Abstract
Many researchers have revealed that relative permeability depends on the gas-water-rock interactions and ultimately affects the fluid flow regime. However, the way that relative permeability changes with fractal porous media has been unclear so far. In this paper, an improved gas-water relative permeability model was proposed to investigate the mechanism of gas-water displacement in fractal porous media. First, this model took the complexity of pore structure, geometric correction factor, water film, and the real gas effect into account. Then, this model was compared with two classical models and verified against available experimental data. Finally, the effects of structural parameters (pore-size distribution fractal dimension and tortuosity fractal dimension) on gas-water relative permeability were investigated. It was found that the sticking water film on the surface of fracture has a negative effect on water relative permeability. The increase of geometric correction factor and the ignorance of real gas effect cause a decrease of gas relative permeability.
Highlights
Unconventional natural gas, especially shale gas, has become increasingly important in the global energy supply in the past decade [1,2]
A relatively primitive permeability model [7]. This model assumes that the sum of the gas and water relative permeability is equal to 1, which does not agree with the actual fluid flow in porous media
An improved gas-water relative permeability model was proposed based on fractal theory. This improved fractal model takes the complexity of pore structure, geometric correction factor, water film, and real gas effect into consideration
Summary
Unconventional natural gas, especially shale gas, has become increasingly important in the global energy supply in the past decade [1,2]. Previous studies focused on the flow characteristics of gas in porous media and ignored the significant effect of water in complex micropores on gas effective permeability. The Purcell model calculated the permeability through capillary pressure data and formulated a relatively primitive permeability model [7] This model assumes that the sum of the gas and water. A relatively primitive permeability model [7] This model assumes that the sum of the gas and water relative permeability is equal to 1, which does not agree with the actual fluid flow in porous media. Brooks and Corey [12] introduced a pore-size distribution index to modify the capillary pressure function and proposed a more generalized gas-water relative index to modify the capillary pressure function and proposed a more generalized gas-water relative permeability model.
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