The Utilization of COMLOG in the Permian Basin

Abstract

Introduction COMLOG is The Pure Oil Co. "Comprehensive Computer System for Log Interpretation". The input is any logged parameter such as resistivity, radioactivity, or acoustic velocity; the output includes such reservoir properties as porosity and water saturation. The system consists of a main routine and 18 subroutines. Each subroutine performs a particular segment of the interpretation such as choosing a zone porosity if more than one porosity log is run, or computing a diameter of invasion. Since the inception of COMLOG, subroutines have been added, deleted and augmented in order to keep abreast of new logging tools and techniques. COMLOG is designed to be comprehensive in two planes of reference -logging and geography. The objective of the COMLOG system is to interpret correctly any combination of logs in any geographic region. In this paper, the latter is stressed: How is COMLOG utilized in a specific region, for example, the Permian Basin of West Texas and Eastern New Mexico?The study can be divided into three segments: communication, interpretation and evaluation. Each of these three subjects will be discussed. Communications COMLOG interpretations are carried out on a company-owned IBM 704 computer located at The Pure Oil Computer Center, Palatine, Ill. In order to present the mechanics of communicating log data from a regional or district office to the Computer Center, an example problem is introduced.The logs to be interpreted are taken from a well in the Permian Basin, and consist of the Deep- and Medium- Investigating Induction log, Laterolog 8. Proximity log and Sonic log (Fig. 1). For the purpose of this example, only a small portion of the entire logged interval is used. (The actual interpretation of this well consisted of over 200 zones.) At the wellsite, or in the district office at Midland, Tex., the logs are subdivided into zones. Those portions of the interval indicated to be shale streaks (no positive separation on the Microlog, gamma activity in excess of 40 API Units) are excluded. Also, the zones in which the Proximity log goes off-scale (>1,000 ohm-m) are not used. Data Sheet I (Fig. 2) is then completed. As outlined on page I II 0 of Ref. 1, this data sheet is used to post log heading and other pertinent information used in the entire interpretation. The interpreter in the Midland office now has an option: he can either post the data for each zone on a data sheet designed for teletype communication, or he can air-mail the logs (and Data Sheet 1) to the Computer Center where a mechanical digitization will rapidly prepare the logs for interpretation. Each of these two options will now be discussed. Teleptyping the Data to the Computer Center Fig. 3 illustrates COMLOG Data Sheet 2. This sheet has been so designed that the data are packed, thereby increasing teletype efficiency. Each horizontal row represents one depth interval or zone. The various columns are identified by a header line with code numbers assigned to each logging curve (such as Sonic) or parameter (such as R,). For example, Col. A is assigned to the Proximity log, code number 10. Various code numbers are shown in Fig. 4, a table that is printed on the back of each Data Sheet 2. If more than 20 zones are to be interpreted, consecutive data sheets are posted. When the data sheets are completed, Data Sheet 1 and Data Sheet(s) 2 are given to the Pure Oil teletype operator in Midland, who creates a paper punch tape. JPT P. 703^