Abstract
Casing integrity is a major concern in wells drilled through salt zones due to the salt time-dependent behaviour. As wellbore closes, the trapped annular experience a pressure build-up that may subject casing to high loads, leading to its collapse. In this scenario, a big concern of the well design engineers is to predict whether or not the string will fail, and the consequences to the integrity of the production casing, which can lead to serious problems and possibly making any workover infeasible. Therefore this paper focus in the contribution of salt creep to the annular pressure build up (APB) phenomenon, and the consequences of wellbore closure in the integrity of both intermediary and production casings. The analyses involve FEM simulations of different case scenarios with considerations of fluid elements, which can account for fluid compressibility, i.e., pressure build-up as the wellbore closes and pressure relief as the casing collapses.
1. INTRODUCTION
Many reservoirs can be found beneath Salt formations. This occurrence is favorable because of Salt extremely low porosity and low permeability, which makes it a excellent sealing rock. In through-Salt environments, well integrity in long-term production is a great concern due to rock creep. For deep wells, where high temperature and high pressure are expected, a proper casing design has to be carefully analyzed so as to guarantee a safe operation until well abandonment.
When crossing Salt formations, intermediary casing has an extremely important role, as it must protect production casing from Salt-related problems. To assure production casing integrity, a series of studies have to be conducted so as to determine whether the casing configuration will withstand different types of loads over time. One of these studies is the analysis of the pressurization on the annulus above top of cement, which can lead to casing system collapse due to trapped drilling mud.
