Full Wave Form Sonic Tool

Parameters Logged:

Full Wave Time per Receiver

Transmitter, ceramic piezoelectric with 20 KHz (50mm) resonant frequency

Shear (S) Velocity

Time of First Arrival (ΔT)

Amplitude of First Arrival

Formation Velocity

Primarily used for geotechnical investigations to determine elastic properties such as compaction and porosity of rock formations.

The tool emits a series of high frequency sonic impulses. Following their passage through the borehole fluid and formations, these impulses are detected by receivers at various distances from the transmitter. At each receiver the arriving waveform is digitally sampled according to a set of predefined tool configuration parameters (sample rate, sampling period, and gain). The digitised waveforms are subsequently transmitted to the surface acquisition and recording system.

Applications:

Sonic logs are widely used (in combination with certain other logs) to provide formation porosity and mechanical properties data. Under suitable acquisition conditions shear wave and slower (e.g. Stonely) arrivals can be detected. The tool will only function in fluid-filled holes and is normally run centralised.

The most common applications are:

• Location of poor or missing cement behind casing (Cement Bond Log).
• Lithology identification.
• Fracture and permeability indication in hard rock.
• Porosity.
• Rock strength and elasticity (Poisson’s ratio).
• Determination of fracture aperture and permeability index.

Example Log Image: