Preparation of a salt-responsive zwitterionic hydrophobically associating polymer and its application in a saturated sodium chloride drilling fluid

Abstract

Conventional drilling fluid viscosity enhancers have poor anti-temperature and anti-salt properties, making it difficult to regulate the rheological properties of drilling fluids in the high-temperature, high-mineralisation environment of deep formations, which is prone to causing downhole accidents such as stuck drills and well-wall instability. In the present study, a salt-responsive amphiphilic hydrophobically attached polymer (PAADS) was synthesised by free-radical micellar polymerisation and used as a viscosity builder for saturated sodium chloride drilling fluids. The molecular structure and thermal stability were characterised by Fourier transform infrared spectroscopy, nuclear magnetic resonance and thermogravimetric analysis. The results reveal that the molecular structure of PAADS is consistent with the expected target and has good thermal stability. The viscosity-increasing performance of PAADS in a saturated sodium chloride drilling fluid was evaluated according to the American Petroleum Institute standard. PAADS can effectively maintain the rheological performance of the drilling fluid under high-temperature and high-salt conditions, and the apparent viscosity retention rate of the saturated sodium chloride drilling fluid containing 2 wt% PAADS can be up to 47.5% after 180 °C hot rolling. NaCl exhibits significant salt-responsive properties by affecting the hydrodynamic radius of PAADS molecules. In addition, PAADS solutions exhibit excellent shear dilution, viscoelasticity and stable internal space structure. This study provides new ideas for salt-resistant drilling fluid additives, which are of great significance for the efficient development of deep oil and gas resources.