Patent ID: 6296057
Filing Date: 2001-10-02
Classification: E21B

Abstract:
A method of defining the properties of a cement sheath for use in positioning a casing in an oil or gas well or the like, the method comprising:(i) estimating at least one of pressure, temperature and in-situ stresses which can occur in the well during its lifetime;(ii) determining geometrical characteristics of the well and the casing and mechanical properties of formations surrounding the well;(iii) for a given sheath in the well, evaluating stresses that will be applied to the sheath as a function of the estimated pressure, temperature and in-situ stresses, and the determined geometrical characteristics and mechanical properties;(iv) determining from the evaluated stresses, the nature of the stress most likely to cause deterioration of the given sheath;(v) evaluating the influence on the determined most likely stress of the mechanical and physical properties of the given sheath, the formations surrounding the well and the casing; and(vi) defining cement sheath properties by adjusting the given cement sheath properties, including its elastic properties, on the basis of the evaluation and determination to provide as high a ratio as possible between its tensile strength and Young's modulus and to attenuate the effect of the determined most likely stress.