954 



EXPLORATION GEOPHYSICS 



Reconnaissance surveys are made on a quarter mile grid pattern, while 

 detail mapping requires that samples be taken at intervals of one-eighth 

 and one-sixteenth mile. Samples of one ounce (by volume) are taken with 

 an earth auger at depths of two feet. Since their fluorescent intensities do 

 not vary, samples may be taken at different times and under varying 

 conditions. 



The high fluorescent intensities are found sometimes over the accumu- 

 lation and sometimes around the edges of the accumulation. 



Figure 588 shows the results of a fluorescent survey made of the Griffin 

 Pool, Jones County, Texas, and illustrates the results obtained over an 

 accumulation trapped by porosity variations in a lime reef formation. This 

 anomaly is a so-called fluorescent minimum. 



LEGEND 

 • OIL WELL 



ABANDONED OIL WELL 

 > DRY HOLE 



Fig. 588. — Fluorescent Survey of the Griffin Pool, Jones County, Texas. 

 (Campbell, World Petroleum, March, 1946.) 



Radioactivity measurements are reportedf to be of value in determining 

 the probable limits of production after the discovery well has been com- 

 pleted. In practice, a four-inch hole is bored to about three feet or to a 

 depth insuring the formation of an adequate shoulder. The hole is extended 

 another foot with a three-inch auger, after which a special packer is set at 

 the shoulder so as to seal off the lower section of the hole from above. 



t R. A. Stothart, "Radioactivity Determinations Set Production Delimitations," The Oil 

 Weekly. January 4, 1943. 



