海底热液循环中矿物沉淀过程数值模拟

为了探索高渗透性洋壳中高温热液循环系统的形成机制,以数值模拟为手段研究热液循环中的矿物沉淀过程及其对洋壳渗透率的反馈.在热液对流-矿物反应模型中考虑了硬石膏、黄铁矿和黄铜矿的沉淀和溶解反应,基于矿物的溶度积计算矿物的沉淀/溶解量,并将其转换为渗透率的变化.结果显示,黄铁矿和黄铜矿分布于350~380℃等温线范围内,并随着热液温度升高而逐渐向海底推移.海水被加热及与热液混合过程中沉淀出硬石膏,在热液上升通道两侧形成低渗透性的烟囱状结构,降低了海水-热液混合程度从而使热液温度升高.高温热液通道建立后,便会有更多的金属物质随着高温热液被运输至浅层洋壳或海底.模拟结果为理解海底高温热液喷口的形成机制提供了借鉴.      

岩体裂隙网络矿物溶解-沉淀-迁移数值模拟

为了研究岩体裂隙网络中矿物溶解-沉淀的变化规律及其对溶质运移的影响,联合矿物溶解-沉淀动力学模型、渗流模型和溶质运移模型建立了岩体裂隙网络矿物溶解-沉淀-迁移模型,经过水溶液络合物计算和矿物成分分析,对研究区域方解石溶解-沉淀作用及溶质运移进行了数值模拟。得出的结论主要有:(1)受裂隙网络分布的影响,溶质运移分布极不均匀,溶质主要通过连通的裂隙从上游向下游迁移;(2)考虑方解石的溶解-沉淀作用之后,在溶解区域溶质浓度增加,在沉淀区域溶质浓度减少;(3)通过对比分析,可知方解石溶解-沉淀受水溶液中CO23-浓度影响较大。     

地下水中酸性污染羽的自然净化作用数值模拟研究

酸法地浸采铀对铀矿层的地下水环境有极大的破坏作用,当开采结束后将形成酸性地下水污染羽。为恢复含矿含水层的水质,必须采取有效的污染治理措施。自然净化是一种较经济的方法,但是必须对其有效性进行评价。本研究以某退役地浸铀矿采区含矿含水层为研究对象,采用反应溶质运移模拟方法来研究酸性污染羽在含水层中的自然净化作用。研究中使用PHT3D模型模拟污染羽的运移,模拟反应组分共12种、沉淀溶解矿物共6种,模拟时长为5a。模拟结果表明:酸性污染物进入地下水后,形成了由方解石、Al(OH)3（a）和 Fe(OH)3（a）反应所控制的pH缓冲区;随着酸性污染羽的向下游高pH值地下水区域移动,方解石溶解与石膏沉淀反应可使SO42-浓度产生明显下降,其他主要金属离子污染物也有明显的自净作用。     

CFP 管道流数值模拟方法综述

岩溶地区往往具有高渗透性的岩溶管道,低渗透性的基岩,与多孔介质相比,水流在管道中的运移速度要大得多,穿过含水层的时间很小。岩溶地区含水层的这种特征给水流的数值模拟带来很大困难。 Conduit Flow Process （ CFP）管道流模拟程序,专门为岩溶地区的地下水数值模拟而设计,本文详细介绍其适用范围、实现原理及使用方法。     

碳酸盐溶解、沉淀控制下的反应－迁移模型研究

以碳酸盐岩中方解石、白云石和石膏的溶解和沉淀化学反应为基础，阐述了反应模型和水流模型，建立了化学动力学方程－水流方程的关系，并且采用解析法－数值法混合解法求解济南岩溶区的反应－迁移模型，计算该区的化学反应速率常数和水动力参数     

碳酸盐溶解,沉淀控制下的反应—迁移模型研究

以碳酸盐岩中方解石，白云石和石膏的溶解和沉淀化学反应为基础，阐述了反应模型和水流模型，建立了化学动力学方程－水流方向的关系，并且采用解法－数值法混合解法求解济南岩溶区的反应－模型，计算该区的化学反应速率常数和水动力参数。     

