川中地区须家河组致密砂岩气藏气水分布形成机理

川中地区须家河组致密砂岩气藏因气源供应不足形成了气水过渡带；因成藏充注较早导致了区域大面积含气；因砂岩储层致密造成了气水混杂分布；由局部构造幅度控制了气水分异程度；由储层裂缝提供了气水渗流通道。该区须家河组气藏气水分布的形成机理可归纳为：晚三叠世末至晚侏罗世的未熟-低熟天然气在局部构造控制下于构造闭合高点处形成纯气顶；早白垩世—古近纪大量生成的天然气因砂岩储层致密而无法完全驱替出孔隙水，形成气水混杂分布格局；古近纪以来的喜马拉雅运动形成大量裂缝，改善了储层物性，在裂缝发育带聚集成藏。

Mechanisms of gas-water distribution in tight sandstone gas reservoirs of Xujiahe Formation,central Sichuan Basin

Tight sandstone gas reservoirs of the Xujiahe Formation in central Sichuan Basin were observed to have many features.They contain gas-water transition zones that may be due to inadequate supply of gas from source rocks,pervasive gas distribution possibly as a result of early gas charging during gas accumulation,mixed gas/water distribution because of the tightness of sandstone reservoirs,control of local structural amplitude on gas-water differentiation and fractures acting as seepage channels for gas and water.The gas-water distribution pattern in the reservoirs may be explained as follows:immature-low mature gas that were generated during the Late Triassic to Late Jurassic accumulated and formed the pure gas cap on structural high under the control of local structure;the large amount of gas generated during the Early Cretaceous to Paleogene could not completely displace pore water due to the tightness of sandstone reservoir,resulting in mixed gas/water distribution;the physical properties of the reservoirs werer greatly improved by numerous fracutures formed during the Himalayan movement since the Paleogene.All these conditions worked together to form the present tight gas reservoirs in the formations of the basin.