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Wellbore construction through salt formation remains a great challenge in
drilling engineering in many oil provinces around the world, notably offshore
Brazil, due to its unique mechanical properties, in particular, its high creep mobility
under downhole conditions. Initially, it is necessary to control wellbore closure
during drilling in order to allow casing installation. Later, the loading of the casing
in both the cemented and uncemented sections is cause of concerns to prevent issues
of long-term wellbore integrity. However, the contact between the salt and the
casing can provide a necessary and economically beneficial natural barrier. This
work consists of extracts of the research project Evaluation of the potential of
clayey and evaporitic formations to act as an external barrier to the casing for the
abandonment of wells, carried out by the Group of Technology and Petroleum
Engineering (GTEP) at the Pontifical Catholic University of Rio de Janeiro, Brazil.
The aim of this work is to model wellbore closure in salt throughout uncemented
casing zones considering open annular. For this, a computational methodology was
developed, using the commercial finite element code ABAQUS. As the first stage
of the study, in order to validate the simulation protocol, the reproduction of studies
about the formation of natural barriers in salt, reported in the literature, is presented,
considering the small and large deformation modes of the ABAQUS. The
comparison between the results obtained demonstrates a time difference for annular
closure ranging from a few months to a few years, depending of depth and type of
salt. Discussions on specific aspects of creep simulation in salt rocks are also made
at this stage. In the second stage of the work, is presented an analysis to estimate
the wellbore closure time under field conditions representative of the Brazilian
basins, coupling the adjustments made in the previous stage. The salt constitutive
behavior used to simulate the steady-state creep was double mechanism model and
the parameters are representative of the Brazilian offshore scenario. As a result, it
is observed the potential for the formation of natural barriers in saline layers for
permanent plug and abandonment operations. In both simulations, annular closure
is performed using 2D models of plane strain and axisymmetric, representing the
cross section and longitudinal section, respectively. The simulation steps are
divided into initial equilibrium stress field (geostatics) followed by drilling and
simulated creep as a viscoelastic material.