03399nam a2200169 4500 20260520010215.0 260224s xxu Rabbani, A.R. 46204 World Gas Conference (24th. : 2009 oct 5-9 : Buenos Aires, Argentina) 45995 ORIGIN OF NATURAL GAS IN SOUTH OF IRAN 2010-08-03 ; 2010-08-03 9 p. Trabajo presentado en el 24 WGC. Disponible en CD en la biblioteca. Solicite este trabajo por email a biblio@iapg.org.ar Isotopic geochemical characteristics were determined in gases and condensates from southern Iran, which is one of the world's richest gas-bearing territories. The isotopic composition of methane and its homologues, the carbon isotope composition of CO2, the chemical composition of gases, the isotopic composition of condensates, and the proportions of individual hydrocarbons in the condensates were analyzed. The analytical results demonstrated fairly uniform chemical compositions for gases and isotopic compositions of methane and its homologues in the section overlying the anhydrite zone. For instance, the values d13C of methane in samples from this part of the section (Late Permian Dalan Formation, zone D,C,E and Early Triassic Kangan Formation) varied from -39.95 to -41.28‰. This allows us to conclude that gas accumulations in the carbonate collectors of the Kangan and upper part of Dalan formations represent a single gas reservoir. Quite different characteristics are displayed by gases from the lower zone (below the anhydrite) of the Dalan Formation (zone G). These gases are characterized by considerable depletion in the light carbon isotope. For instance, methane from the lower part of Dalan formation have d13C = -26.22‰. They show also a number of other distinctive features: significant enrichment in nitrogen, occurrence of isotopically light CO2; (d13C = -21.87‰), and an inversion in the isotope relationships of ethane and propane. These peculiarities suggest that the composition of gases in this zone was modified by the process of the thermal chemical reduction of anhydrite. The isotopic compositions of condensates from the overlying and underlying the anhydrites zone are similar. The source of gases could be either the rocks of the Dalan Formation or Ordovician-Silurian shales. The formation of gas accompanied by condensate began when the Ordovician-Silurian rocks entered the stage of catagenesis corresponding to RO = 1.0-1.2%, which probably took place at the end of the Jurassic and beginning of the Cretaceous. The gas formation continued simultaneously with the burial of the sedimentary prism. Younger deposits including Permian ones entered the stage of gas generation. The Permian-Triassic collector was filled with gas. The subsequent portions of gas and condensate were accumulated in the lower part of the Paleozoic section. At that time, both the graptolite shales and anhydrites occurred at depths where the process of the thermal chemical reduction of sulfates exerted considerable influence on the composition of gases and organic matter. This resulted in the formation of the observed geochemical characteristics of gases in the lower zone, which are significantly different from the geochemical characteristics of gases from the upper zone. CONGTP 175709 175709 0 0 0 0 243528 BAAB BAAB 2026-03-05 200047608 0 200047608 2026-03-05 18:56:06 2026-03-05 CONGTP