Multiple hydrocarbon charging and post-accumulation alternation processes of deep oil and gas: A case from well ZS1, ZS5 and ZH1 in Central Fault Belt, Tarim Basin

Deep subsalt oil and gas reservoirs are important exploration targets due to their substantial potential. This study investigates their thermal evolution and accumulation history using an integrated approach. Geochemical data indicate that oils in the intrasalt and subsalt intervals are highly mature. Fluid inclusion analysis integrating with petrographic observation and microthermometric measurements reveals two major hydrocarbon charging events. An initial oil charge, characterized by yellow-green and blue fluorescent oil inclusions, occurred during the late Caledonian to early Hercynian orogeny. A later phase in the late Hercynian involved light oil (blue-fluorescent inclusions) and natural gas. Post-accumulation processes, including limited oil cracking and thermochemical sulfate reduction (TSR), subsequently altered the reservoirs after hydrocarbons remigrated to suprasalt trap. Several evidence including high-maturity bitumen, dry gas with heavier δ¹³C₁ and U-Pb dating on TSR-calcite support these alteration processes during Indosinian period. This research provides critical insights into the complex history of hydrocarbon generation, migration, accumulation, and alteration in deep reservoirs. The integrated methodology offers a valuable template for assessing exploration potential in similar petroleum systems.