Radioactivity anomalies (low) have been mapped from well logs at various stratigraphic levels by the senior author on more than two dozen known oil fields in this country and abroad; a number of these surveys have been published. There is no longer any doubt that there exists a casual relationship between the origin of oil, its primary migration and its accumulation, and the modifications of the sedimentary column as reflected by the radioactivity lows which form a "chimney" throughout the overlying sediments. In one occasion, over the Wellman field, Terry Co., Texas, the radioactivity low was found disturbed by a pronounced cross-trend. Normalization of the readings to a constant shalyness by means of a radioactive chimney associated with the pooling of oil at Wellman. The secret of successful radioactivity mapping in the search for oil is in selecting significant stratigraphic horizons which can be correlated without question within the area under study and which horizons are free of large facies and compositional variations within this area. If there are lateral variations in shalyness such as at Wellman, in carbonaceous material such as over the Lowe field, Andrews Co., Texas, in calcareous material such as in the Ireton shale, Alberta, Canada, normalizing reduction of the data is required in order to obtain a significant map. The radioactivity chimney should reach the surface of the earth and should be detectable by surface radioactivity measurements made above the surface of the earth or from soil samples derived from bed rock.

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