四川盆地须家河组水溶气的长距离侧向运移与聚集特征

四川盆地水溶气的脱溶成藏是众多地质工作者研究的重要问题，但仅有少数人找到了不同地区水溶气脱溶成藏的证据。经过对大量天然气的组分特征、同位素特征及成藏条件的研究，认识到川中地区上三叠统须家河组确实存在水溶气的长距离侧向运移与脱溶成藏事件，并从天然气性质的变化特征、同位素特征等方面找到了支持这一观点的证据。该区水溶气的长距离侧向运移存在气源区的超高压、非均质致密储层、强烈侧向压差等3个有利条件，同时也具备顺层压差驱动下的水溶气幕式运移、运移过程中的断续脱气与聚集、天然气聚集规模受连通储集体大小控制等3个重要运聚特点。水溶气的脱溶成藏具有运移距离越远、成藏越晚、天然气越干、越富集重同位素¹³C或²H等特征。水溶气的脱溶成藏也解释了川中地区须家河组气藏普遍含水且气水关系复杂现象的原因。丰富的水溶气资源也是四川盆地未来天然气发展的重要新类型与新领域，值得重视。

Long-distance lateral migration and accumulation of water-solved natural gas in the Xujiahe Formation,Sichuan Basin

Degassing and pooling of water-solved natural gas in the Sichuan Basin is most concerned by many geologic researchers.However,only a few of them have found relevant evidences in different areas.Through the study of compositional characteristics,isotopic features,and accumulation conditions of natural gas,we recognized that long-distance migration and accumulation via degassing of water-solved natural gas did occur in the Upper Triassic Xujiahe Formation in the central Sichuan Basin and found some evidences in respect of the change of natural gas properties as well as its isotopic features.Overpressure in the source area,heterogeneous tight reservoirs and strong lateral pressure difference are favorable conditions for long-distance migration of water-solved natural gas in the study area.The migration and accumulation of water-solved natural gas are featured by episodic migration under the driving of large bed-paralleling pressure difference,discontinuous degassing and accumulation in the process of migration,the scale of gas pool controlled by the volume of connected reservoirs.The longer the migration distance of water-solved natural gas,the later the time of gas pooling,the drier the natural gas,and the higher the contents of heavy isotopes such as 13C or 2H will be.The degassing and accumulation of water-solved natural gas can also explain the phenomenon that water is commonly contained and gas-water contact is complex in the Xujiahe Formation.The prolific water-solved natural gas is a new domain for future gas exploration in the Sichuan Basin.