镁氧类油井水泥膨胀剂膨胀机理的研究

THE EXPANSION MECHANISM OF MAGNESIA COMPOUND FOR OIL WELL CEMENT THERMODYNAMIC PRINCIPLE AND VALIDATION

基于膨胀剂原地反应模型和化学热力学原理，讨论了晶体生长压的源动力及水泥浆体体积膨胀与结晶压的关系。经过分析得知：膨胀驱动力来自于水化体系化学势的降低而产生的结晶膨胀压，即化学能被转化成机械功。采用镁氧油井水泥膨胀剂和高抗硫Ｇ级油井水泥，考察了油井水泥浆塑性体的塑性强度和膨胀的关系以及硬化体的膨胀性能，为理论分析提供了有力的实验证据。结果表明：水泥浆体产生膨胀的充要条件是①浆体的塑性强度足够大（受限的晶体生长）；②在水泥浆体中反应物的局部浓度过饱和（反应产物的溶度积比标准状态下大）。

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 a novel 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.