Rheological properties of dense natural cohesive sediments subject to shear loadings

Cohesive sediments exhibit complex rheological behaviors that are non-Newtonian and time-dependent when subjected to external loading. This paper presents the results of an investigation on the theological properties of three types of dense cohesive sediments, collected from the mouth of the Yangtze River, the shoal of the ttangzhou Bay, and the Yangcheng Lake in China. A set of rheological parameters （including viscosity, yield stress, etc.） was studied based on experiments that were conducted with a RheolabQC rheometer. Measurements of the flow curves, shear stress-time responses, and yield stresses were made. The solid-liquid transition of the dense cohesive sediments occurred both in the shear rate ramp tests and the shear stress ramp tests. This transition was not direct, but it was mediated by a transitional deformation regime or stress plateau. Both the Herschel-Bulkley model and Carreau model were able to describe the theological behavior of dense cohesive sediments, and the empirical expressions for calculating the parameters in these models were obtained by a dimensional and regression analysis. The yield stresses determined by the shear stress ramp test and by the vane method were compared and discussed. The influence of the water content on the rheological properties of dense cohesive sediments was considered.     

An examination of the rheology of flocculated clay suspensions

A dense cohesive sediment suspension, sometimes referred to as fluid mud, is a thixotropic fluid with a true yield stress. Current rheological formulations struggle to reconcile the structural dynamics of cohesive sediment suspensions with the equilibrium behaviour of these suspensions across the range of concentrations and shear. This paper is concerned with establishing a rheological framework for the range of sediment concentrations from the yield point to Newtonian flow. The shear stress equation is based on floc fractal theory, put forward by Mills and Snabre (1988). This results in a Casson-like rheology equation. Additional structural dynamics is then added, using a theory on the self-similarity of clay suspensions proposed by Coussot (1995), giving an equation which has the ability to match the equilibrium and time-dependent viscous rheology of a wide range of suspensions of different concentration and mineralogy.     

Evolution of the Gouge Particle Size Distribution: A Markov Model

—The hydrologic and mechanical properties of faults are determined by their internal structures and zoning due to fracturing, grain breakage and diagenesis. The proposed model in this study is a first step in the development of a more complete model of fault internal structure. It describes the evolution of the gouge particle size distribution (PSD) with shear induced grain breakage within a small, assumed uniform volume element. A Markov formalism is applied for binary breakage within each time step over the many time steps constituting the evolution. The particle size, strain- and stress-dependent breaking probability is constructed based on physical arguments and data on natural and simulated gouge PSDs. The model is calibrated by using the results of on Ottawa sand PSD experiments. A perfect fit is obtained between experimental and numerically simulated PSDs for a range of normal effective stress (NES). Results of the numerical simulations capture the bimodal form of gouge PSD and also clearly define two different breakage mechanisms. The gouge development behavior makes a dramatic transition as the normal effective stress exceeds the grain crushing stress of the gouge mineral.¶For a more complete intrafault structure analysis, the interplay of diagenesis and the mechanics of grain breakage can be integrated into a single mechano-chemical model of the type presented here. The model proposed here has great potential for predicting the complex roles of faults as seals or fluid conduits.     

A comparative study on the rheology and wave dissipation of kaolinite and natural Hendijan Coast mud, the Persian Gulf

The objective of this paper is to investigate the rheological behavior of kaolinite and Hendijan mud, located at the northwest part of the Persian Gulf, and the dissipative role of this muddy bed on surface water waves. A series of laboratory rheological tests was conducted to investigate the rheological response of mud to rotary and cyclic shear rates. While a viscoplastic Bingham model can successfully be applied for continuous controlled shear-stress tests, the rheology of fluid mud displays complex viscoelastic behavior in time-periodic motion. The comparisons of the behavior of natural Hendijan mud with commercial kaolinite show rheological similarities. A large number of laboratory wave-flume experiments were carried out with a focus on the dissipative role of the fluid mud. Assuming four rheological models of viscous, Kelvin-Voigt viscoelastic, Bingham viscoplastic, and viscoelastic-plastic for fluid mud layer, a numerical multi-layered model was applied to analyze the effects of different parameters of surface wave and muddy bed on wave attenuation. The predicted results based on different rheological models generally agree with the obtained wave-flume data implying that the adopted rheological model does not play an important role in the accuracy of prediction.     

