Preparation and performance evaluation of polymer intercalated montmorillonite composite high temperature scale inhibitor

In this study, based on the escalating demand for thermally stable scale inhibitors in high-pressure/high-temperature (HPHT) water-gas reservoirs, an organic-inorganic composite scale inhibitor (CT-5) was successfully synthesized via solution polymerization-mediated in situ intercalation using acrylic acid (AA), 2-acrylamido-2-methylpropanesulfonic acid (AMPS) and diallyldimethylammonium chloride (DMDAAC) as monomers, with surface-modified montmorillonite (MMT) as reactive filler. Orthogonal optimization established ideal synthesis parameters, which including a reaction temperature of 75 °C, an initiator dosage of 0.6%, a solution pH of 7, a reaction time of 12 h, and a monomer ratio of m (AMPS): m (AA): m (DMDAAC): m (MMT) = 48:25:23:4. Moreover, the molecular structure and thermal stability of CT-5 were characterized by FTIR, XRD, and TG-DTG, as a result, the polymer intercalated MMT was successful, and CT-5 had a composite intercalation structure of organic polymer/inorganic montmorillonite, with a thermal decomposition temperature of 235.24 °C. Salt tolerance evaluation demonstrated robust performance under saline conditions. The scale inhibition mechanism of CT-5 was explored through scale inhibition rate testing, interlayer spacing testing at different temperatures, characterization of CaCO₃ scale crystal structure and morphology, and chemical binding energy testing of CaCO₃ scale crystals. The CT-5 can release effective chelating groups in the intercalation layer at high temperature, which inhibits the formation of CaCO₃ scale by chelating Ca²⁺ to form chelates, and also forms an adsorption layer on the surface of CaCO₃ scale crystals to interfere with the normal growth of CaCO₃ scale crystals and change the lattice structure of CaCO₃ scale crystals, thereby achieving the scale inhibition effect.