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1.
碳酸盐岩单裂隙渗流-溶蚀耦合模型及其参数敏感性分析 总被引：1，自引：1，他引：0
岩溶地下水系统是由碳酸盐岩裂隙含水介质演化形成的,系统初始的裂隙网络介质特征及边界条件决定了其演化过程。为揭示岩溶系统演化过程中裂隙介质特征和边界条件的影响程度,建立了裂隙溶蚀扩展的渗流-溶蚀耦合模型,并对不同边界条件下不同隙宽的单裂隙溶蚀扩展特征进行了模拟分析。结果表明:裂隙溶蚀扩展受水的侵蚀性(CO2分压)、水动力条件(水力梯度)、裂隙介质特征(裂隙初始隙宽)等综合作用影响,Ca2+的平衡浓度、水力梯度以及裂隙初始隙宽等参数的增加均能促进裂隙的快速扩展。在这些参数中,初始隙宽B0对岩溶发育的影响最为敏感,水力梯度J和Ca2+平衡浓度Ceq对岩溶发育具有相同的敏感性;此外,随着各参数值的不断增大,参数变化对岩溶发育的敏感程度越来越低。 相似文献
2.
ZHENHUA JIANG 《Sedimentology》1995,42(6):935-945
A new model, which couples fluid and particle dynamics, has been developed to study the motion of the sediment-water mixture during intense bedload transport, including the velocity profiles of both sediment and water, the roughness length of an upper plane bed and the thickness of moving sediment layers. Standard mixing length theory is used to model the motion of water above the boundary between the overlying water and the sediment-water mixture. The turbulent flow within the moving sediment layers is described by a shear stress model, in which the effective viscosity of the flowing water is proportional to the velocity difference between the fluid and the sediment. The particle dynamics method, in which the equations of motion of each of many particles are solved directly, is applied to model the movement of sediment particles. The particle-fluid interaction is expressed by a velocity-squared fluid drag force exerted on each sediment particle. Both computer simulation results and theoretical analysis have shown that the velocities of both sediment and fluid during intense sediment transport decrease exponentially with depth in the top layers of a fast-moving sediment—water mixture. The thickness of the moving sediment layers, obtained from the computer simulation results, is proportional to the shear stress, which agrees with previous experimental observations. 相似文献
3.
为揭示隐伏型岩溶含水系统在不同边界条件与介质特征下的发育状况,基于地下水渗流和碳酸盐岩溶蚀理论构建耦合裂隙网络渗流与碳酸盐岩溶蚀的岩溶裂隙网络溶蚀扩展模型,模拟再现了河间隐伏型岩溶含水系统平面上发育演化过程。结果显示:岩溶系统发育过程中流量变化呈现三个阶段:第Ⅰ阶段为缓慢层流阶段,流量增速为2.2×10 -6 mL·(s·a) -1,持续时间与初始水头差呈对数关系;第Ⅱ阶段为极快速紊流阶段,流量增速为5.5×10 2 mL·(s·a) -1,持续时间与初始水头差呈线性关系;第Ⅲ阶段为快速紊流阶段,流量增速为26 mL·(s·a) -1。优势裂隙的存在使得岩溶裂隙网络溶蚀演化加快,非均质系统进入极快速紊流阶段所用时间较均质系统缩短了53%,裂隙溶蚀扩展的速度加快了12.5%。 相似文献
4.
渗流-化学溶解耦合作用下岩石单裂隙渗透特性研究 总被引：3，自引：0，他引：3
为揭示在渗流-化学溶解耦合作用下单裂隙渗透特性的变化规律,建立了描述二维渗流-化学溶解耦合作用的偏微分方程组,并利用COMSOL Multiphysics软件成功地求解该方程组。首先,模拟了文献[1]中的盐岩渗流-溶解耦合渗流试验结果,数值模拟结果与试验结果较为吻合,验证了数学模型的正确性和有效性。然后,利用分形理论生成了一个粗糙的裂隙面数字模型,着重分析了二维石灰岩粗糙裂隙面在水流、矿物溶解和输运过程中其渗透特性的变化规律。数值分析显示,（1）溶质浓度对裂隙面的溶解具有非常重要的作用,从而水流进口端的溶解厚度比出口端大得多。（2）裂隙的整体渗透性在初始时刻增加较慢,随着裂隙开度的增大和贯通,溶解速度会逐渐增大,是一个加速的过程。 相似文献
5.
