珠江口盆地中新统珠江组强制海退沉积层序与有利砂体分布

Sedimentary sequence and favorable sand-body distribution in falling stage system tracts of the Miocene Zhujiang Formation in Pearl River Mouth Basin

针对珠江口盆地中新统珠江组强制海退体系域沉积层序特征认识不足、层序归属不合理等问题,综合利用高分辨率三维地震、岩心和测井数据,采用层序地层学、地震沉积学和石油地质学的相关理论和分析方法,在对强制海退形成机理进行分析的基础上对该体系域的沉积层序特征、演化模式和有利砂体分布进行了探讨分析,指出该体系域顶界面具有明显的顶超侵蚀特征,应归属于SQ1层序的最后一个体系域,并总结了该体系域的沉积层序演化模式。结果表明:强制海退体系域具有退覆式的高角度斜交型前积反射结构,表现为陆架边缘三角洲的沉积特征,钻测井资料显示为多个具反旋回的前三角洲泥、远砂坝、河口砂坝与水下分流河道的组合沉积;强制海退体系域钻井岩心中发育陆坡区常见的生物扰动、泥质条带变形和滑塌、滑动现象,其前端下倾方向发育具强振幅反射结构的浊积扇沉积;强制海退体系域有利储集砂体位于该体系域顶界面和底界面附近,分别为陆架边缘三角洲前缘砂体和浊积扇砂体,是实现岩性油气藏勘探突破的重要方向。

Insufficient understanding in the characteristics of sedimentary sequences of the falling stage system tracts and unreasonable sequence division have hampered the breakthrough of oil and gas exploration in the Zhujiang Formation of Pearl River Mouth Basin.In this study,characteristics of the sedimentary sequence,evolution model and favorable sand body distribution in the falling stage system tracts of the Zhujiang Formation were investigated regarding the formation mechanism of forced regression.Guided by the concepts and methods of sequence stratigraphy,seismic sedimentology,and petroleum geology,comprehensive analyses of the high-resolution 3D seismic,core and logging data were conducted.Based on obvious toplap(erosion)geometries against the upper boundary,the falling stage system tracts should be attributed to the last system tract of the SQ1 sequence.The evolution model of the sedimentary sequence of the falling stage system tracts has also been summarized.The characteristics of the falling stage system tracts in seismic reflection show high angle oblique progradation and offlapping stratal stacking patterns,typical of shelf-edge deltas.The drilling and logging data show many reverse cycles consisting of delta front mud,distal bar,mouth bar and underwater distributary channel in the falling stage systems tract.The bioturbation,muddy strip deformation,slide and slump features,typical of slope areas,are commonly present in the cores of the falling stage system tracts.The turbidite fan with strong amplitude reflection structure is developed in the downdip direction of the falling stage system tracts.The favorable reservoirs include sand bodies of the shelf-edge delta front located close to the upper boundary of the falling stage system tracts and the sand bodies of the turbidite fan located close to the basal surface of forced regression,which are important exploration breakthroughs of lithologic reservoirs.