Miscellaneous Subsurface Methods 



769 



Results and Interpretations 



Horvitz has pointed out that the analytical data collected from a large 

 number of geochemical well logs have indicated the existence of definite 

 relationships between the measured constituents and occurrence of petro- 

 leum at greater depth. Wells centrally located over an oil accumulation 

 have low values of hydrocarbon content in the cuttings from the upper por- 

 tion of the well. At a considerable distance above the accumulation the 

 values begin increasing, gradually reaching a maximum at the reservoir. 



Figure 409. Carbon-anomaly map showing distribution pattern of 

 some organic compounds thought to have a unique relation- 

 ship to petroleum. White area is low concentration, below 15 

 parts per million. Light stippled area ranges from 15 to 25 

 ppm; medium stipled area ranges from 25 to 30 ppm; dark 

 area is above 30 ppm. Note that production discovered to date 

 appears to fall on west edge of a halo pattern. 



If multiple-producing zones are present, the values decrease abruptly after 

 passing the upper zone and then build up gradually again as the next lower 

 production is approached. The higher the gravity of the oil in the reser- 

 voir, the greater the distance above the deposit the increased concentration 

 is observed. 



Approximately equal quantities of ethane-propane-butane and pentane 



