Study On The Characteristics Of Chang 2 Reservoir In ×× Waterflooding Development Area Of Zichang Oilfield

The ×× waterflooding development zone of Zichang Oilfield is located in Siwan Township,southwest of Zichang County,with a development area of about 26 km²,which is located in the middle and eastern part of the northern Shaanxi slope of Ordos Basin.Based on the sedimentary petrology,reservoir geology,logging,petroleum geology and other related theory as a guide,using drilling data,well logging data,core data,casting thin section and scanning electron microscope data obtained by conventional reservoir testing and analysis methods,the reservoir characteristics of Chang 2 member in××waterflooding development zone of Zichang oilfield are systematically studied,and the reservoir classification and evaluation are finally completed,which provides theoretical basis for future development work.In this study,the members of Chang 2¹ and Chang 2² were divided into five sub-layers,namely,Chang 2^1-1,Chang 2^1-2,Chang 2^1-3,Chang 2^2-1 and Chang 2^2-2,with relatively stable thickness.The structural framework showed a gentle monocline dipping to the west.Each small layer inherited the structural characteristics and locally develops small nose uplift,which had a certain influence on oil and gas enrichment.The sedimentary facies type in the study area were delta plain subfacies,mainly developed distributary channel,onshore natural barrier and swamp sedimentary microfacies.According to the plane distribution of sedimentary microfacies,the channels with small layers of Chang 2^1-3 and Chang 2^2-1 were the most developed.The lithology of the reservoir was mainly feldspar sandstone,the interstitials in the pores were mainly chlorite,and the cements were mainly chlorite film,with low compositional maturity and the largest proportion of fine sand.The main diagenesis of the reservoir was compaction and solution,cementation and dissolution,and the main diagenetic stages of the reservoir were:early diagenetic stage A and early diagenetic stage B.The pore types were mainly primary intergranular pores and secondary dissolved pores,and the pore structure types were class II:low porosity,ultra-low permeability and fine throat.The average porosity of Chang 2^1-3,Chang 2^2-1 and Chang 2^2-2were 11.7%,12.8%and 12.4%,respectively,and the average permeability were5.8×10^-3?m²,8.1×10^-3?m² and 6.8×10^-3?m²,respectively,indicating good correlation between porosity and permeability.The correlation between porosity and permeability is good.Permeability was used as a parameter to characterize the reservoir heterogeneity,which indicated that the heterogeneity degree was not high within layers,but high between layers.The sensitivity of the reservoir was generally medium to strong water sensitivity,medium to weak velocity sensitivity,medium to strong salt sensitivity,weak alkali sensitivity and no acid sensitivity.The Chang 2 reservoir were classified into four categories.Class I reservoirs were not developed in the study area,while class II and III reservoirs were the most developed.The area of class IV reservoirs in the Chang 2^1-3sub-layer accounts for 60.23%,class II and class III reservoirs in the Chang 2^2-1 sub-layer account for 90.05%,and class II and class III reservoirs in the Chang 2^2-2 sub-layer accounted for 59.19%.The oil enrichment sites are mainly in the areas where the II and III reservoirs are relatively developed.