Performance and working mechanism of amphoteric polycarboxylate-based dispersant and sulfonated acetone formaldehyde polycondensate-based dispersant in oil well cement

Abstract A comparative study of amphoteric polycarboxylate-based (APC) dispersant and a conventional sulfonated acetone formaldehyde polycondensate-based (SAF) dispersant was conducted to understand their effects on performance and their working mechanism, especially for the high environmental temperatures used in oil well cementing operations. Measurements of fluidity, rheology, thickening time and compressive strength for cement paste with the two dispersants above at 60 °C were carried out. Total organic carbon (TOC) determination and isothermal calorimetry were adopted to observe the adsorption behavior and cement hydration based on APC and SAF dispersants. Formation of hydration products was characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD) and Raman analysis. Results show that the APC dispersant exhibits better dispersion capability and retention ability by electrostatic repulsion and steric repulsion than the SAF dispersant, which significantly improves the rheological properties of cement paste. Moreover, the SAF dispersant, with a stronger adsorption capability, intensely retards cement hydration compared to the APC dispersant, which was confirmed by inhibition of the formation and growth of portlandite (CH) as well as calcium silicate hydrate (C-S-H). The addition of APC dispersant also improves the pore structure and increases the compactness of the set cement, which enhances the early mechanical strength of hardened cement. Such results can enrich the application of APC and SAF dispersants in cementing operation.