Chloride Content - Mg Per Li 



Figure 13-1. Variation with depth in chloride content of water during drill-stem test. 



There is usually evidence, in such a plot, of a transition zone in which the 

 chloride-ion content increases or decreases, and below which it reaches a con- 

 stant value. The transition zone is interpreted as reflecting contamination and 

 the zone of constant salinity as reflecting uncontaminated formation water. In 

 many instances, the chloride content may reach a constant value, then increase 

 or decrease in an erratic manner. These erratic values can be interpreted as 

 indicating that the packer did not hold or, if the test is being made after a 

 squeeze job, that the squeeze job was unsuccessful. If the squeeze job were 

 unsuccessful, it, as well as the drill-stem test, would have to be repeated. With 

 the information available from the titration test, the geologist or petroleum 

 engineer could determine accurately whether the fluid recovered just above the 

 tool was all drilling fluid, a mixture of drilling fluid and formation water, or all 

 formation water. If the sample taken above the tool is found to be uncon- 

 taminated formation water, then at least a i/ 2 -gallon sample of the water should 

 be sent to the laboratory for analysis, accompanied by a copy of the chloride-ion 

 content plot. The laboratory analysis of this water can be used safely for future 

 correlation work. 



252 



