Fluidos de perfuração emulsionados com óleos vegetais e tensoativo derivado de óleo de coco: uma avaliação para altas pressões e altas temperaturas

Abstract

The use of drilling fluids is essential for pressure control, formation stabilization, cuttings transport, and operational safety, particularly in high-pressure and high-temperature environments. Although oil-based fluids are effective under these conditions, environmental concerns and health risks have encouraged the search for more sustainable alternatives. This study proposed the development of emulsified drilling fluids formulated with vegetable oils and a surfactant derived from coconut oil, aiming to reduce environmental impact while meeting API specifications for high-pressure and high-temperature applications. The surfactant used, saponified coconut oil (SCO), was obtained from coconut oil with a saponification index of 267.47 ± 1.72 mg KOH/g. Four emulsions (E1 to E4) were developed with varying proportions of aqueous, surfactant, and oil phases: 75/15/10 (E1 and E2) and 90/5/5 (E3 and E4). The formulations differed by oil type (pine oil in E1 and E2; coconut oil in E3 and E4) and aqueous phase composition (distilled water in E1 and E3; glycerol solution in E2 and E4). All emulsions exhibited high stability, with negative zeta potentials below -25 mV and surface tensions under 39.3 mN/m. The emulsions were converted into drilling fluids (F1 to F4) through the addition of specific additives: calcium carbonate and carboxymethylcellulose for filtrate control, xanthan gum and bentonite as rheological modifiers, barite as a weighting agent, and sodium chloride as an electrolyte. These additives were characterized by X-ray diffraction (XRD), thermogravimetric analysis (TGA), dynamic light scattering (DLS), and zeta potential analysis, and were used in standardized concentrations across all formulations. The fluids were adjusted to a pH range of 10-11 and a density of 1.0 g/cm3. The fluids were evaluated according to API standards, through rheology and filtration tests under low-pressure and low-temperature (LPLT) conditions, dynamic aging at 66 °C for 16 hours, and high-pressure and hightemperature conditions. Under LPLT conditions, the fluids followed the Herschel-Bulkley rheological model, with coefficients of determination above 0.988 and flow behavior indices below 0.54. The presence of glycerol increased apparent viscosity and yield stress, while plastic viscosity remained constant due to the uniform solid composition. F1 and F2 showed superior filtration performance under LPLT, with filtrate volumes below 0.3 mL and thinner filter cakes. After aging, the fluids without glycerol exhibited more significant changes. F3 and F4 showed an increase in gel strength and a reduction in apparent viscosity, plastic viscosity, and yield stress. Under high-pressure and high-temperature conditions, F1 and F2 experienced a marked reduction in rheological properties due to the increased pressure and temperature, whereas F4 maintained good performance, forming a filter cake with a thickness of 1.45 mm and a filtrate volume of 5.5 mL. The results indicate that F3 and F4 are promising and environmentally viable alternatives to conventional oil-based fluids for use under extreme conditions.