关键词: 四川盆地, 海相天然气, 成藏特征, 硫化氢, 硫酸盐热化学还原反应, 原油裂解, 勘探潜力

Abstract: Some giant gas fields recently discovered in the Lower Triassic Feixianguan Formation at the northeast part of Sichuan Basin proved that this basin is very rich in natural gas.Gas is mainly stored in the porous reservoir with high proportion of hydrogen sulfide normally being from 0.2% to 17% of the total gas volume.The hydrocarbon gas components were derived from thermal cracking of crude oil.Plenty of gas sources provided basic materials,and palaeo-uplift provided the traps for oil and gas accumulation.Gypsiferous-rich dolostone reservoir offered sulfur and catalyst conditions for the formation of hydrogen sulfide gas.The most deeply buried marine sediments provided the thermal conditions for thermochemical sulfate reduction (TSR),which leads to the formation of hydrogen sulfide.TSR provided catalysts for oil cracking,which leads to rich methane and hydrogen sulfate in gas reservoir.The Feixianguan and Changxing formations are the most practical exploration targets due to good accumulation conditions.Potential targets exist in the thin and sheet-like porous dolostones near gypsum,particularly in the Triassic Leikoupo and Jialingjiang formations.The best exploration potential is in the east parts of Sichuan Basin.

Key words: Sichuan Basin, marine natural gas, accumulation characteristics, hydrogen sulfide, thermochemical sulfate reduction, oil cracking, exploration potential