川中广安地区上三叠统须六段储层特征及控制因素分析

广安地区上三叠统须六段为辫状河三角洲平原分流河道的大套砂岩复合体沉积,以中—细粒长石岩屑砂岩、岩屑砂岩为主;孔隙度主要分布在3%~15%之间,渗透率主要分布在0.01×10-3~1×10-3μm2之间。主、次分流河道为该区有效储层,复合砂体内渗透层与致密层交互分布形成了复杂的储层分布特征。在此基础上,结合成岩作用分析储层物性的影响因素认为,物源成分的不同影响储层发育富集区的分布,沉积演化特征控制储层发育层段,沉积微相控制层内非均质性。在煤系地层酸性环境下,强烈压实作用是形成普遍低渗的主要原因。主分流河道沉积的中、粗粒长石岩屑砂岩次生孔隙较发育,是主要的储层岩石类型。

Analysis on Controlling Factors and Characteristic of Xu-6 Sandstone Reservoir (Upper Triassic) in Guang'an Region, Central Sichuan Basin

The Xu-6 reservoir of Guangan gas field is a large scale sandstone complex of distributary channels of braided delta plain sub facies, and the sandstones of reservoir are mainly medium grained feldspar detritus sandstone and detritus sandstone. It has low porosity and ultra low permeability, with a porosity distribution range of 3% to 15% and permeability distribution range of 0.01×10~(-3) to 1×10~(-3) μm~2. Main and sub-main distributary channels are effective reservoirs, and the alternate distribution of permeable zones and compact layers in sand complex lead to complicated reservoir distribution. Based on above results, and combined with diagenesis, the controlling factors of reservoirs are discussed. The reservoir development is controlled by three sedimentary factors of different scales: distinctive rock composition of sandstones from different source regions which affects enrichment areas of reservoirs;sedimentary evolution which controls reservoir distribution sections;sedimentary micro facies which determines the heterogeneity in sandstones of favorable sections. Strong compaction of sandstones in acid environment of coal measures layer is the main cause of general low permeability. Medium and coarse grained feldspar detritus sandstones deposited in main distributary channels, which have relatively high secondary dissolved pores, are the main sandstone type of reservoirs.