In the south sector of CP-I, the shallow and deep reservoir fluids have quoted different pH values; in the shallow reservoir an average pH value of 5.5 has been calculated, whereas for the deep reservoir mainly of the southeast part, a pH of 6.4 was obtained. The pH of each reservoir is very uniform, although in the north part of CP-I, the values have decreased
compared to those previously obtained in 1990. In the south of CP-I area hydraulic communication between both reservoirs does not seem to have an influence on the pH values, which indicates that water–rock interaction still controls the pH of the fluid in the system. Although, the slight alkaline pH calculated for fluids from the southeast part seems to be affected by the
boiling processes due to the exploitation.