Low elastic modulus and expansive well cement system: The application of gypsum microsphere

• We invent the method for preparing gypsum microsphere.
• Gypsum microsphere is used to achieve low elastic modulus and expansive well cement.
• Cement sheath with gypsum microsphere has brilliant resistance to stress and strain.
• Massive crystals formed by gypsum powder decrease interfacial bonding strength.

The research objectives in this paper are designed to use gypsum microsphere to achieve low elastic modulus and expansive well cement system. Results show that gypsum microsphere has the ability to compensate for volume shrinkage of hardened cement. Expansive crystals produced by the reaction of tricalcium aluminate and dihydrate gypsum exist around gypsum microsphere. Though compressive strength of hardened cement is improved by gypsum powder, existence of massive crystals increases brittleness of cement sheath. Compared with gypsum powder, due to porous structure, gypsum microsphere decreases elastic modulus of hardened cement, which shows brilliant resistance to stress and strain.