysical applications such as overpressure prediction from seismic data as well as for hydrocarbon production and monitoring using time lapse seismic measurements this quantity is still not completely understood laboratory measurements show that the seismic velocities as a function of effective stress yield effective stress coefficients less than one and usually vary between 0 5 and 1 at the same time theoretical analysis shows that for an idealized monomineral rock the effective stress coefficient for elastic moduli and therefore also for seismic velocities will always equal one we explore whether this deviation of the effective stress coefficient from unity can be caused by the spatial microheterogeneity of the rock the results show that only a small amount less than 1 of a very soft component is sufficient to cause this effect such soft material may be present in grain contact areas of many rocks and may explain the variation observed experimentally

flow of variably fluidized granular masses across three dimensional terrain 1 coulomb mixture theory rock avalanches debris flows and related phenomena consist of grain fluid mixtures that move across three dimensional terrain in all these phenomena the same basic forces govern motion but differing mixture compositions initial conditions and boundary conditions yield varied dynamics and deposits to predict motion of diverse grain fluid masses from initiation to deposition we develop a depth averaged three dimensional mathematical model that accounts explicitly for solid and fluid phase forces and interactions model input consists of initial conditions path topography basal and internal friction angles of solid grains viscosity of pore fluid mixture density and a mixture diffusivity that controls pore pressure dissipation because these properties are constrained by independent measurements the model requires little or no calibration and yields readily testable predictions in the limit of vanishing coulomb friction due to persistent high fluid pressure the model equations describe motion of viscous floods and in the limit of vanishing fluid stress they describe one phase granular avalanches analysis of intermediate phenomena such as debris flows and pyroclastic flows requires use of the full mixture equations which can simulate interaction of high friction surge fronts with more fluid debris that follows special numerical methods described in the companion paper are necessary to solve the full equations but exact analytical solutions of simplified equations provide critical insight an analytical solution for translational motion of a coulomb mixture accelerating from rest and descending a uniform slope demonstrates that steady flow can occur only asymptotically a solution for the asymptotic limit of steady flow in a rectangular channel explains why shear may be concentrated in narrow marginal bands that border a plug of translating debris solutions for static equilibrium of source areas describe conditions of incipient slope instability and other static solutions show that nonuniform distributions of pore fluid pressure produce bluntly tapered vertical profiles at the margins of deposits simplified equations and solutions may apply in additional situations identified by a scaling analysis assessment of dimensionless scaling parameters also reveals that miniature laboratory experiments poorly simulate the dynamics of full scale flows in which fluid effects are significant therefore large geophysical flows can exhibit dynamics not evident at laboratory scales

effects of diagenesis and clays on compressional velocities in rocks experimental results at ultrasonic frequencies in brine or water saturated samples cut perpendicular to bedding demonstrate that compressional velocities vary linearly with porosity and volume fraction clay in detrital silicate rocks characterized by pores with low aspect ratios p wave velocity is more sensitive to porosity than clay content obeying the empirically derived expression vp 2 4c 8 6 5 8 at 800 bars confining pressure and 400 bars pore pressure where the units of vp are kilometers per second is the volume fraction pores and c is the volume fraction clay deviations from this equation are less than 2 with the exception of the high pore aspect ratio st peter sandstone which has a compressional velocity that is 17 higher than the predicted value the equation is insensitive to the chemical compostion of the dominant clay mineral and apparently insensitive to the location of the clay grains with respect to the mineral framework e g in free pore space or in contact zones between mineral grains of lower compressibilities

3d seismic imaging of volcanogenic massive sulfide deposits in the flin flon mining camp canada part 2 forward modeling abstractwe applied seismic modeling for a detailed 3d geologic model of the flin flon mining camp canada to address some imaging and interpretation issues related to a 17 km2 3d survey acquired in the camp and described in a complementary paper part 1 a 3d geologic volumetric model of the camp was created based on a compilation of geologic data constraints from drillholes surface geologic mapping interpretation of 2d seismic profiles and 3d surface and grid geostatistical modeling techniques the 3d modeling methodology was based on a hierarchical approach to account for the heterogeneous spatial distribution of geologic constraints elastic parameters were assigned within the model based on core sample measurements and correlation with the different lithologies the phase screen algorithm used for seismic modeling was validated against analytic and finite difference solutions to ensure that it provided accurate amplitude variation with offset behavior for dipping strata synthetic data were gener

