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Shale with high clay content has caused instability from hydration during the hydraulic fracturing process. Macro-level migration phenomenon of water molecules is induced by the chemical potential difference between low-salinity fracturing fluid and high-salinity formation brine. This study aims to establish the equation for the chemical potential difference between fracturing fluid and formation brine by theoretical deduction in order to investigate the effect of the aforementioned phenomenon on fracturing flowback. Accordingly, a mathematical model was established for the gas–water two-phase flow which driven by the chemical potential difference. Viscous force, capillarity and chemiosmosis were considered as the driving forces. A numerical simulation of fracturing fluid flowback with or without considering of the effect of chemiosmosis was performed. A simulation analysis of the water saturation and salinity profiles was also conducted. Results show that capillarity and chemiosmosis hinder fracturing fluid flowback in different degrees. As the condition worsens, they inhibit more than 80% of water to flow back out of the formation, forming a permanent water lock. This study contributes to improvement of the theory on shale gas–water two-phase flow, establishment of a flowback model that suitable for shale gas wells, and accurate evaluation of the fracturing treatment. 相似文献
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Different sources of lime for the production of precipitated calcium carbonate were studied. The reactivity of lime, its optical properties and those of the final products are reported and discussed, and a comparison made between lime from different sources. The influence of the temperature of hydration water on the optical properties and particle sizes after hydration and precipitation was also studied. It was found that coarser granulations of lime have better optical properties than finer granulations. The hydration temperature does not have an appreciable impact on the optical properties, but influences the intermediate, i.e. the calcium hydroxide particle sizes and subsequently the particle sizes of the precipitated calcium carbonate. Furthermore, the maximum temperatures of lime hydration from different European sources do not vary significantly, but they differ in the kinetics of the hydration process. 相似文献
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The aim of this study is to determine the isotopic composition (δ18O and δ2H) of interstitial water in bentonites. The study had been carried out from adsorbed vapour in homoionic bentonites. We have worked with the fraction <20 μm of a bentonite from Serrata de Níjar (Almería, Spain). Homoionic sodium and calcium bentonites were prepared as well as variable quantities of exchangeable Na/Ca (75Ca/25Na; 50Ca/50Na; 25Ca/75Na), by mixing pure sodium and calcium suspensions in the appropriate quantities. To carry out the hydration of the samples, every one of them was previously dried at 300 °C overnight, they were subjected to controlled saturation conditions in an atmosphere of different relative humidity and at a constant temperature of 20 °C, until equilibrium was achieved. The different vapour pressures were: P/Po = 0.05; P/Po = 0.078; P/Po = 0.15; P/Po = 0.32; P/Po = 0.45; P/Po = 0.63; P/Po = 0.8; P/Po = 1, obtained from the saturated solutions of different salts or sulphuric acid.The saturation water was extracted for isotopic analysis from an aliquot of a saturated sample. The technique used was vacuum extraction based on a modification of the one described by Araguás-Araguás et al. (1995).The differentiation between the isotopes of 18O and 2H from interstitial water in the bentonite samples, depending on the different relative humidity, may affect the ions diffusion in the interstitial solutions, since in those from low relative humidities, there could be a higher diffusion velocity as they are formed by molecules of light isotopes, versus interstitial solutions from higher relative humidities or those near saturation. This fact should be taken into account in studies on cation and solute transport from these solutions inside bentonite, even though it is important to continue studying and corroborating it with a larger number of solutions isotopically marked. 相似文献
