ABSTRACT

Where operational considerations do not require on-location analysis a hydrocarbon log may be obtained from a laboratory measurement of gas components in small drilling mud samples. By collecting these samples at regular intervals, and submitting for analysis only those from zones of particular interest, the well may be selectively logged. Thus it is possible to log only those wells or intervals of wells after it is apparent more evaluation information is desirable. After a section or the entire well has been drilled it often becomes apparent that information obtainable by mud logging would have been helpful for evaluation. Since standard mud logging techniques require that mud be analyzed on location while the zone inn question is being drilled, it has heretofore been necessary to decide in advance of drilling if such information is to be obtained. With the development of more precise analytical instruments, and more recently an accurate, simple method for extracting substantially all of the hydrocarbons from a small sample of drilling mud, it is now possible to produce a reliable mud log days or even weeks after the well has been drilled. This process requires that one-ounce samples of mud be bottled at the well while drilling is in progress. Should an examination of electric logs, drill cuttings or other available information indicate that additional information on a particular zone is needed, the mud samples collected immediately above, through, and if available, below the zone are submitted for analyses. In the laboratory the hydrocarbons are separated from the sample and analyzed by gas chromatography. The results of the analyses are presented in both graph and tabular form.

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