gas permeability calculation of tight rocks based on laboratory measurements with non ideal gas slippage and poroelastic effects considered abstract permeability measurements on low permeable rocks in the laboratory require much higher pressure gradients than those in real reservoirs to produce detectable flow rates in finite laboratory time this may result in a high effective stress gradient that can cause non uniform deformation of the pore system to better understand the measured laboratory data a theoretical model has been developed for calculating gas permeability of tight rock from laboratory measurements which couples the effect of poroelastic deformation with the gas non ideality and slippage effects the proposed characteristic pressure model considers the poroelastic deformation and the real gas effects in the permeability calculation which improves the accuracy of calculated permeability from laboratory measurements of tight rocks under large pressure gradients the new model is validated by independent multiscale simulations in which the poroelastic deformation and slippage effects are captured on the pore scale while the real gas behavior is captured on the core scale the numerical results also indicate that the poroelastic deformation mainly affects the high pressure region while the variation of gas properties dominates the low pressure region the new model is then applied to the calculation of gas permeability based on the laboratory measurements on coal and shale samples with non ideal gas slippage and poroelastic effects considered the poroelastic deformation and the real gas effect can be important as well as the slippage effect and the calculated apparent permeability will be overestimated if these two effects are neglected

effects of local rock heterogeneities on the hydromechanics of fractured rocks using a digital image based technique a digital image based dib finite element approach is developed based on the numerical code rock failure process analysis rfpa to characterize micro scale rock heterogeneity and to understand the impact of micro scale rock heterogeneity on the macro scale hydromechanical response of rocks the dib technique incorporates small scale spatial variability of initial deformation modulus strength and permeability directly into a coupled hydromechanical model variability in young s modulus strength and permeability is applied by a property map defined from the pixel scale of a digital image in the rfpa mechanical deformation is followed including the accumulation of damage applied in individual elements which modifies modulus strength and permeability with the intensity of damage the rfpa simulates progressive failure in fractured rocks representing both the growth of existing fractures and the formation of new fractures without having to identify crack tips and their interaction explicitly in this dib simulation approach image voxels are used to give equivalent mechanical and flow properties these property maps are ported to the model capable of solving directly for the evolving deformation and fluid flow fields the model is validated through comparisons of the simulated results with phenomenological observations documented in previous studies the validated model is then applied to investigate the hydromechanical response of fractured rock characterized by digital image the model is able to reproduce the spatial evolution of damage in the sample the coalescence of existing cracks and the formation of new cracks

positive feedback and momentum growth during debris flow entrainment of wet bed sediment debris flows typically occur when intense rainfall or snowmelt triggers landslides or extensive erosion on steep debris mantled slopes the flows can then grow dramatically in size and speed as they entrain material from their beds and banks but the mechanism of this growth is unclear indeed momentum conservation implies that entrainment of static material should retard the motion of the flows if friction remains unchanged here we use data from large scale experiments to assess the entrainment of bed material by debris flows we find that entrainment is accompanied by increased flow momentum and speed only if large positive pore pressures develop in wet bed sediments as the sediments are overridden by debris flows the increased pore pressure facilitates progressive scour of the bed reduces basal friction and instigates positive feedback that causes flow speed mass and momentum to increase if dryer bed sediment is entrained however the feedback becomes negative and flow momentum declines we infer that analogous feedbacks could operate in other types of gravity driven mass flow that interact with erodible beds the mechanisms by which debris flows acquire mass and momentum as they entrain material are unclear large scale experiments suggest that the pore pressure of wet bed sediment increases as the flow moves over the bed leading to reduced friction and progressive scouring of the base

high resolution 2d seismic imaging and forward modeling of a polymetallic sulfide deposit at garpenberg central sweden we acquired a high resolution 2d seismic profile to test the capability of the seismic method in imaging a sulfide ore body at garpenberg central sweden delineation of the geologic structures wh

