Cement sheath integrity analysis and prediction method and device

Abstract

The invention provides a well cementation cement sheath integrity analysis and forecast method and device. The method comprises the steps that under a homogeneous crustal stress field, and based on the elastic thick wall cylinder theory and Mohr-Coulomb plastic yield guidelines respectively, the stress distribution and the displacement distribution of an elastic area of the well pitshaft and the stress distribution and the displacement distribution of the plasticity of the pitshaft area are calculated and obtained, the pitshaft area comprises a casing pipe, a cement ring and the surrounding rocks distributed from the inside to the outside; the stress distribution and the displacement distribution of the well pitshaft under the inhomogeneous stress field using the Airy stress function are calculated and obtained, the homogeneous stress field and inhomogeneous stress field are linearly overlaid and the result is the original stress field; the stress distribution and the displacement distribution of the pitshaft plastic area, and the stress distribution and displacement distribution of the pitshaft under the inhomogeneous stress field are utilized and linearly super-imposed to obtain the total stress distribution and displacement distribution in the pitshaft, which is used for the analysis and forecasting of cement sheath integrity. The well cementation cement sheath integrity analysis and forecast method and device take into account the cement sheath elastic plasticity, to reflect the work conditions of the real well bottom.

Description

technical field [0001] The invention relates to the technical field of casing cementing oil and gas wells, in particular to a method and device for analyzing and predicting the integrity of a cement sheath. Background technique [0002] The cement sheath is an important barrier to ensure the effective sealing of the wellbore. How to ensure the integrity of the cement sheath is a concern of cementing engineers. In order to improve the sealing performance of the wellbore and ensure the integrity of the cement sheath, researchers have developed several sets of cement slurry systems, such as high density, low density, low elastic modulus, high strength, toughness and micro expansion, etc. However, due to the complexity of the working conditions at the bottom of the well, there are still a large number of cement sheath seal failure problems. [0003] In order to ascertain the cause of cement sheath seal failure, many researchers use the principle of elastic mechanics to start w...

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Problems solved by technology

In addition, some researchers combined plastic mechanics to analyze the detachment of the interface between the cement sheath and the casing due to plastic deformation under plastic deformation conditions, resulting in micro-annulus gaps and sealing failure.

[0004] However, these two types of analysis methods are too simplified, and many actual working conditions at the bottom of the well cannot be truly reflected.

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