Research On Characteristics Of Sedimentary Facies And Hydrocarbon Accumulation In Tongfosi And Dalazi Formation Ofyanji Basin

Yanji basin is a Mesozioc fault basin in the east of jilin province,40km from eastto west,50km from north to south,the basin area of1670km2.Yanji basin is strongly influenced by Yanshanian tectonic movement representedby Tan Lu fault zone. It is one product from the tectonic nappe in the east side of TanLu fault zone, when plate amalgamation with the eastern part of the paleo-Asian platehappens. Yanji basin is a Mesozioc fault basin shown as a tectonic framwork of twodepressions separated by an uplift and a slope in the west. This framework infers thatbasin suffers an intensive tensional stress in E-W direction during the basin formingstage, but it is controlled by tectonic compression in the late of upper Cretaceous.According to lots of outcrops, cores, logging data and seismic data, depositioncharacteristics and sedimentary facies have been seriously studied. Two mainsedimentary are developed in Tongfosi and Dalazi formation, and they are fan deltafacies and lacustrine facies. Fan delta facies are divided to fan-delta plain and frontfan-delta and lacustrine facies are divided to shore-shallow lacustrine and fairlydeep-deep lake. Fan delta facies are identified in both Tongfosi and Dalazi formation,but fan delta facies are most developed in Dalazi fomation and provenance supplyadequate. While lacustrine facies predominantly developed in Tongfosi formation,barely found in Dalazi formation. By studying the sedimentary facies planar graph oftongfosi formation, provenance mostly comes from western,and others comes fromnortheastern and southern of the basin Compared with Tongfosi, Dalazi formationhave an adequate sediment supply from all directions of basin, during this periodmaximum-flooding surface is formed, but water becomes shallower.Through studying the distribution discipline and evaluation of source rocks inTongfosi and Dalazi fomation, it is indicated that source rocks mainly distribute in tongfosi and lower part of dalazi formation. And the average of TOC in the firstmember of Tongfosi formation are2.56%；The average of TOC in the second memberof Tongfosi formation are2.22%；The average of TOC in the third member ofTongfosi formation are1.86%.Kerogens of Tongfosi formation are mainly typeⅠ-Ⅱ.Hydrocarbon source rock vitrinite reflectance distribute0.5%to1.0%, belong to thelow mature-mature stage. According to the source rock thickness map can be seenthat three subdepression in Tongfosi formation have a certain thickness of thehydrocarbon source rocks and the average thickness of the hydrocarbon source rocksare distributed in150~250m.It is belong to good source rock stratigraphicposition.But the average of TOC in Dalazi formation are0.95%. Hydrocarbon sourcerock vitrinite reflectance distribute0.3%to0.6%, belong to the low mature-cruditystage. Kerogens of Dalazi formation are mainly typeⅠ-Ⅱ.It is belong tomedium-poor source rock.By the test analysis of the sandtone reservoir property,the major reservoirsandstone bodies in Yanji basin are fan delta.Sandstone in Dalazi fomation is mostdevelopment, which accumulated the thickest sandstone in Chaoyangchuandepression, the thickness exceeds more than520m, evenly distributed in the200~320m；The thickness of sandstone in Tongfosi formation is much thiner than thesandstone in Dalazi formation.But the sandstone deposit thickest in Dexin depression,the thickness exceeds more than516m. The reservoir sands are dominated by siltstoneand fine sandstone and medium sandstone. The reservoir in this basin mostlyperformance low porosity and low permeability，it is medium porosity and lowpermeability in the third member of Tongfosi fomation and low porosity and mediumpermeability in the frist member of Dalazi formation. Through Mercury penetrationanalysis,main reservoir pore structures are Ⅱ-Ⅲ type and pore throat radius isrelatively small overall.Through analysis of the trap in this region, most of types of traps arefault-controlled structural traps.Six effcetive structural trps are interpreted in Tongfosifomation, and six effcetive structural trps are interpreted in Dalazi fomation.Thesetraps mainly belong to Nose-Shaped structural、fault block、faulted anticline traps.Trap forms on the end of the Upper Cretaceous.when the secondary hydrocarbon migration into the traps which have been formed, so they formed a hydrocarbonreservoir type.The mainly types of hydrocarbon reservoir are structures, lithologicreservoirs, and structural reservoir is further divided into fault block、faultedanticline traps、Nose-Shaped structural.lithologic reservoirs carved out of sandstonelenses hydrocarbon reservoir.Hydrocarbon reservoirs have been found in the threesubdepression.And there is certain commercial oil flow in Yan10well.In Yan4wellthere is also low yield commercial gas flow,and gas type belongs to biogenicgas.These hydrocarbon reservoirs are controlled by the faults.In Yancan1well,there iscertain oil stream,but it doesnot fomatis industrial oil flow...