New combined log and tracer test interpretation method for identifying transfers in fissured aquifers

Tracer tests represent the most appropriate approach for assessing hydrodispersive parameters such as transversal and longitudinal dispersivities or kinematic porosity on an aquifer scale. They are generally carried out by injecting a tracer in a borehole and measuring its concentration over time in neighboring boreholes by extracted volume sampling or downhole measurements. Logging is one of the most suitable methods for evaluating fissured reservoirs. But short circuits between fractures with different hydraulic potential through boreholes induce mixing phenomena that cannot be avoided without packers. This mixing can shift the breakthrough curves deduced from the logs for each producing fracture and distort determination of their location.
The method proposed in this paper aims at measuring the flow rate and the solute breakthrough for hydraulically active fractures, in open boreholes. It involves estimating a velocity profile along the borehole column by the analysis of two successive logs: a shift function according to depth is thus determined by comparison between log portions on each successive one. The velocity gradients reflect the inward or outward flow rates produced by each fracture. On the basis of these flow rates, it is possible to determine the mixing effects inside the borehole and then to plot unbiased breakthrough curves for each producing fracture.
This method was applied at a granitic site in the eastern Pyrenees. In spite of some questionable limitations, the results showed that the method seems adapted to situations with many fractures. The precise hydraulic pattern which is obtained at the borehole scale is discussed in terms of a dual porosity model. Furthermore, interpretation of the breakthrough curves for fractures corrected for mixing effects revealed that Peclet numbers are strongly underestimated if this phenomenon is not considered.     

Thermal radiative fluxes through inhomogeneous cloud fields: a sensitivity study using a new stochastic cloud generator

We analyze the effects of flat and bumpy top, fractional and internally inhomogeneous cloud layers on large area-averaged thermal radiative fluxes. Inhomogeneous clouds are generated by a new stochastic model: the tree-driven mass accumulation process (tdMAP). This model is able to provide stratocumulus and cumulus cloud fields with properties close to those observed in real clouds. A sensitivity study of cloud parameters is done by analyzing differences between 3D fluxes simulated by the spherical harmonic discrete ordinate method and three “standard” models likely to be used in general circulation models: plane-parallel homogeneous cloud model (PPH), PPH with fractional cloud coverage model (FCPPH) and independent pixel approximation model (IPA). We show that thermal fluxes are strong functions of fractional cloud coverage, mean optical depth, mean geometrical thickness and cloud base altitude. Fluctuations of “in-cloud” horizontal variability in optical depth and cloud-top bumps have negligible effects in the whole. We also showed that PPH, FCPPH and IPA models are not suitable to compute thermal fluxes of flat top fractional inhomogeneous cloud layer, except for completely overcast cloud. This implies that horizontal transport of photon at thermal wavelengths is important when cloudy cells are separated by optically thin regions.     

High-resolution imaging of sulfur oxidation states, trace elements, and organic molecules distribution in individual microfossils and contempo rary microbial filaments

Owing to the delicate nature of fossil microorganisms and inherent difficulties for discriminating true fossils from artifacts, an important challenge is to extract unequivocal biogenic information from individual microfossils using high-resolution, nondestructive and sensitive techniques. Here, we use combined synchrotron (X-ray microfluorescence, X-ray absorption near-edge structure and infrared microspectroscopies) and particle-induced X-ray emission analyses to image the spatial distribution at a μm-scale of a variety of potential biogenic markers (major and trace elements, C-H bonds, and sulfur-oxidation states) in individual prokaryotic microfossils. In particular, we analyzed iron-oxide fossil filaments of putative biogenic origin encapsulated with amorphous silica from a fragment of an inactive hydrothermal chimney of the East Pacific Rise. In order to test the biogenic origin of the markers studied, we performed the same analyses on filamentous bacteria corresponding most likely to the ?-Proteobacteria, and collected from substrates exposed to a hydrothermal fluid vent at the Mid-Atlantic Ridge. In both types of fossil and contemporary filaments, the occurrence of CH₂ groups and of three sulfur species (sulfate, sulfite, organic S) showing heterogeneous distribution that underline the cytoplasm of individual cells in the case of the present-day filament, suggests that the original microorganisms were actively metabolizing sulfur. These results show the large potential of combining high-resolution synchrotron techniques to analyze individual microfossils for extracting unequivocal biogenic information. Furthermore, they also suggest that cooccurrence of different sulfur oxidation states within single microfossils could constitute a biogenic metabolic marker indicating S-metabolizing activities.     

Partial molar volume of water in phonolitic glasses and liquids

The volumes and expansivities of four hydrous phonolite glasses and liquids have been measured by dilatometry from 300 K up to the glass transition and over a 50 K interval just above the glass transition. The partial molar volume of water is independent of the water content for the glass and liquid phases, with values of about 11.0ǂ.5 and 17.1ǂ.9 cm³/mol at 300 and 800 K, respectively. The partial molar thermal expansivity of water in phonolite glasses is about 8᎒^-5 K^-1, a result similar to recently published values for different silicate compositions, and about 36.5᎒^-5 K^-1 in phonolite liquids. The implications for melt density and water dissolution are discussed.