Geotape

Description

Previous downturns in the oil industry have forced oil companies to explore every cost cutting avenue available. The retrieval and reprocessing of older data using new processing techniques remains one of the most common cost-reduction methods used. This older data is recorded on such diverse media as analog tapes, 21-track (1-inch tape), 7-track and 9-track (one-half inch tapes). The first step in using the older data is recovery through copying or reformatting. It is during this stage that several tape-related problems begin to become apparent. While these data are generally stored in climate-controlled facilities, the variety of environments they have traversed, and the length of time that they have been in storage, contributes to the extent and severity of their problems. Wrap-tension on tapes stored for an extended period of time creates definite problems. Obviously, near the hub of the tape, pressure is greater than farther out on the spool. This leads to migration of the EOT marker through many layers of tape and causes some read-errors as these indentations pass across the tape head. A periodic cleaning-pass, accompanied by a lower wind tension, helps alleviate this problem. However, care must be taken when running these re-tensioned tapes on today's high-speed tape drives. Another problem uncovered is something called "stiction." This phenomenon is caused in part by extreme changes in humidity and temperature. Unfortunately, "normal operation" in our industry is conducive to exposing the tape media to these extreme changes, causing a type of hydrolysis in the tape oxide. Due to chemical changes in the binder (called "binder breakdown"), debris can be pushed down the tape during read/write operations. The debris forms miniature "speed bumps" across the tape whenever the tape's movement stops. These bumps cause two problems: First, they stick to the adjoining layer of tape. In extreme cases, the bumps spread due to wind tension. The next "read" attempt will result in an uneven unwinding of the tape, causing tape-stretch and/or oxide-separation from the base material. Second, the bumps create a separation between the tape head and the tape surface, causing data dropouts. These dropouts will vary in number based on the severity of the problem. Some dropouts are recovered with the error handling in software DEMUX packages. GeoTape, Limited began a comprehensive study of these problems several years ago. Our operations staff have kept a history of stiction-related jobs during this time. From the information gathered so far, it would appear that almost all of the seismic data acquired before the early 1980's are subject to some level of stiction. Of course, this varies from tape to tape, but is unfortunately not restricted to these early tapes alone; data recorded into the late 80's are beginning to show the tell-tale signs of "stiction." Several major oil companies have started pilot projects to estimate the number of tapes in storage affected by any, or all, of the above problems. Many companies have field data, recorded before 1988, in areas where no recording crew will ever work again. These data should definitely be transferred to new media - or risk being lost forever. Magnetic Tape Storage and Handling - Protect Your Tapes! GeoTape, Limited

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