Controlling filtration loss of water-based drilling fluids by anionic copolymers with cyclic side groups: High temperature and salt contamination conditions

Abstract

Water-based drilling fluids (WDFs) as a thermally unstable colloidal system play an essential role in the drilling operation. The filtration loss control of WDFs under high temperature and salt contamination has been a research hotspot. In this study, the copolymer (named DSA) containing different cyclic side groups was synthesized to control the filtration loss of WDFs. The chemical structure and thermal stability of the DSA were analyzed. The result showed that DSA exhibited only a slight weight loss (6.0 wt%) until 300 °C. The effect of DSA concentration on the rheological performance of WDFs was investigated with a HAAKE rheometer. The filtration loss control ability of DSA was evaluated according to the American Petroleum Institute standards. The filtration loss volume of WDFs with 15 wt% NaCl could be controlled to 9.6 ml with 2.0 wt% DSA after aging at 190 ℃. To study the mechanism, the absorption behavior of DSA on bentonite with concentration was studied. The saturated absorption capacity of 2.0 wt% DSA on bentonite was 94.7 mg/g. The effect of DSA on the dispersion of WDFs was analyzed by measuring the zeta potential and particles size distribution. Then, the micromorphology and permeability of the filter cakes for WDFs were analyzed. According to the results, DSA effectively absorbed on the bentonite surface, reducing the zeta potential and particles size of the bentonite to form filter cakes with low permeability. The filtration loss of WDFs was then controlled by DSA. The research results were instructive for the development of polymer with high temperature and salt resistance for WDFs.