Resolution sequence stratigraphic division of the Da2 member in the Yanji Basin based on INPEFA and Milankovitch...

The Dalazi Formation in the Yanji Basin is primarily composed of fan delta and lacustrine facies, with local development of alluvial fan deposits. The second member of the Dalazi Formation (Da₂) serves as the key oil-bearing interval for exploration and development. Based on logging data, lithological observations, and maximum entropy spectral analysis (MESA), Da₂ is interpreted to mainly represent a continental fan delta system. Due to the complex depositional environment, significant variations exist in sedimentary types, resulting in notable differences in both lithology and logging curves, which hinders regional correlation using conventional logging marker bed pairings. In order to solve this problem, based on the theory of high resolution sequence stratigraphy and astronomical cycle theory, this paper uses the maximum entropy spectrum analysis, spectrum analysis and wavelet time-frequency analysis technology to process and analyze the natural gamma curve (GR) data, and combines the logging lithology information to identify the sequence interface. According to the prediction error trend (INPEFA) curve in MESA, it is identified that Da2 contains 1 long-term base level rise half-cycle and 1 long-term base level fall half-cycle. On this basis, the mid-term base level cycle and short-term base level cycle are identified by combining spectrum analysis technology and wavelet time-frequency technology. Finally, The Da2 sequence is subdivided into 1 long-term, 6 mid-term, and 16 short-term base level cycles, based on which a sequence stratigraphic division scheme is proposed. Based on this, a high-resolution stratigraphic framework is established, which provides accurate geological basis for subsequent comprehensive reservoir evaluation and sand body prediction.