Preparation and characterization of phase change microcapsules for improving the applicable temperature and stability of high temperature resistant drilling fluids

Abstract

High temperature environment has many negative effects on the drilling fluid system. In order to avoid or delay these negative effects, phase change materials (PLMs) microcapsule technology was introduced into the high temperature drilling fluid system in this study to further improve the applicability of the high temperature resistant drilling fluid under extremely high temperature formation environment. The microcapsules circulate with drilling fluid, and PLMs melt endothermically at high temperature in deep formation and solidify exothermically at shallow formation. A PLMs microcapsule with solar salt (NaNO3: KNO3 = 3:2) as core material and nano silica as shell material was prepared by sol-gel interfacial polymerization. The structure and properties of the microcapsules were characterized, the temperature-control performance of the microcapsule and its stability and compatibility with drilling fluid were evaluated. The results showed that the microcapsules were well encapsulated, and the single microcapsule particles were spherical, but there was a certain agglomeration phenomenon. The particle size distribution of microcapsules was concentrated in 4–16 µm, with a median particle size of 7.79 µm. The highest encapsulation rate was 60.6%, and the melting enthalpy was 68.48 J/g. The microcapsules had no obvious mass loss below 400 ℃ and had excellent thermal stability. It was proved that the microcapsules had good sealability, shear stability and cycling stability, with the enthalpy/mass retention rate all above 90%. The addition of microcapsules will not affect the basic properties of drilling fluid, and can reduce the peak temperature of high temperature drilling fluid. Different from existing researches, this paper uses a method that absorbs heat to slow down the heating rate of drilling fluid in the formation. This is a new idea, which is expected to be widely studied in the field of high temperature drilling fluids.