Page 226 - Geochemistry of Oil Field Waters

COMPOSIDION OF OILFIELD WATERS 213

TABLE 7.V
Cretaceous system - highest concentration of a constituent found, average concentration,
and number of samples analyzed
Constituent Concentration (mg/l) Number of samples

highest average
Lithium 13 4 26
Sodium 88,600 31,000 987
Potassium 580 130 38
Rubidium 0.10 0.10 1
Cesium 0.10 0.10 1
Calcium 37,400 7,000 987
Magnesium 8,000 900 987
Strontium 980 200 39
Barium 67 0 40 34
Boron 70 20 38
Chloride 187,000 62,OOb 987
Bromide 1,760 550 173
Iodide 190 25 172
Bicarbonate 1,660 260 864
Sulfate 7,100 280 776
Ammonium 35 23 2

Composition of oilfield waters

To illustrate the variety of oilfield waters found in subsurface petroleum-
bearing formations, samples were taken, and analyzed, from formations of
the following ages: Tertiary, Cretaceous, Jurassic, Permian, Pennsylvanian,
Mississippian, Devonian, Silurian, Ordovician, and Cambrian. Insufficient
samples from Triassic age strata were available. These data are given in Tables
7.IV-XIII, and all of the samples were taken from sedimentary basins in the
United States. Each table gives the highest value found in this study in
milligrams per liter for a given constituent, the average values, and the num-
ber of samples used to estimate the average value. The constituents deter-
mined for most of the brines include lithium, sodium, potassium, rubidium,
cesium, calcium, magnesium, strontium, barium, boron, copper, chloride,
bromide, iodide, bicarbonate, carbonate, sulfate, organic acid as acetic
(actually organic acid salts but calculated as acetic acid), and ammonium.
Comparison of the lithium content in the samples from Tertiary age strata
(Table 7.IV) with the lithium content of sea water (Table 7.1), indicates that
the average lithium content of 169 oilfield waters is enriched by a factor of
20. At least one sample of oilfield water contained 27 mg/l of lithium or an
enrichment factor of 135 compared to sea water. Table 7.11 indicates that
igneous rocks contain up to 65 ppm of lithium and sedimentary rocks con-
tain up to 46 ppm of lithium.