EXPLORATION FOR PETROLEUM 21 
methods, or, perhaps, was satisfied with torsion balance data alone 
prior to drilling, then prospect exploitation would be burdened with 
an unduly great hazard. On the other hand, if these methods, of re- 
solving power less than the reflection seismograph, were neglected 
in prospect discovery, the cost of prospect discovery would probably 
be unduly great. 
EXPLORATION STATUS OF THE VARIOUS PETROLEUM 
PRODUCING PROVINCES 
It may be of interest to examine several petroleum producing 
provinces from the standpoint of the appropriate methods of ex- 
ploration and the present exploration practice. 
GULF COAST 
There has been intensive use of library methods, surface methods, 
airplane mapping, the refraction seismograph, torsion balance, and 
the reflection seismograph. At present, the most effective sequence 
of tactics seems to be, for a company which has recently initiated an 
exploration campaign, 
1. Library methods 
2. Torsion balance 
3. Reflection seismograph 
4. Drill 
There is no doubt, however, that the law of diminishing returns is 
beginning to operate against the present general reliance upon library 
methods and the torsion balance for prospect discovery, and that 
the next and rather imminent phase will be prospect discovery and 
evaluation by the reflection seismograph. This phase, naturally, will 
be materially more expensive, and will be required when prospect 
discovery can no longer be made by any of the lower cost methods. 
There is no doubt but that the prospects now being discovered by the 
torsion balance are approaching the sub-marginal stage, and the time 
will soon come when many companies will find it cheaper to discover 
prospects by simply filling in the gaps between the areas already 
covered by the reflection seismograph in previous prospect evalua- 
tion. At present, the reflection seismograph is mapping at depths from 
8,000 feet to 12,000 feet sub-sea, to keep pace with and to reasonably 
anticipate drilling practice. There is considerable doubt that gravity 
methods would be materially revived even if deeper objectives were 
found, for torsion balance data, once properly taken, hardly justifies 
repetition, and so belongs properly in the past and in the library. 
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