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

Key words:  sequence boundary  sequence architecture  sea level  source  sand body development model  Zhujiang Formation

Abstract:

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.