Organic geochemical characteristics, depositional environment and hydrocarbon potential of bituminous marls in Bozcahüyük (Seyitömer/Kütahya) Basin

Abstract

In this study, the geochemical properties, sedimentation conditions and hydrocarbon potential of the bituminous marls, having quite rich organic carbon content (average 9.27% TOC), composed of gray-green colored, dominant marl lithology with marl-claystone intercalation in the Bozcahüyük (Seyitömer/Kütahya) Basin has been evaluated. In this context, Rock-Eval pyrolysis, Gas Chromatography (GC), Gas Chromatography-Mass Spectrometry (GC-MS) and Modified Fischer Assay (MFA) analyses of the samples taken from the study area were performed and their organic facies have been evaluated. The marls have an excellent source rock characteristics, and include kerogen predominantly as Type I and rarely as Type II. The precipitation of organic matter took place under reducing anoxic redox conditions where oxygen was limited. Analysed samples contain terrestrial phytoclasts and palynomorphs as well as freshwater algae indicating Type-I kerogen such as Botryococcus braunii. Organic geochemical data show that the study area is deposited in the “AB” organic facies continental-marine transition zone. Carbon preference index (CPI), C₂₇, C28 and C29 steran abundance distribution of the samples as well as presence of Gamesaran as a salty environment indicator indicates that the lake enironment has been under marine environment influence from time to time and thereforethe study area have lagoon character. The average of the Tmax values of analysed samples is 432 °C and it was determined that the bituminous marls in the region could not produce conventional petroleum due to their immaturity. However, it has been evaluated that these marls have the potential to produce synthetic petroleum as the kerogen types are dominantly Type-I, TOC and HI contents are high, as well as the analyzed samples have an average of 12.60% (133 L / ton) MFA oil content.