64 Natural Brines of Oil Fields [262 



6000 feet. A slight change in chemical nature with depth 

 is noticed which may be a function of stratigraphic horizon. 

 This possibility will be discussed later. 



Obviously the brines are not like ocean waters yet they 

 are more unlike surface waters and since they are to be con- 

 sidered as originating from one of these sources it is logical 

 to attribute them to that one which they more nearly resem- 

 ble as this requires the explanation of fewer anomalies in 

 the transition from the one water to the other. 



This comparison is shown graphically on page 63. On 

 the horizontal lines P, M, C, D, are plotted, in percentage of 

 total salts present, the amount of each ion in the four mean 

 analyses of the brines from the sands of the Pennsylvanian, 

 Mississippian, Catskill, and Lower Devonian, respectively. 

 On line S is plotted also the percentages of the salts in 

 the mean analyses of ocean and surface waters. With a line 

 drawn through these points a clear idea is obtained of the 

 similarity between the brines and their two possible sources. 



On the assumption that the brines are surface waters which 

 owe their present chemical nature to changes which they have 

 undergone as they passed downward through the rock ma- 

 terial, it would be expected that with increase of depth there 

 would be a progressive change at least to a point of satura- 

 tion. Thus, for example, since there is a decrease say of 

 calcium in the first 1300 feet of from 20.39 per cent, to 8-33 

 per cent., at greater depth it would be expected that the 

 deeper brines would continue to show a decrease in the 

 amount of this ion present. Reference to the graph shows 

 that instead there is a decided increase of calcium with in- 

 crease in depth below 1300 feet. Sodium shows the same 

 anomalous change with depth. It is apparent, on the other 

 hand, that, with the exception of magnesium, the ocean 

 waters fall more in the general alignment of the graphs than 

 do the surface waters. Of course it may be argued that the 

 water would undergo a greater chemical change in the surface 

 strata or in the zone of oxidation than at subsequent depths, 



