INFLUENCE OF CASING DECENTRALIZATION ON THE THERMO POROELASTIC INTEGRITY ASSESSMENT OF CEMENT SHEATHS IN OIL WELLS

Abstract

This study investigates the influence of casing decentralization on the structural integrity of the cement sheath in oil wells under thermo-poroelastic conditions. The cement sheath, located between two casings or the casing and surrounding rock formation, performs essential functions, including ensuring casing support, providing hydraulic isolation between producing zones, and maintaining the structural stability of the well. Traditionally, its design is based on thermoelastic models with circular cross-sections and concentric geometry. However, geometric imperfections, such as casing decentralization, can modify stress distribution significantly, compromising the structural integrity of the cement sheath. In addition, the porous behavior of hardened cement, often disregarded, can influence meaningfully its mechanical response. In this context, the methodology comprises: (i) the definition of the numerical model; (ii) the establishment of material properties and boundary conditions; (iii) the verification of the eccentric model; (iv) the definition of the case studies; and (v) the structural integrity assessment. Results show that decentralization intensifies circumferential stresses in the region of reduced thickness, increasing susceptibility to failure. The inclusion of thermo-poroelastic behavior, although reducing absolute stress levels, amplifies the effects of eccentricity. Thus, this study integrates both factors, providing initial insights for safer and more realistic designs in the oil and gas industry.