Sedimentary System Analysis Of The Fourth Member Of Shahejie Formation In Linbei Area Of Huimin Sag

The Linbei area is located in the eastern part of the central uplift belt of Huimin Sag and it is a large-scale fault-step belt rising towards North.It has been observed that the fourth member of the Shahejie Formation in Panhe area has obtained better exploration results.However,in Linbei area the exploration intensity is relatively less and lacking the systematic sedimentary microfacies study.Therefore,the research on sedimentary system of the fourth member of Shahejie formation in Linbei area shows an important link between oil and gas exploration and development,and it provides effective geological basis for continuing exploration and development deployment.On the basis of a large number of literature research,through sedimentary petrology,sequence stratigraphy and other theories and methods,the strata in the study area are divided and compared by using drilling,logging and other geological data;Determine the type of sedimentary facies by establishing sedimentary facies markers,select typical wells for single well phase analysis and sedimentary micro-relative ratio,and summarize the types and characteristics of sedimentary facies in the study area;Drawing the plane distribution map of sedimentary facies and the isoline map of sandstone thickness,the distribution law and distribution characteristics of sand bodies and sedimentary facies zones in the study area are analyzed,and the sedimentary system of the fourth member of Shahejie formation in Linbei area of Huimin sag is expounded;Finally,the types of trap and favorable phase zone in Linbei area are briefly summarized and predicted.Through the above-mentioned research,following important results and understandings were obtained:?Upon using the high-precision sequence stratigraphy method for the identification of sequence interfaces of different types and levels,it is found that the sedimentary cycles of the fourth member of the Shahejie Formation in the study area can be clearly divided into four cyclic sequence stratigraphic units;?After setting up the E-W and N-S stratigraphic correlation profile,it is found that there is little change in the thickness of strata under the same fault-step belt laterally.While longitudinally,the thickness of the formation is progressively increased southward in the fault-step belt;?The deltaic-lacustrine type sedimentary depositional system were developed in the fourth member of the Shahejie Formation.The delta plain,delta front and the shallow lacustrine subfacies were developed and delta front subfacies can be considered as the prime entity alongside the developed underwater distributary channels,sheet sand,underwater natural levees and interdistributary bay microfacies.Due to the continuous supply of materials from the northwest region,pro-gradational accumulation of sediments in deltaic part of the fourth member of the Shahejie Formation;?Controlled by the sediment supply from source and subsequent development of sedimentary facies,the reservoir sand bodies were primarily formed in the delta front which is described through the underwater distributary channels and mouth bar microfacies.In the near source area,the thickness of sand body is obviously larger,along the source direction,the sand body extends and spreads better;?The structure of the fourth member of the Shahejie Formation in the Linbei area is inherited,and the fault block is broken,the structure is complex,and the sand body is easily staggered to form a occlusion,forming a rich fault block trap.In this paper,after superimposing the top structural map and sandstone thickness isopach map the oil test interpretation results of the fourth member of Shahejie formation in existing exploration wells were combined and compared.