A, Level necessary for 

 Oq a prospect- 



O 



o 

 o 







Terrace 



•Blanket sand 



Reef 

 Lens, 

 Sand- 

 patch 

 Bionerm 

 Fracture 

 Shoestring 

 Wedge edge 

 hydrodynamics 

 Fades changes 

 Permeability variation 

 JDil-gas showing 



Homocline- 



A 



100% 

 Structural 



100% 

 Stratigraphic 



Figure 2-1. Composition of a prospect. Structure alone may form a prospect where there 

 is a blanket sand plus 10 to 15 feet or more of structural closure. Where less closure 

 is present, then such features as showings of oil and gas, permeability variations, 

 facies changes, hydrodynamics, or wedge edges of permeability are necessary to 

 combine with the structure to form a trap. Where there is no structural closure, then 

 some stratigraphic features alone such as shoestring sands, fracture porosity, bioherms or 

 reefs, and sand patches, may form traps. 



the geologist fills in the gaps by use of his imagination, no prospect will develop. 

 Because data are frequently inadequate, the data that are available should be as 

 precise and accurate as possible. 



When one considers that tens or hundreds of geologists are examining the 

 same data and trying to find a clue for a drilling prospect, one realizes that dis- 

 covering a prospect requires dependable data, clear thought, and an active imag- 

 ination. Exploration in almost every district is continually at the fringes of the 

 knowledge of the district. Any obvious prospects would have been drilled. A 

 new prospect, consequently, must usually be developed in a place others have 

 rejected or overlooked. As a result, the subsurface geologist's work is in intensive 

 competition with all others in the same district. 



An expanding future of subsurface mapping seems assured for as long a 

 time as there is a need of discovery and production of oil and gas. Not only are 



13 



