THE GENESIS OF THE ZOHAR GAS AS DEDUCED FROM ITS CHEMICAL AND CARBON ISOTOPE COMPOSITION

The hydrocarbon compositions (C₁/ΣC₁—C₄) = 0.96-0.98) and the carbon isotopes ratios of methane (—51.4 to—52.1%) studied in the Zohar Gas Field indicate that the generations of the gas was associated with an oil-generation process. Thus, gas and heavy oils found in the area could have formed simultaneously within one system.
The carbon isotope composition of the CO₂ is relatively heavy, with δ¹³ CO₂ value ofabout +7% which is probably the original value of the CO₂ generated by biodegradation of the cruded oil.
The dissimilarity in the organochemical characteristics of the Kidod shales, which cap the gas reservoirs and the oils found in the region, as well as the low degree of maturation of the Kidod, shales, negate the accepted hypothesis that these shales are the source rock of the heavy oils and the gas found in the Zohar area. The vitrinite reflectance of the reservoir rocks and of the underlying Jurassic sequences, which is only 0.5%, infers that the gas is not trapped near its site of generation.