SOURCE ROCK EVALUATION AND BASIN MODELLING IN THE GORGAN PLAIN, SE SOUTH CASPIAN BASIN, NORTHERN IRAN

Abstract

Hydrocarbon exploration in the Gorgan Plain to the SE of the South Caspian Basin (northern Iran) has taken place since the 1960s but no economic resources of petroleum have yet been discovered in this area and few studies of potential source rocks have been carried out. In this study, the generation potential and thermal maturity of potential Cenozoic source rocks are investigated on the basis of Rock‐Eval analyses of core and cuttings samples and organic petrographic observations. Hydrocarbon generation, migration and entrapment are evaluated from 2D basin modelling along two seismically‐derived profiles, oriented east‐west and north‐south across the Gorgan Plain area. The models used input data from ten wells.Rock‐Eval analysis of 65 samples from well C in the Gorgan Plain show that organic‐rich intervals with source rock potential are present in the Paleocene‐Eocene section (1.1% TOC) and in the Pliocene Cheleken Formation (1.5% TOC). These intervals in general contain organic matter of terrigenous origin (kerogen Type III) but have poor hydrocarbon generation potential (i.e. Rock‐Eval S1+S2). There is no evidence for an organic‐rich interval in the Oligocene – Miocene succession equivalent to the Maikop Group – Diatom Formation which is a major source rock in eastern Azerbaijan and the adjacent offshore.Results of 2D basin modelling indicate that potential source rocks in the Paleocene – Eocene and Pliocene (Cheleken Formation) intervals are thermally immature throughout most of the study area, but that their maturity increases westwards towards the centre of the South Caspian Basin due to the increasing thickness of the overburden. The source rocks may be sufficiently mature in kitchen areas (at depths of more than 4000 m) to have generated hydrocarbons which may have migrated laterally updip to the basin margins.