Assessment of the thermal maturity of the effective hydrocarbon source rocks in Dongying Depression

The vitrinite reflectance value of the effective source rocks of the upper sub-member of the fourth member and the lower sub-member of the third member of Paleogene Shahejie formation (Es) in Dongying Depression is significantly suppressed.The maturity of the two sets effective source rocks is reassessed by means of FAMM (fluorescence alteration of multiple macerals) analysis results.The study shows that the vitrinite reflectance suppression level of the source rocks of organic matter typeⅠranges from 0.24% to 0.35% generally,and that of organic matter type Ⅱ1 and type Ⅱ2 usually ranges from 0.16% to 0.30% and 0.13% to 0.18% respectively.The true thermal maturity of the effective source rocks of the lower sub-member of Es3 and the upper sub-member of Es4 is mainly in 0.56%～1.01% and 0.58%～1.30% separately;but the thermal maturity of them determined by vitrinite reflectance values is in 0.35%～0.80% and 0.37%～1.10% respectively.The study result in this paper has an important role in recognizing the thermal maturity of the source rocks,reevaluating the genesis of oils and the potential of oil resources,and guiding oil and gas exploration.