952 



Subsurface Geologic Methods 



complex. Maps contoured on the bases of percentages, ratios, or aggregate 

 thicknesses of lithic classes do not take into account the manner in which 

 the individual units occur. As stated before, ten 5-foot units have the same 

 contouring value as one 50-foot unit. There are means of further classi- 

 fying a lithofacies map so that it yields the practical information desired. 



Figure 514. Map showing aggregate thicknesses of reservoir sands over 25 feet thick. 



The following example will illustrate a direct practical application of a 

 lithofacies map. 



The problem is to determine the amount of effective reservoir sand and 

 its relative worth over a broad area. It is assumed here that individual 

 sands less than 25 feet in thickness, even though several such units occur 

 in the section, are not worth exploitation. Since these thin units might 

 coalesce to form more attractive reservoirs, locally, they must be given 

 some consideration. 