A numerical model for simulation of fluid mud with different rheological behaviors

In this paper, a three-dimensional isopycnal approach is presented to simulate the dynamics of fluid mud covering the formation, development, transport, and disappearance of fluid mud. The basic assumption is the assignment of the fluid’s density as the indicating parameter for the rheological behavior. Considering stable stratification, as is usually the case for fluid mud, layers of constant density discretize the vertical domain. The non-Newtonian dynamics of fluid mud is simulated by solving the Cauchy equations for general continuum dynamics. Instead of using a turbulent viscosity approach, the viscosity is allowed to vary according to the rheological behavior of mud suspensions. This apparent viscosity can be determined for different rheological formulations in dependence of the volume solid fraction and the shear rate. An existing three-dimensional isopycnal hydrodynamic model was extended for vertical mass transport processes and was applied on a schematic system with hindered settling. For including the rheological behavior of fluid mud, the Worrall–Tuliani approach was parameterized and implemented. The resulting flow behavior is shown on a model application of fluid mud layers moving down an inclined plane. With these changes, it is demonstrated that the isopycnal model is capable of simulating fluid mud dynamics.     

Mud erosion by waves: a laboratory study

The role of mud erosion under waves in governing cohesive sediment transport in estuarial and coastal waters is well known. A laboratory study was conducted in order to elucidate the mechanism by which soft muds erode under progressive waves in a flume. Two types of cohesive sediment were used, a commercial kaolinite and an estuarial mud. Beds were formed by pouring in a pre-prepared sediment-water slurry and allowing the deposit to consolidate for a period ranging from 2 to 14 days. A multi-layered hydrodynamic model, which considers the mud to be viscoelastic, has been developed and used to evaluate the bed shear stress at the oscillating mud-water interface. The viscoelastic property of the mud has been confirmed by rheological measurements, and model results on velocity, pressure and wave attenuation verified against flume data. Concentration profiles indicate a distinct evolutionary pattern resulting in a highly stratified suspension. Just above the bed, a thin layer of fluid mud is generated. Above this layer, the suspension concentration is significantly lower. This two-layered feature of the concentration profile is related to the oscillatory response of the mud and water layers, and the associated momentum exchange and mass diffusion characteristics. An expression relating the rate of erosion to the bed shear stress in excess of bed shear resistance has been developed. Generation of fluid mud during erosion is a significant feature of the role of waves over mud.     

Characterization of a mud deposit offshore of the Patos Lagoon,southern Brazil

Rapid deposition of mud on the beach along the shoreface of Rio Grande do Sul, Brazil dramatically influences the normal operations in the littoral zone. In the surf zone, fluid and suspended mud opposes water-wave movement and dissipates water-wave energy; on the beach, mud limits trafficability. As part of a multinational, multidisciplinary program to evaluate the influence of mud strength, density and viscosity on water-wave attenuation, sediments were evaluated in situ or collected for evaluation from an area offshore of Cassino Beach, slightly south of the Patos Lagoon mouth. Shear strength of deposited sediments ranged from 0.6 kPa at the seafloor to 3.4 kPa at ∼1 m below the seafloor. Mud sediments were also collected to simulate the in situ response of fluid mud to shear stresses. For this determination, rheological evaluations were made using a strain-controlled Couette viscometer on numerous remixed samples that ranged in density from 1.05 to 1.30 g/cm³. It was determined that this mud is a non-ideal Bingham material in that it has a true initial yield stress as well as a upper Bingham yield stress. Initial yield stress ranged from 0.59 to 2.62 Pa, upper Bingham yield stress ranged from 1.05 to 7.6 Pa. Apparent viscosity ranged from 0.02 to 4.7 Pa s with the highest viscosities occurring between the two yield stresses. Sediment strength in the remixed samples is 2 to 3 orders of magnitude lower than the horizontal shear strength of the sediment bed as determined by shear vane or predicted from penetrometer measurements. This difference is partially due to the fact that rheological evaluations are made on fully remixed sediments, whereas horizontal shear strength is determined within relatively undisturbed sediments. Similar values of viscosity and shear strength are comparable to those determined for mud in other coastal areas where fluid mud deposits occur.     

