Investigation On Distribution And Hydrocarbon Generation Characteristics Of Source Rocks In Carbonate Platform Of Majiagou Formation,Ordos Basin

In order to reveal the development characteristics and hydrocarbon generation mechanism of carbonate platform source rocks,the Majiagou formation in Ordos Basin was taken as the research object.The development characteristics and controlling factors of source rocks were carried out,and the development model was established.On this basis,through hydrocarbon generation simulation experiment and product test,the hydrocarbon generation characteristics of carbonate source rocks under different mineral participation are revealed.It is found that the carbonate platform facies source rocks in the central and eastern Ordos Basin are mainly vertically developed in The Ma1,Ma3 and Ma5 members of the Majiagou Formation,which are widely distributed on the plane.Among which,we have the saline depressions in the early stage of regression and the local deep depressions in the cyclic salt depressions are favorable environments for the development of source rocks,and the organic matter abundance of source rocks is high.In addition,the development of highabundance source rocks is related to the redox conditions,lithology,water depth and salinity of water bodies during deposition.The salt rock depressions in the regression period are blocked and the hypoxic environment is developed,which is conducive to the preservation of organic matter and is easy to get along with high-quality hydrocarbons.The source rock is developed.In order to reveal the influence of salt minerals on organic hydrocarbon generation in carbonate strata,a hydrocarbon-generating thermal simulation experiment was carried out by adding carbonate,sulfate,chloride and mixed salt(carbonate: sulfate: chloride =4:1:1)to the shale samples of the Ordovician Pingliang Formation in Ordos Basin.The results showed that sulfate and chloride had obvious catalytic effect on liquid hydrocarbon generation of organic matter,and the high value of hydrocarbon generation curve was prominent.The mixed salt has a slight catalytic effect and the hydrocarbon generation curve with addition of carbonate was similar to that without salt with a slight decrease in terms of yield.At 350 °C(Ro about 0.8%),the maturity of organic matter is low,and all kinds of salts have little influence on the generation of liquid hydrocarbon.In addition,the peak stage of oil generation at 450 °C,the yield of liquid hydrocarbon increased by 255%,358% and 2% respectively by sulfate,chloride and mixed salt.During the high evolution stage between 500 °C and 500 °C,the yield of organic liquid hydrocarbons decreased rapidly,and the salt catalysis also decreases.Nevertheless,sulfate can increase the yield of liquid hydrocarbons by 49% to 62% and chlorides by 20% to 24%,while carbonates reduced the yield of liquid hydrocarbons by 21% to 23%.In the hydrocarbon generation process and resource evaluation of source rocks,the influence of salt minerals should be considered.The research results have guiding significance for the deep oil and gas resources evaluation and oil and gas exploration area in Ordos Basin.