The Auslog Sonic Tool is of the full wave type. A Delta-T log can be produced by post processing the full wave sonic file.
The Delta-T log is a measure of the vertical transit time, which is the reciprocal of the vertical velocity of the strata adjacent to the borehole. Effectively the sonic log measures the velocity of the strata immediately adjacent to the drillhole wall. This velocity measured in situ will provide data on the particular lithology. This value is also influenced by formation fluids and their saturation, structural features, weathering and shale content. Porosity is obviously a strong influence. The Delta-T is usually measured in micro-seconds/ft (µs/ft).
Apart from indications of rock strength, the main role of the sonic log is to provide a measure of porosity through such relations as the Wylie Time Average Formula.
The accurate detection of the Shear waves (S) and Compressional waves (P) have interesting geotechnical application through relationships between the S and the P waves from which Poisson's Ratio can be calculated. Other engineering properties such as Shear Modulus, Bulk Modulus and Young's Modulus can also be calculated.
Coal seams are very obvious on sonic logs due to their anomalously low velocity.The information in the full wave form can be used to generate a sonic attenuation log or what is commonly know as the Cement Bond Log. Abnormalities will cause attenuation of the acoustic signal and will appear on the log as variations from the normal level.
Fractured zones are indicated when the S-wave arrivals are severely attenuated with or without a corresponding change in the P-wave signal.
Specifications
Detector 3 Piezoelectric transducers Range Full wave form for each receiver recorded Calibration Electronic timing Units of Measure microseconds (Delta T in microsecs/fd) Communication Duplex Digital RS 485 Nominal Current (mA) 150 Power (VDC) at Sonde 50 Diameter (mm) 60 Length (mm) 2750 Weight (Kg/lb) 12/26.4 Pressure Rating (KPg/PSI) 21 000 / 3000 Temperature Rating (C/F) 60°/ 140°