The Study On The Formation Mechanism And The Scale Of The Ordovician Hydrothermal Reservoir At Late Hercynian In The Southeast Slope Of The Tahe Oilfield

The research area is located at the Southeast Slope of Tabei upliftin in the Akekule embossment,which had underwent a strong magma volcano activity at Late Hercynian period.The accompanying deep high-heat hydrothermal fluid had a large effect on the Ordovician carbonate during its moving.The research area in this thesis also had a strong effect.But until nowadays,lots of researcher support this opinion that the surficial Atmospheric water karst is the main Formation Mechanism of the carbonate reservoir in the Tahe area,but have a rare knowledge on the dissolving and reforming of the deep high-heat hydrothermal fluid to the carbonate reservoir.So,through this thesis I wish that enriching the Hydrothermal theory research and providing the basis for the oil-gas exploration furtherly.Revolving the Southeast Slope of the Tahe Oilfield as the research object,based on the knowledge about the Structural geology background in the research area,sufficiently using the Sedimentary petrology,Geochemistry,Seismo-geology,Reservoir-geology,Soild-metallogeny,on the basis of the core observation and thin section analysis,the study is aimed at the Ordovician hydrothermal reservoir at Late Hercynian.The specific research results are listed as the following.(1)Through the observation of the petrographic thin section and analysis,there may be two stage hydrothermal geology process in the research area.The first taken place at mid-Caledonian,and the second occurred at Late Hercynian.The former characterize as saddle dolomite,middle-coarse crystalline dolomite,but distribute at partial region reveled nowadays.The later characterize as fluorite,saddle dolomite,pyrite,anhydrite,barite,quartz,calcite,and so on,hydrothermal mineral and the assemblage,then,thermal fading and thermal breaking of the rock,and the generation of the siliceous rock relating to the hydrotherm.The later hydrothermal geology process had a large distribution in the area,and had a large effect on the study area.(2)Through the Geochemical test,finding two kinds of hydrothermal calcite,which respectively represent two different kind of fountain and character deep hydrothermal fluid.They have the following character: ?1 calcite is positive Euexception,and the average value of ?REE,LREE/HREE,(La/Yb)N,?18O,87Sr/86 Sr and inclusion homogenization temperature respectively is 17.9ppm,7.85,8.64,-12.53‰PDB,0.70658 and 156.23?.?2 calcite is negative Eu exception,and the average value of ?REE,LREE/HREE,(La/Yb)N,?18O,87Sr/86 Sr and inclusion homogenization temperature respectively is28.83 ppm,9.34,12.01,-7.8‰PDB,0.71241 and 167.42?.The two types of hydrothermal calcite respectively represent the character of the crust source basic and the mantle source middle-felsic magma hydrothermal fluid,reflecting that having two types of hydrothermal fluid activity.(3)The deep high-heat hydrothermal fluid arrives at the shallow crust through the basement faults,driven by the heat power and pressure difference.Then it enters into the Ordovician strata through the secondary faults,cracks,lithologic interface,unconformity,and fracture zone.The acidic material existing in the fluid dissolutes the carbonate composition with the deposit and replacement of the hydrothermal mineral.In the process,it forms the dissolution modification area between the both sides of the channel,and improves the oil-gas reservoir performance significantly.(4)Based on the observation of the petrographic thin section and analysis,finding that the Ordovician hydrothermal reservoir in the study area is primary dissolution vugs.Furthermore,classified the reservoir as the limestone dissolution fracture-vug type and the silicified silicalite dissolution vug type.The distribution of the hydrothermal reservoir is controlled by the lithology,formation,fault,and so on.(5)The high temperature by the magma activity at Late Hercynian results in the most region in the study area being at the acting region of the deep hydrothermal fluid.Then,through the seismic interpretation,there have been the well versed in the basal and deep in the earth's surface nature fracture,which can provide an open environment.Adding to the multiple unconformity surface,secondary faults,faults,and considering the superposition reconstruction of the atmospheric water karsting and hydrothermal dissolution,the hydrothermal dissolution can happen on a large scale.(6)Combining with the production test,the reservoir interwell connectivity is better along the fault zone than beyond it,which can constitute a large scale reservoir.The reservoir energy analysis indicates that the energy level of the dissolution(karsting)fracture-vug reservoir is both under the higher energy,and the energy level is generally higher along the fault zone than beyond it.