Analysis on geochemistry of oil shales of the Sargelu formation in central Zagros

Abstract

To investigate the geochemical features of oil shales located in the vicinity of Zardkuh Bakhtiyari (Central Zagros) a section was selected where the sediments have cropped out. The precise location is at the Asal Keshan (AK) in the west of Chaharmahal and Bakhtiyari Province (CMBP). The sediments belong to the Jurassic Sargelu Formation and are composed of black to dark brown shales. The lower boundary is continuous and interfingering with the Neyriz Formation although with the upper formation where lies the Fahliyan Formation the boundary is discontinuous and unconformable. The oil shales in the area have formed at deep sea and in reduction conditions. Notwithstanding, they have never been able to develop oil due to a lack of continuous deposition and high temperature, which the latter is greatly required for oil maturing and development. The sole method to transform kerogen embedded in these shales to oil is Rock-Eval Pyrolysis. Some 10 samples taken from the shales were analyzed by the Rock-Eval Pyrolysis. The result was 9 variables by which diagrams of Tmax, TOC, kerogen type and hydrocarbon generation were constructed. The kerogen is predominantly of II variety. Hydrocarbon generation is restricted to crude oil of good to great oil-generating potential. the data obtained from XRF and ICP geochemical analyses showed that the number of heavy metal indices (NI, Pb, Rb, Sr, V, W, Zr, Zn) and trace elements (Ba, Ce, Co, Cr, Cu, Th, Nb, Ni, Rb, Sr, Mo, U), as well as the percentage of metallic and non-metallic oxides of Sio2, Al2o3, Na2o, Mgo, K2o, Tio2, Mno, Cao, P2o5, Fe203 inside the oil shales, were high. Therefore, the above shales have a dual economic value, which with the increasing reduction of oil and gas energy resources, and minerals can be of special importance in the future in terms of energy and minerals.