High-frequency torsional oscillation (HFTO) is a particularly damaging vibration phenomenon that occurs while drilling HFTO-prone rocks with Polycrystalline Diamond Compact (PDC) bits and aggressive drilling parameters. Mitigation or load reduction strategies are based on weight on bit or bit rotary speed reduction and are associated with lower rate of penetration and therefore limit the drilling efficiency. This paper discusses the suppression of HFTO with a 4.75-inch tool size damper assembly that is placed above the bottom-hole assembly (BHA) and typically below the mud motor. The efficiency of the damper assembly is discussed in a case study with more than 40 runs in Permian Basin targeting different applications, environments, and formations, giving further evidence that providing damping to the BHA can completely mitigate HFTO.

The damper tool is designed for the purpose of mitigating HFTO. Inputs for the design of the inertia-based damper elements are the required damping identified from high-frequency downhole measurement data, laboratory testing and modeling to analyze and optimize the damping principle incorporated in the tool, and numerical simulations to analyze the achievable damping in different BHAs. The tool design is robust as proven in a standard process of tool reliability tests including rotating bending, vibration, temperature, and pressure, and not limiting the drilling parameters. The deployment is preceded by a step that maximizes achievable damping in the deployed BHA enabled by an optimization algorithm and numerical modeling. Herein, the damper elements are optimally placed for the identified critical modes of HFTO, targeting a placement in antinodes of the mode shapes with high vibration amplitudes guaranteeing a high damping effect.

The case study incorporates more than 40 runs in NAL showing that the occurrence of HFTO is reduced significantly in different applications. The case study includes back-to-back runs with similar BHAs with and without the damper assembly in different HFTO prone applications proving the efficiency of the tool in mitigating HFTO. Consecutive runs in the same well and formation using other vibration mitigation tools show a significantly higher HFTO-suppression rate with the damper assembly. The overall performance gain by use of the damper is further proven by a statistical evaluation and in comparison to the second and third best performing vibration mitigation tool, showing significant increase in all relevant performance metrics, including, but not limited to, Mean Distance Between Failure (MDBF) and Mean Time Between Failure (MTBF). BHAs with the new damper tools outperform BHAs with industries currently preferred commercial vibration mitigation tools by as much as +100% in MDBF and +100% in MTBF.

The case study shows that HFTO can be mitigated by use of the new 4.75-inch damper assembly. The damaging HFTO that held back the drilling parameters is suppressed which enables a step change in drilling efficiency and reliability, which ultimately leads to a significant decrease in drilling cost.

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