Application and Analysis of Simultaneous Near Bit and Surface Dynamics Measurements

Abstract

Abstract Axial, torsional and bending vibrations are all present in a 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 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 down-bole and surface vibration measurement devices. Surface sensors included dynamic axial and torsional strain gages and accelerometers, and a single axis magnetometer, all mounted in the drillstring above the rotary table. Down-hole sensors included an axial accelerometer, two orthogonal bending strain gages, dynamic weight on bit and torque strain gages and two orthogonal magnetometers, mounted in an MwD sub. The analysis described in this paper involves (1) the determination of axial & torsional wave velocities in the drillstring, (2) their use in predicting resonant frequencies, (3) a comparison of predicted and measured resonant frequencies, (4) inference of down-hole dynamics using surface measurements (surface noise cancellation) including a comparison of results with measured down-hole data, (5) an example of the detection of BHA whirl using down-hole data, (6) an example of the detection of bit bounce using down-hole axial data, and (7) an examination of precession of the trilobed bottomhole pattern generated by a tricone bit. The advantages of using either surface or down-hole dynamic measurements in identifying different drilling problems is demonstrated, as well as the inference of down- hole dynamics using surface measurements. Once drilling dynamics problems are identified, remedial action can be taken to reduce tool and bit failures while drilling, and to optimize the drilling process. P. 857