مدل سازي بلوغ حرارتي در ميدان نفتي رگ سفيد، جنوب غرب ايران

Thermal Maturity Modeling Of Rag-e-Safid Oilfield, Southwest Iran

In this study thermal maturity of Pabdeh, Gurpi and Kazhdumi Formations in well numbers 112, 2, 33, 99 and 18 of Rag-e-Safid oilfield situated in Dezful Embayment were modeled using Rock-Eval and Vitrinite Reflectance data. Optimization of the model by %Ro and Tmax reveals that there is high geothermal gradient in well number 112 was due to Izeh-Hendijan fault, and also in well number 99, due to the presence of paleo-high (31°C/km and 26°C/km equivalent to 83 and 70 mW/m2 heat flow respectively). Other studied wells had a normal geothermal gradient (with mean of 23°C/km, equivalent to heat flow 63 mW/m2(. TOC data obtained from Rock-Eval analysis, demonstrates a high genetic potential for both Pabdeh and Gurpi Formations, while thermal modeling using Easy%Ro proves that; this rich formations have not entered oil window with respect to their thermal maturity. Gadvan and Kazhdumi Formations have started oil generation at 6 and about 5 million years ago respectively. This is despite the fact that Kazhdumi in Dezful Embayment generally generated oil from 8 to 10 million years before present. This delay in oil generation could be due to low rate of subsidence in the studied oilfield. The model also reveals that the thermal maturity of Kazhdumi Formation has just entered oil window. On the other hand at two locations in the oilfield, Kazhdumi has experienced a higher thermal maturity. At the north of northwest culmination due to Izeh-Hendijan fault and also mid of southeast culmination due to presence of paleo high, the thermal maturity of Kazhdumi has even reached to the end of the oil window. Considering the age of oil generation in the oilfield (5 million years ago), Gachsaran cap rock age (9-13 million years back) and folding in the Zagros to develop the oil traps in 8-10 million years from now, it can be concluded that oil generation started just after cap rocks and oil traps were formed.