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21.
    
The quantitative assessment of COH fluids is crucial in modeling geological processes. The composition of fluids, and in particular their H2O/CO2 ratio, can influence the melting temperatures, the location of hydration or carbonation reactions, and the solute transport capability in several rock systems. In the scientific literature, COH fluids speciation has been generally assumed on the basis of thermodynamic calculations using equations of state of simple H2O–nonpolar gas systems (e.g., H2O–CO2–CH4). Only few authors dealt with the experimental determination of high‐pressure COH fluid species at different conditions, using diverse experimental and analytical approaches (e.g., piston cylinder + capsule piercing + gas chromatography/mass spectrometry; cold seal + silica glass capsules + Raman). In this contribution, we present a new methodology for the synthesis and the analysis of COH fluids in experimental capsules, which allows the quantitative determination of volatiles in the fluid by means of a capsule‐piercing device connected to a quadrupole mass spectrometer. COH fluids are synthesized starting from oxalic acid dihydrate at = amb and = 250°C in single capsules heated in a furnace, and at = 1 GPa and = 800°C using a piston‐cylinder apparatus and the double‐capsule technique to control the redox conditions employing the rhenium–rhenium oxide oxygen buffer. A quantitative analysis of H2O, CO2, CH4, CO, H2, O2, and N2 along with associated statistical errors is obtained by linear regression of the m/z data of the sample and of standard gas mixtures of known composition. The estimated uncertainties are typically <1% for H2O and CO2, and <5% for CO. Our results suggest that the COH fluid speciation is preserved during and after quench, as the experimental data closely mimic the thermodynamic model both in terms of bulk composition and fluid speciation.  相似文献   
22.
    
V. Vilarrasa 《Geofluids》2016,16(5):941-953
Fluid injection in deep geological formations usually induces microseismicity. In particular, industrial‐scale injection of CO2 may induce a large number of microseismic events. Since CO2 is likely to reach the storage formation at a lower temperature than that corresponding to the geothermal gradient, both overpressure and cooling decrease the effective stresses and may induce microseismicity. Here, we investigate the effect of the stress regime on the effective stress evolution and fracture stability when injecting cold CO2 through a horizontal well in a deep saline formation. Simulation results show that when only overpressure occurs, the vertical total stress remains practically constant, but the horizontal total stresses increase proportionally to overpressure. These hydro‐mechanical stress changes result in a slight improvement in fracture stability in normal faulting stress regimes because the decrease in deviatoric stress offsets the decrease in effective stresses produced by overpressure. However, fracture stability significantly decreases in reverse faulting stress regimes because the size of the Mohr circle increases in addition to being displaced towards failure conditions. Fracture stability also decreases in strike slip stress regimes because the Mohr circle maintains its size and is shifted towards the yield surface a magnitude equal to overpressure minus the increase in the horizontal total stresses. Additionally, cooling induces a thermal stress reduction in all directions, but larger in the out‐of‐plane direction. This stress anisotropy causes, apart from a displacement of the Mohr circle towards the yield surface, an increase in the size of the Mohr circle. These two effects decrease fracture stability, resulting in the strike slip being the least stable stress regime when cooling occurs, followed by the reverse faulting and the normal faulting stress regimes. Thus, characterizing the stress state is crucial to determine the maximum sustainable injection pressure and maximum temperature drop to safely inject CO2.  相似文献   
23.
    
F. Wendler  A. Okamoto  P. Blum 《Geofluids》2016,16(2):211-230
Mineral precipitation in an open fracture plays a crucial role in the evolution of fracture permeability in rocks, and the microstructural development and precipitation rates are closely linked to fluid composition, the kind of host rock as well as temperature and pressure. In this study, we develop a continuum thermodynamic model to understand polycrystalline growth of quartz aggregates from the rock surface. The adapted multiphase‐field model takes into consideration both the absolute growth rate as a function of the driving force of the reaction (free energy differences between solid and liquid phases), and the equilibrium crystal shape (Wulff shape). In addition, we realize the anisotropic shape of the quartz crystal by introducing relative growth rates of the facets. The missing parameters of the model, including surface energy and relative growth rates, are determined by detailed analysis of the crystal shapes and crystallographic orientation of polycrystalline quartz aggregates in veins synthesized in previous hydrothermal experiments. The growth simulations were carried out for a single crystal and for grain aggregates from a rock surface. The single crystal simulation reveals the importance of crystal facetting on the growth rate; for example, growth velocity in the c‐axis direction drops by a factor of ~9 when the faceting is complete. The textures produced by the polycrystal simulations are similar to those observed in the hydrothermal experiments, including the number of surviving grains and crystallographic preferred orientations as a function of the distance from the rock wall. Our model and the methods to define its parameters provide a basis for further investigation of fracture sealing under varying conditions.  相似文献   
24.
    
