Abstract: Primary Migration Within the Querecual Formation: Distribution of Biomarkers

L. Lopez, Z. Sequera, F. Galarraga

Variations in the distribution of biomarkers (steranes and terpanes) as the consequences of primary migration were studied in limestone samples of the type section of the Querecual Formation, Venezuela. These variations were compared with conventional parameters of primary migration such as, variations in concentrations of bitumen, its fractions (saturated hydrocarbons, aromatic hydrocarbons, resins and asphaltene), and the n-alkane distribution.

Biomarkers (steranes and terpanes) show variations along the stratigraphic section that allow the suggestion of the following relative mobility of compounds in the consequence of their primary migration: Tricyclic Terpanes > regular Steranes =(approx.)= Rearranged Steranes > Pentacyclic Terpanes.

Variations of bitumen fractions indicate a greater mobility of saturated and aromatic hydrocarbons vs. resins and asphaltenes, and variations in the n-alkane distribution indicate a relative greater migration of the light n-alkanes (<n-C₂₀) vs. those of higher molecular weight (>n-C₂₀).

These results indicate that primary migration was controlled by the molecular weight and structure of bitumen constituents.

The migration tendencies of all geochemical parameters studied point to a vertical migration from the center toward the top and bottom of the type section of the Querecual Formation.

AAPG Search and Discovery Article #90951©1996 AAPG International Conference and Exhibition, Caracas, Venezuela