Effect of Surfactant Modification on Coalbed Methane Desorption and Its Behavioral Mechanism

The efficient development of coalbed methane (CBM) is extremely important for coal mine safety and clean energy. While hydraulic fracturing has long remained the dominant technology for increasing CBM production, fracturing fluid results in self-priming of coal reservoirs, with the consequent water-lock effect decreasing CBM recovery. This study aimed to examine the effect of changes in the wettability of fracturing fluid on the desorption behavior of CBM. Hydrophobic CZH-1 and clear water fracturing fluid were prepared, following which fracturing desorption experiments were conducted on medium- and high-ranking coal-containing gas. The results showed that hydrophobic CZH-1 surfactant leads to a significant increase in the desorption rate of CBM. The rapid desorption rate of Xinjing and Baode coal increased by 11.1 and 48.8%, respectively, in the first 2 min, and the stable desorption rate increased by 34.8 and 21.0%, respectively, in 60 min. Application of Fourier transform infrared (FTIR) spectroscopy showed that the invasion of the hydrophobic CZH-1 surfactant resulted in decreases in the total area of the C–O peak of the oxygen-containing functional group and in the hydrophilic point in the coal. The hydrophilic group of the coal surface absorbed the hydrophilic group of the cationic surfactant molecule through electrostatic and van der Waals forces. Consequently, the facing of the hydrophobic group to the solution reduced the wettability behavior of water, decreasing the capillary force and reducing the degree to which the water-lock effect damaged the coal reservoir, thereby promoting the desorption of CBM. This study can act as a useful reference for the efficient development of CBM in low-permeability and low-pressure coal reservoirs and particularly for the development of CBM fracturing fluid.