涪陵页岩气田发现的启示与思考

Discovery and characteristics of the Fuling shale gas field and its enlightenment and thinking

位于四川盆地东缘焦石坝构造的涪陵页岩气田,已探明地质储量3 806×108 m3,是北美地区以外,首个实现商业开发的页岩气田。焦石坝构造是一个受北东向和南北向两组断裂体系控制形成的菱形断背斜,其特殊的构造背景对页岩气的富集具有重要控制作用。涪陵页岩气田的产层为五峰组-龙马溪组页岩,具有富有机质页岩厚度大、有机质丰度高、有机质热演化程度高、脆性矿物含量高、地层压力系数高、单井产量高、裂缝发育、烷烃碳同位素倒转等特点。3年的勘探开发表明,涪陵页岩气田普遍高产、稳产,证实为高产富集的页岩气田。本文通过对区域地质特征的解剖和对涪陵页岩气田基本特征的总结,结合前人对美国页岩气田的研究,提出了涪陵页岩气田发现的启示与思考。结论认为:首先,证实中国存在高产页岩气田,但富集因素与美国不同,正向构造和晚期区域走滑作用极为重要;其次,天然裂缝的发育是页岩气富集高产的关键;第三,几乎所有的商业性页岩气田都是地层超压;第四,讨论了页岩气的运移问题,认为页岩气通过短距离的运移传递,可以实现大范围的运移聚集;第五,提出基于商业回报和资源利用不同角度的考量,可能会影响生产方式的选择;第六,中国页岩气发展需要技术、思路创新和长远视角,必须重视深层海相、陆相和盆地外常压页岩气的研究。

The Fuling shale gas field is located at the Jiaoshiba structure,eastern margin of the Sichuan Basin,which has proven geological reserves of 380.6billion cubic meters.It is the first commercial shale gas field outside the North America.The Jiaoshiba structure is a rhomboid faulted anticline,which is controlled by the north-east and north-south trending fault systems,whose special structural settings play an important role in shale gas enrichment.The Fuling shale gas production layer is Wufeng-Longmaxi shale,which is characterized by a large thickness of organic-rich shale,high content of total organic matter（TOC）,high degree of thermal maturity,high content of brittle minerals,overpressure,high initial production rates,well-developed natural fracture networks and alkane carbon isotopic reversal.After more than three years of development,it is confirmed that the Fuling shale gas field has abundant shale gas resource with stable production and high formation pressure.Through the analysis of regional geological features and comparison with gas fields in the U.S.,the basic characteristics,enlightenment and thinking of shale gas in Fuling are summarized and put forward.Firstly,there are high production and enrichment of shale gas fields in China;but the controlling factors are different from the gas fields in the U.S.Forward structure and advanced regional strike-slip effect are extremely important.Secondly,the development of natural fractures is key to the enrichment of shale gas.Thirdly,almost all of the commercial shale gas plays have overpressure.Fourthly,through the migration and transportation of shale gas by relatively short distances,a wide range of migration and accumulation could be achieved.Fifthly,the production patterns based on different perspectives of business returns and resource utilization may impact the production performance of the Fuling shale gas field.Finally,the development of China＇s shale gas needs technology,innovative thinking and long-term perspective,and we must pay attention to the studies of shale gas in the deep marine continental strata and normal pressure strata in the outer of basin.