Geochemical evaluation of hydrocarbon source rocks in the Chilingar oilfield along with measuring matrix effect, inert organic material and composition of the active kerogen

Source candidates for the Middle Cretaceous – Early Oligocene petroleum system in the Chilingar oilfield were geochemically evaluated using Rock-Eval pyrolysis and vitrinite reflectance measurements, along with taking matrix retention, inert OM and maturity effects into account. Moreover, the gas-oil ratio potential (GORP) factor was used to split the average live TOC and S2 parameters into the oil-prone and gas-prone constituents. Based on the results, Pabdeh and Gadvan formations have the highest and lowest hydrocarbon potential, respectively. According to the S2 vs. TOC diagram, the mineral retention effect and inert OM content are negligible for the Pabdeh formation. On the contrary, Kazhdumi and Gadvan samples show a significant mineral matrix effect and inert organic material, resulting in a substantial reduction of the hydrogen index and lower apparent quality. Based on the corrected-original parameters, Kazhdumi and Gadvan formations are categorized as mainly oil-prone and gas-prone source rocks, respectively. However, these formations show a low-to-fair quantity of live OM, due to the activities of the Khark-Mish paleo-high during the Cretaceous. In terms of thermal maturity, Pabdeh and Gurpi samples are immature, but Kazhdumi, Dariyan (the upper shaly layers) and Gadvan formations have entered into the preliminary stages of the main oil generation phase. Indeed, insufficient maturity of the source candidates (maximum Ro: 0.72) could be considered as a possible reason for the absence of hydrocarbon reserves in the Asmari and Bangestan reservoirs of the Chilingar oilfield.