numerical modeling of percolating flow path in a caprock formation during aquifer pressurization and its implication for co2 sequestration spatial distribution of sand bodies in caprock is important to its sealing potential in the evaluation of a potential waste disposal site a numerical investigation was conducted to investigate the roles of sand bodies in caprock integrity and a new leaking mechanism associated with the embedded sand bodies has been identified for the first time this numerical model is characterized by a low proportion of sand bodies in caprock formation and stochastic permeability assignments to the shale facies with a consideration of stress sensitive permeability the research revealed that sand bodies in caprock even initially unconnected due to their low concentration represent the foundation for creating a percolating flow path if certain conditions are met these conditions include a relatively high pore pressure gradient across the caprock which may occur during fluid injection and a favorable geometric configuration of these sand bodies sand bodies of different shapes play different roles in forming a percolating flow path sand bars dykes can lead pore pressure front to cover a considerable vertical thickness quickly while thin sand sheets tend to transfer the pore pressure front across a large horizontal range and thus increase the possibility of involving other local sand bodies in the evolution of percolating flow paths on the other hand the presence of percolating flow path in caprock can limit the pore pressure increase in the aquifer formation during fluid injection the more active the flow paths the less increase the pore pressure that occurs in the aquifer stress dependent permeability can facilitate the formation of percolating flow path but evaluating how much impact it may have remains a question for future research the modeling results indicate that the underlying geologically based discrete structure of permeable domains even when masked by a low permeable rock matrix exerts a significant influence on the location and magnitude of fluid flow within the system during fluid injection

determining the maximum overburden along thrust faults using a porosity versus effective confining pressure curve abstract this study aims to quantify the tectonically induced thrusting and erosion here we propose and evaluate a laboratory based method for determining the maximum effective stress ever sustained by a sedimentary rock formation the porosities of nineteen samples collected from two deep boreholes of the taiwan chelungpu fault drilling project were measured under different confining stresses the relation between measured porosity and confining pressure compaction curve is bilinear in log log scale the maximum effective stress of the tested rocks was determined from the intersection point of the two straight lines of the compaction curve the maximum effective stresses of the rocks below the sanyi fault reverse fault are close to the in situ vertical effective stress above the sanyi fault hanging wall where the rocks have been thrust the maximum effective stresses of the rocks are significantly greater than the in situ stress with an average value of 29 48 mpa that is the eroded thickness of the formation on the hanging wall of the sanyi fault is 2482 m a value close to that determined from the geological profile 2773 m it is inferred that the total displacements along the thrust sanyi fault is 11 5 km a value close to that determined from the geological profile 14 16 km these results indicate that the proposed laboratory based method is potentially useful for determining the thrusting and erosion in a fold thrust belt and the total displacements along a thrust fault

simultaneous core sample measurements of elastic properties and resistivity at reservoir conditions employing a modified triaxial cell a feasibility study adaptations of existing triaxial cells for ultrasonic p and s wave measurements are well documented this paper proposes further modification of such a cell so that also resistivity measurements can be carried out simultaneously at reservoir conditions by employing the top cap and the pedestal of the cell as electrodes axial resistivity measurements are now feasible in order to minimize the polarization effect of this two electrode arrangement careful analyses have been carried out to optimize the choice of electrode coating and measurement frequency band radial resistivity measurements are also included in the system by introducing a strap electrode system in a reservoir under production changes in both saturations temperature if steam injection and stresses can take place therefore the modified triaxial system should be able to measure the integrated effects on the acoustic parameters and electric responses caused by variations in each of these parameters the feasibility of the system to obtain such reliable information is demonstrated employing a small selection of core samples in the future such combined measurements on reservoir core samples can be used to link both seismic and electromagnetic observations to the actual earth model and constrain both modelling and inversion

