Abstract
The sealing integrity of cement sheath directly affects the service life of oil and gas wells, and plays an important role in oil well operation and production. In this paper, the evaluation of sealing integrity of cement sheath was divided into two parts: the integrity of formation and cement sheath, and the integrity of cement sheath and casing. Based on the convergence-constraint theory, the effect of convergence stress generated by formation on cement slurry during the hardening process was considered. And the evaluation method for casing-cement-formation sealing integrity was established. In addition, a quantitative relationship between compressive strength of cement sheath and formation characteristic parameters was proposed to determine the cement-formation sealing integrity. Besides, the integrity evaluation method of casing-cement-formation combination was verified by tensile strength, compressive strength and plastic zone of cement. The field application analysis showed that this method is valid to predict the cement failure. During the cementing operation, the integrity of casing-cement-formation interface can be controlled by adjusting the properties of the cement sheath.
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