构造成矿非线性动力学:2.湘西金矿研究实例 总被引：1，自引：0，他引：1
应用递增应力流变学方法对湘西沃溪金矿成矿过程中构造变形、应力、流体流动、地球化学反应及成岩成矿作用等多过程间的耦合作用和非线性特征进行了模拟和分析。构造压溶作用对矿源层中成矿物质的溶解与迁移起了重要作用。断裂作用可以产生比原岩渗透率高近4个数量级的断裂渗透率,从而促进流体的流动、组分扩散和在断裂中的汇聚成矿。不同岩性对断裂作用和断裂渗透率的演化有重要影响,并且构造、流体、岩石之间存在强烈的非线性耦合作用,马底驿组中段是最有利的构造成矿层位。 相似文献
6.
The dissolution process of the rock salt is actually a complicated process in fluid dynamics and chemical kinetics; therefore, the mathematical model for the solute-fluid flow during the cavern building may be established to research the change rule of the form of the cavern boundary based on the kinetic analysis of the convection–diffusion process, with integration of the basic theories of fluid mechanics and the principles of chemical kinetics. In order to research the dissolution mechanism of the rock salt under the condition of dynamic water, the method of numerical simulation has been employed to simulate and study the factors with effect on the fluid transport mechanism in solution mining cavern of the rock salt, and its dissolution in dynamic water has been simulated and researched. The result shows that the model established in this paper may well describe the dissolution process of rock salt under the condition of dynamic water, providing basic analyzing means for the research on the rock salt dissolution in dynamic water. 相似文献
7.
A numerical model is presented to describe the evolution of fracture aperture (and related permeability) mediated by the competing chemical processes of pressure solution and free‐face dissolution/precipitation; pressure (dis)solution and precipitation effect net‐reduction in aperture and free‐face dissolution effects net‐increase. These processes are incorporated to examine coupled thermo‐hydro‐mechano‐chemo responses during a flow‐through experiment, and applied to reckon the effect of forced fluid injection within rock fractures at geothermal and petroleum sites. The model accommodates advection‐dominant transport systems by employing the Lagrangian–Eulerian method. This enables changes in aperture and solute concentration within a fracture to be followed with time for arbitrary driving effective stresses, fluid and rock temperatures, and fluid flow rates. This allows a systematic evaluation of evolving linked mechanical and chemical processes. Changes in fracture aperture and solute concentration tracked within a well‐constrained flow‐through test completed on a natural fracture in novaculite (Earth Planet. Sci. Lett. 2006, in press) are compared with the distributed parameter model. These results show relatively good agreement, excepting an enigmatic abrupt reduction in fracture aperture in the early experimental period, suggesting that other mechanisms such as mechanical creep and clogging induced by unanticipated local precipitation need to be quantified and incorporated. The model is applied to examine the evolution in fracture permeability for different inlet conditions, including localized (rather than distributed) injection. Predictions show the evolution of preferential flow paths driven by dissolution, and also define the sense of permeability evolution at field scale. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
8.
岩溶化裂隙岩体是普遍发育于自然界中具有初始损伤的岩体。为了研究岩溶化裂隙岩体损伤破坏特征,本文以贵州某地赋存的溶蚀岩体为研究对象,运用损伤力学理论构建岩溶化裂隙岩体在单轴压缩条件下的损伤演化模型,并建立岩溶化裂隙岩体损伤演化方程。采用颗粒流数值软件进行单轴压缩数值试验,进一步研究岩溶化裂隙岩体试件在单轴压缩条件下的损伤演化特征,分析岩溶化裂隙岩体的微观损伤特征。结果表明:岩溶化裂隙岩体的初始损伤主要包括溶蚀损伤和裂隙损伤。岩溶化裂隙岩体的初始损伤随着溶蚀率的增加而增加,最终增加速率趋于平缓;岩溶化裂隙岩体的损伤演化曲线均呈“S”型变化,先缓慢增加,再迅速增加,最后缓慢增加至损伤值1;岩溶化裂隙岩体存在异构特征,导致破坏裂隙起源于具有初始损伤的溶蚀孔洞和裂隙处,随后裂隙经历萌发、扩张和剪切作用、数量和长度增加以及裂隙贯通4个阶段后发生宏观破坏。 相似文献
9.
