Drillstring-borehole contact may result in backward whirl: a common and catastrophic phenomenon. To increase BHA (bottom hole assembly) reliability, reduce non-productive time (NPT), and ultimately improve service delivery, an in-house backward whirl testing rig is developed to investigate dynamic loads. Analytical and numerical models elucidate dynamic responses and are validated against backward whirl test results. A 6 ?-in. BHA is tested in an 8.5 in. borehole using a continuous and discontinuous borehole profile. At a rotary speed of 60 rpm, and using a continuous borehole, lateral acceleration amplitudes range between 20 to 30 g with an RMS value of 3 gRMS. In comparison, a discontinuous profile results in acceleration amplitudes between 40 to 50 g with an RMS value of 7 gRMS. In regard to the discontinuous profile, the response spectrum shows a broader range of frequency content up to 200 Hz while distinct frequency peaks are evident in the spectrum when the continuous profile is used. Results indicate that backward whirl may occur from friction induced contact with different borehole profiles. Further, discontinuous profile yields drastically higher dynamic loads with a broader frequency spectrum than a continuous profile. Furthermore, validated models may serve as useful predictions for the backward whirl phenomenon and the system response. Backward whirl testing of full scale drilling tools with realistic, discontinuous borehole contact, supplemented with validated modeling, is a new approach to understand downhole dynamic events.
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机译：钻柱的钻孔接触可能导致向后旋转：一个共同的和灾难性的现象。为了增加BHA（井底组件）的可靠性，减少非生产时间（NPT），并最终提高服务的提供，一个内部向后旋转试验台被显影以调查动态负载。分析和数字模型阐明动态响应，并防止向后旋转试验结果验证。 A 6？-in。 BHA是在8.5测试。井眼使用连续和不连续的井眼轮廓。以60rpm的旋转速度，并使用连续钻孔，横向加速度振幅之间的范围内20〜30克，具有3个GRMS的RMS值。相比之下，在介于40至50g与RMS加速度振幅的不连续的曲线结果看重7个GRMS。关于不连续分布，反应谱节目频率含量高达200赫兹范围更广而不同频率峰值在光谱当使用连续的轮廓是显而易见的。结果表明，可以从具有不同的井眼轮廓摩擦引起接触发生向后旋转。此外，不连续的轮廓产率大幅度高动态负载具有比连续的轮廓更宽的频谱。此外，验证的模型可以用作反向旋转的现象，并且系统响应有用的预测。与现实的，不连续的钻孔接触的满量程钻具向后旋转测试，辅以有效的造型，是一种新的方法来了解井下动态事件。
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