Incorporation of a damage model to salt rocks viscoelastic modelling

Resumo

This work describes a numerical study using finite elements about the structural behavior of vertical
wells through salt rocks, using a coupled viscoelastic damage model. The salt rocks have porosity and permeability
close to zero, performing as a sealing structure, so that is common to find oil reservoirs under these formations.
However, to reach such reservoirs it is necessary to pass through thick layers of these rocks, that develop high
creep strain rates in the direction of the borehole closure. In some situations, this closure can cause problems
like equipment entrapment and poor cementing in casing installation. Depending on the strain rate and on rock
exposure time, the accumulated strain can be too large, leading to material breakdown, which generates washout
regions. Thus, for an accurate prediction of well profile over time it is necessary to consider the damage caused on
rock due to the accumulated strain, searching to map washout regions. Due to the complexity of the problem, the
studies are performed through numerical simulations. The proposed methodology is divided in four main steps:
a) choice of a constitutive model with damage to salt rocks; b) verification of numerical modelling of vertical
well through salt rocks; c) implementation of viscoelastic model with coupled damage for salt rocks; d) numerical
modelling of the well considering the implemented constitutive model. This study identified a damage model for
salt rocks proper to the vertical well scenarios under study. The incorporation of this model to the computational
methodology should contribute to a better understanding of the rupture mechanisms of these rocks and should help
to forecast the washout regions.