Effect of inorganic cations on the rheological properties of polyacrylamide/xanthan gum solution

Natural gas hydrate (NGH) is a type of icing crystallographic substance formed by natural gas and water under high pressure and low temperature conditions. In the process of drilling the NGH core samples, to ensure that the hydrate core is not isolated, the drilling fluid temperature in bore circulation must be reduced below freezing to guarantee that the NGH is in a relatively balanced and stable condition. Inorganic salt cations can not only lower the freezing point of drilling fluid but also reduce the viscosity of the drilling fluid itself. When drilling fluid loses viscosity, its capacity to carry rock dust and protect the bore wall will be weakened. This will cause buried bore and bore wall collapse accidents. Thus, how to ensure stable viscosity and rheological properties in the drilling fluid in an environment with inorganic salt cations is the key to smooth hydrate core sample removal. This article focuses on the effect of Na+, K+, Ca2+, and Mg2+ cations, at varying concentrations, on the rheological properties of polyacrylamide containing anionic and cationic PAMs (HPAM and CPAM) and xanthan gum solution after macromolecules are produced in the interaction of the flocculant (polyacrylamide) and tackifier (xanthan gum). Meanwhile, the cross-linking reaction mechanism of the PAM/XG macromolecule system and the mechanism of cations' disruption of the cross-linking process are also studied. The experimental results show that the CPAM/XG solution is more cation resistant than the HPAM/XG solution. The following analysis of the surface functional groups and the spatial structure of macromolecules by infrared spectroscopy and scanning electron microscopy explains why cations change the macromolecular structure of the solution. Hence, it is easier for divalent cations to change the macromolecular structure than for monovalent cations to do so.