KINETIC MODELING OF CONSTITUTIVE RELATIONS FOR PARTICLE MOTION IN LOW TO MODERATELY CONCENTRATED FLOWS

Formulating underlying mechanisms of concentrated solid-liquid flows is essential for simulation of various industrial processes and natural phenomena. A generalized constitutive model for particle motion in flows with low to moderate solids concentrations is developed. This generalized model facilitates characterization of inelastic collisions, particle-fluid interactions, and shearing effects. Moderately concentrated simple shear flows of a sand-water mixture are analyzed, and comparisons of model predictions and experimental data are in good agreement. This model exhibits sound performance in characterizing particle motion for wide ranges of concentration and shear rate, and may supply a reasonable and competent alternative to previous models developed for dilute and rapid-granular flows when applied to moderately concentrated situations. The concentration approaches zero （C --~ O） asymptote is observed at a relatively high shear rate in model predictions. Assumption of low collisional dissipation of the particle phase as C → 0 is more reasonable for this observation, compared to that without the interstitial fluid effect. Accurately modeling energy dissipation is important for characterizing the stability of dilute simple shear flows of solid-liquid mixtures. Incorporating friction forces will also facilitate improvement of the applicability of this generalized model to flows at extremely high concentrations.     

RHEOLOGICAL PROPERTIES OF SEDIMENT SUSPENSIONS FROM ECKERNF(O)RDE AND KIELER F(O)RDE BAYS, WESTERN BALTIC SEA

Local areas of fine-grained organic-rich sediments in Eckernforde and Kieler Forde Bays may experience disturbances which cause fluidization of the substrate and create a dense suspension （fluid mud） which exists temporarily as a component of the benthic boundary layer before becoming incorporated into the permanent bottom. Laboratory studies indicate this material behaves rheologically as a non-Newtonian substance, and both shear thinning （pseudoplastic） and shear thickening （dilatant） flow behavior can occur （ofien within the same sample） under low to intermediate shear stresses （2 - 40 Pa） and shear rates （0.46 - 122.49 s^-1）. Detailed granulometric analyses （1/4 phi intervals） of the fraction 〈63 μm show differences in the silt/clay ratio （clay 〈2 μm） between the two environments. Little change in the silt/clay ratio is seen in the Kieler Forde sediments （from 0.74 to 0.95）; however, at Eckernforde, the ratio changed from 0.73 to 2.19. Fine silt particles are lacking or were removed from the 4 to 16 μm fraction of the Eckernforde but not from the Kieler Forde sediments. Both shear thickening and shear thinning flow was observed in the Eckernforde sediments. Shear thickening flow behavior was not observed in the Kieler Forde sediments. Samples of organic-rich （10 to 20%） interface sediments from both areas were analyzed rheologically prior to, and atier removal of organic matter by H2O2 treatment. Reduction in ‘apparent＇ viscosity occurred through the entire range of shear rates and stresses, shear thickening behavior was reduced or became nonexistent, and yield stress decreased significantly compared to the natural samples. The differences in yield stress and flow behavior of dense suspensions result primarily from differences in grain size distributions but the role of organic matter on those properties is very significant and adds to the effects of the grain size distribution of the sediment.     

An investigation into the effects of particle texture,water content and parallel plates' diameters on rheological behavior of fine sediment

Siltation,a phenomenon resulted from the presence of fine particles in an aqueous environment,dominated by silt and clay,is a known and common environmental issue worldwide.The accumulation of fine sediments engenders murky water with low oxygen levels,which leads to the death of aquatic life.Thus,investigating the physical and mechanical properties of fine sediment by rheological methods has expanded.Rheology is the science of deformation and flow of matter in stress.This survey investigates the rheological behavior of six samples of soil as the fine particles structure(D 63 μm) from different regions of Malaysia by using a rotational rheometer with a parallel-plate measuring(using two sizes:25 mm and 50 mm) device to explore the flow and viscoelastic properties of fine particles.The samples were examined in two rheological curve and amplitude sweep test methods to investigate the effect of water content ratio,texture,and structure of patticles on rheological properties.It was found that the content of fine sand,clay,and silt had an effect on the stiffness,structural stability,and shear behavior.Thus,the pseudoplastic and viscoelastic behaviot are respectively shown.Moreover,the amount of fine sediments present in water i.e.the concentration of these particles,has a direct effect on the rheological curve.A reduction in viscosity of samples with higher concentrations of water has been observed.As a consequence,a considerable quantity of fine sediments are distributed within the water body and remain suspended over the time.As a result,the sedimentation rate slows down.It needs to be asserted that the stotage modulus G′,loss modulus G″,and yield point can vary depending on particle type.The G′ and G″were instigated for samples(70%and 45%concentrations) that demonstrated viscoelastic characteristics using the same rotational rheometer with a parallel-plate measuring device.     

