Vector characteristics of microscale gas transport in coalbed methane reservoirs

Elucidating the microscale geological control mechanism of gas transport in coalbed methane (CBM) reservoirs is the basis for efficient development of CBM reservoirs. At present, there is a lack of systematic research on the gas transport vector properties under the influence of microscale gravitational field. In this paper, firstly, a coupling model of multi-layer adsorption and surface jump is established, and the gas adsorption/desorption equilibrium mechanism under the condition of multi-layer adsorption is revealed. Secondly, a coupled model of gas transport in bulk gas field and weak adsorption field is established by an area weight method, and the coupling control mechanism of coal rank-pressure on gas transport in the direction parallel to wall is clarified. Thirdly, considering the strength distribution characteristics of microscale gravitational field in the direction perpendicular to wall, the coal rank-pressure coupling influence mechanism on gas transport mechanism conversion in weak adsorption field is revealed. It is found that (a) microscale gas transport is vectorial, and surface jump is not contradictory to multilayer adsorption; (b) under low pressure, the influence of residual pressure on surface jump rate can reach more than 10 times; (c) coal rank has a significant impact on microscale gas transport by controlling residual pressure, microscale gravitational field thickness and pore radius; (d) under low pressure, the flow perpendicular to wall in weak adsorption field has an obvious transition phenomenon of transport mechanism, and the influence of residual pressure is significant.

Automated summary

This paper investigates the microscale geological control mechanism of gas transport in coalbed methane reservoirs. By establishing coupling models, the equilibrium mechanism of multilayer adsorption and surface jump, the coupling control mechanism of coal rank-pressure on gas transport, and the influence mechanism of coal rank-pressure coupling on gas transport mechanism conversion are revealed.