鄂尔多斯盆地西部三叠系长2油层组砂岩成岩演化特征  

CHARACTERISTICS OF DIAGENETIC EVOLUTION OF CHANG 2 SANDSTONES(UPPER TRIASSIC) IN THE WESTERN ORDOS BASIN

作　　者：王琪[1] 史基安[1] 王多云[1] 卢龙飞[1] 王雷[1] 

机构地区：[1]中国科学院地质与地球物理研究所兰州油气资源研究中心

出　　处：《天然气地球科学》2005年第3期261-268,共8页Natural Gas Geoscience

基　　金：国家973项目(编号:2003CB2146);中国科学院知识创新工程重要方向项目(编号:KZCX3-SW-128);气体地球化学重点实验室基金(编号:SJJ-03-04)联合资助.

摘　　要：盐池—姬塬地区延长组长2油层组砂岩由三角洲前缘水下分流河道和河口坝砂体组成,以岩屑长石砂岩和长石砂岩为主(其中石英、长石和岩屑平均含量分别为32.6%、38.9%和8.0%,岩屑以变质岩屑和火成岩屑为主,占岩屑总量的87.5%)。指出砂岩目前处于早成岩阶段B期的晚期,RO为0.8%,温度在70～90℃之间,成岩组构特征受酸性成岩环境控制;长石类易溶颗粒普遍发生溶蚀作用,石英次生加大发育;孔隙类型组成中原生粒间孔隙所占比例多在30%～45%之间,粒间和粒内溶孔占40%～55%。在对砂岩各种组分含量统计和定量计算的基础上,认为机械压实作用是造成研究区原生孔隙消亡的最主要原因,其次为胶结作用,而由溶蚀作用增加的孔隙占初始孔隙度比例较小(<10%)。结合沉积相分析成果,在研究区划分出了5种沉积—成岩相带,其中有利的高孔高渗储层(孔隙度>14%,渗透率>5×10-3μm2)分布区主要由三角洲平原分流河道—次生溶孔相前锋带、三角洲平原分流河道—绿泥石粘土膜胶结次生溶孔相前锋带和台型三角洲前缘—绿泥石粘土膜胶结原生孔相主体以及坡型三角洲前缘—次生溶孔相主体组成。Chang 2 sandstones of Yanchang formation (upper Triassic) in Yanchi-Jiyuan area, southwest Ordos basin, are a set of distributary channel and mouth bar sandstone bodies formed in delta front facies, and mainly composed of lithic feldspathic sandstone and feldspathic sandstone, of which the average content of quartz , feldspar and lithic fragments accounts for 32.6%, 38.9% and 8.0%, respectively. Metamorphic and igneous rock fragments are main lithic constitutes, accounting for 87.5% of the total fragments. At present, these sandstones are at the late A period of the Early diagenetic stage(R_O =0.8%,T=70~90℃), and their diagentic fabrics are controlled by the acidic diagenetic environment, resulting in the widespread dissolution of feldspathic grains and well-developed quartz overgrowth. Primary porosity is the dominant pore types, accounting for 30%～45% of the total porosity,and interganular and intragranular porosity for 40%～55%. On the basis of the statistics on the sandstone compositions, the quantitative calculation shows that mechanic compaction is the main cause for porosity loss and the next cementation, whereas the increase of secondary porosity resulted from the dissolution only accounts for less than 10% of the initial porosity. In combination with the results from sedimentary facies analysis, five types of the favorable sedimentary-diagenetic facies zone could be recognized, and the most favorable zone with porosity>14% and permeability >5×10^(-3) μm^2 is mainly composed of the frontier part of the delta plain distributary channel-secondary porosity facies, the delta plain distributary channel-chlorite rim cementation+ secondary porosity facies, and the platform delta front-chlorite rim cementation+primary porosity facies as well as the main part of the slope delta front-secondary porosity facies. Thus, the exploration strategy in the near future should focus on the above-mentioned favorable sedimentary-diagenetic facies zone.

关 键 词：成岩作用 沉积-成岩相带 优质储层 延长组砂岩 鄂尔多斯盆地 

分 类 号：TE122.221[石油与天然气工程—油气勘探]