Amphoteric tetramer as a filtration-loss reducer in low-solid phase water-based drilling fluids under high thermal-saline conditions

Abstract

In deep well drilling, the filtration-loss reducer remarkably impacted the rheological property of water-based drilling fluids at high temperature and salinity, causing serious problems during the drilling process. In this work, a combination of low molecular weight amphoteric copolymer and bentonite clay was exploited to tackle these issues due to their relatively different thermal-saline-properties dependence. In detail, a novel amphoteric tetramer (AB-47) of N,N-dimethylacrylamide (DMAm), 2-acrylamide-2-methylpropanesulfonic acid (AMPS), diallyl dimethylammonium chloride (DMDAAC), and N-vinylpyrrolidone (NVP) was prepared by free-radical copolymerization technique under optimal conditions. And the molecular structure of AB-47 was evidenced by FT-IR, 1H NMR, and elemental analysis. The filtration and rheological performance of AB-47 in low solid-phase water-based mud (LSWBM) were examined in comparison with Driscal D before and after a 16 h aging at 230 °C according to the American Petroleum Institute (API) standard. Results indicated that, only 1% AB-47 could not only control an API filtration loss volume of 8.9 mL but also the change rate of main rheological parameters were found to be more stable while parameters of Driscal D containing mud not only varied dramatically but also an API filtration loss of 30 mL could be maintained under identical conditions. Although the contamination with NaCl affected both muds properties, AB-47 could still exhibit higher performance. Therefore, the relative stability of AB-47 containing mud with respect to the chemical environment could be achieved through the strong synergistic interactions between AB-47 and bentonite particles, which were examined through particle size distribution, zeta potential and scanning electron microscopic.