裂隙岩体流-热耦合传热的三维数值模拟分析

通过对潘西煤矿水文地质条件的分析,基于裂隙岩体的流-热耦合数学模型,描述了裂隙岩体渗流场分布和水流及岩体的温度场分布,并结合边界条件及计算参数对裂隙岩体的流-热耦合传热进行了数值模拟和分析。数值模拟结果表明,岩体内裂隙水流所引发的热量迁移,对裂隙岩体的温度场分布有重要影响。断裂带及地下水流的存在改变了岩体的原有温度场分布。在渗流初期,温度梯度矢量沿渗流方向向两侧岩体方向流动,由于两侧岩体的渗透性系数低于断裂带处的渗透性系数,右侧等温线及温度梯度矢量方向逐渐向渗流方向移动,改变了两侧岩体的温度场分布。通过对断裂带内裂隙水流渗透性系数的折减,分析渗透性系数发生变化时对岩体温度场分布的影响,渗透性系数越大,伴随的热量迁移增大,对岩体的温度场分布的影响也越大。     

基于反向地球化学模拟的地下水形成作用: 以安徽省泗县为例

在了解安徽省泗县水文地质条件基础上,分析了区域水文地球化学特征及类型,探讨了其空间分布特征。根据开采条件下的地下水动力场条件,选择了3条模拟路径,采用PHREEQC软件进行了水文地球化学模拟研究,定量分析了地下水的形成机理及演化。结果表明,路径Ⅰ发生了岩盐、石膏以及伊利石的溶解,高岭土、石英、白云石、萤石发生了沉淀;钙蒙脱石、方解石不参与反应,NaX解吸,CaX_2被吸附;路径Ⅱ发生了岩盐、石膏、伊利石、石英等的溶解以及钙蒙脱石、方解石的沉淀,NaX解吸,CaX_2被吸附;路径Ⅲ发生的反应基本与路径Ⅰ相同,不同之处在该路径上的白云石发生了溶解,其原因可能是地下水在径流过程中溶解CO_2,使其继续溶解白云石以及受沉淀滞后的影响。研究结果表明地下水开采条件下,泗县地下水化学组分主要受到了岩盐和石膏等矿物的溶解作用、钙钠离子交换作用以及钙蒙脱石、方解石沉淀作用的控制。     

区域地下水流数值模拟的方法和实践 ——以华北平原为例

平原(盆地)和流域尺度的地下水流数值模拟对于区域地下水资源合理开发利用具有重要意义。本文在总结分析国内外区域地下水资源数值模型特点的基础上,重点介绍了华北平原区域地下水流数值模型,并指出了区域地下水流数值模拟中存在的问题。     

大区域地下水流数值模拟研究现状及存在问题

在分析大区域地下水流数值模型构建缘起的前提下,系统论述了近年来地下水流数值模拟在大区域地下水资源评价、水文地质参数确定、地面沉降、溶质运移、海水入侵、盐渍化、风险评估、地下水管理及地表水与地下水的联合开发利用等方面的国内外研究应用现状;归纳、总结了目前大区域地下水流数值模型在灵敏度分析、裂隙和岩溶介质中模型建立、基于地下水流数值模拟的溶质运移模型建立、地下水流数值模型构建所需工作量等理论和方法研究及实际建模过程中存在的一些问题;展望了今后大区域地下水流数值拟在研究范围、模拟技术与方法以及与其它模型耦合等方面的发展趋势。      

Kinetics of urease mediated calcite precipitation and permeability reduction of porous media evidenced by magnetic resonance imaging

The enzyme urease drives the hydrolysis of urea leading to the release of ammonium ions and bicarbonate; in the presence of calcium, the rise in pH leads to increased calcium carbonate saturation and the subsequent precipitation of calcite. Although such alkalinizing ureolysis is widespread in nature, most studies have focussed on bacteria (i.e. indigenous communities or urease-active Sporosarcina pasteurii) for calcite precipitation technologies. In this study, urease-active jack bean meal (from the legume Canavalia ensiformis) was used to drive calcite precipitation. The rates of ureolysis (k _urea ), determined from measured NH₄ ⁺, enabled a direct comparison to microbial ureolysis rates reported in literature. It is also demonstrated that a simple single reaction model approach can simulate calcite precipitation very effectively (3–6 % normalised root-mean-square deviation). To investigate the reduction of permeability in porous media, jack bean meal (0.5 g L^?1) and solutions (400 mM urea and CaCl₂) were simultaneously pumped into a borosilicate bead column. One-dimensional magnetic resonance profiling techniques were used, non-invasively, for the first time to quantify the porosity changes following calcite precipitation. In addition, two-dimensional slice selective magnetic resonance images (resolution of ~0.5 × 1.0 mm) revealed that the exact location of calcite deposition was within the first 10 mm of the column. Column sacrifice and acid digestion also confirmed that 91.5 % of calcite was located within the first 14 mm of the column. These results have important implications for the design of future calcite precipitation technologies and present a possible alternative to the well known bacterial approaches.     

