LEBANON REVISITED: NEW INSIGHTS INTO TRIASSIC HYDROCARBON PROSPECTS

A total of only six exploration wells have been drilled in Lebanon since World War II. The exposed succession consists predominantly of competent carbonates, with only minor occurrences of shales and marls. None of these wells penetrated formations older than the oldest exposed at the suflace, which are of Liassic age. In the majority, reservoirs were invaded by meteoric waters as a result of the proximity of elevated, outcropping recharge areas, inencient seals, or the proximity of major faults. Calculations based on gravity data indicate that the basement beneath the Lebanon uplift is some 3 km below sea level, providing for a sedimentary column over 5,000‐m thick below the Upper Jurassic, most of which is unknown. The Triassic successions in the adjacent Palmyride Basin of Syria and of northern Jordan are, by contrast, well‐known from subsuflace exploration and drilling; over 1,500 m of carbonates, with thinner interbeds of shales and evaporites, are present in the former, where a number of Triassic oil, gas and condensate discoveries have been made. The axis of the Palmyride Basin trends WSW, towards Lebanon, as revealed by isopachs; Upper Triassic (Carnian) evaporites, including major salts, have a similar trend. It has long been proposed that if Triassic evaporites extend to Lebanon, they may provide a major impervious seal between meteoric water‐invaded reservoir strata above, and potentially petroliferous Triassic and Paleozoic successions below. The recent marine reflection‐seismic survey offshore Tripoli (northern Lebanon) has revealed the presence of a deeper and tectonically‐ mobilised salt level, in the core of a compressional structure, directly on trend with the westwards prolongation of the Palmyride salt and peripheral anhydrite basin on the other side of the Levant (Dead Sea) transform fault (lateral slip here <20 km). It has given added credence to the speculative presence of evaporites 650m below the oldest (Liassic) exposures at Nahr Ibrahim, north of Beirut, which were interpreted from an earlier electrical survey. A regional seal in the subsurface of Lebanon is thus assured, and the ingredients for Triassic, hydrocarbon generation, migration, entrapment and preservation can now be regarded as present. Both offshore (deep) and onshore (more shallow) prospects of Triassic age therefore seem attractive. Additionally. well‐penetration and seismic data from Syria indicate the presence of Ordovician andd Silurian successions at least under northern Lebanon. These successions regionally include several organic‐rich source levels. and lie within reach of the drill on the large onshore structures of the Lebanon uplift. A second, east‐west trending, basin of Triassic age (the Hawran Basin) extends under the basalt areas of Jaba1 Druze (Jabal al Arab) in southern Syria and northern Jordan, and into the Risha “panhandle” (NE Jordan), offering a frontier Triassic “play”.