Page 193 - Geochemistry of Oil Field Waters

180 ORGANIC CONSTITUENTS IN SALINE WATERS

siderably among the electrolytes (McDevit and Long, 1952). A limiting law
for determining the influence of electrolytes on the activity of nonpolar
solutes was developed, which related the magnitude of the salt effect to the
volume changes associated with salt and water mixing.
Molecular hydrogen was found in oilfield waters in the Lower Volga region
(Zinger, 1962). Up to 43% of the dissolved gas in these waters was hydrogen;
other gases dissolved in the waters were methane, ethane, butane, pentane,
carbon dioxide, nitrogen, helium, and argon. The pH of these waters was as
low as 3.4, and the iron content was as high as 1,100 ppm.
The solubility of methane increases with pressure and decreases with in-
creased salt concentration at ambient temperature in NaC1-H2 0 and
CaC12-H20 systems (Duffy et al., 1961). From the experimental data, it
was estimated that 1 cubic foot of sedimentary rock with 20% porosity
buried 300 m deep and saturated with a brine containing 50,000 ppm of
NaCl could accommodate 0.3 mole of methane in solution.
A gas-liquid partition chromatographic technique was used to determine
the solubilities of C1 -C9 paraffin and branched-chain paraffins, four
cycloparaffins, and five aromatic hydrocarbons in water (McAuliffe, 1963).
Later this study was extended to seventeen paraffins, seventeen olefins, nine
acetylenes, seven cycloparaffins, seven cycloolefins, and six aromatic hydro-
carbons (McAuliffe, 1966). The data indicated that the solubilities of the
hydrocarbons in water increased as unsaturate bonds were added to the
molecule, with ring closure, with addition of unsaturate bonds in the ring,
and with addition of bonds which decreased the hydrocarbon molar volume.
Branching increased the solubility in water for paraffin, olefin, and acetylene
hydrocarbons but not for the cycloparaffin, cycloolefin, and aromatic hydro-
carbons. Plots of the log of the solubility in water were a linear function of
hydrocarbon molar volume for each homologous series of hydrocarbons.
A capillary-cell method was used to measure the diffusion of methane,
ethane, propane, and n-butane in water (Witherspoon and Saraf, 1964). At
25OC, the results indicated that the diffusion coefficients times los cm2/sec
were 1.88, 1.52, 1.21, and 0.96, respectively, for methane, ethane, propane,
and n-butane. The coefficients increased with higher temperatures.
Near the critical solution temperature and about 300 atm, the solubility
versus pressure curves for some hydrocarbon-water systems show a sharp
maximum. However, pressure has a negative effect on solubility beyond this
maximum, and a second two-phase region appears. The five binary
hydrocarbon-water systems studied were benzene, n-heptane, n-pentane,
2-methyl-pentane, and toluene (Connolly, 1967).
The accommodation of CI2-C& n-alkanes in distilled water was deter-
mined as a function of hydrocarbon supply, settling time, filtration pore-
size, and mode of introduction (Peake and Hodgson, 1967). Apparently it is
possible to accommodate hydrocarbons in water at levels higher than solubil-