南海北部深水盆地多边形断层发育特征的差异性及其控制因素研究

Polygonal faults, usaully arranging in a polygonal structure developing in deepwater sequence, are a network of layer-bound, mesoscale extensional faults with short lengths, small throws and separations. Polygonal faults are found widely developed in sequences of more than 75, 000 square kilometers in deepwater basins and having different developmental charateristics in different basins in South China Sea.In this study, we will compare the devlopments of polygonal faults in southern Pearl River Mouth basin and eastern Qiongdongnnan basin. Using high resolution three dimention (3D) seismic data, seismic geometries of polygonal faults will be studied, and rock physical properties of the sequences where polygonal faults develop will be calculate based on 2D/3D seismic data and wireline log data between the two basins. The tectonic evolution and the process of deposition and diagenesis are inferred to impact diversities of the development of polygonal faults. As a result, 2D and 3D geological models are going to be built in order to analyze ditributions of interior field of stress in sequences hosting polygonal faults　and the development of the faults. The deposition and diagenesis factors such as the content and distribution of sand and mudstone, the deposition rate and the variation of pore pressure are also calculated and studied. Based on the works above, fators controlling the diverse development of polygonal faults are considered to present. The reserches on polygonal faults will help understanding the fluid flow process during the deepwater exploration.

多边形断层在深水盆地广泛发育，具有断层规模小、断距小、密集、受层序边界控制、平面呈不规则多边形展布等特征，对深水盆地流体超压系统、油气和水合物成藏具有重要的意义。南海北部深水盆地发育了大规模的多边形断层，表现出不同的发育特征。本项目拟以珠江口盆地南部和琼东南盆地东部深水区为对比研究靶区，利用高分辨率3D地震数据精细刻画多边形断层的地震几何特征；基于2D/3D地震数据和测井数据计算多边形断层发育地层的岩性、密度、孔隙度、饱和度等岩石物理性质。通过对南海扩张过程中珠江口盆地和琼东南盆地的构造和沉积成岩过程的分析，建立多边形断层发育地层的2D地质模型计算构造应力作用下地层内部的应力场分布，并应用3DMove技术研究多边形断层的开启和生长过程；计算分析沉积成岩过程中的砂泥岩含量和分布、沉积速率、孔隙压力变化等因素对多边形断层发育的影响。最终揭示南海北部深水盆地多边形断层差异性发育的主控因素，为深水油气运移研究提供依据。

本项目基于2D/3D反射地震数据，结合测井和岩芯数据，研究南海不同沉积盆地多边形断层的发育特征的差异性和控制因素。在南海北部和西部陆缘识别了8万多平方公里的多边形断层分布区。应用地震数据的波阻抗反演、蚂蚁追踪和三维可视化等技术对比分析了珠江口盆地白云凹陷和琼东南盆地长昌凹陷、北礁凸起的多边形断层的分布层段和几何特征的差异性。研究结果表明多边形断层的形成与沉积盆地随南海扩张过程中的构造和沉积演化过程密切相关。珠江口盆地白云凹陷在裂后剧烈沉降，由于水力破裂作用，发育了不规则走向的多边形断层，指示了大量细粒沉积物供应而缺少重力流沉积的长期稳定的深水沉积环境。琼东南盆地长昌凹陷和北礁凸起受西北次海盆张裂过程影响，构造断层和较陡地形影响下发育浊流沉积，产生了定向的多边形断层，指示了复杂物源供给的不稳定的深水沉积环境。早中新世，珠江口盆地南部隆起带水道沉积中发育大量的垂直水道走向和平行水道走向的断层，这与Victor and Moretti（2006）的岩石物理模拟结果一致，砂体和下伏塑性层的流变学差异产生的重力扩展作用导致断层的产生。南海多边形断层是重要的油气运移通道，同时对中新世沉积环境的研究具有重要意义。