Abstract: Role of Solubility in Migration of Petroleum from Source (AAPG Short Course: Physical and Chemical Constraints on Petroleum Migration)

C. D. McAuliffe

Several petroleum migration mechanisms have been proposed, including movement as oil-in-water emulsions, micelles, and true solutions. Mechanisms based on emulsions and micelles seem to require porosity, permeability, and surface-chemistry conditions that may not be met. The true solution mechanism would require the movement of water saturated with all classes of hydrocarbons to allow oil accumulation in reservoir rocks. However, the water solubilities of hydrocarbons vary significantly with hydrocarbon class (alkanes, cycloalkanes, aromatics, etc.) and decrease markedly with increasing molecular weight within a class. The relative composition of crude petroleum with respect to the relative water solubilities of petroleum hydrocarbons suggests that solution is not a reasonable migration mechanism.

Physical and chemical constraints suggest a migration mechanism in which generated petroleum hydrocarbons are not suspended or dissolved in a water phase, but move in a continuous oil or oil-like phase, although one of small dimensions. In this mechanism, generated petroleum would migrate as threads or ribbons along hydrocarbon chains protruding from polar compounds attached to mineral surfaces or, more likely, through organic matter deposited with and among the mineral constituents. Oil emerging from these threads or ribbons of petroleum would grow into droplets in the larger pores of the reservoir rock.

AAPG Search and Discovery Article #90961©1978 AAPG Annual Convention and Exhibition, Oklahoma City, Oklahoma