56 



Subsurface Geologic Methods 



Clapp ^^ in 1910 proposed the first detailed classification of natural 

 oil and gas accumulations and modified "- this classification in 1917. Fi- 

 nally in 1929 ^^ he presented the following classification: 



I. 



II. 

 III. 



IV. 



Anticlinal structures 



1. Normal anticlines 



2. Broad geanticlinal folds 



3. Overturned folds 

 Synclinal structures 

 Homoclinal structures 



1. Structural "terraces" 



2. Homoclinal "noses'" 



3. Homoclinal "ravines" 

 Quaquaversal structures (domes) 



1. Domes on anticlines 



2. Domes on homoclines and monoclines 



3. Closed salt domes 



4. Perforated salt domes 



YimL 



Gas 



Water 



A,B,C.D -- Wells 



Figure 25. Diagram showing irregular distribution of gas, oil and water in an asym- 

 metric anticline. Such relationships require orderly development of field to 

 insure maximum and efficient recovery. Rate and pattern of encroachment of 

 edge and bottom waters are of primary concern to operators. 



^^ Clapp, F. G., A Proposed Classification of Petroleum and Natural Gas Fields: Econ. Geo!,, vol. 5, 

 pp. 503-521, 1910. 



*^ Clapp, F. G., Revision of the Structural Classification of Petroleum and Natural Petroleum and 

 Natural Gas Fields: Geol. Soc. American Bull., vol. 28, pp. 553-602, 1917. 



*' Clapp, F. G., Role of Geologic Structure in the Accumulation of Petroleum, in Structure of Typical 

 American Oil Fields, II: Am. Assoc. Petroleum Geologists Bull., pp. 671-672, 1929. 



