FucoPol: Studies for drilling fluids design

Abstract

Although the most effective oil drilling fluids are oil based, they are quite polluting. Alterna-tive water based fluids have been developed in which natural polymers are used as thickening agents, due to their high viscosity at low concentrations. The most used polymers for this appli-cation are xanthan and guar gum, which are also used in food industry. Therefore, the use of these polymers in drilling fluids can trigger an increase in their price, thus inflating the price of the food products. Therefore, this work was focused on the characterization of the rheological properties of the bacterial polysaccharide FucoPol, aiming to develop a water-based fluid, in order to replace fluids composed of natural polymers which are also used in the food industry. FucoPol production through culture of Enterobacter A47 bacteria was performed under controlled temperature and pH controlled conditions (30 ºC and 7, respectively) in a 10 L biore-actor. The volumetric productivity was 1.83 g L-1 d-1, corresponding to a maximum FucoPol con-centration of 7.21 g L-1. The polymer has a high molecular weight (2.14x106) and is composed of fucose (37 wt.%), galactose (23 wt.%), glucose (34 wt.%) and glucuronic acid (6 wt.%). FucoPol flow curves presented a shear-thinning behavior at different concentrations (0.5 -1.5% wt.), temperatures (20-80ºC) and salinity conditions (NaCl, KCl and CaCl2 3% wt.). In aque-ous solution, it showed to be resistant to temperature variation and high salt concentrations. Its apparent viscosity (0.34-15.92 Pa s) is similar to that of guar gum (0.105-387.7 Pa s) and much lower than xanthan (0.56-1164 Pa s). The synergistic relation between FucoPol and xanthan, as well as between FucoPol and Guar gum, was also evaluated for different polymers’ proportions. In the 20:80 formulation (xan-than:FucoPol) the solution’s viscosity increased due to the presence of xanthan. A fluid formulation containing FucoPol was designed showing shear-thinning behavior in deionized water. At high salt concentrations (NaCl 3 wt.%) the apparent viscosity was similar to the values obtained in water. The same stability was not observed in the guar gum formulation. Considering the dynamic measurements, FucoPol formulation showed a liquid-like behavior in deionized water and in salt, while guar gum formula had a weak-gel behavior in deionized water and liquid-like in salt.