Extracting Petrophysical Properties from High Frequency Drilling Vibration for Geosteering in Challenging Environments

Abstract

Drilling vibration data is traditionally used for optimizing drilling operations. Recently, we showed that high frequency drilling vibration data has the potential in identifying lithology and changes in formation properties for qualitative geo-steering. In this paper, we will present in detailed investigations extending previous findings to various drilling conditions and environments. We have explored drilling vibration datasets obtained from triaxial accelerometer measurement module from different drilling environments, with different drilling parameters, borehole sizes, and placement of accelerometer module from the bit. Beside the typical accelerometer measurement sampled every 5 seconds, we configured the accelerometer recording to capture axial, lateral and tangential vibrations at 2,500 Hz sampling rate to record up to 1,250 Hz accelerometer vibration. These high frequency vibration modes were processed in frequency domain by use of Fast Fourier Transform (FFT) and analyzed, in terms of frequency and amplitude, against other drilling parameters such as weight and torque on bit. Insight from the analytical model correlated against formation properties derived from LWD logs. Frequency spectrum showed qualitative correlation between axial vibration amplitudes and formation properties using real-time averaged data. Different correlation trends may exist, but generally axial vibration amplitude is inversely proportional to neutron porosity and directly proportional to bulk density. Significant correlations have been found between vibration peaks at frequencies higher than 500 Hz and formation neutron porosity and bulk density. The characteristics vibration frequency peaks may vary depending on drilling parameters used, borehole conditions and accelerometer offset from drill-bit. The findings of this study further confirm our previous work and open a path for advanced geosteering in complex drilling conditions where bottom hole assembly is restricted such as in slim hole under balanced coil tubing drilling, or when LWD sensors are not available.