Impact of surfactant in fracturing fluid on the adsorption–desorption processes of coalbed methane

Abstract

The effect of three surfactants in the fracturing fluid on the adsorption–desorption processes of coalbed methane (CBM) was studied by conducting an isothermal adsorption–desorption experiment. The adsorption capacity of surfactants and the wettability of the coal surface were also systematically investigated to illustrate the impact of surfactants. The experimental results showed that compared with the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant octadecyl trimethyl ammonium chloride (OTAC), the nonionic surfactant N-(2-hydroxypropyl) perfluorooctane amide (FCS) exhibits lower Langmuir pressure during the entire CBM desorption process, which promotes the desorption of CBM. The adsorption capacity and contact angle results demonstrated that the nonionic surfactant FCS has the weakest adsorption capacity on the coal surface and can increase contact angle slightly, which enhances the hydrophobicity and inhibits water from entering the deep and fine pores of coal. This phenomenon results in reduced damage of the fracturing fluid for CBM desorption. This study is significant with regard to the selection of a fracturing fluid system with high surface activity, high desorption efficiency of CBM, and low damage to the coal reservoir.