Analysis Of RN Measurement With Active Carbon Method Used To Monitor Distribution Characteristics Of CO₂ Injected Into The Coal Seam

For nearly a century, the mass use of fossil fuels（such as coal, oil, etc.） has increased the concentration of CO₂ and other greenhouse gases in the air, by which the global climate change is becoming more and more obvious. If we do not take effective measures to curb its development, it will have an immeasurable impact on the development of natural ecosystems and human society. Therefore, the international community begins to pay attention to and gradually implements a series of energy-saving emission reduction projects, and try to reduce the emissions of greenhouse gases in the air. Given this context, the Carbon dioxide capture and storage technology comes into being.However, in the long-term CO₂ injection and storage process, it is inevitable that CO₂ will escape to the outside world along drilling, fault, faulted zone and reservoir and cover fractures. Therefore, It is of great significance to take effective technical means to monitor the CO₂ migration and distribution in the reservoir and the environmental impact caused by the leakage of CO₂ in order to ensure the whole storage project is carried out safely,continuously and effectively.Current monitoring technology contains a large number of monitoring objects, such as atmosphere, soil vegetation, water, strata and geochemical fluids etc, which involves in geophysics, geochemistry, remote sensing, automatic control and other fields. Now much more mature technical methods have been used, such as remote sensing infrared imaging technology, soil air accumulating chamber technique, micro-seismic monitoring technology without artificial sources, electromagnetic method and Gravity and magnetic technology etc. However, it is the first time to apply Rn measurement with active carbon method to monitor the distribution characteristics of CO₂ injected into coal seam in the country and even in the world.On the basis of collecting and consulting a large amount of documents, this paper summarizes the research status of CO₂ monitoring technology and it mainly studies the principle and characteristics of Rn measurement with active carbon method. In addition, this article is divided into two stages to explore and analyse the reasons for the change of the concentration of radon in the shallow surface when the coal seam is injected CO₂.During the coal seam fracturing construction stage, the amount of free radon released from rock is increasing and the radon migrates migrates to the surface rapidly. However, at the stage of CO₂ continuously injected into the coal seam, the amount of free radon released from rock is decreasing and the pathway of radon migration is blocked. Under the comprehensive influence of the two stages, the radon concentration levels is reducing and radon distribution is more balanced on the surface of the relevant area, which establishes the theoretical foundation for monitoring the distribution characteristics of CO₂ injected into coal seam by Rn measurement with active carbon method.Through comparative analyses of the section chart of radon concentration located around the injection drilling, the contour map and the trend surface chart of radon concentration in the test area before and after CO₂ injection, we find that: after injection of CO₂, the concentration of radon located around the injection drilling in the shallow surface decreases significantly, and the turning point of the whole line is more stable than before injection. On this basis, the author introduces the variation function to deal with the radon-measuring data with regional variation characteristics, and the variation degree of the radon-measuring data is precisely characterized by the specific parameter of the fractal dimension of variation function. Combining fracturing technology with local geological conditions, We draw a conclusion that the migration degree of CO₂ injected into the experimental area in the east-west direction is stronger than north-south direction by analysing the fractal dimension feature of radon data measured in different directions of ZKZS-001 drilling. It also shows that the Rn measurement with active carbon method is an effective means to monitor the distribution of CO₂ injected into the coal seam.