The application of crude oil biomarker and non-biomarker compounds in the determination of migration pathways and filling points of the Asmari reservoir in an oil field from the NE of Dezful Embayment

Reconstruction of migration pathways and filling points in a field provides critical information about the location of the source kitchen and future exploration prospects in the study area. This issue is routinely performed with pyrrolic nitrogen compounds. However, these molecular indicators have encountered some limitations. The alternative solution is using crude oil maturity parameters. The reservoir filling model implies that the early oils that entered the reservoir had lower thermal maturity than the later ones. Hence, the higher-maturity oils are in the closest location to the source kitchen, and the level of maturity has a reverse relationship with the distance from the source kitchen. The signature of maturity differences is also retained after reaching the reservoir to equilibrium, and the composition becomes homogenized during geological time scales. This paper assessed the migration pathways and filling points in the Asmari reservoir from an oil field northeast of the Dezful Embayment. Four crude oil samples were collected and geochemical analyses were performed across the field. The similar geochemical signatures of the studied crude oils indicate that they were sourced from the same source kitchen and belong to the same oil family. The analyzed samples were originated from a marl source rock deposited in an open marine setting with anoxic conditions, and marine organic matter. The oleanane index higher than 20% in the studied samples implies the significant contribution of the Pabdeh Formation in charging the studied field. The thermal maturity of samples shows that all samples were generated from the source rock at the beginning of the oil window. Reconstruction of migration pathways and filling points was performed by biomarker (4-/1-MDBT) and non-biomarker (C29 αββ/(ααα+αββ)) thermal maturity parameters. The isopleth maps of both maturity parameters revealed that the Asmari reservoir was charged from the southeast. Hence, the Pabdeh source rock has a source kitchen in the northeast of the Dezful Embayment