Application of Magnetic Tapes to Well Logging

Abstract

Abstract This paper presents applications for well logs recorded on magnetic tape. When using high-speed, general- purpose computers, a rapid input saves time and money. The computer-compatible magnetic tape produced by this system makes this possible. Digital tape format and the merging of data on the tape from multiple logging runs are discussed. Examples are given for a specific interpretation program to illustrate that the computer can systematically select data from, and perform many complex interpretations with, magnetic tape. Some programs are also available for continuous (i.e., foot-by-foot) computation of tape logs. Example of computed logs include those derived from a special lithology and gas-saturation program which uses density and neutron logs. Introduction Recording well logs on magnetic tape enables new and more complete uses of log data. For years, well logs have offered considerably more information than could practicably be used by analysts. Now, with digital recording of the data on magnetic tape, automatic computers rapidly perform computations required for thorough studies. Relieved of tedious routine, the log analyst can concentrate his attention on interpretation. Processing log data with high-speed electronic computers is not new. Many papers have detailed specific applications. The labor-saving capabilities, speed and operational accuracy of computers are well recognized. However, computer applications have been limited by the lack of compatible input data because conversion of data from optical film records to a form suitable for machine input is time-consuming. Thus, processing by computers has been restricted for the most part to selected log intervals in a limited number of wells. The vast capabilities of automatic computers have not yet been exploited. During recent years there has been considerable speculation on what might be done if well logs were recorded on computer-compatible magnetic tape. Of the various computer input media, magnetic tape is the fastest and most efficient. Digital magnetic tape recording of dipmeter data has been offered commercially since 1961. Now, magnetic tapes of other logs can be recorded. A truck-mounted, recorder-computer system produces magnetic tapes in computer-compatible format at the same time the customary optical records are run. The tapes thus obtained appreciably extend well log applications through the use of office-base computers. In addition to producing magnetic tapes, this versatile system incorporates facilities for wellsite merging and computation of data from separately recorded surveys. The system thus enables immediate recording of a variety of quick look logs that provide a more thorough and more accurate reconnaissance of the penetrated formations than is feasible with only the basic logs. The system offers flexibility both in the type of computations that can be performed and in the presentation of results. Major benefits obtained through use of computers are the saving of time and the ability to use the logging information more comprehensively than by manual method. Decisions can thus be reached in less time, and with more confidence because they are based on more data. This paper presents various applications of the digital magnetic tapes in high-speed electronic computers and reviews briefly the characteristics of the system for recording the tapes. Recorder-Computer System A recorder-computer system is now being used to record well logs in digital form on magnetic tape at the same time the regular film log is run. The format used for recording on tape is such that the tape is usable directly at the input of most digital computers. (How this is accomplished is described in the section, Log Data Processing Center.)Data are grouped into contiguous frames, each of which normally represents 6 in. of formation and contain 12 words. Thus, successive words represent 1/2-in. of cable movement. The first word of each frame is reserved for depth, which is recorded every 10 ft. The remaining 11 words are available for recording 11 different logging signals. JPT P. 687ˆ