Study on the Dispersion Stability and Plugging Performance of Dopamine-Modified Multiwalled Carbon Nanotubes

In this study, the surface modification of multiwalled carbon nanotubes (MWCNTs) was treated by dopamine self-polymerization reaction-cum-physical modification technique to produce the modified product PDA@MWCNTs. With the help of particle size analysis and zeta potential tests, we have investigated the effects of pH, temperature, NaCl concentration, and drilling fluid treatments on the dispersion stability of PDA@MWCNTs. The plugging performance of PDA@MWCNTs was investigated by artificial mud cake filtration loss experiments and the pressure transfer experiments. We found that PDA@MWCNTs can be stable and dispersed under high temperature and alkaline conditions, and the drilling fluid treatment agents SMC and sodium silicate have less effect on their dispersion stability, while SMP has a more significant impact. With the increase of NaCl solution concentration, the diffuse layers of PDA@MWCNTs were compressed; the upper and lower stratification of the dispersion was obvious, and the particle size increased. When PDA@MWCNTs were added to the drilling fluid, the rheological properties of the drilling fluid were hardly affected. What is more, PDA@MWCNTs could effectively plug the microporous joints of artificial mud cake, and 1 wt % PDA@MWCNTs could reduce the high-temperature and high-pressure (HTHP) filtration loss of artificial mud cake to 4.0 mL. Compared to MWCNTs, the pressure transfer rate when using PDA@MWCNTs was lower, and it took longer to reach the same location. The triaxial compressive strength of the rock after being treated with PDA@MWCNTs was 169.15 MPa, which is higher than the 118.05 MPa achieved after treatment with MWCNTs and closer to the original strength of the rock of 210.03 MPa. This indicates that PDA@MWCNTs have better plugging performance than MWCNTs. This study provides a new approach to improve the dispersion stability and plugging effect of nanomaterials, which is significant to promote the development of water-based drilling fluids.