| This paper will focus on the systematically diagenetic investigation on the Ordovician carbonate rocks in Tahe Oil Field, Tarim basin. On the basis of petrological observation of a great number of shin sections, diagenetic mineral components and stable isotope ratio measurements, eight diagenetic processes have been recognized, such as micritization, compaction and pressure solution, cementation, recrystallization, dolomitization and dedolomitization, silication and thermo-brine / rock interaction etc.. Therefore, the diagenetic sequences have been established, which can be linked to tectonic movement, burial history to give the diagenetic environments as following in the Ordovician carbonate rocks: 1) submarine diagenetic environment, 2) meteoric water diagenetic environment, 3) shallow burial diagenetic environment, and 4) deep burial diagenetic environment. Diagenetic assemblages analysis helped me to determine of diagenetic stages, such as 1) contemporaneously and early diagenetic stage, 2) the anadiagenetic stage, 3) the epidiagenetic stage. The Ordovician carbonate rocks in the Tahe Oil Field are presently in the span of the late of epidiagenetic stage.Through the systematic diagenetic researches above, some useful conclusions for reservoir evaluation have been obtained as follows:(1) Most of the pressure solution sutures formed very earlier, which functioned as the hydrocarbon migration conduits during the uplifts and erosions of Caledonian and Hercynian, and have been characterized by the course of primarily pressure solution, and then opening and finally filling processes.(2) Both the regional distribution of dolomites and dolomitization mechanism analysis in the Tahe Oil Field indicate that the dolomites mainly formed during the middle burial stage, and the lower formations such as Yingshan Formation and Penglaiba Formation had been strongly dolomitized which may become the main reservoirs because a great amounts of intergrannular crystalline pores developed.(3) Some new evidences for deep thermal brines interacted with carbonate reservoir rocks have been found, such as fluoritization, chloritization and decoloration. Microelements measurements suggest that the thermal brine may derive from the magma of Permian activities which took place both in the middle and the north areas of Tarim basin. The discovery of multiple imposed hydrocarbon reservoirs in the middle area of Tarim basin that relates to the fluorite veins reveals that the thermal brines can form dissolved pores and caves. More attention should be given to this type of secondary reservoir.(4) Formation water analysis supports that the organic dissolves mainly derived from the Kerogen pyrolysis, degradation of oil and sulfate reductive reaction with hydrocarbon. The density difference due to temperature changes resulted in the thermal fluids convection, which would produce deeply dissolved secondary porosity especially along southern area of S76-S72 wells. Therefore, the quality of reef beach reservoirs has been improved by this dissolvedprocess.(5) Through the integration of diagenesis with the porosity evolution with time, a prediction pattern of reservoir quality has been established: early diagenesis and nearly subsurface diagenesis-the middle burial diagenesis-the uplifted erosion - resubsidence, which are consistent with four phases of porosity evolution, such as the primary porosity reducing-dissolved caves and fractures developing-caves and fractures filling and decreasing-deeply dissolved pores forming and filling.(6) Coupling the petrological indicators with the fluid analysis, seven diagenetic facies have been firstly outlined. The strong meteoric dissolved facies is the best site of caves, fractures development, and deeply burial dissolved facies is the classical pore-type reservoir. Consequently, the lower part of Yingshan Formation is the high quality of dolomites with intergrannular crystalline pores, and the southwest block of No. 6 area is the deeply dissolved reservoir, and S69 well in No. 1 area...
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