Low Damage Fracturing Fluid in Low Water Bearing Coal Bed Based on Micro Mechanism of Foam

Coal bed methane (CBM) reservoir in Eastern-Yunnan and Western-Guizhou area generally has the problems of low water content, sensitive to external fluid, so it is promoted to use the foam fracturing fluid in hydraulic fracturing application. The change of bubble size and shape had been observed by using the long focal length zooming microscope and the environmental scanning electron microscope. The distribution and adsorption of additives had been studied by Cryo-SEM. With the experimental results, we can reveal the relation of the macroscopic properties of the foam fracturing fluid and microstructure of foam. Based on these, a low damage and enhanced desorption foam fracturing fluid suitable for low water bearing coal bed has been developed. The research shows that the film self-repair function determines the foam stability of the foam fracturing fluid, surfactant polarity on its important influence in the adsorption on coal surface, it is positive to select the appropriate surfactant for reducing the adsorption damage and enhancing the foam stability of the fracturing fluid. The foam fracturing fluid developed in this study has a foam quality of 78% and a half-time of 1110 s. According to the SEM and damage experiment, the damage rate of the fluid to coal core is negative, and some secondary micro-fractures generated in the coal after soaking with the foam fracturing fluid. Thus, there is a field application value for the foam fracturing fluid which be studied in this paper.