Comparative study for evaluating the gradient of the failure function of wells drilled on salt rocks

Resumo

This paper presents a comparative study of strategies for obtaining the gradient of the failure function
used in the First Order Reliability Method (FORM) applied to oil wells drilled on salt rocks. The evaluation
of the mechanical behavior of complex structures is commonly performed using the finite element method. In
these cases, several challenges are found when it is desired to carry out a structural reliability analysis, since the
function that defines the structural behavior is numeric and each query requires running a finite element analysis.
This demands a high computational cost, making it practically impossible to perform the reliability analysis from
classical simulation methods. On the other hand, to use transformation methods it is necessary to evaluate the
gradient of the failure function, which is also a numerical expression, requiring the use of alternative techniques
to perform its calculation efficiently. In this context, this work presents the comparison between several numerical
methods to obtain this gradient. Several methodologies such as the response surface method (RSM), the adaptive
response surface method (ARSM) and the finite differences method (FDM) are applied to a model of an oil well
drilled on salt rocks. The main contribution of this paper is to check the efficiency of some procedures for obtaining
the gradient of the failure function in the evaluation of the structural behavior of oil wells drilled on salt zones.