The Characteristics Of Ordovician Reservoir And Paleo-fluid In Tazhong Area

The Yinshan carbonate reservoir formation in Ordovician is the main exploration formation in Tazhong area of the Tarim Basin. Traditionally, the primary pore of sedimentary rock would disappear after it been burded under 6000 meters deep. However, the Yingshan carbonate reservoirs are generally burded more than 6000 meters deep, with a good porosity and permeability, and some dolominate reservoirs porosity can even reach 17%. The pores in those reservoirs are the secondary pores which were formed during the diagenesis stage. Thus the researches on the origin of those secondary pores have important meaning to the exploration and the steadying production in Tazhong area.Firstly, based on the data of the core description of 32 coring wells, microscopic observation and cathode luminescence of core slice and the characteritics of the core slices in the electron microscope, this thesis classified the diagenesis types, described the characters of the carbonate cements and tested the homogenization temperature of fluid inclusions in the carbonate cements, which were used to build the diagenesis sequence. Besides, this thesis used the data of the core, the well logging and the imagery logging technology to describe the characteristics of Yingshan reservoirs, and then classified the reservoir space and tested porosity and permeability of different recervoir. The characteristics and distribution of the karst reservoir and the hydrothermal dissolvent reservoirs were described in Yingshan formation. In addition, based on the testing data of oil field water, strontium isotope and the results of the water injection point on the fracture research in Tazhong area, this thesis analyzed the source of the dissolvent fluid and traced the direction of fluid. Finally, we discussed the evolutionary pattern of the high porosity dolomite reservoirs in Yingshan formation in Tazhong area.Based on the data of the core description, microscopic observation of core slices, the characteritics of the core slice in the electron microscope and geological events in Tazhong area, we believe that the Yingshan formation suffered from dissolution, disruption and cementation after it formed. The formation suffered from karst dissolution when it was uplifted during Caledonian stage. The east part of Yingshan formation in Tazhong area was uplifted and suffered from the disruption during Hercynian stage. The fluorite, celestite and calcite was cemented in its cracks which formed in tectonic activities. The hydrothermal flowed in limestone reservoirs by the cracks and then translated the limestone into dolostone. We believe that the Yingshan formation have three calcite cements, which happened during Caledonian stage, hercynian stage and Himalayan stage separately, after we tested the homogenization temperature of fluid inclusions in calcite cements. The Yingshan formation suffered from pressure solution, metasomatism and hydrothermal dissolution after Hercynian stage. Finally we built the diagenesis sequence of Yingshan formation.Guided by the concept of carbonate reservoir description, and based on the data of well logging, result of diagenesis sequence research and the imagery logging technology, the reservoir space of Yingshan formation in Tazhong area were classified into pores, cracks and caves. The types of Yingshan carbonate reservoirs were also classified into pores-caves-type, cracks-types, caves-type and cracks-pores-caves-type. Finally we found the dolomite reservoirs have greater porosity and better permeability than the limestone reservoirs after tested the porosity, permeability and plane-porosity. The structure-hydrothermal dolomites reservoirs have the highest plane-porosity among the dolomites reservoirs. The Yingshan reservoirs were suffered from karst dissolution when it uplifted on the surface. It multi-period superposed vertically and distributed well horizontally. Then the reservoirs suffered from hydrothermal do lomitization during it burial stage, the size of which is very small. The hydrothermal dolomitized reservoirs are often found by faults, high porosity limestone reservoirs and compacted limestone barrier layer. The reservoirs were dissoluted by the hydrothermal fluid in the late of burial.The hydrothermal dolostone reservoirs are closely related to hydrothermal fluid. Based on the testing data and strontium isotopes of oil field water and the results of the water injection point on the fracture in Tazhong area, we analyzed the source of the dissolvent fluid and traced the direction of fluid. We conclude that the petroleum reservoir have been protected well in ZG5-ZG7 area after it formed. The hydrothermal fluid were injected from the faults-cross-point between the ZG5 strike-slip fault and the NO.I fault. Then the fluid, which dolomitized the limestone reservoir and dissolved the dolomite reservoir, flowed to southwestward, southward and southeastward. Then the limestone reservoir in ZG5-ZG7 area were suffered hydrothermal dolomitization and hydrothermal dissolutionand. Finally, we conclude that the dolostone reservoirs of Yingshan formation in ZG5-ZG7 area were evaluated from high porosity limestone reservoirs, which were suffered from karst dissolution when the formation was uplifted to the suiface and shffered hydrothermal dolomitization and hydrothermal dissolutionand when it burial.