Evaluation of Lower Paleozoic carbonate source rocks in Jiyang depression

In Jiyang depression, Lower Paleozoic Cambrian and Ordovician carbonate source rocks are widely distributed.And whether the carbonate source rocks can be commercial oil source rocks and gas source rocks or not is an important problem, which concerns the direction of exploration and investment.In this paper, oil and gas quantity of generation and losing of Lower Paleozoic carbonate rocks in Jiyang depression(Chezhen, Zhanhua and Dongying)have been calculated by the calculation models of oil and gas quantity of generation, oil and gas adsorption in rocks, gas dissolving in oil, gas dissolving in water and gas diffusion.According to the material balance principle, quantity of oil expelling(=net oil-remained oil)and gas expelling(=gas quantity of generation-gas quantity of adsorption-gas quantity dissolving in oil-gas quantity dissolving in water-gas quantity of diffusion)have been calculated, which can be used to evaluate the oil source rocks and gas source rocks of target source rocks.The result shows that Lower Paleozoic carbonate rocks in Chezhen, Zhanhua and Dongying sags are not oil source rocks;those in Chezhen and Dongying sags are not gas source rocks;and that in Zhanhua sag is bad gas source rock.Combining with hydrocarbon generating section of organic matter of Wells Che 25, Gugu 2 and Caogu 101, it is concluded that the bad evaluation of target source rocks is due to the lower organic matter abundance.