Hydration inhibition and physical plugging to enhance shale stability using zwitterionic polymer/nano-silica composite

In order to enhance shale stability during drilling operations, efficient shale stabilizers in water-based drilling fluids become an urgent demand. In this work, a novel shale stabilizer (ZPS) was synthesized by grafting zwitterionic polymer onto nano-silica through two steps. The particle size of ZPS ranged from 80 to 355 nm, exhibiting a regular spherical shape. The hydration inhibition property was determined by Na-bentonite (Na-BT) immersion, linear swelling and hot-rolling dispersion test. ZPS behaved superior inhibition ability compared with commonly used shale inhibitors in all tests. The plugging performance was evaluated by pressure penetration test. Results indicated that ZPS could slow down pressure penetration rate and decrease shale permeability, which displayed better plugging ability than SiO 2 . The mechanism study showed that the cationic groups in ZPS could be tightly adsorbed on the clay surface through electrostatic attraction to inhibit clay hydration. In addition, ZPS could enter into the pores and fractures of shale to form a plugging layer with weak water affinity, resulting in excellent plugging performance. The dual roles of ZPS in hydration inhibition and physical plugging demonstrated its potential as an efficient shale stabilizer.