Field observations,rheological testing and numerical modelling of a debris‐flow event

Debris flows generated from landslides are common processes and represent a severe hazard in mountain regions due to their high mobility and impact energy. We investigate the dynamics and the rheological properties of a 90 000 m³ debris‐flow event triggered by a rapid regressive landslide with high water content. Field evidence revealed a maximum flow depth of 7–8 m, with an estimated peak discharge of 350–400 m³ s^?1. Depositional evidence and grain‐size distribution of the debris pose the debris flow in an intermediate condition between the fluid‐mud and grain‐flow behaviour. The debris‐flow material has silt–clay content up to 15 per cent. The rheological behaviour of the finer matrix was directly assessed with the ball measuring system. The measurements, performed on two samples at 45–63 per cent in sediment concentration by volume, gave values of 3·5–577 Pa for the yield strength, and 0·6–27·9 Pa s for the viscosity. Based on field evidence, we have empirically estimated the yield strength and viscosity ranging between 4000 ± 200 Pa, and 108–134 Pa s, respectively. We used the Flo‐2D code to replicate the debris‐flow event. We applied the model with rheological properties estimated by means of direct measurements and back‐analyses. The results of these models show that the rheological behaviour of a debris‐flow mass containing coarse clasts can not be assessed solely on the contribution of the finer matrix and thus neglecting the effects of direct grain contacts. For debris flows composed by a significant number of coarse clasts a back‐analysis estimation of the rheological parameters is necessary to replicate satisfactorily the depositional extent of debris flows. In these cases, the back‐estimated coefficients do not adequately describe the rheological properties of the debris flow. Copyright © 2006 John Wiley & Sons, Ltd.     

Modeling of a large‐scale magneto‐rheological damper for seismic hazard mitigation. Part I: Passive mode

Magneto‐rheological (MR) dampers are a promising device for seismic hazard mitigation because their damping characteristics can be varied adaptively using an appropriate control law. During the last few decades researchers have investigated the behavior of MR dampers and semi‐active control laws associated with these types of dampers for earthquake hazard mitigation. A majority of this research has involved small‐scale MR dampers. To investigate the dynamic behavior of a large‐scale MR damper, characterization tests were conducted at the Lehigh Network for Earthquake Engineering Simulation equipment site on large‐scale MR dampers. A new MR damper model, called the Maxwell Nonlinear Slider (MNS) model, is developed based on the characterization tests and is reported in this paper. The MNS model can independently describe the pre‐yield and post‐yield behavior of an MR damper, which makes it easy to identify the model parameters. The MNS model utilizes Hershel–Bulkley visco‐plasticity to describe the post‐yield non‐Newtonian fluid behavior, that is, shear thinning and thickening behavior, of the MR fluid that occurs in the dampers. The predicted response of a large‐scale damper from the MNS model along with that from existing Bouc–Wen and hyperbolic tangent models, are compared with measured response from various experiments. The comparisons show that the MNS model achieves better accuracy than the existing models in predicting damper response under cyclic loading. Copyright © 2012 John Wiley & Sons, Ltd.     

A viscoelastic shear zone model of compressional and extensional plate boundaries

A model is proposed describing the mechanical evolution of a shear zone along compressional and extensional plate boundaries, subject to constant strain rate. The shear zones are assumed as viscoelastic with Maxwell rheology and with elastic and rheological parameters depending on temperature and petrology. Stress and strain are computed as functions of time and depth. For both kinds of boundaries the model reproduces the existence of a shallow seismogenic zone, characterized by a stress concentration. The thickness of the seismogenic layer is evaluated considering the variations of shear stress and frictional strength on faults embedded in the shear zone. Assuming that a fault dislocation takes place, the brittle-ductile transition is assumed to occur at the depth at which the time derivative of total shear stress changes from positive to negative values. The effects of different strain rates and geothermal gradients on the depth of the brittle-ductile transition are studied. The model predictions are consistent with values inferred from seismicity data of different boundary zones.     

Closure relations for mobile bed debris flows in a wide range of slopes and concentrations