The Krafla geothermal system is located in Iceland's northeastern neovolcanic zone, within the Krafla central volcanic complex. Geothermal fluids are superheated steam closest to the magma heat source, two‐phase at higher depths, and sub‐boiling at the shallowest depths. Hydrogen isotope ratios of geothermal fluids range from ?87‰, equivalent to local meteoric water, to ?94‰. These fluids are enriched in 18O relative to the global meteoric line by +0.5–3.2‰. Calculated vapor fractions of the fluids are 0.0–0.5 wt% (~0–16% by volume) in the northwestern portion of the geothermal system and increase towards the southeast, up to 5.4 wt% (~57% by volume). Hydrothermal epidote sampled from 900 to 2500 m depth has δD values from ?127 to ?108‰, and δ18O from ?13.0 to ?9.6‰. Fluids in equilibrium with epidote have isotope compositions similar to those calculated for the vapor phase of two‐phase aquifer fluids. We interpret the large range in δDEPIDOTE and δ18OEPIDOTE across the system and within individual wells (up to 7‰ and 3.3‰, respectively) to result from variable mixing of shallow sub‐boiling groundwater with condensates of vapor rising from a deeper two‐phase reservoir. The data suggest that meteoric waters derived from a single source in the northwest are separated into the shallow sub‐boiling reservoir, and deeper two‐phase reservoir. Interaction between these reservoirs occurs by channelized vertical flow of vapor along fractures, and input of magmatic volatiles further alters fluid chemistry in some wells. Isotopic compositions of hydrothermal epidote reflect local equilibrium with fluids formed by mixtures of shallow water, deep vapor condensates, and magmatic volatiles, whose ionic strength is subsequently derived from dissolution of basalt host rock. This study illustrates the benefits of combining phase segregation effects in two‐phase systems during analysis of wellhead fluid data with stable isotope values of hydrous alteration minerals when evaluating the complex hydrogeology of volcano‐hosted geothermal systems.  相似文献   
25.
    
