Low-Frequency Laboratory Measurements on Rock Samples
Core Lab operates a full service geomechanics laboratory that provides customers with multi-frequency acoustic velocities and elastic properties for revolutionary seismic and log calibration.
- Most rock elastic properties are frequency dependent
- Seismic attributes such as formation reflectivity vary with frequency
- Low frequency data provide a baseline of known rock properties that tie seismic and sonic measurements to ground truth
- Calibrating logs with low-frequency lab data elucidates dispersive and viscoelastic effects
Solutions provided by core testing
- Differentiate dry gas from fizz water gas
- Determine gas/oil/water influences
- Vp/Vs ratio determination for seismic analysis
- Vp and Vs versus frequency and saturation
- Acoustic velocities in crude oils and brines
- Cross-well seismic calibration
- Fracture mapping using microseismic calibration
Low-frequency determination of the behavior of reservoir rocks under changing fluid states and reservoir pressures establishes correlations between static and dynamic data.
Frequency effects: 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 results in overestimation of velocities at lower frequencies. Elastic moduli change dramatically with frequency whereas Poisson’s ratio varies less.
Correlations between static and dynamic elastic constants are difficult to establish because they depend on many reservoir-specific variables. Without core data acquired at low frequencies in the lab, reservoir models are highly variable and subjective.