珠江口盆地番禺4洼珠江组层序地层及其约束下砂体发育模式

Sequence stratigraphy and sand body development model of Zhujiang Formation in Panyu 4 Subsag,Pearl River Mouth Basin

根据钻测井资料及地震资料,对番禺4洼珠江组层序地层进行研究,明确砂体发育特征与层序地层的关系,进一步分析二级层序不同演化阶段海平面变化、物源供给、构造沉降要素对砂体发育的影响,并建立二级层序控制要素作用下砂体发育模式。结果表明研究区珠江组可划分为1个二级层序,5个三级层序,各三级层序均只发育海侵体系域和高位体系域;不同三级层序的结构特征存在差异,其中三级层序SQ1和SQ2海侵体系域和高位体系域均较为发育,而三级层序SQ3~SQ5以高位体系域为主;砂体发育特征与二级层序基准面演化及三级层序结构密切相关,二级层序基准面上升半旋回,砂岩含量整体有降低趋势,单层砂岩厚度减小;二级层序基准面下降半旋回,砂岩含量整体有增大趋势,晚期单层砂岩厚度明显增大;三级层序SQ3~SQ5砂体主要发育在高位域;全球三级海平面升降旋回控制研究区三级层序的发育及结构类型,进一步控制不同结构三级层序的砂体发育规律;物源与二级相对海平面共同控制二级层序内砂体的垂向叠置样式和平面演化。

Based on drilling,well log and seismic data,the sequence stratigraphy of Zhujiang Formation was studied,and the relationship between sequence stratigraphy and sand body development was analyzed.Further analysis about the controlling factors including eustatic sea-level changes,sediment supply and tectonic subsidence on the sand body development was conducted.A sand body development response model on controlling factors under the constraint of the second-order sequence was established.One second-order sequence and five third-order sequences are present within Zhujiang Formation in the study area,with only transgressive system tracts(TST)and highstand system tracts(HST)developed in the third-order sequences.However,the architectural characteristics of different third-order sequences vary,that is,both transgressive system tracts and highstand system tracts are well developed in the third-order sequences including SQ1 and SQ2,and the third-order sequences(SQ3~SQ5)are dominated by highstand system tracts.The vertical stacking characteristics of sand bodies are closely related to datum evolution of the second-order sequence and sequence architecture of the third-order sequence.During the rising semi-cycle of the second-order sequence,the sandstone percentage decreases overall and individual sandstone layers become thinner;however,in falling semi-cycle of the second-order sequence,the sandstone percentage tends to increase,and individual sandstone layers become thicker and thicker in the late stage.Reservoir sand bodies are mainly developed in highstand system tracts of the third-order sequences(SQ3~SQ5).The 3rd-order global sea-level fluctuation cycle controls the development and types of the sequence architectures in the study area,which further controls the sand body development patterns of the third-order sequences.The interplay of sediment supply and the second-order relative sea level change control the evolution of the vertical superposition patterns and planar distribution of sand bodies of the second-order sequence.