Abstract: The upper Triassic formation is the primary hydrocarbon source rock of the western Sichuan Depression.The second section and forth section of Xujiahe Formation are the main reservoirs.The peaks of hydrocarbon generation and expulsion of the upper Triassic formation appeared in the Late Triassic and Middle-Late Jurassic periods.The early hydrocarbon generation and expulsion led to form oil-gas reservoir early.The reservoir evolvement shows that tightening completed at the end of Yanshanian froze up oil and gas of palaeo-trap.The multi-episodic superimposition of the tectonic movement modified the palaeo-trap and made it complicated and subtle.The analysis on known gas reservoirs and exploration areas shows that there are five types of palaeo-trap including palaeostructural-diagenetic trap,palaeostructural-lithologic trap,palaeostructural trap,superposed structural trap and stratigraphic-lithologic trap.The exploration and research results proved that the Late Indosinian and Yanshanian traps are available.Seeking for palaeo-trap by structure evolvement combining seismic-logging technique is a practical way for gas exploration in the tight reservoir of Xujiahe Formation in the western Sichuan Depression.

Key words: western Sichuan Depression, Xujiahe Formation, palaeo-trap type, subtle trap, identification technology, tight reservoir

摘要： 上三叠统是川西坳陷的主力烃源岩,其中须家河组二段、四段是主要储层.上三叠统烃源岩的生、排烃高峰在晚三叠世和中—晚侏罗世,其生、排烃高峰早,成藏早.储层孔隙演化史表明,燕山期末的致密化"冻结"了早期圈闭的油气,喜山期构造运动的叠加改造,使得古圈闭向复杂、隐蔽圈闭转化.对已知气藏和勘探区的解剖分析表明,该区有5种古圈闭类型:即古构造-成岩圈闭、古构造-岩性圈闭、古构造圈闭、古今叠合构造圈闭和地层岩性圈闭.勘探实践证实,印支晚期—燕山期的古圈闭是有效圈闭.利用构造演化分析,结合地震、测井等识别技术寻找古圈闭,是川西须家河组致密储层气藏切实有效的勘探途径.

关键词: 川西坳陷, 须家河组, 古圈闭类型, 隐蔽圈闭, 识别技术, 致密储层