Preventing Drill String Twist Offs Due to HFTO coupled with High Stick-Slip RPM for RSS BHAs

Abstract

Abstract All drilling dysfunctions or vibrations including High Frequency Torsional Oscillation (HFTO) are monitored in real time with current technology of Drilling Bottom Hole Assembly (BHA). There are certain limits set for each kind of vibration and drilling parameters are optimized while drilling to overcome these dysfunctions. The main objective of this paper is to present a detailed case study of showing the impact of HFTO within the permissible limits which can be monitored in real time, combined with lower to moderate levels of stick slip leading to twisting off Rotary Steerable System (RSS) drilling BHAs. This paper covers the implementation of a new strategy to eliminate twisting off BHAs due to HFTO thereby avoiding Non-Productive Time (NPT) and any additional costs that could be incurred due to an incident such as fishing, unplanned sidetracks etc. Drilling with PDC bits across Anhydrites always generates HFTO. However, frequency and amplitude of HFTO depends on the type of Bit, rock strength, BHA configuration and drilling parameters. Historically, in the majority of BHA twist off incidents, real time vibrations and drilling parameters are within the maximum allowable tool limits. Monitoring HFTO in real time (RT) is limited due to high sampling rate of vibration data which cannot be transmitted in real time. With the advancement of technology in RSS all high frequency vibration data is stored while drilling and can be analyzed after the run. Memory analysis along with HFTO modelling were carried out for multiple runs to evaluate the impact of torsional loads. Detailed analysis of this high frequency memory, formation behavior, drilling parameters and bit features was done to compare between good and failed runs. Based on the analysis, new guidelines and corrective actions were implemented to eliminate BHA twist offs. Based on the memory analysis and modeling, torsional loads were higher during stick slip events exceeding tool's limits leading to twist off and it was found to be common in all twist off incidents. New corrective actions were implemented on subsequent runs that resulted in avoiding twist offs by 100%. This translated to reduced trips for failure, tool maintenance cost and improved overall efficiency. In certain applications, depending on the above-mentioned factors HFTO will trigger, however with an optimized well program, drill string twist-off can be avoided. The methods and processes presented in this paper can be applied globally in the areas with similar challenges. This would result in delivering the wells in the most efficient way by reducing lost time and improving efficiency.