Joyce Schmatz Oliver Schenk Janos L. Urai 《Contributions to Mineralogy and Petrology》2011,162(1):193-208
The distribution of fluids in grain boundaries, fluid inclusion morphology and kinetics have important effects on the evolution
of microstructure and transport properties and should be understood for correct interpretations for studies of thermobarometry
and paleorheology. We compare results of in situ annealing experiments on rock analogues in the presence of different pore
fluids in transmitted light: bischofite with saturated brine, camphor with ethanol, and camphor with ethylene glycol. The
solid–liquid systems vary in terms of wettability and solubility, while homologous temperatures, strain rates, annealing times,
and the initial textures are similar. In agreement with earlier work and theory, we observe different types of grain boundary–fluid
inclusion interaction at sufficiently low grain boundary velocity such as drag and drop, necking, and the break up into arrays
of smaller inclusions. In all three systems the maximum possible velocity of a fluid inclusion being dragged by a moving grain
boundary is dependent on the fluid inclusion size. We interpret this to reflect the fluid inclusion mobility, and compare
the trend with theoretical models which suggest that for all three systems the rate-limiting process is bulk diffusion and
not surface diffusion or solution-precipitation. 相似文献
10.
The representation of the surface of a rock fracture and a numerical method to simulate fluid flow in single fractures are the keys to understanding the hydraulic behaviour of rock fractures. In this paper, a cellular automaton (CA) approach is used to generate the single fracture structure, which is assumed to be composed of contacts and voids. We develop a CA evolution rule to produce a contact area, and randomly model a single rock fracture with different contact ratios to reflect natural fracture properties such as dead voids, islands and tortuous flow path. Then, based on the localisation theory of a CA, a numerical method to simulate fluid flow in single fractures with contacts is developed. In this method, the fracture is discretised into a system composed of cell elements. Different apertures, i.e., zero for contacts and non-zero for voids, are assigned to each cell element. Therefore, the contribution of the cell elements in a contact on a cell’s transmissivity can be ignored completely. The local transmissivity is assumed to conform to the cubic law. The fluid flow in a fracture with different contact situations is then modelled using the method established in this paper. The fluid flow path, flow velocity and fluid head distributions as well as the channel flow in the fracture are well-modelled. The flow behaviour of the fracture strongly depends on the effective fluid flow path. 相似文献
11.
Wind‐blown sand movement, considered as a particle‐laden two‐phase flow, was simulated by a new numerical code developed in the present study. The discrete element method was employed to model the contact force between sand particles. Large eddy simulation was used to solve the turbulent atmospheric boundary layer. Motions of sand particles were traced in the Lagrangian frame. Within the near‐surface region of the atmospheric boundary layer, interparticle collisions will significantly alter the velocity of sand. The sand phase is quite dense in this region, and its feedback force on fluid motion cannot be ignored. By considering the interparticle collision and two‐phase interaction, four‐way coupling was achieved in the numerical code. Profiles of sand velocity from the simulations were in good agreement with experimental measurements. The mass flux shows an exponential decay and is comparable to reported experimental and field measurements. The turbulence intensities and shear stress of sand particles were estimated from particle root‐mean‐square velocities. Distributions of slip velocity and feedback force were analysed to reveal the interactions between sand particles and the continuous fluid phase. 相似文献
12.
The evolution of fluid chemistry in compacting rock is controlled by coupled chemical processes and rock deformation. In order to characterize this evolution, we conducted water-rock interaction experiments using quartz aggregates at 150 °C and effective pressure of 34.5 MPa. A coupled fluid flow, chemical reaction, and creep compaction model is developed, in which both free-surface reaction and grain-contact dissolution are considered as system volume and porosity evolve.The direct experimental measurement and numerical modeling indicate that effective pressure has significant effects on pore-fluid chemistry. At the early stages of compaction, pore fluids are supersaturated with respect to bulk quartz. With increasing compaction and time, solute concentrations gradually decrease to saturated conditions. Supersaturation is caused mainly by dissolution of ultrafines and high-energy, unstable surfaces which are produced by stress concentrations at grain contacts during the very early stages of compaction. Grain-contact dissolution also contributes to the solute increase in pore fluid in the early stage of compaction, but the effect is small compared to that of ultrafines and unstable surfaces and only slight supersaturation can be produced by it. The gradual decrease in pore-fluid concentration is related to the mechanical removal of ultrafines by pore-fluid flow and the dissolution of ultrafines and unstable surfaces. It also results from the lessening of grain-contact dissolution.Pore fluids in compacting sedimentary basins of quartz sandstone are nearly saturated throughout most of diagenetic processes. Ultrafines and unstable surfaces produced by stress appear not to be the major sources of quartz cement. 相似文献
13.
