potassium as alkalies (fig. 13-2) ; calcium and magnesium as alkaline earths; car- 

 bonate, bicarbonates, and sulphides as weak acids; and chloride, sulphates, and 

 nitrates as strong acids. 



Palmer calculated the reacting values in percent of the radicals. Using the 

 four groups, he separated natural waters into four classes, according to the 

 reacting values of the radicals. The four classes are primary and secondary 

 salinity, primary and secondary alkalinity. Alkalies in connection with strong 

 acids cause primary salinity. If the strong acids are greater than the alkalies, 

 excess of the strong acids with an equal value of alkaline earths induces second- 

 ary salinity. Primary alkalinity is excess of alkalies over strong acids, with equal 

 value of the weak acids. Secondary alkalinity is excess of the weak acids com- 

 bined with an equal value of alkaline earths. Secondary salinity and primary 

 alkalinity are incompatible. Each natural water will have two or three of these 

 properties of reaction, but never all four. In addition, the percentage of chloride 

 and sulphate salinities are computed and may be used as criteria for comparison. 



Most formation waters contain some of the heavier minerals, generally in 

 minute quantities, as well as some dissolved gases. In the past, these minerals 

 and gases were not analyzed. Today, however, with the special instruments 

 that have been developed, such as flame spectrophotometer and gas chroma- 

 tography instruments, any element or gas present in the water can be determined 

 quantitatively. For gas analysis, a special sampling tool is required so that the 

 sample can be taken and delivered for analysis under bottom-hole conditions. 

 These more complete analyses have given us a better understanding of the 

 geochemistry of formation waters and their application to the waters of 

 petroleum accumulations. 



WATER PATTERNS Water patterns for correlating waters have 



been used for many years. Today, a system 

 developed by Stiff (1950) makes it much easier for geologists to compose a file 

 of analyses and patterns containing information on all formation waters. This 

 preferred system of graphically presenting water analyses uses the reaction 

 values expressed in milli-equivalents per liter directly, rather than on a percentage 

 basis. Thus, the actual concentration of the ions is employed; and two unlike 

 waters, differing only in concentration, can be distinguished from each other. 

 The more important constituents are plotted on horizontal lines extending left 

 and right from a vertical line at zero. Positive radicals are plotted to the left, 

 and the negative radicals to the right. The figure above each radical gives the 

 scale upon which the radical is plotted. Figure 13-3 shows how the pattern 

 system can be used to correlate and classify waters (Sage, 1955). 



We shall assume that a well was drilled to formation B and squeezed off 

 formation A, which lies a few hundred feet above formation B. A drill-stem 



254 



