Study On Distribution Characteristics Of Remaining Oil In Chang 6 Reservoir Formation In Area X Of Ordos Basin

The study area is the key development block in Zhidan Oilfield.With the continuous development of oil fields,the well pattern infill,the oil well production decreases rapidly and the number of low production wells increases sharply,so it is difficult to achieve the purpose of stable production only by increasing the number of wells by well pattern infill.Therefore,it is necessary to carry out detailed reservoir description and study of remaining oil distribution in the study area.Under the guidance of the basic geological theory like petroleum geology and reservoir description and combined with the current development situation in the research area,this study comprehensively uses core observation,well logging,the identification of slice and scanning electron microscope to deeply discuss the relstiondhip between the remaining oil distribution with stratigraphic correlation and division?Characteristics of Sedimentary facies?Reservoir?Reservoir characteristics?water injection development characteristics.And pointed out that the influencing factor of the remaining oil and favorable distribution area.The top structure of each small layer of chang 6 in the study area is generally inclined to the west with high east and low west,and some east-west nose structures with low amplitude and short extension are developed locally.Based on the analysis of the plane and profile sedimentary facies of Chang 6 oil layer in the study area,it is found that the sedimentary microfacies in Chang 6 period belong to delta front subfacies,and the plane connectivity of sand body is better,which is beneficial to the development of the reservoir.The chang 6reservoir rocks in the study area are mainly fine-grained arkose and medium-fine-grained arkose with an average porosity of 9.2%;The average permeability was 0.62×10^-3?m²,and the average pore throat diameter was 0.85?m.Chang 6 reservoir belongs to the ultra low permeability reservoir of ultra-low porosity and fine throat,and has strong heterogeneity.On the basis of in-depth study of reservoir geological characteristics,the geological reserves of chang 6 formation calculated by using the volume method are 1008.62×10⁴t,with the low reserve abundance of 42.97%.According to the actual situation of geology and development in the study area,the method of combining geological reserves with dynamic analysis is used to calculate the remaining oil reserves,and found that the remaining recoverable reserves of the 6^1-2layers are the highest 38.26×10⁴t,and the recovery degree is2.5%;The second is the Chang 6²layer?25.38×10⁴t?and the Chang 6^1-1layer?19.65×10⁴t?,with the recovery rate of 4.7%and 2.7%respectively;The remaining recoverable reserves of chang 6⁴layer,chang 6³layer and chang 6^1-3layer are relatively low,among which chang 6^1-3has a minimum of 13.43×10⁴t.The cumulative remaining recoverable reserves of Chang 6layers are 129.57×10⁴t,and the overall recovery degree is relatively low,which is 3.14%.According to the study and analysis of chang6 residual oil ensemble in the study area,the distribution of residual oil is mainly controlled by sedimentation and reservoir factors.It is concluded that the residual oil is generally concentrated in the high part of the microstructure and the axis of the nose structure;The sedimentary microfacies control the accumulation of the remaining oil through the influence of physical properties,and it can indicate the distribution of the remaining oil;For reservoir heterogeneity,the development of intercalation and interval layer is favorable to the enrichment of residual oil,and the plane heterogeneity can reflect the distribution of remaining oil directly;The layout of well pattern is not perfect and irregular in some area of Chang 6 reservoir in study area,which leads to weak water drive effect and low recovery degree,and finally forms the remaining oil rich area.Comprehensive analysis shows that the remaining oil is still mainly distributed in the main production zones.Among the layers,the highest development potential is Chang 6^1-2,followed by Chang 6²and Chang 6^1-1,and then Chang 6⁴,long 6³and long 6^1-3,the determination of remaining oil enrichment horizon and enrichment zone is of great significance to guide the development and adjustment of oil fields in the later period.