During the decommissioning of nuclear facilities, the tritiated materials must be removed. These operations generate tritiated steel and cement particles that could be accidentally inhaled by workers. Thus, the consequences of human exposure by inhalation to these particles in terms of radiotoxicology were investigated. Their cyto-genotoxicity was studied using two human lung models: the BEAS-2B cell line and the 3D MucilAirTM model. Exposures of the BEAS-2B cell line to particles (2 and 24 h) did not induce significant cytotoxicity. Nevertheless, DNA damage occurred upon exposure to tritiated and non-tritiated particles, as observed by alkaline comet assay. Tritiated particles only induced cytostasis; however, both induced a significant increase in centromere negative micronuclei. Particles were also assessed for their effects on epithelial integrity and metabolic activity using the MucilAirTM model in a 14-day kinetic mode. No effect was noted. Tritium transfer through the epithelium was observed without intracellular accumulation. Overall, tritiated and non-tritiated stainless steel and cement particles were associated with moderate toxicity. However, these particles induce DNA lesions and chromosome breakage to which tritium seems to contribute. These data should help in a better management of the risk related to the inhalation of these types of particles.
New size-controlled microgels formed by crosslinking polymers under shear flow are very promizing for various applications in oil production. Indeed, when produced by using a proper polymer/crosslinker system and under the conditions needed to obtain the desired properties, these microgels should be quasi-ideal products. They are expected to control water mobility at long distances from the wells to improve sweep efficiency and reduce selectively permeability to water for water production control. For this latter application, injecting stable, preformed microgels eliminates the risks inherent to in-situ gelling which is a technique now recognized as being very difficult to control. This paper reports the results of new lab experiments conducted to complete our theoretical description of the crosslinking-under-shear process and to test the properties of these microgels in porous media. The actual properties of these microgels are compared to theoretical predictions. The results provide new theoretical insights into microgel formation and show that such microgels 1) have sizes measured directly by Photon Correlation Spectroscopy which are satisfactorily predicted by our model 2) adsorb quasi-irreversibly, forming adsorbed layers having a thickness equal to two times their viscometric radius of gyration, thus, are capable of controlling permeability more efficiently than the polymer alone 3) can be injected in porous media without any plugging tendency 4) have small internal rigidity as suggested by elastic modulus measurements and thus, they should be ideal disproportionate permeability modifiers 5) have viscosity higher than polymers in the dilute regime and extremely high in the semi-dilute regime, and 6) are stable, showing no tendency to re-form larger microgels when ageing, in presence of a suitable stabilizer. Introduction Reducing water production is an important goal for the oil industry, particularly because of new environmental regulations imposing severe limitations for the disposal of produced water. Among the methods available for reducing water production, injecting a polymer solution together with a crosslinker is currently used due to its low cost (1,2). However, this method based on in-situ gelling is very difficult to control because gelation is a process very sensitive to physico-chemical conditions such as pH, salinity and temperature as well as shear rates (3–6). Since these parameters are often very poorly known around the well bore, it is very difficult to understand why certain well treatments fail or succeed so that the possibilities of improving this technique remain questionnable. Controlling water mobility at reservoir scale to improve sweep efficiency is usually achieved by dissolving anionic polyacrylamides in injection water (7). Recent pioneering work (8) showed that the addition of zirconium to hydrolyzed polyacrylamides could create microgels that provide a better mobility control of water than the polymer alone. Interestingly, zirconium is safer than chromium for an environmental aspect. Lately (5,6) we proposed a new technique to produce microgels which consists in crosslinking polymer under shear. By this way our theory predicted that the microgel size was controlled by the shear stresses.
TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractInjecting stable preformed microgels as relative permeability modifiers to reduce water production is an attractive new procedure to minimize the risk of formation plugging and consequently of inefficiency of in-depth treatments. This paper describes the mains results of theoretical and experimental investigations carried out to know how to control both size and conformation of microgels formed under constant shear flow. Since gelation kinetics strongly depends on crosslinker chemistry, Zr K-edge XANES and EXAFS studies of zirconium speciation were performed under the complex conditions of polymer gelling for water shutoff. The results show that crosslinking species may be dimers, tetramers and associations of tetramers depending on pH and Zr concentration in presence of lactate. In polymer gels, Zr monomers were observed. The generalisation of our crosslinking-under-shear theory described in this paper provides simple power laws. The microgels formed in diffusion regime are isotropic and their size decreases significantly as shear rate increases, while when formed in correction regime, they are anisotropic and their size decreases negligibly with shear rate. All experimental data are in agreement with this theory so that conclusions can be derived to optimize microgel preparation as a function of their role in the aimed application, either relative permeability modifiers for water shutoff or viscosity enhancers for polymer flooding.
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