Chlorides in Oil-Field Waters

Abstract

The waters of many oil fields have been regarded as buried sea water whichhas been retained in the sediments since the time of their deposition. Thepreservation of connate water through geological time has seemed improbable toonly a few geologists, but there is room for doubt that buried sea water couldremain in the strata during their periods of deformation and during the manysubsequent epochs of the circulation of meteoric ground-water. Some have evensuggested that the calcium chloride water in the deep mines of the LakeSuperior region is ancient sea water buried in the Algonkian lavas, but it ishard to understand how such water could be derived from the highly sodic andsulphatic water of the sea. It would seem more plausible to connect the calciumchloride with the highly calcic magmas of the greenstones in which it isfound.Chemical analyses of waters associated, with oil differ widely from thecomposition of sea water, requiring extensive alteration of the latter, if theformer is truly its derivative. The first notable difference is the generalabsence of sulphates from oil-field waters, but this has been explainedsatisfactorily through reduction by hydrocarbons and organic matter. Oilreduces sulphates with the production of hydrogen sulphide (or sulphur), water, and carbonates (or carbon dioxide).The second striking difference is in the high ratio of chlorine to sodium. Anexamination of the analyses of chloride waters from oil fields shows that theycontain a large relative excess of chlorine over that in sea water. Moreover, there is difficulty in finding chemical reactions that are probable in nature, by which sea water could be converted into anything like the chloride waters ofoil fields. In the latter a large part of the chlorine occurs as calcium andmagnesium chloride. This condition might be produced by the removal of sodiumcarbonate, which, however, cannot be precipitated in the presence of muchcalcium or magnesium.AIME 048–52