Synthesis and characterization of a novel sustained-release-type citric acid intercalated hydrotalcite and its application in oil well cement

To address the problems of poor thermal stability and over-retarding of cement slurry by retarders, as well as the sensitivity to the citric acid dosage and poor early strength of cement treated with hydroxycarboxylic acid retarders, citric acid intercalated hydrotalcite (Mg/Al-CA-LDH) with a sustained release effect was prepared by an anion exchange reaction between citric acid and magnesium aluminium layered double hydroxide (Mg/Al-CO3-LDH). The prepared citric acid-intercalated hydrotalcite exhibited good crystallinity and high thermal stability, where 39.92% citric acid could be inserted into the composite. Evaluation of the thickening and compressive strength of oil-well cement showed that Mg/Al-CA-LDH can effectively maintain the fluidity of cement slurry and improve its early compressive strength. Furthermore, because of the seed effect of hydrotalcite and the microrelease of citric acid in Mg/Al-CA-LDH, the synergistic effect of hydrotalcite and Mg/Al-CA-LDH can promote the setting of oil-well cement, where the effect is stable, and the thickening curve is stable, indicating right-angle thickening.