Study On The Sand Body Architecture Of Complex Meandering Belt And Its Control Action On The Remaining Oil Distribution

Most of the oilfields developed in the early stage of China have entered the ultra-high water cut stage due to long-term water injection development.Although a large amount of oil and gas resources have been produced in the middle and late stages of development,a considerable amount of Remaining oil and gas resources are often not recovered.These Remaining oil reserves in the ground have great potential for increasing recoverable reserves and improving recovery efficiency.As the sand bodies in meandering river reservoirs change rapidly laterally and have complex contact relations,meandering sand bodies with complex reservoir spatial distribution and internal structure are formed.The complexity of the internal structure of the meandering zone,the dominant seepage channels under its control and the formation and distribution mode of the Remaining oil are further clarified,which is of great significance for tapping the potential of the Remaining oil in the old oilfields in the high water cut period.In this paper,taking the meandering river sand body of Ng3 sand formation in Guantao Formation of Zhongyi area,Gudao Oilfield as an example,using core,logging,production performance and other data,fine anatomy is carried out on the complex meandering belt sand body architecture,and the complex meandering belt sand body architecture model is established;Carry out research on distribution and evolution characteristics of dominant seepage channels controlled by reservoir architecture,and build distribution mode of dominant seepage channels.On this basis,combined with the information of development well pattern,water flooded condition,production test,etc,using geological analysis,physical simulation,numerical simulation and other technical means,the control effect of reservoir architecture on Remaining oil distribution is analyzed,and the Remaining oil distribution model based on complex meandering belt sand body architecture model is discussed,so as to enrich the theory of fluvial facies reservoir architecture and provide guidance for the next step of oilfield development adjustment.Formation of Gudao Oilfield is established.On the basis of establishing the classification scheme of meandering river reservoir architecture,the complex meandering river reservoir architecture is analyzed step by step and the architecture mode is established by integrating multiple means such as cross well correlation,single well architecture unit sedimentary sequence characteristics,and development performance data analysis.There are mainly 5kinds of sand body composite zones in the composite sand body grade affected by the migration of water system.The vertical composite relationship of single stage river channel includes isolated type,weak undercut type and overlap type,showing the characteristics of splicing and migration of multiple rivers on the plane.The sequence features of the structural unit are subdivided into three rhythms,representing different positions of the plane respectively,so as to identify the trend of the river channel at the end of the period and the tendency of the lateral intercalation.The lateral interbed developed in the point bar makes the sand body show a semi connected mode.Finally,the complex meandering belt sand body architecture model of Ng3 sand formation in Guantao Formation of Zhongyi area of Gudao Oilfield is established based on the architecture relationship of sand bodies of various architecture levels.In this paper,the stratigraphic framework of Ng3 sand formation of Guantao Formation in Central Zone 1 of Gudao Oilfield is finely isochronally compared under the condition of dense well pattern,and the stratigraphic framework of river isochronous in the upper GuantaoOn the basis of the sand body architecture model of complex meandering zone,the flow zone index(FZI)calculated by combining dynamic and static calculation is used as the evaluation parameter of the dominant seepage channel.The formation of the dominant seepage channel is divided into two main factors: the inherent heterogeneity of the reservoir(FZI static)and the change of the reservoir by water injection development(△ FZI).By fitting the relationship between the cumulative water injection volume(Wt)and the index change of flow zone(△ FZI),the index change of flow zone(△ FZI)caused by the water injection volume is combined with the static parameters of the reservoir(FZI static)as the dynamic parameters of the reservoir seepage channel(FZI dynamic).The combination of the two can realize the comprehensive evaluation of the reality of the dominant seepage channels of the reservoir in different periods.From the perspective of evolution characteristics,with the development of water injection,the physical properties of the overall reservoir are getting better,and their changes are mainly controlled by the inherent physical differences of the reservoir(heterogeneity between layers and within layers)and the sand body architecture of complex meandering zone(the lateral deposit is connected in parallel,the river channel is connected at the end,the rotary flow in the middle and lower part of the point bar,the flood connection at the bottom of the point bar,the composite connection of vertical sand bodies,and the bottom connection of plane composite sand bodies).The distribution characteristics of the dominant seepage channels of the reservoir can be vertically divided into the single section type in the layer,the multi section type in the layer and the single section type between layers,which mainly presents the regional potato shape on the plane.To some extent,the existence of dominant seepage channels further increases the research difficulty of Remaining oil on the basis of sand body architecture.On the basis of sand body architecture model and dominant seepage channel in complex meandering zone,the formation mechanism and distribution rule of Remaining oil in complex meandering zone are studied by integrating physical simulation experiment,numerical simulation results and development performance data analysis.The formation of Remaining oil in the complex meandering zone is mainly controlled by geological factors(structural characteristics of sand bodies of different grades)and development factors(injection production relationship,well pattern streamline,and dominant seepage channels).Among them,the influence of single-stage river channel of Level 5 architecture on the Remaining oil is mainly reflected in the different contact relationship between the plane and vertical direction of the sand body,Level 4 architecture is reflected in the heterogeneous flow of injected water caused by the difference of a single structural unit,and Level 3 architecture is reflected in the matching of the distribution of lateral interbeds inside the point bar and the injection production relationship.Based on the integration of different architecture levels,the Remaining oil distribution pattern of 3 categories and 14 subcategories under the control of complex meandering zone sand body architecture is established,The distribution characteristics of Remaining oil are further confirmed by vertical interlayer interference experiment,physical simulation experiment matching 3 groups of different well pattern architectures and 14 groups of numerical simulation experiments with different characteristics.The corresponding potential tapping strategies are formulated for the four main Remaining oil types.