Zagros Oils: Interpretation of Source Rock and Geochemistry

Pierce, Walter H.¹, John Zumberge², Steve Brown² (1) WHPierce Exploration, Cypress, TX (2) GeoMark Research, Houston, TX

Geochemistry of the oils from the Zagros Arabian Plate enables interpretation of 312 oil samples coming from 196 oil and gas fields and seeps. Sample locations extend from Turkey, through Oman. The samples come from 70 different hydrocarbon reservoirs. The interpretation utilized over 30 different parameters, including carbon isotopes and biomark­ers. Cluster and principle component analysis support classification and interpretation. The source rock origin of the oils is supplemented by literature review of source rock character­istics. Over 45 potential source rock units are documented. This study recognizes 17 differ­ent oil families. We identify three major mixed-oil associations. Zagros oils come from a diverse set of source rocks, widely varying in lithology and age. Source rock ages ranges from Silurian to Neogene; however, the most oil comes from Jurassic and Cretaceous units. Important but lessor contributions come from Paleogene, Triassic and Silurian source rock ages. Minor contributions come from Neogene and Devonian source rock ages. The Jurassic source rocks appear to become more sulfur rich in the northern Zagros region. The conse­quent trend toward higher-sulfur content of the Jurassic-sourced oils may have important consequences to exploration in Northern Iraq and southeastern Turkey. Oil occurrence demonstrates that oil has migrated to younger stratigraphic units throughout the Zagros province. Vertical migration and mixing of oils occurs less frequently and is more important in the uplifted, folded belt of the Zagros. Infrequently, structural reversal has enabled oils sourced from younger source rocks to migrate into older reservoirs.