Study On The Main Control Factors Of Chang8 Remaining Oil In Luo228 District Of Huanjiang Oilfield

At present,Luo 228 reservoir in the study area is characterized by high water cut,high recovery rate and high dispersion of remaining oil,but the study found that a large amount of remaining oil is still enriched in the reservoir.It is a very important problem faced by oilfield development geologists to find remaining oil enrichment areas with relatively low water cut during the development of common high water cut oilfields and to maintain stable oil production.In this paper,through stratigraphic division and correlation,structural characteristics research,sedimentary microfacies research,fine characterization of single sand body,reservoir characteristics and its heterogeneity research,logging secondary interpretation and water flooded layer interpretation and other geological research,combined with static and dynamic data analysis,the remaining oil distribution law and the main control factors of remaining oil distribution in the research area are finally completed.The results show that the main controlling factors of remaining oil distribution are microstructure,sedimentary microfacies distribution characteristics,injection-production correspondence of single sand body,reservoir heterogeneity and water flooding degree.We have obtained the following understanding:1.The Chang 8₁ sand group in Luo 228 can be divided into three small layers:Chang 8₁¹,Chang 8₁² and Chang 8₁³.The Chang 8₁² sand group is further subdivided into two units:Chang 8₁²¹ and Chang 8₁²².Through analyzing the structural characteristics of each small layer,it is found that the structure has a weak overall control over the reservoir.Chang 8reservoir in Luo 228 belongs to ultra-low permeability reservoir,and the heterogeneity in the reservoir belongs to medium to strong level.The overall rhythm is mainly reverse rhythm,which is helpful to slow down the uneven effect of water absorption in the profile.Interlayer heterogeneity is strong,interlayer thickness is large and distribution range is wide.2.The vertical contact relationship of single sand body in Chang 8 reservoir of Luo 228can be divided into separation type,superposition type and shear superposition type,with shear superposition type being the main type.The lateral contact relationship of single sand body includes isolated type,butt type and lateral cutting type.The logging interpretation results of watered-out zones are mainly of medium and low water flooding,and the degree of water flooding is comprehensively affected by fractures,physical properties and sand body structure.3.The Chang 8 reservoir in Luo 228 is characterized by low formation energy and large injection-production pressure difference.The plane distribution of water cut is uneven,and the problem of high water cut in central and southwest affected by cracks is more prominent.The water breakthrough time and water cut in lateral wells are generally larger than those in main wells.The whole reservoir belongs to harmonic decline,and the main cause of decline is fractured flooding of oil wells.4.The well pattern on the plane of Chang 8 reservoir in Luo 228 is fully controlled,and the remaining oil is enriched in annular and lumpy shapes between wells.In the longitudinal direction,the remaining oil is the largest in Chang 8₁²1-11-1 sand formation,accounting for 43.5%.On the plane,the remaining oil retention modes are mainly continuous retention of remaining oil in areas with imperfect well patterns,annular enrichment of remaining oil in porous seepage areas and zonal or lumpy enrichment of remaining twisted dough sticks in fracture control areas.The formation mechanism of residual oil in the longitudinal direction is mainly water flooding heterogeneity caused by longitudinal heterogeneity,poor connectivity caused by contact interface of single sand body,and formation of unwashed area caused by fracture thrusting along water line.