EXPLORATION FOR PETROLEUM 17 
This is not a simple problem. Thus, in 1923, an examination of the 
history of the discovery of salt domes in the Gulf Coast would have 
shown that the exploration method with the greatest record of ac- 
complishment was that attained by drilling prospects resulting from 
the search for gas seepages, topographic anomalies and paraffin dirt 
beds. Yet this method had stagnated,’ and two years later the intro- 
duction of geophysical tactics revolutionized the strategy of explora- 
tion. In 1929, the refraction seismograph had attained a remarkable 
record of discoveries in the Salt Dome Provinces of the Gulf Coast 
Embayment, and yet a year later the method had become practically 
obsolete. In considering a choice of tactics, the important question is 
not only whether the method under consideration will reasonably 
define an anomaly at some known producing field, but also to what 
extent the law of diminishing returns has run for that particular 
method in the province under consideration. No matter how strikingly 
an airplane photograph may show the areal geology, the method will 
contribute little if the surface geology was carefully, even though 
laboriously, mapped at an earlier date. 
Assuming an ultimate recovery of twenty thousand barrels to the 
acre, fifty thousand acres, or about two and one-fourth townships 
would produce one billion barrels of oil. Ten billion barrels of oil, 
under such conditions, would be recovered from about twenty-five 
townships, or a square about thirty miles on a side. The area of such 
a square is negligible in comparison with the thousands of square 
miles of potential oil-producing territory in the continental United 
States of America. 
Although from an individual operator’s standpoint, the problem 
is that of finding a structure, from the standpoint of an exploration 
campaign, one major problem is that of eliminating unfavorable 
areas, or rather, selecting areas where the great odds against random 
drilling are minimized. Bearing in mind that good strategy requires 
the use of exploration methods with greater resolving power than 
those previously used, obviously the preliminary phase of the ex- 
ploration should be the critical examination of existing sub-marginal 
prospects. 
The resolving power of a given exploration method might be likened 
to the cone of error for a rifle. As the range increases, the base of the 
cone of error incteases. As long as the target is greater than the base 
® Geology of Salt Dome Oil Fields, DeGolyer et al., p. 776, Occurrence of Sulphur 
Waters in the Gulf Coast of Texas and Louisiana, and their Signeficance in Locating New 
Domes, by W, F. Henninger. 
261 
