Joint Meeting of the Rocky Mountain Petroleum Sections of AIME, 3–4 March, Denver
It has been recognized for many years that velocity measurements in the various formations provide useful information for both geologists and geophysicists. As early as 1934, patent applications were made for a two-receiver sonic logging device. However, in the past, the predominant application of velocity measurements has been in the field of geophysical problems -not in formation logging. The interpretation of seismic records is enhanced by accurate velocity data. Now, recent improvements in instrumentation have developed velocity measurements into an engineering tool which is helpful to both geologist and engineer in oil-well completion. The modern velocity, or sonic, logging tool will still provide the geophysicist with valuable velocity data, but its more important application will be in geological studies and reservoir evaluation.
Correlation problems, sometimes difficult with conventional electrical and radioactive logs, may be improved with sonic logs, however, the main advantage of sonic logs over, other logging devices appears to be the accurate detection and measurement of porosity.
The sonic logging device described in this paper is based on a development by the Humble Oil and Refining Co. It features a two-receiver system and a short spacing (Fig. 1). The spacing used is generally 1 ft. A third receiver at an interval of 3 ft provides an alternate spacing, which can be utilized where more suitable to local geological conditions. Sound pulses are emitted by the transmitter at the rate of 10 or more per second, and the first arrival of energy at each receiver triggers the response system.
The two-receiver system eliminates some deficiencies of the single receiver used on several experimental and commercial tools. In the two-receiver system, the time consumed in the passage of the sound pulse from transmitter to wall of hole, and from wall of hole to receiver, is not added in the recording to the formation transit time. This hole effect is simply eliminated by recording the difference in arrival times at the two receivers. The influence of the mud character and hole size is, therefore, negligible in this system as long as the tool is held parallel to the wall of the hole. Centralizers are provided for this purpose.