Sub-layer division and correlation based on well-seismic combination and step-by-step interface constraint: A case study of the Taiyuan-Lower Shihezi Formation in the Shilijiahan of the Hangjinqi area

This study aims to achieve fine correlation of sub-layers between wells in the Taiyuan-Lower Shihezi Formations in the Shilijiahan of the Hangjinqi area. Based on detailed core observations and core-log-seismic integration, calibrated logging curves are used to summarize the interface characteristics of different levels of marker beds, and high-frequency sequence division is performed by using step-by-step marker bed constraints and well-seismic combination. In combination with development practice, sub-layers division and comparison are carried out. The results indicate that the stratum thickness from the Taiyuan Formation to the Lower Shihezi Formation in the study area is about 230 meters. From bottom to top, the tidal flat facies and delta facies in the transitional environment between sea and land gradually evolved into the braided river delta facies of the Shanxi Formation, and the braided river deposits are mainly developed in the Lower Shihezi Formation. According to the sequence interface types, the target layer is identified as one second-order interface, three third-order interfaces and four fourth-order interfaces. Based on core, logging curve, and seismic response characteristics, the second-fourth order sequence interfaces are divided into four levels. Through detailed core-log calibration, 17-18 fifth-order interfaces are further identified. Under the constraint of seismic profile and the guidance of sedimentary characteristics, the inter-well correlation of different marker interface levels is conducted, and then the high-frequency sequence correlation is achieved by level-by-level constraint. In combination with the actual field development, the Taiyuan Formation to the Lower Shihezi Formation can be further divided into 13 sub-layers. The thickness of each sub-layer is relatively stable, primarily reflecting the sedimentary characteristics of plain braided rivers. High-frequency sequences control the development and distribution of sedimentary reservoirs to a certain extent. The well-seismic combination and step-by-step constraint method enhance the accuracy and fineness of sub-layer division and correlation, providing a foundation for further gas reservoir geological research and evaluation in this area.