Study On Optimizing Of Interwell Tracer In Dingbian Fanxue Oilfield

The Fanxue oilfield is located in the middle and western parts of the Ordos Basin.It is a low-porosity and low-permeability reservoir with anisotropic heterogeneity.The scouring effect of long-term water flooding leads to uneven distribution of injected water and poor injection efficiency.Therefore,reservoir heterogeneity and inter-well connectivity must be analyzed to lay the foundation for the adjustment of oilfield development plans and stimulation measures.At present,chemical tracers are often used in the inter-well tracer monitoring.However,the types of chemical tracer are limited,and they do not fully satisfy the multi-well group tracer monitoring.Fluorescent tracer is a new type of trace tracer,which has the advantages of easy detection,small dosage and less pollution.Therefore,chemical tracers and fluorescent tracers were selected as the optimal tracer for well tracing.According to the principle of oil field tracer screening,well-performed tracers was selected from the chemical tracer and fluorescent tracer for laboratory evaluation.Based on the analysis of water quality,the tracer detection method was determined and the influencing factors in the detection process were studied;then,the compatibility,temperature resistance and static adsorption of different tracers under simulated formation conditions were evaluated.The chemical tracer evaluation results showed that thiocyanate and bromide were less in the formation and well compatible with the formation water,and the temperature and adsorption retention ratios were all higher than 90%,which was suitable for Fanxue oilfield;nitrate is not compatible with formation water,not applicable in the study area.The fluorescent tracer evaluation results show that the three fluorescent tracers have very little content in the formation,excellent temperature resistance,compatibility with formation water,and acceptable retention of adsorption;however,YG-1 and YG-2 have similar emission wavelengths and cannot be used at the same time.Considering the performance of both,YG-1is preferred as a fluorescent tracer in Fanxue.YG-3 is harmful to the Yanchang Formation and is only suitable for Yan'an Formation.Based on the laboratory evaluation,YG-1 fluorescent tracer was selected for field application.The tracer production curve was used to analyze the communication between wells and the distribution of water flooding.The analysis results were consistent with theproduction data,indicating that the fluorescent tracer has a good application effect in the oil field,which provide theoretical and practical basis for the application of tracer in the area.