Estabilidade e reologia de emulsões inversas de olefina linear com soluções saturadas de NaCl e CaCl2

Abstract

Drilling fluids remain under development, being a challenge for the oil industry, which seeks to optimize technical performance, comply with environmental laws, and reduce fluid costs. A nonaqueous based drilling fluid widely used by Petrobras has been reformulated due to recent changes in Brazilian environmental legislation. These changes established that the non-aqueous base of the drilling fluid was modified. Thus, the paraffinic base was replaced by the olefinic base, which is more biodegradable. A saturated NaCl solution constitutes the dispersed phase of the inverse emulsion of the paraffin-based fluid. Nevertheless, the olefin-based fluid is an inverse emulsion in which the dispersed phase is a saturated CaCl2 or NaCl solution. The saturated CaCl2 solution was proposed to replace the saturated NaCl solution, as it gives some advantages to the fluid, such as the most effective inhibition of the interaction between the formation and the fluid, and a higher density, however, the saturated CaCl2 solution exhibits a more pronounced thixotropic behavior. In this context, to improve drilling fluid performance, the characteristics of olefin-based drilling fluid emulsions formulated with saturated NaCl and CaCl2 solutions, as well as a mixture of these, were investigated. Emulsions are mixtures of two immiscible liquids in the presence of an emulsifier, in these mixtures one of the liquids is dispersed in the continuous phase formed by the other component. The droplet size distribution (DSD) of the dispersed phase is fundamental in the characterization of emulsions, as it is directly related to their viscosity and stability. Therefore, for different emulsifier concentrations and stirring speeds, the droplet size distribution and the rheological parameters of three emulsions were evaluated. All these emulsions had linear olefin as the continuous phase, but with distinct dispersed phases, being these saturated solutions of NaCl, CaCl2, and 75% NaCl and 25% CaCl2. The increase of the stirring speed was followed by the emulsified systems apparent viscosities increase, but their polydispersity index (PDI) and D50 values were reduced. The NaCl/Olefin emulsion exhibited lower stability, apparent viscosity, and emulsifier saturation concentration when compared to the CaCl2/Olefin emulsion. Besides, the CaCl2/Olefin emulsion showed more pronounced thixotropic behavior. The NaCl+CaCl2/Olefin emulsion did not exhibit higher stability and intermediate thixotropic behavior.