Automatic Computation of Dipmeter Logs Digitally Recorded on Magnetic Tapes

Abstract

A prototype equipment has been designed and built for the digital recording of well logs on magnetic tape at the same time that the regular film recording is made. The format of the digital tape produced is such that it can be used directly at the input of the IBM 704, 7090 or other models of IBM computers which accept digital magnetic tape. This apparatus has been used for the experimental field recording of dipmeter tape logs which were subsequently computed by means of an IBM 704 or 7090.In this paper the equipment and the digital tape are described briefly, and their application to the computer interpretation of dipmeter data is discussed. A principal element in the interpretation of the dipmeter log is the correlation of the three microresistivity dipmeter curves to determine the depth displacements between them. Several correlation methods for computer use are considered, with particular attention to their sensitivity to error and their consumption of computer time. The tape data were used to compute information content of the dipmeter microresistivity curves in terms of their frequency spectra. The results show that the sampling rate used in recording the digital information is quite adequate and illustrate a use of the digital tape in evaluating the characteristics of new tools. Some examples of field results are shown. It can be foreseen that, when digital tape recording becomes available for general field use, a whole new realm of possibilities will be opened up for the processing of other well logs through computations, which hitherto were not feasible because they were too laborious and time-consuming. Introduction The last few years have seen a revolution in the design and production of data-processing equipment. Stored-program digital computers have progressed from a research curiosity to the basis of a major industry. There are now hundreds of such machines in daily use in the United States. With the acceptance of a technique that was, in fact, already clearly described by John von Neumann in 1945, the last decade has seen great strides in the development of components, reliability, programming systems and, most spectacularly, in the sheer number of machines built and in use. In 1957 there were enough digital computers available to the oil industry to justify the suggestion that it would be worthwhile to investigate the possibility of using these machines in processing well log data. The first result of this investigation was the appearance of what may be referred to as the input-output bottleneck. Well logs are customarily recorded on film. To get these data into a machine required then (and still does): a time-consuming semi-automatic reading of the film; conversion of the log data to digital form; and recording these digital data in some medium acceptable for computer input, such as cards, magnetic tape, or punched paper tape. However, the recording, reading, and re-recording could only result in deterioration of the data. Therefore, it was concluded that the first step should be the development of a new, more direct recording technique supplemental to the film recording, which would provide easy access to the digital computer. There are many solutions to the problem of recording log data in an easily recoverable form. After careful consideration it was decided to adopt the boldest solution which, it was felt, was also the most elegant. It was decided to record well logs directly, in the field, on magnetic tape in such a way that this tape could be used without further modification as an input to the IBM 704 or 7090 computer. To realize practical field recording of magnetic tape logs, it became necessary to develop in a rather small package, an analog-to-digital converter, a tape recorder, and the necessary multiplexing and control circuits to allow the simultaneous recording of a multiplicity of logging signals. The magnetic tape recording was to be made simultaneously with the conventional logging operation in such a way as not to interfere with it. Along with the development of hardware, it was necessary to begin development of interpretation techniques and machine programs that would exploit the power of the digital computer. Here, again, there is a long list of possible applications. After much consideration it was decided to concentrate on the interpretation of the dipmeter log as a first application. It is the object of this paper to describe in some detail the developments sketched in the last three paragraphs. JPT P. 771^

Computer Techniques for the Zoning and Correlation of Well‐logs*

“…Examples of the fixed interval method, discussed earlier as cross correlation in the space and frequency domains, include early papers by Moran, Coufleau, Miller and Timmons (1962), who were among the first to describe the use of a digital computer in the analysis of digitally recorded well-log data, and more recently Schoonover and Holt (1973) and Schoonover (1974). Kemp (1980Kemp ( , 1982 used the idea of planarity to constrain the identified correlations.…”

An Approach to Detailed Dip Determination Using Correlation by Pattern Recognition

“…Large and small geological features have been recognized; general rules of interpretation, followed by local adaptation to specific problems, have assisted a sedimentological approach to the study of reservoirs. 1 Another objective is to overcome the rigidity of the fixed-correlation-interval procedure and to provide more information closer to the geologic image. In difficult cases, the Mark IV results sometimes exhibited excessive scatter that was not of geological origin.…”

“…1 The information provided is useful, but it is deficient in three ways: (1) the correlation interval is preset and is not adapted continuously to the geological context; (2) the basic cause of the correlation (the bedding) is not described; and (3) only similar features of practically identical thickness 'Now retired. 1 The information provided is useful, but it is deficient in three ways: (1) the correlation interval is preset and is not adapted continuously to the geological context; (2) the basic cause of the correlation (the bedding) is not described; and (3) only similar features of practically identical thickness 'Now retired.…”

COMLOG - A Comprehensive Computer System for Log Interpretation

“…Conclusions COMLOG, a comprehensive computer system for interpreting commercial well logs, has been described. This system greatly increases the effectiveness of quantitative log interpretation by: (1) automatically selecting and using the correct interpretation technique for a set of logs run under a particular combination of drilling and lithologic conditions; (2) interpreting a greater number of logs per unit time than is possible with the conventional "hand" calculation methods; (3) Assu med to be very shallow Computed as 13 in.…”