COMLOG is an automatic comprehensive computer system for interpreting all commercial well logs. The input is any logged parameter such as resistivity, radioactivity or acoustic velocity; the output includes such reservoir quantities as porosity and water saturation. In addition to speeding up the process and assuring extreme accuracy of all computations, COMLOG further increases the effectiveness of log interpretation by automatically selecting the best available technique for any given set of logs run or any given borehole condition. The data used for posting log data are described in detail. A more general description of the various subroutines and programs which constitute the system follows. Finally, actual interpretations by COMLOG are given and compared with published results.
The use of computers as an aid in the interpretation of well logs has increased in impetus during the past few years. The published information that has appeared on the data processing of logs during the period has been mostly exploratory in nature; that is, automation of log interpretation has been in a more-or-less experimental stage. A characteristic of this developmental stage is the restricted nature of the studies; the various reports consist of only segments of the entire interpretation tableau. For example, programs have been described which separately compute the standard logging equations such as the Nernst formula for SP, Wyllie's time-average formula for sonic velocity and the Humble formula relating formation factor and porosity. Another program solved various forms of the de Witte shaly sand formula. Recently, a program has been written and will be made commercially available to solve the dipmeter problem. Another recent development involves the digitizing, correlation and discrimination of log data for machine computation. The scope of these studies has not been generally enlarged because of the limited capacity of the available computers. One such pioneering attempt has successfully accomplished this enlargement using an IBM 650A computer with index registers and other additional hardware. For the most part, however, the modernity of present-day log data processing clearly demands the use of large memory computer installations. As a natural outgrowth of these early studies, the comprehensive computer system COMLOG has been developed to interpret all commercial logs. The system is comprehensive to the extent that, regardless of the complexity of the logging program, solutions for such reservoir parameters as porosity and water saturations are produced. This facet of the system has been adequately field-tested; definite and satisfactory results have been obtained from logs from over 100 wells, both foreign and domestic. COMLOG operates on IBM 700 series scientific computers. Their memory capacity exceeds the demands of the program in its present form.
The COMLOG system is outlined in flow chart form in Fig. 1. The figure is more or less self-explanatory, but it involves the following:
the logs to be analyzed are correlated and the information they contain is digitized by zones;
this digitized information is placed on two types of data sheets (details follow);