Late diagenetic indicators of buried oil and gas

Abstract

At least three hydrocarbon seepage mechanisms are interpreted to operate over oil and gas fields. These are: (1) effusion of hydrocarbons through inadequate caprocks and along faults and fractures, (2) low-molecular-weight hydrocarbons dissolved in water moving vertically through capping shales as a result of a hydrodynamic or chemical potential drive, and (3) diffusion of gases dissolved in water. Combinations of these mechanisms may also occur.