Sequence stratigraphy and sedimentary evolution from the 4th member of Quantou Formation to the 3rd member of Nenjiang Formation in Sifangtuozi area, Songliao Basin

The sequence stratigraphy and sedimentary evolution from the 4th member of Quantou Formation to the 3rd member of Nenjiang Formation in Sifangtuozi area of the Songliao Basin were studied based on data collected from 147 exploration wells, 300 development wells and 25 cored wells. Research shows that by analyzing petrology, sedimentary structures and seismic inversions, the targeted strata can be classified into three second order sequences, seven third order sequences and twenty-one fourth order sequences. Under the sequence framework, meandering river deltas and shallow lakes were developed when the 4th member of Quantou Formation was deposited, and braided river deltas, shallow, semi-deep and deep lakes were developed when the Qingshankou and Nenjiang formations were deposited. In this process, the changing of base level, the left-lateral slip of Yanshan Movement and the transgression jointly contributed to the results, including the provenance changing from Baicheng to Yingtai, and then to Nehe drainages. In addition, the depocenter migrated from the Qijia Sag to the Sanzhao Sag, which highlighted the deltaic cycle in a direction of SW-NW-NE and the occurrences of maximum flooding surfaces in the 1st member of Qingshankou Formation and the 2nd member of Nenjiang Formation. We recommend looking for oil and gas on low-scoped ridges and shale resources on MFSs.