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Analysis of the Industry Lower Tertiary Discoveries and Failures in the Gulf of Mexico: Guidelines for Prospect Risk Analysis

William H. Schoellhorn and Gwenael Guerin
Total E&P USA, Inc, Houston, TX

To better assess risk and maintain coherency between prospect assessment and failure analysis with regional trends in the deep plays of the Gulf of Mexico, Total is performing analysis on ninety exploration wells that have targeted Paleocene-Eocene, Lower and Middle Miocene subsalt, sub detachment and Foldbelts.

Since 1995 to present-day, the deep Miocene shows a success ratio of 30%, compared with the more recent exploration of the Paleocene-Eocene that has a success ratio of 60%. The post-mortem analysis shows that the main failure exhibited in both plays is the geometry. This risk has been quite constant through time, but appears in the last two years as nearly the unique reason of failure: the well may be outside of closure, or the trap is incompletely formed, both the results of poor seismic imaging. The reservoir risk was originally important and constant, but has diminished in the last three years, following the learning curve on the Miocene paleogeography, and due to the large extent of the Paleocene-Eocene sands. Reservoir properties are nevertheless still a risk, especially for the Paleocene–Eocene play. The Petroleum System risk has never represented an important reason of failure, following again the industry learning curve concerning maturity prediction for example. The migration/timing failures are difficult to assess, and could constitute a hidden risk. The seal is not seen as a major reason of failure, but may also be underestimated as related to the geometry.

The greatest challenges ahead remain with the correct imaging and interpretation of the prospect geometries.