HYDROTHERMAL FLUID ACTIVITIES AND MAIN CONTROLLING FACTORS OF DEEP RESERVOIR DEVELOPMENTIN THE LOWER PALEOZOIC OF THE TAHE OILFIELD-TAKING WELLS S88 AND TS1 AS EXAMPLES

⁸⁷Sr/⁸⁶Sr,δ³⁴S and fluid inclusions were analyzed on the fracture fillings of thick dolomites in Wells S88 and TS1 in the Tahe Oilfield.The results indicate that the deep hydrothermal fluid has a significant effect on the dolomite reservoirs of the Penglaiba Formation from Well S88 and the Qiulitage Formation from Well TS1.The hydrothermal fluid is characterized by high temperatures and ⁸⁷Sr enrichment,and may have up-migrated with H₂S and CO₂,which resulted likely from thermochemical sulfate reduction(TSR) of hydrocarbons.The migration of acidic hydrothermal fluid resulted in dissolution of carbonates and generation of abundant secondary vugs and micropores in Wells S88 and TS1,thereby,which improves the quality of reservoir properties.Also,faults and micro-fractures may have served as migration pathways for the hydrothermal fluid in Wells S88 and TS1.The degree to which the hydrothermal fluid influenced on quality of Penglaiba Formation in Well S88 was mostly controlled by lithology and cracks.The reservoir of dolomite strata is better than limestone strata,and fracture zone is prone to form better reservoir.In Lower Qiulitage Formation of Well TS1,TSR was enhanced by the occurrence of gypsum/anhydrite in dolomite strata,and thus might be one of main controlling factors in the development of deep favorable reservoirs.