Effect of CaCl2 on the micromorphology of a self-thickening agent (TZXJ) for acidizing diversion

Abstract

The effect of CaCl2 on the micromorphology of a self-thickening agent (TZXJ) was investigated. This study involved analyzing the compositional changes in acid solutions during acid–rock reactions. It combined dynamic light scattering and viscosity testing to confirm that the presence of CaCl2 enhances the aggregation strength of the TZXJ network structure in acid solutions. This enhancement is macroscopically evident as an increase in viscosity. Incorporating 10 % CaCl2 as a promoter into a fresh acid solution, the hydrodynamic radius (Rh) distribution of TZXJ in varying reaction stages was analyzed using dynamic light scattering experiments. The results indicated that the promoter CaCl2 further strengthens the network association of the TZXJ acid solution, thereby improving its thickening capability. Investigating the viscosity of TZXJ aqueous solutions with varying concentrations of CaCl2 revealed that TZXJ exhibits notable salt-thickening effects and can withstand saturated CaCl2 solutions. The microstructural aggregation state and morphology of TZXJ in aqueous solutions were characterized at different CaCl2 concentrations. Dynamic light scattering results demonstrated an increase in the Rh of TZXJ solutions with CaCl2 concentrations. In particular, the mean Rh of a 0.8 % TZXJ solution increased from 150.8 nm to 3078.93 nm. Ultraviolet spectral analysis confirmed that the absorption intensity of the TZXJ solutions increased with CaCl2 concentration, indicating a strengthened network aggregate structure in the TZXJ solutions. Microscopic observations using environmental scanning electron microscopy and transmission electron microscopy revealed that under the influence of calcium chloride, the microstructure of TZXJ transitions from a non-associated, linear carbon chain skeleton to a dense, aggregated network structure. The findings of this study offer theoretical insights for researching polymers resistant to extreme concentrations of CaCl2.