Evaluation of Upper Paleozoic source rocks of the Hangjinqi block in the northern Ordos Basin,China

The source rock problem on Upper Paleozoic of the Hangjinqi block of the northern Ordos Basin has been hotly disputed.The paper researches the Upper Paleozoic source rocks in the study area by the ways of organic geochemistry and basin model.Carboniferous and Permian formations are two sets of source rocks in the study area.Coalbeds are the best source rocks in the study area,while mudstone is a bad source rock.The coalbed is characterized by 61.32% organic carbon.Type Ⅲ kerogen is the main one with 0.8%~1.3% degree of organic metamorphism a gas-generating source rock and reaches the stage of gas-generating climax.The gas-generating intensity of this rock is(0.1~1.3)×109 m3/km2,and this source rock could satisfy the needs of gas accumulation.The total gas-generating content of Shanxi Formation is more than that of Taiyuan Formation,and the former is the main source rock of the study area.The source rock started to generate gas extensively from Late Jurassic,and the gas-generating climax was in Early Cretaceous.The research shows that the coalbed of Carboniferous and Permian is the main source rock of the Upper Paleozoic gas reservoir of the study area.The methane content variety of gas composition and the gas lateral migration distance further verifies the above conclusion and indicates the gas accumulation in place of Upper Paleozoic of the study area.