Full Wave Sonic Logging (FWS)
The Full Wave Sonic (FWS) tool is a probe that measures compressional (P), Shear (S), Stoneley and Tube wave arrivals. The probe operates in a fluid filled hole and emits a high energy source generated by a ceramic piezoelectric transducer that excites the formation. A range of frequencies are developed and propagated in the surrounding rock measured by an acoustic sensor. The probe takes samples of the formation at regular (generally 10cm) intervals. Applications of the FWS include:
- Porosity Evaluation
- Lithology Identification
- Variation of rock strength
- Calculation of rock’s mechanical properties (Shear, Young and Bulk Modulus, Elastic Moduli, Poisson’s ratio, and compressibility)
- Identification and hydraulic characterisation of fractures
Vertical Seismic Profiling (VSP)
Vertical seismic profiling (VSP) is used in order to construct an accurate velocity model of the subsurface for seismic processing and determines if reflections can be followed to the surface. VSP operations use a high sensitivity, single component, omnidirectional geophone probe to record the seismic response from both vibrator and/or weight drop sources. The geophone probe is a modified Mount-Sopris unit operated with electronically driven clamping arm to ensure adequate coupling to the formation wall and maximise the quality of signal being recorded. In our case, a single geophone is lowered to the base of the hole and the seismic source energy is measured as the geophone moves up the hole at 5m intervals. This effectively provides accurate velocities of the subsurface geology in-situ to the hole.
In the figure above left, the majority of notable, strong reflections can be identified across geophone intervals ranging from the depth of the reflector through to the surface/near surface geophones. This indicates that reflection energy is not likely to be attenuated in the case of two way travel (surface seismic). In such cases, the reflection events should be retrievable in 2D/3D surface seismic operations.
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