Page 224 - Geochemistry of Oil Field Waters

SEDIMENTARY ROCKS 21 1

containing dissolved hydrocarbons, which subsequently deposited them in
sedimentary reservoir ,rocks. Al’tovskii et al. (1961) believe that petroleum
forms in subsurface formation waters and moves to traps as an emulsion or
in aqueous solution. Movement of hydrocarbons from the source bed to the
reservoir via aqueous solution or as molecular films was postulated by Brod
(1960). Baker (1960) suggested that, as the sediments compact, the express-
ed water may contain solubilizers capable of releasing sediment hydrocar-
bons into aqueous colloidal solution, and subsequent changes in the aqueous
equilibria cause the colloids to become oil droplets in reservoirs.
The soluble salts of adenosine triphosphate are capable of solubilizing
numerous inorganic and organic compounds in neutral or slightly alkaline
medium and of keeping these compounds in solution (Mandl et al., 1952).
Hydrocarbon solubilization processes are essential to the migration of
petroleum and acquired evidence indicates that nature provides solubilizing
agents. Numerous solvents are evaluated by Mandl (1953), many of which
are useful agents for solubilizing relatively insoluble inorganic and organic
compounds.
Organic as well as inorganic compounds will enter the aqueous phase to
the limit of their solubilities. Interactions of the solubilized compounds
affect the solubility product of other solubilized compounds. For example,
the presence of dissolved sodium chloride may inhibit or increase the solu-
bility of a normal alkane. For any given system, equilibria of all components
will be attained only at a given temperature and pressure. If the temperature
changes, if the pressure changes, or if more inorganic or organic constituents
are added or subtracted, the equilibria will change causing solubilization or
deposition.
Hydrocarbons can exist in the aqueous phase as emulsions or colloids, as
suspended particles, or in true solution. Suspended particles will settle from
an aqueous phase because of gravity, whereas colloids will remain in suspen-
sion. Suspended particles possess colligative effects, but colloidal sols do not
(Van Nostrand Press, 1958). A dissolved particle usually is smaller than 5
mp, while colloidal particles usually range in size from 0.25 mp to 6 mp.
Phenols and alkalinaphthenates capable of acting as emulsifying agents
and causing oil-in-water emulsion to migrate have been detected in crude oils
and in the associated brines (Neumann and Jobelius, 1967). It has been
demonstrated that finite amounts of paraffinic, aromatic, napthenic hydro-
carbons and other organic derivatives are dispersed in recent marine sedi-
ments (Smith, 1954). Surfactant organic acids stabilize hydrocarbon
particles of relatively large size and contribute to solubilization and subse-
quent migration of hydrocarbons from sediments (Baker, 1960). A shift in
the equilibria caused by a pH or Eh change, adsorption of the surfactant,
etc., results in deposition of the pseudo-soluble hydrocarbon. Therefore,
solubilization and mobilization of hydrocarbons from sediments into the
aqueous phase occurs when the equilibria are shifted to the correct con-
ditions. Subsequent migration of the hydrocarbons in the aqueous phase