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Julio Perez-Infante1, Enrique Novoa1, Irene Romero1
(1) PDVSA-Intevep, Losteques, Miranda, Caracas, Venezuela

Abstract: Combining surface geochemistry and axial surface map analysis for petroleum exploration

There is a number of geologic factors that affect the expression of gas anomalies on surface: depth and reservoir quality, seal integrity, presence of fractures or faults, as well as vegetation, climate, topography and hydrology. The understanding of all these elements and migration mechanisms of gases in the petroleum system play a key role to make an appropriate interpretation of surface geochemistry data.

Axial surfaces represent the boundary between two adjacent dip panels within a given fold. Recently, methods have been developed to map this feature: the vertical projection and the parallel projection. Axial surface maps define fold trends, constrain underlying fault geometry and slip, and highlight and connect regions that can be interpreted by a series of balanced cross sections. In this work, we propose the integration of axial surface and geochemistry surface anomaly maps to identify leads in fold belts. Vertical projection is used because it preserves the horizontal position of the structure.

As an example of the application and integration of both techniques, we present the results of a study in a region of approximately 300 km2 located in western Venezuela. Most structural trends in the area have a NE-SW orientation. Two of these structural trends have large methane anomalies on top of them. The agreement between structure and methane anomalies in map view has allowed us to define two leads in the region. This result shows that the combination of both techniques is useful to guide exploration studies in fold belts.

AAPG Search and Discovery Article #90914©2000 AAPG Annual Convention, New Orleans, Louisiana