CLASSIFICATION OF THE OIL-FIELD WATERS. 
51 
or connate but is generally a mixture in which meteoric water pre¬ 
dominates. The waters of the altered group contain practically no 
sulphate; they may be either meteoric or connate, or a mixture of 
che two. Many analyses of altered waters are available, and since 
the two extremes, meteoric and connate, are well represented, three 
types of altered water may be distinguished. Altered water of mete¬ 
oric origin may be called the reversed type; altered connate water may 
Meteoric 
Mixed 
/-ypz 
Figure 3.—Diagram illustrating relation of oil-field waters of the meteoric and connate types, and their 
alteration as the oil zone is approached. 
be called simply brine, and altered mixtures of the two may be called 
the mixed type. This classification may be summarized as follows: 
Group 1. —Normal, strongly sulphate water (typically of meteoric origin). 
Group 2. —Modified, less strongly sulphate water (may be either meteoric or 
connate but is commonly a mixture in which meteoric water predominates). 
Group 3. —Altered, practically sulphate-free water (meteoric and connate 
waters and mixtures of the two). 
Reversed (carbonate water, originally meteoric). 
Brine (chloride water, originally connate). 
Mixed (chloride-carbonate water). 
This is primarily a classification of the ground waters, but for con¬ 
venience surface waters may be included in the normal group. The 
normal group includes most shallow ground water, but the depth to 
which normal waters descend depends principally on the depth of 
the oil zone. Modified waters occupy the zone below the normal 
zone and include the sulphur waters often found some distance above 
the oil. The thickness of the modified zone is generally several 
hundred feet, but it is variable and no definite limits can be assigned. 
In the Westside Coalinga field the oil measures occur at the base of 
the modified zone, and the normal and modified groups are therefore 
