Sedimentary System Of The Paleogene Dongying Formation In The Northern Fault Zone Of Chengdao

Dongying formation in the northern area of Chengdao oilfield is an important oil-bearing section,and is the main oil producing layer in Chengdao oilfield.Based on sequence stratigraphy and sedimentology,and comprehensively using core/logging data,and the interpretation of seismic structure we studied the depositional system characteristics of Dongying formation in the northern part of Chengdao low uplift.First,establish the sequence stratigraphic framework,and then the sedimentary facies model is established by identifying the types of sedimentary facies and the characteristics of development.Finally,based on the analysis of its unique palaeogomorphic features,the distribution law and control factors of the sand body of the deep deep lake bottom fan in the Dongying formation in the northern part of Chengdao are studied.On the basis of regional tectonic and sedimentary background,combined logging / logging and seismic data,the Dongying formation of Chengdao east slope is divided into a two level sequence and four three level sequence,and four three level sequences are SQ1,SQ2,SQ3 and SQ4 from top to bottom.And 5 sequence boundaries are identified,from top to bottom,they are named as: two order sequence interface T1,three order sequence interface,SB1,three order sequence interface,SB2,three order sequence interface,SB3 and two level sequence interface Tr.Then,the sequence stratigraphic framework covering the whole area is established by dividing the single well sequence into the cross well earthquake and the logging sequence section.The Dongying formation in the northern part of Chengdao has been continuously deposited in the lacustrine facies to the fan delta.Based on study of petrological characteristics,particle size and structural feature of combining the logging facies characteristics,determine the area mainly developed fan delta facies,slump sublacustrine fan and flood sublacustrine fan,further identified 7 subfacies and 10 microfacies.Then,the single well phase analysis and log phase analysis of the system are carried out.On the basis of summarizing single well facies and logging facies,we carry out the analysis of sedimentary facies and distribution of sedimentary facies in different periods in the whole area,and confirm the macroscopic distribution framework of sedimentary facies of Dongying formation in the north of Chengdao area.By this “point(well)-line(section)-plane(plane)” research ideas,the sedimentary facies distribution characteristics of the early base level rise period and the late base level fall period in Dongying formation are systematically analyzed,and the sedimentary model is established.Through the restoration of paleoggeomorphology by the three sequence stratigraphic thickness of the Dongying formation in the northern part of Chengdao,and based on the clear sedimentary system and sedimentary characteristics,the characteristics of the provenance in the northern slope area of Chengdao are comprehensively analyzed.Further,the slope break zone and valley position were identified on the edge of the northern slope of the Chengdao.The results of the study show that a number of gullies and fracture-developed tectonic slopebreaking belts in the project area will control the distribution of sub-ocean fan sand bodies in the northern part of Chengdao.This paper compares the distribution characteristics of gravity flow sand bodies in the valleys and slope breaks and the lacustrine sediments in the construction area,and further summarizes the structural patterns of slope breaks and erosion gullies,and analyzes their favorable sand body distribution control in this area.It is of great guiding significance for the further exploration and development of oil and gas in this area.