Yu Qingchun 《中国地质大学学报(英文版)》1999,10(4):314-321
Karstsystemsaredynamicsystemsinspontaneoussuc-cessiveevolutionarisenfromtheinteractionbetweenwaterflowandsolub1emedium-Thecircu1ationofwaterprogres-sivelyandcontinuouslymodifiesthestructureofmediumfield,consequentlymodifyingthehydraulicbehaviorofthesystemitself'Someauthors(e.g.,FordandWilliams,l989)believedthatmostcarbonaterockswillbecomeconduitaquifersifsurficialerosionisnegligibleorsufficienttimeisgiven.Karstsystemsfailtodevelopconnectedconduiteitherduetoincompleteextension(becauseinsuffici… 相似文献
14.
Non-dimensional solutions to the equations for the combined advective and diffusive one-dimensional transport of heat and solute in a layer are derived for fixed temperature/concentration on the boundaries and initial conditions of a linear gradient across the layer or a step function at the lower boundary. The solutions allow distinction of regimes in which advective or diffusive transport of either heat or solute predominate as a function of fluid flux, time and a length scale. The much lower diffusive coefficients for solute than heat results in a significant range of length scales and fluid flux rates characterised by advection of matter and diffusion of heat. The advective velocity of a component is a function of its fluid:rock partition coefficient. The most rapidly transported tracers which partition largely into the fluid phase, such as He, will travel orders of magnitude faster than heat or compatible solutes such as oxygen. Geochemical profiles in boundary layer regions where both advective and diffusive transport are significant are shown to be particularly informative as to properties of the rocks related to fluid flow such as porosity, permeability, time scales and fluid flux rates. The importance of advection can be directly estimated from the asymmetry of the geochemical profiles across individual layers. 相似文献
15.
A fluid dynamics model for the evolution of salt domes and ridges is presented. The model assumes a rigid substrate, finite thickness of both strata with no slip and a rigid or free surface of overburden. Inertial terms in the Navier-Stokes equations are neglected due to the large viscosities considered and the initial perturbation is taken to be sinusoidal. Finite sine and cosine transforms are used to solve the flow equations and the resulting systems of equations reproduce the velocity field equation of Ramberg's model. Assuming an initial interface, the infinite series solution is truncated to obtain the constants of the integration from the boundary conditions. The interface is then moved to a new position. Thus, the new shape for the interface can be traced for any time.For small perturbations, we obtain results that are approximately those obtained by the linear theory. Results of the numerical solution of the model for both large and small perturbations are presented. 相似文献
16.
A fluid-pressure feedback model of dehydration reactions: experiments, modelling, and application to subduction zones 总被引：3，自引：0，他引：3
Dehydration and melting reactions generate large volumes of fluid in the crust and upper mantle, and play an important role in subduction zone seismicity. The fluid pathway must evolve from isolated pockets in low porosity, low permeability rock, coalescing to interconnected permeable pathways to the surface. When fluid pressures generated from a dehydration or melting reaction are sufficient to induce hydrofracture, then hydrofracture significantly influences the porosity–permeability structure within the dehydrating/melting horizon. If a low fluid-pressure boundary is introduced to the dehydrating rock, then fluid will be driven from the rock along the evolved permeable network toward that boundary. The resulting pressure reduction can then accelerate the dehydration reaction and further drive the flow. The sudden introduction of a low fluid-pressure boundary may occur by the co-seismic (dilatant) rupturing of a pressure seal that connects different fluid pressure states. This mechanism is invoked to explain the observed post-seismic evolution of wave velocities (Vp/Vs) following the 1995 Antofagasta, Chile earthquake. We show experimental results and introduce a conceptual and numerical model that reflects this scenario. The model couples the mechanical and thermodynamic effects of fluid pressure with devolitization kinetics, and is quantitatively consistent with experimental studies of the dehydration of gypsum and serpentine. The experimental results show that dehydration is controlled by access to a free (drained) boundary. The model provides a mechanistic explanation for the experimental observations and has applications in understanding the role of transient transport networks on the large-scale behavior of dehydrating and melting systems. 相似文献
17.
