Maximizing drilling performance by pushing the limits of drilling tools is the key to reduce overall drilling cost. The interplay of complex parameters such as lithology, drilling parameters, drilling experience, downhole tool reliability, and the operational process help us to identify the limiting factors. Drilling dysfunction could deteriorate the reliability of downhole drilling tools including the overall drilling performance by causing damaged bits, failure of downhole electronic components, torsional fatigue of drillstring, over-torqued connections, etc. Precise modeling of dynamic responses of a bottomhole assembly in a given formation can help to identify operating limitations as well as post job analysis.
The wellbore-drillstring interaction and well face-drill bit interaction are the sources of excitation of torsional oscillations. Stick-slip is one of the common and well-known torsional oscillation that usually occurs at low frequencies <1 Hz. High-frequency torsional oscillations (HFTO) are also recorded in the field by using high-bandwidth downhole vibration monitoring tools. HFTO occurs at much higher frequencies; >10Hz to 500 Hz. This paper summarizes the HFTO phenomenon that causes high tangential accelerations and torsional loads within the bottomhole assembly (BHA) during drilling in critical formations. HFTO modeling that is validated with high-speed measurements helps to identify tangential accelerations and torsional loads across the BHA components.
This paper highlights the benefits of modeling the rotary steerable system (RSS) BHA for HFTO in order to identify the point in the BHA that is subjected to the highest tangential acceleration and torsional loads. Real time monitoring for drilling optimization of RSS BHA shows that the HFTO modeling and post-job data analysis of high-frequency data confirms the distribution of tangential acceleration and torsional loads along the BHA. The paper also highlights the accuracy of the HFTO modeling based on results of pre-job modeling and post-job high-speed data analysis from drilling runs. Based on the analysis and the study, recommendations for optimal BHA design and operational parameters are provided to yield maximum footage per run and improved BHA performance.
High-frequency torsional oscillations in the BHA can be mitigated if adequate BHA design, drilling parameters, and procedures are implemented. The in-depth analysis of HFTO with accurate modeling and high-frequency measurements can be used to develop a knowledge base to further optimize the drilling process, reduce non-productive time, realize fewer trips for failures, extend the on-bottom drilling time, reduce maintenance costs, and increase the drilling efficiency and performance.