Introduction 5 



regions. Attention must be given the possibilities buried beneath late 

 Tertiary volcanics of the Rocky Mountain and Columbia Plateau areas 

 and in Central and South America. The evaluation of these problems 

 rests with the subsurface geologist. 



Duties of the Subsurface Geologist 



The duties and responsibilities of the subsurface petroleum geologist 

 are numerous and varied. He must be diversely trained and have an ac- 

 curate sense of geologic and economic values. He must be able to present 

 his data concisely, to adhere to his convictions, and to coopera.e fully 

 with the petroleum, production, and development engineer, the field geolo- 

 gist, the geophysicist, the management, and all other personnel that con- 

 tribute to the solution of the subsurface problem. Frequently in explora- 

 tion work he may be called upon to devote many continuous hours to 

 special assignments; or he may be designated to obtain information from a 

 "no dope" well, wherein he must investigate the casing program, the 

 acidizing and shooting procedure, the record of mud, chemicals, and bit 

 sales, and logging activities. 



Some Major Subsurface Problems 



Subsurface problems in the fields of petroleum exploration and 

 development are varied and numerous. The solution of some of these 

 problems is relatively simple, whereas, the solution of others demands 

 voluminous data that must be carefully screened and integrated. Some 

 of the more important problems commonly encountered in subsurface 

 work are as follows: 



1. Correlation of Surface to Subsurface Stratigraphic Units: It 

 has been demonstrated that both recent and ancient deposits 

 of the stable shelf areas frequently are lithologically and faun- 

 ally in discord with deposits of the unstable shelf. The intra- 

 cratonic basin sediments and their organic elements vary widely 

 with those that accumulated under geosynclinal conditions. Thus, 

 wells drilled in a geosynclinal facies penetrate sections which 

 require correlation with equivalent though lithologically and 

 faunally dissimilar marginal strata. The establishment of cor- 

 relations of this type are essential before the tectonic and 

 sedimentational history of the region can be properly evaluated. 



2. Reef Investigations: During the past few years considerable 

 attention has been given reef production in Texas and Canada. 

 Fanatical attempts have been made to improve and devise new 

 methods applicable to the discovery of gas and petroleum res- 

 ervoirs of this type. Seismograph exploration has been extremely 

 instrumental in many of the reef production discoveries. De- 

 tailed lithologic, paleontologic, and well-logging data must be 

 coordinated in reef investigations, as the reef elements (porosity, 



