Filtration and structure of bentonite-β-cyclodextrin polymer microspheres suspensions: Effect of thermal aging time

Effective filtration loss control is a challenge for water-based drilling fluid when drilling high temperature and high pressure (HTHP) formations. After thermal aging at 200 °C for varying times, the static filtration loss controlling capabilities of β-cyclodextrin polymer microspheres (β-CDPs) and synthetic polymer Driscal-D in bentonite suspensions were compared in this study. A comprehensive physicochemical characterization was presented using Fourier transform infrared (FT-IR), X-ray diffraction (XRD), particle size distribution, zeta potential, electrical conductivity and scanning electron microscope (SEM). The results indicated that when exposure to thermal aging of 200 °C, the filtration loss of bentonite suspension increased with the initial 6 h of aging, after that it increased slightly. While for synthetic polymer Driscal-D, the filtration loss increased gradually with thermal aging time until to 36 h. In contrast for β-CDPs, the filtration loss increased firstly and then decreased and maintained relatively stable after thermal treatment for 6 h. High temperature destroyed the hydrated structure of bentonite particles and induced the increase of filtration loss volume. In viewing of Driscal-D, degradation of the polymer in combination with dehydration of bentonite particles led to the gradual losing of suspensions stability. For β-CDPs, after aging of 6 h, the hydrothermal carbonization reaction generated numerous nano and micro carbon spheres and bentonite-carbon sphere composited structures, which fill in the gaps between the larger particles and contribute to reducing the filter cake permeability. This result identified that β-CDPs are superior to synthetic polymer Driscal-D in filtration control when subjected to long term high temperature environments.