Iranian Journal of Oil and Gas Science and Technology

Abstract Knowing the characteristics of suitable environments for the precipitation of oil-prone source rocks facilitates oil explorations and leads to the development of oil fields. The current study investigates the properties of organic matter and sedimentary environment conditions of the Garau formation in various outcrop sections in Lurestan province from southwest of Iran (High Zagros) using elemental analysis, visual kerogen analysis, and Rock–Eval pyrolysis data. The geochemistry parameters indicate that the Garau formation is an excellent oil-prone source rock composed of kerogen types I and II. The oxygen index (OI) is minimal, revealing that organic matter is deposited in an anoxic sedimentary environment, suitable for preserving organic matter and hydrocarbon generation. The visual analysis of isolated kerogens from source rock samples indicates the abundance of dark amorphous organic matter (AOM) with low amounts of phytoclasts and pyrite without any palynomorph. Sedimentation appears to have occurred in deep and reduced parts of a carbonate basin during a rapid transgression. In addition, due to the effect of thermal maturation, the color of amorphous organic matter has darkened. The elemental analysis and van Krevelen diagram are employed to show the type of organic matter and reveal that the thermal maturity is related to the oil window. Elemental analysis reveals the high content of organic sulfur in the structure of kerogen. Moreover, the content of pyritic sulfur (Sp) and organic sulfur (So) is calculated.