AAPG Annual Convention and Exhibition

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Assessment of Controlling Factors in Mixed Biogenic and Thermogenic Petroleum Systems – A Case Study from the Levantine Basin

Abstract

The Levantine Basin in the Eastern Mediterranean has become an attractive area for oil and gas exploration due to pioneering efforts of several E&P companies which have resulted in the discovery of major gas fields in the pre-salt sequences. Information on whether the gas in these new discoveries is of biogenic or thermogenic origin was restricted for a while, as the strategic implications of this knowledge are clear: if the gas is thermogenic, then the chance of deeper thermogenic oil potential could be reduced or even excluded, while biogenic gas would leave an opportunity open for deeper thermogenic systems which could include oil. Publicly available knowledge is developing quickly and it is now accepted that the gas that has been discovered so far in fields such as Tamar and Leviathan is of biogenic origin. As a result, exploration for deeper thermogenic systems is now under way. We will present a sensitivity analysis of the basic elements of the petroleum systems based on the data that is publicly available at the time of the presentation. In the first part, a regional type-section is used to show the data and interpretations related to the construction and calibration of the model, as well as the underlying assumptions that were used to constrain the model properties and boundary conditions. In the second part of the talk, we will then investigate the properties and processes related to the formation of the currently known biogenic system within these constraints. This will include gas generation, migration and accumulation timing and the controlling factors such as biogenic generation kinetics, gas migration volumes and rates, and seal quality evolution through geologic time. This will enable us to illustrate sensitivities in the system and how well it can be constrained, and also to assess the timing relative to the Messinian Salinity Crisis. In the third and final part, we then assess the assumed deeper thermogenic petroleum systems which are at the moment speculative in the study area, and show which range of conditions could lead to the co-existence of biogenic and thermogenic petroleum occurrences. We will be updating the presentation with the latest information available from ongoing exploration efforts in the region. This will be of particular interest, as these activities are expected to result in important enhancements of our knowledge of the role and potential of thermogenic petroleum systems in the area of interest.