A VHF radar has been used in a salt mine in the Cote Blanche Salt Dome to probe horizontally for the dome Rank and vertically for the top of the salt. Discontinuities in the salt' s complex electric permittivity caused by anhydrite stringers, shale, sandstone, water, or fractures will cause radar reflections. A narrow beam, f 9 degrees in salt, helps to determine the dire&on to the discontinuity. The time of the radar reflection determines the range to the discontinuity. The maximum one-way penetration was 2040 ft. The radar speed in Cote Blanche salt was measured by timing radar reflections through known distances of salt. The measured radar speed was 188 ft/usec, slightly less than the radar speed in pure salt (203 ft/wsec). A shear zone in the salt was found to have many discontinuities or radar targets. A discontinuity was detected in a pillar which contained an oil well casing, and a discontinuity about 400 ft above the mine level, but still inside the salt, was also found. The top of the salt dome was detected from several locations in the mine.
Encouraging results of laboratory and field tests of radio‐frequency transmission in piercement‐dome salt led to the construction of a 230 Mhz pulse‐radar well‐logging system. Reflection data gathered during tests of the system in a well drilled into the Pine Prairie salt dome in Evangeline Parish, Louisiana, were reduced using techniques developed to pick out the best reflections from those recorded. An interpretive cross‐section and a contour map of the near flank of the dome were constructed from the reduced data. The upper flank position of the dome was confirmed by surface‐gravity data; the lower flank position was confirmed by slant drilling which intercepted the salt‐sediment interface at 8112 ft.
Four radar systems at three different frequencies are described which are useful in probing into salt for finding information of interest to miners. Ranges in salt to (a) the edge of a salt dome, (b) the top of the salt dome, (c) boreholes in salt, or (d) faults or hazards ahead of mining can be determined using one or more of these radar systems. Radar wave velocities in salt are determined by radar probing through pillars of known length, and then used to determine ranges in salt to timed radar reflections. Radar probing results are shown obtained in different salt mines probing upwards and downwards. Enclosed areas in the mine are the best radar station locations to probe into salt as air reverberation of radar energy is shortened.
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