Atlas - An Interpretive Programming System For Log Analysis
Authors: Schoonover Larry 
Published: December 2007

This paper was prepared for the 48th Annual Fall Meeting of the Society of Petroleum Engineers of AIME, to be held in Las Vegas, Nevada, September 30 - October 3, 1973. Permission to copy is restricted to an abstract of not more than 300 words. Illustrations may not be copied. The abstract should contain conspicuous acknowledgment of where and by whom the paper is printed. Publication elsewhere after publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF publication in the JOURNAL OF PETROLEUM TECHNOLOGY or the SOCIETY OF PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor PETROLEUM ENGINEERS JOURNAL is usually granted upon request to the Editor of the appropriate journal provided agreement to give proper credit is made.
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Abstract
The program described in this paper presents a new approach to the utilization of the interactive capabilities of time-sharing. The system consists of a compiler-loader and an execution sub-system allowing the log analyst to execute catalogued procedures or sub-procedures or to enter new equations and commands to solve analysis problems. The operation of the system and its use for solving log analysis problems is demonstrated in several examples. problems is demonstrated in several examples

Introduction
Time-sharing has proven to be an extremely useful tool to the professional log analyst. It not only provides remote access to large scale computers, but allows intervention and modification of the executing program. This interactive capability greatly reduces the time required to process difficult log data.
With the realization of the widespread use of time-sharing, many interactive log analysis systems have evolved. Worth mentioning is LOGAN, developed by Imperial Oil Company of Canada, which is characterized by several innovative analysis techniques and case of operation. All of the systems with which the author is familiar are collections of standardized procedures which may be executed after another. We have chosen to take a somewhat different approach to the problem. While we retain the procedural approach as a subset of our system, we have allowed the analyst also to execute portions of procedures and in fact to mix portions of several procedures portions of procedures and in fact to mix portions of several procedures for a single analysis. Thus, we feel that our present system offers the log analyst greater flexibility, but not at the expense of ease of operation. To implement this approach, we have chosen to write an interpretive compiler which is described in more detail in the sections that follow.

AN OVERVIEW OF THE SYSTEM
ATLAS (A Time-shared Log Analysis System) consists of three major blocks which may be selected alternately. The first of these is the cross-plot routine. The most common types of cross-plots have been included as options, namely M vs. N, MN vs. Den, log (RT) vs. phi, phiden vs phi neu. Another option allows any data column in the phi, phiden vs phi neu. Another option allows any data column in the in-put file to be cross-plotted against any other. Used in conjunction with the other segments of the program, most types of 2-dimensional cross-plots can be generated. Examination of the cross-plots give good indications of the lithology, the type of analysis best suited for the data, and estimation of the parameters needed.
The second main segment is the compiler-interpreter. Its purpose is to interpret the operator's requests for analyzing the purpose is to interpret the operator's requests for analyzing the data and then to execute those requests. There are three basic levels of requests within this segment. Certain control commands comprise the first level. Many procedures and standard equations have been saved in the program directory, and at the second level, the analyst has access to them by entering the procedure name. More than one procedure may be combined by entering each of the procedure names if it is desired. At the third level of usage, the analyst may type in an equation that he would like used. The compiler compiles, links and loads the equations for use in the analysis. Procedures and equations may be used in combination in any way the analyst wishes subject only to limitations of space within the computer.
The procedures currently saved in the program directory include complete analyses for sand and carbonate lithologies: SANDI, SANDH, CARBI, and CARBII.