Multi-Frequency Laboratory Measurements
Multi-Frequency Laboratory Measurements on Rock Cores
Core Lab operates a full-service geomechanics laboratory that provides customers with multi-frequency acoustic velocities, elastic properties and engineering analyses that revolutionize log calibration.
Applications of Multi-Frequency Sonic Velocities
- Calibrate log to low-frequency seismic waves (20 Hz to 1000 Hz)
- Differentiate fizz gas from dry gas
- Determine gas/oil/water influences
- Vp/Vs ratio determination vs. frequency
- Determine elastic parameters vs. frequency
Rock strength is typically 20-60% of that predicted by high frequency measurements. These high frequency measurements give information about elastic properties, but cannot foretell plastic deformability or brittle behavior. In order to accurately reflect rock mechanical properties, logs must be calibrated with low and ultra-low (static) frequency data that can only be obtained in the laboratory.
Conventional dipole sonic logs are combined with lab measurements and transformed into powerful multi-frequency composite curves.
Both P-wave (compressional) and S-wave (shear) velocities increase as frequency increases from low frequency to seismic to logging and ultrasonic frequencies. Calibration with only ultrasonic data causes overestimation of velocities at lower frequencies. Elastic moduli change dramatically with frequency, whereas Poisson’s ratio varies less.
Knowledge of acoustic velocities in reservoir rocks under changing pore pressures and fluid states secures important data for drilling, completion, and geophysical applications in difficult geologies.