Development of a high temperature resistant nano-plugging agent and the plugging performance of multi-scale micropores

Nano-plugging agents (NPAs) are very important to stabilize the wellbore by reducing pressure transmission and drilling fluid invasion during drilling engineering. A functionalized polystyrene latex (FPL) was synthesized by micellar polymerization as a NPA for drilling fluids. The particle size and thermal stability of FPL were characterized by particle size analysis and thermogravimetric analysis (TGA). The experimental results showed that the initial thermal decomposition temperature of FPL was 310.6 degrees C. The medium value of particle size distribution (D50) of FPL decreased from to 371-235 nm after aging at 220 degrees C, indicating that FPL had good temperature resistance property. The plugging method and plugging performance of FPL for four filter media with pore sizes from 0.01 mu m to 10 mu m were introduced. FPL itself was difficult to plug the filter papers and ceramic filter disks, but FPL could reduce fluid loss of bentonite suspensions. SEM observation indicates that FPL could improve the quality of mud cakes and plug the small pores of ceramic filter disks. For microporous membranes and artificial mud cakes with low permeability, FPL aqueous suspensions had a good plugging performance. The plugging experimental results conformed well to the 2/3 bridging rule. This paper provides a good reference for the development of high temperature NPAs and the establishment of evaluation methods of NPAs.