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川西坳陷中段新场气田首获深层上叠统须家河组二段单井高产工业气流，再次证实了川西地区深部致密－超致密砂岩领域具有十分巨大的天然气勘探潜力，真正形成了新场气田从浅层（300m)至深层（4800m)各种不同类型气藏立体勘探开发的壮观场面。本文从天然气有机地球化学角度入手，利用碳同位素和轻烃气相色谱方法，对X851井及邻区须二气藏天然气进行了研究，结合区域地质和岩石有机地化资料的分析，提出了对新场须二气藏形成机制的认识：即以须二段自身和下伏马鞍塘、小塘子组黑色泥、页岩与煤为气源，天然气呈水溶相经自西向东和自下往上两个方面的运移，于晚三叠世末开始在印支期形成的圈闭中富集，由上覆须三段形成区域性岩性封盖和流体压力及浓度封盖而成藏。文中同时论述了X851井发现须二高产工业气流对勘探深层的重要意义，指出了新场及其以西对龙门山前区域是勘探须二气最有利的地区，印支－燕山期古构造圈闭和复合圈闭的研究对于深部气藏的勘探尤为重要。

Research on the Mechanism of Forming Deep T3x2 Gas Reservoir in Xinchang Gas Field in West SichuanDepression - A Discovery of High-Production Commercial Gas in Well X-851 and Its Significance

??High-production commercial natural gas was first found in well X-851 in the deep second member of Xujiahe Formation,Upper Triassic (T₃x²) in Xinchang gas field in the middle section of West Sichuan Depression.It is proved once again that the deep tight??ultra-tight sandstones in West Sichuan region are of the giant potential for natural gas exploration.A magnificent scene of the cubic exploration and development of various gas reservoirs with depths foom 300 m to above 4800 m has been truthfully formed in Xinchang gas field.According to the principle of natural gas organic geochemistry,the gas collected from well X-851 and its adjacent areas was studied by use of the carbon isotope and light hydrocarbon gas chromatogram methods.In combination with the data on regional geology and rock organic geochemistry,it is proposed in the paper that the mechanism of forming T₃x² gas reservoir in Xinchang gas field is as follows:its gas source rocks include the black mudstones,shales and coal in T₃x²,its underlying Ma'antang,Formation and Xiaotangzi Formation;natural gas as a water-soluble phase migrated both from west to east and from bottom to top and beginning at the end of Late Triassic it was accumulated in the trap formed in Indo-Chinese epoch;and the reservoir's closed condition is composed of regional lithologic seal formed by overlying T₃x³,fluid pressure seal and concentration seal.Great significance of discovering high-production commercial gas in well X-851 in T₃x² on deep exploration is expounded in the paper meanwhile and it is pointed out that the most beneficial region of prospecting T₃x² gas reservoirs is the area including Xinchang structure and its west ending up at the piedmont of Longmenshan Mountains;and the study of the Indo-Chinese??Yanshan epoch palaeostructural trap and combination trap is especially important to the deep gas reservoir exploration.