柴达木盆地西部地区致密油气形成条件和勘探领域探讨

在明确致密油气定义的基础上，分析了柴达木盆地西部(简称“柴西”)地区致密油气形成的地质条件:首先发育多套大面积的烃源岩，具有多个生烃凹陷；其次广泛发育致密储层，主要包括致密砂岩储层和裂缝型(泥质岩和碳酸盐岩)致密储层。致密砂岩储层以南翼山和红柳泉E¹₃砂岩、乌南N¹₂砂岩为代表；裂缝型致密储层以南翼山E²₃、狮子沟E¹₃、开特米里克和油泉子N₁的储层为代表；且源储交互叠置分布。致密油气在柴西地区广泛分布，古构造斜坡区和生油凹陷中心是致密油气分布集中区。致密油气可能的成藏组合包括源内包裹组合、源上广覆组合、源下依伏组合和源侧披覆组合等4种。按照储层成因类型，柴西地区致密油气勘探领域主要有:三角洲前缘砂体致密油气、滩坝和浊积扇砂体致密油气以及碳酸盐岩致密油气3个领域。针对每个领域，通过致密油气形成条件分析，按照区域和层位，共优选出8个有利勘探区带。

Formation Conditions of Tight Oiland Gas and Its Exploration Fields in the Western Qaidam Basin

Based on the definition of tight oil & gas,their geological formation conditions were analyzed in the western Qaidam Basin.Firstly,there are multiple sets of large areas of hydrocarbon source rocks and five hydrocarbon generation sags in the area.Secondly,tight reservoirs are widely distributed in the south area of the western Qaidam Basin,which mainly includes the tight sandstone and fracture-type (mudstone and carbonate) tight reservoir.The reservoirs of E 1 3 in Nanyishan and Hong Liuquan and of N 1 2 in Wu Nan are examples for the tight sandstone,and the reservoirs of E 2 3 in Nanyishan, of E 1 3 in Shizigou and of N 1 in Kai Temilike and Youquanzi are as the representative for the fracture-type tight reservoir.At last,the distribution of source rock and reservoir is superimposed reciprocally.Tight oil & gas reservoirs are distributed in palaeostructure slopes and source sags.There are four types of tight oiland gas reservoir combination,that is,inner source combination,wide distributed upper source combination，distribution under source combination，and draping beside source combination,which are mainly controlled by source depressions.According to the genetic type of reservoir in the western Qaidam Basin,the tight oiland gas exploration fields are delta front sandstone,beach bar and turbidite fan sandstone and the carbonate.For each exploration field,by the analysis of tight oiland gas formation conditions,8 favorable exploration zones are proposed according to the distribution region and horizon.This study has important theoretical and practical significance to the tight oil & gas exploration in the western Qaidam Basin.