| Most of my country's waterflooding oilfields are in the middle and late stages of development.To improve oilfield recovery,the geological conditions of the exploited oilfield should be aware beforetheselection of the type of plugging agent and determination of the amount of plugging agent for the profile control and water shutoff.Cross-well tracer monitoring technology is widely used as a technology that directly enters the oil field to monitor the oilfield development status and recognize the heterogeneity of the oil reservoir.Tracer,constantly developing and updating,is an important substance in the cross-well tracer monitoring technology.At present,chemical tracers was mostly uses was use for the oilfield monitoring in the Zhongyuan Oilfield,Sinopec.However,the biggest disadvantages of chemical tracers,the large amount,the high cost,and the increasement of background value due to long-term use,affects the tracer results.As a common and widespread isotope in nature,14C is used as a tracer in various fields such as environmental science and biomedicine,and it could be one of the ideal cross-well tracers.This work is based on the 200 k V single-stage Accelerator Mass Spectrometer(g XNU-AMS)at guangxi Normal University The main contents of the work are shown as bellow:(1)The establishment of 14C water sample preparation system.the original sample preparation system has been improved to be a solid-liquid 14C Sample preparation system based on the existing conditions.At series of water sample preparation work was carried out on the original solid sample preparation process in the laboratory to investgate the preparation conditions and system performance of the water sample preparation system.The result show that the CO2recovery rate of the final sample was 75.20%,indicating that The gas conduction and airtightness is good,and the graphite yield is 87.48%,indicating that the graphite reduction unit can successfully reduce CO2to graphite.Use as a background sample and place it in deionized water in the laboratory for process preparation.Several independent blank samples The background of the liquid-solid preparation system was determined to be(2.19±0.14)×10-14,with the the samle IAEA-C1 mixed in laberatroty deionized water.and and meet the requirement of tracing experiments.(2)Oilfield tracing experiment and sample preparation.Based on the establishment of a14C water sample preparation device,an oilfield tracing experiment was carried out.14C was used as a tracer to be injected into the oilfield formation.After a laboratory static adsorption experiment,the 14C labeledt Helicobacter pylori used in the breath experiment is selected as the carrier of the oilfield tracer.The 1st well group of the Hu-136 of the Zhongyuan Oilfield was used as the subject to evaluate the application effect of the 14C tracer in the oilfield.The activity of the 14C tracer injected into the oilfield formation is 1.332×107Bq,and the total number of 14C contained in it is 3.472×1018.The oil and water samples will be processed in the laboratory water sample preparation system.(3)Accelerator measurement.The test conditions of the accelerator mass spectrometer were adjusted and optimized.Commercial graphite not prepared by the process was used to evaluate the background value of AMS.The final instrument background was(4.363±0.699)×10-15,and the three process standard samples of the commercial graphite,IAEA-C8 and oxalic acid,were measured with AMS,the good linear fitting tverified the reliability of GXNU-AMS,where the normalized 14C/12C value of process graphite is(6.47±0.48)×10-15,the normalized 14C/12C result of oxalic acid is(1.583±0.009)×10-12,and the14C/12C of IAEA-C8 abundance ratio is(1.917±0.045)×10-14.After oil-water separation,the CO2in the oil samples was purified and graphitized in a 14C water sample preparation device.Finally,fter the graphite target sample were measured with GXNU-AMS,and the abundance ratio of 14C and 12C is obtained.After analysis,the tracer breakthrough curve is obtained.Compared with the tracer breakthrough curve of the trace element tracer holmium(chemical symbol as Ho)injected into the oil field at the same time,the 14C indicator can be seen The tracer breakthrough curve has an obvious tracer peak,while the detection sensitivity of the Ho tracer is low,and an obvious peak of the tracer concentration cannot be obtained.It is verified the advantage of 14C-AMS technology used in oilfield tracing compared with the conventional tracer..After theoretical analysis,laboratory sample preparation and oilfield construction experiments,the 14C-AMS technology for oilfield tracing research was finally completed,and a complete tracer breakthrough curve was obtained.Compared with rare earth element tracers,14C The tracer can enter the oil field and carry out the information of the heterogeneity of the oil reservoir.with high detection sensitivity.In this work,The high permeable bands and large channels could be distinguished with this tracer breakthrough curve,further more,the basic parameters of the well group reservoir,such as the thickness of the high permeability layer,permeability,average oil saturation,fracture width,and the radius of the holee etc.can be further calculated withthe numerical mode,and provide guidance and basis for subsequent development.For example,it can provide a reliable basis for the selection of the type of plugging agent for profile control and water shutting and the determination of the amount of plugging agent.The 14C tracer has the advantages of small dosage,high stability,safety,environmental protection,and low cost;at the same time,the accelerator mass spectrometry is used for measurement and analysis,which has the advantages of high sensitivity,overcomes the low sensitivity,high radioactivity and singleness of existing tracers,and provide more options for use different tracers with low background concentrations in cross-well groups and layered water injection wells.. |
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