鄂尔多斯盆地中东部地区山2段储层沉积特征及勘探目标评选

SEDIMENTARY FEATURE AND OPTIMIZATION OF EXPLORATION PROSPECTS OF SHAN 2 NUMBER IN THE MIDDLEEAST OF ORDOS BASIN

通过对鄂尔多斯盆地中东部地区山西组2段砂体的重点剖析,认为母源分异和水动力强弱控制了区内山2段砂体的东西分带性,即西部榆林砂带的强水动力作用形成的石英砂岩具有高石英、低杂基、低软岩屑、无或低长石的“一高三低”特点;东部神木砂带弱水动力作用形成的岩屑石英砂岩特征正好相反,为高杂基、高软岩屑、高长石的“三高”特点。同时以盆地晚古生代以来的演化为主线,运用层序地层学理论,在等时地层格架内探讨了沉积体系展布及盆地充填特征,认识到中东部地区山2期为一套河流—三角洲—湖泊沉积体系,其沉积演化表现为湖泊持续扩张、冲积体系逐渐北移退缩的过程,该时期发育的3期湖进作用形成了向北溯源沉积的3套叠置砂体,各套砂体的三角洲前缘相带是有利勘探目标区。

Through analyzing shan 2 number sandbody in the middle-east of Ordos basin, it is thought that the east-west zoning of shan 2 number sandbody is controlled by original differentiation and hydrodynamic force strength. The quartz sandstone formed by the strong hydrodynamic force has the characteristics of one-high and three-low that is high quartz, low martix, low-soft lithic-fragment and few feldspar in the wastern sand belt, Yulin. But the litharenite formed by the weak hydrodynamic force is different from the quartz sandstone in the eastern sand belt,Shenmu. It has the three-high property of high martix, high-soft lithic-fragment and high feldspar. At the same time the evolution from late Paleozoic is looked upon as main line. It is studied by the applied of the sequence stratigraphy that the distribution of depositional system and feature of basin filling in the isochron stratigraphic framework. It is thought that shan 2 period is a suit of river-delta-lake depositional system. Its sedimentary evolution is represented as the long expanding process of lake and northward recession of alluvial system. Three suits of superposition sandbody that are the retrogressive deposit northward are formed by three periods of lake process in this age. The delta front facies tract is the favorable exploration prospect area in all suits of sandbody.