Hydrocarbon Generation Characteristics And Shale Oil And Gas Potential Evaluation Of Chang 7 Member Mud Shale In Yan’an Area

The Yanchang Formation in the Ordos Basin is an important stratigraphic series for the exploration and development of continental shale oil and gas.The shale and mudstone source rocks of Chang 7 member of Yanchang Formation have large thickness,wide distribution,high abundance of organic matter,good type,moderate maturity distribution and large retained hydrocarbon content in shale rock.They have good shale oil and gas resources,meet the actual geological conditions of in-situ transformation development,and have great hydrocarbon generation potential in situ transformation.The mudstone and shale of Chang 7 member of Yanchang Formation in Ordos Basin are studied in this paper.Based on geochemical and hydrocarbon generation simulation experiments of Source rock and basin modeling technology.Research on geochemical characteristics,hydrocarbon generation evolution characteristics and shale oil and gas potential evaluation from two aspects of geological history evolution and artificial in-situ conversion for hydrocarbon generation were carried out respectively for mudstone and shale.Research shows:（1）The main distribution range of TOC content in shale is between 5%and 7%,with a maximum of 13.35%and an average of 5.30%.The organic matter type is mainly type II₁;The TOC content of mudstone is mainly distributed in the range of 3%to 5%,with a maximum of 8.77%and an average of 4.03%.The organic matter type is mainly type II₂.（2）The thermal simulation experiment of semi-open column samples shows that the shale R_o of the Yanchang Formation 7 is in a large oil generation stage between 0.8%and 1.5%;The rock powder gold tube closed system simulation experiment shows that the hydrocarbon generation conditions of shale are better than that of mudstone,and the total oil yield of shale is 53.25mg/g TOC higher than that of mudstone at the peak of oil production.（3）Pyrite in Chang 7 shale has obvious positive catalytic effect on hydrocarbon generation of organic matter;The closed gold tube simulation of kerogen sample shows that the lower simulated heating rate is more conducive to shale hydrocarbon generation.The activation energy of large molecule hydrocarbons in the Chang 7 shale is lower,while the activation energy of small molecule hydrocarbons is higher.（4）The hydrocarbon generation potential of shale is stronger than that of mudstone,and the maximum oil generation strength of shale in the Chang 7 section of the study area is currently 220×10⁴t/km²;The maximum gas intensity is 10×10⁸m³/km².The maximum oil generation strength of mudstone is 140×10⁴t/km²;The maximum gas intensity is7×10⁸m³/km².（5）The total oil generation of all shale and mudstone in the study area was close to the maximum after R_o value increased by 0.3%.The total oil generation of shale was220.4×10⁸t,and that of mudstone was 115.1×10⁸t.When the R_ovalue of all shale and mudstone in the study area is increased by 0.6%,the gas generation rate of shale and mudstone reaches the maximum value,which can be used as the economically feasible range for in-situ conversion of natural gas production.（6）Different types of organic matter,different heating powers,different heating rates,and the catalytic effect of inorganic minerals can all influence the hydrocarbon generation of in-situ conversion of organic matter.When in-situ conversion technology is used to exploit shale oil and gas in Chang 7 member of Yanchang Formation,a closed hydrocarbon generation environment should be constructed as far as possible.Shale strata with high pyrite content should be selected as optimization areas,and in-situ heating should be carried out at a low heating rate to maximize economic benefits.