Comparison of rates of ureolysis between Sporosarcina pasteurii and an indigenous groundwater community under conditions required to precipitate large volumes of calcite

Ureolysis-driven calcite precipitation has potential to seal porosity and fracture networks in rocks thus preventing groundwater flow and contaminant transport. In this study urea hydrolysis and calcite precipitation rates for the model bacterium Sporosarcina pasteurii were compared with those of indigenous groundwater communities under conditions required to precipitate large volumes of calcite (up to 50 g L⁻¹). We conducted microcosm experiments in oxic artificial and anoxic natural groundwaters (collected from the Permo-Triassic sandstone aquifer at Birmingham, UK) that were inoculated with aerobically grown S. pasteurii. The rate constants for urea hydrolysis, k_urea, ranged between 0.06 and 3.29 d⁻¹ and were only affected by inoculum density. Higher Ca²⁺ concentration (50-500 mM Ca²⁺) as well as differences in fO₂ did not inhibit the ureolytic activity of S. pasteurii and did not significantly impact k_urea. These results demonstrate that S. pasteurii has potential to improve calcite precipitation in both oxic and anoxic groundwaters, especially if indigenous communities lack ureolytic activity. Urea hydrolysis by indigenous groundwater communities was investigated in anoxic, natural groundwaters amended with urea and CaCl₂. A notable increase in ureolysis rates was measured only when these communities were stimulated with dilute nutrients (with best results from blackstrap molasses). Furthermore, there was a considerable lag time (12-20 days) before ureolysis and calcite precipitation began. Calculated ureolysis rate constants, k_urea, ranged between 0.03 and 0.05 d⁻¹ and were similar to k_urea values produced by S. pasteurii at low inoculum densities. Overall, this comparative study revealed that the growth of ureolytic microorganisms present within groundwaters can easily be stimulated to enhance rates of urea hydrolysis in the subsurface, and thus can be used to induce calcite precipitation in these environments. The time required for urea hydrolysis to begin is almost instantaneous if an inoculum of S. pasteurii is included, while it may take several weeks for ureolytic groundwater communities to grow and become ureolytically active.     

Bio-geochemical reactive transport modeling of microbial induced calcite precipitation to predict the treatment of sand in one-dimensional flow

Microbial induced calcite precipitation (MICP) has been well studied to date in the laboratory as a viable alternative soil improvement technique that harnesses a natural bacterial process to induce cementation. Specifically, MICP utilizes the microbial process of hydrolysis of urea to induce pH increase leading to calcite precipitation. The study presented herein demonstrates the utility of a simple bio-geochemical reactive transport model to predict MICP in one-dimensional column experiments. The mathematical model was originally developed in the framework of the TOUGHREACT code to include kinetically controlled reaction rates for urea hydrolysis and calcite precipitation. Inverse modeling, via UCODE-2005, is utilized to calibrate and verify the model to experimental data including aqueous and mineral chemistry. Results indicate good agreement between data and simulated results for capturing the trends and magnitudes of a variety of MICP treatment schemes in half meter, one-dimensional flow columns. A design procedure is presented for predicting MICP in one-dimensional flow by sequentially coupling UCODE-2005 with TOUGHREACT.     

The coprecipitation of Sr into calcite precipitates induced by bacterial ureolysis in artificial groundwater: Temperature and kinetic dependence

