塔里木盆地上泥盆统—下石炭统东河砂岩沉积相与哈得逊油田的发现

Sedimentary facies of Donghe Sandstone in the Upper Devonian-Lower Carboniferous and discovery of Hadexun Oilfield in Tarim Basin

哈得逊油田是塔里木盆地最大的整装油田之一,储量规模超过亿吨。在其发现过程中,东河砂岩的沉积相及其相变规律起了重要的指导作用。东河砂岩为晚泥盆世晚期至早石炭世早期海侵背景下沉积的一套海侵砂(砾)岩,主体为滨岸海滩相砂体,在全盆地范围内是一个明显的穿时沉积体。东河砂岩从古地貌低部位向高部位持续超覆变薄,以陆源碎屑滨岸—浅海相沉积为主。在靠近古海岸线附近,以滨岸海滩相的临滨—前滨夹后滨沉积为主,向盆地方向逐渐过渡为远滨的泥岩和台地碳酸盐岩。砂体发育主要受古地貌、海平面变化、物源等共同控制,沉积厚度在缓坡处减薄,在陡坡处增厚,遇孤岛或隆起减薄或尖灭。在海侵早期,东河砂岩分布在轮南隆起以西,砂体分布广、厚度大,南北向展布;在海侵早中期,砂体沿古海岸线近东西向呈带状展布。在海侵中期至晚期,古高地被分割为多个岛屿,向海方向为碳酸盐岩台地。东河砂岩这种纵横向的沉积相变为岩性地层油气藏的发育提供了良好地质条件。

The Hadexun Oilfield is one of the biggest integrated oilfield in the Tarim Basin.Its reserves exceeds one hundred million tons.The sedimentary facies and its changing regularity of the Donghe Sandstone plays an important role in the discovery of the Hadexun oilfield.The Donghe Sandstone was deposited in the transgressive background during the Late Devonian to the Early Carboniferous.It is mainly the beach sandbody of littoral facies.The Donghe Sandstone is a distinct diachronous in the whole basin.The Donghe Sandstone is chiefly terrigenous littoral to shallow marine facies.They overlaped thinning from lower to higher paleogeomorphic unit.Sedimentary facies is dominated by shoreface to foreshore intercalated with backshore of the littoral beach facies on the adjacent paleo-coastline.There are offshore mudstones and carbonate platform towards the basin area.The sandbody was controlled by the paleo-geomorphology,eustatic movement,and provenance.The sandbody thickness decreased on the gentle slope side,and increased on the steep slope side,thinning out on the solitary island and big terrace area.In the early transgressive stage,the Donghe Sandstone distributed in the west of Lunnan Uplift.The sandbody spreaded in north-south direction,with wide distributing and large thickness.The sandbody distributed in west-east direction along the paleo-coastline in the early to middle transgressive stage.In the middle to late transgressive stage,the paleo highland was flooded into many island by the sea water.The carbonate platform emerged towards the sea.The sedimentary facies and its variation of the Donghe Sandstone has provided good geologic conditions for forming litho-stratigraphic petroleum reservoirs.