琼东南盆地中央峡谷沉积充填特征与储层分布规律

Depositional filling and reservoir distribution patterns of the central canyon in Qiongdongnan Basin

中央峡谷是平行于陆坡跨盆地发育的深水水道一天然堤体系。应用2D和3D地震数据，结合岩心和测录井资料，分析了琼东南盆地中央峡谷充填的岩性、砂体类型和特征、分布规律及控制因素。认为距今10．5～4．2Ma期间，琼东南盆地中央峡谷内发育5期次级水道充填，沉积了浅灰色砾质细砂岩、厚层块状／粒序细砂岩、粉砂岩和灰黑色粉砂质泥岩、泥岩等，发育4种充填相，包括浊流、碎屑流、滑塌等重力流过程和半深海沉积。应用井一震对比并结合均方根振幅属性分析，识别出4种砂体类型，分别为峡谷轴部砂体、天然堤砂体、侧向加积砂体和侵蚀残余砂体。砂体类型在纵向上的分布具有分异性特征，即峡谷充填总体在底部中部以砂岩为主，上部由粉砂岩构成，在不同次级峡谷充填内，同样是砂岩在下，向上渐变为粉砂岩的正旋回特征。另外，砂体在横向上的分布具有分段性特征，第13期峡谷充填砂体，主要发育在峡谷中游；第4、5期充填砂体仅发育在峡谷中上游。中央峡谷充填砂体分布主要受母源区岩性、长距离及多次搬运、初始流体规模及流态、次级水道的改造与破坏、中央峡谷发育方式和盆地构造等因素控制。

The central canyon is a deep-water channel-levee system developed in parallel to the slope across Qiongdongnan Basin. This study investigated depositional filling characteristics of central canyon in terms of the lithological compositions, the types of sand bodies, the patterns of reservoir distribution, and the controlling factors using 2D/3D seismic data combined with core, drilling and well-logging data. The results show that during the period of 10.5-4.2 Ma, the canyon was filled with five-stage secondary channels and deposited with light-gray gravelly fine sandstone, massive and graded fine sandstone, siltstone, dark-black silty mudstone, and mudstone. Four types of depositionaI filling were developed with hemiplegic deposits and gravity flow of turbidity currents, debris, and slumps. Based on well-seismic calibration and root-mean-square seismic attribution analysis, four types of sand body were identified in the canyon, including canyon-axis sand bodies, natural levee sand bodies, lateral accretion sand bodies, and erosion residual sand bodies. These sand bodies show distinct variations in the vertical distribution. The canyon is mainly filled with sandstone in the bottom to middle part and siltstone in the upper part, with similar characteristics of positive cycles in the secondary fillings. Additionally, the sand bodies show segmented distribution horizontally. Stage 1 3 fillings of sandstone are distributed mainly in the middle reaches of the canyon, while stage 4 and 5 fillings of sandstones are mainly in the middle - upstream. Major factors controlling the distribution of sand bodies in the canyon include lithological composition of the provenance, distant and multiple transports, scale and flow pattern of initial gravity flows, destruction and reconstruction of secondary channels, development mode of the canyon, and tectonic framework of the basin.