The chemical analyses of seventy-eight samples of brine water in the Kujukuri gas field were carried out, and compared formationally and regionally.
At Mohara and Otaki districts, the ratios of I-/Cl- and Br-/Cl- are higher in the water of the lower Otadai and the Kiwada formations, than those of the overlying Umegase, and the underlying Ohara, Namihana and Katsuura formations. Regionally these ratios of the waters of the Kiwada formation decrease in the direction to the North. This fact reveals the coincidence with the tendency of thinning out of the formation to the same direction.
If we assume that dI -and dBr- are the enriched portion of I- and Br- in the brine water after the deposition of sediments, the ratio of dI-/dBr- remains nearly constant as 1.5_??_1.9 in this field. This fact suggests that the sources of I- and Br- are derived from the same materials, which may be the algae having high concentrations of the iodine and the bromine.
The high values of I-/Cl- and Br-/Cl-in the water of the muddy “Kiwada” formation compared to those of the sandy ones (“Umegase”, “Ohara”, etc.) also show that there were enrichment of the organic matters to the Kiwada formation at the time of deposition.