MACGREGOR, DUNCAN S., BP Exploration Operating Company, Uxbridge, England

ABSTRACT: A New Look at an Old Tool: The Exploration Significance of Surface Seepage

The mapping of visible petroleum seepage was one of the most important exploration techniques used to locate wells in past times, with varying levels of success. With seepage again becoming important in offshore frontier exploration, it is appropriate to reexamine the relationship between seeps and commercial reserves. This has been attempted by a study of documented seeps in the mature petroleum provinces of southeast Asia, tied to a broad study of seepage worldwide.

Seepage seems to be a good indicator of petroleum potential on a broad regional scale. Major hydrocarbon provinces that are tectonically active and have generated their petroleum in recent times usually show large numbers of seeps. Correlations can be identified between numbers of seeps and reserves for different basin types.

Good relationships between seeps and petroleum reserves are, however, rarely seen at prospect or field scales. Seep locations seem to be controlled more by local tectonics and often occur well updip of major oil fields. Three main origins of seeps are considered: focused secondary migration, lateral tertiary migration, and vertical leakage from accumulations. Seep and oil field locations correlate only for seeps derived by the latter model, with no general relationship to field size.

It is likely that most of the value of onshore seepage has been realized. The prime value of seeps in the future is therefore thought to lie in regional scale analyses of offshore frontier basins. An example is shown from the Black Sea.

AAPG Search and Discovery Article #90990©1993 AAPG International Conference and Exhibition, The Hague, Netherlands, October 17-20, 1993.