青海湖湖流型滩坝砂体内部构成及沉积模式研究

Beach-bar reservoirs in continental lake basins, as one type of the important lithologic reservoir, get more and more the attention of the people. However, it is can not distinguish beach and bar sand because of the low resolution of dill, well logging and seism. There is not a mature deposition model for beach bar sand body for now. Lake Qinghai as the largest terrestrial lake in China, there were a lot of the ancient beach-bar sandbodies. This research project will select Lake Qinghai as object of study to system research lake current dominated beach-bar sandbodies, using ground penetrating radar (GPR) survey and optically stimulated luminescence (OSL) dating. On the base of identifying orders of bounding surfaces in the sandbodies, we will divide sandbodies into the different architectural elements and quantitative characterize them. Study on the types of architectural elements, geometrical morphology and internal structure of microfacies in beach-bar sandbodies and their inter-superposition relationship, as well as the characteristic of grain size and mineral association, the identification marks of microfacies for lake current dominated beach-bar sandbodies will be established. At last we can establish the sedimentary model for lake current dominated beach-bar sandbodies. This study will have important theory significance for the exploration and exploitation of beach-bar reservoirs in our country.

作为我国最重要的岩性油气藏类型之一，陆相湖盆滩坝储集体越来越受到人们的重视。但受钻、测井和地震分辨率的限制，目前为止还没有一种比较成熟的滩坝砂体沉积模式。青海湖作为我国最大的陆相湖泊，周围发育了大量的古代滩坝砂体，形成了研究滩坝砂体的天然实验室。本课题拟选取青海湖发育的湖流型滩坝砂体作为研究对象，利用GPR探测技术和OSL测年技术对青海湖湖流型滩坝砂体进行系统的解剖，识别砂体内部各级界面，定量表征砂体内部构成单元，明确湖流型滩坝砂体各沉积微相标志及相互叠置关系，建立湖流型滩坝砂体沉积模式，这对于完善滩坝砂体沉积学理论，指导我国滩坝油气藏的勘探和后期开发都具有重要意义。

滩坝储集体作为隐蔽油气藏勘探的重要领域之一，越来越受到人们的重视。但受钻井、测井和地震分辨率的限制，目前还没有一种比较成熟的滩坝沉积模式。针对这一问题，我们选取了青海湖发育的湖流型滩坝砂体作为研究对象，利用野外实地踏勘探测结合室内实验室分析，我们识别出滩坝砂体内部各沉积单元的界面，界面较为复杂多以削截、顶超、上超和下超为主，含整一界面较少。整个滩坝剖面内主要有风暴沉积和正常波浪沉积组成，风暴沉积一般由下伏具有明显的向陆倾斜的交错层理和上部相对平行的层理组成，正常波浪沉积具有向湖方向倾斜的交错层理。滩坝不同部位其各沉积单元的相互叠置关系不同；坝主体，主要由底部少量正常波浪沉积和上部多期风暴沉积为主，具有向湖向陆方向交错层理，界面多以下超为主，沉积物粒度较粗。坝侧缘，主要由多期正常波浪沉积组成，偶见次一级风暴沉积。层理多为向湖倾斜交错层理，界面多以上超和削截为主，沉积物粒度较坝主体变细。坝间，主要由风暴沉积造成的冲溢沉积和泻湖沉积组成，层理主要以水平层理和向陆倾斜的交错层理，界面多以整合和下超为主，沉积物粒度最细。沿湖流方向，由于波浪作用减弱，地形变缓，风暴的影响力减弱，滩坝砂体逐渐变小，由单一坝体变为多条小型坝体，砂体展布由纵向转向横向，随着湖平面的下降，坝体变为由多期风暴沉积叠加转变成单一的风暴沉积叠加在正常波浪沉积之上的砂体。因此，湖流型滩坝砂体有别于正常滩坝砂体沉积，多发于湖湾地区，随着湖流的方向滩坝砂体的厚度，展布及内部单元的叠置关系都发生了变化，本次研究取得的沉积模式对于滩坝砂体的油气勘探及后期开发均能够起到良好的指导作用。