Application of Minimum Homogenization Temperatures of Aqueous Inclusions in Calcite Veins to Determine Time of Hydrocarbon Accumulation in Ordovician of Tahe Oilfield: Evidence from In-Situ Calcite U-Pb Dating by Laser Ablation

The homogenization temperatures of aqueous inclusions coeval with the hydrocarbon inclusions are widely distributed in carbonate minerals, which leads to that the timing of oil charge interpreted by fluid inclusion homogenization temperatures combined with burial and thermal histories of reservoir is ambiguity. Taking the carbonate of Ordovician in Tahe oilfield of the Tarim basin as an example, the timing of oil charge determined by the minimum homogenization temperature of aqueous inclusions coeval with the hydrocarbon inclusions combined with burial and thermal histories is suggested and the timing of oil charge in the Ordovician strata of Tahe oilfield was investigated in this study based on the investigation of the lithography, microspectrofluorimetry and microthermistry of fluid inclusions developed in calcite veins combined with the result of in-situ U-Pb dating by laser ablation. There are four episodes of oil charge in Tahe oilfield. The timing of the first to third episodes of oil charge is consistent with the formation time of three calcite veins and the fourth episode of oil charge occurred after the three calcite veins. The results of the U-Pb dating by laser ablation of the calcite veins associated with primary oil inclusions indicate that the absolute age of calcite veins is consistent with the timing of oil charge determined by the minimum homogenization temperature of aqueous inclusions coeval with the oil inclusions combined with burial and thermal histories, which confirmed that the timing of oil charge determined by the minimum homogenization temperature of aqueous inclusions coeval with the hydrocarbon inclusions combined with burial and thermal histories is more credible. Finally, it is suggested that the timing of the four episodes of oil charge in Ordovician of Tahe oilfield occurred at the periods of the Caledonian, the Hercynian, the Indosinian, and the Yanshanian tectonic movements respectively.