effects of confining pressure on the permeability of three rock types under compression abstract triaxial tests were conducted on three different rocks under confining pressures of 1 15 mpa at 295 k using an ultra compact triaxial cell the samples were held for 24 h under the target consolidation pressure and then constant strain rate compression was applied measuring permeability the structural changes were measured by thin section image analysis and micro focus x ray computed tomography for the shikotsu welded tuff the permeability decreased monotonously with axial compression mainly due to pore collapse for the kimachi sandstone the permeability first decreased with increasing axial stress then began to increase when the total lateral strain recovered its value before the application of confining pressure and then maintained an almost constant value in the post peak region the minimum and final permeability decreased with increasing confining pressure mainly due to compaction and large plastic deformation of clay cementing materials for the inada granite the tendency of permeability change during axial compression was almost the same as for the kimachi sandstone the final permeability was larger than that before compression and the permeability decreased with smaller confining pressure mainly due to a decrease in the number and width of rupture planes and the absence of axial cracks from biotite the permeability however increased under larger confining pressures mainly due to the formation of subrupture planes caused by the high stress concentration at the rough and stiff rupture plane under large confining pressure

catastrophic debris flows on 13 august 2010 in the qingping area southwestern china the combined effects of a strong earthquake and subsequent rainstorms in the wenchuan area in sw china an abundance of loose co seismic landslide debris was present on the slopes after the wenchuan earthquake which in later years served as source material for rainfall induced debris flows or shallow landslides slopes composed of cambrian sandstones and siltstones intercalated with slates appeared to be most susceptible to co seismic landsliding a total of 20 debris flows are described in this paper all were triggered by heavy rainfall on 13th of august 2010 field reconnaissance and measurements supported by aerial photo interpretation were conducted to identify the locations and morphological characteristics of the debris flow gullies in order to obtain information about surface area and volume of landslides and the debris flows the debris flows in the study area were initiated by two processes a run off erosion on co seismic landslide material and concentrated erosion of landslide debris in steep channels b new landslides that transform into debris flows the volume of debris flow deposits on individual fans varies by many orders of magnitude the smallest deposit has a volume of from 5760 to 3 1 million m3 a comparison of the measured volumes deposited on the fan with the volumes of debris stored in the catchment shows the huge potential for future debris flow activity whilst there is a weakly significant positive correlation between these two volumes no significant statistical correlation could be established between volumes of debris flow deposits and other morphometric parameters of the catchment a catastrophic debris flow catchment the wenjia catchment was selected as an extreme case to show in detail the mechanism of debris flow formation as a result of intensive erosion in loose material which was deposited by a rock avalanche during the 2008 earthquake event analyses of the meteorological conditions that triggered these debris flows show one day antecedent precipitation varying between 67 7 and 137 6 mm with a mean rainfall intensity of about 7 3 to 22 5 mm h a rainfall event with peak intensity of 38 7 mm h triggered the largest debris flow event rainfall data related to five debris flow events in the wenjia torrent was used to establish a primary rainfall intensity duration relationship for the triggering of debris flows which was compared to other rainfall duration thresholds from other parts of the world in the discussion emphasis is laid on the need to unravel the process mechanisms which initiated the debris flows for a better understanding and assessment of meteorological thresholds

stress dependence of the permeability and porosity of sandstone and shale from tcdp hole a abstract we utilize an integrated permeability and porosity measurement system to measure the stress dependent permeability and porosity of pliocene to pleistocene sedimentary rocks from a 2000 m borehole experiments were conducted by first gradually increasing the confining pressure from 3 to 120 mpa and then subsequently reducing it back to 3 mpa the permeability of the sandstone remained within a narrow range 10 14 10 13 m2 the permeability of the shale was more sensitive to the effective confining pressure varying by two to three orders of magnitude than the sandstone possibly due to the existence of microcracks in the shale meanwhile the sandstone and shale showed a similar sensitivity of porosity to effective pressure whereby porosity was reduced by about 10 20 when the confining pressure was increased from 3 to 120 mpa the experimental results indicate that the fit of the models to the data points can be improved by using a power law instead of an exponential relationship to extrapolate the permeability or porosity under larger confining pressure e g 300 mpa using a straight line in a log log plot might induce unreasonable error but might be adequate to predict the stress dependent permeability or porosity within the experimental stress range part of the permeability and porosity decrease observed during loading is irreversible during unloading

