ABSTRACT:

This work presents a probabilistic analysis of wellbore integrity using analytical and numerical (finite element method - FEM) approaches. The safety of the wellbore is evaluated through a casing integrity criterion. To evaluate the stresses considering the construction and production phases, the analytical solution considers the main steps of the wellbore lifespan: initial stress state in the formation, drilling operation, casing construction, initial stress state in the cement, pressure changes inside the casing and pore pressure variation. For both approaches, plane strain conditions, continuous homogeneous isotropic media and linear elastic materials are considered. Although the model hypotheses are similar, the FEM modeling allows the construction of a wellbore model with imperfections such as a cement channel. The uncertainties in the elastic parameters of casing, cement and formation are incorporated into the analysis using the AMV+ and LHS methods. The failure criterion to assess loss of wellbore integrity is given in terms of the cumulative distribution curve. In addition, the most important variables are identified. With this information, it is possible to define a risk scenario, mitigation strategies and procedures for better data acquisition and monitoring during wellbore operation lifetime.

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