THE LONG INTERVAL METHOD OF MEASURING SEISMIC VELOCITY

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Abstract
The reverse method of seismic velocity determination, wherein the shot is detonated in the bore hole, has been extended to operate in deep wells. This has been accomplished by the use of a long interval arrangement of a multi‐shot selective firing sound source gun and one or more geophones separated vertically by a cable several hundred feet long. A series of a relatively few such intervals can “strap” a bore hole travel‐time‐wise with good accuracy. Travel time measurements over the cased portion of the hole can generally be accomplished by means of geophones placed at or near the surface. Velocity surveys conducted in this manner become a routine well logging service, in conjunction with other services such as electrical logs. The paper describes in a general way the necessary field equipment, and field examples of surveys are presented.

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