46 OIL-FIELD WATERS IN SAN JOAQUIN VALLEY, CAL. 
Many waters from the Eastside Coalinga field carry considerable 
amounts of sulphide, which is reported in the industrial analyses as 
“sodium sulphide.” In these analyses, however, the alkalies are 
calculated by difference, and as the amount of alkalies present is not 
definitely known, the assumption that a sufficient amount is present 
to balance all of the sulphide is unwarranted. Although some of it 
may be balanced by alkalies, it is probable that much of it is actually 
present as the acid sulphide, which implies only half as much alkali 
as the normal sulphide, and that at least some of it is merely hydrogen 
sulphide. 
Sulphide in the oil-field waters of San Joaquin Valley is probably 
formed by the reduction of sulphate. This reaction generally takes 
place a short distance above the main oil zone, and whether the 
sulphide radicle is first formed or not it is certain that hydrogen 
sulphide is an important product. As hydrogen sulphide is a gas, 
it tends to rise to higher waters or to the surface, if it is free to migrate 
at all, and the current belief that “sulphur” waters are top waters is 
therefore well founded. Like most generalizations, however, it must 
be applied with discretion, for when sulphate water percolates into 
the brown shale below the oil measures, as along the western edge of 
the Midway field, and there encounters small amounts of oil or gas, 
the sulphate may be partly reduced to sulphide and a sulphur water 
thus formed far below the oil zone. Some of the most pronounced 
sulphur waters in the oil fields are obtained from wells located near 
the outcrop of the oil sands, which draw their water from the strata 
below the oil. 
Iron and aluminum .—Iron and aluminum differ from the constitu¬ 
ents already discussed in that they occur in most waters simply as 
hydrated oxides, which are supposed to be in the colloidal state 
rather than in true solution. They are rarely present in large 
amounts and generally do not affect the chemical aspects of the 
water. 
In a great many natural waters much the larger part of the “iron 
oxide and alumina” reported is iron oxide, and the amount of 
alumina is very small. In a few of the analyses given in this report 
the two have been separately determined, and in these oil-field waters 
the reverse seems to be more generally true. The iron is usually very 
low, although it varies widely. It seems probable that the low con¬ 
tent of iron is due to the fact that in the presence of hydrogen sulphide 
it has reverted from the colloidal state and formed iron sulphide, 
which being only slightly soluble has been mostly precipitated. On 
the other hand, the unusually large amounts of iron sometimes found 
are probably derived through the corrosion of the iron casing of 
wells, and some of this iron may be present not as colloid but in true 
solution. 
