Diagenesis of Oil-Field Brines

Analyses of oil-field waters of the United States are assembled in diagrams. From the position of the geological units in these diagrams it follows that in the development of connate water from sea water, two distinct diagenetic phases must be recognized. The first phase is the precipitation of magnesium and calcium and sulphate and carbonate, the second phase is a concentration with a gradual increase of magnesium and calcium ions. It is supposed that the first phase is due to base exchange with the clay sediment, and the second phase to a semi-permeable property of the shales during the later stages of compaction.