Petrophysical Properties Derived from High Frequency Drilling Vibration for Geosteering- A Feasibility Study

Abstract

Abstract Drilling vibration is usually used for drilling operation diagnostic for evaluating downhole fatigue failures, severe wear of bottom hole assembly (BHA) and bit, and wellbore instabilities. This study highlights how formation petrophysical properties such as porosity can be estimated from certain range of high frequency triaxial vibration data, so that quality of geosteering may be enhanced in challenge conditions, such as ultraslim hole drilling where limited logging while drilling (LWD) data may be acquired. In this study we explored some data sets of triaxial accelerometer measurement module, in addition to density, neutron, resistivity, and gamma ray. Although typical accelerometer measurement is sampled every 5 seconds, we customized the accelerometer recording to capture axial, lateral and tangential vibrations at 2,500 Hz sampling rates. These high frequency vibration modes were processed in frequency domain by use of fast Fourier transform and analyzed, in terms of frequency and amplitude, against other drilling parameters such as weight and torque on bit. Data regression and correlation were investigated against formation properties derived on the same drilled section of LWD logs. Example results for a tight carbonate formation showed qualitative correlation between axial vibration average amplitude values and LWD neutron porosity. In addition, when we analyzed the high frequency vibration data and decomposed it to different frequencies, we observed higher frequency vibration peaks, 500Hz and higher, are highly correlated to LWD formation neutron porosity and bulk density. Axial and tangential vibration modes showed better correlation with formation properties than lateral mode. Taking weight-on-bit, bit size, drilling torque and rotation speed into consideration, one can use inverse correlation regression to obtain reasonable porosity values from high frequency axial vibration peak values. These findings open the path for geosteering, and maybe even for formation evaluation, capabilities in complex drilling conditions where BHA is restricted such as in ultraslim hole under balanced coil tubing drilling.