High-resolution Sequence Stratigraphy And Reservoir Physical Property Analysis Of Upper Paleozoic In Gubei Area Of Jiyang Depression

The Upper Paleozoic in Jiyang Depression is an important oil and gas coalbed reservoir.Taking Gubei area of Jiyang depression as the research area and the upper Paleozoic Carboniferous Permian strata as the research object,based on the high-resolution sequence stratigraphic division of the Carboniferous Permian strata,the sedimentary characteristics and sequence of the Carboniferous Permian system in the study area were systematically analyzied in this paper,and the development and evolution of the Carboniferous Permian sedimentary facies and the development characteristics of the favorable reservoirs were further discussed.Based on the comprehensive analysis of basic data including logging,and core of Carboniferous Permian in Gubei area,the high-resolution sequence stratigraphic framework of Carboniferous Permian system is established.Three types of sequence boundaries were identified in the Carboniferous Permian system,including 5 long cycle base level cycles(LSC1-LSC5),19 medium cycle base level cycles(MSC1-MSC20)and at least 31 short cycle base level cycles.The short period base level cycle includes three types:shallowing upward,deepening upward and symmetrical,while the long period and medium period base level cycles are mainly asymmetric cycles dominated by the lower half cycle.The symmetry and thickness changes of different long period cycles show their own regularity.Based on the high-resolution sequence stratigraphic framework,the sedimentary facies evolution characteristics of Carboniferous Permian in Gubei area of Jiyang depression are analyzed.Tidal barrier lagoon facies,delta facies,river lake facies and river lake composite facies are developed successively from early to late,and the development and distribution characteristics of various sedimentary subfacies are further analyzed.Based on the analysis of the material basis of reservoir space,diagenesis,physical property characteristics,heterogeneity and skeleton sand body of the main sequences in the study area,it is concluded that the Permian sandstone reservoirs are mostly ultra-low porosity and low permeability reservoirs,while the bottom sandstone and middle sandstone of Xiaofu river section are of good porosity and permeability due to their large thickness and good connectivity Low porosity and low permeability reservoir.The plane heterogeneity,intraformational heterogeneity and interlayer heterogeneity of reservoirs all appear in the study area.By comparing the sandstone of Kuishan member and Wanshan member,it is found that due to the better development of sandstone in Kuishan member,the continuity is also maintained.Compared with the sandstone of Kuishan member,the interlayer heterogeneity of Wanshan member sandstone is stronger.This paper mainly analyzes the spatial distribution characteristics and laws of sand bodies in different system tracts of long period base level cycle 5.In conclusion,it is found that sandstone reservoirs are more concentrated in the second,third and fourth members of the long-term base level cycle,and they are distributed in the north-south direction and in the east-west direction.The Kuishan section of the upper Shihezi Formation is the best reservoir,and the bottom and middle part of the Wanshan section,Xiaofu river section and the Lower Shihezi Formation are the best reservoirs.This study lays a foundation for further finding out the development,distribution and spatial distribution of Carboniferous Permian reservoirs in Gubei area.