Font Size:
ANALYSIS OF DRILLSTRING VIBRATION BASED ON SIGNAL PROCESSING
Last modified: 2017-05-29
Abstract
Downhole tools failures and drilling inefficiency are often attributed to drillstring vibrations during the drilling process, which can be categorized as axial, torsional and lateral vibrations. These become more pronounced in the context of deep and hard rock drilling. The stick-slip of a drill bit, as dominating source of drill string vibrations, has been extensively studied by coupled axial-torsional with the state-dependent model of the dynamic system. Although drilling processes have been investigated through controlled laboratory testing, a need for reliable data provided by controlled drilling field tests remains.
In this work, dynamic system modeling is used to support the design of controlled and instrumented full-scale drilling tests to be carried out in geothermal field. These field data will contribute to assess the predictive capability of state-of-art models, as well as guide their development. The study will include the following steps:
1) Drilling tests with PDC drill bit are planned between 1000m and 2000m depth, at various revolution per minute (RPM) and weight on bit (WOB) values that will be chosen according to the ranges of interest predicted by existing models. Down-the-hole sensors located at the bit and the BHA will be used to record the 3-axis accelerations, forces, and rpm (by gyro sensor) with a sampling rate up to 800Hz.
2) The axial displacement of the bit is calculated by the double integral of the acceleration signal in time domain after applying a Butterworth low pass filter to remove high-frequency noise in the raw data. A 3D-spectrogram of the torsional vibration signal is constructed to observe the growth rate variation of the amplitude RPM (peak to peak) with respect to the rotary speed of the top drive or the drilling depth.
3) The time histories of axial and torsional vibrations, numerically analyzed by Richard, T. [1], indicate that the large axial stiffness leads to higher frequency axial vibrations compared to torsional vibrations. Moreover, the frequency of the axial vibrations has a tendency to decrease in the slow regimes. The corresponding predictions have been qualitatively discussed by instability analysis in the fast and slow regimes in [2]. These statements will be qualitatively assessed by using the data provided by 2)
4) The signal of the torque on bit in different rotary speeds is tracked to validate the velocity-weakening effect, which has been proposed as a possible cause of torsional vibrations at high RPM in [3]. Besides, the evolution of the vibrations at low WOB and high RPM will be investigated and compared with the stability regimes identified by modeling of the dynamic system in [4]. The output of this work will support the development of further theoretical studies on the stick-slip vibrations.
In this work, dynamic system modeling is used to support the design of controlled and instrumented full-scale drilling tests to be carried out in geothermal field. These field data will contribute to assess the predictive capability of state-of-art models, as well as guide their development. The study will include the following steps:
1) Drilling tests with PDC drill bit are planned between 1000m and 2000m depth, at various revolution per minute (RPM) and weight on bit (WOB) values that will be chosen according to the ranges of interest predicted by existing models. Down-the-hole sensors located at the bit and the BHA will be used to record the 3-axis accelerations, forces, and rpm (by gyro sensor) with a sampling rate up to 800Hz.
2) The axial displacement of the bit is calculated by the double integral of the acceleration signal in time domain after applying a Butterworth low pass filter to remove high-frequency noise in the raw data. A 3D-spectrogram of the torsional vibration signal is constructed to observe the growth rate variation of the amplitude RPM (peak to peak) with respect to the rotary speed of the top drive or the drilling depth.
3) The time histories of axial and torsional vibrations, numerically analyzed by Richard, T. [1], indicate that the large axial stiffness leads to higher frequency axial vibrations compared to torsional vibrations. Moreover, the frequency of the axial vibrations has a tendency to decrease in the slow regimes. The corresponding predictions have been qualitatively discussed by instability analysis in the fast and slow regimes in [2]. These statements will be qualitatively assessed by using the data provided by 2)
4) The signal of the torque on bit in different rotary speeds is tracked to validate the velocity-weakening effect, which has been proposed as a possible cause of torsional vibrations at high RPM in [3]. Besides, the evolution of the vibrations at low WOB and high RPM will be investigated and compared with the stability regimes identified by modeling of the dynamic system in [4]. The output of this work will support the development of further theoretical studies on the stick-slip vibrations.