INTRODUCTION 17 



ment of such a combined technique would allow its application in many 

 areas not amenable to the more common geophysical techniques. 



The diversity of the electrical methods and the relative ease with which 

 a measurable field of force may be established give these methods undeni- 

 able advantages over other potential type methods. However, electrical 

 methods utilizing surface potential measurements have not had sufficiently 

 definite results, due to the masking and disturbing effect of the near-surface 

 materials on the potential distribution. Work during the past few years 

 indicates that many of these near-surface effects can be minimized by a 

 more direct type of measurement (such as the measurement of the magnetic 

 field associated with the flow of current) instead of the indirect measure- 

 ments dependent upon the surface distribution of potential. Proper utiliza- 

 tion of this type of measurement may produce a method giving sufficient 

 accuracy in many areas where other geophysical methods have not proven 

 applicable. 



Soil analysis, including the determination of both the hydrocarbon and 

 mineralization content, has attracted much attention due to its ability to 

 detect and measure diagnostic variables which appear to be directly asso- 

 ciated with known oil and/or gas fields. Unless this method proves 

 useful in directly determining the presence of oil, its value is limited, since 

 its use adds little to the geological knowledge of the structure and strati- 

 graphy of the area surveyed. The usual data must be treated from a 

 statistical viewpoint to evaluate the areal distribution of hydrocarbons or 

 minerals, after which allowance must be made for the effects of surface or 

 near-surface conditions not necessarily related to the deeper existence of 

 oil accumulation. Careful consideration must also be given ground water 

 movements and their effect on the distribution of hydrocarbons and sec- 

 ondary mineralization at the surface of the earth. Present indications seem 

 to point to the use of soil analysis methods for furnishing confirmatory 

 evidence as an adjunct to the other exploratory methods capable of map- 

 ping structure directly and quantitatively. 



Since 1943 there has been a rapid increase in the use and development 

 of seismograph methods for exploring water-covered areas lying off the 

 continental shores. The close relationship and geologic similarity over 

 thousands of square miles of submerged off-shore lands to adjacent rich 

 petroliferous land areas make it highly probable that very sizeable oil 

 reserves await discovery and development. This and other factors have 

 led to a vigorous program of off-shore exploration, and to the development 

 of practical methods for drilling and producing prospects. Limited areas 

 of interest off the California coast have been explored. However the major 

 activity has been in the Gulf Coast region, off the shores of Louisiana 

 and Texas. 



Discovery of the Creole field in 1938 proved an incentive to the present 

 campaign of exploration, leasing, and drilling which began about 1945.f 



t Dean A. McGee, "Gulf Activity Spurred by Eleven Discoveries," Tlie Petroleum Engineer, 

 April, 1949. 



