川中地区上三叠统须四段厚层砂体成因及油气运移通道分析

Thick-bed sand body genesis and oil-gas migration pathway in the forth member of Xujiahe Formation of Upper Triassic in the central Sichuan Basin

川中地区上三叠统须四段砂体厚度大,沉积稳定,具有近物源区的三角洲平原—三角洲前缘—滨浅湖沉积特征。沉积物在形成时期,供应速率与可容纳空间增长之间的关系发生了变化。须四段砂体自下而上由水退式、河道式和水进式3种不同成因类型的砂组纵向叠合而成,层序界面之上的河道式砂组为物性最好的砂体。河道式砂组与水退式砂组为沉积不整合接触,呈现镶嵌关系,对天然气的运移起到通道作用。同时,河道式砂组在平面上分布范围大,物性好,为油气的富集提供了足够的空间。向上的水进式砂组储层发生致密化变化,形成有利的盖层,使河道式砂组发育区成为川中天然气富集的有利部位。

The sand body in the forth member of Xujiahe Formation of Upper Triassic in the central Sichuan Basin has the features of large thickness and continuous sedimentation, where sedimentary facies belongs to deltaic deposit in the proximity of source area. There are different accommodation space and sedimentary supply in the sediment stage. The sand body in the forth member of Xujia-he Formation consists of three vertical superposed types of the regressive model, channel model and transgress model from bottom to top. The channel sand body has the best physical property. The interface between channel sand body and regressive sand body is unconformity and thus shows the mosaic relation, which is favorable for natural gas migration. In addition, the channel sand body is characterized by wide-ranging distribution and high-porosity and can provide the sufficient space for oil-gas enrichment. The reser- voirs in the transgress sand body on the top become tight and turn into favorable cap rock, which promotes the channel sand body be-coming the favorable position of oil-gas enrichment in the central Sichuan Basin.