鄂尔多斯西缘前陆盆地逆冲带下盘山西组储层发育特征

Reservoir Evolution Characteristics of Shanxi formation,permian at the downwallof the western thrust belt of Ordos Basin

鄂尔多斯西缘前陆盆地区逆冲带下盘二叠系山西组埋藏深度大于4500m,但仍然存在高效天然气储层。联合运用铸体薄片、扫描电镜、孔隙图象分析等多种测试技术,研究表明该区砂岩储集空间主要由粒间溶蚀孔隙构成。现今逆冲带上盘的砂岩成岩作用特征能够反映逆冲带下盘披覆前的成岩演化状况,逆冲带上盘、下盘砂岩成岩作用对比分析是恢复逆冲带下盘砂岩成岩演化史的有效方法。在逆冲披覆构造作用发生前,山西组砂岩溶蚀孔隙已经得以形成;在被披覆深埋藏过程中,山西组砂岩粒间溶孔边缘的凝灰质残余及烃类物质的充注在一定程度上抑制了石英次生加大作用和铁方解石胶结作用的进行,粒间溶孔可以得到有效保存。

Shanxi formation of permian is buried below 4, 500 meters at dowmwall of the thrust belt of western Ordos foreland basin, but high-quality reservoir for gas is in existence. The reservoir characters of upwall of thrust belt help to analyze the reservoir evolution of downwall of the thrust belt. Base on many testing measures such as Cast slice, SEM and analysis of pore image, it is verified that the dissolution of sandstone tuff filling apparently enhances the porosity of reservoir before the thrusting takes place, During the draping of downwall of the thrust belt, tuff emhaying the secondary pores restrains quartz regeneration and filled hydrocarbon in the secondary pores prevents carbonate cementing, The mechanism above makes the secondary to be saved, Correlation studying between the upwall and the downwall is very available for recognize the diagenesis history of downwall of the thrust belt at foreland basin.