Research On Control Limits Of Unstable Injection-production Parameters In Heterogeneous Reservoir

Due to long-term water injection and flushing,the remaining oil distribution in the middle and late stages of the development of high water-cut old oilfields is relatively scattered.Due to the faults,sand bodies and the relationship between injection and production,the overall pressure distribution of the oil layer is unbalanced.The heterogeneity contradictions of both interlayer and between layers are prominent.The production degree at the top of the thick oil layer is poor,and there are serious inefficient and invalid circulations at the bottom.Therefore,it is necessary to explore a new method to improve the overall development effect of such heterogeneous thick reservoirs.Based on the concept of reducing costs and increasing efficiency in the development of high water-cut old oilfields,a medium-high permeability reservoir in Daqing Oilfield was taken as the research object in this paper.The research on the limits of unstable injection-production pressure in heterogeneous reservoirs was carried out.By changing the water injection method and adjusting the injection-production pressure,the pressure field of the heterogeneous reservoir was redistributed.The feasibility of increasing the production degree of remaining oil at the top of the thick oil layer in this way was explored.The specific research contents include the following four items.The numerical simulation history matchings were carried out firstly based on the 3D geological model of the target block,which could quantify the distribution characteristics of remaining oil and movable oil in the target block.The influence of heterogeneity on the distribution of remaining oil was clarified.Secondly,inefficient and invalid circulation channels in the target block were identified and the evaluation parameters for judging the dominant seepage channels were determined,so that the water flooding degree between injection-production wells was described.The third and fourth items were combined with physical simulation experiments and numerical simulation.Experiments on oil displacement effect of unstable injection-production interlayer turbulent flow were done with three-tube parallel cores.The numerical simulation study gives the reasonable bottom hole flow pressure range and the production conditions of thin and poor layers under the condition of"strong production",and clarifies the influence of intralayer and interlayer turbulence on the swept volume after the pressure field of the high permeability layer of the plugged oil well changes.And the control limit of the injection-production period and the influence law of disturbance on the swept volume of the unstable reservoir in heterogeneous reservoirs.The results can show four corresponding conclusions.Firstly,the overall recovery degree of the study area is 61.7%,and the average remaining oil saturation is 34%.The movable remaining oil deposited on the middle bank of the delta distributary plain at the fault edge is relatively high.the second one showed the reasons for forming inefficient and invalid circulations are faults and the differences in reservoir heterogeneity.When the water injection intensity is greater than 7 m~3/m/d,the water cut at the oil well end is greater than 96%and the permeability is greater than 340 m D,strong or extremely strong seepage channels are likely to be formed in reservoirs.The prediction and judgment of the position,direction and degree of inefficient and invalid channels can be realized.Thirdly,The control limits of unstable injection-production pressure in heterogeneous reservoirs are 20-23 MPa for strong injection pressure and 1-3 MPa for bottom-hole flow pressure for strong production.The average recovery efficiency of heterogeneous high,medium and low reservoirs increases by 2.25%under strong injection.After plugging the high permeability layer,the turbulent flow expands the swept volume.The recovery rate of between layers and interlayers increases by 0.31%and0.9%respectively,with an average increase of 1.21%,which improves the overall production degree of the heterogeneous reservoir.Fourth,the control limit of injection and production in the unstable period of the study block is that the half period of water injection is three months,and the period of stop injection is one month,the periodic water injection method further expands the swept volume and improves the production degree at the top and middle of the thick oil layer.When the periodic water injection method is applied,the corresponding average increment of the recovery degree at the top of the thick oil layer can reach 1.04%.The research results in this paper provide a reference for solving the problems of poor production degree at the top and inefficient and invalid circulation at the bottom of the heterogeneous thick oil layer in high water-cut old oilfields,improving the development effect of such oil layers.