| Taking the second-fourth upper section of the Qianjiang Formation of Paleogene in Zhoufan area of Jianghan basin as the object of study,using the high-resolution sequence Stratigraphic theory and technology as the guiding idea,and based on a large number of exploration and development data and previous research results,and according to detailed observation and description of the core,and combining the characteristics such as petrology,sedimentology and electrical of the main target intervals of the drilling block,studying on the distribution and evolution of sand body in sequence framework.Through the study of high resolution sequence stratigraphy,the strata of the second-fourth upper section of the Qianjiang Formation are divided into 3 long-term sequence cycles(LSC1—LSC3),11 medium-term sequence cycles(MSC1-1-MSC3-4)and 56 short-term sequence cycles(SSC1-1-1-SSC3-4-6).On the basis of this,the characteristics of different level of base-level cycles sequence structure are discussed in detail.It is believed that the type of sequence structure in the study area is mainly a symmetric(C-type)cycle structure,and according to the thickness of the rising and falling semi-cycle,it is subdivided into three types of substructures,which are the C1-type of close to the symmetric,the C2-type of the large thickness in the rising semi-cycle,and the C3-type of the small thickness in the falling semi-cycle.In the study,using a grid-type comparison work program,and form a gridded vertical and horizontal section of most of wells in the region,and four(2 horizontal and 2 vertical)stratigraphic comparison sections were drawn from the parallel and vertical source directions.The isochronicity comparison of the sequence stratigraphic is carried out by the comparison unit of the medium-term base-level cycle,and a sequence stratigraphic framework of the high-precision isochronicity is established based on the short-term base-level cycle.In the high-resolution sequence stratigraphic framework,the genetic type of sand body is analyzed in detail,and combined the division plan and principle of sand group and small layer sand body,conducted the fine small layer sand body division and isochronicity tracking comparison.Based on the drawing units of the short-term base-level cycle of the main target intervals,and the isoline maps of the formation thickness(40 sheets),sandstone thickness(30 sheets)and sand ratio(30 sheets)with high precision and large scale are compiled,and the distribution and evolution of sand body of different genetic type in the sequence framework are analyzed.It is considered that the sandstone in the area is relatively developed,and mainly develops in the five medium cycle of MSC1-1,MSC1-2,MSC1-3,MSC2-3 and MSC2-4,and mainly in the deltaic front subaqueous distributary channel and mouth bar sand body,followed by the development of distal bar sand body,front sheet sand body and shallow lake beach bar sand body.The sand body thickness changes greatly,mainly in the western part of the research area,mainly group by the deltaic front sand body,from the NWW to the ES direction,the form is flower shape,the South and East is mainly Salt Lake facies sedimentary system.Comprehensive study above,the distribution characteristics of the reservoir in the sequence stratigraphic framework are analyzed comprehensively in combination with the change of the A/S and the development quantity and thickness of reservoir.It is considered that the reservoir in the research area is mainly developed in the falling semi-cycle of C3-type sequence structure,the sedimentary type is mainly mouth bar,followed by the rising semi-cycle of C2-type sequence structure,and the sedimentary type is mainly subaqueous distributary channel. |
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