Geochemical investigation of petroleum source rocks by using Rock- Eval data in the Agha-Jari oilfield

In this study، 40 drilling cutting of the Pabdeh، Gurpi، kazhdumi and Gadvan Formations from the Agha-Jari Oilfield were analyzed by using Rock-Eval pyrolysis. In order to recognizing sedimentary environmental conditions of studied Formations، they are divided to 4 zones which A (Kazhdumi Formation#187) and C (Kazhdumi Formation#140) zones show reduction conditions by presence of sea organic materials and B (Gadvan Formation #140) and D (Gadvan Formation#187) zones show oxidation conditions by presence of continental organic materials to basin. Based on the Rock-Eval pyrolysis data، the Pabeh، Gurpi، Kazhdumi and Gadvan Formations have variable hydrocarbon generative potential. HI vs. OI plot revealed that the kerogen type in this Formations is a mixed of types II & III. The intensity of matrix effect in the Pabdeh، Gurpi، Kazhdumi and Gadvan Formations was compared by using S2 vs. TOC plot and calculating its regression equation. The results show that the significant amount of S2 adsorption by matrix was happened in the Pabdeh (4. 98-6. 96 mg HC/gr rock in wells 113 and 121) and Gurpi Formations (4. 33 mg HC/gr rock in well 113) which is due to their low thermal maturity (Tmax<430) and low Gas-Oil Ratio. In the well number 187 the amount of S2 adsorption by matrix effect in the Gadvan Formation is about 0. 13 mg HC/gr rock showing relatively high thermal maturity. Due to the fact that most of samples are mature، they have reached the oil generation window and show high GORP. Accordingly، the least amount of mineral matrix effect is related to the Kazhdumi and Gadvan Formations. The amount of TOClive in the Pabdeh، Gurpi، Kazhdumi، and Gadvan Formations lies in the ranges of 0. 27-1. 64 (lean to good source rocks)، 0. 14-0. 64 (lean to fair source rocks)، 1. 85-2. 27 (good to excellent source rocks) and0. 30- 0. 51 (lean to fair source rocks). GORP factor for studied formations were (0-1) which reveals variable range of oil and gas generation potential.