Attenuation model of gas breakthrough permeability in porous media under the influence of multiple factors

Breakthrough permeability is an important indicator to evaluate shale gas development and CO2 geological sequestration, but its influential factors and synergistic effect mechanisms have not been figured out. To this end, this paper establishes an attenuation model of breakthrough permeability in partially saturated porous media based on the S-curve model of breakthrough pressure in partially saturated porous media and the slippage effect theory. Then, the validity of this model is verified by means of the visual air breakthrough and seepage experiment through a higher-permeability glass plane porous network, combined with previous breakthrough and seepage experiment results of CO2 and CO2-CH4 in low-permeability sandstone and shale samples. Finally, the influential factors and synergistic mechanisms of breakthrough permeability are analyzed. And the following research results are obtained. First, the synergistic effect of initial wetting phase saturation, outlet backpressure and slippage factor can be taken into consideration to establish an attenuation model of gas breakthrough permeability. Second, the visual air breakthrough and seepage experiment through glass plane porous network and the previous breakthrough and seepage experiment in low-permeability cores verify the validity of the attenuation model of gas breakthrough permeability. Third, compared with the exponential model, the attenuation model can more clearly reveal the inverted S-curve or exponential curve attenuation characteristics of breakthrough permeability with the initial wetting phase saturation. Fourth, initial wetting phase saturation, outlet backpressure and slippage factor have a synergistic effect on gas breakthrough permeability. When initial wetting phase saturation is lower, the increase of outlet backpressure can significantly decrease the breakthrough permeability of gas with a higher slippage factor. When initial wetting phase saturation is higher, the influence of outlet backpressure on gas breakthrough permeability will reduce, no matter whether gas slippage factor is high or not. In conclusion, the attenuation model of gas breakthrough permeability in porous media are of great significance to strengthen the development of unconventional gas reservoirs and guide CO2 geological sequestration and helps drive the realization of "carbon neutrality" in China. © 2021, Natural Gas Industry Journal Agency. All right reserved.