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NSA APPENDIX E <br />Outline for Recommended Full-Scale Monitoring System <br />Access and Settings of TRT Monitoring System <br />Technically, the only access for a seismic monitoring system is through the two steel <br />pipes in a single well, as for the surveyed We1128-21. <br />For a mine zone 400 to 600 feet thick, three combinations of source and receiver sets aze <br />recommended: <br />1. In the first set (figure A3), the string of 10 hydrophones should be <br />installed at the bottom of the production pipe'. The sources should <br />be fired in 10 locations at 20-ff intervals starting from the bottom of <br />the injection pipe. This configuration should target mainly the inner <br />boundaries of the extraction zone with emphasis on the horizontal <br />extent of structural changes. <br />2. In the second set (figure A4), the location of hydrophones should <br />remain unchanged and 10 sources should be fired in 20-ff intervals <br />over a depth range of 180 to 200 feet below the Gas Cap. The <br />depths of the shots should be set so the shots overlapping the <br />hydrophone array be fired half way between the hydrophones. This <br />configuration of sources and receivers should target the upper part <br />of the extraction zone and the vertical features below the line of <br />sources. <br />3. In the third set (figure A5), 10 shots should be fired in 20-ff intervals <br />over a range of 180 feet up starting from 20 ff above the Gas Cap. <br />The hydrophones should be located above the line of shots, with <br />the bottom phone 220 feet above the Gas Cap. This configuration <br />of sources and receivers is intended mainly to target the Gas Cap <br />and the top of the extraction zone. <br />* It maybe beneficial to modify the hydrophone cable so the first five bottom phones aze <br />spaced 10 feet apart, with the remaining phones spaced 20 feet apart. This arrangement <br />should increase the number of phones below the Gas Cap and would be useful for <br />reflections inside the system of caverns within the solution mining zone. <br />The presented sequence appears to offer an optimal approach for sufficient <br />characterization of the solution caverns developing around a single well. <br />Construction and Handling of the Hydrophone Cable <br />The internal structure and hook-up of individual hydrophones needs to be improved to <br />reduce the possibility of mechanical damage to the seal of the phone installation and <br />subsequent malfunction of the hydrophones. This particularly applies to the parts marked <br />as 13 and 29 in the section view of a hydrophone shown in Appendix B. <br />