. Early geophysical papers of the Society of Exploration Geophysicists . Fig. i.—Diagram illustrating use of well for exploring surrounding region for deep domes. Patent applied for. of a wildcat well which may have missed the dome. With the detector in this position, a series of shots is fired on the surface, on a circle having the center approximately at the well and the circumference at a distance ranging from 5 to 7 miles from the well. It is obvious that if a dome exists anywhere within a radius of several miles of the well, as shown in Figure 1, the shots from one direction, as Sx, will
. Early geophysical papers of the Society of Exploration Geophysicists . Fig. i.—Diagram illustrating use of well for exploring surrounding region for deep domes. Patent applied for. of a wildcat well which may have missed the dome. With the detector in this position, a series of shots is fired on the surface, on a circle having the center approximately at the well and the circumference at a distance ranging from 5 to 7 miles from the well. It is obvious that if a dome exists anywhere within a radius of several miles of the well, as shown in Figure 1, the shots from one direction, as Sx, will show greater velocity than from S3 and other directions, thereby indicating the presence and position of the dome. If the top of the dome is no more than 2,000 feet below the bottom of the well, actual salt occurrences will be recorded on the de- tector, thereby giving a very definite lead in the direction of the dome. If the dome is much deeper, however, it can be detected because of the increased velocity in the shale overlying the dome, as this shale is more consolidated and is under abnormally great pressure. In the latter con- dition, the increase in velocity, especially if the dome is extremely deep, may be small enough so that, in order to make certain of exact shooting distances, it may be necessary to determine whether the bottom of the hole is directly under its surface location. This can be accomplished by the seismograph by shooting four additional shots in four different direc- tions approximately a mile from the well, as indicated by S3 and S4 in the section shown in Figure 1. If the bottom of the hole deviates in any direction from vertical, this is revealed by the difference in time of arrival of the sound wave from the four different directions. By this method the direction and amount of drift of the hole can be determined. It is obvious that by this method the intervening region between the well and the distant shots, particularly that part within 2 or 3 mil
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