1104 



EXPLORATION GEOPHYSICS 



creased radioactivity values. A somewhat similar effect results when sands, limes 

 or dolomite are highly interbedded with shale. It is important to note that shales 

 with interbedded sandy shale and thin sand beds show higher average radioactivity 

 values than thicker sand beds separated by thin shales. This is due primarily to the 

 averaging effect of the ionization chamber. 



GRAPHIC INTERPRETATION OF RADIOACTIVITY LOGS 



RADIOACTIVITY INCREASES 



GAMMA RAY NEUTRON 



SURFACE FORMATION (30 '-70') AFFECTED BY 



COSMIC RAY PENETRATION. LOG VALUELESS 



SAND OR LIME NORMAL VALUE 



SHALE 



SAND OR LIME 



SHALE 



SHALY SAND OR SHALY LIME 



SHALE 



SAND OR LIME, BROKEN WITH INTERMITTENT 



SANDY SHALES GRADES TO SHALE ON BOTTOM 



SHALE 



MARINE SHALE, VOLCANIC ASH 



SHALE 



SAND OR LIME, FAIRLY UNIFORM 



SHALE VARIES IN RADIOACTIVE MATERIAL 



LIMESTONE, CALCITE OR LIME, GYPSUM 



ANHYDRITE 

 SALT 



POTASHBEDS, SYLVITE OR POLYHALITE 



SHALE 



ANHYDRITE 



Sri ALE 



SAND OR LIME 



SHALE NOT UNIFORM IN RADIOACTIVE MATERIAL 



SHALY ShNDCOR UME)GRADING TO CLEAN 



SAND (OR LIME) 



SHALE WITH INTERMITTENT SANDY SHALES 



AND THIN SAND STRNGERS NORMAL-^ 



RADIOACTIVE SHALE OR RADIOACTIVE SAND SAND OR c; 



OR LIME DEPENDING ON AREA LIME *~ 



SRI 



'.\l 



ANHY 



SHALE 



LIME 



DOLOMITE 



LIME 



DOLOMITE 



LIME 



BENTONITE 



LIME 



SHALE 



SHALE 



LIME 



DOLOMITE 



LIME NORMAL OR RADIOACTIVE 



RADIOACTIVE 



FUJID BEARING 



SAND 

 OR 



NON FLUID BEARING LIME 



SHALE 



FUilD AND DENSE SAND OR LIME 



SHALE 



SHALY SAND OR LIME 



SHALE 



FLUID AND DENSE SAND OR LIME 



GRADING TO SHALE 



SHALE 



MARINE SHALE, VOLCANIC ASH 



SXALE 



DENSE SAND OR LIME 



FLUID BEARING ON BOTTOM 



SHALE 



LIMESTONE FLUID BEARING OR DENSE 



ANHYDRITE 



SALT 



ANHYDRITE 



POTASH, ETC. 



ANHYDRITE 



SHALE PARTLY WASHED OUT 

 SAND OR LIME. DENSE ON TOP, 

 FLUID ON BCJtTOM 



SHALE WITH SAND STRINGERS 

 DIFFERENTIATED SHALE SAND AND 

 LIME DENSE 

 SHALE 



m'mi 



SHALE 

 LIME DENSE 

 DOLOMITE DENSE 

 LIME DENSE 

 DOLOMITE FLUID 

 LIME DENSE 

 BENTONITE SHALE 

 LIME FLUID 

 LIME DENSE 

 SHALE 

 LIME DENSE 

 LIME FLUID SPOTTED 

 LIME DENSE 

 SHALE 

 LIME DENSE 

 DOLOMITE DENSE 



LIME DENSE 



Fig. 689. 

 (Courtesy of Lane-Wells Company.) 



Clean sand or lime grading into shaly sand or lime is a frequent occurrence and 

 presents a problem in the exact determination of the top or bottom of the clean zone. 

 As a rule, only that part of the zone exhibiting minimum radioactivity represents the 

 clean sand. This is subject to many exceptions, however, and an intimate knowledge 

 of local conditions is desirable for accurate interpretation. 



Formations Exhibiting Unusual Response. — As stated previously, the black, 

 organic marine shales, e.g., the Chattanooga, most frequently show extremely high 