A suite of experiments was performed to investigate the partitioning of Sr²⁺ (to mimic the radionuclide ⁹⁰Sr) between calcite and artificial groundwater in response to the hydrolysis of urea (ureolysis) by Bacillus pasteurii under simulated in situ aquifer conditions. Experiments were performed at 10, 15, and 20°C over 7 days in microcosms inoculated with B. pasteurii ATCC 11859, containing an artificial groundwater and urea (AGW) or an AGW including a Sr contaminant treatment. During the experiments, the concentration of ammonium generated by bacterial ureolysis increased asymptotically, and derived rate constants (k_urea) that were between 13 and 10 times greater at 20°C than at 15 and 10°C. Calcite precipitation was initiated after similar amounts of urea had been hydrolyzed (∼ 4.0 mmol L^-1) and a similar critical saturation state (mean S_critical = 53, variation = 20%) had been reached, independent of temperature and Sr treatment. Because of the positive relationship between the rate of ureolysis and temperature, precipitation began by the end of day 1 at 20°C, and between days 1 and 2 at 15 and 10°C. The rate of calcite precipitation increased with, and was fundamentally controlled by calcite saturation state (S), irrespective of temperature. The presence of Sr slightly slowed calcite precipitation rates at equivalent values of S, which may reflect the screening of active nucleation and crystal growth sites by Sr. Homogeneous partitioning coefficients (D_Sr) exhibited a positive association with calcite precipitation rates, but were greater at higher experimental temperatures at equivalent precipitation rates (20°C mean = 0.46; 15°C mean = 0.24; 10°C mean = 0.29).     

Strontium incorporation into calcite generated by bacterial ureolysis

Strontium incorporation into calcite generated by bacterial ureolysis was investigated as part of an assessment of a proposed remediation approach for ⁹⁰Sr contamination in groundwater. Urea hydrolysis produces ammonium and carbonate and elevates pH, resulting in the promotion of calcium carbonate precipitation. Urea hydrolysis by the bacterium Bacillus pasteurii in a medium designed to mimic the chemistry of the Snake River Plain Aquifer in Idaho resulted in a pH rise from 7.5 to 9.1. Measured average distribution coefficients (D_EX) for Sr in the calcite produced by ureolysis (0.5) were up to an order of magnitude higher than values reported in the literature for natural and synthetic calcites (0.02-0.4). They were also higher than values for calcite produced abiotically by ammonium carbonate addition (0.3). The precipitation of calcite in these experiments was verified by X-ray diffraction. Time-of-flight secondary ion mass spectrometry (ToF SIMS) depth profiling (up to 350 nm) suggested that the Sr was not merely sorbed on the surface, but was present at depth within the particles. X-ray absorption near edge spectra showed that Sr was present in the calcite samples as a solid solution. The extent of Sr incorporation appeared to be driven primarily by the overall rate of calcite precipitation, where faster precipitation was associated with greater Sr uptake into the solid. The presence of bacterial surfaces as potential nucleation sites in the ammonium carbonate precipitation treatment did not enhance overall precipitation or the Sr distribution coefficient. Because bacterial ureolysis can generate high rates of calcite precipitation, the application of this approach is promising for remediation of ⁹⁰Sr contamination in environments where calcite is stable over the long term.     

Reactive transport modeling of the interaction between a high-pH plume and a fractured marl: the case of Wellenberg

In the context of the proposed low- and intermediate-level radioactive waste repository at Wellenberg (Switzerland), calculations simulating the interaction between hyperalkaline solutions and a fractured marl, at 25 °C, have been performed. The aim of these calculations is to evaluate the possible effects of mineral dissolution and precipitation on porosity and permeability changes in such a fractured marl, and their impact on repository performance. Solute transport and chemical reaction are considered in both a high-permeability zone (fracture), where advection is important, and the wall rock, where diffusion is the dominant transport mechanism. The mineral reactions are promoted by the interaction between hyperalkaline solutions derived from the degradation of cement (a major component of the engineered barrier system in the repository) and the host rock. Both diffusive/dispersive and advective solute transport are taken into account in the calculations. Mineral reactions are described by kinetic rate laws. The fluid flow system under consideration is a two-dimensional porous medium (marl, 1% porosity), with a high-permeability zone simulating a fracture (10% porosity) crossing the domain. The dimensions of the domain are 6 m per 1 m, and the fracture width is 10 cm. The fluid flow field is updated during the course of the simulations. Permeabilities are updated according to Kozeny's equation. The composition of the solutions entering the domain is derived from modeling studies of the degradation of cement under the conditions at the proposed underground repository at Wellenberg. Two different cases have been considered in the calculations. These 2 cases are representative of 2 different stages in the process of degradation of cement (pH 13.5 and pH 12.5). In both cases, the flow velocity in the fracture diminishes with time, due to a decrease in porosity. This decrease in porosity is caused by the precipitation of calcite (replacement of dolomite by calcite) and other secondary minerals (brucite, sepiolite, analcime, natrolite, tobermorite). However, the decrease in porosity and flow velocity is much more pronounced in the lower pH case. The extent of the zone of mineral alteration along the fracture is also much more limited in the lower pH case. The reduction of porosity in the fractures would be highly beneficial for repository performance, since it would mean that the solutions coming from the repository and potentially carrying radionuclides in solution would have to flow through low-conductive rock before they would be able to get to higher-conductive features. The biggest uncertainty in the reaction rates used in the calculations arises from the surface areas of the primary minerals. Additional calculations making use of smaller surface areas have also been performed. The results show that the smaller surface areas (and therefore smaller reaction rates) result in a smaller reactivity of the system and smaller porosity changes.     

