The Sedimentary Microfacies Of Lower Third Member Of The Shahejie Formation In Qingxi Area

The sediment source of subsection in the Qingxi area in the eastern section of Dongying sag,Jiyang depression,Bohai bay basin has not been clearly defined,which bring difficulties to subsequent analysis of the sedimentary facies and prediction of favorable oil and gas reservoir.In this paper,using palaeogomorphic analysis method,petrological characteristics analysis,heavy mineral analysis,characteristic element ratio analysis and seismic precursor reflection analysis method to study the sediment source direction of research area,which is the base of analyzing type and distribution law of sedimentary facies.On the east of the study area stands Qingtuozi uplift,and on the north stands Chenjiazhuang uplift,there is a valley in the middle of the study area,therefore palaeo-geomorphology presents eastern area and northern area are respectively high and the middle area is lower,it can be inferred that the source is from the both uplift,and the middle area developed the thickest formation.Analysis of petrology characteristics in the study area and surrounding areas found that the northern source metamorphic rock cuttings were generally >40%,the content of rock cuttings in the eastern source metamorphic rocks and magmatic rocks is generally higher than 70%,and the content of cuttings in the industrial area reflects the mixed characteristics between them.In heavy mineral analysis,using comprehensive analysis of feature elements,rock ore data and other materials,combined with the foundation of previous data,found that the heavy minerals from the eastern Qingtuozi are mainly zircon,garnet,titanomagnetite and epidote,and the content of green epidote is 10% to 60%,and mostly at 10%,Zircon,garnet and titanomagnetite are the main types heavy mineral in Chenjiazhuang.In the southeastern part of the Wangjiagang River area,the heavy mineral compositions of provenance are mainly zircon,garnet and titanomagnetite,but the total content of zircon and garnet can reach over 60%.The mineral zircon,garnet and titanium magnetite in the study area are the highest,and the epidote is also visible,showing the mixed characteristics of the eastern source and the northern source.Characteristics of element analysis,found that in northern Chenjiazhuang uplift,the ratio of characteristic elements of source is characterized by three peak type characteristic,while the southeast of unimodal type characteristics,and the eastern Qingtuozi uplift is the hybrid that shows multimodal features,research area has peak performance type and mixed type.In the study area,the main sedimentary face is fan,which can be identified on the seismic section by foreset.Analyzing seismic reflection angle,calibrating the palaeocurrent direction,found the sediment materials come from both the northern area and the eastern.Through the above analysis methods,it is confirmed that the sediment materials of the study area are come from Qingtuoqi uplift and Chenjiazhuang uplift.Through core observation,identified the micro sedimentary facies and their characters,combined with well logging analysis,established well logging-sedimentary facies model of the area.Based on the high frequency isochronous stratigraphic framework,considering the result of sedimentary source analysis,analyzed the sedimentary facies distribution rule.During Es31 period,the sand body in the study area developed poorly,mainly developed the mud sediments of the shallow lake.During the period of Es32,there was a fan dalta in the eastern while a turbidite fan in the western.In the period of Es31,sand body developed best in the study area,in the east developed a fan delta,still smaller scale than Es32 period,the northern provenance supply was adequate,developed a nearshore subaqueous fan,the west side of the fault still has a tendency to along the direction of development of turbidite fan.