Abstract:

The expansion mechanism of hydroxide expanding phase for oil well cement slurry are discussed on the basis of principle of chemical thermodynamics and topochemical reaction model. It suggests that expansion force results from crystallization pressure, which converted from the reduction of chemical potentials in the reaction of hydroxide formation, i.e., the chemical energy of the reduction was converted into the mechanical work. Furthermore, the special experiments were designed to validate the theoretical analysis by use of class G oil well cement and anovel expandant. The theoretical analysis and experimental findings indicate that two conditions are indispensable: (1) the plastic strength of the slurry must high enough to restrained crystal growth of the solid product (i. e. restrained crystal growth) and (2) solubility product of the pore solution for hydroxide in the slurry should be greater than that of standard condition.

Key words: cement, mechanism, expansion, thermodynamics