Page 15 - Geochemistry of Oil Field Waters

4 INTRODUCTION

these waters were considered waste and had to be disposed of in some
manner. Injection of these waters into the petroleum reservoir rock serves
three purposes: (1) it produces additional petroleum (secondary recovery);
(2) it utilizes a potential pollutant; and (3) in some areas it controls land
subsidence.
The volume of water produced with petroleum in the United States is very
large. In 1970, daily production was about 3.78 trillion liters of water with
about 1.51 trillion liters of oil. In older fields, the production is frequently
95% water and 5% petroleum.
. Waterflooding in petroleum production is expanding rapidly, and in 1970
one-third to one-half of the production in the United States came from fields
into which water was injected. The volume of injected water has grown each
year. In many fields the volume of petroleum produced by secondary re-
covery by waterflooding is equal to the volume recovered by primary
met hods.
To inject these waters into reservoir rocks, suspended solids and oil must
be removed from the waters to prevent plugging of the porous formations.
Water injection systems require separators, filters, and, in some areas,
deoxygenating equipment utilizing chemical and physical control methods to
minimize corrosion and plugging in the injection system.
In waterflooding most petroleum reservoirs, the volume of produced
water is not sufficient to efficiently recover the additional petroleum. There.
fore, supplemental water must be added to the petroleum reservoir. The use
of waters from other sources requires that the blending of the produced
water with supplemental water must yield a chemically stable mixture so
that plugging solids will not be formed. For example, a produced water
containing considerable calcium should not be mixed with a water con-
taining considerable carbonate because calcium carbonate may precipitate
and prevent injection of the flood water. The design and successful operation
of a secondary recovery waterflood requires a thorough knowledge of the
composition of the waters used.
Chemical analyses of waters produced with oil are useful in oil production
problems, such as identifying the source of intrusive water, planning water-
flood and salt-water disposal projects, and treating to prevent corrosion
problems in primary and secondary recovery. Electrical well-log interpreta
tion requires a knowledge of the dissolved solids concentration and composi
tion of the interstitial water. Such information also is useful in correlationof
stratigraphic units and of the aquifers within these units, and in studiesof
the movement of subsurface waters. It is impossible to understandthe
processes that accumulate petroleum or other minerals without insight in to
the nature of these waters.