Stratigraphic Sequence Division And Stratigraphic Sequence Characteristic In Southern Songliao Basin

This article interprets the formation, mutual relationship and characteristics of the stratigraphic sequence in southern Songliao basin, establishes sequence stratigraphic framework of southern Songliao basin, and then explains the relationship between sequence system tracts of the southern Songliao basin and the formation and distribution of the hydrocarbon, aggregates the distribution regularity to guide the hydrocarbon exploration based on the principles and analytical methods of dialectical sequence stratigraphy, especially continental sequence stratigraphy.According to the termination characteristics of reflection above and below the seismic reflection layer and the composite wave characteristics of the seismic reflection layer itself, it can be considered that there are 9 regional seismic marker beds in southern Songliao basin, respectively corresponding to the sequence boundary, the initial marine flooding surface and the maximum marine flooding surface of the second-order sequences. 10 local uncomformable surfaces and the corresponding disconformable surfaces are identified, respectively corresponding to the third-order sequence boundary. By comprehensively analysising a large number of geological, logging, seismic and various types of the laboratory data, the results shows that 12 main lake flooding surfaces are developed from K1q4 to K1n, they are relatively stable mudstone section,corresponding to the initial marine flooding surface or maximum marine flooding surface of the second-order sequence or the third-order sequence boundary. The seismic, geological, logging characteristics and marked characteristics of the stratigraphic interface of every stratigraphic unit are summarized. 9 second-order sequences are divided from J3hs to Tertiary. According to the local marker bed and local unconformity, the faulted period and the depression period of the basin can be divided into 19 third-order sequences in the framework of the second-order sequences. According to the analytical principle of the high-resolution sequence stratigraphy, the K1qn3 can be divided into 13 deposition time units in the framework of the third-order sequences. The different distribution ranges of each time unit can interpret the inconsistency of the sand division and correlation in different areas reasonably.The three major sediment source system in the medium shallow layer of the southern Songliao basin control the sedimentary of the three areas respectively, but each depositional system has different intensity in different period, and has a characteristic of mixed-source. Based on the hydrocarbon show, well testing result and sequence analysis, it can be considered that lowstand fan is developed in lowstand systems tract, overlap trap is developed in transgressive systems tract and nonstructural trap pattern of stratigraphic erosion lithologic trap is developed in high systems tract. The lowstand systems tract and the high systems tract or the regressive systems tract are main layer systems of oil and gas accumulation and are beneficial exploration areas. However, western basin and the front bands of the eastern slopes are the favorable region for searching nonstructural trap, the southern basin is the favorable region for tectonic lithologic combination trap.