Trends in Organic Geochemistry for Petroleum Exploration

B. P. Tissot, L. Mattavelli

Exploration efficiency has increased since 1970 due to improvements in geophysical treatments and the development of organic geochemistry. Further increase of the success ratio in wildcats is expected during the 1990s from integrating all earth sciences in basin modeling.

Explorationists expect from geochemistry a clear answer to several questions essential for prospect evaluation: existence and location of source rock kitchens, amount and type of hydrocarbons generated, migration paths, and quantity and type of petroleum accumulated in traps. Based on the scientific knowledge developed during the last 20 years, such a clear answer can now be given to all questions related to generation. Kinetic models of oil generation will help us quantify the evaluation. Regarding migration, both approaches--observations and basin model--offer promising trends for individual trap evaluation. However, further work is needed before a quantitative figure of in-place reserves can be given.

Examples of bacterial and thermal gas prospects in the Po basin (northern Italy), mainly from lower Tertiary and lower Mesozoic sources, respectively, are presented. Occurrences of liquid oil at great depth in the same basin are also presented, and the influences of kerogen type, burial history, geothermal gradient, and pressure regime are discussed. Immature heavy oils are present in the Adriatic basin and in Sicily. Their conditions of generation are interpreted with respect to specific type of high-sulfur crudes and burial history. More generally the important role of a late subsidence associated with the Europe-Africa collision is emphasized.

AAPG Search and Discovery Article #91032©1988 Mediterranean Basins Conference and Exhibition, Nice, France, 25-28 September 1988.