Estudo da dissolução de NaCl em fluidos de perfuração a base de glicerina e água

Abstract

The drilling of oil wells in the pre-salt layer faces some challenges as the dissolution of salts in the drilling fluid. This dissolution can affect the rheological and physic-chemical properties of fluids and may prejudice the operations in these wells. In recent years, much attention has been given in respect of substances of high toxicity used in drilling fluids and their environmental impacts. Recent studies in the area of environmentally friendly fluids uses Glycerin as base for the formulation of drilling fluids. With the increasing research for less aggressive fluids, the use of Glycerin from biodiesel production, replacing the n-paraffin normally used is of great importance because it meets technical, economic and environmental requirements in addition to be a sustainable alternative. The aim of this work is the study of dissolution kinetics of NaCl in drilling fluids containing glycerin. The study was carried out in four steps, namely: preparation of fluids, characterization (of solids, glycerin and formulated fluids), kinetic experiments and mathematical modelling. For the kinetic tests, an experimental unit that simulates a perfect mixing tank with a volume of 1 L was used. The conductivity measurement was the method used to evaluate how NaCl dissolution occurs over time. The results indicated that the crude glycerin presented lower viscosity than pure. The glycerin/water ratio influences the viscosity of fluids. Pure glycerin presented acid pH and samples prepared with crude glycerin presented basic pH. The fluid prepared with crude glycerin presented a lot of foam, showing the presence of soap residue while fluids prepared with pure glycerin presented some bubbles. The filtration tests have shown that the process is fast, showing large amounts of filtrate, demonstrating the need of an additive. The mass transfer coefficient was estimated and the obtained coefficient values for crude glycerin were lower than those obtained for pure glycerin, evidencing a slower dissolution process