Wellbore construction through salt formation remains a great challenge in drilling engineering in many oil provinces around the world due to its unique mechanical properties, in particular, its high creep mobility under downhole conditions. However, once the casing is defined, the behavior of salt is ideal and can provide a necessary and economically beneficial natural barrier. The aim of this paper is to model wellbore closure in salt throughout uncemented casing zones considering both open annular. For this, a computational methodology was developed and evaluated through the reproduction of studies about the formation of natural barriers in salt, reported in the literature, is presented. 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 discussed at this stage. From that, we present an analysis to estimate the wellbore closure time under field conditions representative of the Brazilian basins, coupling the adjustments made in the previous stage. As a result, it is observed the potential for the formation of natural barriers in saline layers for permanent plug and abandonment operations.
The operations carried out at the end of the useful life of any kind of well (exploration, production or injection) are called permanent plug and abandonment of the well (PP&A) whose objective is to prevent the flow of fluids from the formation and resist the pressures acting above and below.
According to Khalifeh & Saasen (2020), the PP&A operations of a well can reach up to 25% of offshore well drilling costs. Due to the high costs of these operations and the high number of wells to be permanently plugged and abandoned in Brazil in the coming years, the oil and gas industry has increasingly invested in the development of alternative PP&A techniques.
