Sedimentary Characteristics And Geological Significance Of Shahezi Formation In Xunan Area

In order to establish the characteristics of the stratigraphic framework of the Shahezi Formation in Xujiaweizi area,clarify the planar distribution characteristics of sedimentary facies in the Xunan area under the fourth-order sequence framework,and promote further oil and gas exploration in the deep Shahezi Formation in the Xunan area,and comprehensive previous studies Achievements,guided by the theory of sequence stratigraphy,sedimentary petrology,and seismic sedimentology in the continental faulted lake basin,using the core,logging,and seismic data of the Shahezi Formation within the Xujiaweizi fault depression for sequence stratigraphy Identify and divide,establish a stratigraphic framework,identify the sedimentary facies of the Shahezi Formation in Xunan area,clarify the development rules,and establish a basin sedimentation filling model.Observe the cycle characteristics of the new logging curve,observe the unconformity and upper and lower cross-sections on the seismic profile through the observation of logging curves and lithological characteristics,to identify the three-sequence stratigraphic interface;through the three-level intra-sequence logging curve Observation of lithological characteristics and changes in the intensity of the reflection axis in the seismic profile,and then the detailed differentiation and identification of the fourth-order sequence stratigraphic interface;based on the method of combining wells and seismic,the fourth-order sequence stratigraphic grid was established for the entire Xujiaweizi area From bottom to top,four three-level sequences are divided into SQ1,SQ2,SQ3,and SQ4.The nine four-level sequences are SQ1-1,SQ1-2,SQ2-1,SQ2-2,SQ3-1,SQ3-2,SQ4-1,SQ4-2,SQ4-3,the sequence SQ1-1 is missing in the Shahezi Formation in Xunan area.The stratum in the study area is obviously controlled by the Xuxi fault,which is thick in the west and thin in the east.Combining core,logging,and seismic data,the Shahezi Formation in Xujiaweizi area developed fan delta facies,braided river delta facies,lacustrine facies,fan delta distributary plain,front subfacies,braided river delta front,Plain subfacies and semi-deep lake subfacies6 subfacies and 11 microfacies;the distribution range of sedimentary subfacies is predicted through seismic facies,and the seismic attribute prediction technology describes the sedimentary facies and channel distribution of each sequence.Determining the distribution characteristics of the depositional plane,the western steep slope of the study area mainly developed fan delta front subfacies,the central depression mainly developed shallow lake subfacies,deep lakes and semi-deep lakes developed in some areas,and braided river deltas developed in the east.The front-edge subfacies changes to the shore-shallow lake subfacies towards the lake;the overall process from SQ1-2 to SQ3-2 is a gradual deepening process,SQ4-1 begins to become shallower,and the fan reaches its maximum in the SQ4-3 period;The sedimentary filling model is established on the basis of sequence division and sedimentary facies plane;it provides theoretical guidance for the next step of favorable zone prediction in the study area.