Study On Braided River Reservoir Architecture Of Guantao Formation In Yangsanmu Oilfield

Yangsanmu Oilfield has been developed for nearly 50 years.The injection-production well pattern of GⅡoil group in Yangsan fault block is relatively perfect,but the reservoir’s water flooding is serious,water content is more than 94%and residual oil is relatively dispersed.The recognition of reservoir’s sedimentary characteristics can no longer meet the needs of fine development for reservoir at this stage.Therefore,it is urgent to refine the understanding of reservoir sedimentary structure to guide and optimize the water injection and the economic and efficient development of residual oil.In this paper,the detailed description of sedimentary microfacies and its internal reservoir architecture was carried out by synthesizing core,logging,test data and dynamic data of development.On this basis,the control effect of different grades of reservoir architecture on residual oil was analyzed,which can provide guidance for the development and adjustment of the study area.Fine characterization of sedimentary microfacies was carried out based on the regional sedimentary background and making full use of the data of sealed coring wells in the study area.It was found that sandy braided river developed in the target strata of the study area and 10 types of lithofacies and 5 types of sedimentary microfacies were identified.Based on the analysis of logging facies,the distribution characteristics of sedimentary microfacies in the study area were described.The results show that the sand bodies of braided river are well developed and have good continuity in the whole study area.In plane,the size of single braided flow and mid-channel bar are the smallest in Ng II⁴ single layer,and relatively larger in Ng II^3-1,Ng II^3-2,Ng II^5-1and Ng II^5-2 single layers.And the sedimentary microfacies which including fine-grained sediments such as abandoned channel,overbank sediment and floodplain sediment are not developed as a whole in the target strata of the study area,but there are certain regularity:Among the Ng II⁴ single layer,the above three sedimentary microfacies are relatively well developed,while they are relatively undeveloped in Ng II^3-1,Ng II^3-2,Ng II^5-1 and Ng II^5-2 single layers.Vertically,Ng II^5-2 and Ng II^5-1 single layers were in the rising stage of the base level,and their A/S were relatively small.During the single-layer period of Ng II⁴,the base level reached the highest and the A/S was the largest.During the single-layer period of Ng II^3-2 and Ng II^3-1,the base level was in the decline stage and the A/S became smaller.Using the research idea of"hierarchical analysis,model fitting,scale constraints and guidance of dynamic data",the braided river reservoir architecture in the study area was identified and characterized by using core,logging,test data and dynamic data of development.The results show that there are 6 types of the 4^th architecture element,including mid-channel bar,sandy braided channel,semi-argillaceous channel,argillaceous channel,overbank sediment and floodplain sediment.There are three types of the 3^rdarchitecture element:accretion,silt-falling layer and channel cross the bar.The silt-falling layers in the study area appear as interlayer in the sand body.And there are three types of interlayer:argillaceous interlayer,physical interlayer and calcareous interlayer.These interlayers have two distribution patterns on the plane,i.e.local flake distribution pattern and discrete distribution pattern.Among them,the interlayers with locally flake distribution pattern are the most developed,and the interlayers which with distribute discretely are relatively less.Quantitative characterization of different reservoir architecture elements in the study area shows that the widths of single braided flows in the study area are generally1600-2500m.The widths of mid-channel bars are 150-550m,with an average of 340 m.The lengths of mid-channel bars are 380-1000m,with an average of 650 m.And the ratios of length to width of the mid-channel bars are about 2:1.The widths of braided channels are17-171m,with an average of 70m.The thicknesses of the accretions are 1.56-7.96m,with an average of 3.33m.And the thicknesses of the channel cross the bars are 1.48-4.46m,with an average of 2.73m.The dip angles of the silt-falling layers are 0.6-5°,with an average of 2.7°.Based on reservoir architecture characterization,the influence of reservoir architecture on residual oil was analyzed with dynamic data of development and test data.As for the 5^tharchitecture elements,because of the development of high-permeability and extra-high permeability reservoirs in the study area,the development of interlayers is beneficial to improve the development effect of water flooding under the condition of multi-layer combined production,and the residual oil is relatively not enriched.In the 4^th architecture elements,the lateral shielding of semi-argillaceous channels result in poor connectivity in the upper part and good connectivity in the lower part of the sand bodies,which is easy to form residual oil that enriching at the top of the adjacent sand bodies.The argillaceous channels have stronger lateral shielding effect,which form residual oil enrichment of mudstone-shielded type.In the 3^rd architecture elements,the rhythm of pore and permeability in the accretions controls the vertical distribution of residual oil.Ahd the rhythms are usually positive.A few the rhythms of the residual oil are positive in the lower part of mid-channel bars and reverse in the upper part of mid-channel bars.The residual oil in lower part of mid-channel bars is still controlled by the rhythm of porosity and permeability,and the upper part is shielded by the interlayers between the accretions from the injected water to form the interfacial shielding residual oil.According to the actual situation of the study area,the distribution patterns of residual oil in different levels of reservoir architecture units in the study area are summarized,so as to provide suggestions for further development of the oilfield.