塔中地区奥陶纪古地貌及其对储集层的控制作用

塔中地区奥陶系具有埋深大、中下奥陶统剥蚀前地层厚度横向展布稳定的特点。运用地震地层学法、厚度趋势法和R_o法相结合的古地貌恢复方法较准确地表征了该地区加里东运动中期的地貌特征:隆起主体为围绕Ⅱ号构造带的椭圆状区域,地势比较平缓,局部构造并不十分发育;周缘凹陷到隆起主体之间存在坡折区,在由南、北、东向中央隆起地貌渐高的同时,地貌具有凹陷→斜坡→台缘坡折区→台内洼地、缓坡→凸起渐变的特征。上奥陶统礁滩主要分布于古地貌的台缘坡折带、台内凸起缓坡区,具有随着台缘迁移而变迁的特征,古地貌对礁滩储集体的分布及纵向演化、横向迁移具有明显的控制作用。估计塔中南部塘北2井—中3井之间地区在加里东运动中晚期存在台缘相带,具有生物礁发育的有利条件。

Ordovician Palaeogeomorphology and Reservoir-Controlled Process in Tazhong Area, Tarim Basin

The Ordovician in Tazhong area is characterized by large buried depth and stable lateral distribution before the Middlle-Lower Ordovician underwent erosion. By means of seismic stratigraphy, thickness tendency analysis and Ro data, the palaeogeomorphology in middle period of Caledonian tectonic movement in this area is well described as follows: Tazhong uplift is an ellipse shape region around No.2 structural belt with smooth topography and undeveloped local structures; existing slope break zone from surrounding sags to major uplift, and gradual variation of relief by features of sag→slope→platform margin break zone→inner-platform topographic low and ramp→ swell. The Upper Ordovician reef flat mainly distributed in the platform margin break zone and the inner-platform swell ramp zone, with feature of shifting with the platform margin migration. Study shows that the palaeogeomorphology is of remarkable effect on controlling the distribution, vertical evolution and lateral migration of reef flat reservoir body. It is predicted that there existed the platform margin facies in Mid-Late Caledonian tectonic movement in the area between TB-2 well and Z-3 well in southern Tazhong area, meaning that this area has the favorable conditions for biobermal reservoir development.