Sequence Based On Lithofacies Paleogeography During Dongying Formation Of Southwest Sag, Liaodong Bay Depression

This paper is based on the Dongying Formation of Southwest Sag, Liaodong Bay Depression.As one of the most important typies of fault basin, it has experienced extensional tectonics chasmic stage, thermal subsiding stage, strike-slip pull-apart rerifting stage.Generally, Liaodong Bay Depression forms tectonic framework with three depression and two uplift where the Southwest Sag is a tectonic unit close to fault. Besides, the Southwest Sag is close to the Southwest Uplift and gentle slope belt is used as septation function.From the whole aspect, the Southwest Sag is a long strip structural belt. Tectonic movement of the Kongdian to Shahejie Formations has experienced initial rifting, intense rifting and tectonics decline stages. Then the next rifting and subsiding restart in Dongying Formation. It is noteworthy that some depression areas not destructed by faulting have been good reservoir units.Besides,the tectonic and palaeogeomorphology feature is the premise of formation of favorable reservoirs.According to core feature marks, logging curve marks, seismic section marks,four main sequence boundaries and maximum flooding surfaces in the study area layers can be distinguished. Based on the sequence boundaries, a sequence division plan in this area can be determined.Then Dongying Formation is divided in three sequences:SQd3, SQd2, SQd1 and all sequences can be describe in detail.Finally sequence layer framework can be established. The typical drillings from east to west and from south to north can be chose as sequence sectional drillings to compare third-order sequence in study areas.The results show all sequences can be compared in a good way.By recognizing primary sedimentary structures markers,logging facies markers,paleobiochemistry markers, sedimentary facies of the study areas are divided braided river delta, meandering river delta, lake and sublacustrine fan under sequence stratigraphic framework.Then sedimentary facies distribution table in study areas should be established,so as to summarize distribution of drillings and layers in sedimentary facies.Finally depositional systems development characteristics should be described in detail including subfacie and micro facies, in order to summarize depositional system types and main characteristics of the table.Based on identification and division of depositional system, combining tectonic and palaeogeomorphology feature, provenance and handling mechanism, analysising sedimentary evolution feature of sequence periods in Dongying Formation.In SQd3 period, there is mainly braided river delta and laker sedimentary facies.In SQd2 period, there is mainly braided river delta, meandering river delta and laker sedimentary facies.In SQd1 period, there is also braided river delta, meandering river delta and laker sedimentary facies.Combining core,seismic and logging data with single well sedimentary facies,even well sedimentary facies histogram, sand isopach and layer isopach can be established.Then chose interface and sequence as map compilation units to draw dominant sedimentary facies plan in study areas.Combining sedimentary facies model map, tectonic and palaeogeomorphology feature there sedimentary facies plan can be corrected in details.Finally lithofacies paleogeographic maps in study areas can be finished, that can be prepared for next reservoir prediction.