Petroleum Prospects of Lebanon: A New Approach with Implications from Diagenesis Studies and Regional Correlation

Nader, Fadi H.¹, Rudy Swennen², Rob Ellam³ (1) American University of Beirut, Beirut, Lebanon (2) K.U.Leuven, Heverlee, Belgium (3) Scottish Universities Environmental Research Centre, East Kilbride, United Kingdom

This contribution discusses a recent generalized model for hydrocarbon migration in Lebanon, which takes into account rock diagenesis as well as regional facies and reservoir correlations. The model is constructed on the basis of an updated comprehensive review of the petroleum prospects of Lebanon, through description of the known hydrocarbon shows and comparison with adjacent countries. In addition we provide a 3D structural contour model featuring Jurassic and pre-Jurassic potential reservoirs.

The oldest exposed rocks in Lebanon are the Jurassic carbonates of the Kesrouane Formation (over 1,000m thick). This formation is further subdivided into a basal unit domi­nated by dolostone (the Chouane Member) and an overlying limestone-prone unit (the Nahr Ibrahim Member). The Chouane Member consists of stratabound clay/organic rich dolo­stones, similar in texture to Late Triassic and Early Jurassic successions in the Levantine region. These dolostones are gray in hand specimen and have been interpreted to originate through seepage-reflux of evaporated marine water. When least recrystalllized, they exhibit 87Sr/86Sr ratios in the order of 0.707455 confirming their stratigraphic age to be Early Jurassic. Their rock bulk porosity does not exceed 5% and air permeability tests resulted in values not higher than 0.020mD.

Recently, we have discussed a two-stage dolomitization model for the Jurassic carbon­ates in Lebanon, whereby a second stage Late Jurassic hydrothermal dolomitisation is believed to have occurred through the circulation of mixed dolomitised fluids along faults. Hence, the resulting dolostones are fault-controlled, strata-discordant and may occur at any level within the Jurassic rock sequence, locally redolomitising the Chouane Member dolo­stones and replacing the Nahr Ibrahim Member limestones. The hydrothermal dolostone – beige in hand specimen – consist of relatively coarse crystalline planar-e, stoichiometric and well-ordered dolomites, featuring a typical sucrosic texture. They exhibit a clean texture with a higher intercrystalline porosity (average about 6%) and permeability values reaching 0.556mD.