H. Chu  G. Chi  I‐M. Chou 《Geofluids》2016,16(3):518-532
Fluid inclusions of the H2O‐NaCl‐CaCl2 system are notorious for their metastable behavior during cooling and heating processes, which can render microthermometric measurement impossible or difficult and interpretation of the results ambiguous. This study addresses these problems through detailed microscopic examination of synthetic solutions during cooling and warming runs, development of methods to enhance nucleation of hydrates, and comparison of microthermometric results with different degrees of metastability with values predicted for stable conditions. Synthetic H2O‐NaCl‐CaCl2 solutions with different NaCl/(NaCl + CaCl2) ratios were prepared and loaded in fused silica capillaries and glass‐sandwiched films for microthermometric studies; pure solutions were used with the capillaries to simulate fluid inclusions, whereas alumina powder was added in the solutions to facilitate ice and hydrate crystallization in the sandwiched samples. The phase changes observed and the microthermometric data obtained in this study have led to the following conclusions that have important implications for fluid inclusion studies: (i) most H2O‐NaCl‐CaCl2 inclusions that appear to be completely frozen in the first cooling run to ?185°C actually contain large amounts of residual solution, as also reported in some previous studies; (ii) inability of H2O‐NaCl‐CaCl2 inclusions to freeze completely may be related to their composition (low NaCl/(NaCl + CaCl2) ratios) and lack of solid particles; (iii) crystallization of hydrates, which is important for cryogenic Raman spectroscopic studies of fluid inclusion composition, can be greatly enhanced by finding an optimum combination of cooling and warming rates and temperatures; and (iv) even if an inclusion is not completely frozen, the melting temperatures of hydrohalite and ice are still valid for estimating the fluid composition.  相似文献   
26.
This article explores the securitisation of water aimed at avoiding a political crisis for the Chun Doo-Hwan regime in South Korea (1979–1988) using the case of the Peace Dam. The legitimacy of the Chun regime was vulnerable because of diverse factors such as internal and external crises inherited from the previous regime and Chun’s rise to power through a military coup and civilian massacres. In this political situation, the securitisation of nature could be an effective method of curbing potential resistance and ruling a people facing a complex crisis. The constructed threat of an attack by flooding by North Korea and the consequent alleged need for the Peace Dam were part of a scheme by Chun to maintain political power through the securitisation of water, specifically by establishing North Korea as an external enemy and unifying the South Korean people.  相似文献   
27.
Russia has tried to use economic incentives and shared historical and cultural legacies to entice post-Soviet states to join its regional integration efforts. The Ukraine crisis exposed the weaknesses of this strategy, forcing Russia to fall back on coercive means to keep Kiev from moving closer to the West. Having realized the limits of its economic and soft power, will Russia now try to coerce post-Soviet states back into its sphere of influence? Fears of such an outcome overestimate Russia’s ability to use coercion and underestimate post-Soviet states capacity to resist. Rather than emerging as a regional bully, Russia is trying to push Eurasian integration forward by becoming a regional security provider. The article relates these efforts to the larger literature on regional integration and security hierarchies – bridging the two bodies of theory by arguing that regional leaders can use the provision of security to promote economic integration. Despite initial signs of success, we believe that the new strategy will ultimately fail. Eurasian integration will continue to stagnate as long as Russia’s economic and soft power remain weak because Russia will be unable to address the economic and social problems that are at the root of the region’s security problems.  相似文献   
28.
    
Festivals and carnivals are social‐cultural assemblages of human and non‐human entities. This paper investigates interactions between humans and animals by focusing on the Scone Racing Carnival, a key event in the Scone and Upper Hunter Horse Festival. This paper contributes to existing studies of non‐metropolitan festivals and animal–human relations by questioning how and why non‐humans are enrolled in these cultural events, and the impact this has on place identity. The central argument is that the relationship between humans and thoroughbred horses, in particular, has played a significant role in the creation of a distinctive landscape, a regional identity for the Upper Hunter region of New South Wales, and a local identity for Scone. In turn, the carnival has assisted in maintaining an ‘eque‐cultural’ identity through the marketing and annual public celebration of human–horse relationships.  相似文献   
29.
Over the years, many members of the Rhodes University community have proudly claimed their university to be a kind of transplanted Oxford, while others have viewed this claim as pretentious – hence the derogatory label ‘Oxford in the bush’. This article explores the connections and comparison between the two institutions. In the early twentieth century, both universities strongly identified with the British imperial cause; and for decades Rhodes University regularly celebrated its symbolic association with the historical figure of Cecil Rhodes, who also happens to be one of the most commemorated figures in Oxford. There was also a shared ethos, as both laid stress on a style of education that was character-building, a prerequisite for which was a strong grounding in the classics. There was, too, a cultural affinity between Rhodes and Oxford, exemplified in the strict segregation of the sexes, the importance attached to sporting achievement, and a tendency to engage in frivolous activities. The article goes on to show how over time the Oxford tradition at Rhodes came to be challenged and undermined, especially from the late 1960s onwards.  相似文献   
30.
    
This essay will discuss the hegemonic role that texts have come to play in the historiography of subcontinental mathematical traditions. It will argue that texts need to be studied as records of practices of people's working lives, grounded in social hierarchies. We will take particular mathematical texts to show how different occupational registers have come to shape practices that defy the binaries of concrete and abstract, high and low mathematics or the pure and applied conundrum. Measuring, counting and accounting practices as part of the routine work of practitioners performing their caste occupations then provide us with a spectrum of the computational activities that controlled and regulated the lives of people in the past. In the process the act of computing itself gained certain political values such as cunning and manipulation, identified with professions of village accountant and merchant, for example. Drawn from my earlier work on these records, I discuss the occupational role of the accountant as a political functionary who assessed and authenticated the measurements of land and produce in the village, making values of the labor performed by others, and creating avenues for his own proficiency as a mathematical practitioner.  相似文献   
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