INTRODUCTION: Material selection is one of the critical issues of well integrity programs, considering the impact of damage mechanisms on fitness for service, residual life and maintenance costs. In recent years, Pan American Energy(1) implemented a systematic process for materials selection of wells components, as part of its Well Integrity Management System, in order to ensure compatibility between design life and operative forecasts projections. The implementation of this initiative began with high pressure gas production wells, considering their business importance and the role of active damage mechanisms on residual life. According to both in company and industrial experience, the primary causes of materials degradation and damage were the following: ? Internal corrosion, due primarily to carbon dioxide. ? Internal erosion, due primarily to high flow rates and geometric effects. ? Erosion-corrosion, due to the synergic action of corrosion and erosion. Since key factors on initiation and propagation of these mechanisms are related to fluid characteristics, operation variables and material properties, materials selection requires a comprehensive approach to the following issues: ? Multiphase flow behavior, including flow patterns, velocities, densities, liquid volume fraction and water cut. ? Pressure and temperature, which govern corrosion thermodynamics, through CO2 partial pressure, pH and scaling temperature. ? Electrochemical behavior, considering both free and mitigated corrosion, under specific chemical treatment. ? Remaining strength evolution, due to thickness loss and localized damage.
Analytical Approach The analytical approach implemented for material selection involved the following steps: ? Selection of high pressure wells with production forecasts available. ? Multiphase flow and compositional modeling, required to determine flow patterns, velocities (gas, liquid and mix), densities (gas, liquid and mix), water cut, pressure and temperature profiles. ? Thermodynamic modeling, in order to estimate pH and scaling temperature. ? Kinetics modeling, resulting in metal loss rates estimates. ? Remaining strength projections, due to metal loss.