In this work, nonionic surfactant NP100 and pine oil influences on the filtrate volume (FV) and the filter-cake thickness (thkns) of microemulsified drilling fluids were studied. A ternary phase diagram was obtained to define the microemulsion region, where a 2k factorial design was used with the addition of four center points and axial points. Twelve microemulsion points were defined and used later in the formulation of the investigated drilling fluids. The results showed that the increase in the surfactant and pine oil’s concentration increased FV and thkns, withthe oil phase being the most influential component in the filtrate volume and the surfactant being the most influential in the filter-cake thickness. Statistically significant models were obtained. The optimal concentrations were determined for the lowest FV and thkns; 45% of surfactant and 5% of pine oil for the filtrate volume (1.3 mL), and 45% of surfactant and 15% of pine oil for the filter-cake thickness (0.64 mm).

This work has developed and evaluated a microemulsion-based drilling fluid formulation with characteristics to be applied in oil wells. The microemulsion was formulated with a solution of water/glycerol, pine oil, and Tween 80, a nonionic and biodegradable surfactant. The physical and chemical properties of the drilling fluid obtained in this work were investigated through rheology and filtration analysis, solids content, aging, lubricity, toxicity, and thermal degradation. A non-toxic microemulsion-based drilling fluid oil-in-water (O/W) with high lubricity (0.07638) and thermal stability was obtained with suitable viscosity, gel strength and low fluid loss (4.0 mL), low solids content (6%), stability in a wide range of salinity conditions, and the possibility of high water content (above 85% in mass fraction). The fluid presented a pseudoplastic behavior, and statistically significant Herschel–Bulkley parameters were obtained.

Microemulsion is a thermodynamically stable dispersion consisting of an aqueous and an organic phases, both stabilized by surfactant molecules and when in need, co-active surfactant. The nature and structure of these components are essential in the formulation of microemulsified systems. For this, the construction of phase diagrams can be a fundamental tool to characterize the ideal experimental conditions for the existence and operation of microemulsions. Thus, the present work had as objective to obtain a comparison between microemulsions with different compositions through the construction of ternary diagrams, aiming to achieve the most stable system. To produce microemulsified systems, a non-ionic surfactant (Ultranex NP 60), a co-surfactant (Isopropyl Alcohol), two organic phases (pine oil and castor oil) and an aqueous phase (glycerin solution) were used. Also complementing the study, rheological tests of the oleic phases were accomplished, as well as their thermogravimetric analysis. The focus of the reached ternary diagrams was to find the system with the largest Winsor type IV region (microemulsion). It was verified this region had a significant increase by the addition of the co-surfactant in the medium and using a vegetable oil, such as pine oil, since it promotes strong surfactant-oil interactions on the interface.

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