network modeling of the evolution of permeability and dilatancy in compact rock rock deformation and fluid transport are coupled together in many crustal settings nonhydrostatic stress can greatly affect pore structure and transport properties of a rock when a compact rock is stressed to failure dilatancy and permeability enhancement are generally observed whether the failure mode is brittle faulting or cataclastic flow laboratory data for the brittle faulting regime in westerly granite and for the cataclastic flow regime in carrara marble and synthetic halite are modeled dilatancy is simulated by incorporating an increasing number of stress induced microcracks with similar geometric attributes in a random network model thus enhancing permeability the microcracks are represented by sheet like conduits with crack length and aspect ratio distributions constrained by microstructural data before the onset of dilatancy a rock under overall compression has very low density of open cracks that occur in isolated clusters with relatively low connectivity nonhydrostatic loading induces damage in the form of extensile microcracks that gradually form a fully connected percolation network significant permeability increase of up to several orders of magnitude may occur in this percolative regime once the crack network is fully connected the accumulation of additional cracks is not as effective in enhancing permeability and our model predicts permeability and porosity changes to be linearly related in this fully connected regime after accounting for the existence of fine cracks that are below the microscope resolution our simulation results agree reasonably well with laboratory data

real time measurement and preliminary analysis of debris flow impact force at jiangjia ravine china impact forces associated with major debris flows jiangjia ravine china august 25 2004 were recorded in real time by a system consisting of three strain sensors installed at different flow depths this provides the first real time and long duration record of impact forces associated with debris flows a comprehensive approach including low pass filtering and moving average methods were used to preprocess the recorded signals the upper limit of impact frequency in the debris flows was estimated at 188 66 hz under the assumption that only coarse grains cause effective impact loadings thus a low pass filter with a 200 hz cut off frequency was needed to denoise the original data in order to extract the impact force then the moving average method was applied to separate long term and random components of the filtered data these were interpreted as respectively the fluid pressure and grain impact loading it was found that the peak grain impacts at different depths were non synchronous within the debris flows the impact loadings were far greater than and not proportional to the fluid pressures analysis of the impact force of 38 debris flow surges gives an empirical value for the ratio of the hydrodynamic pressure to the momentum flow density i e the product of debrisflow density and mean velocity square which provides a very valuable basis for understanding debris flow dynamics and designing debris flow management systems copyright c 2011 john wiley sons ltd

the perfect debris flow aggregated results from 28 large scale experiments 1 aggregation of data collected in 28 controlled experiments reveals reproducible debris flow behavior that provides a clear target for model tests in each experiment 10 m3 of unsorted water saturated sediment composed mostly of sand and gravel discharged from behind a gate descended a steep 95 m flume and formed a deposit on a nearly horizontal runout surface experiment subsets were distinguished by differing basal boundary conditions 1 versus 16 mm roughness heights and sediment mud contents 1 versus 7 percent dry weight sensor measurements of evolving flow thicknesses basal normal stresses and basal pore fluid pressures demonstrate that debris flows in all subsets developed dilated coarse grained high friction snouts followed by bodies of nearly liquefied finer grained debris mud enhanced flow mobility by maintaining high pore pressures in flow bodies and bed roughness reduced flow speeds but not distances of flow runout roughness had these effects because it promoted debris agitation and grain size segregation and thereby aided growth of lateral levees that channelized flow grain size segregation also contributed to development of ubiquitous roll waves which had diverse amplitudes exhibiting fractal number size distributions despite the influence of these waves and other sources of dispersion the aggregated data have well defined patterns that help constrain individual terms in a depth averaged debris flow model the patterns imply that local flow resistance evolved together with global flow dynamics contradicting the hypothesis that any consistent rheology applied we infer that new evolution equations not new rheologies are needed to explain how characteristic debris flow behavior emerges from the interactions of debris constituents

quantitative analysis of debris torrent hazards for design of remedial measures debris torrents which are rapid flows of soil and organic debris down steep mountain channels are a major natural hazard in many parts of british columbia a series of recent occurrences along the

prediction of impact force of debris flows based on distribution and size of particles a debris flow is a solid liquid two phase flow the composition and gradation of the particles within have a significant influence on its impact force this paper proposes a new method for studying the impact force according to the composition of a debris flow based on analysis of existing calculation methods the impact force is divided into three parts 1 the dynamic pressure provided by the debris flow slurry which is composed of fine particles and water 2 the impact force of coarse particles and 3 the impact force of boulders this paper analyzes the established formulations used to calculate the impact force by using hydrodynamic theory and contact mechanics to propose a debris flow impact model according to the debris flow type the results show that the impact force is closely related to the solid volume fraction composition of particle materials motion velocity and depth of a debris flow among all the components of the impact force the boulder impact force is the largest followed by the impact force of coarse particles the dynamic pressure is minimal

