| Abstract: | Drilling in the eastern continental margin of the Levant Basin (southeastern Mediterranean), offshore southwestern Israel encountered light oil shows, numerous vertically stacked gas pockets and, more recently, commercial gas discoveries. Chemical and stable isotopic compositions obtained for 24 gas samples from Middle Jurassic to Pliocene reservoir rocks suggest that they represent a few genetic systems which are distributed vertically in the section in accordance with the stratigraphy. These groups include bacterial gas in the Pliocene, a mixture of bacterial and thermogenic gas in the Lower Cretaceous, and thermogenic gas in the Jurassic section. The bacterial gases in the Pliocene and the Lower Cretaceous appear not to be cogenetic, and likewise the thermogenic gas in the Lower Cretaceous and the Jurassic sections. Excluding one case, where the thermogenic gas appears to represent phase separation from a probably cogenetic light oil, the relationship of either the bacterial or other thermogenic gas samples to particular potential source rocks in the section or to light oil shows encountered in the Middle Jurassic section is at this stage inconclusive. |
