Gas Accumulation Mechanism And 3D Modeling In Denglouku Formation Of Changling Gas Field, Southern Songliao Basin, China

The Changling gas field occurs in tight sandstone reservoirs of the Lower Cretaceous Denglouku Formation in the Changling fault depression,southern Songliao Basin,China,which constitutes a new gas-producing area in the depression.Using information on the source-reservoir-cap rock assemblage of the Denglouku Formation,fault activity,and single well burial history of CS1,together with data on reservoir fluid sourcereservoir-cap and laser Raman spectroscopy.Collected data and a large number of data analysis that:we describe the formation of the Changling Gas field and determine that this fault depression did not possess suitable conditions for hydrocarbon generation,Coal-derived methane generated from underlying hydrocarbon source rock accumulated in the Lower Cretaceous Yingcheng Formation.Toward the end of the Late Cretaceous Qingshankou Stage,submarine volcanic eruptions occurred in the northern part of the Changling Gasfield near Qian'an,resulting in the reactivation of deep faults.Mantle-sourced inorganic CO₂ migrated along faults to hydrocarbon gas reservoirs in volcanic rocks of the Yingcheng Formation in the upper crust;at the same time,displaced methane?hydrocarbon gas?migrated upward to sand reservoirs of the Denglouku Formation.The methane accumulated and formed secondary gas reservoirs;thus,fault activity was the main factor controlling the generation of gas reservoir in the Denglouku Formation.Under the microscope,there are gas and liquid phase of inclusion in Changling gas field reservoirs.According to homogeneous temperature data of inclusion analysis,the numerial value is in the range of 99.2¹38.6 ?,the main peak is between 120¹25?.The main peak frequency is about 33%.The main accumulation period of the Yingcheng hydrocarbon gas reservoirs was 82Ma;gas reservoir formation in the overlying Denglouku Formation was 79 Ma,slightly later than the time of formation of the Yingcheng gas reservoir in CS1 well area.At this time?we mean is 79 Ma?,the burial depth of the Denglouku Formation was 1800-2000 m,the degree of diagenesis is relatively weak and the physical characteristic of the reservoir are relatively good,which is not only at gas generation peak time of three sets of source rock but also at reactivation of deep faults in fault-depression stage,providing favorable conditions for the migration and accumulation of methane.