بررسي و تعيين عامل واماندگي غير عادي رشته حفاري در ميادين نفتي گچساران و بي بي حكيمه ايران

Analysis and Determination of the Principal Factor for the Abnormal Drill-string Failures in Gachsaran and Bibihakimeh Oil Fields Of Iran

Results for a typical abnormal drill-string failure (DSF) in a specific formation in oil fields located in the Southern part of Iran are presented. In this work efforts were made to define the challenge as precisely as possible as to where, how and why the problem occurred. Possible reasons and practical solutions to this challenge are evaluated. Drill-string vibration in torsion mode (stick-slip vibration phenomenon) is the most probable reason of failure in Iranian oil fields due to two reasons. Firstly, it was observed in practice that abnormal drill-pipe failures occurred only in a specific formation while in other formation it did not, even though the bottom hole assembly (BHA) structures were designed identically. Secondly, the rock characterization of the hazardous formation is sticky and hard compared to the layers above and below the hazardous formation. Stick-slip vibrations are self-excited by the interaction of drill-string, drill bit, and formation. Self-excited stick-slip vibrations may also induce severe axial and lateral vibration excitations in the BHA, causing damage to the equipment. The work is motivated by the need to understand the complex vibration states and concludes that vibrations are the main factor leading to drill-string failures (DSF) for the field under investigation in the southern part of Iran. In order to reduce abnormal DSF, several methods and recommendations are presented and discussed.