Sata Log

A new logging technique known as the Sata log is now being routinely run which exhibits two curves of the acoustic family. One curve is the transmission amplitude of the received signal, the other curve is the attenuation of the acoustic signal as shown by the difference in amplitude between two receivers. The log has shown that gas, oil and water may be distinguished on a qualitative basis in both high-and low-porosity media. The basis principles of the two curves are discussed which covers the consideration of the coefficient of coupling of the fluid to the formation and, also, the coefficient of coupling with respect to formation to formation in a vertical sense and the relative relationship of the transmission of the acoustic signal within the formation as an independent entity bearing little influence from the mud to formation effect. Examples of logs are shown which illustrate the effects of fresh-water sands on other logs, as compared to its effect on the Sata log. Wet or dry sands are illustrated, and comparisons of gas and wet formations are illustrated. No quantitative claims for this logging technique are being made. The Sata log also has the unique ability to log in casing, showing conditions behind the casing which lead to the location of cement tops. Formations may be logged through the casing when the formations are in contact with the casing. Introduction A new type of log called the Sata log, which appears to give direct indications of water, oil and gas content of porous media in a borehole, is being made available to the oil industry. The name "Sata" comes from the identifying letters applied to the two curves represented by this logging technique. SA is the abbreviation for signal attenuation; TA is the abbreviation for transmission amplitude. These two curves are part of the family of acoustic parameters - velocity, wave length, frequency, amplitude, attenuation, acoustic impedance and others. Theory The Sata log differs from acoustic velocity logging by logging the amplitude and attenuation of the signal rather than the travel time. Signal character has been described in literature previously. Fig. 1 shows an idealized-received logging signal as seen on the monitoring scope. The horizontal sweep is in time and the vertical displacement is in amplitude. Only the first peak of the negatively going signal is measured since this cycle is probably the result of the bulk modulus wave. Isolation of the measurement of this cycle is made to prevent the questionable influence of the water, shear, tube and reflected waves which follow.