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Polymeric viscosifiers are added to cement slurries for a variety of reasons, including prevention of particle settling and control of fluid loss, gas migration, and free water. Many of these functions are critically important after the cement slurry has been placed behind the casing but before the setting of the cement. Some functions, such as particle-settling prevention, are also important during the pumping phase. Unfortunately, most of the viscosifying polymers suffer from thermal thinning at bottomhole temperatures, especially under shear. The amount of polymer required to maintain the required level of viscosity at elevated bottomhole temperatures causes excessive surface-slurry viscosification at ambient temperature. Pumping such slurries can require higher pump pressures, which, in some cases, might exceed formation breakdown pressures causing unintended fractures.This becomes a serious challenge when the window between the fracture pressure and the pore pressure of the formation is narrow. It would be a significant improvement to oilfield cementing technology to develop polymers that do not cause excessive slurry viscosification on the surface but gradually increase the slurry viscosity as it reaches downhole temperatures, with the maximum viscosity reached at the time the slurry becomes static behind the casing. This paper describes a chemical method, not based on encapsulation, for modifying biopolymers and their derivatives-for example, hydroxyethylcellulose (HEC) and xanthan-that renders them insoluble in cement slurries at room temperature (RT). When the cement slurries containing modified HEC are heated, the slurries develop viscosity upon heating, as reflected by changes to slurry rheology with temperature. The method also provides for increased viscosification efficiency of the modified polymers because of the increased molecular weights of the modified biopolymer products. Synthesis details, slurry rheologies at different temperatures, and job-placement simulation details are presented. A possible reaction mechanism that is operative in the chemicalmodification step is also discussed.

The aim of this study is the synthesis, characterization and photocatalytic degradation of ZnO and Ag doped ZnO nanocatalysts of various compositions synthesized by using co-precipitation method. The nanocatalysts were annealed at the 723.15 K temperature. The obtained nanocatalysts were characterized in concerns their crystalline structure using X-ray diffraction, morphology using scanning electron microscopy (SEM) and electron dispersive X-ray spectroscopy (EDS) in concern with their composition. Photocatalytic activity of nanocatalyst was tested by applying it for photocatalytic degradation of Methylene Blue under different experimental conditions. The photocatalytic activity found to increase with the increase of dopant concentration.

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