Logging Oddities


J. T. (Ted) Costello



Gamma ray logs run by different companies over the Milk River and Second Specks Zones do not always repeat on a peak to peak basis. Because the logs are run under open hole and cased hole conditions a difference in count rate is to be expected. In the examples cited however, anti-correlations are apparent with zones that have little radioactivity on one run appearing to be radioactive on another run. When the open-hole log is followed by a cased hole log by the same company, good repeats are obtained, suggesting that the phenomenonis not a function of the formation or the introduction of casing. A possible explanation is that the counting systems of the logging companies differ in their response to gamma ray of a particular energy level. If this is the reason then a flaw is present in the API calibration system in that two tools calibrated by the standard, might produce the same count rate in zones of a particular energy level but differ in zones of another energy level. Examples one and two show the poor repeat phenomena, example three shows the repeat by the same company under open hole and cased hole conditions.