Rheology and stability of drilling fluids formulated with saturated NaCl and CaCl2 solutions

Abstract

Drilling fluids continue under development, being a challenge for the oil industry, which attempts to optimize technical performance, to comply with environmental laws, and to reduce fluid costs. A non-aqueous based drilling fluid widely used by Petrobras has been reformulated due to changes in Brazilian environmental legislation. The paraffinic base of the drilling fluid was replaced by an olefinic base, which is more biodegradable. Hence, to improve drilling fluid performance, the characteristics of olefin emulsions formulated with saturated NaCl and CaCl2 solutions were investigated. Therefore, for different emulsifier concentrations and stirring speeds, the droplet size distribution, the stability, and the rheological parameters of three emulsions were evaluated. All these emulsions had 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 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 behaviour.