Brines metastable

The ice generator consists of two vertically assembled 5-foot sections of 6-inch borosilicate glass pipe. The refrigerant and brine mixture jets toward the wall near the top of the column. The refrigerant flashes off immediately, leaving the ice slurry to slide down the walls. A large wall area is provided to allow time for the small amount of methylene chloride hydrate which forms to decompose. Although metastable at the column pressure, the hydrate which does form decomposes slowly. At the bottom of... 

Ramboz, C., Orphanidis, E., Oudin, E., Thisse, Y., and Rouer, O. (2008), Metastable fluid diseharge by the Atlantis Deep submarine geyser the heat-mass balance of the stratified lower brine revisited in the light of new fluid inelusion data. This volume. 

The isothermal evaporation method was used in metastable phase equilibria study. According to phase equilibrium composition, the appropriate quantity of salts and DDW calculated were mixed together as a series of artificial synthesized brines and loaded into clean polyethylene containers (15 cm in diameter, 6 cm high), then the containers were put into the box for the isothermal evaporation at (308.15 0.2) K. The experimental conditions with air flowing velocity of 3.5-4.0 m/s, relative humidity of 20-30%, and evaporation rate of 4-6 mm/d are presented, just like the climate of the Qaidam Basin. For... 

If such a metastable equilibrium between acetic and propionic acids exists in basin brines, plots of log(acetate, mol kg ) versus log(propionate, mol kg ) for data from all basins would be expected to display slopes of 3/2. Acetate and propionate concentrations in brines near 100 °C, reported by Carothers and Kharaka (1978) and used by Shock and similar results from other authors, are shown in Fig. 6. Taken as a whole, the results indicate a linear trend. However, it is apparent that for each basin, the data sets rarely display a slope of 3/2. Explanations for the weak overall linear trend, other than the metastable oxidation reaction between acetate and propionate, abound. For example, the overall linear correlation may be an artifact of short-chain carboxylic acid formation, which in turn is a manifestation of the relative abundance of suitable precursor molecules within the parent kerogen. In addition, mixing of brines with meteoric water, or with brines from other hydrologic units, would also result in linear trends on log(acetate)/log(propionate) correlation plots. Conversely, the linear trend may originate from an uneven distribution of kerogen/oil in the host sediment. Specifically, if a cubic meter of sediment contains kerogen with... 

Although the concentrations of acetic acid in oil-field brines cannot be in equilibrium with both CO2 and CH4, they may be in redox equilibrium with CO2 as demonstrated by additional calculations described in this chapter. This means that there is an enormous kinetic barrier blocking reactions between acetic acid and CH4 under sedimentary basin conditions. Therefore, acetic acid is preserved in a metastable state in oil-field brines, and appears to be in metastable equilibrium with CO2. 

In addition, thermodynamic evaluation of acetic acid and propanoic concentrations in many brines indicates that these acids are in homogeneous metastable equilibrium. As a consequence, the ratio of the concentrations of acetic and propanoic acids in basinal brines can be used as a tracer of the oxidation state of sedimentary basins. Additional thermodynamic calculations described in this chapter allow tests of the plausibility of the hypothesis... 

It can be seen in Fig. 8 that the high concentrations of acetic acid in oilfield brines (activities typically from 10 to 10 ", see below) are preserved metastably with respect to the decarboxylation reaction. In other words, if stable equilibrium was reached in sedimentary basin brines, concentrations of acetic acid would be several orders of magnitude lower than they are. Similar results can be obtained for propanoic acid with the data in Table 3. This disequilibrium with respect to the decarboxylation reaction indicates that large kinetic barriers to decarboxylation of organic acids exist under sedimentary basin conditions. 

If we assert that oxidation states in sedimentary basin brines are likely to be intermediate between those set by MH and PPM, then it is possible to determine whether CO2 or CH4 may be in metastable equilibrium with acetic acid. Using an activity of 10 for CH3COOH (see below), the 100°C plots show that attainable fugacities of CO2 are less than the total pressure of 500 bar at all/H2 values above about 10. In contrast, the same activity of CH3COOH can only be in equilibrium with high fugacities of CH4 between values of /H2 set by MH and about which is a very narrow... 

Values of /H2 revealed by the relative concentrations of acetic and propanoic acid can be used to test explicitly whether the organic acids can be in metastable equilibrium with CO2, CH4, hydrocarbons, or other organic compounds. At present, little is known about the concentrations of hydrocarbons and other organic compounds in sedimentary basin brines. Little is also known about the mixing of hydrocarbons in petroleum and how to evaluate activities of individual components in such complex mixtures. Nevertheless, thermodynamic calculations allow the construction of a variety of plausibility arguments regarding the compositional extent of metastable... 

Helgeson HC, Knox A, Shock EL (1991) Petroleum, oil field brines and authigenic mineral assemblages are they in metastable equilibrium in hydrocarbon reservoirs 15th Int European Assoc Meet of Organic Geochemists, Manchester, Program and Abstracts, p 39... 

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