Leading effect of high-class source rock of Chang 7 in Ordos Basin on enrichment of low permeability oil-gas accumulation——Hydrocarbon generation and expulsion mechanism

Based on geochemical testing,hydrocarbon-generation thermal simulation experiment,and the basin petroleum geologic characteristics,the paper analyzes the hydrocarbon-expulsion and mechanism of the high-class source rock in Chang 7 oil-shale section,and calculated the hydrocarbon expulsion rate.The yield of Chang 7 is up to 400kg/t.TOC and its increasing pressure action from hydrocarbon-generation expanding can offer enough energy for oil primary migration(hydrocarbon-expulsion).The kerogen network system and the pore-fracture system constitute a three-dimensional network system for the migration.The continuous oil phase is the main phase of primary migration.The intense compaction before the oil shale section matured and generated oil do not have any effect on the hydrocarbon-expulsion efficiency,on the contrary,the lower residual porosity reduces the capacity to occlude hydrocarbon, which is helpful to enhance hydrocarbon-expulsion efficiency(the average reaches 72%) and makes the high-class source rock have the good quality fluid with high hydrocarbon and low water.This provides advantageous conditions for crude oil concentration of low permeability reservoir.