Sedimentary Characteristics And Controlling Factors Of The 2nd Member Of Kongdian Formation In Dongying Depression

Dongying depression is located in the southeast of Jiyang Depression in Bohai Bay Basin.The Kongdian Formation is the earliest sedimentary filling of Paleogene in Bohai Bay Basin,with deep burial and low degree of research.It is a new field for remaining oil and gas exploration.In this paper,the 2nd member of Kongdian Formation in Dongying Depression is taken as the research object.By comprehensively using regional geology,core,thin section,well logging,logging and 3D seismic data.the types,planar distribution characteristics and control factors of sedimentary facies in the study area are studied,and the following achievements and understandings have been obtained:(1)Determine the types of sedimentary facies of the 2nd member of Kongdian Formation in Dongying sag: Based on the detailed observation and description of cores and thin sections,through the analysis of lithology and sedimentary structure,it is considered that the study area is mainly developed block structure fine breccia facies,oblique bedding conglomeratic sandstone facies,wavy bedding argillaceous siltstone and massive tectonic mudstone phase.With core calibration logging facies,the use of logging curve shape,set up suitable for the mapping relationship between log facies and sedimentary facies in the study area,and think that the study area mainly develops rectilinear,gear box,funnel-shaped,tooth shape and finger log facies types.Seismic facies are calibrated with core facies,and seismic reflection structure and reflection configuration are used to define the seismic facies types of the 2nd member of Kongdian Formation in the study area on the basis of reasonable interpretation and closure of seismic strata of the 2nd member of Kongdian Formation in Dongying Depression,The common consensus is that the spiral proproduct phase,the S-shaped proproduct phase,the chaotic reflection wedge phase,the weak reflection mound phase,the high amplitude medium frequency high continuous parallel sheet phase and the continuous wedge phase in the medium amplitude medium frequency phase.Based on the research of core facies,logging facies and seismic facies,it is considered that fan delta facies,delta facies and lacustrine facies are developed in the 2nd member of Kongdian Formation of Dongying Depression,among which lacustrine facies includes shoreline shallow lake beach bar,semi-deep lake to deep lake,nearshore subaqueous fan and sublacustrine fan.(2)Analysis of Sedimentary Facies Planar Distribution Characteristics of the 2nd member of Kongdian Formation in Dongying Depression: A horizontal and longitudinal seismic profile was selected to analyze the seismic facies planar combination characteristics of the 2nd member of Kongdian Formation in Dongying Depression.Combined with the stratigraphic thickness map of the 2nd member of Kongdian Formation,the 2nd member of Kongdian Formation in Dongying sag is considered to be distributed in two independent depressions,which are located in Dongying Depression in the north and Shicun depression in the south.The Dongying sag is controlled by NWW trending Chennan boundary fault,There are nearshore subaqueous fan and fan deltas in the northern steep slope,sandy beach bar and delta in the southern gentle slope,lacustrine delta in the entrance of the long axis of the basin,and semi-deep lacustrine-deep lacustrine subfacies in the deep sag.The Shicun sag is controlled by NW trending Shicun fault.Semi-deep lacustrine-deep lacustrine subfacies are developed in deep depression zone,and fan-delta facies are developed in the southern slope.(3)The controlling factors of the sedimentation of the 2nd member of Kongdian Formation in Dongying Depression are analyzed.Based on the analysis of palaeogeomorphology,it is considered that the Purified Caoqiao,Chenguanzhuang-Wangjiagang structural belts are high and exposed in the 2nd member of Kongdian Formation,and the sedimentation of the 2nd member of Kongdian Formation is distributed in two relatively independent depressions.Based on the analysis of paleo-current orientation and ancient provenance by geophysical method,it is considered that there are mainly four provenance areas of the 2nd member of Kongdian Formation in Dongying Depression: Chenjiazhuang uplift,Guangrao uplift,Wudi uplift and Luxi uplift.Based on palynological analysis and elemental analysis,the paleoclimate of the 2nd member of Kongdian Formation in Dongying Sag is considered to be warm,hot and humid climate,and the lake basin water is in fresh-brackish water environment.According to the controlling effect of paleogeomorphology,ancient provenance and paleoclimate on the sedimentation,the lacustrine fecies model of the 2nd member of Kongdian Formation in Dongying Depression was finally established.