Origin of Oils in Helez Region, Israel—Implications for Exploration in the Eastern Mediterranean¹ Available to Purchase

In this case study of oils in the Helez-Brur-Kokhav oil field and nearby shows, organic geochemical criteria were integrated with geologic data to identify the source rocks and migration paths of the oils. The data presented, which include terpenoid biomarkers, isoprenoid ratios, carbon preference indexes, and stable carbon isotopes, clearly indicate that the oils in Helez, Brur, Kokhav, Ashdod, and Ashqelon wells are genetically related and were derived from the same source rocks. Rock extracts (bitumen) from the Lower Cretaceous Gevaram shales differ geochemically from the oils, whereas those of the Jurassic Barnea Formation are similar. Some Barnea samples are apparently stained by oil, whereas others are indigenous rock extracts. Therefore, we concluded that the Barnea samples represent both the rock type from which the oils were derived and the migration path.

The maturity of the oils, determined by C₂₉ 20S/20R sterane ratio (about 0.85% R_o equivalent) as compared with the maturation configuration in the area, implies generation and expulsion from the Barnea rock type at a depth of about 4,500-5,500 m. The impervious blanket of Gevaram shales covering the Jurassic Barnea limestone and the westward inclination of this unconformable boundary funneled the oils updip eastward. The oils were trapped around the zero isopach line of the Gevaram shales in Jurassic and Lower Cretaceous rocks under a combination of stratigraphic and structural controls.

Consequently, further oil exploration should focus on: (1) delineating the Gevaram zero isopach line and identifying adjacent traps, and (2) identifying barriers on the migration path below the Gevaram seal.