Comparative experimental study on the effects of water- and foam-based fracturing fluids on multiscale flow in coalbed methane

Abstract

To quantitatively evaluate their influence on coalbed methane (CBM) flow, water- and foam-based fracturing fluids were prepared. The effects of these two fracturing fluids on the flow of methane in coal were compared and analyzed using isothermal adsorption, diffusion capacity, and seepage tests. The results showed that an increase in the concentration of the fracturing fluid can exacerbate damage to methane flow. After immersed with water-based gel, gas diffusivity in the coal sample dropped to less than one fifth of the original level. However, when immersed with foam-based fracturing fluid, the diffusion coefficient of coal samples exceeded 3 × 10−13 m2/s. The residual permeability of the coal samples measured at a high pressure was significantly greater than that measured at a low pressure. Compare with the foam, the gel will cause a more serious adverse impact on the permeability of coal samples. Foam fracturing fluids with low viscosity and higher volume fraction of the gas phase will cause lesser damage to methane adsorption, desorption, or percolation. These results can help in the development of a coal seam clean fracturing technology.