| Abstrakt: |
In order to reveal the overlapping area of coal and oil resources, the flow law and distribution characteristics of oil-bed gas in the coal seam around abandoned oil wells, the diffusion movement of oil-bed gas in the coal body system and the seepage movement of oil-bed gas in the fracture system are reasonably coupled together, and combined with their deformation characteristics, the dynamic change equation of coal permeability and the control equation of coal body deformation during the flow of oil-bed gas under pressure are deduced. A mathematical model for the control of gas diffusion and seepage in coal seams around abandoned oil wells is obtained. Through the test and analysis of gas characteristics, the main parameters of oil-bed gas diffusion and seepage are obtained. The coupling model is numerically solved by COMSOL Multiphysics software, and the variation law of oil-bed gas pressure and velocity with time and distance is further obtained. We found that with the increase in flow distance, the flow velocity of oil gas decreases, and it decreases rapidly within 100 m around the abandoned oil wells, and decreases insignificantly beyond the 100 m distance. We also developed the relationship between the flow velocity of oil-bed gas in coal seam and the flow distance, and obtained the influence radius of 310 m when the oil-bed gas pressure increases linearly at a rate of about 1/2 MPa per year to 30 years, which is basically consistent with the measured data. According to the attenuation regularity of oil-bed gas in coal seam, the coal seam near the oil well is greatly influenced by the high-pressure gas, while the coal seam in the distance is less affected. Finally, we established the distribution equations of the oil-bed gas pressure with the flow distance, when the pressure of oil-bed gas increases linearly to the 30th year. This study should provide theoretical guidance to support safe and efficient mining of coal seam affected by abandoned oil wells. [ABSTRACT FROM AUTHOR] |
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