Abstract
Slickwater is commonly used during hydraulic fracturing in coalbed gas well, which is often prepared with polyacrylamide as the friction reducer. To investigate the impact of polyacrylamide on CBM ad-/desorption after a fracturing operation, slickwater with different concentrations of polyacrylamide were prepared and used to treat Illinois coal samples. Both isothermal ad-/desorption experiments and molecular simulations were conducted to investigate the impact of slickwater. Nuclear magnetic resonance measurements were performed to analyse the evolution of surface functional groups of coal during slickwater treatment. The results show that there is no significant chemical reaction between the coal component and polyacrylamide. Because of the porosity of the polyacrylamide coating adhered onto the surface of the pore, polyacrylamide has a significant sorption capacity of methane. The methane sorption amount of the 'coal-slickwater' system is higher than that of raw coal. However, with the increase of the amount of residue entering the pores, the porous structure of the polyacrylamide coating becomes denser, blocking some pores and the pore surface area is reduced;; thus, the overall sorption capacity of the 'coal-polyacrylamide' system decreases.
NSTL