Page 170 - Geochemistry of Oil Field Waters

AMMONIUM NITROGEN 157

bility of silicon in the presence of calcium chloride solutions decreased with
increasing Concentration of calcium chloride and with increasing temperature
above about 100°C. The solubility increased with increasing pressure and
with increasing temperature between 30' and about 100°C. Subsurface
petroleum-associated brines usually contain less than 30 mg/l of dissolved
silica; Rittenhouse et al. (1969) report that their silica content ranges from
about 1 to 500 ppm as silicon, and that some low salinity waters contained a
higher median content of silica than more saline waters in other areas.

Ammonium nitrogen
Ammonium contains nitrogen in the N-3 oxidation state, a reduced form.
Nitrogen can occur in all of its states of oxidation, ranging from -3 to +5.
Oxidation of the reduced forms produces nitrogen gas, N2, and other
nitrogen species up to nitrate, NO3-. Ammonia, NH3, forms during the
anaerobic decay of organic nitrogenous material. The petroleum genetic
environment produces ammonia, which transforms to ammonium, NH4, in
many petroleum-associated waters because the redox potential is too low to
oxidize the ammonia to nitrate. The ammonium ion is too weak to be
successfully titrated; however, Collins et al. (1969), developed a technique
using formaldehyde, whereby a produced strong acid can be titrated.

TABLE 5.V
Ammonium content of 10 subsurface brine samples

Sample State Formation

1 Utah Navaho 30-143 0
2 Utah Green River 852-1,719 71
3 Utah Lower Green River 914-1,737 91
4 Okla. Morrow 2,713-2,715 0
5 Okla. Rue 1,958-1,963 116
6 Utah Uinta Surface, Green River 717-1,111 2,069
7 Utah Green River 68 1-1,5 5 6 5
8 Okla. Hunton 2,696-2,77 1 434
9 Okla. Oswego 1,928-1,951 233
10 Okla. Chester 2,408-2.437 23

The NH4N content of several oilfield brines was determined and a wide
variation in concentration was found. Table 5.V illustrates the amounts of
NH4N found in 10 samples taken from subsurface rocks in Oklahoma and
Utah.