Sedimentary System Analysis And Subtle Traps Prediction Of Shahezi Group In Lishu Fault Depression

Lishu fault depression lies in the southeast of the southeasten uplift of Songliao basin which is a graben basin controlled by Sangshutai arc fault in the west since early Cretaceous. In order to analyze the sequence development and distribution of deposition system, the thesis applied the analytical method of sequence stratigraphy, structural geology, sedimentology and three-dimensional geomorphological technology. This paper systematically analyzed the sequence stratigraphic characteristics, structural features and paleo-geomorphology of the ShaHezi group in LiShu fault depression.Based on core, drilling, logging and 3D seismic, in LiShu fault depression, three second-order sequences and seven third-order sequences were identified. The characteristics of them were different with sedimentary centre and subsidence center migration regularly controlled by episodic rift. Horizontally , the developing characteristics were different between sequences in different periods and different structural position. Vertically, they formed the orderly superposition of different sequences.By adopting the comprehensive methods of qualitative analysis on 3D seismic materials, the timing sequence stratigraphic framework, the tectonic evolution, quantitative analysis on palaeothickness and visualization mapping of 3D geomorphological modeling, the thesis recovers the 3D paleo-geomorphology map of ShaHezi group in LiShu depression, and analyses the paleo-geomorphology characteristic and evolution history of every period.Alluvial fan, fan delta, nearshore subaqueous fans and lake facies are found according to a variety of sedimentary marks.The supplycation came from southeast and north in the ShaHezi group. Six seismic phases are identified and drawn out. The planes of sedimentary facies distribution of each sequence cycle phase are completed combined with lithology statistical law.Through detailed anatomical Shahezi sequence structure, stratigraphic stacking patterns and paleo-geomorphology features, analyze the controlling of sequence and deposition. Various types of subtle traps are closely related to the various systems tracts of sequence. The subtle traps related to LST include incised-valley traps, block unconformity traps, lenticular sand traps; TST are related to the subtle traps overlying unconformity stratigraphic traps, subaqueous fan sand traps, block unconformity traps, sandstone updip pinch out traps; HST are related to sand updip pinch out traps, lenticular sand traps, channel sand traps.Combined with the quality and distribution of hydrocarbon source rocks, reservoir type and distribution, combination of source-reservoir-seal assemblage, etc., predict the favorable subtle trap of ShaHezi group in LiShu dpression.