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The results of a series of experiments are reported in this paper which were designed to differentiate between the forces of crystal growth and hydration in salt weathering, using a single salt-hydrate system (sodium sulphate), five contrasting rock types, and several diurnal temperature-relative humidity cycles which permitted or inhibited these processes and simulated ground surface climates in hot, arid environments. It was shown that hydration of sodium sulphate is an effective mechanism of rock disintegration but that it is significantly less destructive than crystal growth pressure. Crystallization of thenardite (Na2SO4) is, in turn, more effective in rock weathering than the crystal growth of mirabilite (Na2SO4.10H2O). In general, rates of disintegration were most rapid where the diurnal temperature range was extreme and relative humidity lowest. 相似文献
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由密度泛函理论(DFT)和扩展X-射线吸收精细结构(EXAFS)光谱研究硫酸镍溶液的微观水合结构。对硫酸镍水合团簇[NiSO4(H2O)n]0 (n=1-12) 的结构优化和能量计算采用DFT计算中的B3LYP方法进行。对于每一个团簇尺寸尽可能考虑所有初始构型，并以此确定能量最低结构。 DFT计算结果表明，在[NiSO4(H2O)n]0团簇中六配位结构的Ni2+为稳定构型. 水合能计算结果表明，当水合团簇尺寸较小时(n≤5),六配位直接接触离子对(CIP)为稳定构型；而当6≤n≤10时, 溶剂共享离子对 (SSIP)为稳定结构。随着团簇尺寸的增加，当n≥11时，x个水分子分割离子对 (xSIP, x是Ni2+和SO42-之间的水分子数目，且x≥2)为稳定构型。对 NiSO4溶液和NiSO4?6H2O进行EXAFS实验，结果证实Ni2+第一水合层是由六个水分子形成的稳定八面体结构，且当 NiSO4溶液浓度从0.70 mol/L到2.22 mol/L(近似饱和溶液)并未发现CIP构型。Ni-O距离和配位数(CN)分别是 2.040±0.020 ? 和6.0±1.0，这些结论与[NiSO4(H2O)n]0水合团簇的DFT计算结果一致。 相似文献
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以添加不同掺量填料的氯氧镁水泥(MOC) 试件为基体,在空气和碳化箱中分别养护至规定龄期,研究碳化对掺加填料MOC力学性能的影响,并与空气环境进行对比,运用XRD和SEM分析碳化后水化产物和微观结构的变化规律。结果表明,28d龄期内,随着填料掺量的增加MOC试件碳化后的抗折强度均有所增加,碳化后的抗压强度均有提升,碳化过程反应生成了MgCO<sub>3</sub>,不同碳化龄期的主要物相均为5Mg(OH)<sub>2</sub>.MgCl<sub>2</sub>.8H<sub>2</sub>O(5.1.8),而掺加填料不影响MOC的水化产物的组成。 相似文献
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以青海盐湖水氯镁石为初级原料,采用喷雾热解法制备原料氧化镁,原料氧化镁通过水化制备硅钢级氧化镁前驱体氢氧化镁。原料氧化镁水化实验中对水化剂、水化温度、水化时间、液固比、搅拌速度及陈化时间对水化率、过滤速度和纯度的影响进行系统研究。采用均匀实验设计和DPS数据处理,(依次)通过建模分析、二次多项式模型回归建立数学模型,再通过各因素方差分析和总方差分析,确定了理论最优实验条件,再用理论最优条件作重复实验进行验证,最终确定了原料氧化镁的最佳水化条件。在水化温度60℃,水化时间105 min,液固比4,陈化时间4 h,水化剂1含量4.0%,水化剂2含量3.15%,洗水量4倍,搅拌速度120 r/min时,原料氧化镁的水化率达99.50%以上,得到的硅钢级氧化镁前驱体氢氧化镁纯度高、过滤性能良好。 相似文献
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An improvement to the volcano-scan algorithm for atmospheric correction of CRISM and OMEGA spectral data 总被引：1，自引：0，他引：1
Patrick C. McGuire Janice L. Bishop Adrian J. Brown Giuseppe A. Marzo Scott L. Murchie Mario Parente Ted L. Roush Michael D. Smith Michael J. Wolff 《Planetary and Space Science》2009,57(7):809-815
The observations of Mars by the CRISM and OMEGA hyperspectral imaging spectrometers require correction for photometric, atmospheric and thermal effects prior to the interpretation of possible mineralogical features in the spectra. Here, we report on a simple, yet non-trivial, adaptation to the commonly-used volcano-scan correction technique for atmospheric CO2, which allows for the improved detection of minerals with intrinsic absorption bands at wavelengths between 1.9 and 2.1 μm. This volcano-scan technique removes the absorption bands of CO2 by ensuring that the Lambert albedo is the same at two wavelengths: 1.890 and 2.011 μm, with the first wavelength outside the CO2 gas bands and the second wavelength deep inside the CO2 gas bands. Our adaptation to the volcano-scan technique moves the first wavelength from 1.890 μm to be instead within the gas bands at 1.980 μm, and for CRISM data, our adaptation shifts the second wavelength slightly, to 2.007 μm. We also report on our efforts to account for a slight ∼0.001 μm shift in wavelengths due to thermal effects in the CRISM instrument. 相似文献