Optimization Of CO₂ Flooding Injection And Production Parameters In Strong Heterogeneous And Low Permeability Reservoirs

CCUS technology in low permeability reservoirs in China is in the ascendant,and is currently in the pilot test stage.Due to the particularity of the continental sedimentary reservoir and the impact of fracturing production,the reservoir is highly heterogeneous,with development of fractures,water channels and dominant channels.It is easy to cause the CO₂-EOR effect is not ideal.Therefore,the combination of dynamic and static comprehensive evaluation and characterization of low permeability reservoir heterogeneity and targeted optimization of injection and production parameters is one of the important research topics in the CO₂-EOR process.Chang 6 Reservoir in EYH Oilfield is a typical low-permeability reservoir.The development dynamics of planes,wells and well groups are very different,and the degree of heterogeneity is serious.It is expected to have a significant impact on the subsequent CO₂-EOR effect.Based on production dynamics and dynamic monitoring date,and utilizing the established water channel quantification method and low-fluidity well test interpretation technology,a reservoir dynamic heterogeneity evaluation study was carried out.On this basis,the well groups in the study area were classified.Using geological modeling technology,a structural model and an attribute model were established.From the perspective of development geology,the static heterogeneity of the reservoir was analyzed.Based on the understanding of static and dynamic heterogeneity of reservoirs,fine numerical simulation studies were carried out,development history matching was completed,and heterogeneous features such as water channels were loaded.Based on the classification of well groups,the optimization of the differential gas injection technology policy limits of well groups was carried out,the outline scheme of gas injection development was designed,and the development indicators were predicted.Research shows:(1)The reservoir plane and wells dynamic heterogeneity in the study area are severe,and the test well group can be divided into three categories.In the plane heterogeneous direction,oil and water wells all have composite characteristics.The severity of water wells exceeds that of oil wells.Among them,the average effective permeability of inner zone of water wells is 138.3 m D;the effective permeability of outer zone of water wells is 13.76 m D;the inner radius of water well is 28.57 m.the average effective permeability of inner zone of oil wells is 15.64 m D;the effective permeability of the outer zone of oil wells is 1.23 m D;the radius of the inner zone of oil wells is 11.51 m.According to the dynamic heterogeneity and the water flooding characteristics of the well group,the well groups are divided into three categories:the first type group has no water flooding wells,and the well conditions are good;the second type group has medium-to-high water cut wells after the production and has partial oil poor performance;the third type well group has water channeling wells.(2)The static heterogeneity of the reservoir plane and section in the study area are serious.In the geological model,the plane continuity of the sand body in area and direction are very different.The development of the main sand body in the section is different.The dynamic and static heterogeneous superposition is an effective means to understand the heterogeneous characteristics of low permeability reservoirs.According to the geological model,the degree of connectivity of the sand bodies along the river is high,and the sand bodies change fast in the direction of the cross-river channel,and the degree of connectivity is low.There are multiple sand bodies in a small layer,and the heterogeneity of the main sand bodies in different well groups are different.Compared with well water cut variation with or without loading plane composite feature and water channeling,it is believed that the numerical model based on the dynamic and static heterogeneous superposition can more realistically simulate the impact of reservoir heterogeneity on development performance.(3)The study of injection and production parameter optimization based on well group classification shows that there are obvious differences between the optimal injection parameters and production parameters of the three types well groups,and one type of well group corresponds to a policy can meet the needs of gas injection development optimization design.The best injection and production plan for the three types of well groups in the study area:the gas injection rate is 10 t/d,20 t/d,20 t/d;the gas injection methods are 2GASWAG11,5GASWAG11,2GASWAG11;the initial oil recovery rate is 0.5 MPa,0.5?1.5 MPa,1.5?3 MPa.The recovery degree of the injection and production parameters of the well group classification design reached 31.7%,which was 1.26%higher than the single method.A type of one-strategy injection and production parameter optimization method is adopted in this paper.For the low-permeability reservoir gas flooding injection and production technology policy,it has good pertinence.