65 / 2022-01-23 17:30:45

Seismic geomorphology, facies analysis and its significance of petroleum geology in delta：A case study of the Jurassic Shaximiao Formation in the northeastern Sichuan Basin

Sequence stratigraphy,Seismic geomorphology,Delta,Shaximiao Formation,tight sandstone reservoir

The Shaximiao Formation is one of the important tight oil and gas producing intervals in the Sichuan Basin. With the aid of  modern sedimentology, seismic geomorphology, and the comprehensive analysis of geophysical data, this study conducts research on high-resolution sequence stratigraphy, sedimentary micro-identification, and sedimentary evolution of the Jurassic Shaximiao Formation in the northeastern Sichuan Basin. The Sha₂ member of Shaximiao Formation, Jurassic, in the northeastern Sichuan Basin is divided into three third-order sequences (SQ1~SQ3), which can be further subdivided into 10 fourth-order sequences (SSQ1~SSQ10). The 90° phase conversion, frequency division, slice processing and RGB attribute fusion of seismic data have clarified the filling process of multi-phase channel sand bodies in the delta of the Shaximiao Formation. Sedimentary microfacies such as delta plain distributary channels, floodplains, underwater distributary channels, and interdistributary bays were successfully identified. The results show that the Sha₂ member of Shaximiao Formation is a delta sedimentary system under the background of lacustrine regression as a whole, and the underwater distributary channel is the most favorable sedimentary facies belt for reservoir development; The RGB color mixing of stratigraphic slice amplitude, coherence and sweet spot attributes can better identify the channel; The rise and fall of the base level and the supply of provenance control the migration of the channel shape, which in turn controls the spatial distribution of sand bodies; Large-scale channel sands develop in the four-level sequence SSQ1, SSQ5 and SSQ8; Based on the above analysis, combined with Hydrocarbon source and structure, established a sweet spot prediction model for shallow tight sandstone gas reservoirs in the second member of the Shaximiao Formation. This achievement enriches the application of seismic sedimentology in the study of delta sedimentary facies, and has guiding significance for the exploration and development of shallow tight gas reservoirs.