Fault Activities And Their Controls On Deposition Of Shahejie Formation In Changdi Area

Jiyang depression is a typical extension-strike-slip superimposed basin with abundant oil and gas resources.The process of strike-slip action and its control over strata and sediments is one of the key factors to deepen the study of reservoir distribution and oil and gas exploration strategy.This paper takes the 3rd and 4th member of the paleogene Shahejie Formation in the steep slope zone of Changdi in Gubei Sag as an example,guiding by basin dynamics,sequence stratigraphy and seismic sedimentology,making full use of drilling,logging,logging,and three-dimensional seismic data,studying detailed stratigraphic division and correlation,fault development characteristics and tectonic style analysis,sedimentary facies distribution and its relationship with tectonic activity and paleogeomorphology.The following progress and understanding have been achieved:1.Combined with well and seismic,the third-and fourth-order sequence stratigraphic framework of Shahejie Formation was established,and the spatial and temporal distribution of strata was implemented.The lower submember of Es₄,the upper submember of Es₄,the lower submember of Es₃,the middle submember of Es₃and the upper submember of Es₃can be divided into five third-order sequences（numbered as SQ1,SQ2,SQ3,SQ4 and SQ5 from the bottom up）by well seismic calibration.Based on third-order sequence,by introducing the cyclic stratigraphy analysis technology,the upper submember of Es₄and the lower submember of Es₃are divided into 9 and 6 fourth-order sequences（parasequence sets）respectively.Through the closure interpretation of the whole region,the stratigraphic temporal and spatial distribution is implemented.2.We identified seven fault groups and six fault combination styles,and refined the characteristics of fault activity groups and stages.Through the detailed classification of faults,six typical fault combination styles were identified,the geometric and dynamic characteristics of each fault were defined,the strike-slip activity time of the Changdi fault was determined,and the transformation process of extensional and strike-slip tectonic systems was cleared.During the extensional activity stage,the differential development of the north-south Changdi faults formed the nose-convex structure and controlled the near east-west regulatory strike-slip faults.In the strike-slip stage,en-echelon faults subduction thrust faults,broom branch faults and distal derived faults are mainly developed.3.On the basis of implementing the distribution of sedimentary system,we analyze the control effect of fault activity on strata and sedimentary filling.Combined with core,logging and seismic attribute analysis,three sedimentary facies types of delta-fan,nearshore subaqueous fan and sublacustrine fan are identified,and the sedimentary system of 3rd and 4th section of Shahejie Formation in the steep slope zone of Changdi is implemented.Combined with the analysis of fault properties and activity,the relationship between tectonic activity,paleogeomorphic pattern and sedimentary response is analyzed comprehensively,and the law of fault sand control is deepened.In the extensional tectonic stage,there was a large elevation difference,sufficient provenance supply,and sufficient basin capacity.The geomorphic pattern showed north-south zonation and nose-convex interphase,and the sand control characteristics were that the transition zone controlled the provenance entrance,and the difference strike-slip fault and microgeomorphology affected the sediment distribution pattern.In the strike-slip structure stage,the elevation difference of the terrain is small,the basin capacity space is limited,and the provenance supply is relatively insufficient.Influenced by the reverse fault parallel to the main fault,the landform presents an east-west zonation pattern and north-south connectivity.After the provenance is mainly confined to the low-amplitude subdepression of the fault after injection along the en-echelon faults,and it is easy to be distributed laterally.