The objective of this work is to evaluate the effective removal of mud cake formed by drilling fluid for microemulsion-based flushing fluid. The microemulsions were prepared with vegetable castor oil, 2%wt KCl as aqueous phase, and nonionic surfactant (Ultranex NP40). Thermal stability, rheological, removal, and wettability inversion were performed to evaluate the performance of the microemulsion-based flushing fluid. Rheological tests showed that microemulsions behaved like Newtonian fluids. The best formulation of flushing fluid was 70% surfactant/25% oil phase/5% aqueous phase, with cloudy temperature at 365.25 K, removal efficiency of mud cake of 84.85 %, and high capability of wettability inversion.
Oil well cleanup fluids (pre-flushes) are intermediate fluids pumped ahead of the cement slurry; they are able to clean the well walls by removing the filter cake formed by the drilling fluid, and leave the surface water-wet. This work’s main objective was to use biodegradable microemulsion systems as cleanup fluids in order to reduce the environmental impact. Three microemulsion systems were formulated, each composed of an oil phase, a surfactant and three different aqueous phases: glycerol, glycerol:water (mass ratio 1:1), and fresh water. The results show that all microemulsion systems were effective with 100% filter cake removal, with a removal time of less than 60 s. The wettability test and fluid compatibility analyses exhibited advantageous performances, without phase separation, variations in viscosity, gelation, or flocculation. The compressive strength and X-ray diffractometry (XRD) analysis showed the influence of the glycerol on the cement slurry properties, with the compressive strength resistance ranging from 8.0 to 10.7 MPa, and resulted in the formation of portlandite.
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