Estimating Total Organic Carbon Content and Source Rock Evaluation, Applying ΔlogR and Neural Network Methods: Ahwaz and Marun Oilfields, SW of Iran

Abstract

Well logging is a useful method for sedimentary basin and source rock evaluation. Source rocks have special responses in porosity and resistivity logs that can make them distinguishable from surrounding rocks. Therefore, well logging data and diagrams can be used as indicators of determination of source rock potential. Characterizations of Kazhdomi, Pabdeh, and Gurpi source rocks have been determined by geochemical analysis in some Iranian oilfields, but no total organic carbon (TOC) zonation and interpretation have been carried out in these formations yet. Several studies have confirmed the petroleum potential of the Kazhdomi formation in Dezful Embayment, but Pabdeh formation (more significant) and Gurpi (less significant) have been always the topics of Iranian petroleum geologist discussions in order to deermine whether these formations have the potential of generating oil and what the organic matter properties of these formations are. The purpose of this article is to calculate TOC values of the Pabdeh formation in Ahwaz and Marun oilfields using a combination of sonic and resistivity logs (ΔlogR method) and a neural network method. Then these TOC values were compared with TOC from geochemical analysis. Finally, the zonations of source rock in terms of TOC richness were carried out and TOC changes in the oilfields were shown by plotting Iso-TOC maps. It was found that due to the high local temperature gradient Pabdeh reaches an oil window level in some parts of Ahwaz and Marun oilfields. Hence, Pabdeh acts as a source rock for these two oilfields in some sections.