Debris flows are flows of water and sediment driven by gravity that initiate in the upper part of a stream, where the slope is very steep, allowing high values of solid concentration (hyperconcentrated flows), and that stop in the lower part of the basin, which is characterized by much lower slopes and reduced speeds and concentrations. Modelling these flows requires mathematical and numerical tools capable of simulating the behavior of a fluid in a wide range of concentrations of the solid phase, spanning from hyperconcentrated flows to flows in the fluvial regime. According to a two-phase approach, the depth integrated equations of mass and momentum conservation for water and sediments, under the shallow water hypothesis, are employed to solve field problems related to debris flows. These equations require suitable closure relations that in this case should be valid in a very wide range of slopes. In the hypothesis of absence of cohesive material, we derived these closure relations properly combining the relative relations valid separately in the fluvial and in the hyperconcentrated regimes. In the intermediate regime, the shear stress is due to the combined effect of the deformation of the liquid phase (grain roughness turbulence) and of inter-particle collisions. Therefore, an approach based on the sum of the effects of the two causes has been proposed, combining the Darcy–Weisbach equation and the Bagnoldian grain-inertia theory.A similar treatment has been made for the transport capacity relations, combing the Bagnold expression of the collisional regime with a transport capacity monomial formula valid in the fluvial regime.The closure relations are expressed in non-dimensional form as a function of the Froude number, of the solid concentration, of the relative submergence, and of the slope.In order to test the closure relation, a set of experiments with mixtures of non-cohesive sediments and water have been carried out in a laboratory flume under steady uniform flow conditions, with different solid and liquid discharges and different grain size distributions. The closure equations are satisfactorily tested against experimental investigation.     

Bedload stresses and Bagnold's bedform theory for water flows

Bagnold's theory of bedload stresses and bedforms requires that the tangential stress exerted at the base of a moving bedload dispersion in high stage plane beds is carried entirely by the grain stress T. Derivation of T from experimental data in flow channnels shows, however, that the fluid contribution τ′ is still dominant (≈ 1 to 2 × T). Particle concentrations in the experimental bedload dispersions approached 10 per cent and it is inferred that no appreciable concentration gradient exists. Grain collisions are thought to be most probable whenever more than 1 former stationary grain layer is in forward motion. High stage plane beds may be unstable when grain collisions cease. Current ripples evolve from the amplification and migration of chance defects due to unsteady fluid impulses generated by injection, or burst, phenomena in the viscous sublayer and not through any inherent static shear resistance deficit exerted by stationary bed grains.     

The Mechanical Coupling of Fluid-Filled Granular Material Under Shear

The coupled mechanics of fluid-filled granular media controls the physics of many Earth systems, for example saturated soils, fault gouge, and landslide shear zones. It is well established that when the pore fluid pressure rises, the shear resistance of fluid-filled granular systems decreases, and, as a result, catastrophic events such as soil liquefaction, earthquakes, and accelerating landslides may be triggered. Alternatively, when the pore pressure drops, the shear resistance of these geosystems increases. Despite the great importance of the coupled mechanics of grain–fluid systems, the basic physics that controls this coupling is far from understood. Fundamental questions that must be addressed include: what are the processes that control pore fluid pressurization and depressurization in response to deformation of the granular skeleton? and how do variations of pore pressure affect the mechanical strength of the grains skeleton? To answer these questions, a formulation for the pore fluid pressure and flow has been developed from mass and momentum conservation, and is coupled with a granular dynamics algorithm that solves the grain dynamics, to form a fully coupled model. The pore fluid formulation reveals that the evolution of pore pressure obeys viscoelastic rheology in response to pore space variations. Under undrained conditions elastic-like behavior dominates and leads to a linear relationship between pore pressure and overall volumetric strain. Viscous-like behavior dominates under well-drained conditions and leads to a linear relationship between pore pressure and volumetric strain rate. Numerical simulations reveal the possibility of liquefaction under drained and initially over-compacted conditions, which were often believed to be resistant to liquefaction. Under such conditions liquefaction occurs during short compactive phases that punctuate the overall dilative trend. In addition, the previously recognized generation of elevated pore pressure under undrained compactive conditions is observed. Simulations also show that during liquefaction events stress chains are detached, the external load becomes completely supported by the pressurized pore fluid, and shear resistance vanishes.     

Laboratory and theoretical evaluation of impact of packing density,particle shape,and uniformity coefficient on erodibility of coarse-grained soil particles

Sedimentation – including erosion, transport, and deposition of coarse-grained particles – is a primary and growing environmental, engineering, and agricultural issue around the world. Soil erosion occurs when the hydrodynamic force induced by flowing water exceeds the geotechnical resistance of soils, as measured by critical shear stress for initiation of soil-particle motion. Even though various quantitative methods have been suggested with respect to different types of soil, the most widely accepted formula to estimate critical shear stress for coarse-grained soil is a direct function of the median grain size of the soil particles; however, the erosion resistance of soils also varies with other geotechnical properties, such as packing density, particle shape, and uniformity coefficient. Thus, in this study, a combined rolling–lift model for particle detachment was derived based on theoretical analysis. A series of experimental flume tests were conducted with specimens prepared with standard soil types, as well as laboratory-prepared mixtures of coarse-grained soil to validate the theoretical model and determine the effect of other geotechnical properties on the erosion characteristics of coarse grains, coupled with the effect of median particle size. The results indicated that the median grain size is the primary variable determining the resistance of coarse grains, but the critical shear stress also varies with the packing density of the soil matrix. In addition, angular particles show more erosion resistance than rounded particles, and the erosion potential of a soil decreased when the grain is well graded (higher value of uniformity coefficient). Additionally, regression analysis was performed to quantify the effect of each parameter on the critical shear stress of coarse grains. © 2020 John Wiley & Sons, Ltd.     