permeability enhancement due to microcrack dilatancy in the damage regime a three dimensional microscopically based permeability model incorporating inelastic deformation has been developed to account for the modification of transport properties due to fracturing the basic hypothesis investigated is that permeability enhancement during brittle deformation is caused by the formation of dilatant microcracks which are associated with friction sliding on a preexisting random population of shear cracks additional dilatancy produced as a result of frictional sliding over asperities is also accounted for by the introduction of a crack roughness parameter linear elastic fracture mechanics is used to calculate the evolution of crack length and crack area as a function of applied stress and fluid pressure after making a geometrical simplification the microcrack parameters derived from the deformation model can be used to calculate the permeability tensor assuming that fluid transport results from poiseuille flow through a connected distribution of cracks the model enables investigation of the macroscopic permeability variation as a function of two loading parameters three constant material parameters and the crack roughness parameter results demonstrate that permeability is a smooth but strongly increasing near power law function of the terzaghi effective stress ratio and is strongly dependent on the initial crack density young s modulus the friction coefficient and the effective confining pressure numerical results are in quantitative agreement with published experimental measurements and display behavior similar to results obtained with a relatively simple analytical model the model enables calculation of the degree of stress induced anisotropy which is shown is be relatively small 10 for resonable effective stress ratios the modeling presented provides a quantitative tool with which the effects of microcrack induced permeability enhancement can be investigated within the broader context of coupled fluid flow and brittle deformation in the crust

geologically driven 3d modelling of physical rock properties in support of interpreting the seismic response of the lalor volcanogenic massive sulphide deposit snow lake manitoba canada 3d lithofacies and physical rock property models were generated to interpret 3d seismic data acquired over the lalor volcanogenic massive sulphide deposit manitoba canada the lithofacies model revealed that strong seismic reflectivity is associated with ore host rock and mafic felsic lithofacies contacts including their hydrothermally altered equivalents different physical rock property models were subjected to 3d seismic forward modelling using the sofi3d finite difference code seismic synthetics from discrete and interpolated models in which kriging of p wave velocity and density was conditioned by curvilinear grids conformable to the 3d modelled geological structure showed a much better match to the seismic data in comparison to those generated by kriging in cartesian space synthetics from these curvilinear grid models corroborate the origin of seismic reflectors as qualitatively inferred from the lithofacies model seismic synthetics generated from physical rock property models in which physical rock properties were augmented by densely sampled secondary variables such as feo percentage enhanced lateral continuity of seismic reflectivity although these co kriged petrophysical models were not more accurate than their kriged equivalents the physical rock property modelling methodology was also useful for testing the utility of passive interferometric seismic surveys as this highlighted the limitations of the discrete physical rock property model

saturated heating and quenching of three crustal rocks and implications for thermal stimulation of permeability in geothermal reservoirs abstract thermal stimulation is a reservoir enhancement technique that relies on the generation of permeable fractures by thermal gradients replication of thermal stimulation in a controlled laboratory environment provides insight to the physical changes that may be expected at the field scale and assist in stimulation optimization we present a new methodology designed to replicate thermal stimulation in such an environment we developed an apparatus to allow rocks to be heated to 375 c at up to 35 mpa confining pressure and rapidly quenched with cold water to ambient temperature while maintaining system pressure to test our methodology we characterized three rocks that represent a range of geothermal developments and laboratory based investigations lanhelin granodiorite granite from brittany france allandale rhyolite from the lyttelton volcano new zealand and halswell basalt also from the lyttelton volcano our characterization consists of profiling microstructure porosity density dynamic elastic moduli and permeability prior to thermal stressing results indicate that we have increased porosity decreased density attenuated elastic moduli and significantly enhanced the permeability of the rocks rapidly cooled and slowly cooled samples are presented with the rapidly cooled samples showing an increase in permeability the results are compared to similar studies previously carried out under dry conditions and implications discussed for geothermal operations