THE HYDROCARBON POTENTIAL OF LEBANON: NEW INSIGHTS FROM REGIONAL CORRELATIONS AND STUDIES OF JURASSIC DOLOMITIZATION

F. H. Nader¹ and R. Swennen²

¹ American University of Beirut, Department of Geology, PO Box 11-0236/26, Beirut, Lebanon. email: fadi.nader@aub.edu.lb

² Katholieke Universiteit Leuven, Afd. Fysico-chemische Geologie, Celestijnenlaan 200C, B-3001 Heverlee, Belgium.

This paper presents an updated comprehensive review of the petroleum prospects of Lebanon. We briefly describe the known hydrocarbon shows in Lebanon and compare them with adjacent countries, leading to the construction of a model for hydrocarbon migration which takes into account regional facies and reservoir correlations.

The oldest exposed rocks in Lebanon are the Jurassic carbonates of the Kesrouane Formation (over 1,000m thick). This formation can be divided into a basal unit dominated by seepage-reflux stratabound dolostones (the Chouane Member,) and an overlying limestone-prone unit (the Nahr Ibrahim Member). A two-stage dolomitization model for the Jurassic carbonates in Lebanon has recently been proposed. According to this model, second-stage Late Jurassic hydrothermal dolomitisation is believed to have occurred as a result of the circulation of mixed dolomitised fluids along faults. Hence, the resulting dolostones are fault-controlled and strata-discordant, and may occur at any level within the Kesrouane Formation, locally redolomitising the Chouane Member dolostones and replacing the Nahr Ibrahim Member limestones. Here, we discuss the implications of diagenesis (especially dolomitisation) on the petroleum prospects of the Kesrouane Formation in Lebanon. The hydrothermal fault-related dolostones possess porosities of up to 20%, which result from intercrystalline and mouldic porosity enhancement. Porosities in the stratabound reflux dolostones (Early Jurassic) and limestones are much lower.

The fact that most of the Jurassic system in onshore Lebanon was affected by meteoric diagenesis, during the Late Jurassic - Early Cretaceous and the Cenozoic, may downgrade hydrocarbon prospectivity. However, areas far from the meteoric realm (i.e. offshore) may have been less (or not) affected by meteoric invasion. If effective seals are present here, these areas may include promising Jurassic reservoirs. In addition, we review the prospectivity of unexposed Triassic potential reservoir units in onshore Lebanon (e.g. the "Qartaba"). By analogy with the Syrian portion of the Palmyride Basin, Triassic strata here may include both reservoir units and evaporite seals.

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