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Colloidal silver nanoparticles were prepared by -irradiating Ag þ in aqueous solution in the presence of 2% polyvinyl pyrrolidone (PVP) as stabilising agent and ethyl alcohol as free radical (OH . ) scavenger. The saturated conversion dose of Ag þ into Ag was determined by UV-Vis spectroscopy and the silver nanoparticles size was characterised by transmission electron microscopy. The influence of Ag þ concentration (1-50 mM) on the saturated conversion dose and average diameter of silver nanoparticles was investigated. Results showed that the saturated conversion dose was from 8 to 48 kGy and the silver particles size was in the range of 6-21 nm for Ag þ concentration from 1 to 50 mM. The effect of PVP molecular weight on silver particles size was studied as well.

TX 75083-3836, U.S.A., fax 01-972-952-9435. AbstractCo-deposition of calcium carbonate and calcium sulfate scale was detected in the some of the wells in the White Tiger oilfield, but, up to now, not much attention has been paid to this problem. In fact, these salts (calcium carbonate and calcium sulfate) co-exist and co-precipitate in the system of seawater and squeeze (injected) water. The mixed CaSO 4 -CaCO 3 scale was found to adhere to a test tube wall more strongly than the pure CaCO 3 or CaSO 4 . More importantly, the treatment of this mixed scale in the field is much more difficult. This study investigates the inhibition efficiency on mixed scale by using scale inhibitors such as DETPMP, EDTMP, and copolymer MVA (these inhibitors were synthesized by the Lab of Magnetochemistry and Production Chemicals -Institute of Materials Science-NCST) and the chelants such as citric acid, maleic acid and ethylenediamintetraacetic acid. The experimental results show that the mixed DETPMP: MA in ratio 4:1, 1:1, and mixed DETPMP:CA in ratio 4:1; 3:1, and mixed DETPMP: EDTA (2:1) have given the high inhibition efficiency of 98.32%; 93.85%; 96.09%; 96.09%, 92.52% for mixed scale CaSO 4 -CaCO 3 inhibition. These precipitations were analyzed by Scanning Electron Microscopy (SEM). From the SEM photos, it can be observed that for the pure CaSO 4 in seawater, the crystals exhibited long needle shape structures (which is typical for calcium sulfate dihydrate) whereas the hexagonal structures were observed for the pure CaCO 3 precipitant, which is a typical structure for calcite. In the mixed system, the morphology of CaSO 4 -CaCO 3 crystals changes and spherical shape crystals are predominant. In the presence of the inhibitors, especially with the right inhibitors, the morphology of mixed scale changes and the size of crystals strongly decreases (from 100µm decreases to 1-2µm) and are non-adherent. The relation between the inhibition efficiency and the scale morphology for CaSO 4 -CaCO 3 deposits were clearly illustrated.

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Laboratory investigations of paraffin deposition process and the remarkable changes in the crystal structure of waxes resulted in the development of several copolymer paraffin crystal modifiers. Their mixtures with surfactants have caused strong viscosity reduction in Various Vietnam high paraffin crudes. The changes in form and size of paraffin crystals due to co-crystallization between effective pour point-viscosity depressants and crude oil waxe s, were investigated and the results were recorded by means of scanning electronic microscopy (SEM). The mechanisms of pour point and viscosity reductions were examined using Infrared and Raman spectroscopes. The advantages and disadvantages of these tools were noted. Introduction The pour point and viscosity of crude oil are important physical properties. High pour point and high viscosity crude oil cause deposits at the critical wellbore, and in the tubing, flowlines and pipelines. Deposits in the wellbore reduce production. Deposits in pipelines can have disastrous consequences, both in lost oil and in environmental costs caused by pipeline ruptures. Waxy crude oils are also extremely difficult to transport in pipelines, especially in cold weather.[1,2] Various methods[3,4,5] have been designed to reduce the pour point and viscosity of high wax content crudes, including: thermal, and mechanical, and chemical methods, or a combinations of these methods. The use of chemical additives for pour point-viscosity reduction is receiving constant attention from researchers, with many improved formulations now available. Since no additive has proved universally effective, the selection of an efficient additive becomes critical, and a better understanding of the mechanism of crude oil pour point and viscosity reduction is extremely important. The purpose of this work is to study the mechanism of pour point and viscosity reduction of Vietnam crude oils such as White Tiger and Dragon using advanced analytical tools. Theory Of Pour Point and Viscosity Reduction Pour point reduction Numerous works[8,9] have shown that wax content and the molecular weigh distribution of waxes are primary factors in determing whether a crude oil has a high or low pour point. The additive used to reduce crude oil pour point must have the ability to change the crystalline state of wax during the crude oil cooling process. To form a paraffin crystal, a stable nuclei must first act as a growth center for the attachment of paraffin molecules. Certain chemicals are effective in inhibiting the growth of crystal by cocrystallizing or modifying the crystal or breaking up the molecular cluster. Other additives slow down the paraffin crystallization by coating the molecule of wax as it comes out of solution. Thusly, these additives can keep the paraffin in a liquid state. The first treating chemical group is polymers and copolymers, which inhibit or alter wax and crystal growth. They appear to work best in "water free" and low water content crudes. The second treating chemical group is surfactants that work best in the presence of water by water-wetting the paraffin flowline and pipelines.[10] The pour point depends on the shape and size of the crystal; any pretreatment which affects size and shape also effects the pour point reduction.[11,12]