Failure Analysis of Cement Sheath Mechanical Integrity Based on the Statistical Damage Variable.

Area of Science:

• Petroleum Engineering
• Materials Science
• Geomechanics

Background:

• Cement sheath integrity is critical for oil and gas well safety and production.
• Effective evaluation of cement sheath sealing performance remains a significant challenge.
• Cement sheaths isolate hydrocarbon reservoirs from water layers, preventing fluid channeling.

Purpose of the Study:

• To analyze cement sheath seal failure mechanisms.
• To develop a model for evaluating cement sheath mechanical integrity.
• To establish a quantitative damage variable for cement sheath assessment.

Main Methods:

• Cement sheath annulus isolation experiments.
• Analysis of cement sheath, casing, and rock interactions.
• Development of an analysis model using nonlinear elastic constitutive equations.
• Application of statistical damage variables from continuum mechanics.

Main Results:

• Identified tensile crack damage and micro-annulus formation due to plastic yielding as primary failure modes.
• Established a damage variable that quantitatively describes cement sheath mechanical integrity.
• Demonstrated a strong correlation between the damage variable and wellbore pressure in field cases.

Conclusions:

• The proposed damage variable accurately quantifies cement sheath mechanical integrity.
• Reducing wellbore pressure is crucial for maintaining cement sheath integrity and sealing.
• Findings provide a basis for optimizing cement sheath design and enhancing sealing capabilities.