18.
Two-dimensional reactive transport modeling of the Maqarin Eastern Springs site, a natural analogue for the alteration of a fractured limestone by high-pH Portland cement waters, has been performed using the CrunchFlow code. These 2D calculations included transport by advection–dispersion–diffusion along a single fracture and diffusion in the wall rock. Solute transport was coupled to mineral dissolution and precipitation. A limited sensitivity analysis evaluated the effect of different values of primary mineral surface areas, flow velocity and sulfate concentration of the inflowing high-pH solution.Major secondary minerals include ettringite–thaumasite, C–S–H/C–A–S–H and calcite. C–S–H/C–A–S–H precipitation is controlled by the dissolution of primary silicates. Ettringite precipitation is controlled by diffusion of sulfate and aluminum from the wall rock to the fracture, with aluminum provided by the dissolution of albite. Calcite precipitation is controlled by diffusion of carbonate from the wall rock. Extents of porosity sealing along the fracture and in the fracture-wall rock interface depend on assumptions regarding flow velocity and composition of the high-pH solution. The multiple episodes of fracture sealing and reactivation evidenced in the fracture infills were not included in the simulations. Results can qualitatively reproduce the reported decrease in porosity in the fractures and in the wall rock next to the fractures. Instances of porosity increase next to fractures caused by carbonate dissolution were not reproduced by the calculations. 相似文献
19.
岩溶地区地下发育着大量的溶洞和地下河管道,地下水流状态既有层流也有紊流,而紊流是溶洞管道形成的重要条件。紊流的形成受到岩石初始裂隙的影响,初始裂隙的张开度、分布、走向、迹长、密度等因素都影响着裂隙发育过程中水流状态的变化。通过对不同统计特征的初始裂隙网络进行水流和溶蚀的数值模拟发现,以张开度标准差反映的裂隙网络非均匀性越强,模拟紊流出现的时间就越早;主要裂隙的存在使裂隙网络的非均性增强,主要裂隙与水力梯度总方向的角度越小,紊流出现的时间就越早;当裂隙平均迹长过小时会导致裂隙连通性较差,影响裂隙水流和溶蚀作用;裂隙密度,尤其是主要裂隙密度,对岩溶发育的影响较大。相对于次要裂隙,如果主要裂隙密度偏小,紊流形成时间会大大增加,甚至很难形成紊流。当初始裂隙张开度小于0.001 cm,增大水力梯度仍没有紊流发生,岩溶几乎不发育。 相似文献
20.
Grain boundaries as microreactors during reactive fluid flow: experimental dolomitization of a calcite marble 总被引：2，自引：0，他引：2
Limestone dolomitization is an example of a fluid-induced mineralogical transformation that commonly affects extensive rock volumes. To understand the mechanisms enabling these efficient replacement reactions, we investigated experimentally the dolomitization of a fractured calcite marble under flow-through conditions at mild hydrothermal conditions. Contrary to most earlier studies of coupled dissolution reprecipitation reactions that were conducted using small, individual grains, in this study, the integrity of the rock was preserved, so that the experiment explored the links between flow in a fracture and fluid–rock interaction. In these experiments, grain boundaries acted as microreactors, in which a Mg-poor ‘protodolomite’ formed initially, and then transformed into dolomite. The difficulty in nucleating dolomite played a key role in controlling the evolution of the porosity, by allowing for (1) initial dissolution along grain boundaries, and (2) formation of coarse porosity at the reaction interface. This porosity evolution not only enabled the reaction to progress efficiently, but also controlled the mineralogy of the system, as shown by brucite replacing calcite near the fracture once the fluid along calcite grain boundaries became sufficiently connected to the fluid flowing through the fracture. This study illustrates the role of grain boundaries, porosity evolution and nucleation in controlling reaction progress as well as the nature and textures of the products in pervasive mineralogical transformations. 相似文献