Geophysical monitoring and reactive transport modeling of ureolytically-driven calcium carbonate precipitation

Ureolytically-driven calcium carbonate precipitation is the basis for a promising in-situ remediation method for sequestration of divalent radionuclide and trace metal ions. It has also been proposed for use in geotechnical engineering for soil strengthening applications. Monitoring the occurrence, spatial distribution, and temporal evolution of calcium carbonate precipitation in the subsurface is critical for evaluating the performance of this technology and for developing the predictive models needed for engineering application. In this study, we conducted laboratory column experiments using natural sediment and groundwater to evaluate the utility of geophysical (complex resistivity and seismic) sensing methods, dynamic synchrotron x-ray computed tomography (micro-CT), and reactive transport modeling for tracking ureolytically-driven calcium carbonate precipitation processes under site relevant conditions. Reactive transport modeling with TOUGHREACT successfully simulated the changes of the major chemical components during urea hydrolysis. Even at the relatively low level of urea hydrolysis observed in the experiments, the simulations predicted an enhanced calcium carbonate precipitation rate that was 3-4 times greater than the baseline level. Reactive transport modeling results, geophysical monitoring data and micro-CT imaging correlated well with reaction processes validated by geochemical data. In particular, increases in ionic strength of the pore fluid during urea hydrolysis predicted by geochemical modeling were successfully captured by electrical conductivity measurements and confirmed by geochemical data. The low level of urea hydrolysis and calcium carbonate precipitation suggested by the model and geochemical data was corroborated by minor changes in seismic P-wave velocity measurements and micro-CT imaging; the latter provided direct evidence of sparsely distributed calcium carbonate precipitation. Ion exchange processes promoted through NH4+ production during urea hydrolysis were incorporated in the model and captured critical changes in the major metal species. The electrical phase increases were potentially due to ion exchange processes that modified charge structure at mineral/water interfaces. Our study revealed the potential of geophysical monitoring for geochemical changes during urea hydrolysis and the advantages of combining multiple approaches to understand complex biogeochemical processes in the subsurface.     

低温条件下微生物诱导固化对比研究

低温条件下微生物诱导沉淀产率低,制约着微生物诱导固化(MICP)技术的实际工程应用。通过控制不同温度和pH值,对比分析巴氏芽孢杆菌和巨大芽孢杆菌的生长繁殖特征和脲酶活性,同时在胶凝液中添加营养物质和控制尿素浓度和钙离子浓度,研究提高沉淀产率的方法,利用XRD测试分析沉淀晶型。进行渗透性试验和无侧限抗压强度试验,对比分析了不同菌种的砂土固化效果,结果表明,低温条件下巨大芽孢杆菌生长繁殖比巴氏芽孢杆菌快,脲酶活性更高,且巨大芽孢杆菌最适宜p H=8,更适合于碱性环境;可以通过在胶凝液中添加营养物质,控制尿素浓度为1.5 M和醋酸钙浓度为0.5 M增加碳酸钙沉淀产率;低温条件下巨大芽孢杆菌沉淀产率总高于巴氏芽孢杆菌,沉淀晶型为更稳定的方解石;采用巨大芽孢杆菌固化的试样渗透性可降低3～4个数量级,而巴氏芽孢杆菌固化的砂柱渗透性只降低2～3个数量级,其中颗粒粒径越小,渗透性降低越明显,且同等条件下巨大芽孢杆菌固化的砂柱试样强度也大于巴氏芽孢杆菌固化试样。因此,低温条件下巨大芽孢杆菌更适合进行实际工程应用。     

