板桥凹陷同沉积断层主控的滩坝砂体沉积机制与分布样式

Sedimentary mechanism and distribution pattern of beach-bar sandbodies mainly dominated by contemporaneous faults in Banqiao Sag

关键词:  滩坝  同沉积断层  分布规律  沙二段  板桥凹陷

Key words:  beach-bar  contemporaneous fault  distribution regularity  2nd member of Shahejie Formation  Banqiao Sag

摘要:

根据测井、地震、岩心等资料,以板桥凹陷沙二段为例,对不同区块滩坝砂体的沉积特征进行对比,在此基础上对滩坝的形成机制和分布规律进行研究。结果表明:板桥凹陷沙二段滩坝储层中单砂体平均厚度大于10 m,累积厚度可接近100 m,除了熟知的粉、细砂岩外,还有许多砾质组分;同沉积断层的活动造成凹陷内部不同断块的滩坝砂体在岩性、岩矿、粒度和沉积构造等方面都具有明显的差异性,从根本上控制了滩坝砂体的沉积机制和分布规律;以同沉积断层为主控因素的滩坝沉积存在两种分布模式,即断层下降盘原地式连续型滩坝沉积和断层上升盘错叠式间歇型滩坝沉积;前者单砂体厚度大,内部夹层发育,以正旋回沉积为主,平面上“依附”同沉积断层下降盘分布;后者更多反映出反旋回相序特征,纵向上相互错叠,平面上呈“条带状”平行湖盆边缘展布。

Abstract:

The sedimentary characteristics of beach-bar sandbodies were compared among different fault-blocks of Es₂ in Banqiao Sag using the seismic,logging and core data, and the formation mechanism and distribution pattern of beach-bar were studied. The results indicate that the reservoirs of Es₂ in Banqiao Sag have single beach-bar sandbodies whose average thickness is higher than 10 m,and the cumulative thickness nearly reaches 100 m. In addition to siltstone and fine sandstone, there are also gravel deposits. The contemporaneous faults result in the differences in lithology, mineral, grain size and sedimentary tectonics between fault blocks,which fundamentally control the deposition mechanism and distribution regularity of beach-bar sandbodies. There are two kinds of distributary models of the beach-bar sediments where the contemporaneous fault is the main controlling factor:the autochthonous and continuous type of beach-bar deposition in down-throw side of the fault,and the staggered and intermittent type of beach-bar deposition in up-throw side of the fault. The former has thick single sandbody and well developed interlayers,generally presents a positive cycle,and horizontally adjoins the footwall of the contemporaneous fault. The latter shows more inverse cycle characteristics,has single sandbodies staggering with each other vertically,and has a banding distribution which runs parallel to the edge of the lake basin horizontally.