A Practical Methodology to Assess Casing Integrity and Service Life with Salt Collapse Loads in Unconventional Developments

Abstract

Damage from salt stress is always an unwelcome occurrence in oil and gas wells; particularly in unconventional wells where productive longevity and slim cost to benefit margins are at risk. Many studies have been conducted that offer fixes in the form of pat algorithms or universal design modifications. The authors believe that each field or well offers unique challenges. This paper will outline successful methods for estimating salt creep rate, estimates of damage from salt for a casing scheme and field conditions. These are used to determine the economic-driven optimum well designs and production practices for addressing salt damage in both new wells and those already damaged. Further studies may allow these methods to be used in many other fields and wells. It is important to ascertain the local load paradigm for a specific field-development. To this end the specific pipe manufacturing data was reviewed for as-built conditions. Also, the regional salt movement environment and salt creep rate were determined through review of field data from existing wells with issues. Standard casing design analysis was applied to determine the non-salt loading, temperature and pressure environments, and to eliminate non-salt loading as sole cause of damage. A first pass survey made of the well population was conducted with several applied stress analytical methods such as Hackney for combined salt and non-salt loads up to yield. A second pass on critical wells was performed with a finite element analysis (FEA) matched against published studies. Most analytical stress models developed for salt loading are based on limited or incomplete data. Nor do they account for non-salt loading or pipe manufacture defects. These limitations are complicated by large variations on what constitutes ‘failure’ in the oil and gas industry. The best analytical solutions stop short of providing a complete stress picture due to inability to predict behavior beyond the yield point. Thus, it is necessary to apply FEA models with calibration by lab data. Published FEA on salt collapse is reported for specific weight and grades of pipe. These results were matched and then it is shown how to replicate this analysis and related trends with new pipe and grade selections. No solutions were found that were universal with the most successful solutions being based on a limited geographic area. Field wide studies in areas with multiple salt zones were completed to provide a forecast time-to-failure for existing wells in a development population. Based on this study, recommended modifications to existing wells were made to extend life and optimize economics. Finally, a recommended optimum design can be proposed for new wells as well as recommended monitoring and action plans.