The role of reaction affinity and secondary minerals in regulating chemical weathering rates at the Santa Cruz Soil Chronosequence, California

In order to explore the reasons for the apparent discrepancy between laboratory and field weathering rates and to determine the extent to which weathering rates are controlled by the approach to thermodynamic equilibrium, secondary mineral precipitation, and flow rates, a multicomponent reactive transport model (CrunchFlow) was used to interpret soil profile development and mineral precipitation and dissolution rates at the 226 ka Marine Terrace Chronosequence near Santa Cruz, CA. Aqueous compositions, fluid chemistry, transport, and mineral abundances are well characterized [White A. F., Schulz M. S., Vivit D. V., Blum A., Stonestrom D. A. and Anderson S. P. (2008) Chemical weathering of a Marine Terrace Chronosequence, Santa Cruz, California. I: interpreting the long-term controls on chemical weathering based on spatial and temporal element and mineral distributions. Geochim. Cosmochim. Acta72 (1), 36-68] and were used to constrain the reaction rates for the weathering and precipitating minerals in the reactive transport modeling. When primary mineral weathering rates are calculated with either of two experimentally determined rate constants, the nonlinear, parallel rate law formulation of Hellmann and Tisserand [Hellmann R. and Tisserand D. (2006) Dissolution kinetics as a function of the Gibbs free energy of reaction: An experimental study based on albite feldspar. Geochim. Cosmochim. Acta70 (2), 364-383] or the aluminum inhibition model proposed by Oelkers et al. [Oelkers E. H., Schott J. and Devidal J. L. (1994) The effect of aluminum, pH, and chemical affinity on the rates of aluminosilicate dissolution reactions. Geochim. Cosmochim. Acta58 (9), 2011-2024], modeling results are consistent with field-scale observations when independently constrained clay precipitation rates are accounted for. Experimental and field rates, therefore, can be reconciled at the Santa Cruz site.Additionally, observed maximum clay abundances in the argillic horizons occur at the depth and time where the reaction fronts of the primary minerals overlap. The modeling indicates that the argillic horizon at Santa Cruz can be explained almost entirely by weathering of primary minerals and in situ clay precipitation accompanied by undersaturation of kaolinite at the top of the profile. The rate constant for kaolinite precipitation was also determined based on model simulations of mineral abundances and dissolved Al, SiO₂(aq) and pH in pore waters. Changes in the rate of kaolinite precipitation or the flow rate do not affect the gradient of the primary mineral weathering profiles, but instead control the rate of propagation of the primary mineral weathering fronts and thus total mass removed from the weathering profile. Our analysis suggests that secondary clay precipitation is as important as aqueous transport in governing the amount of dissolution that occurs within a profile because clay minerals exert a strong control over the reaction affinity of the dissolving primary minerals. The modeling also indicates that the weathering advance rate and the total mass of mineral dissolved is controlled by the thermodynamic saturation of the primary dissolving phases plagioclase and K-feldspar, as is evident from the difference in propagation rates of the reaction fronts for the two minerals despite their very similar kinetic rate laws.     

Calcite precipitation instability under laminar, open-channel flow

We present a 2D numerical model for the growth of calcite from supersaturated aqueous solutions under laminar, open-channel flow conditions. The model couples solution chemistry, precipitation at solution/calcite interfaces, hydrodynamics, diffusion and degassing. The model output is compared with experimental results obtained using an oversaturated calcite solution produced by mixing CaCl₂ and Na₂CO₃. The precipitation rate is observed to increase when the supersaturated solution flows over an obstruction, leading to a growth instability that causes the formation of terraces. At relatively high flow rates, the most important mechanism for this behaviour seems to be hydrodynamic advection of dissolved species either towards or away from the calcite surface, depending on location relative to the obstruction, which deforms the concentration gradients. At lower flow rates, steepening of diffusion gradients around protrusions becomes important. Enhanced degassing over the obstruction due to shallowing and pressure drop is not important on small scales. Diffusion controlled transport close to the calcite surface can lead to a fingering-type growth instability, which generates porous textures. Our results are consistent with existing diffusive boundary layer theory, but for flow over non-smooth surfaces, simple calcite precipitation models that include empirical correlations between fluid flow rate and calcite precipitation rate are inaccurate.