Preparation of 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 citric acid (CA) dosage and poor early strength of cement treated with hydroxycarboxylic acid retarders, CA-intercalated magnesium aluminium hydrotalcite (Mg/Al-CA-LDH; henceforth called CAIH) with a sustained-release effect was prepared by an anion exchange reaction between CA and magnesium aluminium carbonate layered double hydroxide (Mg/Al-CO3-LDH). The prepared CAIH exhibited good crystallinity and high thermal stability, and 39.92% CA could be inserted in the composite. Evaluation of the thickening and compressive strength of oil-well cement showed that the addition of CAIH effectively maintained the fluidity of the cement slurry and improved its early compressive strength. Furthermore, because of the seed effect of hydrotalcite and the microrelease of CA in CAIH, the synergistic effect of hydrotalcite and CAIH can promote the setting of oil-well cement: the effect was stable and the thickening curve was stable, indicating right-angle thickening.