Nano SiO 2 /Welan gum nanocomposite—microbial polysaccharide thickener used for 220 ℃ water-based drilling fluid, high-temperature sedimentation control stability

In the paper, nano-silica (nano-SiO 2 )/Welan gum (RSWG) nanocomposite was synthesized as thickener to improve the sedimentation stability of high-temperature drilling fluid. Experimentally, Fourier transform infrared spectrum (FTIR) analysis, X-ray photoelectron spectrum (XPS) analysis, and thermogravimetric analysis (TGA) were conducted for chemical structure analysis of the synthesized product. As a result, test results showed that nano SiO 2 was successfully grafted onto Welan gum through the silanization coupling technique. Also, by using nano-silica (nano-SiO 2 )/Welan gum nanocomposite (RSWG) thickener, water-based drilling fluid was found the excellent resistance to rheological sedimentation via the testing of 16-h thermal aging. The temperature resistance of water-based drilling fluid was up to 220 ℃. And when 1.5 wt.% nano-silica (nano-SiO 2 )/Welan gum (RSWG) nanocomposite thickener was used, the density deviation of the high-density drilling fluid (2.30 g/cm 3 ) at 220 ℃ was kept at 0.02 g/cm 3 . Also, no free water was precipitated out. It is found that Welan gum can avoid being damaged by drilling environment caused by high temperature and high-shearing effect. As a reconstructed nanocomposite structure, nano SiO 2 and coupling agent have constructed the outer covalent-bonded protection shell, and they show excellent thermal insulation effect and better resistance to mechanical shear for protecting the flexible and polymeric structure of Welan gum. Thus, the use of nano-silica (nano-SiO 2 )/Welan gum (RSWG) nanocomposite offers us a better understanding and potential opportunity for using polymer component to develop new types of clayless or clay-free water-based drilling fluid systems for the high-temperature drilling industry.