Assessment of the structural integrity of cement sheaths in oil wells.

Resumo

This work proposes a study on the analytical modeling of the system composed of casing-cement-formation, considering the displacements and stresses acting at the interfaces, in order to assess the structural integrity of the cement sheath in oil wells. The interaction of this system is also evaluated through numerical modeling, using the commercial software Abaqus, aiming to verify the results provided by the studied analytical model. In the process of oil well construction, the cementing phase is one of the most important and demands integrity analyses and risk assessment, as poorly executed results in increased costs and operational problems. Cement failure can be modeled using the traditional Mohr-Coulomb criterion, which provides the limiting stress for shear failure. In this context, a comparative case study is presented to illustrate the proposed investigations and verify the results obtained from the following methodology: a) implementation of a discrete analytical model that estimates the mechanical behavior of the system and evaluates the integrity of the cement sheath and b) modeling of a discrete numerical model, evaluated by a static structural analysis, considering the effect of temperature and the debonding failure mode. Through a comparative analysis of the results obtained, it is noted that the two strategies used (analytical and numerical) provide very similar results. Thus, the computational implementation of the analytical solution is an important tool for the design of oil wells, allowing rapid analysis and prediction of the structural integrity of cement sheaths.