Preparation of light weight paraffin microspheres based on CO2/N2 switchable emulsion for enhancing plugging performance of drilling fluid

Abstract

Owing to the synthesis complexity and environmental hazards for the preparation of paraffin sealants by conventional methods, an alternative strategy for paraffin microspheres preparation was still required. Herein, a simplified and economic method based on CO2/N2 switchable paraffin emulsion that was stabilized by surfactant tween-80/span-80 system, was proposed for paraffin microspheres preparation. Paraffin microspheres were obtained upon CO2-induced stability changes of emulsion. The prepared paraffin microsphere has a small mean diameter of 8814.5 nm which meets the demand for the particle size of practical production. With the paraffin microsphere dosage of 0.5%, the mud cake permeability decreased to 50.4%, which indicates the good plugging performance of microspheres. When repeatedly preparing the separated aqueous phase and the recovered emulsion containing dissolved emulsion, it was found that the mean diameter of paraffin microspheres changed slight, which indicates the recyclability of switchable solvent. Paraffin microspheres, as plugging additive, pose remarkable effects on other properties of drilling fluid. It was found that the density decreased from 1.05 g/cm3 to 0.89 g/cm3, AV from 4.0 to 10.50, PV from 1.0 to 7.50, YP from 1.0 to 3.0, and FLAPI decrease continually with the paraffin microspheres dosage increases to 2.5%. The recovery rate of shale is above 80% with the introduction of paraffin microspheres, which indicates that paraffin microspheres emulsion has good compatibility with drilling fluid matrix in a certain range. Herein, a paraffin microspheres preparation method based on CO2/N2 switchable emulsion is also proposed which has wide application in the preparation of paraffin microspheres.