Application and Analysis of Simultaneous Near Bit and Surface Dynamics Measurements

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Abstract
Summary: Axial, torsional, and bending vibrations are all present in a bottomhole assembly (BHA) while drilling. The dynamic response of the BHA depends on many variables, such as drilling parameters, BHA design, hole condition and inclination, and formation properties. Events, such as bit bounce, forward and backward whirl of the BHA and the bit, and drillstring resonance can occur during drilling. Some of these events are very detrimental and can cause drillstring component failures, twist-offs, etc. This paper deals with the analysis of measured drilling vibration data from a field test that used both downhole- and surfacevibration measurement devices. Surface sensors included dynamic axial and torsional strain gauges and accelerometers and a singleaxis magnetometer, all mounted in the drillstring above the rotary table. Downhole sensors included an axial accelerometer, two orthogonal bending-moment strain gauges, dynamic weight-on-bit (WOB) and torque strain gauges, and two orthogonal magnetometers, mounted in a measurement while drilling (MWD) sub. The field test involved several drilling runs that included drilling and reaming with polycrystalline diamond compact (PDC) and tricone bits in rotary and motor assemblies. The analysis described in this paper involves the determination of axial and torsional wave velocities in the drillstring; their use in predicting resonant frequencies; a comparison of predicted and measured resonant frequencies; inference of downhole dynamics with surface measurements (surface noise cancellation), including a comparison of results with measured downhole data; an example of the detection of BHA whirl with downhole data; an example of the detection of bit bounce with downhole axial data; and an examination of precession of the trilobed bottomhole pattern generated by a tricone bit. The advantages of using either surface or downhole dynamic measurements in identifying different drilling problems are demonstrated as well as the inference of downhole dynamics with surface measurements. Once drilling dynamics problems are identified, remedial action can be taken to reduce tool and bit failures while drilling, thus optimizing the drilling process.

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