Page 262 - Geochemistry of Oil Field Waters

246 ORIGIN OF OILFIELD WATERS

meteoric water reacted with weathered rock, soil, and organic matter. The
excess waters that did not penetrate the rock or soil caused the rock and soil
to erode and channels formed through which the water could move more
easily. Forces of gravity caused the water to move from areas of high poten-
tial to areas of low potential, and as the waters moved, the concentrations of
dissolved solids in them increased. Some of these waters found their way to
lakes and the sea. As they entered the lakes or seas their movement slowed,
causing some of the suspended particles in them to deposit. Mixing of the
waters with the more saline waters in the sea caused dissolved carbonate and
organic compounds to precipitate.
Evaporation of the sea and lake waters caused other compounds such as
sulfates to precipitate. The pH of the waters changed slightly because of
reactions with the atmosphere, the sediments, and other waters. Each pH
change caused precipitation of compounds or dissolution of new com-
pounds.
Some of the waters became highly concentrated in dissolved solids in the
more shallow marine environments. Evaporites formed in these lagoons,
pans, and exposed supratidal sabkhas. Evaporites also formed in deep-water
basins when the salinity of the water at the bottom of the basin became
sufficiently high.
The sediments were buried as additional sediments were deposited on
them, and water surrounding the sediment particles also was buried. As the
depth of burial increased, the sediments compacted and some of the water
was squeezed out. Both the squeezed-out water and the remaining interstitial
water reacted with minerals in the sediments to change the composition of
the dissolved solids in the water and the composition of the sediments.
Mechanisms that cause the oilfield waters to differ in composition from
water originally deposited with the sediments include ion exchange, infil-
trating waters, sediment leaching, mineral formation, sulfate reduction, and
ultrafiltration through clay-shale membranes.

References

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(English Transl. by Consultants Bureau). Plenum Press, New York, N.Y., 107 pp.
Anonymous, 1964. Chemistry of the oceans. Chem. Eng. News, 42:12A.
Atwater, G.I. and Miller, E.E., 1965. The effect of decrease in porosity with depth on
future development of oil and gas reserves in South Louisiana. Presented at Annual
Meet., Am. Assoc. Pet. Geol., New Orleans, La., 1965 -Bull. Am. Assoc. Pet. Geol.,
49:334.
Ault, W.U., 1959. Isotopic fractionation of sulfur in geochemical processes. In: P.H.
Abelson (Editor), Researches in Geochemistry. John Wiley and Sons, New York, N.Y.,
pp.241-259.
Baas Becking, L.G.M., Kaplan, I.R. and Moore, D., 1960. Limits of the natural environ-
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