长英质岩石的流变学特征及其影响因素

在总结岩石变形机制与岩石流变学实验进展的基础上,讨论了岩石流变学数据的重复性。虽然高温高压流变学实验积累了大量的数据,但中、上地壳长英质岩石和早期获得的石英集合体的流变实验数据重复性比较差,而近年来发表的石英、长石的流变学实验数据重复性相对较好。虽然利用经验理论模型,根据端元组分可以拟合两相矿物集合体的流变律,但并不能满足定量确定复杂组分和特殊流变性的长英质岩石流变参数的需要。因此,利用长英质岩石流变参数估计大陆地壳流变强度剖面时,即使在相同地温和应变速率条件下,给出的流变曲线、脆-塑性转化带深度也有一定差别,还需要通过大量实验给出更精细的长英质岩石流变学实验数据。根据近年来流变学实验研究的新进展,讨论了在实验室条件下影响长英质岩石流变的各种因素,重点分析了流体、岩石成分、样品粒度和组构对流变的影响。微量结构水对岩石流变有显著的弱化作用,而熔体对流变的影响与熔体含量和分布相关,只有熔体呈薄膜状湿润颗粒边界时,熔体的弱化作用才显著。成分对岩石流变的影响不仅体现在样品的应力指数等流变参数的变化方面,还体现在样品从半脆性变形向塑性变形的转化温度方面。粒度主要影响岩石的变形机制,其中,细粒样品在扩散蠕变域具有应力与粒度线性负相关特性,是理想的应力计,可以用来定量确定韧性剪切带的流变强度;而在位错蠕变域,应力与粒度没有依存关系,这为将实验室条件得出的流变数据外推估计地壳流变提供了重要依据。组构和各向异性是地壳中岩石存在的普遍现象,但关于层状组构对多相矿物组成的岩石流变影响的研究非常少,需要通过新的实验来深入研究。     

A Study of Permeability Changes Due to Cold Fluid Circulation in Fractured Geothermal Reservoirs

Reservoir behavior due to injection and circulation of cold fluid is studied with a shear displacement model based on the distributed dislocation technique, in a poro‐thermoelastic environment. The approach is applied to a selected volume of Soultz geothermal reservoir at a depth range of 3600 to 3700 m. Permeability enhancement and geothermal potential of Soultz geothermal reservoir are assessed over a stimulation period of 3 months and a fluid circulation period of 14 years. This study—by shedding light onto another source of uncertainty—points toward a special role for the fracture surface asperities in predicting the shear dilation of fractures. It was also observed that thermal stress has a significant impact on changing the reservoir stress field. The effect of thermal stresses on reservoir behavior is more evident over longer circulation term as the rock matrix temperature is significantly lowered. Change in the fracture permeability due to the thermal stresses can also lead to the short circuiting between the injection and production wells which in turn decreases the produced fluid temperature significantly. The effect of thermal stress persists during the whole circulation period as it has significant impact on the continuous increase in the flow rate due to improved permeability over the circulation period. In the current study, taking into account the thermal stress resulted in a decrease of about 7 °C in predicted produced fluid temperature after 14 years of cold fluid circulation; a difference which notably influences the potential prediction of an enhanced geothermal system.     

The relationship between the deep-level structure in crust and brewing of strong earthquakes in Xingtai area

IntroductionWiththefurtherstudyonthefinestructureofcrustandapplicationoftheCTtechnologytotheresearchonthecontinentaldeepstructureinNorthChina,thenon-heterogeneityofcrustanduppermantleintheseareashasbeenclearlyacknowledged.Zeng,etal(1991)gavethefocalmodeloflargeearthquakeinNorthChina,inwhichthemostimportanttraitisthetransversenonuniformoftemperaturedistributiononthetopofthemantle.Liu,etal(1986)studiedtheseismictomographyofNorthChinaregion,andindicatedthattherearemanydifferentlowervelocityare…